Content:

CL – Climate: Past, Present & Future

CL1.1 – Studying the climate of the last two millennia

EGU21-10979 | vPICO presentations | CL1.1

Advancing community-led research into the climate of the Common Era

Sarah S. Eggleston, Steven Phipps, Oliver Bothe, Helen V. McGregor, Belen Martrat, Hans Linderholm, Bronwen Konecky, Nerilie Abram, and Scott St. George

The past two thousand years is a key interval for climate science. This period encompasses both the era of human-induced global warming and a much longer interval when changes in Earth’s climate were governed principally by natural drivers and unforced variability. Since 2009, the Past Global Changes (PAGES) 2k Network has brought together hundreds of scientists from around the world to reconstruct and understand the climate of the Common Era using open and collaborative approaches to palaeoclimate science, including virtual meetings. The third phase of the network will end in December 2021. Here we highlight some key outputs of PAGES 2k and present the major themes and scientific questions emerging from recent surveys of the community. We explore how these might boost a new phase of PAGES 2k or a successor project(s). This year we will further reach out to the community through Town Hall consultations, vEGU and other meetings, and a PAGES 2k global webinar series. The aim of these activities is to foster development of post-2021 community-led PAGES initiatives that connect past and present climate.

How to cite: Eggleston, S. S., Phipps, S., Bothe, O., McGregor, H. V., Martrat, B., Linderholm, H., Konecky, B., Abram, N., and St. George, S.: Advancing community-led research into the climate of the Common Era, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10979, https://doi.org/10.5194/egusphere-egu21-10979, 2021.

EGU21-6663 | vPICO presentations | CL1.1

Climate of Moscow at the end of Little Ice Age

Mikhail A. Lokoshchenko

Better understanding of current climate changes needs a full knowledge about regional specific of thermal conditions at the end of Little Ice Age. So, the earliest available meteorological data are important. First regular daily qualitative meteorological observations were taken in Moscow city from 1657 to 1675. Episodic short series of instrumental measurements were made there for the first time in 1731; regular daily measurements started in 1779 when one of Mannheim network stations was founded in Moscow.

         All known old data series of the air temperature T measurements in Moscow since 1779 were collected and analyzed. Mannheim station existed there from 1779 to 1797 but average values of T are available from issues of Ephemerides Societatis Meteorologicae Palatinae only for the period 1779–1792. High accuracy of measurements at Mannheim network is confirmed by high correlation co-efficient between monthly-averaged T values in Moscow and at closest stations (Warsaw and St. Petersburg): up to 0.82-0.84 on separate months.

         Different methodical questions (unknown location of the station, unknown conditions of thermometer installation, its height and shading, an accuracy of its calibration, etc.) were studied. As a result it was found that the most probable error due to thermometer installation close to the northern building wall is ±0.1÷0.2 ºС; the error of daily-averaged T due to unknown height of measurements is ±0.1 ºС; the calibration accuracy in Mannheim was about ±0.1 ºС. Thus, a total error of T on average of a day in the 18th century was not higher than ±0.3÷0.4 ºС. Probably it was even less because separate components of the error may be multidirectional. For the first time mean-annual T in Moscow was received for 1783, and the most probable values were estimated for 1784 and 1785 using the data of the closest Mannheim station (Saint-Petersburg) for separate months with data gaps. The end of Little Ice Age manifeted at extremely low minimal values of T: up to –31 ˚R (–38.8 ˚С) in December 17th, 1788. However, thermal conditions from June to September changed only a bit since the 18th century till nowadays (differences are not statistically significant with the 0.95 confidence probability).  

         Later measurements in Moscow were renewed since 1808 and broken again in August of 1812 due to Napoleon’s invasion and terrible Moscow fire. For the first time unknown data series of everyday measurements which were made by Ivan Lange in 1816–1817 were found and studied. As is known the famous 1816 ‘Year Without a Summer’ was noted almost all over the World by extremely cold summer as probable result of Mount Tambora eruption in 1815. Nevertheless, it was found that summer of 1816 in Moscow was comparatively cool but not extremely cold: monthly-averaged T there was 15.7, 17.3 and 14.5 ˚С in June, July and August, respectively, and 15.8 ˚С on average of the summer. Thus, 1816 occupies only 27th place among the coldest summers in the city during 216 years.

         Author is thankful to the memory of his late PhD student Ekaterina L. Vasilenko.

How to cite: Lokoshchenko, M. A.: Climate of Moscow at the end of Little Ice Age, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6663, https://doi.org/10.5194/egusphere-egu21-6663, 2021.

EGU21-11953 | vPICO presentations | CL1.1

Analysis of Subdaily Meteorological Measurements by Louis Morin in the Late Maunder Minimum 1665 – 1709 in Paris

Thomas Pliemon, Ulrich Foelsche, Christian Rohr, and Christian Pfister

Based on copies of the original data (source: Oeschger Center for Climate Change Research) we perform climate reconstructions for Paris between 1665 - 1709. The focus lies on the following meteorological variables: temperature, cloudiness, direction of movement of the clouds, precipitation and humidity. Apart from humidity, these meteorological variables were measured three times a day over the entire period from Louis Morin. Temperature and humidity were measured with instruments, whereas cloud cover, direction of movement of the clouds and precipitation were measured in a descriptive manner. In addition to the quantitative temperature measurements, conclusions about synoptic air movements over Europe are possible due to the additional meteorological variables. The Late Maunder Minimum is characterised by cold winters and moderate summers. Winter is characterised by a lower frequency of westerly direction of movement of the clouds. This reduction of advection from the ocean leads to cooling in Paris and also to less precipitation in winter. This can be seen very strongly between the last decade of the 17th century (cold) and the first decade of the 18th century (warm). A lower frequency of westerly direction of movement of the clouds can also be seen in summer, but the influence is stronger in winter than in summer. However, this reduction leads to moderate/warm temperatures in summer. So unusually cold winters in the Late Maunder Minimum can be attributed to a lower frequency of westerly direction of movement of the clouds.

How to cite: Pliemon, T., Foelsche, U., Rohr, C., and Pfister, C.: Analysis of Subdaily Meteorological Measurements by Louis Morin in the Late Maunder Minimum 1665 – 1709 in Paris, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11953, https://doi.org/10.5194/egusphere-egu21-11953, 2021.

EGU21-15903 | vPICO presentations | CL1.1

Global Instrumental Meteorological Database Before 1890 – a useful overview

Elin Lundstad, Yuri Brugnera, and Stefan Brönnimann

This work describes the compilation of global instrumental climate data with a focus on the 18th and early 19th centuries. This database provides early instrumental data recovered for thousands of locations around the world. Instrumental meteorological measurements from periods prior to the start of national weather services are designated “early instrumental data”. Much of the data is taken from repositories we know (GHCN, ISTI, CRUTEM, Berkeley Earth, HISTALP). In addition, many of these stations have not been digitized before. Therefore,  we provide a new global collection of monthly averages of multivariable meteorological parameters before 1890 based on land-based meteorological station data. The product will be form as the most comprehensive global monthly climate data set, encompassing temperature, pressure, and precipitation as ever done. These data will be quality controlled and analyzed with respect to climate variability and they be assimilated into global climate model simulations to provide monthly global reconstructions. The collection has resulted in a completely new database that is uniform, where no interpolations are included. Therefore, we are left with climate reconstruction that becomes very authentic. This compilation will describe the procedure and various challenges we have encountered by creating a unified database that can later be used for e.g. models. It will also describe the strategy for quality control that has been adopted is a sequence of tests.

How to cite: Lundstad, E., Brugnera, Y., and Brönnimann, S.: Global Instrumental Meteorological Database Before 1890 – a useful overview, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15903, https://doi.org/10.5194/egusphere-egu21-15903, 2021.

EGU21-589 | vPICO presentations | CL1.1

Long-Term Global Ground Heat Flux and Continental Heat Storage from Geothermal Data

Francisco José Cuesta-Valero, Almudena García-García, Hugo Beltrami, J. Fidel González-Rouco, and Elena García-Bustamante

Energy exchanges among climate subsystems are of critical importance to determine the climate sensitivity of the Earth's system to changes in external forcing, to quantify the magnitude and evolution of the Earth's energy imbalance, and to make projections of future climate. Additionally, climate phenomena sensitive to land heat storage, such as permafrost stability and sea level rise, are important due to their impacts on society and ecosystems. Thus, ascertaining the magnitude and change of the Earth's energy partition within climate subsystems has become urgent in recent years. 

Here, we provide new global estimates of changes in ground surface temperature, ground surface heat flux and continental heat storage derived from geothermal data using an expanded database and new techniques developed in the last two decades. This new dataset contains 253 recent borehole profiles that were not included in previous estimates of global continental heat storage. In addition, our analysis considers additional sources of uncertainty that were not included in previous borehole studies. Results reveal markedly higher changes in ground heat flux and heat storage within the continental subsurface during the second half of the 20th century than previously reported, with a land mean temperature increase of 1 K and continental heat gains of around 12 ZJ relative to preindustrial times. Half of the heat gained by the continental subsurface since 1960 have occurred in the last twenty years. These results may be important for estimates of climate sensitivity based on energy budget constrains, as well as for the evaluation of global transient climate simulations in terms of the Earth’s heat inventory and energy-dependent subsurface processes. Our estimate of land heat storage is included in the new assessment of the components of the Earth’s heat inventory recently released (von Schuckmann et al. 2020), together with the oceans, the atmosphere and the cryosphere.

How to cite: Cuesta-Valero, F. J., García-García, A., Beltrami, H., González-Rouco, J. F., and García-Bustamante, E.: Long-Term Global Ground Heat Flux and Continental Heat Storage from Geothermal Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-589, https://doi.org/10.5194/egusphere-egu21-589, 2021.

EGU21-9222 | vPICO presentations | CL1.1

Assessing Arctic Ground Surface Temperatures from Borehole Temperatures and Paleoclimatic Model Simulations

Hugo Beltrami, Fracisco José Cuesta-Valero, Almudena García-García, Stephan Gruber, and Fernando Jaume-Santero

The surface temperature response to changes in our planet’s external forcing is larger at higher latitudes, a phenomenon known as polar amplification. The Arctic amplification has been particularly intense during the last century, with arctic-wide paleoclimatic reconstructions and state-of-the-art model simulations revealing a twofold arctic warming in comparison with the average global temperature increase. As a consequence, Arctic ground temperatures respond with rapid warming, but this response varies with snow cover and permafrost processes. Thus, changes in arctic ground temperatures are difficult to reconstruct from data, and to simulate in climate models.

Here, we reconstruct the ground surface temperature histories of 120 borehole temperature profiles above 60ºN for the last 400 years. Past surface temperature evolution from each profile was estimated using a Perturbed Parameter Inversion approach based on a singular value decomposition method. Long-term surface temperature climatologies (circa 1300 and 1700 CE) and quasi-steady state heat flow are also estimated from linear regression through the depth range 200 to 300 m of each borehole temperature profile. The retrieved temperatures are assessed against simulated ground surface temperatures from five Past Millennium and five Historical experiments from the Paleoclimate Modelling Intercomparison Project Phase III (PMIP3), and the fifth phase of the Coupled Model Intercomparison Project (CMIP5) archives, respectively.

Preliminary results from borehole estimates and PMIP3/CMIP5 simulations reveal that changes in recent Arctic ground temperatures vary spatially and are related to each site’s earlier thermal state of the surface. The magnitudes of ground warming from data and simulations differ with large discrepancies among models. As a consequence, a better understanding of freezing processes at and below the air-ground interface is necessary to interpret subsurface temperature records and global climate model simulations in the Arctic.

How to cite: Beltrami, H., Cuesta-Valero, F. J., García-García, A., Gruber, S., and Jaume-Santero, F.: Assessing Arctic Ground Surface Temperatures from Borehole Temperatures and Paleoclimatic Model Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9222, https://doi.org/10.5194/egusphere-egu21-9222, 2021.

EGU21-8323 | vPICO presentations | CL1.1

Accounting for small bipolar magnetic regions in solar irradiance reconstructions

Bernhard Hofer, Natalie A. Krivova, Sami K. Solanki, Robert Cameron, Chi-Ju Wu, and Ilya G. Usoskin

Historical solar irradiance is a critical input to climate models. As no direct measurements are available before 1978, reconstructions of past irradiance changes are employed instead. Such reconstructions are based on the knowledge that solar irradiance on time scales of interest to climate studies is modulated by the evolution of the solar surface magnetic structures, such as sunspots and faculae. This calls for historical records or proxies of such features. The longest direct, and thus mostly used, record is the sunspot number. It allows a reasonable description of the emergence and evolution of active regions, which are larger magnetic regions containing sunspots. At the same time, a significant amount of the magnetic flux on the Sun emerges in the form of the so-called ephemeral magnetic regions, which are weaker short-lived bipolar regions that do not contain sunspots. Due to their high frequency, ephemeral regions are an important source of the irradiance variability, especially on time scales longer than the solar cycle. Difficulties in their proper accounting are a main reason for the high uncertainty in the secular irradiance variability. Existing models either do not account for their evolution at all or link them linearly to active regions. We use a new, more realistic model of the ephemeral region emergence, relying on recent independent solar observations, as input to a surface flux transport model (SFTM) to simulate the evolution of the magnetic field in such regions. The latter can then be used to reconstruct the solar irradiance since the Maunder minimum.

How to cite: Hofer, B., Krivova, N. A., Solanki, S. K., Cameron, R., Wu, C.-J., and Usoskin, I. G.: Accounting for small bipolar magnetic regions in solar irradiance reconstructions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8323, https://doi.org/10.5194/egusphere-egu21-8323, 2021.

EGU21-1893 | vPICO presentations | CL1.1

Late-Holocene climate variability of coastal East Asia reconstructed from the Yongneup fen in central Korea

Jinheum Park, Qiuhong Jin, Jieun Choi, and Jungjae Park

This study presents a reconstruction of climate change in central Korea during the last 3,000 years, using a core from a montane peatland of Yongneup. Multiple proxies of pollen, macrocharcoal, and geochemistry were analysed to provide three findings as follows: First, abrupt climate events at ca. 2.8 and 2.3 ka BP possibly accompanied dry summer as well as cold and arid winter seasons on the Korean peninsula. The first macrocharcoal analysis on the peninsula indicates increased wildfire activities during these dry periods. Next, a weakening of summer monsoon during El Niño-like phases was clearly found during the late Holocene. This confirms previous findings of a dominant oceanic influence on hydroclimate variability on the Korean peninsula. Finally, changes in temperature were likely synchronous with a global trend, indicated by the total organic content (TOC) and arboreal pollen percentages. Due to its location at a high-altitude, the environment of Yongneup has possibly sensitively responded to fluctuations in temperature. Altogether, these findings suggest that temperature and precipitation changes on the Korean peninsula have been separately influenced by insolation and oceanic circulations, respectively.

How to cite: Park, J., Jin, Q., Choi, J., and Park, J.: Late-Holocene climate variability of coastal East Asia reconstructed from the Yongneup fen in central Korea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1893, https://doi.org/10.5194/egusphere-egu21-1893, 2021.

EGU21-2789 | vPICO presentations | CL1.1

Oxygen isotopic evidence of climate variability in southern England since the Medieval Period.

Joanna Tindall, Jonathan Holmes, Ian Candy, Melanie Leng, Kira Rehfeld, Louise Sime, Irene Malmierca Vallet, Thierry Fonville, Pete Langdon, and David Sear

Late Holocene climatic variations pre-1850 CE are associated with volcanic and solar forcing (Schurer et al., 2013).  Whilst these variations are recorded in speleothems and ice-cores, these archives are often spatially restricted leaving gaps in our knowledge about short-term climate variability in a range of regions. Here, we investigate the potential of using the high-resolution δ18O analysis of lake carbonates formed within artificially constructed water bodies dating back to the Medieval period. Whilst the isotopic analysis of lake carbonates is a well-established Quaternary palaeoclimate proxy (Leng and Marshall, 2004) it has received less attention as a tool for climate reconstruction over the historic period. In this study we use the δ18O analysis of winter calcifying ostracod species from lake sediments recovered from Medieval fishponds from the town of Alresford, in southern England, combined with a programme of monitoring within the present-day water body to establish the hydrology and thermal regime of the system. This analysis shows that over the studied interval (the end of the Medieval period through to the 20th century) the lake system underwent regular inter-annual/decadal isotopic shift of relatively high magnitude (1-2‰).

