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This study presents the application of an interactive downscaling in Europe using iLOVECLIM (a model of intermediate complexity), increasing its atmospheric resolution from 5.56 to 0.25∘ kilometric. A transient simulation using the appropriate climate forcings for the entire Holocene (11.5–0 ka BP) was done for both the standard version of the model and with an interactive downscaling applied. Our results show that simulations from downscaling present spatial variability that agrees better with proxy-based reconstructions and other climate models as compared to the standard model. The downscaling scheme simulates much higher (by at least a factor of 2) precipitation maxima and provides detailed information in mountainous regions. We focus on examples from the Scandes mountains, the Alps, the Scottish Highlands, and the Mediterranean. The higher spatial resolution of the downscaling provides a more realistic overview of the topography and gives local climate information, such as precipitation and temperature gradient, that is important for paleoclimate studies. With downscaling, we simulate similar trends and spatial patterns of the precipitation changes reconstructed by other proxy studies (for example in the Alps) as compared to the standard version. Our downscaling tool is numerically cheap, implying that our model can perform kilometric, multi-millennial simulations and is suitable for future studies.

The Last Interglacial period (LIG), which occurred approximately between 130 and 116 kyr BP, is characterized by similar/warmer temperatures and higher sea levels compared to the present-day conditions due to the orbital variation of the Earth. Hence, the period provides insights into the behavior of the Earth's system components under stable and prolonged warm climates and their subsequent evolution into a glacial state. To better understand the ice sheet's surface mass balance that ultimately drives the advance and retreat of ice-sheets, we study the snow cover changes in the Northern Hemisphere during the LIG. In order to do so, we used BESSI (BErgen Snow Simulator), a physical energy balance model with 15 vertical snow layers and high computational efficiency, to simulate the snowpack evolution. First, BESSI was validated using the regional climate model MAR (Modèle Atmosphérique Régional) as forcing and benchmark for snow cover over the Greenland and Antarctica Ice Sheets under present-day climate. Using two distinct ice sheet climates helps constrain the different processes in place (e.g., albedo and surface melt for Greenland and sublimation for Antarctica). For the LIG simulations, the latest version of an Earth system model of intermediate complexity iLOVECLIM was used to force BESSI in different time slices to fully capture the snow evolution in the Northern Hemisphere throughout this period. Impacts of the downscaling component of iLOVECLIM, which provides higher resolution data and accounts for the influences of the topography, on BESSI performance are also discussed. The results show that BESSI performs well compared to MAR for the present-day climate, even with a less complex model set-up. Through the LIG, with the ability to model the snow compaction, the change of snow density and snow depth, BESSI simulates the snow cover evolution in the studied area better than the simple snow model (bucket model) included in iLOVECLIM. The findings suggest that BESSI can provide a more physical surface mass balance scheme to ice sheet models such as GRISLI of iLOVECLIM to improve simulations of the ice sheet - climate interactions.

According to geological records, the sea level during the Last Interglacial (∼ 129–116 ka) peaked 6 to 9 m higher than during the pre-industrial with a major contribution from the Antarctic ice sheet (Dutton et al. 2015). According to Clark et al. 2020, a longer period of reduced Atlantic Meridional Overturning Circulation (AMOC) during the penultimate deglaciation compared to the last deglaciation could have led to greater subsurface warming and subsequent larger Antarctic Ice Sheet retreat.Here we study the response of the Antarctic ice sheet to climate forcing with a forced AMOC shutdown at different timing and duration during the penultimate deglaciation (∼ 138–128 ka). The simulations are done with the Earth System Model of Intermediate Complexity iLOVECLIM (Roche et al. 2014) and the ice sheet model GRISLI (Quiquet et al. 2018), using the recently implemented sub-shelf melt module PICO (Reese et al. 2018). In the present simulations the GRISLI is forced with the iLOVECLIM simulations and is a step towards a fully coupled climate - ice sheet set up to take into account the climate - ice sheet interactions in a physical way.We hypothesize that both the duration and timing of reduced AMOC can significantly affect the sensitivity of the Antarctic Ice Sheet. A longer period of AMOC reduction will lead to a larger subsurface warming in the Southern Ocean and subsequently a larger ice sheet retreat. On the other hand, an AMOC reduction earlier (later) in the deglaciation implies that the ice sheet that is affected by this subsurface warming is still fairly large (already small). We will discuss both the individual as well as combined effect of duration and timing on the ice sheet evolution.

During the last deglaciation, the climate evolves from a cold state at the Last Glacial Maximum (LGM) at 21 ka (thousand years ago) with large ice sheets to the warm Holocene at ∼9 ka with reduced ice sheets. The deglacial ice sheet melt can impact the climate through multiple ways: changes of topography and albedo, bathymetry and coastlines, and freshwater fluxes (FWFs). In the PMIP4 (Paleoclimate Modelling Intercomparison Project – Phase 4) protocol for deglacial simulations, these changes can be accounted for or not depending on the modelling group choices. In addition, two ice sheet reconstructions are available (ICE-6G_C and GLAC-1D). In this study, we evaluate all these effects related to ice sheet changes on the climate using the iLOVECLIM model of intermediate complexity. We show that the two reconstructions yield the same warming to a first order but with a different amplitude (global mean temperature of 3.9 ∘C with ICE-6G_C and 3.8 ∘C with GLAC-1D) and evolution. We obtain a stalling of temperature rise during the Antarctic Cold Reversal (ACR, from ∼14 to ∼12 ka) similar to proxy data only with the GLAC-1D ice sheet reconstruction. Accounting for changes in bathymetry in the simulations results in a cooling due to a larger sea ice extent and higher surface albedo. Finally, freshwater fluxes result in Atlantic meridional overturning circulation (AMOC) drawdown, but the timing in the simulations disagrees with proxy data of ocean circulation changes. This questions the causal link between reconstructed freshwater fluxes from ice sheet melt and recorded AMOC weakening.

The spatio-temporal structure of natural climate variability has to be taken into account when unraveling observed climatic changes and simulate future climate change. However, based on the comparison of temperature reconstructions and climate model simulations covering the past two millenia, it has been argued that climate models are biased. They would simulate too little temporal temperature variability and too high correlations between temperature time series from different continents. One of the proposed causes is the lack of internal climate variability in climate models on centennial time scales, for instance variability related to the Atlantic Meridional Overturning Circulation (AMOC). We present a perturbed-parameter ensemble with the iLOVECLIM earth system model containing various levels of AMOC-related internal climate variability to investigate the effect on the spatio-temporal temperature variability structure. The model ensemble shows that indeed enhanced AMOC variability leads to more continental-scale temperature variability, but it also increases the spatio-temporal temperature correlations between different continents. However, combining the iLOVECLIM results with CMIP5 model results and various PAGES-2K temperature field reconstructions, we find that neither model results or reconstructions are robust. We show overall agreement for the magnitude of continental temperature variability in models and reconstructions, but both the simulated and the reconstructed ranges are large. This is even more true when considering higher order metrices like inter-continental temperature correlations or temperature variability land-sea contrasts. For such metrices, uncertainties in both model results and temperature reconstructions are so large that they hamper our ability to constrain simulated spatio-temporal structure of centennial temperature variability. As a result, we cannot determine the importance of AMOC variability for the climatic evolution over the past two millenia.

