We invite contributions on palaeoclimate-specific model development, tuning, 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 or juxtapose time-slice equilibrium experiments and long transient climate simulations (e.g. transient simulations covering the entire last glacial cycle as per the goal of the PalMod project). Comparisons may include different time periods (e.g., deep time, Quaternary, historical as well as future simulations), and focus on comparison of mean states, spatial gradients, circulation or modes of variability using different models, or contrast model results with reconstructions of temperature, precipitation, vegetation or circulation tracers (e.g. δ18O, δD or Pa/Th).
Presentation and discussion of results from the latest phase of PMIP4-CMIP6, and early-stage tests of new models or simulations for PMIP5/CMIP7 are particularly encouraged. However, we also solicit comparisons across time periods, between models and data, and analyses of underlying mechanisms of change as well as contributions introducing novel model or experimental designs that allow to improve future projections.
Orals: Fri, 2 May | Room 0.49/50
Warm, high-CO2 climates of Earth's past provide an opportunity to both evaluate climate models under extreme forcing and to explore mechanisms that lead to such warmth. One such time period is the early Eocene, when global mean surface temperatures were 10-16 oC higher than preindustrial, and CO2 concentrations were about ~1500 ppmv.
In this presentation we present the experimental design for Phase 2 of the Eocene component of the Deep-time Model Intercomparison project (DeepMIP-Eocene-p2). The aim is to provide a framework within which modelling groups can carry out a common set of simulations, thereby facilitating exploration of inter-model dependencies. Focus is on the early Eocene Climatic Optimum (EECO, ~53.3-49.1 million years ago). Relative to Phase 1 of DeepMIP, we provide a new paleogeography (topography, bathymetry) derived from four independent reconstructions, a new vegetation derived from vegetation model simulations that have been evaluated with paleobotanical data, and a new CO2 specification derived from the boron isotope proxy. The core set of simulations consists of a preindustrial control, an abrupt increase to 4x preindustrial CO2 concentrations under modern conditions, a standard control EECO simulation at 5x preindustrial CO2 concentrations, and an EECO simulation with preindustrial CO2 concentrations. In addition to these core simulations, we suggest a suite of optional sensitivity studies, which allow various sensitivities to be explored, such as to topography/bathymetry, greenhouse gases, land-surface parameters, astronomical and solar forcings, and internal model parameters. Overall, we hope that the updated boundary conditions and guidance on initialisation in Phase 2 will allow more robust model-data comparisons, more accurate insights into mechanisms influencing early Eocene climate, and increased relevance for informing future climate change projection.
In addition to the exprimental design, we present intitial simulations with the HadCM3 model with the new boundary conditions, and compare with the results from Phase 1, illustrating the sensitivity to the new paleogeography and vegetation.
How to cite: Lunt, D. and the The DeepMIP-Eocene Team: Experimental design for DeepMIP-Eocene Phase 2 - impact of new paleogeography and vegetation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13785, https://doi.org/10.5194/egusphere-egu25-13785, 2025.
In paleoclimate simulations, the insolation forcing at the top of the atmosphere needs to be altered to reflect Earth's orbital history during the time interval of interest. General Circulation Models (GCMs) often rely on either a modern orbital configuration to allow for direct comparison to modern and near-future climate simulations—sometimes with snapshot sensitivity experiments (DeepMIP, PlioMIP, etc.)—or they use the Berger (1978) (Ber78) routines to compute the orbital parameters. For snapshot simulations targeting older time periods such as the Eocene, using the modern orbital configuration is inappropriate, because the obliquity amplitude, for example, was much smaller than in the recent past. Our astronomical solutions ZB18a and ZB20a have been shown to produce the best match with geologic data to 58 Ma and 71 Ma, respectively (Zeebe & Lourens 2019, Kocken & Zeebe 2024). The eccentricity of the Ber78 solution diverges from these astronomical solutions already at ~33 ka, shows a different amplitude throughout, and drifts out of phase at ~1.6 Ma. It has been noted in the literature as well as code that the Ber78 routines are not appropriate for an analysis of time periods older than ~1 Myr. However, even recent transient simulations of the past 3 Myr sometimes fall back to using these outdated routines for the full time period. This is likely because of their ease of use; for example, the Ber78 routines are well-integrated into the Community Earth System Model (CESM).
In this study, we analyze the effects of using recent astronomical solutions on the insolation at the top of the atmosphere. Here we show that the absolute difference between insolation from Ber78 and our solution ZB18a increases periodically with increasing age, reaching values up to 88 Wm−2 at 2.68 Ma. This difference is of the same order of magnitude as the difference between a precession minimum and maximum. To facilitate using recent astronomical solutions in GCMs such as the CESM, we make the ZB18a and ZB20a orbital solutions readily available: We provide Fortran subroutines that calculate insolation and interpolate the astronomical parameters to a certain calendar date, and provide drop-in replacements to existing Fortran subroutines from the CESM. In this presentation we will show several examples of previous studies that could have benefited from these new routines.
Berger, A. (1978). Long-term variations of caloric insolation resulting from the earth’s orbital elements, Quaternary Research, 9, 139–167. https://doi.org/10.1016/0033-5894(78)90064-9
Zeebe, R. E., & Lourens, L. J. (2019). Solar System chaos and the Paleocene–Eocene boundary age constrained by geology and astronomy. Science, 365(6456), 926–929. https://doi.org/10.1126/science.aax0612
Kocken, I.J., & Zeebe, R. E. (2024). Testing Astronomical Solutions With Geological Data for the Latest Cretaceous: An Astronomically Tuned Time Scale. Paleoceanography and Paleoclimatology, 39(11). https://doi.org/10.1029/2024PA004954
How to cite: Kocken, I. J. and Zeebe, R. E.: New Insolation Forcing for Paleoclimate Models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14317, https://doi.org/10.5194/egusphere-egu25-14317, 2025.