In order to investigate whether these high magnitude δ18O fluctuations are explainable by climatic variability or are a result of intra-lake processes we provide a data-model comparison. This approach allows an understanding of the likely mechanistic drivers of climatic change as well as testing if proxy observations are consistent with modelled outputs (Evans et al., 2013). This study compares the δ18O ostracod record with a synthetic δ18Ocarbonate record derived from the Millennium Data iHadCM3 runs for the period 1200 CE to 1850 CE. The iHadCM3 model generates modelled values for temperature and δ18Oprecipitation on an annual and monthly basis. These data were used to produce a synthetic δ18Ocarbonate record on both an annual and seasonal basis using Kim and O’Neil's (1997) equation that describes the relationship between temperature, δ18Ocarbonate and δ18Olakewater.

The preliminary outputs of this proxy-model output comparison demonstrate that the magnitude of δ18Ocarbonate variability predicted by the model data is similar to the magnitude of change recorded in the proxy data. This suggests that these variations are real and driven by climatic rather than catchment-specific processes. Ongoing work aims to disentangle primary climate drivers of interannual δ18O change, at this site, using δ18O enabled climate model simulations. Our approach of considering what drives interannual δ18O changes over the last few hundred years, in these lacustrine settings, will help enable more robust palaeoclimatic reconstructions from these records.

References: Evans, M.N. et al., (2013), QSR, 76, pp.16–28.; Kim, S.-T. and O’Neil, J.R. (1997) Geochimica et Cosmochimica Acta, 61(16), pp.3461–3475; Leng, M.J. and Marshall, J.D. (2004) QSR, pp.811–831; Schurer, A.P. et al., (2013) Journal of Climate, 26(18), pp. 6954–6973.

How to cite: Tindall, J., Holmes, J., Candy, I., Leng, M., Rehfeld, K., Sime, L., Malmierca Vallet, I., Fonville, T., Langdon, P., and Sear, D.: Oxygen isotopic evidence of climate variability in southern England since the Medieval Period., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2789, https://doi.org/10.5194/egusphere-egu21-2789, 2021.

EGU21-3748 | vPICO presentations | CL1.1

Pacific Walker circulation variability during the last millennium reconstructed from a network of water isotope proxy records

Georgina Falster, Bronwen Konecky, Sloan Coats, Samantha Stevenson, and Midhun Madhavan

Changes in the strength of the Pacific Walker circulation (PWC) can have a significant impact on global mean surface temperatures, as well as regional temperature, precipitation, and extreme weather events far beyond the tropical Pacific. Understanding PWC variability is therefore important for constraining future climate. But observational records of the PWC are short, and single-site proxy records for changes in the strength of the PWC during the last millennium offer contrasting interpretations. This leaves a critical gap in our understanding of PWC variability on the decadal to centennial timescales relevant to future climate change.

Falster et al. (in prep.) demonstrated that the PWC is strongly imprinted in modern global precipitation δ18O (δ18OP). This relationship arises via multiple complementary mechanisms, including but not limited to ENSO dynamics. We exploit this relationship to reconstruct changes in the strength of the PWC over the past millennium, using six different statistical and machine learning reconstruction methods in conjunction with a globally-distributed network of palaeo-δ18OP records (Konecky et al. 2020). Although δ18OP from a relatively small number of locations explains a large proportion of PWC variance in the calibration interval, we use a larger network of sites because larger networks are less susceptible to non-stationary teleconnections or non-signal biases than individual sites or smaller networks. 

Preliminary results indicate that reconstructed PWC variability is coherent across methods, particularly for the past 400 years. Our reconstructions are also robust to both the calibration window used, and the particular palaeo-δ18OP records included in the reconstruction. This provides confidence that our network comprises sufficient proxy timeseries i.e. that we successfully extracted the common underlying climate signal (the PWC) from site-specific information inherent in individual palaeo-δ18OP records. Thus, we are confident that our reconstruction of changes in the strength of the PWC through the last millennium is robust, and it will therefore help to constrain the PWC’s long-term internal variability and sensitivity to external forcing.


References:

Falster, G. M., B. Konecky, M. Madhavan, S. Coats, S. Stevenson. 2021. “Imprint of the Pacific Walker circulation in global precipitation δ18O”. In preparation for Journal of Climate

Konecky, B. L., N. P. McKay, O. V. Churakova (Sidorova), L. Comas-Bru, E. P. Dassié, K. L. DeLong, G. M. Falster, et al. 2020. “The Iso2k Database: A Global Compilation of Paleo-δ18O and δ2H Records to Aid Understanding of Common Era Climate.” ESSD. https://doi.org/10.5194/essd-2020-5.

How to cite: Falster, G., Konecky, B., Coats, S., Stevenson, S., and Madhavan, M.: Pacific Walker circulation variability during the last millennium reconstructed from a network of water isotope proxy records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3748, https://doi.org/10.5194/egusphere-egu21-3748, 2021.

EGU21-6292 | vPICO presentations | CL1.1

Impact of fires, earthquakes, and climate on catchment response since 600 CE, Pallett Creek, San Gabriel Mountains, Southern California USA

Katherine Scharer, Jenifer Leidelmeijer, Matthew Kirby, Nicole Bonuso, and Devin McPhillips

In tectonically active regions, sedimentary records are overprinted by landscape response to climate, fire, and local earthquakes.  We explore this issue using a new paleoclimate record developed at the Pallett Creek paleoseismic site in southern California USA, a recently incised distal fan located along the San Andreas Fault at the base of a 35 km2 catchment in the San Gabriel Mountains.  To date, we have analyzed 6 m of section, spanning the last 1300 yr, for grain size, total organic material (TOM), carbon/nitrogen (C/N) ratios, magnetic susceptibility, and charcoal count. Existing C-14 dates (Scharer et al., 2011) inform rates of sediment deposition and charcoal accumulation (CHAR). Additional dating and macrofossil analysis is ongoing.  Sedimentological variability within the section is dominated by two general units. Unit 1 is characterized by high % clay, % silt, and % TOM, while Unit 2 is distinctly coarser with higher % sand and lower % TOM.  Pulses of high CHAR occur from 1150-1260 yr BP and during the Little Ice Age (100-500 yr BP) and are associated with high sedimentation rates (0.3-2 cm/yr), while only a few relatively weak fire episodes are recorded in the Medieval Climate Anomaly (700-1000 yr BP), despite similarly high sedimentation rates (0.6 cm/yr).  Ten earthquakes documented at the site (Sieh et al., 1989) occurred about every 135 years and impart no obvious short-term impact on sedimentation rates, perhaps reflecting the distance between the site and steeper portions of the drainage network (>4 km) likely to produce mass wasting.  Overall, the landscape response of this large, integrated catchment appears to reflect a stronger influence of fire and climate than earthquakes. Future work will focus on the impact of the fire episodes on sediment delivery and resultant paleoearthquake ages.

How to cite: Scharer, K., Leidelmeijer, J., Kirby, M., Bonuso, N., and McPhillips, D.: Impact of fires, earthquakes, and climate on catchment response since 600 CE, Pallett Creek, San Gabriel Mountains, Southern California USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6292, https://doi.org/10.5194/egusphere-egu21-6292, 2021.

EGU21-8550 | vPICO presentations | CL1.1

Marine records of Holocene glacier variability in the Kerguelen Islands (South Indian Ocean): sedimentology, chronology, and paleoclimatic drivers

Léo Chassiot, Emmanuel Chapron, Elisabeth Michel, Vincent Favier, Vincent Jomelli, Joanna Charton, Deborah Verfaillie, and Xavier Crosta

The strength and the location of Southern Hemisphere winds (SHW) define an annular mode (SAM), a major component of interannual climatic variability in the Southern Hemisphere. SAM has a significant impact on mid-latitude westerly winds, but also acts on the meridional moisture transport over the Southern Ocean (for example, in the case of atmospheric rivers), with dramatic consequences on the cryosphere at high latitudes. Assessment of past, present and future changes in the SAM is essential for understanding climate variations and impacts at high latitudes. To date, Holocene proxy-based reconstructions of SAM are limited to South America, Australia/New Zealand, and Antarctica. In opposite, the paucity of SAM-related records for the Southern Indian Ocean presently limits our understanding of the spatial and temporal extent of SHW behavior in this region.

To this aim, we present a series of 30-m long marine records retrieved from a fjord fed by glacial melt of the Ampere glacier belonging to the Cook Ice Cap in the Kerguelen Archipelago (49˚20’S, 69˚20’E). A new chronological framework, based on Bayesian modelling of 50 radiocarbon ages along with 137Cs and 210Pb measures, allows reconstructing 4 kyrs of sediment discharge related to glacier variability. Sedimentological and geochemical analyses from XRF and GEOTEK core scanners highlight (i) a regional tephra at 950 cal BP; (ii) regular occurrences of floods during the LIA; and (iii) a background sedimentation related to glacial flour inputs through hypo- and hyperpycnal flows favoring very high sedimentation rates (1-2 cm.a-1) in the fjord. Phases of glacier advances and retreats linked to moisture transport by SHW are reflected by fluctuations in sedimentological and geochemical signals, and correlated with moraines dating on land. Over the past 4 kyrs, four cycles of glacier advances/retreats can be evidenced, reflecting wet/dry periods in response to shifts in the position and changes in magnitude of the SHW, associated with moisture transport and precipitation in the Southern Indian Ocean. On centennial timescales, wet/dry periods inferred from Kerguelen are in-phase with Holocene SAM-related records from South America and Tasmania over the last 2 kyrs, suggesting the long-term glacier dynamic at Kerguelen is also related to a centennial expression of SAM.

Acknowledgments : Marion Dufresne Crew, ARTEMIS program, UGA-ARCA.

How to cite: Chassiot, L., Chapron, E., Michel, E., Favier, V., Jomelli, V., Charton, J., Verfaillie, D., and Crosta, X.: Marine records of Holocene glacier variability in the Kerguelen Islands (South Indian Ocean): sedimentology, chronology, and paleoclimatic drivers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8550, https://doi.org/10.5194/egusphere-egu21-8550, 2021.

EGU21-13653 | vPICO presentations | CL1.1

Planktic Foraminifera changes in the western Mediterranean Anthropocene

Sven Pallacks, Patrizia Ziveri, Belen Martrat, Graham P. Mortyn, Michael Grelaud, Ralf Schiebel, Alessandro Incarbona, Jordi Garcia-Orellana, and Griselda Anglada-Ortiz

The increase in anthropogenic induced warming over the last two centuries is impacting marine environments. Marine planktic calcifying organisms interact sensitively to changes in sea surface temperatures (SST), and the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly (MCA) to present. Reconstructed SSTs are in good agreement with other results, tracing temperature changes through the Common Era, and show a clear 20th century warming signal. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides) a common group of marine calcifying zooplankton. The abundance ratios between these species show the switch between winter / spring surface productivity and deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of North Atlantic Oscillation (NAO), and, to lesser extent, by the Atlantic Multidecadal Oscillation (AMO). In the industrial era, starting from about 1800 Common Era (CE), this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles and influences are being overprinted by human influences.

How to cite: Pallacks, S., Ziveri, P., Martrat, B., Mortyn, G. P., Grelaud, M., Schiebel, R., Incarbona, A., Garcia-Orellana, J., and Anglada-Ortiz, G.: Planktic Foraminifera changes in the western Mediterranean Anthropocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13653, https://doi.org/10.5194/egusphere-egu21-13653, 2021.

There is a major knowledge gap in the past climate oscillation of the Arabian desert, especially during the past two millennium. Reliable continuous continental records that archives at high resolution past environmental variability are useful sentinels of paleoclimate changes. Reliable interpretation from climatic proxies retrieved from lake records are crucial for identifying periodicities and the onset of climatic events and evaluating inter-annual and decadal trends driven by shifting of the Intertropical Convergence Zone (ITCZ). A multiproxy approach is presented for a ~3.3 m composite core from a karst lake located in Gayal el Bazal, southern Yemen. Sedimentary proxies, including grain size distribution and magnetic susceptibility (MS) coupled with geochemistry (XRF), provide an initial picture of centennial-scale environmental changes over the southern Arabian desert. The chronology of the core was anchored by five radiocarbon (14C) dates of terrestrial plants (wood) extracted from sediment samples and indicates the core extends to ~800 AD. Our data provides a snapshot for better understanding the impact of Indian Ocean monsoon variability at an exceptional resolution for a region that lacks sufficient information. Our data indicates that during the ‘Little Ice Age’ (~1500-1800 AD) was arid relative to the warm conditions that prevailed during the Medieval Warming Period (~800 to 1200 AD). The arid phase was marked by high Ca/(Al, Fe, Ti) values, increased inorganic carbon content, decreased MS values, and gypsum precipitation. Furthermore, end-member mixing analyses (EMMA) derived from the grain-size distribution corroborates the production of carbonate sand probably due to an increase in flash floods occurring concurrently with low lake levels under generally dry conditions. Aridity during the Little Ice Age is consistent with evidence and theory for weakened boreal summer monsoons during intervals of northern hemisphere cooling. Overall, this study will provide insight into the monsoon variability and a record for understanding the interactions between northward migrations of the ITCZ and tropical monsoonal dynamics during the late Holocene. In the context of current climate change and increasing population pressure, a deeper understanding of their long-term hydrological variability, this study is highly essential to satisfactorily forecast the sustainability of lakes as a resource in a warming world.

How to cite: Parth, S., Russell, J. M., and Waldmann, N.: Reconstructing 1200 years of hydroclimate variability in the southern margins of the Arabian Desert, inferred from an ancient lake in southern Yemen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14756, https://doi.org/10.5194/egusphere-egu21-14756, 2021.

Corals are distributed throughout the tropical oceans, making them useful for resolving climate information covering time before the satellite era when instrumental data is often scarce. Coral δ18O has been used to reconstruct changes in both sea surface temperature (SST) and hydrology, while coral Sr/Ca is thought to mainly record SST. Coral δ18O data, when used in conjunction with Sr/Ca, can therefore be used to reconstruct seawater δ18O (δ18Osw), an indicator of the local precipitation-evaporation balance as well as other surface ocean hydrological changes. Coral Sr/Ca-SST relationships are critical for reconstructing δ18Osw from paired Sr/Ca and δ18O records, but vary across existing literature. Some of this variation is due to existing natural differences between corals, but variation also stems from differences in calibration methods or SST products used to determine the Sr/Ca-SST relationship. Such methodological differences complicate the comparison of results across studies and slow efforts to create a global picture of reconstructed tropical ocean hydroclimate.

Here, we use the PAGES CoralHydro2k database - a collection of 45 paired coral Sr/Ca-δ18O records and 70 coral δ18O records - to assess different methodological choices such as SST product and regression method and develop a calibration framework to use as a set of “best practices” moving forward. We also examine the sensitivity of δ18Osw to our calibration framework and to existing δ18Osw calculation methods. The PAGES CoralHydro2k project aims to leverage its coral database and apply these best practices and insights to a global reconstruction of tropical marine hydrology over the past 200 years.

How to cite: Walter, R. and the PAGES CoralHydro2k: Assessing the impact of Sr/Ca-SST calibrations on coral-based seawater δ18O reconstructions - First results from PAGES CoralHydro2k, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13949, https://doi.org/10.5194/egusphere-egu21-13949, 2021.

Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although the changes over recent decades are well studied, the short instrumental record limits our ability to determine if such asymmetric patterns are common for Antarctica and the processes at their origin. Here, we will focus on the years 0-1000 CE as some ice core records display very contrasted trends during this period. Furthermore, the climate models are unable to reproduce the warming displayed in some reconstructions from 1 to 500 CE over East Antarctica. In order to understand the origin of these apparent incompatibilities and investigate the effect of proxy selection on regional reconstructions over 0-1000 CE, we performed several offline data assimilation experiments based on different groups of d18O records and the isotope-enabled general circulation models (iCESM). When assimilating different d18O data sets, large differences appear in the pattern of temperature trend over 0-500 CE, but the patterns over 500-1000 CE are more consistent among the various experiments. This implies that the spatial pattern of temperature trend over 0-500 CE is still uncertain because of this high sensitivity on the choice of the proxies to constrain the model results, while the pattern over 500-1000 is more robust, with the greater cooling over West Antarctica than East Antarctica. This pattern over 500-1000 CE relates to the intensifying of the low pressure centered in the Amundsen Sea, which induces enhanced southerly flow through most of WAIS.

