第二届未来大气科学论坛

The response of tropical sea surface temperature (SST) to global warming significantly influences both global and regional climates, so it receives immense attention and keeps debated. Most previous studies have focused on the hotly-debated zonal SST gradient changes in the tropical Pacific, which is marked by discrepancies between observations and models. Climate models tend to project a weakening of the zonal SST gradient (i.e., an El Niño-like change) and Walker Circulation under greenhouse gas forcing, while observations show a La Niña-like change during past several decades. Here, based on observations and CMIP6 models, including all forcing and single-forcing experiments, we found that theenhanced equatorial warming (EEW) is a more robust response to global warming compared to the Pacific zonal SST gradient in the historical period. In particular, the EEW has emerged in the Atlantic since 1950s, which is primarily attributed to greenhouse gas (GHG) forcing. The formation of EEW is driven by weakened equatorial upwelling, resulting from the slowdown of equatorial zonal winds. The identification of Atlantic EEW as a fingerprint of global warming has important implications for understanding changes of the tropical oceans in a warming climate and the associated impacts. 
In the Indian Ocean, the positive Indian Ocean Dipole-like (pIOD-like) warming pattern, with stronger warming in the western than the eastern Indian Ocean, has emerged in observations during 1979-2020. GHGs make a major contribution to the observed pIOD-like warming pattern through weakening the Walker circulation, with anthropogenic aerosols also contributing through the local ocean-atmosphere interaction driven by the increased aerosol emissions from South Asia. Before the satellite era (1920-1978), although GHG forcing favors the pIOD-like warming pattern, the increased aerosol emissions from Northern Hemisphere offset the contribution of GHGs via influencing the inter-hemispheric temperature contrast, resulting in an insignificant pIOD-like warming pattern in observations. This study highlights the importance of the combined effects of GHGs and anthropogenic aerosols in the recent emergence of pIOD-like warming pattern.

温室气体，气溶胶，热带大洋，海气相互作用