Increasing Coupling Between NPGO and PDO Leads to Prolonged Marine Heatwaves in the Northeast Pacific

The marine heatwave of 2014/2015 in the Northeast Pacific caused significant impacts on marine ecosystems and fisheries. While several studies suggest that land and marine heatwaves may intensify under climate change, less is known about the prolonged multiyear nature (~2 years) of the Northeast Pacific events. Examination of reanalysis products and a 30‐member climate model ensemble confirms that prolonged multiyear marine heatwaves are linked to the dynamics of the two dominant modes of winter sea surface temperature variability in the North Pacific, the Pacific Decadal Oscillation (PDO), and the North Pacific Gyre Oscillation (NPGO). Specifically, we find a significant correlation between winter warm NPGO anomalies and the following winter PDO arising from extratropical/tropical teleconnections. In the model projections for 2100 under the RCP8.5 scenario, this NPGO/PDO 1 year lag correlation exhibits a significant positive trend (~35%) that favors more prolonged multiyear warm events (>1 ° C) with larger spatial coverage (~18%) and higher maximum amplitude (~0.5 ° C for events >2 ° C) over the Northeast Pacific.