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Abstract: Using the results of 25 climate models under the framework of the Paleoclimate Modelling Intercomparison Project (PMIP) and available proxy data, this study examines the regional climate of China during the Last Glacial Maximum (LGM: 21,000years ago). Compared to the baseline climate, results show that annual surface temperature decreased by 2.00°–7.00°C in China during that period, with an average of 4.46°C, for the ensemble mean of all models. Annual precipitation and evaporation during the LGM were 5–40% less than the baseline values, with an average reduction of 20% (0.60mm/day) and a reduction of 21% (0.41mm/day) at the national scale, based on results from 15 out of the 25 models. These models were selected for their ability to simulate the modern precipitation climatology and for the availability of suitable evaporation data. Both the geographical distribution and magnitude of changes in surface temperature, precipitation, and evaporation during the LGM varied with the seasons and with the models, particularly at the sub-regional scale. Model-data comparisons revealed that the 25 models successfully reproduced the surface cooling trend during the LGM, but they failed to reproduce its magnitude in all four regions of comparison, particularly in the Hexi Corridor and in North and Northeast China. The simulations with computed sea surface temperatures (SSTs) were in better agreement with proxy estimates of surface temperature than those with prescribed SSTs. On the other hand, large-scale LGM-minus-baseline anomalies in annual precipitation minus evaporation agreed well, in a qualitative manner, with lake status-based reconstructions of changes in annual water budgets in East China and the region of 35°–42°N, 74°–97°E. On the eastern Qinghai–Tibetan Plateau, drier climates from the 15 models agreed with pollen-based reconstructions. For most parts of West China excluding the Qinghai–Tibetan Plateau, the simulations with computed (prescribed) SSTs are consistent (inconsistent) with reconstructed moister conditions. [Copyright &y& Elsevier]

Identifying potential external forcings on dryland aridity at various timescales and clarifying underlying mechanisms can advance our knowledge of dryland climate behaviors. To address this issue, we examine the past 21 ka using a set of transient simulations driven by realistic climatic forcings, as well as multiple types of proxies. The simulations suggest the evolution of dryland aridity and dominant forcings vary over time and region. On average, global drylands feature two-phase aridification at the orbital scale: the first phase occurs before the Holocene and is dominated by ice sheet melting and rising greenhouse gas (GHG) concentrations, followed by the second phase driven by the summer insolation decrease over northern high latitudes after the early Holocene; different from the wetness during the orbital-scale glacial period, millennium-scale cold events forced by meltwater discharges correspond to desiccation, punctuating the long-term trend during the last deglaciation. In addition, the average aridity changes for drylands are larger than those for global landmasses under all forcings except GHG concentrations. Spatially, the dominant external forcings and aridity responses to the same forcing vary regionally, mainly related to the latitude and hemisphere. Further diagnosis indicates the manners to affect aridity, namely through altering precipitation or evaporative capacity, vary by forcing. The aforementioned evolution of the simulated aridity matches well with the proxies in most dryland zones. This study provides a scenario of time-varying responses of dryland aridity to external forcings over the last 21 ka and may shed light on the future changes. • Dryland aridity over the past 21 ka is examined using simulations and proxies. • It is consistent across simulated aridity index, runoff, and soil moisture. • Dominant external forcings on dryland aridity have varied with time and region. • Aridity changes over dryland are larger than those over the global land. • Simulations match well with proxies. [ABSTRACT FROM AUTHOR]

