Chapter 12 - Responses of the Indian Summer Monsoon and the East Asian Summer Monsoon to Different Land–Sea Temperature Increases under a Warming Scenario

Abstract

In this chapter, the responses of the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM) circulations to different warming over land and oceans under a medium warming scenario were evaluated based on the simulation of climate models that participated in the fourth assessment of the Intergovernmental Panel on Climate Change. Our results suggest that, even though near-surface warming over the Tibetan Plateau (TP) is greater than that over the tropical Indian Ocean (TIO) and the western North Pacific (WNP), the upper-tropospheric land–sea thermal contrasts between the TP and the TIO (TP–TIO) and between the TP and the WNP (TP–WNP) will decrease. At interdecadal and longer timescales, the change in the ISM circulation is consistent with the TP–TIO upper-troposphere thermal contrast. Conversely, the change in the EASM circulation is consistent with the TP–WNP lower-troposphere thermal contrast. However, at the interannual timescale, both changes in the EASM and ISM are significantly correlated with the upper-troposphere thermal contrast. Further analyses suggest that increases in moisture and changes in cloud cover induced by global warming may cause amplified upper-tropospheric warming over the TP and the oceans resulting in inconsistent changes in the vertical temperature distribution over these regions. Because the warming over the TIO and WNP is greater than that over the TP, the TP–TIO meridional and TP–WNP zonal thermal contrasts will decrease. However, at the lower layer, the difference in thermal capacity between land and sea results in a larger thermal effect in the near-surface region of the TP than those over the surrounding oceans. We showed that a range of factors that affect thermal conditions will likely cause changes in the Asian monsoon across a range of timescales under a warming scenario. These changes reflect differences in the influence of the greenhouse effect and natural variability.