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Understanding the variations of water cycle on orbital timescale and their response to astronomical parameters, greenhouse gases (GHG) and ice sheets is one of the focuses in paleoclimate study. Sea ice and precipitation, two important components of the water cycle, are paid much attention. A better understanding of their variations on orbital timescale, especially their response to external forcing and related processes and feedbacks, could provide insight on their long-term variations in the future. The latest research results show that, on orbital scale, the Arctic sea ice is more sensitive to insolation, while the Southern Ocean sea ice is more sensitive to GHG. Under the combined influence of insolation and GHG, the last nine interglacials all have much less summer Arctic sea ice, as compared to both the present-day and the future, due to the much higher Northern Hemisphere (NH) summer insolation. As compared to the future, the last nine interglacials all have much more annual and seasonal Southern Ocean sea ice due to their much lower CO2. In terms of the astronomical parameters, the Arctic sea ice is more influenced by precession, whereas obliquity plays a more important role in the Southern Ocean sea ice. The different responses of Arctic and Southern Ocean sea ice to astronomical parameters and CO2 are mainly due to their different geographical locations. The Arctic ocean is relatively closed and it is located in the northern highest latitudes, which make it only receives very little insolation during winter and it is mainly influenced by precession-dominated summer insolation. The summer insolation not only influences the summer Arctic sea ice, but also has an effect on the winter one through the summer remnant effect. In addition, the Arctic sea ice is also affected by the vegetation in the northern mid and high latitudes, which is mainly dominated by precession. As compared to the Arctic, the latitudes of Southern Ocean are lower and it is more open, whi

Quaternary monsoon changes in East Asia have been extensively investigated by proxy records from continental and marine archives. However, these proxy indicators often show controversial characteristics in terms of trends and rhythms, perplexing understanding of orbital-scale monsoon dynamics. Here we review the orbital-scale monsoon variability and dynamics in East Asia by comparing multiple proxies from loess, lake, speleothem, and marine records with the HadCM3 modeling result. Evolutionary power spectra of loess grain size and sea surface temperature exhibit a remarkable shift from 41- to 100-kyr cycles across the mid-Pleistocene transition (MPT), whereas other proxy records (e.g. 13C of loess carbonate, pollen concentration in lake sediments, and magnetic mineral compositions in marine sediments) display strong and persistent precession cycles through the Quaternary, along with distinct 100-kyr cycles after the MPT. Simulations with the HadCM3 climate model reveal that the effects of orbital parameters, ice volume, and CO2 concentration on the temperature, precipitation, and southerly winds are seasonally and spatially different in East Asia. In the summer season, orbitally induced insolation plays a dominant role in driving changes in these three climate variables except for summer precipitation in south China (20-30ºN), whilst annual changes in precipitation and temperature are jointly affected by insolation, ice volume, and CO2. Proxy-model comparison suggests that several land-based proxies are sensitive to changes in summer precipitation, annual precipitation, and annual temperature, though their responses to astronomical, ice, and CO2 forcing being quite different between north and south China. Our proxy-model comparison reveals that diverse expression of Quaternary climate periodicities was provoked by different sensitivities of marine and terrestrial proxies to seasonal and/or annual changes in precipitation and temperature, and by different responses

Disentangling the links between terrestrial vegetation changes and astronomical forcing as well as CO2 is of great help to understand the sensitivity of contemporary vegetation and predict future vegetation and climate changes, yet it remains challenging. Given the distinct differences in astronomical configurations and CO2 concentration between Marine Isotope Stage (MIS) 11 and 13, here we investigate the role of astronomical forcing and CO2 on global vegetation changes during these two interglacials based on transient simulations performed with the model LOVECLIM1.3. Our results show that during these two interglacials, astronomical forcing plays a dominant role on the vegetation evolution, with the effect of CO2 being relatively small. The effect of astronomical forcing on vegetation can be explained successively by the relationship between climate (temperature, precipitation) and the astronomical parameters and by the relationship between vegetation and climate. The relative effect of precession and obliquity on vegetation strongly depends on regions and on interglacials. In general, obliquity plays a more important role on vegetation variations during MIS-11, while precession is more important during MIS-13. Our results also reveal a clear half-precession cycle (~ 10 ka) in the variations of temperature, precipitation and vegetation in the tropical area during MIS-13, as a direct response to the tropical insolation. However, no obvious half-precession cycle is simulated during MIS-11 due to its weak precession variation but large obliquity variation, indicating that half-precession cycle is not stable in time.

