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CL5.3.1

EDI
Palaeoclimate modeling: from time-slices and sensitivity experiments to transient simulations into the future

Modelling past climate states, and the transient evolution of Earth’s climate remains challenging. Time periods such as the Paleocene, Eocene, Pliocene, the Last Interglacial, the Last Glacial Maximum or the mid-Holocene span across a vast range of climate conditions. At times, these lie far outside the bounds of the historical period that most models are designed and tuned to reproduce. However, our ability to predict future climate conditions and potential pathways to them is dependent on our models' abilities to reproduce just such phenomena. Thus, our climatic and environmental history is ideally suited to thoroughly test and evaluate models against data, so they may be better able to simulate the present and make future climate projections.

We invite papers on palaeoclimate-specific model development, model simulations and model-data comparison studies. Simulations may be targeted to address specific questions or follow specified protocols (as in the Paleoclimate Modelling Intercomparison Project – PMIP or the Deep Time Model Intercomparison Project – DeepMIP). They may include anything between time-slice equilibrium experiments to long transient climate simulations (e.g. transient simulations covering the entire glacial cycle as per the goal of the PalMod project) with timescales of processes ranging from synoptic scales to glacial cycles and beyond. Comparisons may include past, historical as well as future simulations and focus on comparisons of mean states, gradients, circulation or modes of variability using reconstructions of temperature, precipitation, vegetation or tracer species (e.g. δ18O, δD or Pa/Th).

Evaluations of results from the latest phase of PMIP4-CMIP6 are particularly encouraged. However, we also solicit comparisons of different models (comprehensive GCMs, isotope-enabled models, EMICs and/or conceptual models) between different periods, or between models and data, including an analysis of the underlying mechanisms as well as contributions introducing novel model or experimental setups.

Co-organized by BG5/NP4/OS1
Convener: Kira Rehfeld | Co-conveners: Heather AndresECSECS, Julia Hargreaves, Nils WeitzelECSECS
Presentations
| Mon, 23 May, 13:20–14:50 (CEST), 15:10–18:30 (CEST)
 
Room F2

Mon, 23 May, 13:20–14:50

Chairpersons: Kira Rehfeld, Janica Bühler, Heather Andres

13:20–13:23
Overview and introduction to time block 1

13:23–13:33
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EGU22-11955
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solicited
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Highlight
Masa Kageyama et al.

The amplitude of the Last Glacial Maximum (LGM) cooling compared to pre-industrial has long been a topic of debate, which partly arises from the fact that this cooling is spatially heterogeneous. Paleotemperature reconstructions shows that this cooling is larger on land than over the oceans, a feature which is well captured by Global Climate Models. However the amplitude of the LGM cooling at high altitudes is still not well constrained, with available data showing an important disparity from a region to another (Blard et al., 2007; Tripati et al., 2014). Here we present a new compilation of glacier-based temperature reconstructions at high elevation (> 2500 m) for the LGM, which are compared to synchronous changes of sea surface temperatures (Pacific Ocean), along the American Cordillera, from 40°S to 40°N. This new reconstruction confirms that lapse rates were steeper during the LGM in the tropics and shows that this feature relates to a drier atmosphere. To further analyse this observation, we first use the IPSL global climate model PMIP4 results (Kageyama et al., 2021), which, in agreement with the reconstructions, yields a steeper tropical lapse rate in its LGM simulation, compared with the pre-industrial one. Next, we disentangle the impacts of the lower atmospheric CO2 concentration and of lower humidity using a single column radiative-convective equilibrium model (Kluft et al., 2019), and show the strong impact of changes in humidity in the tropical lapse rate steepening at the LGM.

References

Blard, P.-H., Lavé, J., Wagnon, P. and Bourlès, D : Persistence of full glacial conditions in the central Pacific until 15,000 years ago, Nature, 449, 591–594, https://doi.org/10.1038/nature06142, 2007.

Tripati, A. K., Sahany, S., Pittman, D., Eagle, R. A., Neelin, J. D., Mitchell, J. L. and Beaucoufort, L.: Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing, Nature Geoscience, 7, 205–209, https://doi.org/10.1038/ngeo2082, 2014.

Kageyama, M., Harrison, S. P., Kapsch, M.-L., Lofverstrom, M., Lora, J. M., Mikolajewicz, U., Sherriff-Tadano, S., Vadsaria, T., Abe-Ouchi, A., Bouttes, N., Chandan, D., Gregoire, L. J., Ivanovic, R. F., Izumi, K., LeGrande, A. N., Lhardy, F., Lohmann, G., Morozova, P. A., Ohgaito, R., Paul, A., Peltier, W. R., Poulsen, C. J., Quiquet, A., Roche, D. M., Shi, X., Tierney, J. E., Valdes, P. J., Volodin, E., and Zhu, J.: The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations, Clim. Past, 17, 1065–1089, https://doi.org/10.5194/cp-17-1065-2021, 2021.

Kluft, L., Dacie, S., Buehler, S. A., Schmidt, H., & Stevens, B. (2019). Re-Examining the First Climate Models: Climate Sensitivity of a Modern Radiative–Convective Equilibrium Model, Journal of Climate, 32(23), 8111-8125

How to cite: Kageyama, M., Blard, P.-H., Bourdin, S., Charreau, J., Kluft, L., Leduc, G., and Legrain, E.: Last Glacial Maximum atmospheric lapse rates: a model-data study on the American Cordillera case, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11955, https://doi.org/10.5194/egusphere-egu22-11955, 2022.

13:33–13:40
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EGU22-9768
James Annan et al.

We present a new reconstruction of global climatological temperature fields for the Last Glacial Maximum, which improves on our previous work in several important ways.

The method combines globally complete modelled temperature fields, with sparse proxy-based estimates of local temperature anomalies. We use a localised Ensemble Kalman Smoother, which ensures spatially coherent fields that both respect the physical principles embodied in the models, and are also tied closely to observational estimates.

We use the full set of PMIP2/3/4 model simulations, but perform some filtering of the simulations to remove duplicates and closely related models. We also de-bias the ensemble and show via sensitivity tests that this can be an essential step in the process, although it has little effect in this particular application. Specifically, any bias in the prior ensemble leads to a significant bias (which may take roughly 70-80% of its initial magnitude) in the posterior estimate. Thus we recommend that this step is taken in similar reconstructions unless the researcher is confident that the bias in the prior ensemble is low.

We combine the prior ensemble 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 -4.5 +- 0.9C relative to the pre-industrial climate, and thus is slightly cooler than the estimate of Annan and Hargreaves (2013), but rather less cold than the estimate of Tierney et al (2020). We show that much of the reason for this latter discrepancy is due to the choice of prior.

How to cite: Annan, J., Hargreaves, J., and Mauritsen, T.: Reconstructing the surface temperature fields of the Last Glacial Maximum using climate models and data., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9768, https://doi.org/10.5194/egusphere-egu22-9768, 2022.

13:40–13:47
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EGU22-12620
Tobias Zolles and Andreas Born

Simulations of continental ice sheets require climate forcing over time periods that are infeasible to run with comprehensive climate models. The alternative to use climate models of reduced complexity often yields data of insufficient quality for a good simulation of the ice sheet surface mass balance. Here we reconstruct the climate of the last glacial climate based on 22 marine proxy records and two Greenland ice cores for the Atlantic region. The reconstruction is based on multiple climate simulations, which serve as potential analogs.

The analog search is based on air and sea surface temperatures.  To mitigate regional biases due to the availability of reconstructions, and to filter non-essential modes of variability, the search is carried out in the reduced space of the first few principal components. For every hundred years of proxy data the best ten climate analogs are identified and their weighted sum serves as the reconstruction. The obtained climate fields provide a full set of atmospheric variables to be used as input for our surface mass balance model.

