Anthropogenic climate change is causing stronger and more extreme western Pacific subtropical high.

Abstract

The western Pacific subtropical high (WPSH) is a crucial system controlling weather anomalies in East Asia. Early studies defined the WPSH using either thermodynamic or dynamic metrics, but these metrics yield inconsistent trends and coverages in WPSH under anthropogenic warming. Subsequently, consensus on the response of WPSH to climate change has not been reached. Here, we investigate the response of WPSH to past and future climate change by developing a novel WPSH definition based on thermodynamic-dynamic synergy, which provides higher trend consistency of WPSH and better spatiotemporal agreement with weather anomalies. Our results reveal robust increases in WPSH area (0.25-1.03 × 10⁵ km²/decade) and intensity (0.35-1.98 × 10⁵ km² gpm/decade), as well as a northwestward extension of WPSH boundary (-0.18 to -0.32 °E/decade), under a warmer climate, which are consistent across datasets and supported by a strong inter-model consensus. Particularly, climate models project an increased likelihood of record-breaking WPSH events on both seasonal and synoptic scales, with stronger intensity, longer durations, and higher occurrences under higher-emission scenarios. The findings indicate an increasing exposure of human societies to intense monsoon rainfall and heatwave risks associated with WPSH beyond historical records.