Distilling the Evolving Contributions of Anthropogenic Aerosols and Greenhouse Gases to Large-Scale Low-Frequency Surface Ocean Changes Over the Past Century.

Anthropogenic aerosols (AER) and greenhouse gases (GHG)-the leading drivers of the forced historical change-produce different large-scale climate response patterns, with correlations trending from negative to positive over the past century. To understand what caused the time-evolving comparison between GHG and AER response patterns, we apply a low-frequency component analysis to historical surface ocean changes from CESM1 single-forcing large-ensemble simulations. While GHG response is characterized by its first leading mode, AER response consists of two distinct modes. The first one, featuring long-term global AER increase and global cooling, opposes GHG response patterns up to the mid-twentieth century. The second one, featuring multidecadal variations in AER distributions and interhemispheric asymmetric surface ocean changes, appears to reinforce the GHG warming effect over recent decades. AER thus can have both competing and synergistic effects with GHG as their emissions change temporally and spatially.