Hai Wang, Xiao-Tong Zheng, Wenju Cai, Zi-Wen Han, Shang-Ping Xie, Sarah M. Kang, Yu-Fan Geng, Fukai Liu, Chuan-Yang Wang, Yue Wu, Baoqiang Xiang, and Lei Zhou

Published in Proceedings of the National Academy of Sciences (PNAS), May 2024

Significance

The period of 2010 to 2020 has witnessed the warmest Northeast Pacific (NEP) sea surface temperatures ever recorded, with several prolonged extreme ocean warming events. Though year-to-year internal climate variability may partially explain the appearance of these events, why they occurred dramatically more frequent remains elusive. We find that the rapid aerosol abatement in China triggers atmospheric circulation anomalies beyond its source region, driving a substantial mean surface warming in the NEP, which provides a favorable condition for extreme ocean warming events. Our findings provide an important insight into the mechanisms of the North Pacific ocean-atmosphere changes, highlighting the need to consider the exacerbated risks arising from a reduction in anthropogenic aerosol emissions in assessment of climate change impacts.

Abstract

During 2010 to 2020, Northeast Pacific (NEP) sea surface temperature (SST) experienced the warmest decade ever recorded, manifested in several extreme marine heatwaves, referred to as “warm blob” events, which severely affect marine ecosystems and extreme weather along the west coast of North America. While year-to-year internal climate variability has been suggested as a cause of individual events, the causes of the continuous dramatic NEP SST warming remain elusive. Here, we show that other than the greenhouse gas (GHG) forcing, rapid aerosol abatement in China over the period likely plays an important role. Anomalous tropospheric warming induced by declining aerosols in China generated atmospheric teleconnections from East Asia to the NEP, featuring an intensified and southward-shifted Aleutian Low. The associated atmospheric circulation anomaly weakens the climatological westerlies in the NEP and warms the SST there by suppressing the evaporative cooling. The aerosol-induced mean warming of the NEP SST, along with internal climate variability and the GHG-induced warming, made the warm blob events more frequent and intense during 2010 to 2020. As anthropogenic aerosol emissions continue to decrease, there is likely to be an increase in NEP warm blob events, disproportionately large beyond the direct radiative effects.

Wang, H., Zheng, XT., Cai, W., et al. 2024. Atmosphere teleconnections from abatement of China aerosol emissions exacerbate Northeast Pacific warm blob events. Proc. Natl. Acad. Sci. U.S.A. 121 (21) e2313797121, https://doi.org/10.1073/pnas.2313797121