Key regions in the modulation of seasonal GMST variability by analyzing the two hottest years: 2016 vs. 2020

Abstract

Following the end of the decadal-warming-hiatus in 2016, the global mean surface temperature (GMST) abruptly showed a 3-yr warming slowdown and peaked again in 2020, overturning the conventional concept that highest GMST occurs with strong El Niño. The high GMST in 2016 was controlled by secular trend (SCT) and annual variability (ANV). However, the dominator of the sharp GMST rise in 2020 was SCT alone because the ANVs in different seasons canceled each other out in 2020, contributing little to the annual mean GMST. By analyzing the two hottest years, 2016 and 2020, we identified that seasonally varying ANVs are mainly located in Eurasia, North America, the Arctic Ocean, and the tropical eastern Pacific Ocean. Dominance by surface temperatures over the four crucial regions on the subseasonal-to-seasonal (S2S) GMST variations was also observed in 73% of the years during 1982-2021, indicating a potential opportunity to improve the S2S GMST forecast.