The climate of the Late Pliocene (3.60-2.58Ma), has been extensively studied using models and data, as it represents the most recent period in Earth history where CO2 levels were similar to the present day. Within this interval, Marine Isotope Stage (MIS) KM5c (~3.205Ma) also had similar to present day orbital configuration, and hence was the subject of the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2).
Phase 3 of PlioMIP (PlioMIP3) is now underway and includes a number of sensitivity experiments to assess how the Late Pliocene climate would have been expected to respond to different CO2 levels (280ppmv, 400ppmv, 490ppmv and 560ppmv), extreme orbits and vegetation.
Here we will present results from these sensitivity experiments, which have been run using the Hadley Centre Climate Model (HadCM3). We find that the CO2 changes have a slightly smaller effect on temperatures when using Late Pliocene boundary conditions, than when using preindustrial, however the differences are region dependent. For example, Southern Ocean warming due to CO2 is notably lower with Pliocene boundary conditions than with preindustrial. This is partly because non-CO2 Pliocene forcing has already warmed this region significantly, however non-linearities will be discussed.
Results from the Late Pliocene experiment with a warm northern hemisphere summer orbit, and a warm southern hemisphere summer orbit will also be presented. This will allow us to assess how temperature and precipitation patterns could have varied throughout the Late Pliocene. The relative importance of paleogeography changes, CO2 changes, orbital changes and vegetation changes on Pliocene warming will be analysed.
How to cite: Tindall, J., Haywood, A., and Hunter, S.: Sensitivity of the Pliocene Climate to CO2, Orbital Forcing and Vegetation. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13365, https://doi.org/10.5194/egusphere-egu25-13365, 2025.
According to hydrographic profiles, about 2-5% of the present deep Southern Ocean waters have temperatures below the freezing point. Which role these supercooled waters may have played under glacial conditions is an open question. To elucidate the variations and mechanisms of deep ocean supercooling in the past we analyze a recently conducted quasi-transient earth system model simulation (CESM1.2), which covers the climate history of the past 3 million years. After the mid-Pleistocene Transition (MPT, ~1.2-0.75 million years ago, Ma) the simulation shows the presence of substantial volumes of supercooled glacial intermediate/deep waters primarily in the equatorial to northern Pacific. Our study explores the formation mechanisms of these waters in the subarctic North Pacific and their importance in creating deep ocean stratification with potential impacts on ocean carbon storage. We also address several modeling caveats in representing only surface sea ice in the present generation of climate models (not allowing for subsurface freezing) and in ensuring tracer conversation in longterm transient climate model simulations.
How to cite: Ishizu, M., Timmermann, A., and Kyung-Sook, Y.: A brief note on Supercooled Glacial Deep Waters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14091, https://doi.org/10.5194/egusphere-egu25-14091, 2025.
During the Last Glacial Maximum (LGM), atmospheric pCO2 was approximately 90 ppm lower than in the pre-industrial era. Several hypotheses have been proposed to explain this decrease, including changes in nutrient supply, increased iron input to the ocean, and variations in overturning circulation strength driven by differences in wind stress and moisture diffusivity. Current modeling approaches that simulate LGM marine biogeochemistry typically use parameter sets calibrated under pre-industrial boundary conditions, introducing uncertainty due to the imperfect knowledge of the values that can be assigned to the parameters for the LGM environment. The extent to which this uncertainty affects the simulated LGM marine biogeochemistry remains unclear. In this study, we employ an optimality-based non-Redfield plankton ecosystem model coupled with a 3D Earth system model to simulate LGM conditions. We conduct sensitivity analyses with 24 combinations of biogeochemical parameters (reduced benthic denitrification rate, decreased sedimentary iron input, higher PO4 levels, and increased atmospheric iron deposition) and physical boundary conditions (changes in wind stress pattern and increased meridional moisture diffusivity over the Southern Ocean). For each scenario, we perform 20 simulations using 20 biogeochemical parameter sets selected out of 600—each representing pre-industrial biogeochemistry and evaluated based on the misfit between observations and model outputs—resulting in a total of 480 simulations. Our results show that iron input exerts the most profound influence on LGM marine biogeochemistry and atmospheric pCO2, while changes in major nutrient supplies have minor effects. Additionally, the impact of physical conditions on biogeochemical tracers varies, depending on the specific biogeochemical settings. Compared to pre-industrial reference conditions, atmospheric pCO2 under full LGM conditions decreases by 36 to 58 ppm across the 20 simulations. The difference between the maximum and minimum pCO2 changes amounts to 50% of the 43 ppm average decrease. These findings highlight that, although the 20 parameter sets effectively reproduce pre-industrial marine biogeochemistry, significant cross-model variance in pCO2 responses and marine biogeochemical changes persists under LGM conditions.
How to cite: Chien, C.-T., Pahlow, M., Schartau, M., Somes, C., and Oschlies, A.: Simulating marine biogeochemistry and atmospheric pCO2 for the Last Glacial Maximum using an ensemble of calibrated parameter sets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17858, https://doi.org/10.5194/egusphere-egu25-17858, 2025.
