Large-scale drivers of Northeast Pacific MHWs in a changing climate

The Northeast Pacific Ocean has experienced episodes of intense and persistent warm conditions, also known as marine heatwaves, with devastating ecological impacts. Being able to predict these extreme events a few seasons in advance is therefore very important, but has proven elusive in many cases. While the intensity of Northeast Pacific marine heatwaves has been related to local stochastic atmospheric forcing with limited predictability, their evolution and persistence may be controlled by large-scale climate influences. Here we use a multi-variate statistical approach to identify these large-scale drivers, as well as the initial states that optimally develop into a marine heatwave at a later time in this region. Results indicate that a decadal mode of variability related to the Pacific Decadal Oscillation plays a key role in creating conditions favorable to the development of Northeast Pacific marine heatwaves. This mode is also implicated in the development of Central Pacific El Niño events, which may contribute to the persistence of the Northeast Pacific warm anomalies. In addition, this mode of variability appears to be responsible for the increased Northeast Pacific sea surface temperature variance in recent decades, suggesting that changes in internal climate variability may be responsible for the enhanced MHW activity in this region during this recent period.