How to cite: Lyu, Z., Goosse, H., and Dalaiden, Q.: Spatial patterns of multi-centennial temperature trend in Antarctica over 0-1000 CE: insights from ice core records and modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-571, https://doi.org/10.5194/egusphere-egu21-571, 2021.

EGU21-3756 | vPICO presentations | CL1.1

Synoptic climatology of southern Indian Ocean and paleoclimate proxy interpretation

Danielle Udy, Tessa Vance, Anthony Kiem, Neil Holbrook, and Mark Curran

Weather systems in the southern Indian Ocean drive synoptic-scale precipitation, temperature and wind variability in East Antarctica, sub-Antarctic islands and southern Australia.  Over seasonal to decadal timescales, the mean condition associated with combinations of these synoptic weather patterns (e.g., extratropical cyclones, fronts and regions of high pressure) is often referred to as variability in the westerly wind belt or the Southern Annular Mode (SAM). The westerly wind belt is generally considered to be zonally symmetric around Antarctica however, on a daily timescale this is not the case. To capture the daily variability of regional weather systems, we used synoptic typing (Self-Organising Maps) to group weather patterns based on similar features, which are often lost when using monthly or seasonal mean fields. We identified nine key regional weather types based on anomaly pattern and strength. These include four meridional nodes, three mixed nodes, one zonal node and one transitional node. The meridional nodes are favourable for transporting warm, moist air masses to the subantarctic and Antarctic region, and are associated with increased precipitation and temperature where the systems interact with the Antarctic coastline.  These nodes have limited association with the SAM, especially during austral spring.  In contrast, the zonal and mixed nodes were strongly correlated with the SAM however, the regional synoptic representation of SAM positive conditions is not zonally symmetric and is represented by three separate nodes.  These different types of SAM positive conditions mean that the commonly used hemispheric Marshall index often fails to capture the regional variability in surface weather conditions in the southern Indian Ocean. Our results show the importance of considering different synoptic set ups of SAM conditions, particularly SAM positive, and identify conditions that are potentially missed by SAM variability (e.g., extreme precipitation events). Our results are particularly important to consider when interpreting SAM or westerly wind belt reconstructions in the study region (from ice cores, tree rings, or lake sediments).  Here we present a case study using the synoptic typing results to enhance our understanding of the Law Dome (East Antarctica) ice core record, focussing on links to large scale modes of climate variability and Australian hydroclimate.  These results enhance the usefulness of ice core proxies in coastal East Antarctica and assist with determining where and how it is appropriate to use coastal East Antarctic ice core records for reconstructions of large scale modes of climate variability (e.g. SAM and ENSO) and remote hydroclimate conditions.

How to cite: Udy, D., Vance, T., Kiem, A., Holbrook, N., and Curran, M.: Synoptic climatology of southern Indian Ocean and paleoclimate proxy interpretation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3756, https://doi.org/10.5194/egusphere-egu21-3756, 2021.

EGU21-8661 | vPICO presentations | CL1.1

Comparison of isotopic signatures in ice core and speleothem records to an isotope enabled climate model simulation for the last millennium

Yannick Heiser, Janica Bühler, Mathieu Casado, and Kira Rehfeld

Stable water isotope ratios (δ18O) measured in e.g. ice-cores or speleothems have long been established as temperature proxies and are used to reconstruct past climate variability but still require more quantification on spatial and temporal scales. The high resolution ice-core archives are mainly found in polar and alpine regions, whereas the speleothem records mostly grow in caves in low to mid-latitudes. To bridge between the archives, models are needed to compare the climate variability stored in both ice-cores and speleothems, which will help to evaluate future projections of climate variability.

Here, we compare a transient isotope enabled simulation from the Hadley Center Climate Model version 3 (iHadCM3) [1, 2] to polar ice-core records from the iso2k database [3] for the last millennium (LM, 850-1850 CE). We analyze time-averaged isotope ratios and their variability on decadal to centennial timescales to systematically evaluate the offsets and correlation patterns between simulated and recorded isotopes to specific climatic drivers. For better comparability between speleothem and ice core-archives, we also include non-polar ice core records, as well as monitored precipitation δ18O from a global database.

We find the time-averaged δ18O offsets between the simulation and ice-core records to be fairly small for most of the polar ice-core sites, indicating a low simulation climate offset.
As expected, we find the simulated δ18O variability to be higher in the polar regions of ice-core locations, compared to the simulated variability at speleothem cave locations. Recorded δ18O variability is also generally higher as stored in ice-cores, compared to that stored in speleothems. Both speleothems and ice-core records show damping effects on decadal time scales, which can in part be attributed to the temporal resolution of the individual records. This comparison of different proxy archives to isotope-enabled GCM output shows a promising way to evaluate the model’s capability to resolve δ18O variability.

[1]  Bühler, J. C. et al. Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium. Climate of the Past: Discussions 1–30 (2020).

[2]  Tindall, J. C., Valdes, P. J. & Sime, L. C. Stable water isotopes in HadCM3: Isotopic signature of El Niño-Southern Oscillation and the tropical amount effect. Journal of Geophysical Research Atmospheres 114, 1–12 (2009).

[3] Konecky, B. L. et al. The Iso2k database: A global compilation of paleo-δ18O and δ2H records to aid understanding of Common Era climate. Earth System Science Data 12, 2261–2288 (2020).

How to cite: Heiser, Y., Bühler, J., Casado, M., and Rehfeld, K.: Comparison of isotopic signatures in ice core and speleothem records to an isotope enabled climate model simulation for the last millennium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8661, https://doi.org/10.5194/egusphere-egu21-8661, 2021.

EGU21-12729 | vPICO presentations | CL1.1

The contribution of different climate forcings on the global glacier climatic mass balance over the last millennium

Anouk Vlug, Fabien Maussion, Ben Marzeion, Matthias Prange, and Kristin Richter

The mass loss of glaciers and ice caps is one of the major contributors to sea-level rise over the past 120 years. Different climate forcings, both natural and anthropogenic, have an influence on the climate and therefore on glacier mass balance. Glaciers have a slow and delayed response to climate change, and at any point in time, their properties are therefore also a result of past climate changes. In this context, we present global glacier simulations over the last millennium. For these simulations, the Open Global Glacier Model was forced with the fully forced, single forced and control simulations of the Community Earth System Model Last Millennium Ensemble. These simulations show how different climate forcings, i.e., volcanic, greenhouse gasses, solar, orbital, land use & land cover and ozone-aerosol, impact the climatic mass balance, both individually and combined. These influences are then analyzed over time and regionally. In addition to addressing the role of the different forcings, we present the contribution of natural vs anthropogenic forcings on glacier mass balance over the last millennium.

How to cite: Vlug, A., Maussion, F., Marzeion, B., Prange, M., and Richter, K.: The contribution of different climate forcings on the global glacier climatic mass balance over the last millennium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12729, https://doi.org/10.5194/egusphere-egu21-12729, 2021.

EGU21-15684 | vPICO presentations | CL1.1

Sea ice changes in the Chukchi Sea over the Industrial Era based on biomarkers

Youcheng Bai, Marie-Alexandrine Sicre, Jian Ren, Bassem Jalali, Hongliang Li, Long Lin, Zhongqiang Ji, Liang Su, Qingmei Zhu, Haiyan Jin, and Jianfang Chen

EGU21-15966 | vPICO presentations | CL1.1

Compiling a chemistry database from Antarctic ice cores records spanning the past 2000 years

Diana Vladimirova, Elizabeth Thomas, and on behalf of CLIVASH2k

Trends in sea ice extent and atmospheric circulation around Antarctica have exhibited large variability over recent decades. Direct observations such as satellite data cover the past four decades only. Thus, a comparison with paleoclimate archives is essential to understand the natural and anthropogenic components of these recent changes. We have initiated a data call within CLIVASH2k community (http://pastglobalchanges.org/science/wg/2k-network/projects/clivash) to collect all available sodium (Na+) and sulfate (SO42-) concentration and fluxes from Antarctic ice cores. We aim to improve our understanding of large-scale sea-ice variability and atmospheric circulation over the past 2000 years. In this respect, ice cores are a unique archive.

Here we present the new database, which builds on previous efforts by the PAGES community in gathering snow accumulation (Thomas et al. 2017) and stable water isotope data (Stenni et al. 2017).  To date, 88 published and 14 unpublished records have been submitted, 10 of which span the full 2000 years. The data, especially 2000 years-long records are equally distributed over the Antarctic continent and all coastal regions are well represented.  The new data will allow us to investigate interannual and decadal-to-centennial scale variability in sea ice extent and atmospheric circulation and its regional differences over the past 2000 years.

How to cite: Vladimirova, D., Thomas, E., and CLIVASH2k, O. B. O.: Compiling a chemistry database from Antarctic ice cores records spanning the past 2000 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15966, https://doi.org/10.5194/egusphere-egu21-15966, 2021.

EGU21-15355 | vPICO presentations | CL1.1

A multi-century spring precipitation history for northern Iran derived from tree-ring δ18O 

Zeynab Foroozan, Jussi Grießinger, Kambiz Pourtahmasi, and Achim Bräuning

Knowledge about the long-term hydroclimatic variability is essential to analyze the historic course and recent impact of climate change, especially in semi-arid and arid regions of the world. In this study, we present the first tree-ring δ18O chronology for the semi-arid parts of northern Iran based on juniper trees. We were able to reconstruct past hydroclimatic variability for the past 500 years. The highly significant correlation between tree-ring δ18O and spring precipitation indicates the primary influence of spring moisture availability on δ18O variations. The thereof derived precipitation reconstruction reveals short and long-term variability of precipitation intensity, duration, and frequency of dry/wet events. During the past 500 years, the driest period occurred in the 16th century, whereas the 18th century was comparably wet. A gradual decline in the reconstructed spring precipitation is evident since the beginning of the 19th century, culminating in the continuing drought of the 20th century. An analysis of dry/wet years indicated that over the last three centuries, the occurrence of years with a relatively dry spring is increasing. In contrast, more humid spring conditions are decreasing. However, the overall frequency of the occurrence of extreme events increased over the past five centuries. In addition, past hydrological disasters recorded in Persian history were well represented in our reconstruction. Correlations between our reconstructed precipitation record and large-scale circulation systems revealed no significant influence of large-scale climatic drivers on spring precipitation variations in north Iran, which therefore seem to be mostly controlled by a regional climate forcing.

How to cite: Foroozan, Z., Grießinger, J., Pourtahmasi, K., and Bräuning, A.: A multi-century spring precipitation history for northern Iran derived from tree-ring δ18O , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15355, https://doi.org/10.5194/egusphere-egu21-15355, 2021.

EGU21-7550 | vPICO presentations | CL1.1

Maximum latewood density records of Great Basin Bristlecone pine (Pinus Longaeva) from the White Mountains, California

Tom De Mil, Matthew Salzer, Charlotte Pearson, Valerie Trouet, and Jan Van den Bulcke

Great Basin Bristlecone pine (Pinus longaeva) is known for its longevity. The longest continuous tree-ring width chronology covers more than 9000 years. Tree-ring width of upper treeline bristlecone pine trees is influenced by summer temperature variability at decadal to centennial scales, but to infer a temperature signal on interannual scales, Maximum Latewood Density (MXD) is a better proxy. Here, we present a preliminary MXD chronology to investigate the temperature signal in upper treeline and lower elevation bristlecone pines. MXD was measured with an X-ray Computed Tomography toolchain in 24 dated cores,  with the oldest sample dating back to 776 CE. Ring and fibre angles were corrected and two MXD chronologies for different elevations were developed, which will be used to study climate-growth relationships and the effect of elevation on them. Future scanning will allow constructing a 5000+ year-long MXD chronology from upper treeline sites, which will provide an annual-resolution North American temperature record covering the mid-to-late Holocene.

How to cite: De Mil, T., Salzer, M., Pearson, C., Trouet, V., and Van den Bulcke, J.: Maximum latewood density records of Great Basin Bristlecone pine (Pinus Longaeva) from the White Mountains, California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7550, https://doi.org/10.5194/egusphere-egu21-7550, 2021.

EGU21-8995 | vPICO presentations | CL1.1

Response of Siberian trees to climatic changes over the past 1500 years

Olga Churakova (Sidorova), Marina Fonti, Rolf Siegwolf, Tatyana Trushkina, Eugene Vaganov, and Matthias Saurer

We use an interdisciplinary approach combining stable isotopes in tree rings, pollen data, ice cores from temperature-limited environment in the Siberian north and developed a comprehensive description of the climatic changes over the past 1500 years. We found that the Climatic Optimum Period was warmer and drier compared to the Medieval one, but rather similar to the recent period. Our results indicate that the Medieval Warm period in the Taimyr Peninsula started earlier and was wetter compared to the northeastern part of Siberia (northeastern Yakutia). Summer precipitation reconstruction obtained from carbon isotopes in tree-ring cellulose from Taimyr Peninsula significantly correlated with the pollen data of the Lama Lake (Andreev et al. 2004) and oxygen isotopes of the ice core from Severnaya Zemlya (Opel et al. 2013) recording wetter climate conditions during the Medieval Warm period compared to the northeastern part of Siberia. Common large-scale climate variability was confirmed by significant relationship between oxygen isotope data in tree-ring cellulose from the Taimyr Peninsula and northeastern Yakutia, and oxygen isotope ice core data from Severnaya Zemlja during the Medieval Warm period and the recent one. Finally, we showed that the recent warming on the Taimyr Peninsula is not unprecedented in the Siberian north. Similar climate conditions were recorded by stable isotopes in tree rings, pollen, and ice core data 6000 years ago. On the northeastern part of Siberia newly developed a 1500-year summer vapor pressure deficit (VPD) reconstruction showed, that VPD increased recently, but does not yet exceed the maximum values reconstructed during the Medieval Warm period. The most humid conditions in the northeastern part of Siberia were recorded in the Early Medieval period and during the Little Ice Age. However, the increasing VPD under elevated air temperature in the last decades affects the hydrological regime of these sensitive ecosystems by greater evapotranspiration rates. Further VPD increase will significantly affect Siberian forests most likely leading to drought even under additional access of thawed permafrost water.

This work was supported by the FP7-PEOPLE-IIF-2008 - Marie Curie Action: "International Incoming Fellowships" 235122 and "Reintegration Fellowships" 909122 “Climatic and environmental changes in the Eurasian Subarctic inferred from tree-ring and stable isotope chronologies for the past and recent periods” and the Government of Krasnoyarsk Kray and Russian Foundation for Basic Research and Krasnoyarsk Foundation 20-44-240001 “Adaptation of conifer forests on the north of the Krasnoyarsk region (Taimyr Peninsula) to climatic changes after extreme events over the past 1500 years“ awarded to Olga V. Churakova (Sidorova).

How to cite: Churakova (Sidorova), O., Fonti, M., Siegwolf, R., Trushkina, T., Vaganov, E., and Saurer, M.: Response of Siberian trees to climatic changes over the past 1500 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8995, https://doi.org/10.5194/egusphere-egu21-8995, 2021.

EGU21-10485 | vPICO presentations | CL1.1

Europe-Atlantic jet caused dipole mode of European climate and increased climatic extremes

Guobao Xu, Meko Matthew, Lara Klippel, Isabel Dorado-Liñán, and Valerie Trouet

The jet stream configuration over the Atlantic Ocean and the European continent substantially affects climatic extremes in Western Eurasia by transporting heat and vorticity. However, how the Europe-Atlantic jet configuration varies and how it affects European climate on the long time-scales are still unclear. We compiled a network of tree-ring width, blue intensity, and maximum density chronologies from Europe to explore past variability in the summer Europe-Atlantic Jet stream and its influence on regional climate. By combining five regional chronologies, we were able to reconstruct July-August jet stream latitude (JSL) PC2 variability over the past millennium (978-2010 CE) for the Europe-Atlantic domain (30°W to 40°E). Our reconstruction explains 40% of summer JSL PC2 variability over the instrumental period (1948-2010 CE) with strong skill. Our millennial-long reconstruction shows that summer JSL is a relevant driver of the temperature, precipitation, and drought dipoles observed between Northwestern and Southern Europe. Positive summer JSL PC2 values (northward jet position) generally lead to a strengthening of the European summer climate dipole, while negative values (southward jet position) lead to a weak or insignificant dipole mode. Our summer JSL reconstruction shows large variability and a high occurrence rate of extremes over the 20th century, as well as 1200-1350 CE Medieval Climate Anomaly (MCA). The high occurrence rate of summer JSL extremes corresponds to periods with increased number of climatic extremes. Our results suggest that the summer JSL contributes to the European climate dipole both in a long-term context and in its extremes. We also reveal that the occurrence rate of summer JSL extremes is double during the 20th century compared to other periods, especially for the negative extremes, which might be related to anthropogenic warming. Our results suggest a high occurrence rate of summer JSL extremes during the 20th century, leading to more climatic extremes in Europe, as well as a prevailing northward summer JSL position resulting in a weakening climatic dipole.