We assess the quality and uncertainty of our reconstruction by using different objectives for the analog search as well as accounting for the different spatial and temporal distributions of the proxies. In addition, the method is evaluated in comparison to reconstructions based on the glacial index. 

The performance of the method decreases during the deep glacial period with the used model pool. In addition, the climate model data does not sufficiently explain the variability observed in the marine proxy data.

How to cite: Zolles, T. and Born, A.: Climate analogs as input for ice sheet models during the glacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12620, https://doi.org/10.5194/egusphere-egu22-12620, 2022.

13:47–13:54
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EGU22-5749
André Paul et al.

Our goal is to investigate the structural uncertainty in the isotope-enabled atmospheric general circulation models iCAM5 and ECHAM6-wiso. In order to reduce all other sources of uncertainties, in particular, those that stem from different boundary conditions, we forced the two models by the same sets of pre-industrial (PI) and Last Glacial Maximum (LGM) surface boundary conditions; the latter were taken from GLOMAP  (Paul et al., 2021), which in turn were based on the MARGO project (MARGO Project Members, 2009) and recent estimates of LGM sea-ice extent. We compared our model results to reconstructions from ice cores (cf. Risi et al., 2010) and speleothems (cf. Comas-Bru et al., 2020). This comparison showed to what degree realizations of the atmospheric state of the LGM obtained from different models, due to different model set-ups and parameterizations, are in agreement with the proxy data. For example, the precipitation during the LGM was generally less depleted in the ECHAM6-wiso as compared to iCAM5, and as it turned out, the iCAM5 simulation produced only a rather weak LGM anomaly during summer (June-July-August, JJA) over the South Asian monsoon region.

How to cite: Paul, A., Tharammal, T., Cauquoin, A., and Werner, M.: Evaluating atmospheric simulations of the Last Glacial Maximum using oxygen isotopes in ice cores and speleothems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5749, https://doi.org/10.5194/egusphere-egu22-5749, 2022.

13:54–14:01
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EGU22-766
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ECS
Kim Helen Stadelmaier et al.

During the Last Glacial Maximum (LGM), a very cold and dry period around 26.5–19 kyr BP, permafrost was widespread across Europe. In this work, we explore the possible benefit of using regional climate model data to improve the permafrost representation in France, decipher how the atmospheric circulation affects the permafrost boundaries in the models, and test the role of ground thermal contraction cracking in wedge development during the LGM. With these aims, criteria for possible thermal contraction cracking of the ground are applied to climate model data for the first time. Our results show that the permafrost extent and ground cracking regions deviate from proxy evidence when the simulated large-scale circulation in both global and regional climate models favours prevailing westerly winds. A colder and, with regard to proxy data, more realistic version of the LGM climate is achieved given more frequent easterly winds conditions. Given the appropriate forcing, an added value of the regional climate model simulation can be achieved in representing permafrost and ground thermal contraction cracking. Furthermore, the model data provide evidence that thermal contraction cracking occurred in Europe during the LGM in a wide latitudinal band south of the probable permafrost border, in agreement with field data analysis. This enables the reconsideration of the role of sand-wedge casts to identify past permafrost regions.

How to cite: Stadelmaier, K. H., Ludwig, P., Bertran, P., Antoine, P., Shi, X., Lohmann, G., and Pinto, J. G.: A new perspective on permafrost boundaries in France during the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-766, https://doi.org/10.5194/egusphere-egu22-766, 2022.

14:01–14:08
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EGU22-1224
Andreas Schmittner et al.

Increased ocean carbon storage and reductions in deep ocean oxygen content during the cold phases of the Pleistocene ice age cycles have been mostly attributed to a stronger biological pump. However, recent studies have emphasized that changes in air-sea disequilibrium played a major role. Here we diagnose a data-constrained model of the ocean during the Last Glacial Maximum to decompose carbon and oxygen cycling into its different components. Individual drivers such as temperature, sea ice, circulation and iron fertilization have been quantified for each component. We show that due to differences in air-sea gas exchange between carbon and oxygen, the components respond differently, which complicates/invalidates interpretations of oxygen changes in terms of carbon. We find changes in disequilibrium dominate both carbon and oxygen changes, whereas the biological pump was not more efficient in terms of global changes for both elements. However, whereas for carbon both the physical and the biological disequilibrium play important roles, for oxygen the biological disequilibrium is dominant, while the physical disequilibrium is negligible. Moreover, whereas for carbon temperature (amplified by physical disequilibrium) and iron fertilization (amplified by biological disequilibrium) are the dominant drivers, oxygen disequilibrium changes are driven mostly by sea ice, with iron fertilization playing a secondary role.

How to cite: Schmittner, A., Khatiwala, S., and Cliff, E.: Glacial Ocean Carbon and Oxygen Cycles: Biological Pump or Disequilibrium?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1224, https://doi.org/10.5194/egusphere-egu22-1224, 2022.

14:08–14:15
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EGU22-5069
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ECS
Patrizia Schoch et al.

Jet streams control hydroclimate variability in the mid-latitudes with important impacts on water availability and human societies. According to future projections, global warming will change jet stream characteristics, including its mean position. Variability of these characteristics on hourly-to-daily timescales is key to understanding the mid-latitudes circulation. Therefore, most analysis methods of present-day jet streams are designed for 6-hourly data. By modelling the climate since the Last Glacial Maximum, we can investigate the long-term drivers of jet stream characteristics. However, for transient simulations of the last deglaciation, 3d wind fields are only archived with a monthly resolution due to storage limitations. Hence, jet variability at shorter timescales cannot be identified, and established methods can’t be used.

Here, we study to what extent changes of jet stream characteristics can be inferred from monthly wind fields. Therefore, we compare latitudinal jet stream positions, strength, tilt and their variability from daily and monthly wind fields in reanalysis data and for LGM and PI simulations. We test three different methods to construct jet stream typologies and metrics. This comparison identifies to which extend these jet stream characteristics can be robustly studied from monthly wind fields. In addition, our analysis assesses the added value of archived daily data for future research. Once the limitations of monthly wind output are known, jet stream characteristics in transient simulations of the last deglaciation can be analysed. This analysis provides new insights on jet stream changes on decadal-to-orbital timescales and identifies the factors controlling these changes.

How to cite: Schoch, P., Baudouin, J.-P., Weitzel, N., Kapsch, M., Kleinen, T., and Rehfeld, K.: Characterising simulated changes of jet streams since the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5069, https://doi.org/10.5194/egusphere-egu22-5069, 2022.

14:15–14:22
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EGU22-2496
Ruza Ivanovic et al.

Studying the Last Glacial Maximum (LGM), 21000 years ago, provides insights into climate sensitivity to greenhouse gases and critical interactions within the earth system (e.g. atmosphere, ocean, cryosphere) operating in a climate different from today. Much effort has been put into reconstructing the Sea Surface Temperatures (SST) at the LGM using a range of palaeoclimate records, statistical techniques and models. Large disagreements exist amongst reconstructions and between models and data. Disentangling the causes of these differences is challenging. How much of these differences are due to the choice of data used, their interpretation, the statistical method or climate models used? The polar regions are particularly difficult to reconstruct, yet are key for assessing polar amplification and key processes driving cryospheric changes. Combining the information gained from sea ice and SST proxies has the potential to improve reconstructions in those regions.  

Here, we provide a new probabilistic joint reconstruction of global SST and sea ice concentration (SIC) that incorporates information from the ensemble of PMIP3 and PMIP4 models (Kageyama et al., 2021) and existing compilations of SST and sea ice. Our reconstruction was specifically designed to provide ensembles of plausible monthly mean fields that can be used to drive atmosphere models to investigate uncertainty in LGM climate and their potential effects/interactions on e.g. vegetation, ice and atmospheric circulation.  

