The Key Role of Cloud-Climate Coupling in Extratropical Sea Surface Temperature Variability

Cloud radiative effects have long been known to play a key role in governing the mean climate. In recent years, it has become clear that they also contribute to climate variability in the tropics. Here we build on recent work and probe the role of cloud radiative effects in extratropical sea surface temperature (SST) variability. The im-pact of cloud radiative effects on climate variability is explored in "cloud-locking" simulations run on an Earth System Model. The method involves comparing the output from two climate simulations: one in which clouds are coupled to atmospheric dynamic and thermodynamic processes, and another in which clouds are prescribed and thus decoupled from them. The results reveal that cloud-climate coupling leads to widespread increases in the amplitudes of extra -tropical SST variability from monthly to decadal time scales. Notably, it leads to ;40%-100% increases in the ampli-tude of monthly to decadal variability over both the North Atlantic and North Pacific Oceans. These increases are consistent with the "reddening" of cloud shortwave radiative effects that arises when clouds respond to the dynamic and thermodynamic state of the atmosphere. The results suggest that a notable fraction of observed Northern Hemi-sphere SST variability -including that associated with North Pacific and North Atlantic decadal variability -is due to cloud-climate coupling.