Marine Isotope Stage (MIS) 5, between about 130 and 70 ka BP, is a relatively long warm period characterized by climate oscillations consisting of three interstadials and two stadials. In this study, two sets of snapshot simulations by a step of 2 ka covering the whole MIS-5 period are performed with the model HadCM3 to investigate the relative impacts of insolation, CO2 and Northern Hemisphere ice sheets on the internal variations within MIS-5 and spatial variations of the East Asian climate, including the East Asian summer monsoon (EASM) intensity. The first set of experiments are forced by varying insolation and GHGs (OrbGHG) and the second ones are forced by varying insolation, GHGs and ice sheets (OrbGHGIce). Results show that a similar trend with precession can be found in the simulated summer precipitation, temperature and EASM index in both OrbGHG and OrbGHGIce, indicating the dominant role of precession on the EASM. Within the range of CO2 variability during MIS-5, the change of CO2 causes similar degree of warming effect, but much lower degree of humidifying effect compared to insolation. Insolation and CO2 change the precipitation through different dynamic and thermodynamic processes. Our results also show that the influence of ice sheets on temperature and precipitation is less important than the effect of insolation and it varies from regions and in time. The effect of ice sheets depends on background insolation and also the location, height and area of ice sheets. The simulated spatial-temporal variations of the EASM climate are compared with proxy records and the mechanisms involved are investigated.

Marine Isotope Stage (MIS) 5, between about 130 and 70 ka BP, characterized by climate oscillations consisting of three interstadials and two stadials. In this study, two sets of snapshot simulations by a step of 2 ka covering the whole MIS-5 period are performed with the model HadCM3 to investigate the relative impacts of insolation, CO2 and Northern Hemisphere ice sheets on the spatial and temporal variations of the East Asian climate, including the East Asian summer monsoon (EASM). Results show that precession plays a dominant role in the simulated summer precipitation, temperature and the EASM index. Within the range of CO2 variability during MIS-5, the change of CO2 causes similar degree of warming effect but much lower degree of humidifying effect compared to insolation. Insolation and CO2 affect the summer precipitation mainly through dynamic and thermodynamic processes, respectively. Our results also show that the influence of ice sheets on temperature and precipitation is less important than the effect of insolation and it varies from regions and in time. The effect of ice sheets depends on background insolation and also the location, height and area of the ice sheets. The simulated spatial-temporal variations of the EASM climate are compared with proxy records and the mechanisms involved are investigated. The simulated MIS-5 climate is also compared with the present and the future to investigate to which degree it can be considered as an analogue for the future in terms of East Asian climate.

Paleoclimate and paleovegetation reconstructions and simulations of the past interglacials has been paid significant attention, as it facilitates the prediction of future climate changes, especially in a warming world. However, understanding the mechanisms of how astronomical forcing and CO2 influence global climate and vegetation pattern remains challenging. Given the distinct differences in orbital configurations and climate/vegetation variations between MIS-11 and MIS-13, we performed two sets of transient simulations using LOVECLIM 1.3, one driven by insolation change only, and another one by changes in both insolation and CO2. These simulations offer us a good opportunity to investigate the relative effect of astronomical forcing and CO2 on global and regional vegetation changes. Our results show that the effects of precession and obliquity on vegetation depend strongly on regions, and the simulated results are in good agreement with vegetation reconstructions at key regions. The vegetation response differs widely between MIS-11and MIS-13, which is mainly caused by the difference in their astronomical configurations, and the difference in CO2 concentration between these two interglacials plays minor role. In addition to the effect of precession and obliquity, our simulations are also able to capture the half precession signal (~ 10 ka) in the climate and vegetation changes in the tropical regions in response to the tropical insolation.

Numerous studies have been made on paleoclimate and paleovegetation reconstructions and simulations of the past interglacials. However, systematical analysis of the global patterns of the correlation between vegetation pattern and astronomical forcing as well as CO2 between different interglacials is rare. Given the distinct differences in orbital configurations and climate/vegetation variations between MIS-11 and MIS-13, we performed two sets of transient simulations using LOVECLIM 1.3, one driven by insolation change only, and another one by changes in both insolation and CO2. These simulations allow us to investigate the relative effect of astronomical forcing and CO2 on global and regional vegetation changes during these two interglacials. Our results show that the effects of precession and obliquity on vegetation depend strongly on regions, and the simulated results are in good agreement with vegetation reconstructions at key regions. The vegetation response differs widely between MIS-11and MIS-13, which is mainly caused by the difference in their astronomical configurations, and the difference in CO2 concentration between these two interglacials plays a minor role. In addition to the effect of precession and obliquity, our simulations are also able to capture the half precession signal (~ 10 ka) in the climate and vegetation changes in the tropical regions in response to the tropical insolation.