During the Last Deglaciation, the climate evolves from a cold state at the Last Glacial Maximum at 21 ka with large ice sheets, to the warm Holocene at ~9 ka with reduced ice sheets. The deglacial ice sheet melt can impact the climate through multiple ways: changes of topography and albedo, bathymetry and coastlines, as well as fresh water fluxes. In the PMIP4 protocol for deglacial simulations, these changes can be accounted or not depending on the modelling group choices. In addition, two ice sheet reconstructions are available (ICE-6G_C and GLAC-1D). In this study, we evaluate all these effects related to ice sheet changes on the climate using the iLOVECLIM model of intermediate complexity. We show that the two reconstructions yield the same warming to a first order, but with a different amplitude (3.9 °C with ICE-6G_C and 3.8 °C with GLAC-1D) and evolution. We obtain a stalling of temperature rise during the Antarctic Cold Reversal (from ~14 ka to ~12 ka) similar to proxy data only with the GLAC-1D ice sheet reconstruction. Accounting for changes in bathymetry in the simulations results in a cooling due to a larger sea ice extent and higher surface albedo. Finally, fresh water fluxes result in AMOC drawdown, but the timing in the simulations disagrees with proxy data of ocean circulation changes. This questions the links between reconstructed fresh water fluxes from ice sheet melt and recorded AMOC weakening and their representation in models.

Changes in water mass distribution are considered to be a significant contributor to the atmospheric CO2 concentration drop to around 186 ppm recorded during the Last Glacial Maximum (LGM). Yet simulating a glacial Atlantic Meridional Overturning Circulation (AMOC) in agreement with paleotracer data remains a challenge, with most models from previous Paleoclimate Modelling Intercomparison Project (PMIP) phases showing a tendency to simulate a strong and deep North Atlantic Deep Water (NADW) instead of the shoaling inferred from proxy records of water mass distribution. Conversely, the simulated Antarctic Bottom Water (AABW) is often reduced compared to its pre-industrial volume, and the Atlantic Ocean stratification is underestimated with respect to paleoproxy data. Inadequate representation of surface conditions, driving deep convection around Antarctica, may explain inaccurately simulated bottom water properties in the Southern Ocean. We investigate here the impact of a range of surface conditions in the Southern Ocean in the iLOVECLIM model using nine simulations obtained with different LGM boundary conditions associated with the ice sheet reconstruction (e.g., changes of elevation, bathymetry, and land–sea mask) and/or modeling choices related to sea-ice export, formation of salty brines, and freshwater input. Based on model–data comparison of sea-surface temperatures and sea ice, we find that only simulations with a cold Southern Ocean and a quite extensive sea-ice cover show an improved agreement with proxy records of sea ice, despite systematic model biases in the seasonal and regional patterns. We then show that the only simulation which does not display a much deeper NADW is obtained by parameterizing the sinking of brines along Antarctica, a modeling choice reducing the open-ocean convection in the Southern Ocean. These results highlight the importance of the representation of convection processes, which have a large impact on the water mass properties, while the choice of boundary conditions appears secondary for the model resolution and variables considered in this study.

Affinity selection-mass spectrometry (AS-MS) is a high-throughput screening (HTS) technique for drug discovery that enables rapid screening of large collections of compounds to identify ligands for a specific biomolecular target. AS-MS is a binding assay that is insensitive to the functional effects a ligand might have, which is important because it lets us identify novel ligands irrespective of their binding site. This approach is gaining popularity, notably due to its role in the emergence of useful agents for targeted protein degradation. This Perspective highlights the use of AS-MS techniques to explore broad chemical space and identify small-molecule ligands for biological targets that have proven challenging to address with other screening paradigms. We present chemical structures of reported AS-MS hits to illustrate the potential of this screening approach to deliver high-quality hits for further optimization. AS-MS has, thus, evolved from being an infrequent alternative to traditional HTS or DNA-encoded library strategies to now firmly establishing itself as a HTS approach for drug discovery. Affinity selection-mass spectrometry enables rapid screening of compound mixtures against a specific biomolecular target. This assay lets us identify ligands irrespective of their binding site and is amenable to the discovery of novel drugs.

Volcanism is one of the main natural climate forcings at annual to multi-decadal timescales. Therefore, this forcing is important to study Holocene climate variability. Our main objective is to examine the impact of volcanism on the climate in the 6th century AD within the iLOVECLIM model and analyze the results with archeological data. We hypothesize that large volcanic eruptions around 536 AD and 540 AD contributed to cooling of the climate, resulted to the adversities of Late ancient societies throughout Europe, and caused a major environmental event in Iron Age Scandinavia.In this work, we have made three groups of simulations with the iLOVECLIM model, representing the climate of 536 AD and 540 AD. Two scenarios include high and low volcanic activity forcing, while in the third scenario, volcanic forcing is absent. We applied a model version with dynamical downscaling to reach a spatial resolution that allows for a meaningful comparison with archeological data. We compared our model results with C14-dated archaeological records from Scandinavia to analyze the spatial intensity of land use during these time periods. An evaluation of the difference between these simulations will highlight the impact of the volcanic activity on early to mid-6th century Scandinavia.This study demonstrates the link between climate and volcanism during these periods and shows the advantage of combining the archaeological records with climate data to understand human-environment interactions. Future research that considers both climatological and archaeological data can benefit our understandings of the impact extreme natural events had on the environment, the climate and people.

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.

The desertification and vegetation feedbacks of the “green Sahara” during the last interglacial (LIG) and the Holocene have been investigated by many studies. Yet the abruptness of climate and vegetation changes and their interactions are still under discussion. In this study, we apply an Earth system model of intermediate complexity (iLOVECLIM) in combination with two dynamical vegetation models (VECODE and LPJ-GUESS) to simulate climate–vegetation changes during the Holocene and the LIG to compare the patterns of North African vegetation evolutions and mechanisms of their feedbacks during these two interglacials. Our results confirmed the existence of the green Sahara during the early LIG, which is as an analogue to the green Sahara during the Holocene. During both interglacials, an overall consistent transition from vegetated Sahara to desert is shown in our results, but the amplitudes of these transitions vary. These simulated Sahara vegetation transitions are nearly linearly related to the summer insolation declines at 20∘ N, resulting in faster declines of vegetation cover during the LIG than in the Holocene. The decline of vegetation cover peaks at 25% kyr−1 at around 122 ka, while during the Holocene the steepest vegetation cover decline is 10 % kyr−1 at around 6 ka. Our results suggest net positive vegetation feedbacks to climate during the two interglacials. During the early LIG and Holocene, vegetation strengthens precipitation by a factor of 2 to 3 through the vegetation–albedo feedback when the vegetation cover is greater than 60 %. Vegetation cover decreases with declines of the incoming moisture transport by the atmosphere due to the reduced summer insolation at 20∘ N, weakening the summer monsoon during both interglacials. This desertification is accelerated when the positive vegetation–albedo feedback cannot offset the reduction of precipitation due to a weaker summer monsoon. The impacts of this positive vegetation feedback on precipitation decrease with decreased vegetation cover, during which the impacts of negative vegetation–evaporation feedbacks increase, accelerating the loss of soil moisture and vegetation cover. Overall, the net positive vegetation feedback is strong during the early phases of both interglacials, but the vegetation transition is more abrupt during the LIG than during the Holocene due to the more rapid changes in summer insolation during the LIG. The main difference between the two interglacials is the rate of precipitation change, which is relatively gradual during the Holocene, leading to a more gradual vegetation transition in comparison to the LIG.

A complete understanding of past El Niño–Southern Oscillation (ENSO) fluctuations is important for the future predictions of regional climate using climate models. One approach to reconstructing past ENSO dynamics uses planktonic foraminifera as recorders of past climate to assess past spatio-temporal changes in upper ocean conditions. In this paper, we utilise a model of planktonic foraminifera populations, Foraminifera as Modelled Entities (FAME), to forward model the potential monthly average δ18Oc and temperature signal proxy values for Globigerinoides ruber, Globigerinoides sacculifer, and Neogloboquadrina dutertrei from input variables covering the period of the instrumental record. We test whether the modelled foraminifera population δ18Oc and Tc associated with El Niño events statistically differ from the values associated with other climate states. Provided the assumptions of the model are correct, our results indicate that the values of El Niño events can be differentiated from other climate states using these species. Our model computes the proxy values of foraminifera in the water, suggesting that, in theory, water locations for a large portion of the tropical Pacific should be suitable for differentiating El Niño events from other climate states. However, in practice it may not be possible to differentiate climate states in the sediment record. Specifically, comparison of our model results with the sedimentological features of the Pacific Ocean shows that a large portion of the hydrographically/ecologically suitable water regions coincide with low sediment accumulation rate at the sea floor and/or of sea floor that lie below threshold water depths for calcite preservation.