This study investigates terrestrial moisture changes and associated mechanisms during the last glacial maximum (LGM; approximately 21,000 calendar years ago) using multi-model simulations from the Paleoclimate Modelling Intercomparison Project phase 3 (PMIP3). Considering that terrestrial moisture is not determined solely by precipitation, an aridity index (AI) is employed for measuring the terrestrial moisture by combining the effects of both precipitation and potential evapotranspiration (PET), where the latter represents atmospheric water demand and is greatly decreased mainly by the intense cooling during the LGM. Compared to the preindustrial period, the magnitude of global mean terrestrial moisture change is small, as the wetness brought by decreased PET counteracts the dryness induced by decreased precipitation. Regionally, the moisture changes depend on the different combinations of changes in precipitation and PET: (i) drying occurs where precipitation deceases and PET hardly changes, such as the northern tropical Americas and Southeast Asia; (ii) wetting is found in regions with precipitation increases and PET decreases (e.g., northwestern Africa and the central Andes), and their contributions are comparable; (iii) in particular, wetting can also occur in regions of decreased precipitation if a sufficient decrease in PET also occurs (i.e., southeastern North America and the northern and southern parts of eastern Asia), with the latter wetting effect reversing the former drying effect. The multi-model median field is consistent with available paleo-records in southern North America, the northern tropical Americas, the Andes, northwestern Africa, the southern Iberian Peninsula, southwestern Africa, the central part of eastern Asia, and Java but disagrees with proxies in Australia, central Brazil, southeastern Africa, the northern Iberian Peninsula, and the southern part of eastern Asia. [ABSTRACT FROM AUTHOR]

The last glacial maximum (LGM, ca. 21,000 years ago) has been extensively investigated for better understanding of past glacial climates. Global-scale monsoon changes, however, have not yet been determined. In this study, we examine global monsoon area (GMA) and precipitation (GMP) as well as GMP intensity (GMPI) at the LGM using the experiments of 17 climate models chosen from the Paleoclimate Modelling Intercomparison Project (PMIP) according to their ability to reproduce the present global monsoon climate. Compared to the reference period (referring to the present day, ca. 1985, for three atmospheric plus two atm–slab ocean models and the pre-industrial period, ca. 1750, for 12 fully coupled atmosphere–ocean or atmosphere–ocean–vegetation models), the LGM monsoon area increased over land and decreased over the oceans. The boreal land monsoon areas generally shifted southward, while the northern boundary of land monsoon areas retreated southward over southern Africa and South America. Both the LGM GMP and GMPI decreased in most of the models. The GMP decrease mainly resulted from the reduced monsoon precipitation over the oceans, while the GMPI decrease was derived from the weakened intensity of monsoon precipitation over land and the boreal ocean. Quantitatively, the LGM GMP deficit was due to, first, the GMA reduction and, second, the GMPI weakening. In response to the LGM large ice sheets and lower greenhouse gas concentrations in the atmosphere, the global surface and tropospheric temperatures cooled, the boreal summer meridional temperature gradient increased, and the summer land–sea thermal contrast at 40°S – 70°N decreased. These are the underlying dynamic mechanisms for the LGM monsoon changes. Qualitatively, simulations agree with reconstructions in all land monsoon areas except in the western part of northern Australia where disagreements occur and in South America and the southern part of southern Africa where there is uncertainty in reconstructions. Simulations do not support an inter-hemispheric anti-phasing of monsoon intensity change as suggested by proxy data. [ABSTRACT FROM AUTHOR]

Abstract: Many efforts have been made to reconstruct the moisture conditions over China during the mid-Holocene, approximately 6000 calendar years ago. However, most of them have been performed at the single site level or local scale, and the nationwide distribution of the mid-Holocene precipitation and net precipitation (precipitation minus evaporation) changes from both proxy data and simulations remains unclear. Here we first selected 36 out of 51 climate models participating in the Paleoclimate Modeling Intercomparison Project (PMIP) for their demonstrable ability to simulate the baseline climate and for the availability of evaporation data. Our analysis of the ensemble mean results of the 36 models shows that the mid-Holocene annual precipitation, evaporation, and net precipitation were 3.0%, 0.9%, and 6.9% more than the baseline period, respectively, and seasonally all three variables decreased in boreal winter and spring but increased in boreal summer and autumn on the national scale. For that period, both the pattern and magnitude of the above changes differed between the models and the sub-regions, and the interactive ocean effect had little impact overall on the country. Compared with the wetter-than-present climates derived from the records at 64 out of 69 sites across China, the models agreed qualitatively with the multi-proxy data in most parts of China, except Xinjiang and the areas between the middle and lower reaches of the Yangtze and Yellow River valleys, where drier-than-baseline climates were obtained from the 36 models. [Copyright &y& Elsevier]