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Atmospheric CO2 and polar ice volume have been strongly coupled over the past 805,000 years. However, the prior extent of coupling, during times of lower-amplitude ice-volume variability, is unknown because continuous high-resolution CO2 records are lacking. We reconstructed the past 1,460,000 years of atmospheric CO2 (similar to 1,700year sample resolution) by taking advantage of the unique relationship between CO2 concentration and leaf-wax delta C-13 resulting from changes in the extent of C-3 and C-4 vegetation in East India. Notably, reconstructed interglacial CO2 concentrations were lower before the transition to large volume variability during the mid-Pleistocene Transition (900,000 years ago). Prior to the mid-Pleistocene Transition, CO2 exhibited a secular trend similar to that of deep-ocean carbon isotopes. At orbital time scales, phase analysis indicates that the CO2 lead relative to ice volume changed to a lag during the mid-Pleistocene Transition. Combined, these findings suggest that deep-ocean circulation controlled the long-term CO2 trend, and that interaction between CO2, continental ice and deep-ocean circulation was reorganized during the mid-Pleistocene Transition, involving a decrease in carbon storage in the deep Pacific.

Glacial cycles during the Early Pleistocene (EP) are characterized by a dominant 41-kyr periodicity and amplitudes smaller than those of glacial cycles with ~ 100-kyr periodicity during the Late Pleistocene (LP). However, it remains unclear how the 41-kyr glacial cycles during EP respond to Earth’s astronomical forcings. Here we employ a three-dimensional ice-sheet model to simulate the glacial cycles at ~ 1.6–1.2 Ma and analyse the phase angle of precession and obliquity at each deglaciation. We show that each deglaciation occurs at every other precession minimum, when obliquity is large. This behaviour is explained by a threshold mechanism determined by ice-sheet size and astronomical forcings. The lead-lag relationship between precession and obliquity controls the length of each glacial/interglacial period. The large amplitudes of obliquity and eccentricity during this period help to establish robust 41-kyr glacial cycles. These findings support the combined role of astronomical forcings common for both EP and LP.

Following the protocol of the fourth phase of the Paleoclimate Modelling Intercomparison Project (PMIP4), we performed numerical experiments targeting distinctive past time periods using the Model for Interdisciplinary Research on Climate, Earth System version 2 for Long-term simulations (MIROC-ES2L), which is an Earth system model. Setup and basic performance of the experiments are presented. The Last Glacial Maximum was one of the most extreme climate states during the Quaternary and conducting numerical modeling experiments of this period has long been a challenge for the paleoclimate community. We conducted a Last Glacial Maximum experiment with a long spin-up of nearly 9000 years. Globally, there was reasonable agreement between the anomalies relative to the present day derived from model climatology and those derived from proxy data archives, while some regional discrepancies remained. By changing orbital and greenhouse gas forcings, we conducted experiments for two interglacial periods: 6000 and 127 000 years before present. Model anomalies relative to the present day were qualitatively consistent with variations in solar forcing. However, anomalies in the model were smaller than those derived from proxy data archives, suggesting that processes that play a role in past interglacial climates remain lacking in this state-of-the-art model. We conducted transient simulations from 850 to 1850 CE and from 1850 to 2014 CE. Cooling in the model indicated a clear response to huge volcanic eruptions, consistent with paleo-proxy data. The contrast between cooling during the Little Ice Age and warming during the 20th to 21st centuries was represented well at the multidecadal timescale.

Past interglacials allow investigating the climatic processes and associated feedbacks during warm periods, which are characterized by different combinations of climatic forcing such as solar radiation, GHGs, and ice sheets. Arctic warming amplification, a common phenomenon between past interglacials and present warming, has seasonality in its feedback mechanism, and detailed study of these internal feedbacks is still lacking despite its global impact. In this study, the simulation experiments under conditions close to the past interglacial periods (MIS1; Holocene, MIS5e; Last Interglacial, and MIS11) are conducted using a coupled atmosphere-ocean-vegetation model MIROC (4m) AOVGCM, particularly focusing on the role of ice sheets and Arctic sea ice. Climate responses to inputs and conditions are compared to examine the seasonal effects of atmosphere-ocean-ice feedbacks on Northern hemisphere high-latitudes temperature. Ice sheet distribution is set as a boundary condition in addition to the orbital elements, land cover, and GHGs to account the effect of remaining ice sheets at the timing of peak insolation. Feedback Analysis is also conducted to quantify the contribution of each feedback element to the surface temperature change. It is demonstrated that an inter-seasonal effect of air-sea-ice-vegetation feedbacks contributes to Arctic warming amplification, where heat gained in summer is used for sea ice melting and ocean absorption, and is released in autumn and winter, resulting in annual warming. This process is amplified when considering vegetation feedbacks and seen commonly in MIS1, 5e, and 11. In periods when ice sheets remain, Arctic sea ice keeps a high degree of concentration in summer, and annual mean temperatures at Northern high latitudes are lower than would be expected from insolation intensity. These results imply that the presence of Northern hemisphere ice sheet has a significant effect on Arctic climate response to insolation intensity by suppressing feedbacks that contribute to Arctic amplification through the reduced melt of summer sea ice.