We present our statistical approach (Astfalk et al., 2021) in simplified terms for non-specialists, and discuss how different interpretations of the palaeo-records can be included in our statistical framework. Our results are compared to other recent reconstructions such as Tierney et al. (2020) and Paul et al. (2021). To interpret these differences, we test the effect of the choices of input proxy data and models on the reconstructed monthly mean SSTs and SIC.  

References: 

  • Astfalck, L., Williamson, D., Gandy, N., Gregoire, L. & Ivanovic, R. Coexchangeable process modelling for uncertainty quantification in joint climate reconstruction. arXiv:2111.12283 [stat] (2021).
  • Kageyama, M. et al. The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations. Climate of the Past 17, 1065–1089 (2021).
  • Paul, A., Mulitza, S., Stein, R. & Werner, M. A global climatology of the ocean surface during the Last Glacial Maximum mapped on a regular grid (GLOMAP). Climate of the Past 17, 805–824 (2021).
  • Tierney, J. E. et al. Glacial cooling and climate sensitivity revisited. Nature 584, 569–573 (2020).

How to cite: Ivanovic, R., Gregoire, L., Astfalk, L., Williamson, D., Gandy, N., Burke, A., and Schmidt, D.: Quantifying uncertainties in global monthly mean sea surface temperature and sea ice at the Last Glacial Maximum , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2496, https://doi.org/10.5194/egusphere-egu22-2496, 2022.

14:22–14:29
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EGU22-8364
Lukas Jonkers et al.

The Last Glacial Maximum (23,000 – 19,000 years ago; LGM) is the most recent time when Earth’s climate was fundamentally different from today. The LGM hence remains a prime target to evaluate climate models outside current boundary conditions. Evaluation of paleoclimate simulations is usually done using proxy-based reconstructions. However, such reconstructions are indirect and associated with marked uncertainty, which often renders model-data comparison equivocal. Here we take a different approach and use macro-ecological patterns preserved in fossil marine zooplankton to evaluate simulations of LGM near-surface ocean temperature.

 

We utilise the distance-decay pattern in planktonic foraminifera to evaluate modelled temperature gradients. Distance decay emerges because of differences in habitat preferences among species that cause the compositional similarity between assemblages to decrease the further apart they are from each other in environmental space. Distance decay is a fundamental concept in ecology and is observed in many different taxa and ecosystems, including planktonic foraminifera that show a monotonous decrease in similarity with increasing difference in temperature. Because the ecological niches of planktonic foraminifera are unlikely to have changed since the LGM, the distance-decay relationship based on simulated LGM temperatures and LGM assemblages should in principle be identical to the modern distance decay pattern. Thus we can use fossil planktonic foraminifera species assemblages to evaluate climate model simulations based on ecological principles.

 

Our analysis is based on an extended new LGM planktonic foraminifera database (2,085 assemblages from 647 unique sites) and a suite of 10 simulations from state-of-the-art climate models (PMIP3 and 4). We find markedly different planktonic foraminifera distributions during the LGM, primarily due to the equatorward expansion of polar assemblages at the expense of transitional assemblages. The distance-decay pattern that emerges when the LGM assemblages are combined with simulated ocean temperatures is different from the modern pattern. All simulations suggest large thermal gradients between regions where the planktonic foraminifera indicate no, or only weak, gradients. This pattern arises from the pronounced shift to polar species assemblages in the North Atlantic where the simulations predict only moderate cooling. In general, the models predict spatially rather uniform cooling, whereas the microfossil evidence suggests more pronounced regional differences in the temperature change. The difference between reconstructions and the simulations reaches up to 10 K in the North Atlantic.

 

Importantly, simulations with a reduced AMOC and hence lower North Atlantic near sea surface temperatures, yield a distance-decay pattern that is much more similar to the modern pattern. The planktonic foraminifera assemblages thus question the view of the LGM ocean as an equilibrium response to external forcing.

How to cite: Jonkers, L., Laepple, T., Rillo, M., Dolman, A., Lohman, G., Paul, A., Mix, A., and Kucera, M.: Modelled equilibrium LGM seawater temperatures inconsistent with plankton biodiversity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8364, https://doi.org/10.5194/egusphere-egu22-8364, 2022.

14:29–14:36
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EGU22-784
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ECS
Frerk Pöppelmeier et al.

The Atlantic overturning circulation plays a critical role in inter-hemispheric transport of heat, carbon, and nutrients, and its potential collapse under anthropogenic forcing is thought to be a major tipping point in the climate system. As such, painstaking efforts have been dedicated to a better understanding of the Atlantic circulation’s past variability and mean-state under different boundary conditions. Yet, despite decades of research many uncertainties remain regarding the state of the ocean circulation over the past 20,000 years, during which Earth’s climate was propelled out of the last ice age. Here, we employed the Bern3D intermediate complexity model, which is equipped with all major water mass tracers (Δ14C, δ13C, δ18O, εNd, Pa/Th, nutrients, and temperature), to search for converging constraints on the often conflicting interpretations of paleo-reconstructions from individual proxies focusing on the Last Glacial Maximum (LGM). By varying formation rates of northern- and southern-sourced waters we explore a wide range of circulation states and test their ability to reproduce the spatial patterns of newly compiled proxy data of the LGM. Generally, we find that late-Holocene to LGM anomalies give more consistent pictures of proxy distributions than absolute values, since systematic biases, that plague some of the proxies, cancel out. This has the additional advantage that also systematic model biases are minimized. Considering this, we find that the previously opposing neodymium and stable carbon isotope-based interpretations of the glacial water mass structure can be reconciled when non-conservative effects are appropriately taken into account. Furthermore, combining the information from all proxies indicates some shoaling of glacial northern-sourced water, yet not to the same extent as previous studies suggested.

How to cite: Pöppelmeier, F., Jeltsch-Thömmes, A., Joos, F., Scheen, J., Lippold, J., and Stocker, T.: Converging constraints on the glacial Atlantic overturning circulation from multiple proxies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-784, https://doi.org/10.5194/egusphere-egu22-784, 2022.

14:36–14:43
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EGU22-10696
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ECS
Noam Vogt-Vincent and Satoshi Mitarai

The Kuroshio Current is the western boundary current of the North Pacific Subtropical Gyre and flows through the East China Sea, entering through a relatively narrow, 800m-deep sill (the Yonaguni Depression). The warm surface waters associated with the Kuroshio support habitable conditions in the East China Sea for some of the world’s most northerly warm-water coral reefs. However, it has been suggested that sea-level fall at the LGM, with a possible further contribution from tectonics, obstructed the glacial Yonaguni Depression and diverted the Kuroshio to the east of the Ryukyu Arc.

Using a set of 2km-resolution dynamically downscaled ocean simulations with LGM boundary conditions from four PMIP3 contributions, we present regional state estimates for the glacial East China Sea which are both physically consistent, and compatible with sea-surface temperature proxy compilations. We find that, whilst the Kuroshio Current transport in the East China Sea is slightly reduced at the LGM, its path is relatively unchanged, with limited sensitivity to glacioeustatic sea-level change, glacial-interglacial changes in climate, and tectonic shoaling of the Yonaguni Depression. Simulations with the best model-proxy agreement predict only minor changes in the zone of habitability for warm-water coral reefs in the glacial East China Sea. Strong surface currents associated with the glacial Kuroshio may have maintained or even improved long-distance coral larval dispersal along the Ryukyu Arc, suggesting that conditions may have enabled coral reefs in this region to remain widespread throughout the last glacial. These findings are supported by seismic evidence for glacial coral reefs in the northern East China Sea. Further field studies are needed to investigate whether this is genuinely the case, and to provide additional constraints on how the coral reef front responds to long-term environmental change.