The ocean carbon sink and deoxygenation are two key research focuses under the current anthropogenically warming climate, as the former is essential in regulating atmospheric CO2, and the latter is a vital factor for the marine ecosystem. The oceanic carbon and oxygen cycles are closely linked as they are commonly influenced by several processes, such as temperature-dependent gas solubility, organic matter remineralisation in the interior ocean, and ventilation. Future predictions of ocean carbon sink and deoxygenation are still subject to considerable uncertainties as the observational data in the present-day ocean is too sparse to constrain the relevant natural processes. To deepen our understanding of the natural carbon and oxygen cycles, we use the state-of-the-art Max Planck Institute Earth System Model (MPI-ESM) to conduct transient simulations for the last deglaciation (21 ka to the present day).
The deglacial evolution of oceanic CO2 outgassing is mainly controlled by gradual global warming and the Atlantic Meridional Overturning Circulation (AMOC) variability driven by the meltwater from the prescribed ice sheet reconstruction. The global ocean oxygen content generally captures the features of the qualitative oxygen proxies, with lower oxygen content in the glacial ocean compared to the Holocene and a decrease in global oxygen content as the AMOC declines. The low oxygen content in the glacial ocean results from lower oxygen content in the deep ocean (below 2000 m), which is partially counteracted by higher oxygen content in the upper ocean, owing to solubility increase under colder temperatures. The glacial deep-ocean deoxygenation is governed by the air-sea disequilibrium under a more extensive, longer-lasting sea ice cover in the Southern Ocean and a more sluggish transport between the upper and interior ocean. Unlike the ocean carbon content, which closely follows the temporal variation of the North Atlantic Deep Water (NADW) strength, the evolution of the oxygen content is slow and decoupled from the NADW during its recovery phase, suggesting the Southern Ocean ventilation has a more significant impact on the oxygen dynamics. For the mid and late Holocene, when the ocean circulation is quasi-stable, the global air-sea CO2 flux is near zero, whereas the replenishment of deep-sea oxygen continues. Such different response time scales between the ocean carbon and oxygen cycles are also seen in additional sensitivity simulations where an AMOC decline and recovery are simulated by freshwater hosing. Our preliminary findings suggest that the past changes in the climate and ocean circulation are likely to have a long-lasting impact on oxygen dynamics and drive oxygen concentrations away from equilibrium states, which should be accounted for when conducting model-data comparisons.
How to cite: Liu, B., Rückert, E., and Ilyina, T.: Different time scales in the transient response of the ocean carbon and oxygen cycles to deglacial climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11435, https://doi.org/10.5194/egusphere-egu25-11435, 2025.
A rapid change in the Atlantic overturning circulation (AMOC) can have a major impact on the hydrological cycle over land and ecosystems. Examples of such events have been widely discussed in palaeoclimate studies investigating the response of the AMOC to rapid freshening of the North Atlantic caused by ice sheet instability and melting during ice ages or in the early Holocene (Wunderling et al. 2024). The rapid decline of the AMOC and the possibility of its collapse in the future could also have a major impact on terrestrial ecosystems. An open question is the identification of precursors to such shifts and the anticipation of impacts and feedbacks on ecosystems. Here we use as a starting point a transient simulation of the last 6 000 years with version IPSLCM6-LR of the IPSL model (Boucher et al. 2020), starting from the PMIP mid-Holocene simulation with this model (Braconnot et al. 2021). Surprisingly, this simulation shows a rapid shift of 2 Sv in the AMOC, while this type of bifurcation was not seen in the set of CMIP6 simulations run with the same version of the model. (Boucher et al. 2020). Such a shift doesn't occur in a parallel simulation using a slightly different version of the model with fully interactive vegetation. The presentation will discuss the set of simulations used to identify 1) the reason for the shift, 2) the impact of the shift on the vegetation in Africa and Europe. For the latter, we run snapshot coupled simulations using as initial state the ocean state of the Holocene simulation with the AMOC shift, and the corresponding Earth’s orbit and trace gas configuration. This allows us to estimate the amplification of the changes induced by the vegetation feedback on the regional changes in the hydrological cycle.
Boucher O, Servonnat J, Albright AL, et al (2020) Presentation and Evaluation of the IPSL-CM6A-LR Climate Model. J Adv Model Earth Syst 12:e2019MS002010. https://doi.org/10.1029/2019ms002010
Braconnot P, Albani S, Balkanski Y, et al (2021) Impact of dust in PMIP-CMIP6 mid-Holocene simulations with the IPSL model. Clim Past 17:1091–1117. https://doi.org/10.5194/cp-17-1091-2021
Wunderling N, Von Der Heydt AS, Aksenov Y, et al (2024) Climate tipping point interactions and cascades: a review. Earth Syst Dyn 15:41–74. https://doi.org/10.5194/esd-15-41-2024
How to cite: Braconnot, P. and Marti, O.: Rapid change in AMOC intensity in a Holocene transient simulation provides insight into the ocean long term ocean memory , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7053, https://doi.org/10.5194/egusphere-egu25-7053, 2025.
Vegetation plays a critical role in regulating climate, not least as a sink of atmospheric carbon. How will anthropogenic warming affect the future distribution and behaviour of vegetation? The study of past warm intervals can contextualise biosphere responses to changes in temperature and precipitation. Pollen archives from central North America, in the Great Plains region, suggest that mid-Holocene (10-4 ka) warming was characterized by an abrupt expansion of grasslands and reduced forest cover. It has been suggested that these changes were a response to drying triggered by an increase in insolation and the abrupt collapse of the Laurentide Ice Sheet but evidence in support of this explanation is lacking. Here we report results from a new dynamic vegetation simulation of the mid-Holocene (6 ka) using the United Kingdom Earth System Model version 1.1 (UKESM1.1), in an atmosphere-land-only configuration. Our simulation is forced by sea-surface temperatures and sea-ice concentrations derived from the PMIP4 HadGEM3-GC3.1 midHolocene experiment and the orbit and greenhouse gas concentrations follow the PMIP4 protocol. In response to summer warming of between 0.5 and 1.5 °C, the model simulates a drying of up to 200 mm yr-1 in the North American continental interior and a substantial decrease in soil moisture. These land surface changes drive shifts in the distribution of plant functional types (PFTs) with a widespread decline in the fractional coverage of forests and a concurrent expansion of grasslands. The forest dieback is most intense in the north and central US and Canadian Great Plains where coverage falls by an area roughly equivalent to half the size of Texas.