The modeling of paleoclimate, using physically based tools, is increasingly seen as a strong out-of-sample test of the models that are used for the projection of future climate changes. New to the Coupled Model Intercomparison Project (CMIP6) is the Tier 1 Last Interglacial experiment for 127 000 years ago (lig127k), designed to address the climate responses to stronger orbital forcing than the midHolocene experiment, using the same state-of-the-art models as for the future and following a common experimental protocol. Here we present a first analysis of a multi-model ensemble of 17 climate models, all of which have completed the CMIP6 DECK (Diagnostic, Evaluation and Characterization of Klima) experiments. The equilibrium climate sensitivity (ECS) of these models varies from 1.8 to 5.6 ∘C. The seasonal character of the insolation anomalies results in strong summer warming over the Northern Hemisphere continents in the lig127k ensemble as compared to the CMIP6 piControl and much-reduced minimum sea ice in the Arctic. The multi-model results indicate enhanced summer monsoonal precipitation in the Northern Hemisphere and reductions in the Southern Hemisphere. These responses are greater in the lig127k than the CMIP6 midHolocene simulations as expected from the larger insolation anomalies at 127 than 6 ka. New synthesis for surface temperature and precipitation, targeted for 127 ka, have been developed for comparison to the multi-model ensemble. The lig127k model ensemble and data reconstructions are in good agreement for summer temperature anomalies over Canada, Scandinavia, and the North Atlantic and for precipitation over the Northern Hemisphere continents. The model–data comparisons and mismatches point to further study of the sensitivity of the simulations to uncertainties in the boundary conditions and of the uncertainties and sparse coverage in current proxy reconstructions. The CMIP6–Paleoclimate Modeling Intercomparison Project (PMIP4) lig127k simulations, in combination with the proxy record, improve our confidence in future projections of monsoons, surface temperature, and Arctic sea ice, thus providing a key target for model evaluation and optimization.

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

The modeling of paleoclimate, using physically based tools, is increasingly seen as a strong out-of-sample test of the models that are used for the projection of future climate changes. New to CMIP6 is the Tier 1 lig127k experiment, designed to address the climate responses to stronger orbital forcing than the midHolocene experiment, using the same state-of-the-art models and following a common experimental protocol. We present a multi-model ensemble of 17 climate models, all of which (except for two) have also completed the CMIP6 DECK experiments. The Equilibrium Climate Sensitivity (ECS) of these models varies from 2.1 to 5.6 °C. The seasonal character of the insolation anomalies results in strong warming over the Northern Hemisphere (NH) continents in the lig127k ensemble as compared to the piControl in June–July–August and a much-reduced minimum (August–September) summer sea ice extent in the Arctic. The multi-model results indicate enhanced summer monsoonal precipitation and areal extent in the Northern Hemisphere and reductions in the Southern Hemisphere. These responses are greater in the lig127k than midHolocene simulations as expected from the larger insolation anomalies at 127 ka than 6 ka. New syntheses for surface temperature and precipitation, targeted for 127 ka, have been developed for comparison to the multi-model ensemble. The lig127k model ensemble and data reconstructions are in good agreement for summer temperature anomalies over Canada, Scandinavia, and the North Atlantic and precipitation over the Northern Hemisphere continents. The model-data comparisons and mismatches point to further study of the sensitivity of the simulations to uncertainties in the specified boundary conditions and of the uncertainties and sparse coverage in current proxy reconstructions. The CMIP6-PMIP4 lig127k simulations, in combination with the proxy record, have potential implications for confidence in future projections of monsoons, surface temperature, Arctic sea ice, and the stability of the Greenland ice sheet.

