Amplification of tropics-wide SST contrast under global warming

Abstract

The contrast between SSTs in the convective and non-convective regimes of the tropics is closely coupled to the tropical atmospheric temperature structure. Prevailing theory for the tropical atmosphere suggests that this warm-cold contrast is the aspect of the tropical SST pattern most related to tropics-wide top-of-atmosphere fluxes, providing a potential mechanism for a tropical SST ‘pattern effect’ (Stevens et al. 2016). However the response of the tropical cold-warm contrast to an increase in atmospheric CO 2 is unknown. Here we quantify it for the first time. We find that in models and observation-based products over the historical period, and in the simulated response to a CO 2 increase, the warm-cold contrast increases. This increased contrast in response to abrupt quadrupling of atmospheric CO 2 is linked to a wind-induced pattern of latent heat flux. This organized change in wind speed represents an enhancement of the mean pattern in wind speed (surface winds are low in the convective regime which is characterized by low-level convergence). The amplified patterns in wind and SST are accompanied by amplified patterns in cloud radiative effect and precipitation which may suggest a large-scale convective aggregation in the tropics.