How to cite: Xu, G., Matthew, M., Klippel, L., Dorado-Liñán, I., and Trouet, V.: Europe-Atlantic jet caused dipole mode of European climate and increased climatic extremes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10485, https://doi.org/10.5194/egusphere-egu21-10485, 2021.

EGU21-5405 | vPICO presentations | CL1.1

Statistical Characteristics of Global Daily Extreme Precipitation during the last 3350 years (1501BC – 1849 AD) 

Woon Mi Kim, Richard Blender, Michael Sigl, Christoph Raible, and Martina Messmer

Torrential rainfall and floods have had devastating impacts on civilizations throughout history. Thus, understanding long-term characteristics of extreme precipitation is necessary to identify physical mechanisms involved in such events and to be able to assess, not only the past, but also the present and future risk of extreme precipitation for society. However, the scarce spatial and temporal distribution of existing datasets on extreme precipitation complicates a detailed study of such events in the paleo climate context.  

In this study, we employ the newly produced seamless simulations from the Community Earth System Model v1.2.2 that covers the period from 1501 BC to 1849 AD to analyze the daily extreme precipitation before the preindustrial period. We explore the statistical characteristics of extreme precipitation and their association with natural external forcing, such as changes in the orbital parameters, solar cycle, insolation, and volcanic eruptions. For this, we applied to the simulations an extreme value analysis  by adopting a peak-over-threshold method (Coles et al., 2001). The 99th percentile of daily precipitation anomalies with respect to 1501BC - 1849AD are taken as the extreme values and these extremes are fitted to the Generalized Pareto Distribution to create time-stationary and covariate models (GPD models) at each grid point.  

The stationary GPD model shows that over the mid-latitudes, high scale and negative shape parameters predominate in the Pacific while the opposite condition occurs in the Atlantic sector. Over the Southern Ocean, low scale and negative shape parameters are more common. The covariate GPD models indicate some connection between the external forcing and extreme precipitation. The changes in the orbital parameters are slightly connected to the extreme precipitation over the tropical Atlantic and southern Indian oceans. Among all the forcing, the volcanic eruptions are the most influential in the extreme precipitation during the past 3350 years. The return periods of extreme precipitation decrease over the tropical Pacific, and the mid-latitude oceans and lands after volcanic eruptions, indicating that such eruptions likely increase the occurrence of extreme precipitation in these regions. Over the regions where a decrease in extreme precipitation is followed after the eruptions, such as India, Australia, and eastern Asia, the return periods decrease after volcanic eruptions.  

Overall, our study provides a long-term continuous view on the global extreme precipitation, which elucidates some complementary information to the currently available proxy and instrumental observations on extreme precipitation events. 

 

Coles, S., Bawa, J., Trenner, L., & Dorazio, P. (2001). An introduction to statistical modeling of extreme values (Vol. 208, p. 208). London: Springer. 

How to cite: Kim, W. M., Blender, R., Sigl, M., Raible, C., and Messmer, M.: Statistical Characteristics of Global Daily Extreme Precipitation during the last 3350 years (1501BC – 1849 AD) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5405, https://doi.org/10.5194/egusphere-egu21-5405, 2021.

EGU21-1692 | vPICO presentations | CL1.1

Depth and seasonal biases in organic temperature proxies: a modelling study

Devika Varma, Gert-Jan Reichart, and Stefan Schouten

For more than a decade TEX86 and UK’37, derived from ratios of biomarker lipids have widely been used as organic paleotemperature proxies. Yet, these proxies, especially TEX86, have several uncertainties associated with factors such as depth and seasonal biases which are complicating its application as an annual mean sea-surface temperature (SST) proxy. To constrain this impact, we performed a relatively simple modelling exercise where we use instrumental temperature and nutrient data from 40 locations across the globe to predict theoretical proxy values and compare them with measured core-top proxy values.

The model first uses instrumental nutrient and temperature data, and probability density functions to predict the theoretical depth occurrence of the source organisms of the two proxies. Additionally, seasonal bias was introduced by predicting seasonal occurrences using instrumental nutrient and chlorophyll data. This was used to calculate the depth- and season weighed temperature signal annually deposited in the sediment, which in turn was converted to theoretical proxy values using culture or mesocosm calibrations. This showed, as expected, that depth and seasonal biases introduced scatter in the correlation between theoretical proxy values and annual mean SST but still highly significant for both UK’37 (r2= 0.96), and TEX86 (r2= 0.77). We find that the theoretical proxy values are much lower than measured proxy value for TEX86, which tentatively suggests that TEX86 might in fact be coming from shallower depths or that the mesocosm calibration is incorrect. Our model for UK’37 results in theoretical values similar to measured values except for low temperature locations. This might suggest an influence of seasonal bias towards more warmer summer seasons which is more pronounced in high latitudes than in tropics.

How to cite: Varma, D., Reichart, G.-J., and Schouten, S.: Depth and seasonal biases in organic temperature proxies: a modelling study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1692, https://doi.org/10.5194/egusphere-egu21-1692, 2021.

EGU21-12106 | vPICO presentations | CL1.1

Transient simulations over the Common Era in PMIP4/CMIP6

Johann Jungclaus, Eduardo Alastrue de Asenjo, Alexandre Cauquoin, Shih-Wei Fang, Myriam Khodri, Stephan Lorenz, Rumi Ohgaito, Teffy Sam, Claudia Timmreck, Matthew Toohey, Martin Werner, Kohei Yoshida, Davide Zanchettin, and Qiong Zhang

The Common Era (CE, i.e. the two millennia before the industrialization) is among the periods selected by the Paleo Model Intercomparison Project (PMIP) for transient experiments contributing to PMIP4. For PMIP4, novel estimates and updates of external forcing have been compiled (Jungclaus et al., GMD, 2017).  In addition to the Tier-1 category simulation “past1000” for the period 850 CE to 1849 CE, the Tier-3 “past2k” experiment covers the entire CE. After serious delays, the ESGF is now being filled by modeling groups running the transient simulations.

Here we provide an overview of the simulations, discuss the range of applied models, and present first results of common analyses from past1000 and subsequent historical simulations. We discuss the long-term climate evolution, the range of internally-generated and externally-forced variability and specific aspects of the response to volcanic forcing.

Another focus is the presentation of the first MPI-ESM ‘past2k’ simulations and their extension to include water isotopes in MPI-ESM-WISO. These simulations extend the pool of current ESM simulations into the 1st millennium CE and represent an important basis to assess the models’ response to external forcing and improved model-data comparison. We analyze regional trends and variations over the last 2000 years in comparison with PAGES2k reconstructions.

 

How to cite: Jungclaus, J., Alastrue de Asenjo, E., Cauquoin, A., Fang, S.-W., Khodri, M., Lorenz, S., Ohgaito, R., Sam, T., Timmreck, C., Toohey, M., Werner, M., Yoshida, K., Zanchettin, D., and Zhang, Q.: Transient simulations over the Common Era in PMIP4/CMIP6, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12106, https://doi.org/10.5194/egusphere-egu21-12106, 2021.

EGU21-16004 | vPICO presentations | CL1.1

Sahel droughts induced by large volcanic eruptions over the last millennium in IPSL-CM6A-LR model

Julián Villamayor and Myriam Khodri

The Sahel region is extremely sensible to alterations in its characteristic precipitation regime, associated with the West African Monsoon (WAM). In fact, the WAM presents strong variability at several timescales which has focused the attention of many works that mainly attribute such changes to variations in the sea surface temperature, the emerging increase of greenhouse gases concentration and to alterations in land use. However, the impact of large volcanic eruptions has been just tentatively addressed. This work aims at shedding more light on the influence of large volcanic eruptions on Sahel rainfall relying on past1000 simulations, covering the last millennium, of the IPSL-CM6A-LR model. The results show the mechanisms involved and the differences between tropical and high-latitude eruptions.

How to cite: Villamayor, J. and Khodri, M.: Sahel droughts induced by large volcanic eruptions over the last millennium in IPSL-CM6A-LR model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16004, https://doi.org/10.5194/egusphere-egu21-16004, 2021.

EGU21-16519 | vPICO presentations | CL1.1

Long-term Surface Temperature (LoST) Database as a Complement for Transient and Control Preindustrial Simulations

Francisco José Cuesta-Valero, Almudena García-García, Hugo Beltrami, Eduardo Zorita, and Fernando Jaume Santero
Estimates of climate sensitivity from Atmosphere-Ocean Coupled General Circulation Model (GCM) simulations present a large spread despite the continued improvements in climate modeling since the 1970s. This variability is partially caused by the dependence of several long-term feedback mechanisms on the reference climate state. However, it is difficult to provide a reference to assess the climatology of preindustrial control simulations as there are no long-term preindustrial observations.
In the ground, recent changes in ground surface temperature are observed at shallow depths as perturbations to the quasi-steady state geothermal regime. However, if undisturbed by recent surface temperature changes, the deep ground temperatures vary linearly as a function of depth, and the extrapolation of this linear behavior to the surface can be interpreted as the past long-term surface temperature climatology.
We assemble a new gridded database of past long-term ground surface temperatures (LoST database) obtained from 514 borehole temperature profiles measured across North America, and we explore its use as a potential reference for the evaluation of GCM preindustrial control simulations and past millennium simulations. All temperature profiles are truncated at 300 m depth, allowing to estimate the ground surface climatology for the period 1300-1700 of the common era. We compare the LoST database with observations from the CRU database, as well as with five past millennium simulations and five preindustrial control simulations from the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3) and the fifth phase of the Coupled Model Intercomparison Project (CMIP5) archives. Our results suggest that LoST temperatures could be employed as a reference to narrow down the spread of surface temperature climatologies on GCM preindustrial control and past millennium simulations.

How to cite: Cuesta-Valero, F. J., García-García, A., Beltrami, H., Zorita, E., and Jaume Santero, F.: Long-term Surface Temperature (LoST) Database as a Complement for Transient and Control Preindustrial Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16519, https://doi.org/10.5194/egusphere-egu21-16519, 2021.

CL1.2 – Palaeoclimate modeling: from time-slices and sensitivity experiments to transient simulations into the future

EGU21-6574 | vPICO presentations | CL1.2 | Highlight

North American rainfall patterns during past warm states: A proxy network-model comparison for the Last Interglacial and the mid-Holocene

Cameron de Wet, Jessica Oster, Daniel Ibarra, and Bryce Belanger

The Last Interglacial (LIG) period (~129,000–116,000 years BP) and the mid-Holocene (MH) (~6,000 years BP) are the two most recent intervals with temperatures comparable to low emissions scenarios for the end of the 21st century. During the LIG and the MH differences in the seasonal and latitudinal distribution of insolation led to enhanced northern hemisphere high-latitude warmth relative to the pre-industrial, despite similar greenhouse gas concentrations, marking these intervals as potentially useful analogs for future change in regions like North America. Further, the inclusion of both LIG (127 ka) and MH (6 ka) experiments in the CMIP6-PMIP4 effort provides an opportunity to better understand the regional hydroclimate responses to radiative forcing during these two intervals. The dense coverage of paleoclimate proxy records for North America during the MH (N=260 sites) reveals a pattern of relative aridity in the Pacific Northwest and Western Canada and wetness in the southern Great Basin and Mexico. However, the seasonality and driving mechanisms of rainfall patterns across the continent remain poorly understood. Our understanding of terrestrial hydroclimate in North America during the LIG is more limited (N=39 sites), largely because the LIG is beyond the range of radiocarbon dating.

Here we present spatial comparisons between output from 14 PMIP4 global circulation models and LIG and MH networks of moisture-sensitive proxies compiled for the North American continent. We utilize two statistical measures of agreement – weighted Cohen’s Kappa and Gwet’s AC2 – to assess the degree of categorical agreement between moisture patterns produced by the models and the proxy networks for each time-slice. PMIP4 models produce variable precipitation anomalies relative to the pre-industrial for both the LIG and MH experiments, often disagreeing on both the sign and magnitude of precipitation changes across much of North America. The models showing the best agreement with the proxy network are similar but not identical for the two measures, with Gwet’s AC2 values tending to be larger than Cohen’s Kappa values for all models. This pattern is enhanced for the much larger MH proxy network and is likely related to the fact that Gwet’s AC2 is a more predictable statistic in the presence of high agreement. Overall agreement is lower for the mid-Holocene than for the LIG, reflecting smaller MH rainfall anomalies in the models. The models with the highest agreement scores during the LIG produce aridity in the Rocky Mountains and Pacific Northwest and wetness in Alaska, the Yukon, the Great Basin, and parts of the Mid-West and Eastern US, although spatial coverage of the proxies in these latter two regions is poor. The models with the highest agreement score for the mid-Holocene tend to produce aridity across Canada and the northern US with dry conditions extending down the US Pacific coast and increased wetness in the American Southeast and across the North American Monsoon region. Our analyses help elucidate the driving mechanisms of rainfall patterns during past warm states and can inform which models may be the most useful for predictions of near-future hydroclimate change across North America.

How to cite: de Wet, C., Oster, J., Ibarra, D., and Belanger, B.: North American rainfall patterns during past warm states: A proxy network-model comparison for the Last Interglacial and the mid-Holocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6574, https://doi.org/10.5194/egusphere-egu21-6574, 2021.

EGU21-3185 | vPICO presentations | CL1.2

Paleo-climate shifts in the Atacama Desert from PMIP4 simulations

Mark Reyers, Stephanie Fiedler, and Yaping Shao

The Atacama Desert in Northern Chile is considered to be the driest desert on Earth. At present, the annual rainfall amount is less than 1mm for parts of the hyper-arid core of the desert. The processes controlling this hyper-aridity are known, but the mean state and variability of the regional climate on geological time scales is not well understood. In this study, we aim to analyse climate conditions in the Atacama Desert from PMIP4 simulations. Our focus is on the Last Glacial Maximum (LGM), when climate records from the Central Atacama point to a substantially different climate with wetter conditions than at present (Diederich et al., 2020). We statistically analyse and evaluate PMIP4 historical simulations with respect to circulation patterns over the Southeast Pacific and Western South America which are associated with rare rainfall events in the Atacama Desert. For the evaluation, PMIP4 simulations for the historical period are compared to Reanalysis data, and we will focus on troughs and cutoff lows over the subtropical Southeast Pacific, and on the Bolivian High (Reyers et al., 2020). We then assess changes of the characteristics, e.g., the frequency of occurrence, of such circulation patterns for Paleo-climate conditions compared to the present. In the framework of our study, we perform km-scale simulations with the regional climate model WRF, using results from PMIP4 experiments for the historical period and for the LGM as boundary conditions. In the future, these simulations will be used to better understand the meso-scale processes, e.g., involved in local wind systems, that contribute to changes in the hydrological cycle and potentially impact the dust-emission activity of the desert. This study is part of the Collaborative Research Centre 1211 “Earth- Evolution at the dry Limit” (https://sfb1211.uni-koeln.de/).

Diederich, J,  Wennrich, V, Bao, R, and co-authors (2020). A 68 ka precipitation record from the hyperarid core of the Atacama Desert in northern Chile. Global and Planetary Change, 184, 103054. DOI:10.1016/j.gloplacha.2019.103054.

Reyers, M, Boehm, C, Knarr, L, Shao, Y, and Crewell, S (2020). Synoptic-to-Regional-Scale Analysis of Rainfall in the Atacama Desert (18°–26°S) Using a Long-Term Simulation with WRF. Monthly Weather Review, 149, 91-112. DOI:10.1175/MWR-D-20-0038.1.

How to cite: Reyers, M., Fiedler, S., and Shao, Y.: Paleo-climate shifts in the Atacama Desert from PMIP4 simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3185, https://doi.org/10.5194/egusphere-egu21-3185, 2021.