Following the protocol of the fourth phase of the Paleoclimate Modeling Intercomparison Project (PMIP4), we performed numerical experiments targeting distinctive past time periods using the Model for Interdisciplinary Research on Climate Earth System Model (MIROC-ES2L), which is an Earth System Model. Setup and basic performance of the experiments are presented. The Last Glacial Maximum was one of the most extreme climate states during the Quaternary and conducting numerical modeling experiments of this period has long been a challenge for the paleoclimate community. We conducted a Last Glacial Maximum experiment with a long spin-up of nearly 9,000 years. Globally, there is reasonable agreement between the anomalies relative to present day derived from model climatology and those derived from proxy data archives while some regional discrepancies remain. By changing orbital and greenhouse gas forcings, we conducted experiments for two interglacial periods: 6,000 and 127,000 years before present. Model anomalies relative to present day are qualitatively consistent with variations in solar forcing. However, anomalies in the model are smaller than those derived from proxy data archives, suggesting that processes that play a role in past interglacial climates are still missing in this state-of-the-art model. We conducted transient simulations from 850 CE to 1850 CE and from 1850 CE to 2014 CE. Cooling in the model indicates clear responses to huge volcanic eruptions, which are consistent with paleo-proxy data. The contrast between cooling during the Little Ice Age and warming during the 20th to 21st centuries is well represented at the multi-decadal time scale.

The effect of aerosols is one of many uncertain factors in projections of future climate. However, the behaviour of mineral dust aerosols (dust) can be investigated within the context of past climate change. The Last Glacial Maximum (LGM) is known to have had enhanced dust deposition in comparison with the present, especially over polar regions. Using the Model for Interdisciplinary Research on Climate Earth System Model (MIROC-ESM), we conducted a standard LGM experiment following the protocol of the Paleoclimate Modelling Intercomparison Project phase 3 and sensitivity experiments. We imposed glaciogenic dust on the standard LGM experiment and investigated the impacts of glaciogenic dust and non-glaciogenic dust on the LGM climate. Global mean radiative perturbations by glaciogenic and non-glaciogenic dust were both negative, consistent with previous studies. However, glaciogenic dust behaved differently in specific regions; e.g. it resulted in less cooling over the polar regions. One of the major reasons for reduced cooling is the ageing of snow or ice, which results in albedo reduction via high dust deposition, especially near sources of high glaciogenic dust emission. Although the net radiative perturbations in the lee of high glaciogenic dust provenances are negative, warming by the ageing of snow overcomes this radiative perturbation in the Northern Hemisphere. In contrast, the radiative perturbation due to high dust loading in the troposphere acts to warm the surface in areas surrounding Antarctica, primarily via the longwave aerosol–cloud interaction of dust, and it is likely the result of the greenhouse effect attributable to the enhanced cloud fraction in the upper troposphere. Although our analysis focused mainly on the results of experiments using the atmospheric part of the MIROC-ESM, we also conducted full MIROC-ESM experiments for an initial examination of the effect of glaciogenic dust on the oceanic general circulation module. A long-term trend of enhanced warming was observed in the Northern Hemisphere with increased glaciogenic dust; however, the level of warming around Antarctica remained almost unchanged, even after extended coupling with the ocean.

Liquid water is one of the most important materials affecting the climate and habitability of a terrestrial planet. Liquid water vaporizes entirely when planets receive insolation above a certain value, which is called the runaway greenhouse threshold. This threshold forms the inner most limit of the habitable zone. Here, we investigate the effect of the distribution of surface water on the runaway greenhouse threshold for Earth-sized planets using a three-dimensional dynamic atmosphere model. We considered a 1-bar atmosphere whose composition is similar to the current Earth's atmosphere with a zonally uniform distribution of surface water. As previous studies have already shown, we also recognized two climate regimes: the land planet regime, which has dry low latitude and wet high latitude region, and the aqua planet regime, which is globally wet. We showed that each regime is controlled by the width of the Hadley circulation, the amount of surface water, and the planetary topography. We found that the runaway greenhouse threshold varies continuously with the surface water distribution from about 130% (an aqua planet) to 180% (the extreme case of a land planet) of the present insolation at Earth's orbit. Our results indicate that the inner edge of the habitable zone is not a single sharp boundary, but a border whose location varies depending on planetary surface condition, such as the amount of surface water. Since land planets have wider habitable zones and less cloud cover, land planets would be good targets for future observations investigating planetary habitability., Comment: 25 pages, 9 figures. Accepted for publication in Journal of Geophysical Research - Planets

