Trends in the occurrence of pan-Arctic warm extremes in the past four decades

The most recent historic heat wave in Siberia with record-shattering temperatures is a reflection that, as a manifestation of global warming, the Arctic is experiencing more frequent and severe warm-temperature extremes that could have global consequences. Here, we apply the self-organizing map (SOM) clustering method to 6-hr data from ERA-Interim from 1979 to 2017 to document the spatial and seasonal variations of the trends in the number of warm-extreme days over the pan-Arctic region, and to apportion the trends into a dynamic component representing changes in atmospheric circulation patterns, a thermodynamic component not directly related to circulations, and an interaction component. We show significant upward trends in the occurrence of warm extremes across much of the Arctic Ocean in all seasons except for summer when regions of significant upward trends move from the Arctic Ocean to the Canadian Arctic Archipelago, Greenland, and the northern North Atlantic. The direction and magnitude of the trends in seasonal warm extremes as well as their seasonal and spatial variations are dominated by the thermodynamic component, with the dynamic component and the interaction component at least an order of magnitude smaller. Although negligible to the long-term, pan-Arctic averaged trend, the dynamic component may be comparable with, or even larger than, the thermodynamic component at some locations and under certain atmospheric circulation patterns.

Automated summary

The study shows that the occurrence of warm extremes in the Arctic region is significantly increasing in all seasons except for summer. The direction and magnitude of these trends are mainly influenced by the thermodynamic component, with the dynamic component and the interaction component being relatively smaller.