EGU21-12167 | vPICO presentations | CL1.2

External and internal forcing of African Humid Periods from MIS 6 to MIS 1

Mateo Duque-Villegas, Martin Claussen, Victor Brovkin, and Thomas Kleinen

During the last million years, northern Africa has alternated between arid and humid conditions, as recorded by different kinds of climate archives, including fossil pollen, lake sediments, marine sediments and archaeological remains. Variations occur at millennial scale, with dry phases being similar to the current desert state in the region, and with wet phases, known as African Humid Periods (AHPs), characterised by a strong summer monsoon which can carry enough moisture inland to support rivers, lakes and lush vegetation further north than seen today. Recent sediment records from the Mediterranean Sea revealed that the previous five AHPs had different intensities, in relation to rainfall and vegetation extent. Motivated by these findings, our work focuses on explaining what caused such differences in intensity. To this end, we use the CLIMBER-2 climate model to study the AHP response to changes in three drivers of atmospheric dynamics: Earth's orbit variations, atmospheric concentration of CO2 and inland ice extent. Global transient simulations of the last 190,000 years are used in new factorisation analyses, which allow us to separate the individual contributions of the forcings to the AHP intensity, as well as those of their synergies. We confirm the predominant role of the orbital forcing in the strength of the last five AHPs, and our simulations agree with previous estimates of a threshold in orbital forcing above which an AHP develops. Moreover, we show that atmospheric CO2 and the extent of ice sheets can also add up to be as important as the orbital parameters. High values of CO2, past a 205 ppm threshold, and low values of ice sheets extent, below an 8 % of global land surface threshold, yield the AHPs with the most precipitation and vegetation. Additionally, our results show that AHPs differ not only in amplitude, but also in their speed of change, and we find that the non-linear vegetation response of AHPs does not correlate with a single forcing and that the vegetation growth response is faster than its subsequent decline. In regards to future change, an extension of the simulations until the next 50,000 years, shows CO2 to be the main driver of AHPs, with orbital forcing only setting the pace and their intensities being scenario-dependent.

How to cite: Duque-Villegas, M., Claussen, M., Brovkin, V., and Kleinen, T.: External and internal forcing of African Humid Periods from MIS 6 to MIS 1, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12167, https://doi.org/10.5194/egusphere-egu21-12167, 2021.

During the mid-Holocene, an expansion of vegetation, lakes and wetlands over North Africa reinforced the West African monsoon precipitation increase that was initiated by changes in the orbital forcing. Sedimentary records reflect these surface changes, however, they provide only limited spatial and temporal information about the size and distribution of mid-Holocene lakes and wetlands. Previous simulation studies that investigated the influence of mid-Holocene lakes and wetlands on the West African monsoon precipitation, prescribed either a small lake and wetland extent or focusing on mega-lakes only. In contrast to these simulation studies, we investigate the range of simulated West African monsoon precipitation changes caused by a small and a potential maximum lake and wetland extent during the mid-Holocene.

Therefore, four mid-Holocene sensitivity experiments are conducted using the atmosphere model ICON-A and the land model JSBACH4 at 160 km resolution. The simulations have a 30-year evaluation period and only differ in their lake and wetland extent over North Africa: (1) pre-industrial lakes, (2) small lake extent, (3) maximum lake extent and (4) maximum wetland extent. The small lake extent is given by the reconstruction map of Hoelzmann et al. (1998) and the potential maximum lake and wetland extent is given by a model derived map of Tegen et al. (2002).

The simulation results reveal that the maximum lake extent shifts the Sahel precipitation threshold (> 200 mm/year) about 3 ° further northward than the small lake extent. The major precipitation differences between the small and maximum lake extent results from the lakes over the West Sahara. Additionally, the maximum wetland extent causes a stronger West African monsoon precipitation increase than the equally large maximum lake extent, particularly at higher latitudes.

How to cite: Specht, N., Claußen, M., and Kleinen, T.: Influence of a small and maximum lake and wetland extent on the simulated West African monsoon precipitation during the mid-Holocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15050, https://doi.org/10.5194/egusphere-egu21-15050, 2021.

EGU21-10640 | vPICO presentations | CL1.2

Dominant role of the global monsoon intensity on large-scale Holocene vegetation transitions

Anne Dallmeyer, Martin Claussen, and Ulrike Herzschuh

We give an overview on the global change in mid-to late Holocene vegetation pattern derived from a transient MPI-ESM1.2 simulation and discuss the vegetation trend in the context of the simulated Holocene climate change. The model captures the main trends found in reconstructions. Most prominent are the southward retreat of the northern treeline, coinciding the strong reduction of forest cover in the high northern latitudes during the Holocene, and the vast increase of the Sahara desert that is embedded in a general decrease and equator-ward retreat of the vegetation in the northern hemispheric monsoon margin regions. In contrast, large parts of the extratropical North American continent experience a greening during the Holocene, caused by an increase in forest and grass cover.

While the broad forest decline in the high northern latitudes can mainly be explained by the cooling of the warm season climate, precipitation is the driving factor for the tropical and extratropical vegetation trends on the northern hemisphere south of 60°N. The model indicates that most of the changes in rainfall can be related to the weakening of the northern hemispheric monsoon systems and the response of the global atmospheric circulation to this weakening.

The southern hemisphere is less affected by changes in total vegetation cover during the last 8000 years, but the monsoon related increase in precipitation and the insolation-induced cooling of the winter climate lead to shifts in the vegetation composition, mainly in between the woody plant functional types (PFTs).

The simulated large-scale global vegetation pattern almost linearly follow the subtle, approximately linear orbital forcing. Non-linear and more rapid changes in vegetation cover occur only on a regional level. The most striking area is the western Sahel-Sahara domain that experiences a rapid vegetation decline to a rather desertic state, in line with a strong decrease in moisture availability. The model also indicates rapid shifts in the vegetation composition in some regions in the high northern latitudes, in South Asia and in the monsoon margins of the southern hemisphere. These rapid transitions are mainly triggered by changes in the winter temperatures, which go into, or move out of, the bioclimatic tolerance range of the individual PFTs defined in the model and therefore have to be interpreted differently.

In summary, our model results identify the global monsoon system as the key player in Holocene climate and vegetation history and point to a far greater importance of the monsoon systems on the extra-monsoonal regions than previously assumed.

How to cite: Dallmeyer, A., Claussen, M., and Herzschuh, U.: Dominant role of the global monsoon intensity on large-scale Holocene vegetation transitions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10640, https://doi.org/10.5194/egusphere-egu21-10640, 2021.

EGU21-3792 | vPICO presentations | CL1.2

PMIP4/CMIP6 last interglacial simulations using three different versions of MIROC: importance of vegetation

Ryouta O'ishi, Wing-Le Chan, Ayako Abe-Ouchi, Sam Sherriff-Tadano, Rumi Ohgaito, and Masakazu Yoshimori

We carry out three sets of last interglacial (LIG) experiments, named lig127k, and of pre-industrial experiments, named piControl, both as part of PMIP4/CMIP6 using three versions of the MIROC model: MIROC4m, MIROC4m-LPJ, and MIROC-ES2L. The results are compared with reconstructions from climate proxy data. All models show summer warming over northern high-latitude land, reflecting the differences between the distributions of the LIG and present-day solar irradiance. Globally averaged temperature changes are −0.94 K (MIROC4m), −0.39 K (MIROC4m-LPJ), and −0.43 K (MIROC-ES2L).
Only MIROC4m-LPJ, which includes dynamical vegetation feedback from the change in vegetation distribution, shows annual mean warming signals at northern high latitudes, as indicated by proxy data. In contrast, the latest Earth system model (ESM) of MIROC, MIROC-ES2L, which considers only a partial vegetation effect through the leaf area index, shows no change or even annual cooling over large parts of the Northern Hemisphere. Results from the series of experiments show that the inclusion of full vegetation feedback is necessary for the reproduction of the strong annual warming over land at northern high latitudes. The LIG experimental results show that the warming predicted by models is still underestimated, even with dynamical vegetation, compared to reconstructions from proxy data, suggesting that further investigation and improvement to the climate feedback mechanism are needed.

How to cite: O'ishi, R., Chan, W.-L., Abe-Ouchi, A., Sherriff-Tadano, S., Ohgaito, R., and Yoshimori, M.: PMIP4/CMIP6 last interglacial simulations using three different versions of MIROC: importance of vegetation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3792, https://doi.org/10.5194/egusphere-egu21-3792, 2021.

EGU21-4304 | vPICO presentations | CL1.2

Contribution of forcings to Holocene climate evolution

Peter Hopcroft and Paul Valdes

The climate evolution of the past few thousand years is essential for understanding the context in which civilisation arose and for understanding the natural background of anthropogenic influence. Proxy-inferred records show a complex picture of earlier warming and later cooling during the Holocene depending on region and reconstruction method. In contrast climate model simulations almost uniformly show warming throughout the past 10,000 years and for example also fail to reproduce a major advance of rainbelt over the Sahara.  These discrepancies raise questions about the reliability of climate models on longer-time scales.

We present a suite of four new transient Holocene simulations covering the last 8500 years using the HadCM3B-M21aD coupled general circulation. We use an optimised version of this model which is able to replicate the greening of the Sahara through changes to the atmospheric convection and vegetation schemes. We apply transient changes in Earth’s orbit, ice-sheets and sea-level and greenhouse gases, and optionally solar output, volcanic eruptions and anthropogenic land-use change.  The simulations without land-use show a warming throughout the Holocene, albeit with significantly higher variability once volcanic eruptions are included. With the inclusion of land-use change temperature trends in Northern Hemisphere are reversed from around 4000 years before present.

We explore the contribution of different forcings to the regional trends in the model ensemble and we compare the simulations against the Holocene reconstructions to evaluate the relative importance of each forcing. We also use the model ensemble to quantify the terrestrial coverage of proxy locations that is required to reliably infer global mean temperature variations.

How to cite: Hopcroft, P. and Valdes, P.: Contribution of forcings to Holocene climate evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4304, https://doi.org/10.5194/egusphere-egu21-4304, 2021.

EGU21-13896 | vPICO presentations | CL1.2

Speleothems of South American and Asian Monsoons Influenced by a Green Sahara

Clay Tabor, Bette Otto-Bliesner, and Zhengyu Liu

Compared to preindustrial, the mid-Holocene (6 ka) had significantly greater Northern Hemisphere summer insolation, slightly warmer global surface temperature, and slightly lower CO2 concentration. Vegetation was also different during the mid-Holocene. Possibly most prominent was the growth of temperate vegetation in the now barren Sahara. This Saharan vegetation response was related to intensification of the African Monsoon associated with the mid-Holocene orbital configuration. Hydroclimate of the Asian Monsoon and South American Monsoon also responded to mid-Holocene forcings, with general wetting and drying, respectively.

The mid-Holocene is frequently used for model-proxy comparison studies. However, climate models often struggle to replicate the proxy signals of this period. Here, we attempt to reduce these model-proxy discrepancies by exploring the significance of a vegetated Sahara during the mid-Holocene. Using the water isotopologue tracer enabled version of the Community Earth System Model (iCESM1), we perform mid-Holocene simulations that include and exclude temperate vegetation in the Sahara. We compare our model results with δ18O values from mid-Holocene speleothem records in the Asian and South American Monsoon regions.

We find that inclusion of vegetated Sahara during the mid-Holocene leads to global warming, alters the hemispheric distribution of energy, and generally amplifies the δ18O of precipitation responses in the South American and Asian Monsoon regions; these feedbacks improve the δ18O agreement between model outputs and speleothem records of the mid-Holocene. Our results highlight the importance of regional vegetation alteration for accurate simulation of past climate, even when the region of study is far from the source of vegetation change.

How to cite: Tabor, C., Otto-Bliesner, B., and Liu, Z.: Speleothems of South American and Asian Monsoons Influenced by a Green Sahara, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13896, https://doi.org/10.5194/egusphere-egu21-13896, 2021.

EGU21-1842 | vPICO presentations | CL1.2

Comparing temperature trends and variability over the Holocene in climate models of low and high complexity

Christian Wirths, Elisa Ziegler, Matthew Toohey, Julie Christin Schindlbeck-Belo, Steffen Kutterolf, Heather Anders, and Kira Rehfeld

Modeled and observed temperature trends over the Holocene disagree. Proxy reconstructions suggest global cooling during the late Holocene. Model simulations, on the other hand, show a warming trend for the entire Holocene, a contradiction known as the Holocene temperature conundrum.  

A recent study by Bader et. al. (2020) introduced a new approach to the question by proposing the coexistence of a cooling and warming climate mode. While the warming mode is proposed to be related to changes in greenhouse gas concentrations, the physical process behind the cooling mode might be a change in the seasonal cycle of Arctic sea-ice. It’s unclear to what extent this process is responsible for the observed climate response. Depending on their strength and location these modes have strong implications for proxy data interpretation and location selection when calculating global mean temperatures.   

Here, we investigate if similar modes and temperature trends can be found in models of different complexity. Therefore, we use a 2D Energy Balance Model (EBM), with solar, volcanic, ice-sheet and greenhouse gas forcing, for transient simulations of the Holocene climate. We analyze these Holocene climate simulations in terms of global and regional temperature trends, modes and variability patterns. We conduct sensitivity tests to examine the influence of the forcings on those trends and modes. In particular, we are interested in the influence of volcanic eruptions on the Holocene climate. Furthermore, we compare our model results with temperature reconstructions and simulations from Earth System Models.    

Altogether, we comprehensively analyze Holocene climate as simulated by a conceptual EBM, a state-of-the-art Earth System Model and proxy reconstructions. The results provide insight into whether models of different complexity produce similar modes and trends and whether these occur due to climate forcing rather than internal processes of the earth system. Finally, we will provide a better understanding of Holocene cooling and warming and the interpretation of differences between Holocene temperature proxy reconstructions and climate model simulations.    

 

References:  
Bader, J., Jungclaus, J., Krivova, N. et al. Global temperature modes shed light on the Holocene temperature conundrum. Nat Commun 11, 4726 (2020). https://doi.org/10.1038/s41467-020-18478-6 

How to cite: Wirths, C., Ziegler, E., Toohey, M., Schindlbeck-Belo, J. C., Kutterolf, S., Anders, H., and Rehfeld, K.: Comparing temperature trends and variability over the Holocene in climate models of low and high complexity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1842, https://doi.org/10.5194/egusphere-egu21-1842, 2021.

EGU21-15712 | vPICO presentations | CL1.2

Temporal evolution of sea surface temperatures in the coastal upwelling off North Africa

Marie-Alexandrine Sicre, Eva Moreno, Vincent Klein, Anna Alves, and Simon Puaud

This study presents new high-resolution reconstructions of sea surface temperatures (SSTs) obtained from alkenones off the coast of North West Africa between 19 °N and xx 27°N latitude. Sediment grain-size distributions were also generated to provide new information on the Moroccan and Mauritanian upwelling zone over the Industrial Era. Our data shows that over the past two centuries, SSTs gradually increased in the southernmost cores, while in the northernmost sites they show cooling. Changes in sea level pressure and temperature gradients between land and sea would have caused major changes in atmospheric circulation by disrupting and intensifying the system of North-East winds (Trade winds) and southwest Monsoon winds. With global warming, increase in the monsoon might be expected, causing the weakening easterly winds favorable to the formation of upwellings. Enhanced stratification of the water column would prevent upwelling to develop accounting for surface water warming with consequences on the ecosystems and fisheries.

How to cite: Sicre, M.-A., Moreno, E., Klein, V., Alves, A., and Puaud, S.: Temporal evolution of sea surface temperatures in the coastal upwelling off North Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15712, https://doi.org/10.5194/egusphere-egu21-15712, 2021.

EGU21-12364 | vPICO presentations | CL1.2

AMOC instability during the Last Inerglacial

Augustin Kessler, Didier Roche, Eirik Galaasen, Jerry Tjiputra, Nathaelle Bouttes, and Ulysses Ninnemann

Multiple evidences from the analysis of satellite, in-situ and proxy data show that the climate is already changing toward a warmer Earth System due to our emissions of CO2 into the atmosphere. However, the magnitude and the extent of changes remain difficult to predict. A change in the ocean thermohaline circulation and its consequences for climate, such as drought, regional sea-level and ocean carbon uptake remain under debate as this circulation has been long thought to be stable during warm Earth periods – Interglacials. However, recent high-resolution reconstructions of carbon isotopes (δ13C) from the deep North Atlantic challenge this idea of stability and point toward abrupt modifications in the ocean interior biogeochemistry and/or ocean thermohaline circulation during the Last Interglacial (LIG, 125ka – 115ka).

 

Our model simulation of the LIG reproduces the observed magnitude and timescale of the reconstructed variations of δ13C, highlighting crucial dynamical changes in two regions of the North Atlantic deep-water formation (south of Greenland and south of Svalbard). These regions are found to drive the variations in the strength of the Atlantic Overturning Circulation (AMOC) when the Arctic sea-ice extent is perturbed.

