Response of East Asian summer monsoon to precession change during the mid-Pliocene warm period

Numerous palaeoclimatic records have shown that precession plays a dominant role in the Asian monsoon precipitation. However, the impact and mechanism of precession change on the East Asian summer monsoon (EASM) under high CO2 conditions have yet to be studied. The mid-Pliocene (∼3.3–3.0 Ma) was the most recent warm interval during which atmospheric CO2 concentrations were similar to the present level of ∼400 ppmv. Therefore, it is often regarded as an analog for a near-future climate scenario. Here, the influence of precession change on EASM is investigated through numerical climate modeling using the mid-Pliocene as a test case. The results show that from the minimum to maximum of the precession, the summer temperature maximum zone shifted northward from ∼30°N to ∼45°N and the summer precipitation increased by ∼60% over the mainland East Asia. The simulations also show that the top-of-atmosphere insolation increased significantly in the Northern Hemisphere summer over mid- and high-latitudes and increased slightly over low latitudes from the precession minimum to maximum, leading to a substantial increase in the thermal contrast between the mainland East Asia and the equatorial western North Pacific. In this scenario, the western North Pacific subtropical high intensified and expanded, and the ITCZ migrated northward over South and Southeast Asia and was shifted southward over the area between the 110°E and 130°E, thereby leading to the rain belt penetration into northern China.