The Last interglacial (LIG) is a period with increased summer insolation at high northern latitudes, which results in strong changes in the terrestrial and marine cryosphere. Understanding the mechanisms for this response via climate modelling and comparing the models’ representation of climate reconstructions is one of the objectives set up by the Paleoclimate Mod-elling Intercomparison Project for its contribution to the sixth phase of the Coupled Model Intercomparison Project. Here we analyse the results from 12 climate models in terms of Arctic sea ice. The mean pre-industrial to LIG reduction in minimum sea ice area (SIA) reaches 59 % (multi-model mean LIG area is 2.21 mill. km2, compared to 5.85 mill. km2 for the PI), and the range of model results for LIG minimum sea ice area (from 0.02 to 5.65 mill. km2) is larger than for PI (from 4.10 to 8.30 mill. km2). On the other hand there is little change for the maximum sea ice area (which is 12 mill. km2 for both the PI and the LIG, with a standard deviation of 1.04 mill. km2 for PI and 1.21 mill. km2 for LIG). To evaluate the model results we synthesize LIG sea ice data from marine cores collected in the Arctic Ocean, Nordic Seas and northern North Atlantic. South of 78° N in the Atlantic and Nordic seas the LIG was seasonally ice-free. North of 78° N there are some discrepancies between sea-ice re-constructions based on dinocysts/foraminifers/ostracods and IP25: some sites have both seasonal and perennial interpretations based on the same core, but different indicators. Because of the conflicting interpretations it is not possible for any one model to match every data point in our data synthesis, or say whether the Arctic was seasonally ice-free. Drivers for the inter-model differences are: different phasing of the up and down short-wave anomalies over the Arctic ocean, associated with differences in model albedo; possible cloud property differences, in terms of optical depth; LIG ocean circulation changes which occur for some, but not all, LIG simulations. Finally we note that inter-comparisons between the LIG simulations, and simulations with moderate CO2 increase (during the transition to high CO2 levels), may yield insight into likely 21C Arctic sea ice changes using these LIG simulations.

We carry out a Last Interglacial (LIG) experiment, named lig127k and a Tier1 experiment of PMIP4/CMIP6, using three versions of the MIROC model, MIROC4m, MIROC4m-LPJ and MIROC-ES2L. The results are compared with reconstructions from climate proxy data. All models show summer warming over northern high latitude land, reflecting the differences between the distributions of the LIG and present-day solar irradiance. Only MIROC4m-LPJ, which includes dynamical vegetation feedback from the change in vegetation distribution, shows warming signals, even for the annual mean, at northern high latitudes, as shown by proxy data. However, the latest Earth System Model (ESM) of MIROC, MIROC-ES2L, in which there is only a partial vegetation effect through the leaf area index, shows no change or even annual cooling over large parts of the northern hemisphere. Results from the series of experiments show that the inclusion of vegetation feedback is necessary for the reproduction of the strong annual warming over land at northern high latitudes. The LIG experimental results show that the warming predicted by models is still underestimated, even with dynamical vegetation, compared to reconstructions from proxy data, suggesting that further investigation and improvement to the climate feedback mechanism are needed.

When planets receive insolation above a certain critical value called the runaway threshold, liquid surface water vaporizes completely, which forms the inner edge of the habitable zone. Because land planets can emit a large amount of radiation from the dry tropics, they have a higher runaway threshold than aqua planets do. Here we systematically investigated the runaway threshold for various surface water distributions using a three-dimensional dynamic atmosphere model. The runaway threshold for the meridionally uniform surface water distribution increases from the typical value for the aqua-planet regime (~130% S0) to one for the land-planet regime (~155% S0) as the dry surface area increases, where S0 is the present Earth's insolation. Although this result is similar to the previous work considering zonally uniform surface water distributions, the runaway threshold for the land-planet regime is quite low compared to that of the previous work. This is because a part of the tropical atmosphere is always wet for the meridionally uniform case. We also considered the surface water distributions determined by the Earth's, Mars' and Venus' topographies. We found that their runaway thresholds are close to that for the meridionally uniform cases, and the amount of water at the boundary between an aqua- and land-planet regime is around 10% of the Earth's ocean. This clearly shows that the runaway threshold is not determined uniquely by the luminosity of the central star, but it has a wide range caused by the surface water distribution of the terrestrial water planet itself., Comment: 28 pages, 12 figures, accepted for publication in Journal of Geophysical Research - Planets

