Atlantic-Pacific constructive interference drives decadal East Asian Summer Monsoon variations

The East Asian summer monsoon (EASM) has undergone two distinct decadal transitions recently: a weakening in the late 1970s that established the “southern-flood-northern-drought” pattern, followed by a recovery around the late 1990s that shifted the rain belt northward. Yet, why the summer monsoon exhibits such changes in a warmer climate remains debated. Identifying the mechanisms controlling recent monsoon changes is a demanding task, with great societal and economic value across this densely populated region.

Here we examine the relative roles of internal climate variability and external forcing using eight large ensemble simulations, finding that recent observed EASM variations are largely governed by internal variability, whereas external forcing exerts a limited positive effect. Pacemaker model experiments further show that the out-of-phase shifts of Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation play a dominant role in these monsoon changes, through both tropical and midlatitude pathways.