The team of the Institute of Atmospheric Physics of the Chinese Academy of Sciences predicted through the study "Past warm periods indicate future changes in the South Asian summer monsoon" that under the future global warming scenario, the South Asian monsoon precipitation will increase overall, especially in the area along the Himalayas.
This important result of global climate change research was published online in the internationally renowned academic journal Nature on the night of May 14th, Beijing time. The corresponding author of the paper, researcher Zhou Tianjun, said that this study revealed the consistency of the South Asian summer monsoon change mechanism under different climate warming backgrounds, and also emphasized the important potential of paleoclimate references in improving the accuracy of future climate projections.
He Linqiang, the first author of the paper, a doctoral graduate of the Institute of Atmospheric Physics, Chinese Academy of Sciences, and a postdoctoral fellow at Columbia University, said that this study combined six past and future warming scenarios covered by the sixth phase of the International Coupled Model Intercomparison Project (CMIP6), including the Middle Pliocene (about 3.3 million to 3 million years ago), the Last Interglacial (about 127,000 years ago), the Middle Holocene (about 6,000 years ago), and the low, medium, and high scenarios of future warming (2071-2100). These warm periods are driven by different external forcing factors, including increased atmospheric carbon dioxide concentrations, increased vegetation and ice sheet retreat, and changes in the Earth's orbit.
The study found that the South Asian summer monsoon showed similar change characteristics in past warm periods and future projections, which are manifested in an overall increase in precipitation in South Asia, a weakening of the monsoon trough circulation in the Bay of Bengal, and an enhancement of the monsoon circulation in the northern Arabian Sea. The increase in monsoon precipitation comes from the increase in atmospheric water vapor content caused by global average warming, and the related thermal terms follow the characteristics of "wetter wetter, drier drier"; on the other hand, it comes from the changes in monsoon circulation driven by the intensified surface warming in subtropical Eurasia and North Africa, which leads to the non-uniform spatial pattern of "dry in the south and wet in the north" in the dynamic terms of South Asia through temperature advection.
The research team further constructed a statistical model based on the physical relationship between the warming characteristics of the past warm period and the changes in the South Asian summer monsoon. Under the future high emission scenario, given the warming characteristics, the changes in monsoon circulation and precipitation predicted by the model and the direct prediction results of the climate model are spatially correlated by about 80% and 70%, respectively.
This shows that although the past warm period and the future warming scenario are driven by different external forcing factors, they still have important indicative value for the future changes of the South Asian summer monsoon. Combined with geological records, the research team predicts that the South Asian monsoon precipitation will increase overall under the future warming scenario, especially in the area along the Himalayas. This will lead to an increase in heavy rainfall events, which will in turn increase the risk of meteorological-derived disasters.