How to cite: Wilson, A. J., Hopcroft, P. O., Crocker, A. J., Stockey, R. G., Williams, C. J. R., and Wilson, P. A.: North American forest dieback simulated in response to warm mid-Holocene summers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11848, https://doi.org/10.5194/egusphere-egu25-11848, 2025.
The mid-Holocene (MH: 6,000 years before present) is a key time slice for paleoclimate studies, and is one of the two entry cards for participation in the current Paleoclimate Modelling Intercomparison Project (PMIP4). The MH was characterized by high boreal summer insolation, leading to an intensification of the Northern Hemisphere monsoons. In northern Africa, the strengthening of the West African Monsoon was further amplified by nonlinear feedbacks, resulting in the development of vegetation referred to as the “Green Sahara”. The vegetation and land surface changes over northern Africa had various remote effects impacting the global climate through teleconnections.
In this study, we analyse outputs from five fully coupled global climate models to identify the remote impacts of the Green Sahara on global climate. Through the difference of two sets of mid-Holocene simulations – with and without the Green Sahara – we isolate the effect of the northern African vegetation and land cover changes on South American hydroclimate and tropical modes of climate variability such as the El Niño Southern Oscillation and the Atlantic Niño. Using an atmosphere-only climate model, we further investigate the Saharan-Arctic teleconnection invoked to explain the Arctic cooling concurrent with Saharan desertification. We quantify proxy-model agreement through metrics such as the Cohen’s Kappa index and the Root Mean Square Error to assess if the inclusion of the Green Saharan changes leads to greater coherence of model simulations with proxy reconstructions. Our results demonstrate the critical role of the Green Sahara in modulating the MH climate.
How to cite: Tiwari, S., S. R. Pausata, F., N. LeGrande, A., Griffiths, M., Wainer, I., Beltrami, H., de Vernal, A., O. Hopcroft, P., Tabor, C., Chandan, D., and Peltier, W. R.: Remote impacts of the mid-Holocene Green Sahara, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14580, https://doi.org/10.5194/egusphere-egu25-14580, 2025.
The hydrological cycle plays a crucial role in the Earth’s climate and has a direct impact on human populations. Despite advances, the IPCC AR6 report highlights persistent uncertainties concerning future projections of potential changes in the hydrological cycle, in particular for low latitudes monsoonal systems. This is because numerical climate models exhibit significant spread in their projections.
Traditionally, to estimate the future value of a climate variable, the distribution of projections from an ensemble of models is examined. However, this uncertainty is very high for water cycle, and the best estimates may be biased. To improve these projections, observational constraint, or emergent constraint methods, have been developed. These approaches adjust the distribution of projected variables based on observations, helping to reduce uncertainty. Furthermore, some studies show that the spatial pattern of sea surface salinity (SSS) is strongly correlated with the mean spatial pattern of the evaporation-precipitation (E-P) balance. Given that, water surface density is mainly influenced by salinity changes in region with strong precipitation and coastal runoff, both salinity and density could provide a useful tracer of the hydrological cycle.
In this study, we reconstruct past sea surface density based on geochemical analyses (ẟ18Oc) on foraminifera extracted from marine sediment cores in the Bay of Bengal. Density changes in this dilution basin are mainly related to south Asian monsoon precipitation changes. We used our density reconstructions for the last glacial maximum (LGM) and Mid-Holocene (MH) as a predictor for the observational constraint method. Our goal is to reduce uncertainties in future South Asian monsoon precipitation projections in climate models by linking paleoclimatic information with future climate projections. To do so, we used PMIP and CMIP numerical climate modelling experiments.
Our preliminary results show an underestimation of South Asian monsoon precipitation in the future (2000-2100) in most models, when using historical surface density and salinity (1900-2000) as a predictor. We are currently finalizing the use of LGM and MH surface density as predictor, in order to compare results when past predictors (LGM and MH) are used rather than an historical predictor.
How to cite: Barathieu, H., Caley, T., Portmann, V., Swingedouw, D., Kageyama, M., Braconnot, P., Roche, D., Rieger, N., Malaizé, B., Peral, M., Dassié, E., Charlier, K., and Bassinot, F.: Using Past Surface Water Density to Constrain Future South Asian Monsoon Precipitation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6568, https://doi.org/10.5194/egusphere-egu25-6568, 2025.
Posters on site: Fri, 2 May, 10:45–12:30 | Hall X5
The Paleoclimate Modelling Intercomparison Project (PMIP) was launched in 1995 and has since closely followed the phases of the Coupled Model Intercomparison Project (CMIP) providing understanding of past climate states based on the latest Global Climate Models and evaluation of their capacity to represent climates very different from the recent one. PMIP is planning its next phase, in the wake of CMIP7 launch (Dunne et al., 2024).