How to cite: Vogt-Vincent, N. and Mitarai, S.: The Kuroshio Current at the Last Glacial Maximum and implications for coral palaeobiogeography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10696, https://doi.org/10.5194/egusphere-egu22-10696, 2022.

14:43–14:50
Discussion of topics arising from time block 1

Mon, 23 May, 15:10–16:40

Chairpersons: Nils Weitzel, Jean-Philippe Baudouin, Julia Hargreaves

15:10–15:13
Introduction to time block 2

15:13–15:20
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EGU22-9897
Barbara Goudsmit et al.

Under continued high anthropogenic CO2 emissions, the atmospheric CO2 concentration around 2100 will be like that of the Early Eocene Climate Optimum (EECO, 56–48 Ma) hothouse period. Hence, reconstructions of the EECO climate give insight into the workings of the climate system under the possible future CO2 conditions. Our current understanding of global mean surface temperature (GMST) during the Cenozoic era relies on paleo-proxy estimates of deep-sea temperature (DST) combined with assumed relationships between global mean DST (GMDST), global mean sea-surface temperature (GMSST), and GMST. The validity of these assumptions is essential in our understanding of past and future climate states under hothouse conditions.
We analyse the relationship between these global temperature indicators for the end-of-simulation global mean temperature values in 25 different millennia-long model simulations of the EECO climate under varying CO2 levels, performed as part of the Deep-Time Model Intercomparison Project (DeepMIP). The model simulations show limited spatial variability in DST, indicating that local DST estimates can be regarded representative of GMDST. Linear regression analysis indicates that GMDST and GMST respond stronger to changes in atmospheric CO2 than GMSST by factors 1.18 and 1.17, respectively. Consequently, the responses of GMDST and GMST to atmospheric CO2 changes are similar in magnitude. This model-based analysis indicates that changes in GMDST can be used to estimate changes in GMST during the EECO, validating the assumed relationships. To test the robustness of these results, other Cenozoic climate states besides EECO should be analysed similarly.

How to cite: Goudsmit, B., Lansu, A., von der Heydt, A. S., Zhang, Y., and Ziegler, M.: The relationship between the global mean deep-sea and surface temperature during the Early Eocene , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9897, https://doi.org/10.5194/egusphere-egu22-9897, 2022.

15:20–15:27
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EGU22-1468
Charles J. R. Williams and the The African monsoon DeepMIP team

Here we present a study of African climate (with a focus on precipitation) during the early Eocene (~55-50 million years ago, Ma), as simulated by an ensemble of state-of-the-art climate models under the auspices of the Deep-time Model Intercomparison Project (DeepMIP).  The early Eocene is of particular interest, because with CO2 levels ranging between 1200-2500 ppmv (and a resulting temperature increase of ~5°C in the tropics and up to ~20°C at high latitudes) it provides a partial analogue for a possible future climate state by the end of the 21st century (and beyond) under extreme emissions scenarios.  This study is novel because it investigates the relatively little-studied subject of African hydroclimate during the early Eocene, a period from which there are very few proxy constraints, requiring more reliance on model simulations.

 

A comparison between the DeepMIP pre-industrial simulations and modern observations suggest that model biases aremodel- and geographically dependent.  However, the model ensemble mean reduces these biases and is showing the best agreement with observations.  A comparison between the DeepMIP Eocene simulations and the pre-industrial suggests that, when all individual models are considered separately, there is no obvious wetting or drying trend as the CO2 increases.  However, concerning the ensemble mean, the results suggest that changes to the land sea mask (relative to the modern) in the models may be responsible for the simulated increases in precipitation to the north of Eocene Africa, whereas it is likely that changes in vegetation (again relative to the modern geographical locations) in the models are responsible for the simulated region of drying over equatorial Eocene Africa.  When CO2 is increased in the simulations, at the lower levels of increased CO2, precipitation over the equatorial Atlantic and West Africa appears to be increasing in response.  At the higher levels of CO2, precipitation over West Africa is even more enhanced relative to the lower levels.  These precipitation increases are associated with enhanced surface air temperature, a strongly positive P-E balance and cloud cover increases.  At the lower levels of increased CO2, anticyclonic low-level circulation increases with CO2, drawing in more moisture from the equatorial Atlantic and causing a relative drying further north.  At higher levels of CO2, the increased anticyclonic low-level circulation is replaced by increased south-westerly flow.

 

Lastly, a model-data (using newly-compiled Nearest Living Relative reconstructions) comparison suggests that whether the Eocene simulations (regardless of CO2 experiment) over- or underestimate African precipitation is highly geographically dependent, with some of the CO2 experiments at some of the locations lying within the uncertainty range of the reconstructions.  Concerning the ensemble mean, the results suggest a marginally better fit with the reconstructions at lower levels of CO2.

How to cite: Williams, C. J. R. and the The African monsoon DeepMIP team: The African monsoon during the early Eocene from the DeepMIP simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1468, https://doi.org/10.5194/egusphere-egu22-1468, 2022.

15:27–15:34
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EGU22-913
Joel Arnault et al.

It is well accepted that global circulation models equipped with stable water isotopologues help to better understand the relationships between atmospheric circulation changes and isotope records in paleoclimate archives. Still, isotope-enabled models do not allow to precisely understand the processes affecting precipitation isotopic compositions, such as changes in precipitation amounts or moisture sources. Furthermore, the relevance of this model-oriented approach relies on the realism of modeled isotope results, that would support the interpretation of the records in terms of modeled climate changes. In order to alleviate these limitations, the newly developed WRF-Hydro-iso-tag, that is the version of the isotope-enabled regional coupled model WRF-Hydro-iso enhanced with an isotope tracing procedure, is presented. Physics-based WRF-Hydro-iso-tag ensembles are used to regionally downscale the isotope-enabled Community Earth System Model for Southern Africa, for two 10-year slices of mid-Holocene and pre-industrial times. The isotope tracing procedure is tailored in order to assess the origin of the hydrogen-isotope deuterium contained in Southern African precipitation, between two moisture sources that are the Atlantic and Indian Oceans. In comparison to the global model, WRF-Hydro-iso-tag simulates lower precipitation amounts with more regional details, and mid-Holocene-to-pre-industrial changes in precipitation isotopic compositions that better match plant-wax deuterium records from two marine sediment cores off the Orange and Limpopo River basins. Linear relationships between mid-Holocene-to-pre-industrial changes in temperature, precipitation amount, moisture source and precipitation deuterium compositions are derived from the ensembles results.

How to cite: Arnault, J., Niezgoda, K., Jung, G., Hahn, A., Zabel, M., Schefuss, E., and Kunstmann, H.: Disentangling the contribution of moisture source change to isotopic proxy signatures: Deuterium tracing with WRF-Hydro-iso-tag and application to Southern African Holocene sediment archives, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-913, https://doi.org/10.5194/egusphere-egu22-913, 2022.