The Ninth Symposium on Polar Science/Interdisciplinary sessions: [IA] Open session for the interdisciplinary Arctic Science, Thu. 6 Dec. / Entrance Hall (1st floor), National Institute of Polar Research

The Ninth Symposium on Polar Science/Special session: [S] Antarctic ice-ocean interaction ～observation, reconstruction, and modeling～, Tue. 4 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research

The sixth version of the Model for Interdisciplinary Research on Climate (MIROC), called MIROC6, was cooperatively developed by a Japanese modeling community. In the present manuscript, simulated mean climate, internal climate variability, and climate sensitivity in MIROC6 are evaluated and briefly summarized in comparison with the previous version of our climate model (MIROC5) and observations. The results show that overall reproducibility of mean climate and internal climate variability in MIROC6 is better than that in MIROC5. The tropical climate systems (e.g., summertime precipitation in the western Pacific and the eastward propagating Madden-Julian Oscillation) and the mid-latitude atmospheric circulations (e.g., the westerlies, the polar night jet, and troposphere-stratosphere interactions) are significantly improved in MIROC6. These improvements can be attributed to the newly implemented parameterization for shallow convective processes and to the directly resolved stratosphere. While there are significant differences in climates and variabilities between the two models, the effective climate sensitivity of 2.5 K remains the same because the differences in radiative forcing and climate feedback tend to offset each other. With an aim towards contributing to the sixth phase of the Coupled Model Intercomparison Project, designated simulations tackling a wide range of climate science issues, as well as seasonal-to-decadal climate predictions and future climate projections, are currently ongoing using MIROC6.

As part of the terrestrial branch of the Japan-funded Arctic Climate Change Research Project (GRENE-TEA), which aims to clarify the role and function of the Arctic terrestrial system in the climate system, and assess the influence of its changes on a global scale, this model intercomparison project (GTMIP) is planned and being conducted to (1) enhance communication and understanding between the "minds and hands" (i.e., between the modelling and field scientists) and (2) assess the uncertainty and variations stemming from variability in model implementation/design and in model outputs due to climatic and historical conditions in the Arctic terrestrial regions. This paper provides an overview and the experiment protocol of Stage 1 of the project, site simulations driven by statistically fitted data created using the GRENE-TEA site observations for the last three decades. The target metrics for the model evaluation cover key processes in both physics and biogeochemistry, including energy budgets, snow, permafrost, phenology, and carbon budgets. The preliminary results on four metrics (annual mean latent heat flux, annual maximum snow depth, gross primary production, and net ecosystem production) already demonstrate the range of variations in reproducibility among existing models and sites. Full analysis on annual as well as seasonal time scales, to be conducted upon completion of model outputs submission, will delineate inter-dependence among the key processes, and provide the clue for improving the model performance.

The effect of aerosols is one of the many uncertain factors in projections of the future climate. However, the behaviour of mineral dust aerosol (dust) can be investigated in the context of past climate changes. The Last Glacial Maximum (LGM) is known to have resulted in an enhancement of the dust deposition, especially over the polar regions. Using the Model for Interdisciplinary Research on Climate Earth System Model (MIROC-ESM), we investigated the impact of glaciogenic dust on the climate of the LGM and found that the effect of the enhancement of dust results in less cooling over the polar regions. One of the major reasons of the reduced cooling is the ageing of snow or ice, resulting in the reduction of the albedo by a high dust deposition, especially in the vicinity of high glaciogenic dust emissions. Although the net radiative perturbations in the lee of high glaciogenic dust provenances are negative, warming by ageing of snow overcomes this radiative perturbation in the Northern Hemisphere. In contrast, the radiative perturbation by the high dust loading in the troposphere acts to warm the surface surrounding Antarctica, which is mainly caused by the longwave aerosol–cloud interaction of dust and is likely the result of the greenhouse effect of the enhanced cloud fraction in the upper troposphere. Although our analysis mainly focused on the results of the experiments using the atmospheric part of the MIROC-ESM, we also conducted full MIROC-ESM experiments for a first trial of glacial dust modelling. The long-term trend to enhance warming in the Northern Hemisphere with the increase of glaciogenic dust was observed, whereas the warming level around Antarctica is almost unchanged, even after an extended interaction with the ocean.

