Increasingly Powerful Tornadoes

Storm reports over the past few decades show a clear trend toward more powerful tornadoes from longer and wider paths and higher damage ratings. Quantifying the magnitude of this increase is important for understanding its possible connection to climate change but doing so is difficult given strong diurnal and seasonal influences on tornado activity embedded within large natural variations. The problem is made worse by changes in procedures for rating storm damage. Here we solve this problem by fitting a statistical model to a metric of power using all tornado reports since 1994. We find a substantial increase of 5.5% [(4.6, 6.5%), 95% CI] per year in power controlling for the diurnal cycle, seasonality, natural climate variability, and the switch to a new damage scale. Further we find that a portion of the trend is statistically attributable to rising ocean temperatures across the Gulf of Mexico and western Caribbean Sea. Results support the hypothesis that with added instability from more heat and moisture in a warming world tornadoes are becoming more powerful qualitatively consistent with climate models showing increasingly favorable conditions for stronger tornadoes with higher concentrations of greenhouse gases.