15:34–15:41
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EGU22-3239
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Highlight
Dan Lunt and Paul Valdes

During the Phanerozoic (the last ~0.5 billion years), the Earth has experienced massive changes in climate, spanning the extensive glaciations of the Permo-Carboniferous (~300 million years ago), to the mid-Cretaceous super-greenhouse (~100 million years ago). Recently, several studies have used geological data to reconstruct global mean temperatures through this period, as a way of characterising the zeroth-order response of the Earth system to its primary forcings.  However, there has been little modelling work that has focussed on these long timescales, due to uncertainties in the associated boundary conditions (e,g., CO2 and paleogeography) and to the computational expense of carrying simulations spanning these long timescales.  Recently, paleogeographic (Scotese and Wright, 2018) and CO2 reconstructions (Foster et al, 2017) have emerged, and model and computational developments mean that we can now run large ensembles of relatively complex model simulations.  In particular, here we present an ensemble of 109 simulations through the Phanerozoic, with a tuned version of HadCM3L that performs comparably with CMIP5 models for the modern, and is also able to produce meridional temperature gradients in warm climates such as the Eocene in good agreement with proxy data.  We show that the model produces global mean temperatures in good agreement with proxy records.  We partition the response to changes in the different boundary conditions (CO2, paleogeography, ice extent, and insolation), and, through energy balance analysis, to surface albedo versus cloud versus water vapour changes.  We also illustrate the ocean and atmospheric circulation changes, with a focus on the role of the changing geography (e.g. the role of a coherent circumglobal ocean in the early Phanerozoic). 

How to cite: Lunt, D. and Valdes, P.: Modelling 500,000,000 years of climate change with a GCM – the role of CO2, paleogeography, insolation, and ice extent during the Phanerozoic, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3239, https://doi.org/10.5194/egusphere-egu22-3239, 2022.

15:41–15:48
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EGU22-8423
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ECS
Eva Hartmann et al.

The climate of the last 2500 years is documented in natural (speleothems, tree rings, sediments and pollen) and human-historical archives. Proxy records and subsequent climate reconstructions can be subject to a considerable amount of uncertainty, as the proxies can only capture a fraction of the entire variability. Climate model simulations can contribute to the interpretation of variations observed in the paleoclimate data and better understanding of dynamics, mechanisms and procedures. The state-of-the-art simulations following the CMIP6-protocol are highly resolved in time but still present a rather coarse horizontal resolution (200 km or more) to adequately address regional paleoclimate questions/hypotheses. Dynamical downscaling can close the gap between the regional archives and the coarsely resolved Earth System Models (ESMs). Using regional climate models to downscale ESM output requires a consistent implementation of the climate forcings in the regional model used also for the driving ESM. State-of-the-art and CMIP6 compliant reconstructions of volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, precession), solar (irradiance), land-use and greenhouse-gas changes used for the MPI-ESM are therefore implemented in the regional climate model COSMO-CLM (CCLM, COSMO 5.0 clm16). The functionality of each implemented forcing is tested separately and in combination for the period (1255-1265) that covers the Samalas volcanic eruption of 1257. The orbital forcing is found to have the largest impact in general and the volcanic forcing has a strong but short-lasting effect after the eruption. The other climate forcings only show very small impact in the chosen period. At the moment, a transient CCLM simulation with all forcings implemented with a horizontal resolution of 50 km is running for the last 2500 years in the Eastern Mediterranean, the Middle East and the Nile River basin.

How to cite: Hartmann, E., Zhang, M., Xoplaki, E., Wagner, S., and Adakudlu, M.: Implementation of Climate Forcings (volcanic, orbital, solar, LUC, GHG) for Paleoclimate Simulations (500BCE-2000CE) in the COSMO-CLM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8423, https://doi.org/10.5194/egusphere-egu22-8423, 2022.

15:48–15:55
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EGU22-4582
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ECS
Martin Renoult et al.

The use of paleoclimates to constrain the equilibrium climate sensitivity (ECS) has seen a growing interest. In particular, the Last Glacial Maximum (LGM) and the mid-Pliocene Warm Period have been used in emergent constraint approaches using simulations from the Paleoclimate Modelling Intercomparison Project (PMIP). Despite lower uncertainties regarding geological proxy data for the LGM in comparison with the Pliocene, the robustness of the emergent constraint between LGM temperature and ECS is weaker at both global and regional scales. Here, we investigate the climate of the LGM in models through different PMIP generations, and how various factors contribute to the spread of the model ensemble. Certain factors have large impact on an emergent constraint, such as state-dependency in climate feedbacks or model-dependency on ice sheet forcing. Other factors, such as models being out of energetic balance and sea-surface temperature not responding below -1.8°C in polar regions have a restricted influence. We quantify some of the contributions and show they mostly have extratropical origins, which contribute to a weak global constraint, and remotely impact tropical temperatures. Statistically, PMIP model generations do not differ substantially, unlike what has been previously suggested. Furthermore, we find that the lack of high or low ECS models in the ensembles critically limits the strength and reliability of the emergent constraints.

How to cite: Renoult, M., Sagoo, N., Zhu, J., and Mauritsen, T.: Causes of the weak relationship between modeled Last Glacial Maximum cooling and climate sensitivity, with consequences for emergent constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4582, https://doi.org/10.5194/egusphere-egu22-4582, 2022.

15:55–16:02
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EGU22-10449
Ozan Mert Göktürk et al.

Paleoclimatic changes in South Africa, especially around the southern Cape region, are of intense interdisciplinary interest; as this is an important area in the context of human evolution, hosting a number of prominent archaeological sites such as Klipdrift Shelter and Blombos Cave (both located near today’s shoreline). Questions surrounding how large-scale and local variability (and change) influenced the local human populations are abundant. Here we present results from downscaling simulations performed for southern Africa, with a high resolution (12 km) regional climate model (WRF), forced by a global earth system model (NorESM). We focus on two time-slices, 82 and 70 ka BP, when orbital parameters and global sea level were markedly different from each other. Changes from 82 to 70 ka BP are generally in line with orbital forcing; indicating, for example, a widespread and significant (> 40%) increase in summer precipitation over inland southern Africa (south of 15°S) due to higher insolation at 70 ka BP compared to 82 ka BP. In contrast, the western and southern Cape coasts became drier at 70 ka BP, owing in part to a 40 m lower sea level, as the coastline shifted and the paleo-Agulhas plain got exposed. The effect of the coastline shift on temperatures in the southern Cape region is evident from the significant (up to 6°C) increases (decreases) in maximum (minimum) temperatures, which are strong enough to overwhelm changes arising from orbital forcing. These inferences are further supported with a separate set of coastline-sensitivity simulations at 70 ka BP, which indicate not only drying, but also larger diurnal and interseasonal temperature ranges when the coastline extends southwards, and once-coastal areas become more continental. For instance, at the archaeological site of Blombos Cave, temperature extremes (1st and 99th percentiles) of the modelled marine climate become 25 to 50-fold more probable to occur as the coastline shift leads to a continental climate. Our results indicate that regional to local-scale processes, which tend to not be represented in most coarse resolution global models, have a strong influence on the paleoclimate of southern Africa, highlighting both the coastal-inland contrasts and the importance of changes in coastline position. 

How to cite: Göktürk, O. M., Sobolowski, S. P., Simon, M. H., Zhang, Z., and Jansen, E.: Modelling the regional paleoclimate of southern Africa: Sub-orbital-scale changes and sensitivity to coastline shifts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10449, https://doi.org/10.5194/egusphere-egu22-10449, 2022.

16:02–16:09
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EGU22-10715
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ECS
Nitesh Sinha et al.

The interpretation of East Asian monsoon speleothem δ18O records is heavily debated in the paleoclimate community. Besides developing new speleothem proxies, the use of isotope-enabled climate simulations is one of the key tools to enhance our understanding of speleothem δ18O records. Here we present results from novel climate simulations performed with the fully coupled isotope-enabled Community Earth System Model (iCESM1.2), which simulates global variations in water isotopes in the atmosphere, land, ocean, and sea ice. The model closely captures the major observed features of the isotopic compositions in precipitation over East Asia for the present-day conditions. To better understand the physical mechanisms causing interannual to orbital timescale variations in δ18O in East Asian speleothems, we ran a series of experiments with iCESM. We perturbed solar, orbital, bathymetry, ice-sheet, and greenhouse gas radiative forcings. The simulations supporting of observations/reconstructed records (GNIP/SISAL) from East Asia, help understand the controls on the isotope composition of East Asian monsoon rainfall and how speleothem δ18O records may be interpreted in terms of climate. The study provides new insights into the mechanisms of East Asian monsoon changes on different timescales.