The previous chapters focused on climate variations stemming from factors external to the climate system: tectonics, orogeny, variations in insolation. Yet the study of glacial records and marine sediments over the past three decades has revealed major changes within the climate system over much shorter time scales than previously envisaged. These abrupt reorganisations of the climate system, which cannot be explained by forcings external to the system, are true climate ‘surprises’. In this chapter, we describe the expression of these events on a global scale and give examples of modelling studies which have helped understanding these events and their impacts.

Model intercomparison studies of coupled carbon-climate simulations have the potential to improve our understanding of the processes explaining the (Formula presented.) drawdown at the Last Glacial Maximum (LGM) and to identify related model biases. Models participating in the Paleoclimate Modeling Intercomparison Project (PMIP) now frequently include the carbon cycle. The ongoing PMIP-carbon project provides the first opportunity to conduct multimodel comparisons of simulated carbon content for the LGM time window. However, such a study remains challenging due to differing implementation of ocean boundary conditions (e.g., bathymetry and coastlines reflecting the low sea level) and to various associated adjustments of biogeochemical variables (i.e., alkalinity, nutrients, dissolved inorganic carbon). After assessing the ocean volume of PMIP models at the pre-industrial and LGM, we investigate the impact of these modeling choices on the simulated carbon at the global scale, using both PMIP-carbon model outputs and sensitivity tests with the iLOVECLIM model. We show that the carbon distribution in reservoirs is significantly affected by the choice of ocean boundary conditions in iLOVECLIM. In particular, our simulations demonstrate a (Formula presented.) GtC effect of an alkalinity adjustment on carbon sequestration in the ocean. Finally, we observe that PMIP-carbon models with a freely evolving (Formula presented.) and no additional glacial mechanisms do not simulate the (Formula presented.) drawdown at the LGM (with concentrations as high as 313, 331, and 315 ppm), especially if they use a low ocean volume. Our findings suggest that great care should be taken on accounting for large bathymetry changes in models including the carbon cycle. © 2021. American Geophysical Union. All Rights Reserved.

The Last Glacial Maximum (LGM, ∼ 21 000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models has been used to generate LGM simulations as part of the Paleoclimate Modelling Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here, we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4, most of which are PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3, most of which are PMIP3-CMIP5). We show that the global averages of the PMIP4 simulations span a larger range in terms of mean annual surface air temperature and mean annual precipitation compared to the PMIP3-CMIP5 simulations, with some PMIP4 simulations reaching a globally colder and drier state. However, the multi-model global cooling average is similar for the PMIP4 and PMIP3 ensembles, while the multi-model PMIP4 mean annual precipitation average is drier than the PMIP3 one. There are important differences in both atmospheric and oceanic circulations between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large. Therefore, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land–sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the paleoclimate reconstructions. Nevertheless, regional climate changes are less well simulated: the models underestimate extratropical cooling, particularly in winter, and precipitation changes. These results point to the utility of using paleoclimate simulations to understand the mechanisms of climate change and evaluate model performance.

International audience; During the last deglaciation (21–7 kaBP), the gradual retreat of Northern Hemisphere ice sheet margins produced large proglacial lakes. While the climatic impacts of these lakes have been widely acknowledged, their role on ice sheet grounding line dynamics has received very little attention so far. Here, we show that proglacial lakes had dramatic implications for the North American ice sheet dynamics through a self‐sustained mechanical instability which has similarities with the known marine ice sheet instability consequently providing fast retreat of large portions of the ice sheet over the continent. This instability mechanism is likely important in contributing to deglaciation of terrestrial glaciers and ice sheets with proglacial lakes at their margins as it can substantially accelerate the mass loss. Echoing our knowledge of Antarctic ice sheet dynamics, proglacial lakes are another manifestation of the importance of grounding line dynamics for ice sheet evolution.

The last deglaciation offers an unique opportunity to understand the climate – ice sheet interactions in a global warming context. In this paper, to tackle this question, we use an Earth system model of intermediate complexity coupled to an ice sheet model covering the Northern Hemisphere to simulate the last deglaciation and the Holocene (26–0 ka BP). We use a synchronous coupling every year between the ice sheet and the rest of the climate system and we ensure a closed water cycle considering the release of freshwater flux to the ocean due to ice sheet melting. Our reference experiment displays a gradual warming in response to the forcings, with no abrupt changes. In this case, while the amplitude of the freshwater flux to the ocean induced by ice sheet retreat is realistic, it is sufficient to shut down the Atlantic meridional overturning from which the model does not recover within the time period simulated. However, with reduced freshwater flux we are nonetheless able to obtain different oceanic circulation evolutions, including some abrupt transitions between shut-down and active circulation states in the course of the deglaciation. The fast oceanic circulation recoveries lead to abrupt warming phases in Greenland. Our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions, even though the abrupt sea level rise at 14.6 kaBP is underestimated, possibly because the climate model underestimates the millenial- scale temperature variability. In the course of the deglaciation, large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets. The first instability occurs in the Barents-Kara seas for the Eurasian ice sheet at 14.5 kaBP. A second grounding line instability occurs circa 12 kaBP in the proglacial lake that formed at the southern margin of the North American ice sheet. With additional asynchronously coupled experiments, we assess the sensitivity of our results to different ice sheet model choices related to surface and sub-shelf mass balance, ice deformation and grounding line representation. While the ice sheet evolutions differ within this ensemble, the global climate trajectory is only weakly affected by these choices. In our experiments, only the abrupt shifts in the oceanic circulation due to freshwater fluxes are able to produce some millenial-scale variability since no self-generating abrupt transitions are simulated without these fluxes.

This study compares the dynamic vegetation response in two Dynamic Global Vegetation Models (DGVMs) with contrasting processes complexity to changes in climate and atmospheric CO2. We consider observed pre-industrial climates and four different simulated climate change states relative to preindustrial conditions: the mid-Holocene (6 ka), the pre-industrial state with halved CO2 levels (140 ppm), doubled CO2 (560 ppm), and quadrupled CO2 (1120 ppm). The two DVGMs are LPJ-GUESS and VECODE. The input climate is derived from an earth system model of intermediate complexity (iLOVECLIM). We evaluate the sensitivities of these two DGVMs to changing climate and CO2 levels and assess the impact of their respective complexity on these sensitivities. Our results show that both DGVMs yield results consistent with the broad features of pre-industrial vegetation dynamics and changes in vegetation from mid-Holocene to pre-industrial. They also agree with the patterns of vegetation responses to the more extreme varying CO2 scenarios, yet with stronger magnitudes in LPJ-GUESS than in VECODE; in particular, large uncertainties are associated with the response of tropical vegetation to varying CO2 levels. LPJ-GUESS simulates stronger positive responses of global net primary production (NPP) to elevated CO2 levels than VECODE, particularly in tropical regions. The increase in global NPP differs by 8% between the two DGVMs under 2*CO2 scenarios. Also, LPJ-GUESS simulates tropical vegetation sensitivities, defined here as the changes in tree-cover per degree of temperature anomaly, varying from 0.5 (°C−1), 0.25 (°C−1) to 0.15 (°C−1) under ½*CO2, 2*CO2, and 4*CO2 scenarios. In VECODE these values are around 0.05 (°C−1) for all scenarios. The higher sensitivity of LPJ-GUESS to CO2 concentration levels is likely related to the inclusion of more detailed ecophysiological processes. The two DGVMs' different complexity of eco-physiological processes also impacts on vegetation requirements for rainfall due to the physiological effects that more efficient water use of vegetation is facilitated under elevated atmospheric CO2 concentration. The sensitivity of global Leaf Area Index (LAI) in the two DGVMs decreases with the increasing atmospheric CO2 from pre-industrial level to 4*CO2 scenario. The uncertainties of vegetation simulations are mainly contributed by the tropical vegetation response to climate and CO2 concentration due to the inclusion of ecosystem processes in both DGVMs and the scheme of vegetation classification. Based on our results, we recommend to use a standard set of vegetation types and to set up systematic simulations detecting the range of vegetation sensitivity to varying CO2 and climate forcing when inter-comparing different DGVMs.