CMIP7 is organised along two main phases: the Fast Track, to be delivered in time for its results to be analysed and published for the seventh assessment report of the IPCC (Intergovermental Panel on Climate Change), followed by the main phase of CMIP7. This poster will describe the rationale of including an idealised paleoclimate simulation, "abrupt-127k", in the Fast Track set of experiments. This experiment starts from the Fast Track pre-industrial control experiment and then abruptly changes the astronomical parameters to those for 127,000 years ago (as well as some minor greenhouse gas changes). This will allow analyses of the sensitivity of the Arctic sea ice to conditions favouring its summer decrease or even collapse, and can be extended to become a last interglacial simulation (lig127k). The poster will also briefly describe the other experiments that are expected to be included in the next phase of PMIP. We are looking forward to discussions of key experiments, analyses, challenges with the PMIP and CMIP communities alike.
Dunne et al., 2024: https://doi.org/10.5194/egusphere-2024-3874
How to cite: Brierley, C., Kageyama, M., Peterschmitt, J.-Y., Stepanek, C., and Sime, L.: Planning for the next phase of the Paleoclimate Modelling Intercomparison Project (PMIP7), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17910, https://doi.org/10.5194/egusphere-egu25-17910, 2025.
The PalMod project, funded by the German Federal Ministry of Education and Research (BMBF), aims at addressing key knowledge gaps in the understanding of the dynamics and variability of the climate system during the last glacial cycle. This period, which is marked by strong and rapid climatic fluctuations, serves as a testbed for complex Earth system models (ESMs). The models tested in this way will be used in climate-change scenarios for the next millennia to enhance future climate-change assessments. PalMod uses three ESMs—AWI-ESM, MPI-ESM, and CESM— that integrate physical and biogeochemical processes and employ advanced parameterizations regarding, for example, ice sheet-ocean interactions.
In Phases I and II, the project focused on key epochs of the last glacial cycle including inception, MIS3, and the last deglaciation. The ongoing final Phase III leverages these insights to project the climate over the next millennia. Central to this last project phase is to answer some of the major societally critical questions in association with climate change: What are the potential tipping points and at which global warming may they become relevant? Under what conditions could polar ice sheets collapse catastrophically, and how rapidly could sea levels rise under different future climate scenarios? How will permafrost evolve in a warming world? This presentation reflects on the progress made during the past two phases of the project and presents preliminary answers to the aforementioned pressing questions.
How to cite: Fieg, K., Latif, M., Schulz, M., and Ilyina, T.: Advancing Climate System Understanding: Insights from the PalMod Project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3861, https://doi.org/10.5194/egusphere-egu25-3861, 2025.
The early Eocene is the warmest epoch in the last 65 million years, with a global mean temperature 9 to 23°C higher than the modern era. According to state-of-the-art climate models, the tropical rainfall contracted towards the equator during this extremely warm period. However, the physical mechanism causing this phenomenon remains unclear. In this study, we examined the hemispheric energy balance in the early Eocene that causes the equatorward contraction of tropical precipitation. A novel mechanism underlying this phenomenon is revealed. Based on the climate modeling of CESM1.2, we show that the GHG-induced warmth enhances the sensitivity of evaporation to surface wind speed changes in the early Eocene. Thus, the stronger tropical trade wind in the winter hemisphere will drive out stronger latent heat flux than in the summer hemisphere. This interhemispheric asymmetric response reduces the interhemispheric heating contrast in the solstice seasons. As a result, the ascending motion in the tropical atmosphere migrates towards the equator, finally decreases the width of tropical precipitation in the early Eocene.
How to cite: Ren, Z., Zhou, T., Guo, Z., Zuo, M., He, L., Chen, X., Zhang, L., Wu, B., and Man, W.: Enhanced “wind-evaporation effect” drove the “deep-tropical contraction” in the early Eocene, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18941, https://doi.org/10.5194/egusphere-egu25-18941, 2025.
The Earth experienced dramatic climate changes during the past million years, including a long-term gradual cooling from the Pliocene (5.3-2.6 million years ago; Ma) to the Pleistocene (2.6-0.011 Ma) and an abrupt transition from 41-kyr to 100-kyr glacial-interglacial cycles at ca. 1.2-0.8 Ma (i.e., the Mid-Pleistocene transition). Investigating the mechanisms that triggered these climatic responses requires long-term transient climate simulations which can be used to quantify the sensitivity of the Earth’s climate to different external and internal forcings. However, few such simulations exist and therefore, key questions regarding the long-term evolution of the earth system remain unanswered.
Here, we used iLOVECLIM, a coupled Earth system numerical climate model of intermediate complexity, to generate a 4.5 Ma transient climate simulation, the longest to date. iLOVECLIM is ideally suited for this task as it requires substantially less computational resources and time to perform transient climate simulations compared to fully coupled general circulation models. We performed the simulations with interactive atmosphere, ocean and vegetation components and used the methodology of previous long-term transient simulations. Briefly, we applied an acceleration factor of five to the external forcings (orbital parameters, greenhouse gases concentration and ice-sheets) and split the 4.5 Ma simulation into 44 chunks run in parallel to reduce the computing time from several years to a couple of months. Each chunk was initialized from an interglacial period, covers at least one glacial-interglacial cycle and has an overlap period of 20,000 years in order to compensate for issues related to spin-up effects and initial conditions. The complete simulation is a composite of all the individual chunks and time-sliding linear interpolation performed on the overlap intervals.
While the simulations are still ongoing, preliminary results demonstrate that our new model set-up and experimental design are able to produce reasonable outputs. When it is completed, the final simulation will be evaluated against available paleoclimate data and existing transient climate simulations. Apart from running a simulation with all the external forcings combined, we also plan to run subsequent simulations with each individual forcing alone to evaluate the climate responses associated with each. This unique long transient simulation will provide a better mechanistic understanding of the major climate reorganizations that occurred during the Plio-Pleistocene and will be useful for future data-model comparisons and data assimilation endeavours.