Subgrid snow cover is one of the key parameters in global land models since snow cover has large impacts on the surface energy and moisture budgets, and hence the surface temperature. In this study, the Subgrid Snow Distribution (SSNOWD) snow cover parameterization was incorporated into the Minimal Advanced Treatments of Surface Interaction and Runoff (MATSIRO) land surface model. SSNOWD assumes that the subgrid snow water equivalent (SWE) distribution follows a lognormal distribution function, and its parameters are physically derived from geoclimatic information. Two 29-yr global offline simulations, with and without SSNOWD, were performed while forced with the Japanese 25-yr Reanalysis (JRA-25) dataset combined with an observed precipitation dataset. The simulated spatial patterns of mean monthly snow cover fraction were compared with satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) observations. The snow cover fraction was improved by the inclusion of SSNOWD, particularly for the accumulation season and/or regions with relatively small amounts of snowfall; snow cover fraction was typically underestimated in the simulation without SSNOWD. In the Northern Hemisphere, the daily snow-covered area was validated using Interactive Multisensor Snow and Ice Mapping System (IMS) snow analysis datasets. In the simulation with SSNOWD, snow-covered area largely agreed with the IMS snow analysis and the seasonal cycle in the Northern Hemisphere was improved. This was because SSNOWD formulates the snow cover fraction differently for the accumulation season and ablation season, and represents the hysteresis of the snow cover fraction between different seasons. The effects of including SSNOWD on hydrological properties and snow mass were also examined.

When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM.

Paleoclimate experiments using contemporary climate models are an effective measure to evaluate climate models. In recent years, Earth system models (ESMs) were developed to investigate carbon cycle climate feedbacks, as well as to project the future climate. Paleoclimate events can be suitable benchmarks to evaluate ESMs. The variation in aerosols associated with the volcanic eruptions provide a clear signal in forcing, which can be a good test to check the response of a climate model to the radiation changes. The variations in atmospheric CO2 level or changes in ice sheet extent can be used for evaluation as well. Here we present implementations of the paleoclimate experiments proposed by the Coupled Model Intercomparison Project phase 5/Paleoclimate Modelling Intercomparison Project phase 3 (CMIP5/PMIP3) using MIROC-ESM, an ESM based on the global climate model MIROC (Model for Interdisciplinary Research on Climate). In this paper, experimental settings and spin-up procedures of the mid-Holocene, the Last Glacial Maximum, and the Last Millennium experiments are explained. The first two experiments are time slice experiments and the last one is a transient experiment. The complexity of the model requires various steps to correctly configure the experiments. Several basic outputs are also shown.

Climate models struggle to reproduce the amplitude of polar temperature change observed in palaeoclimatic archives. A synthesis of observational and model data was used to reconstruct atmospheric dust concentrations in the Holocene and Last Glacial Maximum. The impact of aerosols in polar areas is underestimated in simulations for dustier-than-modern conditions; the inclusion of the amplified response to aerosols at high latitudes would improve model predictions.

In this study, we constructed a perturbed physics ensemble (PPE) for the MIROC5 coupled atmosphere–ocean general circulation model (CGCM) to investigate the parametric uncertainty of climate sensitivity (CS). Previous studies of PPEs have mainly used the atmosphere-slab ocean models. A few PPE studies using a CGCM applied flux corrections, because perturbations in parameters can lead to large radiation imbalances at the top of the atmosphere and climate drifts. We developed a method to prevent climate drifts in PPE experiments using the MIROC5 CGCM without flux corrections. We simultaneously swept 10 parameters in atmosphere and surface schemes. The range of CS (estimated from our 35 ensemble members) was not wide (2.2–3.2 °C). The shortwave cloud feedback related to changes in middle-level cloud albedo dominated the variations in the total feedback. We found three performance metrics for the present climate simulations of middle-level cloud albedo, precipitation, and ENSO amplitude that systematically relate to the variations in shortwave cloud feedback in this PPE.