Version 1.1 of the editorial of Geoscientific Model Development (GMD), published in 2015 (GMD Executive Editors, 2015), introduced clarifications to the policy on publication of source code and input data for papers published in the journal. Three years of working with this policy has revealed that it is necessary to be more precise in the requirements of the policy and in the narrowness of its exceptions. Furthermore, the previous policy was not specific in the requirements for suitable archival locations. Best practice in code and data archiving continues to develop and is far from universal among scientists. This has resulted in many manuscripts requiring improvement in code and data availability practice during the peer-review process. New researchers continually start their professional lives, and it remains the case that not all authors fully appreciate why code and data publication is necessary. This editorial provides an opportunity to explain this in the context of GMD. The changes in the code and data policy are summarised as follows: The requirement for authors to publish source code, unless this is impossible for reasons beyond their control, is clarified. The minimum requirements are strengthened such that all model code must be made accessible during the review process to the editor and to potentially anonymous reviewers. Source code that can be made public must be made public, and embargoes are not permitted. Identical requirements exist for input data and model evaluation data sets in the model experiment descriptions. The scope of the code and data required to be published is described. In accordance with Copernicus' own data policy, we now specifically strongly encourage all code and data used in any analyses be made available. This will have particular relevance for some model evaluation papers where editors may now strongly request this material be made available. The requirements of suitable archival locations are specified, along with the recommendation that Zenodo is often a good choice. In addition, since the last editorial, an “Author contributions” section must now be included in all manuscripts.

This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. The VAMPERS (Vrije Universiteit Amsterdam Permafrost Snow Model) has been coupled within iLOVECLIM, an earth system model. This advancement allows the thermal coupling between permafrost and climate to be examined from a millennial timescale using equilibrium experiments during the Last Glacial Maximum (21 ka) and transient experiments for the subsequent deglaciation period (21–11 ka). It appears that the role of permafrost during both stable and transitional (glacial–interglacial) climate periods is seasonal, resulting in cooler summers and warmer winters by approximately ±2 °C maximum. This conclusion reinforces the importance of including the active layer within climate models. In addition, the coupling of VAMPERS also yields a simulation of transient permafrost conditions, not only for estimating areal changes in extent but also total permafrost gain/loss.

The last deglaciation is a time of large climate transition from a cold Last Glacial Maximum at 21,000 years BP with extensive ice sheets, to the warmer Holocene 9,000 years BP onwards with reduced ice sheets. Despite more and more proxy data documenting this transition, the evolution of climate is not fully understood and difficult to simulate. The PMIP4 protocol (Ivanovic et al., 2016) has indicated which boundary conditions to use in model simulations during this transition. The common boundary conditions should enable consistent multi model and model-data comparisons. While the greenhouse gas concentration evolution and orbital forcing are well known and easy to prescribe, the evolution of ice sheets is less well constrained and several choices can be made by modelling groups. First, two ice sheet reconstructions are available: ICE-6G (Peltier et al., 2015) and GLAC-1D (Tarasov et al., 2014). On top of topographic changes, it is left to modelling groups to decide whether to account for the associated bathymetry and land-sea mask changes, which is technically more demanding. These choices could potentially lead to differences in the climate evolution, making model comparisons more complicated.We use the iLOVECLIM model of intermediate complexity (Goosse et al., 2010) to evaluate the impact of different ice sheet reconstructions and the effect of bathymetry changes on the global climate evolution during the Last deglaciation. We test the two ice sheet reconstructions (ICE-6G and GLAC-1D), and have implemented changes of bathymetry and land-sea mask. In addition, we also evaluate the impact of accounting for the Antarctic ice sheet evolution compared to the Northern ice sheets only.We show that despite showing the same long-term changes, the two reconstructions lead to different evolutions. The bathymetry plays a role, although only few changes take place before ~14ka. Finally, the impact of the Antarctic ice sheet is important during the deglaciation and should not be neglected.ReferencesGoosse, H., et al., Description of the Earth system model of intermediate complexity LOVECLIM version 1.2, Geosci. Model Dev., 3, 603–633, https://doi.org/10.5194/gmd-3-603-2010, 2010Ivanovic, R. F., et al., Transient climate simulations of the deglaciation 21–9 thousand years before present (version 1) – PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev., 9, 2563–2587, https://doi.org/10.5194/gmd-9-2563-2016, 2016Peltier, W. R., Argus, D. F., and Drummond, R., Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model, J. Geophys. Res.-Sol. Ea., 120, 450–487, doi:10.1002/2014JB011176, 2015Tarasov,L., et al., The global GLAC-1c deglaciation chronology, melwater pulse 1-a, and a question of missing ice, IGS Symposium on Contribution of Glaciers and Ice Sheets to Sea-Level Change, 2014

Multiple evidences from the analysis of satellite, in-situ and proxy data show that the climate is already changing toward a warmer Earth System due to our emissions of CO2 into the atmosphere. However, the magnitude and the extent of changes remain difficult to predict. A change in the ocean thermohaline circulation and its consequences for climate, such as drought, regional sea-level and ocean carbon uptake remain under debate as this circulation has been long thought to be stable during warm Earth periods – Interglacials. However, recent high-resolution reconstructions of carbon isotopes (δ13C) from the deep North Atlantic challenge this idea of stability and point toward abrupt modifications in the ocean interior biogeochemistry and/or ocean thermohaline circulation during the Last Interglacial (LIG, 125ka – 115ka). Our model simulation of the LIG reproduces the observed magnitude and timescale of the reconstructed variations of δ13C, highlighting crucial dynamical changes in two regions of the North Atlantic deep-water formation (south of Greenland and south of Svalbard). These regions are found to drive the variations in the strength of the Atlantic Overturning Circulation (AMOC) when the Arctic sea-ice extent is perturbed. Our study suggests that the AMOC may have experienced great instability phase during some parts of the LIG. The water mass geometry reorganization from the warm onset at 125ka to the glacial inception at 115ka could also have greatly impacted the distribution of carbon in the interior Ocean. Changes in sea-ice cover either south of Svalbard or in the Southern Ocean seem to play a determining role. However, in our global warming context, our study suggests that the mechanisms responsible for the LIG AMOC instability of the LIG may not occur by the end of the century if the Arctic sea-ice retreats from the high latitudes of the North Atlantic as projected by climate models.

