Atmospheric CO2 Forcing and Subsequent Sea Surface Warming

4 The early summer regional climate change of the East Asian summer monsoon (EASM) is 5 investigated in the Coupled Model Intercomparison Project – Phase 5 (CMIP5) archive. In 6 the greenhouse gas forced scenario, reduction of radiative cooling and increase in continen7 tal surface temperature occur much more rapidly than changes in sea surface temperatures 8 (SSTs). Without changes in SSTs, the early summer rainfall in the monsoon region decreases 9 (increases) over ocean (land) in most models. On longer timescales, as SSTs increase, rainfall 10 changes are opposite. The total response to atmospheric CO2 forcing and subsequent SST 11 warming is a large (modest) increase in rainfall over ocean (land) in the EASM region. Dy12 namic changes, in spite of significant contributions from the thermodynamic component, play 13 an important role in setting up the spatial pattern of precipitation changes. Early summer 14 rainfall anomalies over East China are a direct consequence of local land-sea contrast, while 15 changes in the large-scale oceanic rainfall band are closely associated with the displacement 16 of the larger-scale North Pacific Subtropical High (NPSH). Ad hoc numerical simulations 17 with the AM2.1 general circulation model show that topography and SST patterns play an 18 important role in early summer rainfall changes in the EASM region. 19