Scientists look to the mid-Pliocene to learn about the future behavior of the East Asian summer monsoon

The East Asian summer monsoon (EASM) is the most northerly monsoon system and is characterized by its pronounced seasonal march. It is characterized by a gradual shift northward in the rainfall stages, starting with the pre-rainy season in southern China in mid-May and ending in mid-June to mid-July (known as the rainy season in Japan and changma in South Korea). Proceed to. It will eventually spread to northern China by mid-July.

Although the future behavior of this seasonal march remains uncertain, atmospheric CO2 levels (approximately 400 ppm) were similar to today during the mid-Pliocene warm period (approximately 3.3 to 3 million years ago). year ago) was the last time. The continent became vastly greener and the ice sheets decreased. The geography of the land and the composition of ocean basins had changed little, and many flower and animal species were still extant. Therefore, the mid-Pliocene is thought to be a possible future parallel.

However, it remains unclear what the mid-Pliocene can tell us about the future seasonal progression of the East Asian summer monsoon rain belt. A study recently published in the Journal of Climate reveals that the seasonal march of the EASM during the mid-Pliocene, driven primarily by the greening of temperate vegetation and the exposure of tropical shelves, was about 10 days earlier than today. It became.

The study, led by Professor Zhou Tianjun of the Institute of Atmospheric Physics, Chinese Academy of Sciences, synthesizes simulations of multiple source models to understand the effects of atmospheric carbon dioxide, vegetation, and topography on the EASM.

“The seasonal march of the East Asian summer monsoon during the mid-Pliocene may have implications for future changes from a paleoclimate perspective,” Zhou said.

The results showed that the greening of temperate vegetation and the exposure of tropical shelf forests modulate zonal and meridional atmospheric teleconnections, respectively, causing anticyclone anomalies over East Asia. This causes the subtropical high in the western Pacific to move further north, ultimately pushing the monsoon rain belt forward.

As a long-term indirect response to persistent CO2 forcing, greening of temperate vegetation promotes faster seasonal progression. In contrast, the direct effects of CO2 tend to slow the march of this season.

“These findings suggest that future changes in the seasonal march of the EASM will result from a tug-of-war between direct and indirect effects of CO2,” explained Dr. He Linqiang, lead author of the study. did. He received his Ph.D. He received his PhD from the University of the Chinese Academy of Sciences and is currently a postdoctoral fellow at Columbia University.