 

Our study suggests that the AMOC may have experienced great instability phase during some parts of the LIG. The water mass geometry reorganization from the warm onset at 125ka to the glacial inception at 115ka could also have greatly impacted the distribution of carbon in the interior Ocean. Changes in sea-ice cover either south of Svalbard or in the Southern Ocean seem to play a determining role. However, in our global warming context, our study suggests that the mechanisms responsible for the LIG AMOC instability of the LIG may not occur by the end of the century if the Arctic sea-ice retreats from the high latitudes of the North Atlantic as projected by climate models.

 

How to cite: Kessler, A., Roche, D., Galaasen, E., Tjiputra, J., Bouttes, N., and Ninnemann, U.: AMOC instability during the Last Inerglacial, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12364, https://doi.org/10.5194/egusphere-egu21-12364, 2021.

EGU21-7707 | vPICO presentations | CL1.2

Simulation of the mid-Pliocene Warm Period using HadGEM3-GC31-LL: Pliocene climate relative to the pre-industrial era, previous model versions, other climate models and proxy data

Charles Williams, Daniel Lunt, Alistair Sellar, William Roberts, Robin Smith, Peter Hopcroft, and Emma Stone

To better understand the processes contributing to future climate change, palaeoclimate model simulations are an important tool because they allow testing of the models’ ability to simulate very different climates than that of today.  As part of CMIP6/PMIP4, the latest version of the UK’s physical climate model, HadGEM3-GC31-LL (hereafter, for brevity, HadGEM3), was recently used to simulate the mid-Holocene (~6 ka) and Last Interglacial (~127 ka) simulations and the results were compared to the preindustrial era, previous versions of the same model and proxy data (see Williams et al. 2020, Climate of the Past).  Here, we use the same model to go further back in time, presenting the results from the mid-Pliocene Warm Period (~3.3 to 3 ma, hereafter the “Pliocene” for brevity).  This period is of particular interest when it comes to projections of future climate change under various scenarios of CO2 emissions, because it is the most recent time in Earth’s history when CO2 levels were roughly equivalent to today.  In response, albeit due to slower mechanisms than today’s anthropogenic fossil fuel driven-change, during the Pliocene global mean temperatures were 2-3°C higher than today, more so at the poles.

 

Here, we present results from the HadGEM3 Pliocene simulation.  The model is responding to the Pliocene boundary conditions in a manner consistent with current understanding and existing literature.  When compared to the preindustrial era, global mean temperatures are currently ~5°C higher, with the majority of warming coming from high latitudes due to polar amplification from a lack of sea ice.  Relative to other models within the Pliocene Modelling Intercomparison Project (PlioMIP), this is the 2nd warmest model, with the majority of others only showing up to a 4.5°C increase and many a lot less.  This is consistent with the relatively high sensitivity of HadGEM3, relative to other CMIP6-class models.  When compared to a previous generation of the same UK model, HadCM3, similar patterns of both surface temperature and precipitation changes are shown (relative to preindustrial).  Moreover, when the simulations are compared to proxy data, the results suggest that the HadGEM3 Pliocene simulation is closer to the reconstructions than its predecessor.

How to cite: Williams, C., Lunt, D., Sellar, A., Roberts, W., Smith, R., Hopcroft, P., and Stone, E.: Simulation of the mid-Pliocene Warm Period using HadGEM3-GC31-LL: Pliocene climate relative to the pre-industrial era, previous model versions, other climate models and proxy data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7707, https://doi.org/10.5194/egusphere-egu21-7707, 2021.

EGU21-11408 | vPICO presentations | CL1.2

Enhanced humidity in SW Iberia driven by the combination of insolation and ice-sheet forcing during MIS 13 interglacial

Dulce Oliveira, Stéphanie Desprat, Qiuzhen Yin, Teresa Rodrigues, Filipa Naughton, Ricardo Trigo, Qianqian Su, Joan O. Grimalt, Montserrat Alonso-Garcia, Antje H.L. Voelker, Fátima Abrantes, and Maria Fernanda Sánchez Goñi

Marine Isotope Stage (MIS) 13, ~500 ky ago, represents a Quaternary interglacial of primary interest due to the unexpected enhancement of monsoon systems under a cool climate characterised by low atmospheric CO2 and larger ice volume than the present interglacial. Yet, key questions remain about its regional expression (intensity, climate variability, length) and underlying forcing factors. Here we examine the SW Iberian vegetation and terrestrial climate during MIS 13 directly compared with the sea surface temperatures using sediments from IODP Site U1385, and combine those terrestrial-marine profiles with climate-model experiments. We show for the first time that MIS 13 stands out for its large forest expansions with a reduced Mediterranean character alternating with muted forest contractions, indicating that this stage is marked by a cool-temperate climate regime with high levels of humidity. Results of our data-model approach reveal that that the dominant effect of MIS 13 insolation forcing on the regional vegetation and precipitation regime in SW Iberia is amplified by the relatively large extent of the ice-sheets in high northern latitudes. In qualitative agreement with the pollen-based evidence, model results show that ice-sheet forcing triggers an increase in the SW Iberian tree fraction along with both intensified winter and summer rainfall. We propose that the interactions between ice-sheets and major atmospheric circulation systems may have resulted in the persistent influence of the mid-latitude cells over the SW Iberian region, which led to intensified moisture availability and reduced seasonality, and, in turn, to a pronounced expansion of the temperate forest.

How to cite: Oliveira, D., Desprat, S., Yin, Q., Rodrigues, T., Naughton, F., Trigo, R., Su, Q., Grimalt, J. O., Alonso-Garcia, M., Voelker, A. H. L., Abrantes, F., and Sánchez Goñi, M. F.: Enhanced humidity in SW Iberia driven by the combination of insolation and ice-sheet forcing during MIS 13 interglacial, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11408, https://doi.org/10.5194/egusphere-egu21-11408, 2021.

EGU21-13907 | vPICO presentations | CL1.2

Mid-Pliocene mesic subtropical hydroclimate over continents driven by land surface changes

Ran Feng, Tripti Bhattacharya, Bette Otto-bliesner, and Esther Brady and the PlioMIP2

Earth System Models (ESMs) project drying of the northern subtropics by the end of the 21st century. However, geologic evidence from intervals with elevated concentrations of atmospheric carbon dioxide (pCO2), like the mid-Pliocene, suggest mesic subtropical conditions. Several hypotheses, including an El Niño-like SST pattern and weaker Hadley circulation, have been proposed to explain this mismatch. Here, we show that PlioMIP2 ensemble broadly capture the pattern of proxy reconstructed Pliocene hydroclimate, notably a wetter Sahel and southeast Asia. Sensitivity simulations reveal that this pattern is driven by summertime rainfall increases as a result of lowered albedo and a distinct surface warming pattern, generated by prescribed vegetation and ice sheet changes. The resultant tropospheric moistening and stationary wave pattern enhance moisture convergence into the northern subtropics. Our results suggest that mid-Pliocene hydroclimate is part of the Earth system feedback to sustained CO2 concentrations similar to today.

How to cite: Feng, R., Bhattacharya, T., Otto-bliesner, B., and Brady, E. and the PlioMIP2: Mid-Pliocene mesic subtropical hydroclimate over continents driven by land surface changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13907, https://doi.org/10.5194/egusphere-egu21-13907, 2021.

EGU21-9760 | vPICO presentations | CL1.2

Impact of Arctic gateways closure on the Atlantic Meridional Overturning Circulation in the Pliocene

Julia Weiffenbach, Michiel Baatsen, and Anna von der Heydt

The mid-Pliocene climate is the most recent geological period with a greenhouse gas concentration of approximately 400 ppmv, similar to the present day. Proxy reconstructions indicate enhanced warming in the high North Atlantic in the mid-Pliocene, which has been suggested to be a response to a stronger Atlantic Meridional Overturning Circulation (AMOC). PlioMIP2 ensemble results show a stronger AMOC and simulated North Atlantic sea surface temperatures (SSTs) match reconstructions better than PlioMIP1. A major difference between PlioMIP1 and PlioMIP2 is the closure of the Bering Strait and Canadian Archipelago in the Pliocene. Previous studies have shown that closure of these Arctic gateways leads to an enhanced AMOC due to altered freshwater fluxes in the Arctic.

Analysis of our Community Earth System Model (CESM1) simulations shows that the simulated increase in North Atlantic SSTs and strengthened AMOC in the Pliocene is a result of Pliocene boundary conditions rather than CO2 concentration increase. Here we compare results from two runs with pre-industrial boundary conditions and 280 and 560 ppmv CO2 concentrations and three runs with PlioMIP2 boundary conditions and 280, 400 and 560 ppmv CO2 concentrations. Results show a 10-15% stronger AMOC in the Pliocene simulations as well as enhanced warming and saltening of the North Atlantic sea surface. While there is a stronger AMOC, the Atlantic northward ocean heat transport (OHT) in the Pliocene simulations only increases 0-3% with respect to the pre-industrial. Analysis indicates there is an altered relationship between the AMOC and OHT in the Pliocene, pointing to fundamentally different behavior of the AMOC in the Pliocene simulations. This is supported by a specific spatial pattern of deep water formation (DWF) areas in the Pliocene simulations that is significantly different from that of the pre-industrial. In the Pliocene simulations, DWF areas adjacent to south Greenland disappear and new DWF areas appear further southwards in the Labrador Sea off the coast of Newfounland. These results indicate that insight into the effect of the palaeogeographic boundary conditions is crucial to understanding the Pliocene climate and its potential as a geological equivalent to a future greenhouse climate.

How to cite: Weiffenbach, J., Baatsen, M., and von der Heydt, A.: Impact of Arctic gateways closure on the Atlantic Meridional Overturning Circulation in the Pliocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9760, https://doi.org/10.5194/egusphere-egu21-9760, 2021.

EGU21-8383 | vPICO presentations | CL1.2

Model-data comparison in a strongly eddying Eocene ocean

Peter Nooteboom, Michiel Baatsen, Peter Bijl, Erik van Sebille, Appy Sluijs, Henk Dijkstra, and Anna von der Heydt

Simulations of the geological past using General Circulation Models (GCMs) are computationally expensive. Mainly because of the long equilibration time scales, most of these GCMs have ocean components with a horizontal resolution of 1° or coarser. Such models are non-eddying and the effects of mesoscale ocean eddies on the transport of heat and salt are parameterized. However, from present-day ocean modeling studies, it is known that eddying ocean models better represent regional and time-mean ocean flows compared to non-eddying models. At the same time, proxy data from sediment sample sites represent climate at specific locations. Hence, the coarse ocean resolution of typical palaeo-GCMs lead to a challenge for model-data comparison in past climates.

Here we present the first simulations of a global eddying Eocene ocean with a 0.1° (horizontal) resolution model, which are initialized and forced with data from a coarser resolution (1° horizontally) equilibrated coupled ocean-atmosphere GCM. We investigate the response of the model equilibrium state to the change in ocean resolution and the consequences this has for model-data comparison in the middle-late Eocene (38Ma). We find that, compared to the non-eddying model, the eddying ocean resolution of palaeomodels reduce the biases in both sea surface temperatures and biogeographic patterns which are derived from proxy data.

How to cite: Nooteboom, P., Baatsen, M., Bijl, P., van Sebille, E., Sluijs, A., Dijkstra, H., and von der Heydt, A.: Model-data comparison in a strongly eddying Eocene ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8383, https://doi.org/10.5194/egusphere-egu21-8383, 2021.

Early Eocene Climatic Optimum (EECO, ~53-51 million years) is one of the past warm periods, associated with high CO2 concentrations (~900-2500 ppmv), which can serve as an analogue for our possible future, high C02 climate. One notable feature of this hothouse climate state is the weaker meridional temperature gradient relative to pre-industrial values. This have been confirmed by both proxies and models, but the extent of the temperature gradient still requires more research. Models are challenged to reproduce the stronger than present day polar amplification signal, and it is also shown that high latitude proxy data are often influenced by seasonal bias. Thus, there is an uncertainty regarding both the observed and modelled meridional gradient and the mentioned issues complicate also the comparison between modeled and proxy data.

In our work we aim to investigate the EECO period with a simple energy balance box model and apply the maximum entropy production principle to explore the possible scenarios of meridional temperature gradients. We find that the maximum entropy production principle could be beneficial in the paleoclimate context since it has the utility to give an accurate prediction for non-equilibrium systems with the minimal amount of information. We also assess the heat transport signaled by proxy data and by state-of-the-art model outputs in accordance to our theoretical constrains based on the idealized test case.

How to cite: Kelemen, F. D. and Ahrens, B.: Exploring the possible meridional temperature gradient of Early Eocene Climatic Optimum with an energy balance model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7365, https://doi.org/10.5194/egusphere-egu21-7365, 2021.

EGU21-15417 | vPICO presentations | CL1.2 | Highlight

Global temperature and hydroclimate in warmer climates of the past and future: the Last Interglacial versus greenhouse scenarios

Paolo Scussolini, Pepijn Bakker, Paolo De Luca, Dim Coumou, Joyce Bosmans, Gerrit Lohmann, Zoë Thomas, Chris Turney, Laurie Menviel, Takashi Obase, Ayako Abe-Ouchi, Pascale Braconnot, Bette Otto-Bliesner, Qiuzhen Yin, Matthias Prange, Chronis Tzedakis, Emilie Capron, Hans Renssen, Philip Ward, and Jeroen Aerts

Past climates contain precious information about the workings of the climate system, and about what can be expected in a changed climate. The Last Interglacial (LIG; ca. 125,000 years ago) is the most recent period of climate warmer than modern, at least in the Northern Hemisphere. Because of this, it has been often proposed that the LIG holds a partial analogy with a future warmer climate forced by enhanced greenhouse effect. Still, such analogy has never been examined in a quantitative manner. Here we address the question: for which scenario, time horizon, regions and season is the climate of the LIG a useful analogue of the future? We use the results of 13 climate models that performed the standard experiments of PMIP4 and CMIP6, and present a comparison of hemispheric temperature and precipitation between the LIG and SSP scenarios of the future. We also two independent assessments of models performance, by comparing their temperature and precipitation to climate reanalysis of the last decades and to proxies of the LIG. Insights gained from this comparison can inform studies in disciplines beyond climate studies, such as hydrology and ecology.

How to cite: Scussolini, P., Bakker, P., De Luca, P., Coumou, D., Bosmans, J., Lohmann, G., Thomas, Z., Turney, C., Menviel, L., Obase, T., Abe-Ouchi, A., Braconnot, P., Otto-Bliesner, B., Yin, Q., Prange, M., Tzedakis, C., Capron, E., Renssen, H., Ward, P., and Aerts, J.: Global temperature and hydroclimate in warmer climates of the past and future: the Last Interglacial versus greenhouse scenarios, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15417, https://doi.org/10.5194/egusphere-egu21-15417, 2021.

EGU21-11083 | vPICO presentations | CL1.2

From the last interglacial to the future – new insights from modeling the last glacial-interglacial cycle in PalMod

Kerstin Fieg, Mojib Latif, Michael Schulz, and Tatjana Ilyina

We present new insights from the project PalMod, which started in 2016 and is envisioned to run for a decade. The modelling initiative PalMod aims at filling the long-standing scientific gaps in our understanding of the dynamics and variability of the climate system during the last glacial-interglacial cycle. One of the grand challenges in this context is to quantify the processes that determine the spectrum of climate variability on timescales that range from seasons to millennia. Climatic processes are intimately coupled across these timescales. Understanding variability at any one timescale requires understanding of the whole spectrum. If we could successfully simulate the spectrum of climate variability during the last glacial cycle in Earth system models, would this enable us to more reliably assess the future climate change? Such simulations are necessary to deduce, for example, if a regime shift in climate variability could occur during the next centuries and millennia in response to global warming. PalMod is specifically designed to enhance our understanding of the Earth system dynamics and its variability on timescales up to the multimillennial with complex Earth System Models.

The following major goals were achieved up to now:

  • Full coupling of atmosphere, ocean and ice-sheet models, enabling investigation of Heinrich Events and bi-stability of the AMOC, and millennial-scale transient climate-ice sheet simulations.
  • Implementation of a coupled ocean and land biogeochemistry enabling simulations with prognostic atmospheric CO2 concentrations and including improved representation of methane (CH4) in transient deglaciation runs.
  • Systematic comparison of newly compiled proxy data with model simulations.

