Exploring Connections between Arctic Sea Ice and Tornado Activity in the United States

The significant losses in Arctic sea ice over the past decade appear to have been accompanied by changes in global- and regional-scale atmospheric circulation. Such circulation changes have in turn been used to support arguments that low Arctic sea-ice extent (SIE) has helped to promote extreme weather events within the mid-latitudes. The contemporaneous variability in U.S. tornado incidence over the past decade provides motivation to explore whether the essence of these arguments also applies to tornadoes. Here, we find robust statistical correlations between tornado activity and pan-Arctic SIE during boreal summer, specifically in July; consistently strong correlations are also found using summer SIE over the Barents–Kara Seas, which therefore provides a regional context. These statistical relationships are supported by a physical linkage manifest as a regional circulation anomaly that is unfavorable (favorable) for tornado-bearing thunderstorm formation when SIE is low (high). The anomalous circulation appears to be attributable to sea-ice changes rather than simply to changes in greenhouse-gas concentrations.