Understanding interglacial climate diversity and intra-interglacial variability can help assess the sensitivity of the Earth system to different forcings during warm periods. This study examines the individual and combined effects of astronomical parameters (obliquity, precession, and eccentricity), Greenhouse gases concentrations and ice sheets as well as internal feedback mechanisms on the East Asian climate during the last nine interglacials. It has been achieved through simulations with an atmosphere-ocean coupled general circulation model HadCM3 using two different approaches. The first approach is to use a Gaussian emulator that was developed based on 61 well-designed HadCM3 experiments, which allows quantifying the sensitivity of the East Asian precipitation and temperature to orbital parameters, CO2 and ice volume during the past 800 ka. The second is to perform two groups of snapshot experiments covering the entire period of each interglacial and by a time step of 2-ka, which leads to 468 experiments in total. Results based on the emulator approach show that in the East Asian summer monsoon domain north of 25° N, the variation of the summer precipitation is dominated by precession, leading to strong 23-ka cycles. However, in the southern part, ice sheets play a more important role than insolation, generating the 100-ka cycles, by influencing the latitude of the Intertropical Convergence Zone and the Hadley cell. Obliquity and CO2 have little effect on the summer precipitation as compared to precession and ice sheets. To study the detailed mechanisms and internal feedbacks involved in the impact of astronomical forcing, GHG and ice sheets on the East Asian climate, MIS-5 is presented as an example. Results show that during MIS-5, astronomical and GHG forcings both have positive effects on the summer temperature and precipitation. Within the range of its variability during MIS-5, CO2 can cause a similar degree of warming effect but much a lower degree of humi, (SC - Sciences) -- UCL, 2022

The relative influence of insolation, CO2, and ice sheets on the East Asian summer monsoon (EASM) is not well understood especially at regional scale. We use a Gaussian emulator based on simulations with HadCM3 to quantitatively assess how astronomical forcing, CO2, and northern hemisphere ice sheets affect the variation of the summer precipitation over the last 800 thousand years. Our results show that in the north of 25° N of the EASM domain, the variation of the summer precipitation is dominated by precession, and ice volume only modulates the effect of insolation through influencing the land-sea pressure contrast. This leads to strong 23-ka cycles in the summer precipitation. In the southern part (south of 25° N),the impact of ice volume becomes more important, leading to strong 100-ka cycles. Ice volume controls the precipitation in the southern part via its dominant control on the location of the Intertropical Convergence Zone and the Hadley cell. The effect of ice volume on summer precipitation depends on background astronomical configurations and vice versa. The relationship between summer precipitation and glaciation level varies among latitudes and for different astronomical configurations. Obliquity and CO2 have little effect on the summer precipitation as compared to precession and ice sheets.

The East Asian summer monsoon (EASM) is an important component of the climate system and it influences about one-third of the world’s population. Numerous paleoclimate records and climate simulations have been used to study its long-term evolution and response to different forcings. The strong regional dependence of the EASM variation questions the relative role of ice sheets and insolation on the EASM precipitation in different sub-regions in East Asia. A Gaussian emulator, which was generated and calibrated by interpolating the outputs of 61 snapshot simulations performed with the model HadCM3, is used to quantitatively assess how astronomical forcing, CO2 and northern hemisphere ice sheets affect the variation of the summer precipitation over the last 800 ky. Our results show that in the north of 25°N of the EASM domain, the variation of the summer precipitation is dominated by precession and insolation. This leads to strong 23-ky cycles in the summer precipitation. However, in the southern part (south of 25°N), the impact of ice volume becomes more important, leading to strong 100-ky cycles. Ice sheets influence the summer precipitation in the south mainly through its control on the location of the Intertropical Convergence Zone (ITCZ) which is very sensitive to ice volume. ITCZ is shifted significantly to the south under large ice sheets conditions. Therefore, the region under control of the ITCZ is more sensitive to the influence of ice volume than other regions. Our results also show that obliquity and CO2 have relatively small effect on the summer precipitation as compared to precession and ice sheets.