Measurements of δ18O on planktonic foraminifera represent an important geological archive. In the study of climate change on orbital time-scales, δ18O is used either as a proxy for temperature change, to construct age models through pattern matching, to deduce the drivers of climate change by looking at frequency power spectra or all of the above. The validity of these approaches hinges on a two-step assumption, namely that the signal of the orbital cycles is transferred unaltered from 1) solar radiation that reaches the top of the atmosphere, insolation, to the sea surface, and 2) from the sea surface translated into the δ18O composition of the foraminiferal shell. The complexity of these two steps make it difficult to validate the assumptions behind these major paleoclimatological approaches. In this research we aim to disentangle the problem, here focussing only on the latter part: how do species-specific living habitats of foraminifera in the water column and throughout the year shape the δ18O response were the Earth’s surfce climate to perfectly reflect the orbital forcing(s). To this end we combine an isotope-enabled climate model (iLOVECLIM) with a foraminifera growth model and investigate the response of δ18O from three species of foraminifera (Globigerinoides ruber, Neogloboquadrina pachyderma, and Globigerina bulloides) to obliquity and precessional cycles.Our results show that the planktonic foraminifera δ18O response to astronomical forcings is dominated by annual mean changes in sea-surface temperature, thus corroborating a key assumption underlying many geological climate reconstructions. However, in various places changes in the depth habitat, temperature-dependent growth rates, seasonality and δ18O of the sea water dominate the foraminifera δ18O signal. Because of these modulations, planktonic foraminifera δ18O time series can have very different characteristics compared to the orbital forcings, including limited spatial coherence as well as limited inter-species coherence at a single location.

Understanding the processes causing variations in the carbon cycle is critical to accurately simulate the future carbon cycle and climate. Paleoclimate models can provide insights about these processes since they are used under different conditions than present-day’s and evaluated against paleoproxy data. In particular, the Last Glacial Maximum (LGM) has been a focus of the Paleoclimate Modelling Intercomparison Project (PMIP) as it is well-documented thanks to numerous paleoclimate archives. Around 21,000 years ago, the LGM was a colder period with extensive ice sheets in the Northern Hemisphere and a resulting lower sea-level. Although this period has been studied for years, the causes of the lower atmospheric CO2 concentration at the time (around 186 ppm, against 280 ppm at the pre-industrial) remain unclear, and models struggle to simulate this low CO2 value. The ocean is thought to have played a significant role due to different processes (through changes of the biological pump efficiency, ocean circulation, sea-ice, and CO2 solubility due to colder temperatures), but no consensus has been reached yet as to their contribution (Khatiwala et al. [2019], Yu et al. [2016], Marzocchi and Jansen [2019]).Despite the carbon cycle being simulated by more and more climate models, it has not been systematically analysed within the framework of PMIP multimodel comparisons. In this context, the ongoing PMIP-carbon project aims at comparing climate-carbon interactions in LGM simulations, and includes results from both intermediate complexity models and general circulation models. The PMIP protocol proposes standardized forcing parameters and boundary conditions (Kageyama et al. [2017]) and specifies a few recommendations for ocean biogeochemistry models (adjustment of salinity, dissolved inorganic carbon, alkalinity, and nutrients to account for the change in ocean volume). Indeed, the bathymetric changes associated with a sea-level drop of 133 m entail a change of the reservoir size and potential technical issues concerning the conservation of carbon.In this study, we use outputs from PMIP-carbon models and other models available on the ESGF (MIROC4m-COCO, MIROC-ES2L, CESM, IPSL-CM5A2, UVic, LOVECLIM, iLOVECLIM, CLIMBER_2P ; GISS-E2-R, MRI-CGCM3, MPI-ESM-P, CNRM-CM5, MIROC-ESM) to compute total ocean volumes and compare them to high resolution topographic data (etopo1 for the PI, GLAC-1D and ICE-6G-C for the LGM). We show that the deglacial volume change is rarely accurate. We then use the iLOVECLIM model with a new bathymetry implementation method (Lhardy et al. [in review, 2020]) to demonstrate the effect of an improved ocean volume on the simulated oceanic carbon content, resulting in an increase of the already overestimated atmospheric CO2 concentration. We also quantify the effect of the mentioned adjustments of salinity, alkalinity, and carbon. The results reinforce the idea that a realistic ocean volume is needed, as well as consistency between models in dealing with large changes in bathymetry.

Osteoporosis is currently treated with drugs targeting the differentiation or viability osteoclasts, the cells responsible for physiological and pathological bone resorption. Nevertheless, osteoporosis drugs that target only osteoclast activity are expected to preserve bone formation by osteoblasts in contrast to current treatments. We report here the design, synthesis, and biological characterization of a series of novel N-arylsufonamides featuring a diazaspiro[4,4]nonane nucleus to target the guanine nucleotide exchange activity of DOCK5, which is essential for bone resorption by osteoclasts. These compounds can inhibit both mouse and human osteoclast activity. In particular, 4-chlorobenzyl-4-hydroxy-2-phenyl-1-thia-2,7-diazaspiro[4,4]nonane 1,1-dioxide (compound E197) prevented pathological bone loss in mice. Most interestingly, treatment with E197 did not affect osteoclast and osteoblast numbers and hence did not impair bone formation. E197 could represent a lead molecule to develop new antiosteoporotic drugs targeting the mechanism of osteoclast adhesion onto the bone.

Ice core data have shown that atmospheric CO2 concentrations during interglacials were lower before the Mid-Brunhes Event (MBE, ~430 ka), than after the MBE by around 30 ppm. To explain such a difference, it has been hypothesized that increased bottom water formation around Antarctica or reduced Atlantic Meridional Overturning Circulation (AMOC) could have led to greater oceanic carbon storage before the MBE, resulting in less carbon in the atmosphere. However, only few data on possible changes in interglacial ocean circulation across the MBE have been compiled, hampering model-data comparison. Here we present a new global compilation of benthic foraminifera carbon isotopic (δ13C) records from 31 marine sediment cores covering the last 800 ka, with the aim of evaluating possible changes of interglacial ocean circulation across the MBE. We show that a small systematic difference between pre- and post-MBE interglacial δ13C is observed. In pre-MBE interglacials, northern source waters tend to have slightly higher δ13C values and penetrate deeper, which could be linked to an increased northern sourced water formation or a decreased southern sourced water formation. Numerical model simulations tend to support the role of abyssal water formation around Antarctica: Decreased convection there associated with increased sinking of dense water along the continental slopes results in increased δ13C values in the Atlantic in agreement with pre-MBE interglacial data. It also yields reduced atmospheric CO2 as in pre-MBE records, despite a smaller simulated amplitude change compared to data, highlighting the need for other processes to explain the MBE transition.

Disrupting deep circulation Atlantic Meridional Overturning Circulation (AMOC) and the related process of North Atlantic Deep Water (NADW) have been thought to be stable during warm, interglacial periods. Galaasen et al. report that episodes of reduced NADW over the past 500,000 years actually have been relatively common and occasionally long-lasting features of interglacials and that they can occur independently of the catastrophic freshwater outburst floods normally thought to be their cause (see the Perspective by Stocker). This discovery implies that large NADW disruptions might be more likely than we have assumed in the warmer climate of the future. Science , this issue p. 1485 ; see also p. 1425