The major goal for the next two years is to set up the fully coupled physical-biogeochemical model which will be tested for three time periods: deglaciation, glacial inception and Marine Isotope Stage 3 (MIS3). This fully coupled model will be eventually used to simulate the complete glacial cycle and project the climate over the next few millennia.

How to cite: Fieg, K., Latif, M., Schulz, M., and Ilyina, T.: From the last interglacial to the future – new insights from modeling the last glacial-interglacial cycle in PalMod, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11083, https://doi.org/10.5194/egusphere-egu21-11083, 2021.

EGU21-8512 | vPICO presentations | CL1.2 | Highlight

Evolution of the climate in the next million years: A reduced-complexity model for glacial cycles and impact of fossil fuel CO2

Stefanie Talento and Andrey Ganopolski

We propose a reduced-complexity process-based model for the long-term evolution of the global ice volume, atmospheric CO2 concentration and global mean temperature. The model only external forcings are the orbital forcing and anthropogenic CO2 cumulative emissions. The model consists of a system of three coupled non-linear differential equations, representing physical mechanisms relevant for the evolution of the climate – ice sheets – Carbon cycle system in timescales longer than thousands of years. The model is successful in reproducing the glacial-interglacial fluctuations of the last 800 kyr, in good agreement with paleorecords both in terms of timing and amplitude, with a correlation between modelled and paleo global ice volume of up to 0.86.

Using different model realisations, we generate a probabilistic forecast of the evolution of the Earth system over the next 1 million years under natural and several fossil-fuel CO2 release scenarios. In the natural scenario, the model assigns high probability of occurrence of long interglacials in the periods between present and 50 kyr after present, and between 400 kyr and 500 kyr after present. The next full glacial conditions are most likely to occur 90 kyr after present. The model shows that even already achieved cumulative CO2 anthropogenic emissions (500 PgC) are capable of affecting the climate evolution for up to half million years, indicating that the beginning of the next glaciation is highly unlikely in the next 150 kyr. If cumulative fossil-fuel CO2 emissions reach 3000 PgC, or higher, the model predicts with high probability ice-free Northern Hemisphere landmass conditions will prevail in the next half million years, postponing the natural occurrence of the next glacial inception to 600 kyr after present.

How to cite: Talento, S. and Ganopolski, A.: Evolution of the climate in the next million years: A reduced-complexity model for glacial cycles and impact of fossil fuel CO2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8512, https://doi.org/10.5194/egusphere-egu21-8512, 2021.

EGU21-12440 | vPICO presentations | CL1.2 | Highlight

Methane in the climate system -- from the last glacial to the future

Thomas Kleinen, Sergey Gromov, Benedikt Steil, and Victor Brovkin

Between the last glacial maximum (LGM) and preindustrial times (PI), the atmospheric concentration of CH4, as shown by reconstructions from ice cores, roughly doubled. It then doubled again from PI to the present. Ice cores, however, cannot tell us how that development will continue in the future, and ice cores also cannot shed light on the causes of the rise in methane, as well as the rapid fluctuations during periods such as the Bolling-Allerod and Younger Dryas.

We use a methane-enabled version of MPI-ESM, the Max Planck Institute for Meteorology Earth System Model, to investigate changes in methane cycling in a transient ESM experiment from the LGM to the present, continuing onwards into the future for the next millennium. The model is driven by prescribed orbit, greenhouse gases and ice sheets, with all other changes to the climate system determined internally. Methane cycling is modelled by modules representing the atmospheric transport and sink of methane, as well as terrestrial sources and sinks from soils, termites, and fires. Thus, the full natural methane cycle – with the exception of geological and animal emissions – is represented in the model. For historical and future climate, anthropogenic emissions of methane are considered, too.

We show that the methane increase since the LGM is largely driven by source changes, with LGM emissions substantially reduced in comparison to the early Holocene and preindustrial states due to lower temperature, CO2, and soil carbon. Depending on the future climate scenario, these dependencies then lead to further increases in CH4, with a further doubling of atmospheric CH4 easily possible if one of the higher radiative forcing scenarios is followed. Furthermore, the future increases in CH4 will persist for a long time, as CH4 only decreases when the climate system cools again.

How to cite: Kleinen, T., Gromov, S., Steil, B., and Brovkin, V.: Methane in the climate system -- from the last glacial to the future, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12440, https://doi.org/10.5194/egusphere-egu21-12440, 2021.

EGU21-14136 | vPICO presentations | CL1.2 | Highlight

Using paleoclimate data to constrain cloud parameterizations in GISS-E2.1

Riovie D. Ramos, Allegra N. LeGrande, Michael L. Griffiths, Gregory S. Elsaesser, Daniel T. Litchmore, Jessica E. Tierney, Francesco S. R. Pausata, and Jesse Nusbaumer

Much of the inter-model spread in equilibrium climate sensitivity (ECS) estimates is attributed to cloud and convective parameterizations which model cloud and water vapor feedbacks. These parameterizations also directly influence water isotopes, which may be retrieved not only from modern observations, but also a plethora of paleoclimate archives that represent a much broader range of variability than is available in modern measurements. And thus, these water isotope tracers can be used to constrain ECS by flagging unrealistic parts of the parameterization phase space via model biases in a perturbed parameterization ensemble (PPE) of paleoclimate simulations. In this proof-of-concept study, we evaluate a suite of isotope-enabled atmosphere-only GISS-E2.1 simulations, each with varying cloud and convective perturbations, against speleothem and ice core δ18O for the Last Glacial Maximum (LGM, 21000 years ago), mid-Holocene (MH, 6000 years ago) and pre-Industrial periods. The first-order spatial pattern of δ18O of precipitation (δ18Op) is in excellent agreement between proxy data and all parameterizations across all time periods. While the simulations generally capture large scale δ18Op patterns, the magnitude of change is consistently smaller in all simulations than those of the proxies, highlighting uncertainties in both models and proxies. Not a single set of parameterizations worked well in all climate states, indicating that improving future simulations requires determining all plausible parameter combinations critical in refining ECS. Further, it may be that certain parameterization choices represent certain types of variability better than others, and there may be a non-unique solution to ideal clouds/convection parameterization choices that is modulated by the question asked.

How to cite: Ramos, R. D., LeGrande, A. N., Griffiths, M. L., Elsaesser, G. S., Litchmore, D. T., Tierney, J. E., Pausata, F. S. R., and Nusbaumer, J.: Using paleoclimate data to constrain cloud parameterizations in GISS-E2.1, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14136, https://doi.org/10.5194/egusphere-egu21-14136, 2021.

EGU21-2305 | vPICO presentations | CL1.2

Sensitivity of simulated oxygen isotopes in ice cores and speleothems to Last Glacial Maximum surface conditions

André Paul, Alexandre Cauquoin, Stefan Mulitza, Thejna Tharammal, and Martin Werner

In simulations of the climate during the Last Glacial Maximum (LGM), we employ two different isotope-enabled atmospheric general circulation models (NCAR iCAM3 and MPI ECHAM6-wiso) and use simulated (by coupled climate models) as well as reconstructed (from a new global climatology of the ocean surface duing the LGM, GLOMAP) surface conditions.

The resulting atmospheric fields reflect the more pronounced structure and gradients in the reconstructions, for example, the precipitation is more depleted in oxygen-18 in the high latitudes and more enriched in low latitudes, especially in the tropical convective regions over the maritime continent in the equatorial Pacific and Indian Oceans and over the equatorial Atlantic Ocean. Furthermore, at the sites of ice cores and speleothems, the model-data fit improves in terms of the coefficients of determination and root-mean square errors.

In additional sensitivity experiments, we also use the climatologies by Annan and Hargreaves (2013) and Tierney et al. (2020) and consider the impact of changes in reconstructed sea-ice extent and the global-mean sea-surface temperature.

Our findings imply that the correct simulation or reconstruction of patterns and gradients in sea-surface conditions are crucial for a successful comparison to oxygen-isotope data from ice cores and speleothems.

How to cite: Paul, A., Cauquoin, A., Mulitza, S., Tharammal, T., and Werner, M.: Sensitivity of simulated oxygen isotopes in ice cores and speleothems to Last Glacial Maximum surface conditions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2305, https://doi.org/10.5194/egusphere-egu21-2305, 2021.

EGU21-11047 | vPICO presentations | CL1.2

Reconstructing the surface temperature fields of the Last Glacial Maximum and mid-Pliocene Warm Period using climate models and data.

James Annan, Julia Hargreaves, and Thorsten Mauritsen

We present new reconstructions of global climatological temperature fields for the Last Glacial Maximum and the mid-Pliocene Warm Period.

The method is based on an Ensemble Kalman Smoother which combines globally complete modelled temperature fields, with sparse proxy-based estimates of local temperature anomalies. This ensures spatially coherent fields which respect physical principles and which are also tied closely to observational estimates. 

For the Last Glacial Maximum, we use the full set of PMIP2/3/4 model simulations, and we combine this with a wide range of proxy-based SST and SAT estimates of local temperature to ensure the best possible global coverage. Our reconstruction has a global mean surface air temperature anomaly of -5.3 +- 0.9C relative to the pre-industrial climate, and thus lies roughly half-way between the estimates of Annan and Hargreaves (2013) and Tierney et al (2020). We examine the reasons for these differences and discuss their implications.

For the mid-Pliocene Warm Period, we use the PlioMIP 1 and 2 model simulations and the PRISM proxy estimates for the 3.2 Ma time slice. These data are considerably more sparse and uncertain than for the LGM and our reconstruction is correspondingly more uncertain. We obtain an estimate of 5.6 +- 1.6C which is considerably warmer than most previous estimates, suggesting a significant discrepancy between the models and the data. We investigate the reasons for this and discuss the implications.

How to cite: Annan, J., Hargreaves, J., and Mauritsen, T.: Reconstructing the surface temperature fields of the Last Glacial Maximum and mid-Pliocene Warm Period using climate models and data., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11047, https://doi.org/10.5194/egusphere-egu21-11047, 2021.

EGU21-9847 | vPICO presentations | CL1.2

Last Glacial to present-day variability of surface climate from oxygen isotope signatures in speleothems and model simulations

Janica Buehler, Nils Weitzel, Jean-Philippe Baudouin, Martin Werner, and Kira Rehfeld

Comparing simulations and data from paleoclimate archives such as speleothems can test the capability of climate models to capture past climate changes. In past, present, and future, the hydrologic response to radiative forcing changes is far less understood and more uncertain than thermal changes.
 
Speleothems store terrestrial climate information in the form of isotopic oxygen in mineral and are found mostly in the low-to mid-latitudes of the landmasses. Their usually well preserved (semi-)continuous time series of oxygen isotope ratio δ18O can cover full Glacial-Interglacial cycles and are used for past climate reconstructions. However, the measured δ18O in the mineral is influenced by multiple climate and cave-related variables and does, therefore, not directly represent past temperature or precipitation. 

We assess the capability of the isotope-enabled models HadCM3 and ECHAM5-MPI/OM to simulate decadal to centennial climate variability beyond the instrumental period. In particular, we investigate the relationship between simulated δ18O and precipitation variability under different background conditions. By comparing simulated δ18O values at cave locations to the large global speleothem database SISALv2 (Comas-Bru et al. 2020), we also examine the consistency between modeled and archived temporal changes in δ18O in the mean state and variability. Our strategy involves forward-modeling of cave processes such as temperature-dependent fractionation and transit times to constrain a simple speleothem proxy model for the simulation output. For the late Holocene, we observe a strongly underestimated simulated isotopic variability on decadal to centennial timescales. We further test how much this underestimation depends on the background radiative forcing conditions by comparing the Last Glacial Maximum, the mid-Holocene, and the late Holocene. This provides deeper insight on low to mid-latitude state-dependent climate variability on decadal to centennial time scales. 

Reference:

Comas-Bru, L., et. al. SISALv2: a comprehensive speleothem isotope database with multiple age-depth models. Earth System Science Data 12, 2579-2606 (2020) https://essd.copernicus.org/articles/12/2579/2020/

How to cite: Buehler, J., Weitzel, N., Baudouin, J.-P., Werner, M., and Rehfeld, K.: Last Glacial to present-day variability of surface climate from oxygen isotope signatures in speleothems and model simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9847, https://doi.org/10.5194/egusphere-egu21-9847, 2021.

EGU21-12889 | vPICO presentations | CL1.2 | Highlight

Tracking the sources of water isotopes in water vapor and monsoon precipitation over India using iCESM1.2 simulations

Thejna Tharammal, Govindasamy Bala, and Jesse Nusbaumer

Stable isotopes of water are common proxies used to reconstruct the past precipitation in the tropics, based on the climate-dependent fractionation of the water molecule. Hence, an investigation of the factors affecting the present-day isotope ratios in precipitation in the tropical monsoon regimes could aid the interpretation of the paleo-proxies. Along with the degree of rainouts and strength of convection, the isotope ratios in precipitation over a region depend on the source of water vapor. We use the water vapor-isotope tagging capabilities in the isotope-enabled earth system model iCESM1.2 to estimate the relative contribution of different oceanic sources and regional land water recycling to the present-day distribution of precipitation and isotope ratios in precipitation in the Indian land region. We choose two major precipitation seasons for our study – the Southwest monsoon [SW, June to September], the major contributor of annual precipitation in the region, and the Northeast monsoon [NE, October to December] that is important for the annual precipitation in the southern Indian region. It is expected that these two monsoon seasons should have different major sources of water vapor because of the reversal in monsoon circulation between these two seasons. Preliminary results suggest that the model can reproduce the seasonal distribution of precipitation and water isotopes in precipitation in the Indian region. The water-tagging method successfully identifies the sources of precipitation in the Indian region. The detailed results of this study will be presented at the meeting.

How to cite: Tharammal, T., Bala, G., and Nusbaumer, J.: Tracking the sources of water isotopes in water vapor and monsoon precipitation over India using iCESM1.2 simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12889, https://doi.org/10.5194/egusphere-egu21-12889, 2021.

EGU21-2476 | vPICO presentations | CL1.2

Workflow and tools to analyse the PMIP4-CMIP6 ensemble

Anni Zhao and Chris Brierley

Experiment outputs are now available from the Coupled Model Intercomparison Project’s 6th phase (CMIP6) and the past climate experiments defined in the Model Intercomparison Project’s 4th phase (PMIP4). All of this output is freely available from the Earth System Grid Federation (ESGF). Yet there are overheads in analysing this resource that may prove complicated or prohibitive. Here we document the steps taken by ourselves to produce ensemble analyses covering past and future simulations. We outline the strategy used to curate, adjust the monthly calendar aggregation and process the information downloaded from the ESGF. The results of these steps were used to perform analysis for several of the initial publications arising from PMIP4. We provide post-processed fields for each simulation, such as climatologies and common measures of variability. Example scripts used to visualise and analyse these fields is provided for several important case studies.

How to cite: Zhao, A. and Brierley, C.: Workflow and tools to analyse the PMIP4-CMIP6 ensemble, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2476, https://doi.org/10.5194/egusphere-egu21-2476, 2021.

EGU21-9683 | vPICO presentations | CL1.2

Towards model-data comparison of the deglacial temperature evolution in space and time

Nils Weitzel, Heather Andres, Jean-Philippe Baudouin, Oliver Bothe, Andrew Dolman, Lukas Jonkers, Marie Kapsch, Thomas Kleinen, Maximilian May, Uwe Mikolajewicz, Andre Paul, and Kira Rehfeld

The increasing number of Earth system model simulations that try to simulate the climate during the last deglaciation (ca 20 to 10 thousand years ago) creates a demand for benchmarking against environmental proxy records synthesized for the same time period. Comparing these two data sources over a period with changing background conditions requires new methods for model-data comparison that incorporate multiple types and sources of uncertainty.

Natural archives of past reality are distributed sparsely and non-uniformly in space and time. Signals that can be obtained are in addition perturbed by uncertainties related to dating, the relationship between the proxy sensor and environmental fields, the archive build-up, and measurement. On the other hand, paleoclimate simulations are four-dimensional, complete, and physically consistent representations of the climate. However, they are subject to errors due to model inadequacies and sensitivity to the forcing protocol, and will not reproduce any particular history of unforced variability. 