How to cite: Sinha, N., Timmermann, A., Wessenburg, J. A., and Lee, S.-S.: Understanding climate, precipitation and δ18O linkages over Eastern Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10715, https://doi.org/10.5194/egusphere-egu22-10715, 2022.

16:09–16:16
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EGU22-3771
Marlene Klockmann and Sam Sherriff-Tadano

Understanding the response of the Atlantic Meridional Overturning Circulation (AMOC) to different climate conditions is a crucial part of understanding the climate system. Proxy-based reconstructions suggested that the AMOC during the Last Glacial Maximum (LGM) was likely shallower than today. Generations of climate models from PMIP2 to PMIP4 have shown large inter-model differences and often struggled to simulate a shallower AMOC. In the present study, we revisit hypotheses that have emerged over time and test them consistently across the PMIP ensembles from phase 2 to 4. We start by repeating the analyses by Weber et al (2007), who showed that there was a relationship between the glacial AMOC change and the density difference between the Southern Ocean and the subpolar North Atlantic in many PMIP2 models. Additional analysis will include hydrographic changes (e.g., stratification, water mass properties), the role of global and local LGM cooling as well as biases in the models. In our model evaluation, we will also consider recent reconstructions based on multi-proxy evaluations which indicate that the response of the glacial AMOC geometry and strength may have been less unambiguous than previously thought.

How to cite: Klockmann, M. and Sherriff-Tadano, S.: Drivers of LGM AMOC change from PMIP2 to PMIP4, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3771, https://doi.org/10.5194/egusphere-egu22-3771, 2022.

16:16–16:23
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EGU22-8788
Elisa Ziegler et al.

Projections of anthropogenic climate change suggest possible surface temperature increases similar to those during past major shifts of the mean climate like the Last Deglaciation. Such shifts do not only affect the mean but rather the full probability distributions of climatic variables such as temperature and precipitation. Changes to their distributions can thus be expected for the future as well and need to be constrained.  

To this end, we examine transient simulations of the Last Deglaciation from a hierarchy of climate models, ranging from an energy balance model to state-of-the-art Earth System Models. Besides the mean, we use the higher moments of variability – variance, skewness, and kurtosis – to characterize changes of the distribution. The analysis covers annual to millennial timescales and examines how patterns vary with timescale and region in response to warming. Furthermore, we evaluate how the changes of the distributions affect the occurrence of extremes.  

To analyze the influence of forcings on the distributions, we compare the patterns of the fully-forced simulations to those in sensitivity experiments that isolate the effects of individual forcings. In particular, the effect of volcanism is examined across the hierarchy, as well as changes in ice cover, freshwater input, CO2, and orbit. While large-scale global patterns can be found, there are significant regional differences as well as differences between simulations, relating for example to differences in the modelling of ice cover changes and freshwater input. Finally, we investigate whether climate model projections show the same trends with respect to the change in moments as those found in the deglacial simulations and thus whether the patterns found might hold for future climate. 

How to cite: Ziegler, E., Wirths, C., Andres, H., Gregoire, L., Ivanovic, R., Kapsch, M.-L., Kutterolf, S., Mikolajewicz, U., Schindlbeck-Belo, J. C., Toohey, M., Valdes, P. J., Weitzel, N., and Rehfeld, K.: Temperature and precipitation distribution changes in response to global warming – results from transient simulations of the Last Deglaciation from a hierarchy of climate models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8788, https://doi.org/10.5194/egusphere-egu22-8788, 2022.

16:30–16:40
Discussion of topics arising from time block 2

Mon, 23 May, 17:00–18:30

Chairpersons: Julia Hargreaves, Heather Andres, Elisa Ziegler

17:00–17:03
Introduction to time block 3

17:03–17:10
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EGU22-11090
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Highlight
Georg Feulner and Mona Bukenberger

The instability with respect to global glaciation is a fundamental property of the climate system caused by the positive ice-albedo feedback. The atmospheric concentration of carbon dioxide (CO2) at which this Snowball bifurcation occurs changes through Earth’s history because of the slowly increasing solar luminosity. Quantifying this critical CO2concentration is not only interesting from a climate dynamics perspective, but also an important prerequisite for understanding past "snowball Earth" episodes and the conditions for habitability on Earth and other planets. Earlier studies are limited to investigations with very simple climate models for Earth’s entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons difficult. Here we use a coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth’s history in one consistent model framework. We find that the critical CO2concentration decreases more or less logarithmically with increasing solar luminosity until about 1 billion years ago, but drops faster in more recent times. Furthermore, there is a fundamental shift in the dynamics of the critical state about 1.8 billion years ago, driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance.

How to cite: Feulner, G. and Bukenberger, M.: Tracing the snowball bifurcation of aquaplanets through time reveals a fundamental shift in critical-state dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11090, https://doi.org/10.5194/egusphere-egu22-11090, 2022.

17:10–17:17
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EGU22-12916
Evgeny Loskutov et al.
17:17–17:24
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EGU22-7379
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ECS
Stefanie Talento et al.

Glacial inception represents a bifurcation transition between interglacial and glacial states and is governed by the non-linear dynamics of the climate-cryosphere system. It has been previously proposed that to trigger glacial inception, the orbital forcing defined as the maximum of summer insolation at 65oN and determined by Earth’s orbital parameters must be lower than a critical level. This critical level depends on the atmospheric CO2 concentration. While paleoclimatic data do not constrain the critical dependence, its accurate estimation is of fundamental importance for predicting future glaciations and the effect that anthropogenic CO2 emissions might have on them. 

In this study we use the new Earth system model of intermediate complexity CLIMBER-X (which includes modules for atmosphere, ocean, land surface, sea ice and the new version of the 3-D polythermal ice sheet model SICOPOLIS) to estimate the critical orbital forcing - CO2 relationship for triggering glacial inception. We perform a series of experiments in which different combinations of orbital forcing and atmospheric CO2 concentration are maintained constant in time. Each model simulation is run for 1 million years using an acceleration technique with asynchronous coupling between the climate and ice sheet model components. SICOPOLIS is applied only to the Northern Hemisphere with a 40 km horizontal resolution.

We analyse for which combinations of orbital forcing and CO2 glacial inception occurs and trace the critical relationship between them, separating conditions under which glacial inception is possible from those where glacial inception is not materialised. We study how adequate it is to use the maximum summer insolation at 65°N as a single metric for orbital forcing, as well as consider the differential effect each one of Earth’s orbital parameters might have. In addition, we investigate the spatial and temporal patterns of ice cover during glacial inception under different orbital forcings.

How to cite: Talento, S., Willeit, M., Calov, R., Höning, D., and Ganopolski, A.: New estimation of critical orbital forcing – CO2 relationship for triggering of glacial inception, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7379, https://doi.org/10.5194/egusphere-egu22-7379, 2022.

17:24–17:31
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EGU22-11116
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ECS
Jonathan Buzan et al.

