Abstract
It is widely accepted that natural decadal variability played a major role in the slowdown in global warming observed in the 21st century, with sea surface cooling in the tropical Pacific recognized as a major contributor. However, the warming pause was most pronounced during boreal winter, with Northern Hemisphere flow anomalies also playing a role. Here we quantify the contribution of extratropical heat exchanges by comparing geopotential and temperature anomalies simulated by ensembles of seasonal forecasts with similar ocean temperature but different heat fluxes north of 40°N, as a result of planetary wave variability. We show that an important part of heat flux anomalies is associated with decadal variations in the phase of a specific planetary wave pattern. In model simulations covering the last three decades, this variability pattern accounts for a decrease of 0.35°C/decade in the post‐1998 wintertime temperature trend over northern continents.
Key Points
Decadal variations in heat fluxes over the northern oceans are related to planetary wave patterns
Contributions to winter temperature trends are estimated from large ensembles of seasonal forecasts
Differences in warming trends induced by planetary wave variability reach 0.35 degrees Celsius/decade over northern continents