Tug of war on summertime circulation between radiative forcing and sea surface warming

摘要

During summertime, monsoons and subtropical anticyclones shape precipitation and regional circulation patterns across globe. In state-of-the-art climate models, the average response of the Asian monsoon cyclone, Pacific ocean anticyclone and jet stream to global warming is weak and responses of different models are diverse. Here we use a suite of simulations with atmospheric general circulation models with prescribed sea surface temperatures to separate the circulation responses to direct radiative forcing and indirect sea surface temperature warming. We find that the two contributions oppose each other. Using idealized aquaplanet simulations, we show that the different circulation responses are directly connected to the opposite responses of land-sea thermal contrast to the two forcing components. This tug of war on the circulation response to global warming is analogous to the seasonal response to insolation, which involves opposite land-sea thermal contrasts and circulation patterns governed by quasi-equilibrium thermodynamics and stationary-wave dynamics. We conclude that it is important to distinguish weak circulation responses to global warming that arise owing to compensating effects that are robust and physically understood from those that are associated with genuine uncertainty. We note that compensation places fundamental limits on the detection and attribution of circulation responses to global warming.