Changes between icehouse and greenhouse states are known to be the result from non-linear climate responses. However, the magnitudes of these responses are not well constrained. Recent work shows that climate models, specifically the Community Earth System Model version 1 (CESM1), have improved substantially in their capacity to quantify the Last Glacial Maximum (LGM) state. Given that CESM1 can reproduce the LGM well, we consider the combined impacts of estimated ice sheet heights, Quaternary orbits, and greenhouse gas changes for a range of Quaternary climate states. To that end, we conducted two sets of experiments: first, a series of sensitivity experiments on the Preindustrial climate and second, experiments on Quaternary glacial states.

In the first set of the experiments, we show how CESM1 quantifies the impacts of ice height, orbit, and greenhouse gas changes by considering each component incrementally. Then we demonstrate that they combine through non-linear impacts. The analysis is based on seven sensitivity experiments: 1) Late Holocene orbit, 2) Representative Concentration Pathway 8.5 (RCP85) greenhouse gases, 3) LGM orbit, 4) LGM greenhouse gasses, and 5) Greenland icesheet height changes, 6) LGM orbit with Greenland icesheet height changes, and 7) LGM orbit with LGM greenhouse gases and Greenland icesheet height changes. We show that adding individually these component changes do not linearly combine to match the simulations with combined changes.

These non-linear effects guide the second set of experiments, because non-linear systems are predictable due to state dependent outcomes. We use of 4 glacial ice sheet height differences and 4 glacial maximum orbital states (LGM, and Marine Isotopic Stage 4,6, and 8), for a total of 16 sensitivity experiments. These orbits are known glacial maximal states, and the 4 ice sheet heights are within the range of estimated ice volumes. We analyze these simulations in two ways, 1) the explicit effect of changes in orbit while holding the ice sheet constant, and 2) the explicit effect of changes in ice sheet height, while holding the orbit constant.

Our results show that ice sheet heights dominate the changes in climate system, regardless of orbit. But, there are subtle regional effects that orbit has that are not explained by ice sheet height changes. For example, higher ice sheets induce a global temperature increase, but regionally within Europe, there are non-linear changes in warming or cooling that are unexplained by the ice sheets. As the ice sheet height is lowered, the changes in Europe do not linearly change, and are dependent on the orbit configuration.

These results show that there are specific pathways for climate that occur due to the combination of icesheet height and orbit, and theoretically imply a constraint on the real climate state. In a linear system, these 16 states would represent the variability of the Quaternary, but as this is a non-linear system only 1 state is physical for a given orbit. As proxy data spatial and temporal resolution improves for the Quaternary, combined with these modeled climates, we expect substantial constraints on the available realistic climate states.

How to cite: Buzan, J., Russo, E., Kim, W., and Raible, C.: Sensitivity of glacial states to orbits and ice sheet heights in CESM1.2, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11116, https://doi.org/10.5194/egusphere-egu22-11116, 2022.

17:31–17:38
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EGU22-5710
Anais Bretones et al.
According to the recent generation of global climate models, a weakening of the Atlantic Meridional Overturning Circulation (AMOC) is unequivocal in the context of global warming. However, a recent study (Bretones et al, 2021) showed that the weakening of the AMOC at the reference latitude of 26N is decorrelated from the overturning trend north of the Greenland-Scotland Ridge.
From a paleo perspective, AMOC oscillations are believed to be one of the main drivers of the Dansgaard–Oeschger events, an alternation of cold and warm periods during the last glacial period in Greenland and with global signatures. During a warming phase, the AMOC is believed to be in a strong mode compared to the cold phase, thereby with increased amount of northward heat transport, and hence increased air temperature.
 In this study, we investigate the presence and evolution of the Arctic Meridional Overturning Circulation(ArMOC) during the abrupt warming transition from Heinrich event 4 (H4) to the Greenland interstadial 8 (GI8) in the NorESM climate model (Guo et al, 2019). The simulation is based on a validated GI8 simulation and freshwater hosing experiments to simulate H4 conditions. In the model, the transition of H4 to GI8 presents a warming of around 10°C within 30 years in Greenland, which is similar with what was observed in ice cores.

How to cite: Bretones, A., Nisancioglu, K. H., and Guo, C.: Changes in Arctic Meridional Overturning (ArMOC) under past abrupt warming , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5710, https://doi.org/10.5194/egusphere-egu22-5710, 2022.

17:38–17:45
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EGU22-839
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ECS
Irene Malmierca Vallet et al.

Frequent well documented Dansgaard-Oeschger (D-O) events occurred throughout the MIS3 period. This study lays the ground-work for a MIS3 D-O protocol for CMIP-class models. We consider the over-arching question: Are our models too stable? In the course of laying out groundwork we review: necessary D-O definitions; current progress on simulating D-O events in IPCC-class models (processes and published examples); and consider evidence of boundary conditions under which D-O events occur. Greenhouse gases and ice-sheet configurations are found to be crucial and the effect of orbital parameters is found to be small on the important features of MIS3 simulations. Oscillatory D-O type behaviour is found to be more likely, although not guaranteed, when run with low-intermediate MIS3 CO2 values, and reduced ice-sheets compared to the LGM. Thus, we propose performing a MIS3 baseline experiment centered at 38 ky (40 to 35 ky) period, which (1) shows a regular sequence of D-O events, and (2) yields the ideal intermediate ice-sheet configuration and central-to-cold GHG values. We suggest a protocol for a single baseline MIS3 PMIP protocol, alongside a preconditioned (kicked Heinrich) meltwater variant. These protocols aim to help unify the work of multiple model groups when investigating these cold-period instabilities. The protocol covers insolation-, freshwater-, GHG-, and NH ice sheet-related forcing. This addresses the currently gap in PMIP guidance for the simulation of a MIS3 state conducive to D-O oscillations under a common framework

How to cite: Malmierca Vallet, I., Sime, L. C., and Valdes, P. J.: Dansgaard-Oeschger events in climate models: A PMIP baseline MIS3 protocol, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-839, https://doi.org/10.5194/egusphere-egu22-839, 2022.

17:45–17:52
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EGU22-8892
Rolf Sonnerup and Mariona Claret

The 13C/12C of dissolved inorganic carbon (δ13C DIC ) carries valuable information on ocean
biological C-cycling, air-sea CO2 exchange, and circulation. Paleo-reconstructions of oceanic 13C
from sediment cores provide key insights into past as changes in these three drivers. As a step
toward full inclusion of 13C in the next generation of Earth system models, we implemented 13C-
cycling in a 1° lateral resolution ocean-ice-biogeochemistry Geophysical Fluid Dynamics
Laboratory (GFDL) model driven by Common Ocean Reference Experiment perpetual year
forcing. The model improved the mean of modern δ13C DIC over coarser resolution GFDL-model
implementations, capturing the Southern Ocean decline in surface δ13C DIC that propagates to the
deep sea via deep water formation. The model is used here to quantify controls on modern and
anthropogenic δ13C DIC as well as to test their sensitivity to wind speed/gas exchange
parameterizations.
We found that reducing the coefficient for air-sea gas exchange following OMIP-CMIP6
protocols reduces deep sea modern δ13C DIC by 0.2 permil and improves the depth-integrated
anthropogenic δ13C DIC relative to previous gas exchange parameterizations. This is because the
δ13C DIC of the endmembers ventilating the deep sea and intermediate waters are highly sensitive to
the wind speed dependence of the air-sea CO2 gas exchange. Additionally, meridional gradients
of surface modern δ13C DIC are better resolved with OMIP-CMIP6. While this model was initially
constructed to study the anthropogenic 13C response, it has promising applications toward longer
time scales. For example, BLING 13 C includes controls on the biological C-pump thought to be
important in the glacial ocean: light and iron limitation, and controls on 13C of organic matter
formation, and thus on ocean δ13C DIC and its vertical gradient, that depend on pCO2 .

