Detecting anthropogenic effects on the record-warm northwestern Pacific sea surface temperature in August 2020

<p>August 2020 set a new record high sea surface temperature (SST) in the northwestern Pacific (NWPac; 120&#176;E&#8211;180&#176;E, 20&#176;N&#8211;35&#176;N). This anomalous condition potentially intensified tropical cyclones such as Typhoon Haishen, causing severe damage to the Korean Peninsula and Japan. Although the NWPac Ocean has gradually warmed due to human-induced greenhouse gas emissions since the mid&#8208;20th century, the extent to which anthropogenic climate changes increase the occurrence likelihood of such regionally unprecedented warm SSTs is unclear yet. Here we analyzed the historical and SSP2-4.5 scenario simulations of CMIP6 and DAMIP as well as observational datasets. Our results show that owing to historical anthropogenic forcing, the occurrence probability of the 2020 record-warm NWPac SST is increased from once-in-1000 years to about once-in-15 years in 2001-2020. As warming caused by greenhouse gases was largely canceled by aerosol cooling, anthropogenic effects on the NWPac SST were not distinguishable from internal variability in the 20th century. The SSP2-4.5 scenario simulations also indicate that the 2020 record-warm SST is becoming a new normal climate condition of August by 2031&#8211;2050, or once the global air temperature above preindustrial level exceeds 1.5&#176;C.</p>