A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Niño–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between the two MIROC3.2 versions, indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution. The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements. MIROC5 reveals an equilibrium climate sensitivity of 2.6 K, which is lower than that in MIROC3.2 by 1 K. This is probably due to the negative feedback of low clouds to the increasing concentration of CO2, which is opposite to that in MIROC3.2.

A dynamic global vegetation model (DGVM) is coupled to an atmospheric general circulation model (AGCM) to investigate the influence of vegetation dynamics on climate change under conditions of global warming. The model results are largely in agreement with observations and the results of previous studies in terms of the present climate, present potential vegetation, present net primary productivity (NPP), and pre-industrial carbon budgets. The equilibrium state of climate properties are compared among pre-industrial, doubled, and quadrupled atmospheric CO2 values using DGVM–AGCM and current AGCM with fixed vegetation to evaluate the influence of dynamic vegetation change. We also separated the contributions of temperature, precipitation and CO2 fertilization on vegetation change. The results reveal an amplification of global warming climate sensitivity by 10% due to the inclusion of dynamic vegetation. The total effects of elevated CO2 and climate change also lead to an increase in NPP and vegetation coverage globally. The reduction of albedo associated with this greening results in enhanced global warming. Our separation analysis indicates that temperature alters vegetation at high latitudes such as Siberia or Alaska, where there is a switch from tundra to forest. On the other hand, CO2 fertilization provides the largest contribution to greening in arid/semi-arid region. Precipitation change did not cause any drastic vegetation shift.

In this study an integrated simulation of the global distribution and the radiative forcing of soil dust aerosols at the Last Glacial Maximum (LGM) is performed with an aerosol climate model, SPRINTARS. It is compared with another simulation for the present climate condition. The global total emission flux of soil dust aerosols at the LGM is simulated to be about 2.4 times as large as that in the present climate, and the simulated deposition flux is in general agreement with estimations from ice core and marine sediment samplings though it appears to be underestimated over the Antarctic. The calculated direct radiative forcings of soil dust aerosols at the LGM is close to zero at the tropopause and −0.4 W m−2 at the surface. These radiative forcings are about twice as large as those in the present climate. SPRINTARS also includes the microphysical parameterizations of the cloud-aerosol interaction both for liquid water and ice crystals, which affect the radiation budget. The positive radiative forcing from the indirect effect of soil dust aerosols is mainly caused by their properties to act as ice nuclei. This effect is simulated to be smaller (−0.9 W m−2) at the LGM than in the present. It is suggested that atmospheric dust might contribute to the cold climate during the glacial periods both through the direct and indirect effects, relative to the interglacial periods.

[1] AOGCM simulations of the mid-Holocene tend to largely underestimate annual mean temperature over land in northern hemisphere compared to that of paleodata reconstruction. While the vegetation feedback has not been yet quantitatively reported, its neglect is suggested to be one of the cause of this underestimation. Here, we perform several experiments using an atmosphere-ocean-vegetation coupled model and quantify a vegetation-induced feedback in the mid-Holocene climate using MIROC GCM. Our result indicates an annual warming of +1.3K over land north of 40°N in the mid-Holocene, much larger than the previous GCM results. This warming is due to direct amplification of warming over high latitude land through increases in vegetation and reduced albedo during the summer and indirect amplification through sea-ice feedback in autumn and winter and snow albedo feedback in spring. These feedback were not properly represented in previous GCM analysis.

[1] An atmosphere-ocean-vegetation coupled model is used to quantify the biogeophysical feedback that emerges as vegetation adjusts dynamically to a quadrupling of atmospheric CO2. This feedback amplifies global warming by 13%. About half of it is due to climatically induced expansion of boreal forest into tundra, reinforced by reductions in snow and sea ice cover. The other half represents a global climatic effect of increased vegetative cover (an indirect consequence of plant physiological responses to CO2) in the semi-arid subtropics. Enhanced absorption of shortwave radiation in these regions produces a net surface warming, which the atmosphere communicates poleward. The greatest vegetation-induced warming is co-located with large, vulnerable carbon stores in the north. These lose carbon, so that in the long term, the biospheric response to CO2 and climate change becomes dominated by positive feedbacks that overwhelm the effect of CO2 fertilization on terrestrial carbon stocks.