At the interface of the atmosphere and the oceans, sea ice is a thin and reactive layer which depends on the surface temperatures of the two and with significant impact on both. In this vein, sea ice affects the regional energy budget due to its high albedo, modulates the transfer of gas and energy at the ocean-atmosphere by its simple presence and modifies the water column vertical structure through brine rejection during freezing and freshwater input during melting. As the densification of surface waters can lead to deep water formation, sea ice has an impact on deep ocean circulation (Ferrari et al. [2014], Marzocchi et al. [2019]). Around 21,000 years ago, the glacial period called the LGM was marked by extensive ice sheets in the Northern Hemisphere, a consequent lower sea-level, and lower atmospheric CO2 concentrations than today’s. However, the processes driving these lower atmospheric CO2 concentrations are still not fully understood. Paleotracer data (Curry and Oppo [2005]) suggest that the Antarctic Bottom Water was a poorly ventilated and voluminous water mass, therefore efficiently trapping carbon. Proxies also allow for the reconstruction of LGM sea ice (de Vernal et al. [2013]), and their studies have indicated both an extended Southern Ocean sea ice and an enhanced seasonality (Gersonde et al. [2005], Allen et al. [2011], Benz et al. [2016]). Models are very helpful to investigate the potentially complex response of the climate system to any perturbation. The Paleoclimate Modelling Intercomparison Project (now in phase 4) has proposed standardized LGM boundary conditions which notably allows for an evaluation of the model performance under cold conditions. During past PMIP phases, the simulation of the LGM deep ocean circulation has proven to be challenging (Otto-Bliesner et al. [2007], Muglia and Schmittner [2015]), which could be linked – at least partially – to the limitations in modelling past sea-ice changes (Goosse et al. [2013], Roche et al. [2012]). In this study, the iLOVECLIM model – of intermediate complexity – (Goosse et al. [2010]) is used under the PMIP4 experimental design with both the ICE-6G-C and GLAC-1D topographies. The simulated sea ice is compared with a recent compilation of proxy data (Crosta, pers. com.). We look for potential sources of the observed model-data discrepancies using different model configurations. We examine in particular the simulated SSTs compared to MARGO [2009] data and show a regional and seasonal model-data disagreement that is quite consistent with the sea-ice model-data comparison.

Glacial-interglacial changes of the Earth's climate are largely controlled by internal mechanisms that drive changes in greenhouse gases and ice sheets. In this study, we present model experiments of the penultimate deglaciation into the the last interglacial period, obtained with the Earth system model of intermediate complexity iLOVECLIM (v. 1.1.4). We show experiments with an imposed ice-sheet scenario together with initial results with both North and South interactive ice sheets using the GRISLI (v. 2.0) 3-D ice-sheet model. To this aim, we use a recently developed dynamical downscaling procedure to compute temperature and precipitation fields from the relative low resolution atmospheric model grid (T21, ~5.6º) to the GRISLI spherical grids of both the Northern Hemisphere and Antarctica (both 40 x 40 km). We investigate the separate impact of variations of greenhouse gases (GHG), orbital parameters and ice sheets on glacial-interglacial climate change over the past 240 kyr. Using prescribed greenhouse gases or ice sheets induce comparable changes in global mean temperature. Greenhouse gases, predominantly CO2, mainly have a global impact through radiative forcing on atmospheric temperatures. On the other hand, ice sheets have a more regional impact over the Northern Hemispheric (NH) continents and Antarctica during glacial times. Henceforth, polar amplification is more pronounced during glacial periods following large ice-sheet induced changes. Overall these results are comparable to other studies using a similar experimental design. In order to initiate the coupling between the ice sheets and climate model, we perform a large ensemble of experiments to calibrate ice-sheet model parameters for the present day. We will present how the optimal settings for the two ice-sheet regions are selected, based on a comparison with the present-day ice sheets on Antarctica and Greenland. For the coupling, iLOVECLIM generates downscaled SMB, surface temperatures, ocean temperature and salinity, and GRISLI provides surface elevation and ice extent, the coupling interval is 5 years. These experiments are started during the penultimate glacial maximum. We initialize the coupled iLOVECLIM - GRISLI experiments from a climatic forcing experiment using prescribed greenhouse gases and ice sheets, and generate a spin-up simulation of GRISLI using the optimal settings for three different time points at 136, 135 and 134 kyr ago. Initial experiments show a clear linkage between changes in ice sheets, sea ice and ocean circulation. Following the forced rise in atmospheric GHGs, the magnitude of retreat varries between ice sheets, related to location and insolation change (which increases for the NH but decreased for Antarctica). Moreover, sea ice both decrease following GHGs increase, and vary more in phase with global mean temperature.

The Last Glacial Maximum (LGM, ~ 21,000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models have been used to generate LGM simulations as part of the Palaeoclimate Modelling Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3-CMIP5). We show that the PMIP4-CMIP6 are globally less cold and less dry than the PMIP3-CMIP5 simulations, most probably because of the use of a more realistic specification of the northern hemisphere ice sheets in the latest simulations although changes in model configuration may also contribute to this. There are important differences in both atmospheric and ocean circulation between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large so, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land-sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the palaeoclimate reconstructions. Nevertheless, regional climate changes are less well simulated: the models underestimate extratropical cooling, particularly in winter, and precipitation changes. The spatial patterns of increased precipitation associated with changes in the jet streams are also poorly captured. However, changes in the tropics are more realistic, particularly the changes in tropical temperatures over the oceans. Although these results are preliminary in nature, because of the limited number of LGM simulations currently available, they nevertheless point to the utility of using paleoclimate simulations to understand the mechanisms of climate change and evaluate model performance.

International audience; Recent reconstructions of bottom water δ 13 C during the last interglacial (LIG) suggest short-lived variability in the Atlantic meridional overturning circulation (AMOC). Spontaneous (multi) centennial-scale variability of the AMOC simulated in the Earth system model of intermediate complexity iLOVECLIM are investigated for that period. The model simulates abrupt AMOC transitions occurring at 300 years frequency and correspond to a switch of the AMOC vigor between a strong (∼17 Sv) and a weak (∼11 Sv) state. The onset of these abrupt transitions is associated with changes in orbital forcings resulting in the decline of summer insolation in the high latitudes of the North Atlantic and affecting the sea ice cover in two key deep convection regions: (1) the northern Nordic Seas (NNS) and (2) the northwest North Atlantic (NWNA). Northward inflow of Atlantic surface water increases the convection depth in (1) and strengthens the Greenland Iceland Norway (GIN) Seas overturning circulation. Subsequent ocean-atmosphere interactions involving sea ice, ocean heat release, anomalies of evaporation-precipitation, and wind stress over the Nordic Seas lead also to an increase in deep convection in (2), followed by increase in the AMOC strength.

There is compelling evidence of a strong relation between the Atlantic Meridional Overturning Circulation (AMOC) and millennial scale climate variability during the last glacial period. Part of the advances in understanding the underlying mechanisms rely on the analysis of the sedimentary Pa/Th ratio, which can be used to qualitatively infer past flow rates in the Atlantic. The compilation of existing North Atlantic records indicates repeated, consistent and significant Pa/Th increases across millennial-scale events, indicating significant reductions of deep-water formation in the Northwest Atlantic. However, the use of sedimentary Pa/Th as a pure kinematic circulation proxy is challenging because Pa and Th are also highly sensitive to changes in particulate flux intensity and composition that have probably occurred across these millennial scale events. A primary control of particles on the available Pa/Th records has been ruled out ensuring the absence of correlation between the reconstructed particle fluxes (e.g. Th-normalized opal fluxes) and the sedimentary Pa/Th. However, quantitative estimates of the impact of particles on the available paleo Pa/Th are still missing.In this study, we use the Pa/Th enabled iLOVECLIM Earth System Model of Intermediate Complexity to decipher the impact of particles on the sedimentary Pa/Th. We evaluate the impact of imposed changes in biogenic particle flux intensity and composition on the Atlantic Pa/Th in a 3-D geographical perspective. We find that up to 30% of the observed Pa/Th increase across Heinrich Stadial 1 could be explained by changes in particle fluxes and composition. Besides, changes in the Particulate Organic Carbon (POC) most efficiently affects the sedimentary Pa/Th, followed by biogenic opal. Last but not least, the global Atlantic sedimentary Pa/Th response is very sensitive to shifts in the geographical distribution of particles and high scavenging areas. In our simulations, a decrease of the opal production in the Northwest Atlantic can induce a far field Pa/Th increase in a large part of the North Atlantic basin, suggesting that a local monitoring of the particle fluxes might not be enough to rule out any influence of the particles on paleo sedimentary Pa/Th records.