How to cite: Extier, T., Hou, A., Caley, T., Roche, D. M., Köhler, P., and van de Wal, R. S. W.: Transient climate simulation of the past 4.5 million years based on the coupled intermediate complexity model iLOVECLIM, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12057, https://doi.org/10.5194/egusphere-egu25-12057, 2025.
Hyperthermal events, such as the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) and Early Eocene Climatic Optimum (EECO, 52 million years ago), are of significant interest because they offer critical insights into how the Earth’s climate reacts to rapid increases in greenhouse gas concentrations. These events, marked by intense global warming and ocean acidification, improve our understanding of the long-term effects of sudden carbon releases and help assess the potential impacts of today's human-driven climate change.
In this study, we use a version of the Planet Simulator (PlaSim), an Earth Model of Intermediate Complexity (EMIC) improved with a 3D ocean model (Large-Scale Geostrophic ocean model, LSG), to simulate these hyperthermal periods. This modeling approach allows for detailed analyses of ocean-atmosphere interactions and their role in shaping global climate patterns under extreme GHG scenarios. The simulations include boundary conditions derived from Herold et al. (2014) and use an experimental approach similar to the DeepMIP protocol. We explore a range of atmospheric CO2 levels (from 1× to 16× pre-industrial concentrations) to evaluate the sensitivity of the climate system to these factors.
The focus is on understanding feedback mechanisms and climate dynamics under extreme greenhouse gas forcing, while also considering equilibrium climate sensitivity (ECS) and polar amplification, with attention to Antarctic warming and its implications for ice-free conditions during the late Paleocene–early Eocene. Current work involves testing and refining paleoclimate boundary conditions in the Planet Simulator, particularly adjusting paleogeography, vegetation parameters, and ocean circulation to match the climate conditions of that period. This study improves our understanding of past extreme greenhouse climates and evaluates the ability of modern Earth System Models (ESMs) to predict future climate changes.
How to cite: Ghirardo, I. and Hardenberg, J.: Modeling Paleocene-Eocene Hyperthermals with the PlaSim-LSG Earth System Model of Intermediate Complexity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13628, https://doi.org/10.5194/egusphere-egu25-13628, 2025.
During the mid-Pliocene, carbon dioxide (CO2) concentrations were comparable to current levels, ~350-450 p.p.m., making the mid-Pliocene a valuable analog for current and potentially future climates. However, the global average temperature in the mid-Pliocene is estimated to have been ~3 ºC higher than today, implying factors beyond greenhouse gases contributed to the warmth. Surface wind velocity, a key driver of ocean mixing and air-sea turbulent heat flux, significantly affects ocean heat content and global heat distribution. Understanding the role of surface wind speed in warm climates is therefore important to uncover the causes of the Pliocene warmth.
In this study, we utilized a set of climate models from the Coupled Model Intercomparison Project (CMIP) and the Paleoclimate Modeling Intercomparison Project (PMIP) archives to analyze surface wind variability in the tropics during the mid-Pliocene and the Pre-industrial periods. Over the tropics, surface wind velocity is strongly influenced by sea surface temperature (SST) patterns, predominantly El Niño-Southern Oscillation. To explore the underlying mechanisms of surface wind variability, we applied Empirical Orthogonal Functions (EOF) to tropical SST data to extract SST patterns and decompose surface wind speed into SST-dependent and SST-independent components. Our results revealed that the ratio of SST-dependent and SST-independent wind variability could vary substantially in space and with season, and it could differ between the mid-Pliocene and the Pre-industrial period with a large inter-model spread. Implications for understanding the mid-Pliocene warmth and constraining future climate projection will be discussed.
How to cite: Kawashima, H. and Hu, S.: Ocean surface wind variability under the Pliocene warmth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13793, https://doi.org/10.5194/egusphere-egu25-13793, 2025.
Geomagnetic variations are the perfect testbed to study the effect of Galactic Cosmic Rays (GCR) on climate, as they disentangle solar variability from direct GCR effects. We use the 3D chemical transport model GEOS-CHEM to simulate the change in the cloud condensation nuclei number density during the Brunhes-Matuyama magnetic field reversal assuming present day aerosol conditions. We then estimate the change in cloud condensation nuclei for low level clouds under both solar minimum and solar maximum ionisation conditions. We also test whether the effect of ion-enhanced growth significantly enhances the process. We find a cloud condensation nuclei enhancement for low level clouds throughout the magnetic field reversal of several percent, which supports the observational findings of a wetter and colder climate during the Brunhes-Matuyama magnetic field reversal.
How to cite: Thaler, I., Svensmark, J., Bødker Enghoff, M., Shaviv, N., and Svensmark, H.: Estimating the change in low level cloud cover during the Brunhes-Matuyama magnetic field reversal: A first modelling approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15686, https://doi.org/10.5194/egusphere-egu25-15686, 2025.
Substantial snow accumulation over northern continents during glacial periods contributed to the growth of the Laurentide and Eurasian ice sheets. As a result sea level dropped by ~120-130 m, which led to an increase in global mean ocean salinity by about 1 permil. Pore water chlorinity data from deep ocean sediment cores interestingly show even higher values regionally. Despite this superficial understanding of glacial ocean salinity shifts, the three-dimensional patterns of paleosalinity changes are still not well understood. Here, we argue that northern hemisphere ice-sheets effectively blocked pan-Arctic river discharge into the Arctic Ocean for millennia. In the absence of ice-sheet calving and melting, this process was responsible for the gradual accumulation of the 1 permil global mean salinity anomaly during glacial periods. To better understand the underlying physical mechanisms, we use the Community Earth System Model and mimic the freshwater withholding of the ice-sheets as an idealized negative freshwater perturbation. Applying this forcing scenario, we find that the river blockage due to the Laurentide and Eurasian ice-sheets removes the polar halocline, strengthens the Atlantic Meridional Overturning Circulation and contributes to the global increase of salinity at a rate of 0.1 permil/1000 years. Moreover, the process creates a characteristic pattern of deep ocean salinity anomalies, which is distinct from the vertical salinity redistribution due to sea-ice/brine formation in the Southern Ocean. Eventually, for glacial conditions both, the Arctic and Southern Ocean-generated salinity patterns combine.