The East Asian summer monsoon (EASM) is an important component of the climate system, and it influences the economy and life of a large population. Numerous paleoclimate records have been used to reconstruct the long-term evolution of the EASM. The strong regional dependence of the EASM variation as recorded in various proxy records questions the relative role of ice sheets and insolation on the EASM precipitation in different subregions in East Asia. In this study, we used a Gaussian emulator based on simulations with HadCM3 to investigate the relative importance of the orbital forcing and ice sheets on the summer precipitation in different latitudes of the EASM domain over the last 800 ky. Sensitivity analyses are performed to quantitatively assess the role of different factors. Our results show that a strong precessional signal exists in the long-term variation of the summer precipitation in all latitudes, while precipitation shows a different degree of response to ice volume between the northern and southern part of the EASM domain. In the north of 25°N, the ice sheets only modulate the effect of insolation by influencing the land-sea pressure gradient. Reduced land-sea pressure contrasts lead to a weakening of the EASM. Accordingly, the water vapor flux from the Northwest Pacific, one of the major moisture sources for the EASM precipitation, is also reduced. In the southern part, EASM is more sensitive to the glaciation level. A southward shift of the Intertropical Convergence Zone and the Hadley cell in response to the ice sheet forcing explains the stronger drought in southern China than in northern China. The relationship between precipitation and glaciation level varies for different astronomical configurations, showing the necessity of considering the background astronomical forcing when discussing the effect of ice sheets on the EASM.

Despite significant progress in paleoclimate reconstructions and modelling of different aspects of the past interglacial cycles, the mechanisms which transform the impact of solar insolation variations into long-term and global-scale terrestrial vegetation changes are still not fully understood. Here using the Earth system model of intermediate complexity LOVECLIM, we performed simulations of the coevolution of climate and vegetation during MIS 11 and MIS 13 setting the orbital forcing alone or both orbital forcing and GHGs as external forcings. Through simple and multilinear regression analysis, the results indicate that in most regions worldwide, the climate and vegetation show both obliquity and precession signals during MIS-11 and MIS-13. The amplitude variation of precession is low during MIS-11 but relatively much higher during MIS-13. This leads to a much stronger precession signal in GDD0, precipitation, the tree and grass fraction, and a weaker obliquity signal during MIS-13 than MIS-11. Compared with insolation, CO2 plays a minor role, but it plays a slightly more important role due to the larger amplitude of variation during MIS-13. MIS-11 was a relatively stable interglacial with a long-lasting optimum phase (i.e., generally warmer than PI) during early MIS-11 (lasts till ~ 405 ka BP). Although the available climate/vegetation proxy-based reconstructions show different magnitudes and fluctuation amplitudes in different sites, the peak and abrupt decline events tend to agree with simulation results.

Astronomical and Greenhouse gases (GHG) forcings are two important factors influencing the global and regional climate. However, how climate responds to different configurations of astronomical parameters and GHG is not yet fully understood in particular at regions with complex climate and orographic conditions such as in East Asia. In this study, we investigate the temperature and precipitation response to insolation and GHG in six sub-regions within East Asia during the last interglacial. We performed snapshot simulations every 2 kyr with HadCM3 covering the entire period of the last interglacial. Boundary conditions comprise astronomical parameters and GHG concentrations, while other forcings are kept as PI values. Our results show that the surface air temperature can largely be explained by the direct effect of summer insolation and is positively related to GHG. Temperature shows a consistent and good relationship with precession, obliquity and CO2 concentrations in different sub-regions. However, summer precipitation shows a relatively heterogeneous pattern. In East Asia summer monsoon regions, precipitation is strongly controlled by summer insolation, and the summer monsoon intensity can be explained by land-sea pressure gradient and thermal contrast. In South China Sea, summer precipitation is less directly related to insolation and internal feedbacks are more important. Our results also show that the relative effects of precession, obliquity and GHG on precipitation are different between sub-regions, partly explaining the regional diversity within East Asia.

Orbital parameters and Greenhouse gases (GHG) are two crucial factors influencing the climate at global and regional scales. How climate responds to different configurations of astronomical parameters and GHG is not yet fully understood in East Asia with relatively complex climate and orographic conditions. In this study, we study the separate effects of insolation and GHG on the temperature and precipitation in six sub-regions within East Asia during the last interglacial. We performed a series of snapshot simulations every 2 ka with HadCM3 which covered the last interglacial. Boundary conditions comprise astronomical parameters and GHG concentrations, and other forcings are kept as pre-industrial values. The results show that the summer surface air temperature can largely be explained by the direct effect of summer insolation and is positively related to GHG. Temperature shows a consistent and good relationship with precession, obliquity and CO2 concentrations among different sub-regions. However, summer precipitation shows a relatively heterogeneous pattern. In East Asia summer monsoon regions, precipitation is strongly controlled by insolation, and the monsoon intensity can be explained by land-sea pressure gradient and thermal contrast. In South China Sea, summer precipitation is less directly related to insolation and internal feedbacks are more important. The relative effects of precession, obliquity and GHG on precipitation are different between sub-regions, partly explaining the regional diversity within East Asia. The modeled climate are consistent with the proxy-based reconstruction in general.

