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Proxy records of the East Asia summer monsoon (EASM) and temperature reveal an in-phase relationship of the two since the Last Glacial Maximum (LGM), which is consistent with their expected physical relationship; but the response amplitude of EASM to temperature variation seemed larger over the Holocene than over the last deglaciation. Using a state-of-the-art transient climate simulation, we confirm this proxy-inferred phenomenon, and estimate the "sensitivity of EASM circulation to summer temperature over adjacent region" (defined as S-MT here) is about five times over the Holocene of that over the last deglaciation. This varying S-MT attributed to the diverse S-MT under the solo forcing of orbital insolation and CO2 (eight times of the former vs. the latter), and their varying confounding effect along time. The results presented here should improve our understanding of the past change of EASM, and help project its variation magnitude under ongoing CO2-forced global warming.

Plain Language Summary The East Asia summer monsoon (EASM) dominates the eco-environment of a region where nearly 1.6 billion people live. Its past change pushed the evolution of ancient Chinese culture, and its future change under global warming will force 1/5 of the world population to adapt. Paleoclimate records reveal a robust phenomenon of stronger EASM under a warmer world and vice versa, but the sensitivity of EASM to temperature seemed varying since the last ice age. Climate simulation confirms this phenomenon and illustrates the dominance of forcing (changes in orbital parameter and CO2 concentration) in terms of response magnitude of EASM. Compared to the response of EASM to the orbital forcing in past, the response to ever-growing CO2 forcing is relatively small.