Drivers of Marine Heatwaves in a Changing Climate

Marine heatwaves are periods of extreme sea surface temperatures (SSTs) which can have serious ecological and socioeconomic impacts. From a shifting baseline perspective, future changes to marine heatwaves statistics are almost entirely a result of changes to SST variance. The projected changes to SST variance in the future climate are spatially heterogeneous, with some areas experiencing less variance in the future, and others increased variance in the current generation of climate models. Moreover, the pattern of SST variance change differs between climate models. To determine the physical mechanisms behind these changes, we used a local linear stochastic-deterministic conceptual model to attribute the projected SST variance change in the extratropics to three drivers: ocean memory, El Niño-Southern Oscillation (ENSO) teleconnections, and stochastic noise forcing. We found that climate models generally agree that ocean memory will decline, resulting in decreased SST variance. Models also generally agree that the variance of the noise forcing will increase, resulting in enhanced SST variance. Changes to the ENSO teleconnection differ greatly between models, likely as a result of the substantially different future changes to ENSO in different models.