We present a method for probabilistic, multivariate quantification of the deviation between paleo-data and paleoclimate simulations that draws on the strengths of both sources of information and accounts for the aforementioned uncertainties. We compare the shape and magnitude of orbital- and millennial-scale temperature fluctuations during the last deglaciation and compute metrics of regional and global model-data mismatches. We test our algorithm with an ensemble of published simulations of the deglaciation and simulations from the ongoing PalMod project, which aims at the simulation of the last glacial cycle with comprehensive Earth system models. These are evaluated against a compilation of temperature reconstructions from multiple archives. Our work aims for a standardized model-data comparison workflow that will be used in PalMod. This workflow can be extended subsequently with additional proxy data, new simulations, and improved representations of proxy uncertainties. 

How to cite: Weitzel, N., Andres, H., Baudouin, J.-P., Bothe, O., Dolman, A., Jonkers, L., Kapsch, M., Kleinen, T., May, M., Mikolajewicz, U., Paul, A., and Rehfeld, K.: Towards model-data comparison of the deglacial temperature evolution in space and time, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9683, https://doi.org/10.5194/egusphere-egu21-9683, 2021.

EGU21-5716 | vPICO presentations | CL1.2

Model-data comparison challenges in paleo-climate analyses: Towards an evaluation toolbox for transient climate model simulations 

Jean-Philippe Baudouin, Oliver Bothe, Manuel Chevalier, Nils Weitzel, Anne Dallmeyer, Chris Brierley, and Kira Rehfeld

Modelling studies are evaluated by comparing the simulation outputs to an observational reference. In climate science, the number and complexity of the models and the mass of data have led the community to develop standardised methods and automated tools, such as the Climate Variability Diagnostic Package or the ESMValTool. However, these tools are mostly designed to evaluate simulations of the instrumental period. Different methods are required to compare paleoclimate simulations to palaeodataFor example, new variables are being modelled, such as vegetation, ice sheet extent, or isotopic ratio, and are used for the evaluation. Changing boundary conditions in transient simulations further complicate the evaluation process: traditional indices that characterise circulation (e.g. monsoon) or modes of variability (e.g. NAO, ENSO) need to be adapted, while new ones are needed to investigate modes of longer timescale and abrupt events. Finally, the palaeodata also present challenges: various type of uncertainty, complex relation to climate variables, and different spatio-temporal representativeness compared to model outputs. Here, we summarise the challenges of model-data comparison in paleo-climate studies. We then review some of the different methods and tools already developed by the community, such as biome comparison and Bayesian approaches to quantify model-data deviation. We finally discuss the implementation of an evaluation framework which aims to provide both adaptable tools to the community and automated standardised analyses.

How to cite: Baudouin, J.-P., Bothe, O., Chevalier, M., Weitzel, N., Dallmeyer, A., Brierley, C., and Rehfeld, K.: Model-data comparison challenges in paleo-climate analyses: Towards an evaluation toolbox for transient climate model simulations , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5716, https://doi.org/10.5194/egusphere-egu21-5716, 2021.

The increasing availability of time-evolving or transient palaeoclimatic simulations makes it imperative to develop “best-practices” for comparing simulations with palaeoclimatic observations including both climate reconstructions and environmental data.  There are two sets of considerations, temporal and spatial, that should guide those comparisons.  The chronology of simulations can in some ways be viewed as exact, as determined by the insolation forcing, but data archiving and reporting conventions, such as reporting summaries that use the modern calendar (that leads to the long-recognized palaeo-calendar effect) can, if ignored, lead to “built-in” temporal offsets of thousands of years in such features as temperature or precipitation maxima or minima.  Likewise, there are age uncertainties in time series of palaeoclimatic data that are often ignored, despite the fact that these are large during “climatically interesting times” such as the Younger Dryas chronozone.  Similarly, although model resolution is increasing, there is still a mismatch in topography (and its climatic effects) between a model and the “real world” sensed by the palaeoclimatic data sources. 

There are existing approaches for dealing with some of these issues, such as calendar-adjustment programs, Monte-Carlo approaches for describing age uncertainties in palaeoclimate time series, or clustering approaches for objectively defining appropriate regions for the calculation of area averages, but there is certainly room for further development.  This abstract is intended to serve as platform for discussion of some of best practices for data-model comparisons in transient mode.

How to cite: Bartlein, P. and Harrison, S.: Temporal and spatial considerations in data-model comparisons involving transient paleoclimatic simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6799, https://doi.org/10.5194/egusphere-egu21-6799, 2021.

EGU21-11006 | vPICO presentations | CL1.2

State-dependency of temperature variability in transient simulations of the last Deglaciation from models of varying complexity

Elisa Ziegler, Heather Andres, Beatrice Ellerhoff, Marie-Luise Kapsch, Steffen Kutterolf, Uwe Mikolajewicz, Julie Christin Schindlbeck-Belo, Matthew Toohey, Christian Wirths, Nils Weitzel, and Kira Rehfeld

Much about the response of temperature variability to a change in the climate's mean state, as the one projected for the current century, remains uncertain. These uncertainties include spatiotemporal patterns, the magnitude, and, in some cases, even the sign. For the last Deglaciation, - the last change in global mean temperature of a similar degree to that expected in projections - variability analyses of climate model simulations and temperature proxies produce conflicting results. 

Here, we build a hierarchy of transient simulations covering the period since the Last Glacial Maximum about 26k years ago. We include a range of climate models, from conceptual to complex Earth System Models. The simulations cover a variety of temporal and spatial resolutions, parameterizations, and modeled processes. For annual to multi-millennial temporal as well as regional to global spatial scales, we compare variability patterns and power spectra and analyze how they relate to model properties and the background state of Earth's climate. This allows for the examination of regional temperature differences between low, middle, and high latitudes and at locations of available paleoclimate proxy records. For sets of sensitivity experiments, we investigate effects of changes to ice sheets, sea ice, and in volcanic, solar, greenhouse, and orbital forcing on modeled climate variability.  

Thus, our analysis provides insights into when and how models disagree with each other and with proxies, and what differences arise due to specific models, simulation setups, and boundary conditions. Based on these results, we can then gauge the degree of complexity which is required to reproduce past temperature variability and predict its changes in the future. 

How to cite: Ziegler, E., Andres, H., Ellerhoff, B., Kapsch, M.-L., Kutterolf, S., Mikolajewicz, U., Schindlbeck-Belo, J. C., Toohey, M., Wirths, C., Weitzel, N., and Rehfeld, K.: State-dependency of temperature variability in transient simulations of the last Deglaciation from models of varying complexity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11006, https://doi.org/10.5194/egusphere-egu21-11006, 2021.

Fossil pollen datasets can help to understand the temporal and spatial distribution patterns and driving forces of the past terrestrial biomes in high northern latitudes. Here we present a global pollen dataset since the Last Glacial Maximum, synthesized from 2821 palynological records from the Neotoma Paleoecology Database and additional literature. All terrestrial pollen taxa were taxonomically harmonized on genus (woody taxa) or family level (herb taxa) and temporally standardized by using a defined parameter setting for Bayesian age-depth modeling based on 14C dating. The age-depth models were statistically compared with existing models for each record. With a biomization approach, we reconstructed biomes for several time-slices throughout the last 22000 years with a temporal resolution of roughly 500 years. The reconstructed biome distributions are compared to simulated biome distributions inferred from a transient simulation for the last 25000 years, performed in the comprehensive Earth System Model of the Max Planck Institute (MPI-ESM). The overall biome trend agrees well, but the simulation shows lower forest cover in the high northern latitudes and reaches the maximum forest cover in the Holocene much earlier than the reconstructions indicate.

How to cite: Li, C., Dallmeyer, A., Böhmer, T., Postl, A., and Herzschuh, U.: Northern hemispheric biome changes synthesized from taxonomically harmonized and temporally standardized fossil pollen record since the Last Glacial Maximum in comparison to MPI-ESM simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12224, https://doi.org/10.5194/egusphere-egu21-12224, 2021.

EGU21-3550 | vPICO presentations | CL1.2

Last Glacial Maximum Antarctic sea ice linked with global mean ocean temperature: evidence from PMIP3, PMIP4 and MIROC-4m simulations

Tristan Vadsaria, Sam Sherriff-Tadano, Ayako Abe-Ouchi, Takashi Obase, Wing-Le Chan, and Xavier Crosta

Southern Ocean sea ice and oceanic fronts are known to play an important role on the climate system, carbon cycles, bottom ocean circulation, and Antarctic ice sheet. However, many models of the previous Past-climate Model Intercomparison Project (PMIP) underestimated sea-ice extent (SIE) for the Last Glacial Maximum (LGM)(Roche et al., 2012; Marzocchi and Jensen, 2017), mainly because of surface bias (Flato et al., 2013) that may have an impact on mean ocean temperature (MOT). Indeed, recent studies further suggest an important link between Southern Ocean sea ice and mean ocean temperature (Ferrari et al., 2014; Bereiter et al., 2018 among others). Misrepresent the Antarctic sea-ice extent could highly impact deep ocean circulation, the heat transport and thus the MOT. In this study, we will stress the relationship between the distribution of Antarctic sea-ice extent and the MOT through the analysis of the PMIP3 and PMIP4 exercise and by using a set of MIROC models. To date, the latest version of MIROC improve its representation of the LGM Antarctic sea-ice extent, affecting the deep circulation and the MOT distribution (Sherriff-Tadano et al., under review).

Our results show that available PMIP4 models have an overall improvement in term of LGM sea-ice extent compared to PMIP3, associated to colder deep and bottom ocean temperature. Focusing on MIROC (4m) models, we show that models accounting for Southern Ocean sea-surface temperature (SST) bias correction reproduce an Antarctic sea-ice extent, 2D-distribution, and seasonal amplitude in good agreement with proxy-based data. Finally, using PMIP-MIROC analyze, we show that it exists a relationship between the maximum SIE and the MOT, modulated by the Antarctic intermediate and bottom waters.

How to cite: Vadsaria, T., Sherriff-Tadano, S., Abe-Ouchi, A., Obase, T., Chan, W.-L., and Crosta, X.: Last Glacial Maximum Antarctic sea ice linked with global mean ocean temperature: evidence from PMIP3, PMIP4 and MIROC-4m simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3550, https://doi.org/10.5194/egusphere-egu21-3550, 2021.

EGU21-15463 | vPICO presentations | CL1.2 | Highlight

Simulation of LGM ice sheets with the Community Earth System Model version 2 

Sarah L Bradley, Michele Petrini, Raymond Sellevold, Miren Vizcaino, William H. Lipscomb, and Sotiria Georgiou

The last deglaciation provides as unique a framework to investigate the processes of ice sheet and climate interaction during periods of mass loss as in the current climate. Here we simulate the Last Glacial Maximum (LGM) northern hemisphere ice sheets climate, surface mass balance (SMB), and dynamics with the Community Earth System Model version 2 (CESM2, Danabasoglu et al., 2020)) and the Community Ice Sheet Model version 2 (CISM2, Lipscomb et al., 2019). This LGM simulation will be later used as starting point for coupled CESM2-CISM2 simulations of the last deglaciation.

 

CESM2 is run at the nominal resolution used for IPCC-type projections (approx. 1 degree for all components). The model includes an advanced snow/firn and SMB calculation (van Kampenhout et al, 2019; Sellevold et al, 2019) the land component (CLM, cite) that has been evaluated and applied to the simulation of the future Greenland melt (van Kampenhout et al, 2020, Muntjewerf et al., 2020a,b, Sellevold & Vizcaino, 2020).

 

Our analysis examines how the global, Arctic, and North Atlantic climate result in the simulated radiative and turbulent heat fluxes over the ice sheets, and the mass fluxes from precipitation, refreezing, runoff, and sublimation. We also examine the simulated ice streams in CISM2, which is run at 8 km under a higher-order approximation for ice flow.

How to cite: Bradley, S. L., Petrini, M., Sellevold, R., Vizcaino, M., Lipscomb, W. H., and Georgiou, S.: Simulation of LGM ice sheets with the Community Earth System Model version 2 , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15463, https://doi.org/10.5194/egusphere-egu21-15463, 2021.

EGU21-8730 | vPICO presentations | CL1.2

Possible pathways to a Dansgaard-Oeschger (DO) PMIP protocol

Irene Malmierca-Vallet, Louise C. Sime, and Paul J. Valdes

The DO events of the last ice age represent one of the best studied abrupt climate transitions, yet we still lack a comprehensive explanation for them. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. Current Earth system models (ESMs) seem overly stable against external perturbations and incapable of reproducing most abrupt climate changes of the past (Valdes, 2011). If this holds true, this could noticeably influence their capability to predict future abrupt transitions, with significant consequences for the delivery of precise climate change projections.  In this task, the objectives of this study are (1) to cross compare existing simulations that show spontaneous DO-type oscillations using a common set of diagnostics so we can compare the mechanisms and the characteristics of the oscillations, and (2) to formulate possible pathways to a DO PMIP protocol that could help investigate cold-period instabilities through a range of insolation-, freshwater-, GHG-, and NH ice sheet-related forcings, as well as evaluating the possibility of spontaneous internal oscillations.

Although most abrupt DO events happened during MIS3, only few studies investigate DO events in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we thus propose that the MIS3 period could be the focus of such a DO-event modelling protocol. More specific sensitivity experiments performed under MIS 3 boundary conditions are needed in order to (1) better understand the mechanisms behind millennial-scale climate variability, (2) explore AMOC variability under intermediate glacial conditions, and (3) help answer the question: “are models too stable?”.

How to cite: Malmierca-Vallet, I., Sime, L. C., and Valdes, P. J.: Possible pathways to a Dansgaard-Oeschger (DO) PMIP protocol, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8730, https://doi.org/10.5194/egusphere-egu21-8730, 2021.

EGU21-6693 | vPICO presentations | CL1.2

Exploring the complex uncertainties in coupled climate-ice simulations of the Last Glacial Maximum

Lauren Gregoire, Niall Gandy, Lachlan Astfalck, Robin Smith, Ruza Ivanovic, Daniel Williamson, and Jonathan Gregory

Simulating the co-evolution of climate and ice-sheets during the Quaternary is key to understanding some of the major abrupt changes in climate, ice and sea level. Indeed, events such as the Meltwater pulse 1a rapid sea level rise and Heinrich, Dansgaard–Oeschger and the 8.2 kyr climatic events all involve the interplay between ice sheets, the atmosphere and the ocean. Unfortunately, it is challenging to simulate the coupled Climate-Ice sheet system because small biases, errors or uncertainties in parts of the models are strongly amplified by the powerful interactions between the atmosphere and ice (e.g. ice-albedo and height-mass balance feedbacks). This leads to inaccurate or even unrealistic simulations of ice sheet extent and surface climate. To overcome this issue we need some methods to effectively explore the uncertainty in the complex Climate-Ice sheet system and reduce model biases. Here we present our approach to produce ensemble of coupled Climate-Ice sheet simulations of the Last Glacial maximum that explore the uncertainties in climate and ice sheet processes.

We use the FAMOUS-ICE earth system model, which comprises a coarse-resolution and fast general circulation model coupled to the Glimmer-CISM ice sheet model. We prescribe sea surface temperature and sea ice concentrations in order to control and reduce biases in polar climate, which strongly affect the surface mass balance and simulated extent of the northern hemisphere ice sheets. We develop and apply a method to reconstruct and sample a range of realistic sea surface temperature and sea-ice concentration spatio-temporal field. These are created by merging information from PMIP3/4 climate simulations and proxy-data for sea surface temperatures at the Last Glacial Maximum with Bayes linear analysis. We then use these to generate ensembles of FAMOUS-ice simulations of the Last Glacial maximum following the PMIP4 protocol, with the Greenland and North American ice sheets interactively simulated. In addition to exploring a range of sea surface conditions, we also vary key parameters that control the surface mass balance and flow of ice sheets. We thus produce ensembles of simulations that will later be used to emulate ice sheet surface mass balance.  

How to cite: Gregoire, L., Gandy, N., Astfalck, L., Smith, R., Ivanovic, R., Williamson, D., and Gregory, J.: Exploring the complex uncertainties in coupled climate-ice simulations of the Last Glacial Maximum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6693, https://doi.org/10.5194/egusphere-egu21-6693, 2021.

EGU21-7297 | vPICO presentations | CL1.2

The impact of bathymetry on the simulated carbon at the Last Glacial Maximum

Fanny Lhardy, Nathaelle Bouttes, Didier Roche, Ayako Abe-Ouchi, Zanna Chase, Ruza Ivanovic, Markus Jochum, Masa Kageyama, Hidetaka Kobayashi, Laurie Menviel, Juan Muglia, Roman Nuterman, Akira Oka, Andreas Schmittner, Guido Vettoretti, and Akitomo Yamamoto