How to cite: Kim, H., Timmermann, A., and Ishizu, M.: Arctic river blockage and the formation of glacial deep ocean salinity anomalies , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5445, https://doi.org/10.5194/egusphere-egu25-5445, 2025.
The global ocean plays a crucial role in redistributing and storing heat, carbon, nutrients and other essential elements in the Earth’s climate system. As a prominent part of the global ocean circulation, the Atlantic Meridional Overturning Circulation (AMOC) shapes the spatial distribution of these elements and links the atmosphere to the deep ocean.
The state of ocean oxygenation and the carbon storage capacity are tightly connected to biogeochemical activity. High oxygen levels facilitate the efficient remineralization of organic matter, helping to stabilize the CO2 content in the upper ocean layers. In contrast, low oxygen levels enhance carbon storage in the deep ocean temporarily but increase the risk of pronounced outgassing during ocean circulation changes or upwelling events. Thus, ocean oxygenation acts both as an indicator and a control on biogeochemistry and thus long-term climate regulation.
Proxy data indicate substantial changes in AMOC strength in the past, particularly during Termination 1, when high freshwater fluxes disrupted deep water formation and significantly slowed down the ocean circulation. Despite these insights, the interplay between changes in ocean circulation, oxygenation and carbon storage and release during such abrupt events is still not fully understood.
To address these knowledge gaps, we used the Max Planck Institute for Meteorology Earth system model (MPI-ESM) coupled with the interactive Hamburg ocean carbon cycle model (HAMOCC) to simulate transient climate changes during the last deglaciation.
We focused on periods of major AMOC disruptions during the last deglaciation to investigate their impact on the ocean’s oxygen levels in the water column.
Preliminary results indicate a delayed increase of the global oxygen minimum zone (OMZ) volume following abrupt AMOC changes. The most significant changes in the oxygen levels can be observed in the Atlantic Sector of the Southern Ocean. Additionally, we explore the feedbacks between changes in oxygenation, carbon storage, and biological activity across these events.
This research provides new insights into the complex interplay between ocean circulation, oxygen dynamics, and carbon storage during deglacial periods, advancing our understanding of the mechanisms underlying abrupt climate events and their biogeochemical impacts.
How to cite: Rückert, E. M., Liu, B., and Ilyina, T.: Impact of Past AMOC Disruptions on Ocean Oxygenation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8946, https://doi.org/10.5194/egusphere-egu25-8946, 2025.
The topography of the Laurentide Ice Sheet (LIS) during glacial periods, particularly the Last Glacial Maximum (LGM), played a pivotal role in shaping atmospheric circulation and teleconnection patterns. This study investigates the impact of LIS elevation changes on global atmospheric dynamics using fully coupled paleoclimate simulations with the isotope-enabled Community Earth System Model (CESM) version 1.2. Previous studies have shown that a higher LIS elevation significantly amplifies Arctic warming, reducing the equator-to-pole temperature gradient and influencing jet streams and stationary waves (Liakka & Lofverstrom, 2018 ; Beghin et al., 2014 ; Lofverstrom et al., 2014). This mechanism may also extend to the Southern Hemisphere, affecting teleconnection pathways.
By systematically modifying LIS elevation, we explore its role in altering large-scale atmospheric circulation features such as the Intertropical Convergence Zone (ITCZ), Southern Annular Mode (SAM), and Walker circulation, as well as modes of variability including El Niño–Southern Oscillation (ENSO). We show the critical influence of LIS topography on global teleconnections and how ice sheet dynamics shaped glacial climate variability and atmospheric feedbacks.
How to cite: Abdelkader Di Carlo, I., Pausata, F., Kageyama, M., Davrinche, C., Lofverstrom, M., and Ninnemann, U.: Ice-sheet topography changes in North America affect teleconnection patterns on glacial time scales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18286, https://doi.org/10.5194/egusphere-egu25-18286, 2025.
The Last Glacial Maximum (LGM) Antarctic ice sheet extent is relatively well constrained with an ice sheet reaching to the continental shelf edge in most places. The ice mass stored in the ice sheet and especially the ice sheet mass loss evolution since the Last Glacial Maximum is more debated. Reconstructed relative sea-level (RSL) variations along the Antarctic coast capture the interplay between ice mass changes, variations in the isostatic response and gravitational forces between the ocean water and the ice mass and therefore, can aid to reconstruct the Antarctic ice sheet evolution from the LGM to the present day.
Here we use the Antarctic ice sheet model AISMPALEO that includes a spatially variable Elastic Lithosphere Relaxing Asthenosphere isostasy model with an approximation of the gravitational consistent sea level equation. A large suite of Antarctic ice sheet model simulations is performed and analyzed from the Last Glacial Maximum to the present-day. The simulations are forced by different global sea-level reconstructions, PMIP4 climate model output for the ocean and the atmosphere and different Earth rheological parameters in the isostasy model. The model runs are compared with published datasets of relative sea-level along the coast of Antarctica to derive the best agreement between the RSL data and the Antarctic ice sheet evolution.