The Atlantic Meridional Overturning Circulation (AMOC) is thought to be relatively vigorous and stable during Interglacial periods on multimillennial (equilibrium) timescales. However, recent proxy (δ13C benthic) reconstructions suggest that higher frequency variability in deep water circulation may have been common during some interglacial periods, including the Last Interglacial (LIG, 130–115 ka). The origin of these isotope variations and their implications for past AMOC remain poorly understood. Using iLOVECLIM, an Earth system model of intermediate complexity (EMIC) allowing the computation of urn:x-wiley:palo:media:palo20866:palo20866-math-0001 and direct comparison to proxy reconstructions, we perform a transient experiment of the LIG (125–115 ka) forced only by boundary conditions of greenhouse gases and orbital forcings. The model simulates large centennial‐scale variations in the interior urn:x-wiley:palo:media:palo20866:palo20866-math-0002 of the North Atlantic similar in timescale and amplitude to changes resolved by high‐resolution reconstructions from the LIG. In the model, these variations are caused by changes in the relative influence of North Atlantic Deep Water (NADW) and southern source water (SSW) and are closely linked to large (∼50%) changes in AMOC strength provoked by saline input and associated deep convection areas south of Greenland. We identify regions within the subpolar North Atlantic with different sensitivity and response to changes in preformed urn:x-wiley:palo:media:palo20866:palo20866-math-0003 of NADW and to changes in NADW versus SSW influence, which is useful for proxy record interpretation. This could explain the relatively large δ13C gradient (∼0.4%0) observed at ∼3 km water depth in the subpolar North Atlantic at the inception of the last glacial. publishedVersion

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. The 8.2 ka bp cooling event is assumed to be the most clearly marked abrupt climate event in the Holocene at northern mid‐ to high latitudes. In this study, we simulate the vegetation responses to the 8.2 ka bp climate change event over Europe and Northern Africa. Our results show that all dominant plant functional types (PFTs) over Europe and North Africa respond to these climate changes, but the magnitude, timing and impact factor of their responses are different. Compared with pollen‐based vegetation reconstructions, our simulation generally captures the main features of vegetation responses to the 8.2 ka bp event. Interestingly, in Western Europe, the simulated vegetation after perturbation is different from its initial state, which is consistent with two high‐resolution pollen records. This different vegetation composition indicates the long‐lasting impact of abrupt climate change on vegetation through eco‐physiological and ecosystem demographic processes, such as plant competition. Moreover, our simulations suggest a latitudinal gradient in the magnitude of the event, with more pronounced vegetation responses to the severe cooling in the north and weaker responses to less severe cooling in the south.

The use of an interleukin β antibody is currently being investigated in the clinic for the treatment of acne, a dermatological disorder affecting 650M persons globally. Inhibiting the protease responsible for the cleavage of inactive pro-IL1β into active IL-1β, caspase-1, could be an alternative small molecule approach. This report describes the discovery of uracil 20, a potent (38 nM in THP1 cells assay) caspase-1 inhibitor for the topical treatment of inflammatory acne. The uracil series was designed according to a published caspase-1 pharmacophore model involving a reactive warhead in P1 for covalent reversible inhibition and an aryl moiety in P4 for selectivity against the apoptotic caspases. Reversibility was assessed in an enzymatic dilution assay or by using different substrate concentrations. In addition to classical structure-activity-relationship exploration, topical administration challenges such as phototoxicity, organic and aqueous solubility, chemical stability in solution, and skin metabolic stability are discussed and successfully resolved.

This paper presents the inclusion of an online dynamical downscaling of temperature and precipitation within the model of intermediate complexity iLOVECLIM v1.1. We describe the following methodology to generate temperature and precipitation fields on a 40 km × 40 km Cartesian grid of the Northern Hemisphere from the T21 native atmospheric model grid. Our scheme is not grid specific and conserves energy and moisture in the same way as the original climate model. We show that we are able to generate a high-resolution field which presents a spatial variability in better agreement with the observations compared to the standard model. Although the large-scale model biases are not corrected, for selected model parameters, the downscaling can induce a better overall performance compared to the standard version on both the high-resolution grid and on the native grid. Foreseen applications of this new model feature include the improvement of ice sheet model coupling and high-resolution land surface models.

International audience; This paper presents the inclusion of an online dy-namical downscaling of temperature and precipitation within the model of intermediate complexity iLOVECLIM v1.1. We describe the following methodology to generate temperature and precipitation fields on a 40 km × 40 km Cartesian grid of the Northern Hemisphere from the T21 native atmospheric model grid. Our scheme is not grid specific and conserves energy and moisture in the same way as the original climate model. We show that we are able to generate a high-resolution field which presents a spatial variability in better agreement with the observations compared to the standard model. Although the large-scale model biases are not corrected , for selected model parameters, the downscaling can induce a better overall performance compared to the standard version on both the high-resolution grid and on the native grid. Foreseen applications of this new model feature include the improvement of ice sheet model coupling and high-resolution land surface models.

A complete understanding of past El Niño-Southern Oscillation (ENSO) fluctuations is important for the future predictions of regional climate using climate models. Reconstructions of past ENSO dynamics use carbonate oxygen isotope ratios (δ18Oc) and trace metal geochemistry (Mg / Ca) recorded by planktonic foraminifera to reconstruct past spatiotemporal changes in upper ocean conditions. We investigate whether planktonic foraminifera-based proxies offer sufficient spatiotemporal continuity with which to reconstruct past ENSO dynamics. Concentrating upon the period of the instrumental record, we use the Foraminifera as Modelled Entities model to statistically test whether or not δ18Oc and the Temperature signal (Tc) in planktonic foraminifera directly records the ENSO cycle. Our results show that it is possible to use δ18Oc from foraminifera to disentangle the ENSO signal only in certain parts of the Pacific Ocean. Furthermore, a large proportion of these areas coincide with sea-floor regions exhibiting a low sedimentation rate and/or water depth below the carbonate compensation depth, thus precluding the extraction of a temporally valid palaeoclimate signal using long-standing palaeoceanographic methods.

An estimate of permafrost extent and thickness in the northern hemisphere during the Last Glacial Maximum (LGM, ~ 21 ka) has been produced using the VU University Amsterdam Permafrost Snow (VAMPERS) model, forced by iLOVECLIM, an Earth System Model of Intermediate Complexity. We present model results that give both permafrost thickness and extent. In the northern hemisphere, permafrost is estimated to have extended southwards to approximately 50°N in Asia and have achieved 1500 m thickness in Russia. The simulated distribution is compared with a reconstruction of northern hemisphere permafrost extent (Vandenberghe et al., 2014). We contend that the areas which agree with Vandenberghe et al. (2014) are the approximate areas of continuous permafrost during the LGM. In Asia, the model results agree well until approximately 50°N, which is also the approximate 0°C mean annual ground temperature isotherm estimated by iLOVECLIM. South of this limit, therefore, were likely the areas of discontinuous, sporadic and isolated permafrost during the LGM. However, it becomes difficult to model these more sensitive areas of permafrost extent since formation is dependent on local factors that are too fine for our grid's spatial resolution. In Europe, the model results disagree with the reconstruction but this was to be expected since iLOVECLIM is known to carry a warm bias in this region. For permafrost thickness, we compare our estimates with previous research and find that we have reasonably close approximations but there is a wide range of uncertainty since the subsurface parameters of lithology and water content are generalised. Copyright © 2015 John Wiley & Sons, Ltd.