How to cite: Sonnerup, R. and Claret, M.: A Next Generation Ocean Carbon Isotope Model for Climate Studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8892, https://doi.org/10.5194/egusphere-egu22-8892, 2022.

17:52–17:59
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EGU22-4376
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ECS
Anhelina Zapolska et al.

The main objective of this study is to develop and test a method of bias correction for paleoclimate model simulations using the “Cumulative Distribution Functions – transform” (CDF-t) method. The CDF-t is a quantile-mapping based method, extended to account for climate change signal. Here we apply the CDF-t to climate model outputs for the Mid-Holocene and the Last Glacial Maximum, simulated by the climate model of intermediate complexity iLOVECLIM at 5.625° resolution. Additionally, we test the proposed methodology on iLOVECLIM model outputs dynamically downscaled on a  0.25° resolution.

The results are validated through inverse and forward modelling approaches. The inverse approach implies comparing the obtained results with proxy-based reconstructed climatic variables. Here we use temperature and precipitation reconstructions, obtained with inverse modelling methods from pollen data. In this study, both gridded and point-based multi-proxy reconstruction datasets were used for the analysis.

The forward approach includes a further step of vegetation modelling, using the climatologies derived from bias-corrected outputs of the iLOVECLIM model in CARAIB (CARbon Assimilation In the Biosphere) global dynamic vegetation model. The modelled biomes are evaluated in comparison with pollen-based biome reconstructions BIOME6000.

The findings of this study indicate that the use of the proposed methodology results in significant improvements in climate and vegetation modelling and suggest that the CDF-t method is an valuable approach to reduce biases in paleoclimate modelling.

How to cite: Zapolska, A., Vrac, M., Quiquet, A., Arthur, F., Renssen, H., François, L., and Roche, D. M.: Validation of a CDF-t bias correction method using palaeo-data for the Mid-Holocene and the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4376, https://doi.org/10.5194/egusphere-egu22-4376, 2022.

17:59–18:06
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EGU22-3684
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ECS
Jean-Philippe Baudouin et al.

Recent progress in modelling the Earth system has made it possible to produce transient climate simulations longer than 10.000 years with comprehensive ESMs. These simulations improve our understanding of slow climatic feedbacks, climate state transitions, and abrupt climate changes. However, assessing the quality and reliability of such paleoclimate simulations is particularly challenging due to the inherent characteristic differences between model data and the climate reconstructions used to validate them.

Here, we present a collection of software packages for inter-model and model-data comparisons called Palaeo ToolBox (PTBox). Its first intent is to evaluate transient simulations of the PalMod project (deglaciation, glacial inception, MIS3) using several proxy data syntheses. Various variables are evaluated (including temperature, precipitation, oxygen isotopes, vegetation, carbon storages and fluxes), across a range of timescales (from decadal to multi-millenial). PTBox provides integrated model-data workflows, from data pre-processing to visualisations, organised into a series of (mostly R) packages. So far, PTBox includes 1) tools for pre-processing simulations and proxy data, 2) ensemble and pseudo-proxy methods to bridge the gap between simulations and proxies and to quantify uncertainties, 3) spectral methods to analyse timescale-dependent climate variability, and 4) newly developed metrics for spatio-temporal model-data comparisons.

Finally, PTBox is accompanied by a website (http://palmodapp.cloud.dkrz.de/) with examples on how to use PTBox and interactive visualisations of the datasets produced in the PalMod project.

How to cite: Baudouin, J.-P., Bothe, O., Chevalier, M., Ellerhoff, B., Adam, M., Schoch, P., Weitzel, N., and Rehfeld, K.: PTBox, a toolbox to facilitate palaeoclimate model-data analyses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3684, https://doi.org/10.5194/egusphere-egu22-3684, 2022.

18:06–18:13
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EGU22-6562
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ECS
Nils Weitzel et al.

An increasing number of Earth System Models has been used to simulate the climatic transition from the Last Glacial Maximum to the Holocene. This creates a demand for benchmarking against environmental proxy records, which have been synthesized for the same time period. Comparing these two data sources in space and time over a period with changing background conditions requires new methods. We employ proxy system modeling for probabilistic quantification of the deviation between temperature reconstructions and transient simulations. Regional and global scores quantify the mismatch in the pattern and magnitude of orbital- as well as millennial-scale temperature variations.

In pseudo-proxy experiments, we test the ability of our algorithm to accurately rank an ensemble of simulations according to their deviation from a prescribed temperature history, dependent upon the amount of added non-climatic noise. To this purpose, noisy pseudo-proxies are constructed by perturbing a reference simulation. We show that the algorithm detects the main features separating the ensemble members. When scores are aggregated spatially, the algorithm ranks simulations robustly and accurately in the presence of uncertainties. In contrast, erroneous rankings occur more often if only a single location is assessed.

Having established the effectiveness of the algorithm in idealized experiments, we apply our method to quantify the deviation between data from the PalMod project: an ensemble of transient deglacial simulations and a global compilation of sea surface temperature reconstructions. No simulation performs consistently well across different regions and components of the temperature evolution which we attribute to the larger spatial heterogeneity in reconstructions. Our work provides a basis for a standardized model-data comparison workflow, which can be extended subsequently with additional proxy data, new simulations, and improved representations of uncertainties.

How to cite: Weitzel, N., Andres, H., Baudouin, J.-P., Bothe, O., Dolman, A. M., Jonkers, L., Kapsch, M., Kleinen, T., Mikolajewicz, U., Paul, A., and Rehfeld, K.: Towards spatio-temporal comparison of transient simulations and temperature reconstructions for the last deglaciation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6562, https://doi.org/10.5194/egusphere-egu22-6562, 2022.

18:13–18:20
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EGU22-6979
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Highlight
Anne Dallmeyer et al.

The forest expansion in the Northern Hemispheric extra-tropics during the deglaciation, i.e. the last some 22,000 years, starts earlier and occurs much faster in our model simulation using the MPI-ESM 1.2 than in the recently published synthesis of biome reconstructions by Cao et al. (2019). As a result, the simulated Northern Hemisphere maximum in forest cover is reached at 11ka in the model, whereas the forest distribution peaks substantially later (at 7ka in the spatial mean) in the reconstructions. The model-data mismatch is largest in Asia, particularly in Siberia and the East Asian monsoon margin. The simulated temperature trend is in line with pollen-independent temperature reconstructions for Asia. Since the simulated vegetation adapt to the simulated climate within decades, the temporal model-data mismatch with respect to the forest cover may indicate that pollen records are not in equilibrium with climate on multi-millennial timescales.

Our study has some far-reaching consequences. Pollen-based vegetation and climate reconstructions are commonly used to evaluate Earth System Models against past climate states, but to what extent the reconstructed vegetation is in equilibrium with the climate at the reconstructed time slice is still a matter of discussion. Our results raise the question on which time-scales pollen-based reconstructions are reliable. Although, it is so far not possible to identify the causes of the mismatch between our simulations and the reconstruction, we suggest critical re-assessment of pollen-based climate reconstructions. Last, but not least, our results may also point to a much slower response of forest biomes to current and future ongoing climate changes than Earth System Models currently predict.

 

References:

Cao, X., Tian, F., Dallmeyer, A. and Herzschuh, U.: Northern Hemisphere biome changes (>30°N) since 40 cal ka BP and their driving factors inferred from model-data comparisons, Quat. Sci. Rev., 220, 291–309, doi:10.1016/j.quascirev.2019.07.034, 2019.

How to cite: Dallmeyer, A., Kleinen, T., Claussen, M., Weitzel, N., Cao, X., and Herzschuh, U.: The deglacial forest conundrum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6979, https://doi.org/10.5194/egusphere-egu22-6979, 2022.

18:20–18:30
Discussion and summary