Ongoing intensification of El Niño impacts on East Asia's summer climate with achieved carbon neutrality

Abstract A notable anomalous lower-tropospheric anticyclone appears over the western North Pacific (WNP) during post-El Niño summer, exerting a profound influence on the East Asia summertime climate. Here, we employ a suite of global climate model projections under symmetric CO₂ ramp-up (RU) and ramp-down (RD) scenarios to reveal the asymmetric response of the WNP anticyclone (WNPAC). Our results demonstrate a progressive strengthening of the WNPAC with rising CO₂ concentrations, a trend that persists as CO₂ declines, followed by gradual recovery, and the anomalous anticyclone fails to return to its initial state when CO₂ concentrations return to pre-industrial levels, attributed to Indo-Pacific zonal SST gradient variations. In contrast to the CO₂ RU phase, the increased zonal SST gradient is witnessed in the CO₂ RD phase, favoring anomalous moisture convergence over the Maritime Continent (MC). This strengthens the WNPAC through Kelvin wave-induced Ekman divergence or local Hadley circulation adjustment. The increased zonal SST gradient is associated with strengthened SST warming in the MC and accelerated decay of El Niño-related positive SST anomalies in the equatorial Central Pacific, ultimately attributed to a climatological equatorial Pacific El Niño-like warming pattern driving intricate air-sea interactions and processes. Our findings indicate that the overshoot of the WNPAC during the CO₂ RD phase may exacerbate the flood and high temperature risks in densely populated East Asia.