The long-term orbital changes have been proved to produce changes in global and regional climate, which arereflected in the geological records. However, the relationships between climate and astronomical parameters arenot yet fully understood at regional scale. Here, based on climate model simulations, we study the climate responseof several sub-regions over Eastern and Southern Asia to continuously changing astronomical parameters underinterglacial conditions (MIS-1, MIS-5, MIS-9, MIS-11 and MIS-19). The outputs are obtained with two methods.The first one is based on the transient simulations using the model LOVECLIM driven by varying insolation forcing(Yin and Berger, 2015). The second one is a Gaussian process emulator (Araya-Melo et al., 2015) calibrated onan ensemble of well-chosen snapshot simulations by the model HadCM3. Data are obtained under the conditionsthat obliquity is fixed, precession is fixed and all the three parameters vary. The results obtained by the two modelsare generally consistent. Among the three orbital parameters, precession is the main factor regulating temperatureand precipitation, and obliquity is a secondary effect. In general, the relative effects of the three astronomicalparameters are quite similar over the selected sub-regions over Eastern and Southern Asia although differencesexist. In order to quantify the individual and combined effects, more sensitivity experiments and regression analysiswill be carried out.

The long-term orbital changes have been proved to produce changes in global and regional climate, which are reflected in the geological records. However, how astronomical parameters influence climate is not yet fully understood at regional scale. Here, based on climate model simulations, we study the climate response of several sub-regions over Eastern and Southern Asia to continuously changing astronomical parameters under interglacial conditions (MIS-1, MIS-5, MIS-9, MIS-11 and MIS-19). The outputs are obtained with two methods. The first one is based on the transient simulations using the model LOVECLIM driven by varying insolation forcing (Yin and Berger, 2015). The second one is a Gaussian process emulator (Araya-Melo et al., 2015) calibrated on an ensemble of well-chosen snapshot simulations by the model HadCM3. In order to assess the individual effects of each parameter, data are also obtained when obliquity and precession vary respectively. The results obtained by the two models are generally consistent. Among the three orbital parameters, precession is the main factor regulating temperature and precipitation. In general, the relative effects of the three astronomical parameters are quite similar over the selected sub-regions over Eastern and Southern Asia although differences exist. In the next stage, more sensitivity experiments and regression analysis will be carried out.

It is noted that certain recurring vegetation patterns appear to be a result of climate changes linked to specific astronomical parameters. However, proxy reconstructions show that the response of vegetation to the astronomical forcing is complex and varies with regions. Our study aims at exploring how the astronomical forcing controls vegetation development in different regions and under interglacial climate. It will be based on a set of transient climate simulations of the interglacials of the last 800 ka performed with the model LOVECLIM where a dynamic vegetation model is included. We will focus on the vegetation response in several key regions from both high latitudes to low latitudes to investigate the regional diversity. By analyzing the components of vegetation in different latitudinal zones and the related changes in precipitation and temperature, which are driven by astronomicallyinduced insolation changes, we intend to discuss the relative role of each astronomical parameter on vegetation at different latitudes and the related mechanisms. Furthermore, through combining proxy studies in specific area, it is expected to get an improved assessment of the relationship between the astronomical parameters and vegetation along the latitudes.

Many proxy and modelling studies have shown that insolation plays a fundamental role in global and regional climate variations. The relationship between climate and astronomical parameters could be complex. This is especially true over Southern and Eastern Asia due to its complex monsoon system that could be significantly influenced by both low and high latitude processes. Indeed, different proxy records from this region show that the climate response to astronomical parameters varies between regions and between climatic variables. However, the mechanisms remain unclear. Based on a series of snapshot and transient climate simulations performed for the last nine interglacials, we investigate how temperature, precipitation and vegetation respond to obliquity, precession and eccentricity in different sub-regions of Southern and Eastern Asia under warm climate conditions and try to understand the differences between different sub-regions and between different proxy records.