Abstract
Change of global monsoon (GM) during the Last Glacial Maximum (LGM) is investigated using results from the multi-model ensemble of seven coupled climate models participated in the Coupled Model Intercomparison Project Phase 5. The GM changes during LGM are identified by comparison of the results from the pre-industrial control run and the LGM run. The results show (1) the annual mean GM precipitation and GM domain are reduced by about 10 and 5 %, respectively; (2) the monsoon intensity (demonstrated by the local summer–minus–winter precipitation) is also weakened over most monsoon regions except Australian monsoon; (3) the monsoon precipitation is reduced more during the local summer than winter; (4) distinct from all other regional monsoons, the Australian monsoon is strengthened and the monsoon area is enlarged. Four major factors contribute to these changes. The lower greenhouse gas concentration and the presence of the ice sheets decrease air temperature and water vapor content, resulting in a general weakening of the GM precipitation and reduction of GM domain. The reduced hemispheric difference in seasonal variation of insolation may contribute to the weakened GM intensity. The changed land–ocean configuration in the vicinity of the Maritime Continent, along with the presence of the ice sheets and lower greenhouse gas concentration, result in strengthened land–ocean and North–South hemispheric thermal contrasts, leading to the unique strengthened Australian monsoon. Although some of the results are consistent with the proxy data, uncertainties remain in different models. More comparison is needed between proxy data and model experiments to better understand the changes of the GM during the LGM.
Highlights
Objectives of the Paleoclimate Modeling Intercomparison Project Phase 3 (PMIP3) are to understand the mechanisms of past climate changes and to test the capability of the models used for future climate projections to represent a climate different from the modern one (Braconnot et al 2011)
It was found that the Northern Hemisphere summer monsoon (NHSM) intensification is primarily attributed to a Mega-ENSO and the Atlantic Multidecadal Oscillation (AMO), and further influenced by hemispherical asymmetric global warming (Wang et al 2013a)
An important finding is that the NHSM precipitation is enhanced by the increased NH land–ocean thermal contrast and hemispheric thermal contrast and it responds to greenhouse gas forcing more sensitively than Southern Hemisphere summer monsoon (SHSM) precipitation, whereas the SHSM precipitation responds to the solar-volcanic radiative forcing more sensitively than the NHSM precipitation
Summary
Objectives of the Paleoclimate Modeling Intercomparison Project Phase 3 (PMIP3) are to understand the mechanisms of past climate changes and to test the capability of the models used for future climate projections to represent a climate different from the modern one (Braconnot et al 2011). The future change of the GM precipitation and intensity has been investigated (Kitoh et al 2013; Christensen et al 2013; Hsu et al 2013; Chen and Sun 2013; Lee and Wang 2014) using the Representative Concentration Pathways scenarios (RCP4.5 and/or RCP 8.5) for 2006–2100 as projected by models participated in CMIP5. The climate during LGM is quite opposite to the global warming, which can provide a test for the models used to predict future change. We use the simulated results from 7 coupled models participated in the CMIP5/PMIP3 to investigate the characteristics of GM precipitation change under the LGM boundary conditions, and explore the possible causes of the changes.
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