During glacial periods, atmospheric CO2 concentration increases and decreases by around 15 ppm. At the same time, the climate changes gradually in Antarctica. Such climate changes can be simulated in models when the AMOC (Atlantic Meridional Oceanic Circulation) is weakened by adding fresh water to the North Atlantic. The impact on the carbon cycle is less straightforward, and previous studies give opposite results. Because the models and the fresh water fluxes were different in these studies, it prevents any direct comparison and hinders finding whether the discrepancies arise from using different models or different fresh water fluxes. In this study we use the CLIMBER-2 coupled climate carbon model to explore the impact of different fresh water fluxes. In both preindustrial and glacial states, the addition of fresh water and the resulting slow-down of the AMOC lead to an uptake of carbon by the ocean and a release by the terrestrial biosphere. The duration, shape and amplitude of the fresh water flux all have an impact on the change of atmospheric CO2 because they modulate the change of the AMOC. The maximum CO2 change linearly depends on the time integral of the AMOC change. The different duration, amplitude, and shape of the fresh water flux cannot explain the opposite evolution of ocean and vegetation carbon inventory in different models. The different CO2 evolution thus depends on the AMOC response to the addition of fresh water and the resulting climatic change, which are both model dependent. In CLIMBER-2, the rise of CO2 recorded in ice cores during abrupt events can be simulated under glacial conditions, especially when the sinking of brines in the Southern Ocean is taken into account. The addition of fresh water in the Southern Hemisphere leads to a decline of CO2, contrary to the addition of fresh water in the Northern Hemisphere.

This paper studies the control of the Atlantic Warm Pool (AWP) on atmospheric moisture transport across the Central American isthmus as a potential feedback on rapid glacial climate fluctuations. Defined as a region of the Atlantic with surface temperatures above 28.5 °C, the modern AWP expands from the tropical Northwest Atlantic up to the Gulf of Mexico during boreal summer. Due to enhanced deep convection over these warm waters, changes in AWP area cause inverse changes in the strength of the Caribbean low level jet. This low level jet drives atmospheric moisture transport from the Atlantic across the Central American isthmus towards the Pacific. Changes in cross-isthmus moisture transport, potentially related to the AWP, may therefore have affected North Atlantic salinity and the partly density driven Atlantic Meridional Overturning Circulation (AMOC) during the glacial. Based on available proxy evidence we hypothesize that the AWP evolved independent of extratropical North Atlantic temperatures during most of the last glacial, except during periods of AMOC collapse when intense extratropical North Atlantic cooling may have limited eastward AWP expansion. We investigate the implications of this hypothesis for cross-isthmus moisture transport by simulating the coupled ocean-atmosphere response to AMOC collapse and the atmospheric sensitivity to additional variations in AWP area. Our simulations suggest that a decrease in AWP area may increase cross-isthmus moisture transport, whereas extratropical North Atlantic cooling beside a persistent AWP may decrease cross-isthmus moisture transport. Interpretation of these effects throughout an idealized Bond Cycle suggests a positive feedback of reduced cross-isthmus moisture transport in response to Greenland cooling prior to AMOC collapse. During AMOC collapse, when AWP expansion is proposed to have been inhibited, this positive feedback turns negative as enhanced cross-isthmus moisture transport may help AMOC recovery. Supported by reconstructed sea surface salinity changes, we propose that the AWP may have played a key role in the glacial climate by acting as a gatekeeper to regulate moisture transport across the Central American isthmus.

The oxygen-18 to oxygen-16 ratio recorded in fossil planktonic foraminifer shells has been used for over 50 years in many geoscience applications. However, different planktonic foraminifer species generally yield distinct signals, as a consequence of their specific living habitats in the water column and along the year. This complexity is usually not taken into account in model–data integration studies. To overcome this shortcoming, we developed the Foraminifers As Modeled Entities (FAME) module. The module predicts the presence or absence of commonly used planktonic foraminifers and their oxygen-18 values. It is only forced by hydrographic data and uses a very limited number of parameters, almost all derived from culture experiments. FAME performance is evaluated using the Multiproxy Approach for the Reconstruction of the Glacial Ocean surface (MARGO) Late Holocene planktonic foraminifer calcite oxygen-18 and abundance datasets. The application of FAME to a simple cooling scenario demonstrates its utility to predict changes in planktonic foraminifer oxygen-18 to oxygen-16 ratio in response to changing climatic conditions.

The past two million years of eastern African climate variability is currently poorly constrained, despite interest in understanding its assumed role in early human evolution1–4. Rare palaeoclimate records from northeastern Africa suggest progressively drier conditions2,5 or a stable hydroclimate6. By contrast, records from Lake Malawi in tropical southeastern Africa reveal a trend of a progressively wetter climate over the past 1.3 million years7,8. The climatic forcings that controlled these past hydrological changes are also a matter of debate. Some studies suggest a dominant local insolation forcing on hydrological changes9–11, whereas others infer a potential influence of sea surface temperature changes in the Indian Ocean8,12,13. Here we show that the hydroclimate in southeastern Africa (20–25° S) is controlled by interplay between low-latitude insolation forcing (precession and eccentricity) and changes in ice volume at high latitudes. Our results are based on a multiple-proxy reconstruction of hydrological changes in the Limpopo River catchment, combined with a reconstruction of sea surface temperature in the southwestern Indian Ocean for the past 2.14 million years. We find a long-term aridification in the Limpopo catchment between around 1 and 0.6 million years ago, opposite to the hydroclimatic evolution suggested by records from Lake Malawi. Our results, together with evidence of wetting at Lake Malawi, imply that the rainbelt contracted toward the Equator in response to increased ice volume at high latitudes. By reducing the extent of woodland or wetlands in terrestrial ecosystems, the observed changes in the hydroclimate of southeastern Africa—both in terms of its long-term state and marked precessional variability—could have had a role in the evolution of early hominins, particularly in the extinction of Paranthropus robustus.

To analyze the global hydroclimate response during the Younger Dryas cold event, we evaluate climate model results that have been constrained with proxy-based temperatures from the North Atlantic region. We find that both the temperature and the hydroclimate response have a clear global signature. A marked cooling is simulated over the North Atlantic Ocean (more than 5 °C) and the downwind continents (2–4 °C). This response is related to the weakening of the Atlantic meridional overturning circulation under influence of meltwater discharges. The hydroclimate response is most expressed over Eurasia in a belt between 40 and 60°N, and over Northern Africa in the Sahel region. In both areas, a strong decrease in soil moisture is simulated (up to 20% reduction). In contrast, a striking increase in moisture is found over southeastern North America (15% increase), where southerly atmospheric flow brings moist air to the continent. Outside these areas that are clearly affected by the cold North Atlantic Ocean, the responses of temperature and moisture are decoupled, with different causes for these temperature and hydroclimate responses. In the tropics, the hydroclimate response is governed by the southward shift of the intertropical convergence zone (ITCZ) due to the cooling of the North Atlantic Ocean. This causes drier conditions north of the equator and wetter conditions in the Southern Hemisphere tropics. The associated changes in soil moisture are relatively gradual here, taking up to two centuries to complete, suggesting that the impact of the ITCZ shift on the tropical hydroclimate is building up. Our experiment indicates that Southern Hemisphere continents experienced a small cooling (less than 0.5 °C) during the Younger Dryas, caused by the negative radiative forcing associated with reduced atmospheric methane concentrations and enhanced dust levels. In our simulation, the bi-polar seesaw mechanism is relatively weak, so that the associated warming of the South Atlantic Ocean is not overwhelming the reduction in radiative forcing. Our results thus indicate that in the tropics and/or Southern Hemisphere, the cooling is a response to the negative radiative forcing, while the hydroclimatic changes are predominantly resulting from ITCZ variations. Consequently, when interpreting hydroclimatic proxy records from these regions, data should not be compared directly to key records from high latitudes, such as Greenland ice core stable isotope records. © 2018 Elsevier Ltd