How to cite: Van Breedam, J., Huybrechts, P., and Verleyen, E.: Antarctic ice sheet evolution from the Last Glacial Maximum to the present day constrained by relative sea-level variations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17020, https://doi.org/10.5194/egusphere-egu25-17020, 2025.
The Central Mediterranean's complex topography and dynamic land-sea interactions provide a compelling opportunity for high-resolution paleoclimate modelling aimed at enhancing our understanding of natural climate variability. This study utilizes the RegCM5 regional climate model to conduct km-scale simulations, focusing on fine-scale climate dynamics for a reduced Mediterranean domain across five pivotal paleoclimate periods: Modern (ca. 1995 CE), Pre-Industrial (ca. 1850 CE), Medieval Climate Anomaly (MCA, ca. 1000 CE), mid-Holocene (6000 BP), and Last Glacial Maximum (LGM, 21000 BP). Simulations are driven by MPI-ESM-LR model outputs from PMIP4, with ERA5 reanalysis data used for evaluation runs.
A novel land-use mapping technique is applied, leveraging Köppen-Geiger climate classifications and current vegetation distributions to reconstruct paleoclimate vegetation patterns. Simulation results are benchmarked against E-OBS, ModE-RA, MCruns, and lgmDAnomaly datasets, revealing typical biases. Historical data exhibits a cold bias, while the 6000 BP period shows scattered low-level wet and cold biases, and the 21000 BP period presents warm and wet biases. Despite these challenges, the km-scale simulations effectively capture detailed climatic patterns, providing crucial insights into the Mediterranean’s paleoclimate and regional implications. These findings highlight the value of downscaling global models to km scales, which can advance our understanding of past climate dynamics and informing strategies for future climate adaptation.
How to cite: Ciarlo`, J., Lamoliere, A., Giuliani, G., Coppola, E., Micallef, A., and Mifsud, D.: Convection Permitting Regional Paleoclimate Simulations with Climate-Driven Land-Use Mapping for a reduced Mediterranean domain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4864, https://doi.org/10.5194/egusphere-egu25-4864, 2025.
The Holocene started about 10000 years before present and is the period during civilizations as we know them today emerged. However, during that time several regions such as Sahel-Sahara or the Indus valley in the tropics experienced severe aridification and dramatic environmental changes for ecosystems and humans. There is general agreement that this has been caused by the southward shift of the boreal monsoon rain belt and that slow variations of Earth’s orbital parameters are the long-term driver. In addition to insolation forcing, several feedbacks involving the ocean, sea-ice, or vegetation have had a profound impact on regional changes and on the multiscale monsoon variability, including extreme monsoon years. They have shaped the magnitude and the timing of environmental changes depending on monsoon systems. Although these feedbacks have been widely discussed, their relative strength is still under debate. These unknows prevent proper anticipation and simulation of future monsoon behavior. Long transient simulations of the Holocene climate allow us to revisit these questions by shedding light on monsoon multiscale variability and the representation of vegetation feedbacks. Using a set of transient mid to late Holocene simulations (last 6000 years), we will discuss the relative evolution of the global monsoons. Highlights will be on the relative responses to changes in insolation seasonality between African and Indian monsoons, the role of dynamical versus thermodynamical atmospheric feedbacks in monsoon precipitation, and on the relationship between long term trends, interannual to multicentennial variability and periods of extreme dry or wet monsoon seasons. Comparisons of model results with proxy reconstruction of climate variability over land and ocean from speleothems, coral and shells has been done considering the chaotic nature of multiscale monsoon variability. They provide us with indication of the consistency of model inferred trends in monsoon variability and the real climate trajectory.
How to cite: D'Agostino, R., Braconnot, P., Harrison, S. P., Crètat, J., Wang, Z., and Zhang, Q. and the PACMEDY: Monsoon trend and multi-scale variability changes over the last 6000 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19034, https://doi.org/10.5194/egusphere-egu25-19034, 2025.
Precessional forcing is a key driver of quaternary climate change. Based on 24 experiments covering a full precession cycle, this study explores spatio-temporal variations of both climate and isotope signals in northern Africa. We find a synchronous phasing of precipitation variations with solar radiation levels and an asynchronous timing of surface air temperature changes across different sub-regions of northern Africa. Based on daily precipitation, our results reveal earlier onset and withdrawal, as well as a shorter duration of the West Africa summer monsoon (WASM) at minimum precession compared to maximum precession. The onset of the WASM is controlled by the intensity of the Sahara Heat Low, while the monsoon termination is linked to subtropical solar radiation and interhemispheric thermo contrast. Using a novel scale-flux tracing technique, we find that, precipitation during minimum precession is more influenced by evaporation from warmer and more humid regions compared to maximum precession. Additionally, certain inland areas of northern Africa exhibit positive temporal isotope-precipitation gradients, violating the "amount effect". This phenomenon mainly occurs during precession phases associated with Green Sahara periods. The isotope composition changes in such places primarily reflect changes in upstream rainfall quantity, rather than changes in local precipitation as is inferred from present day analogs. Conversely, the "amount effect" remains applicable during dry periods in Africa when the Sahara desert is present. This suggests that isotope-based reconstruction of past precipitation variations during Green Sahara periods over North Africa needs to be taken with caution.
How to cite: Shi, X., Werner, M., Yang, H., Gao, Q., Liu, J., and Lohmann, G.: Insights from AWIESM-wiso: climate and water isotope signals in northern Africa in a precession cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20327, https://doi.org/10.5194/egusphere-egu25-20327, 2025.
