Last updated December 4, 2018

Tornado Risk Increase

Tornadoes are convective storms, born from severe thunderstorms, that feed on warm, moist air from strong winds that change direction with altitude (known as wind shear). While global warming may increase the fuel available for tornadoes, it is not yet possible to determine whether and how climate change may be affecting tornado activity. The mechanics of tornado generation is still not perfectly understood. The available weather reporting data on past tornado activity is limited and makes it difficult to identify whether there have been any long-term trends in tornado frequency, intensity or range. At the same time, climate modeling of tornado activity is not robust enough to confidently determine future trends, though existing modeling projects a greater frequency of the severe weather conditions that might generate more or more severe tornadoes  in the United States. This uncertainty translates as increased risk in a changing climate.

Physical considerations

Storm data indicates that the number of tornadoes per outbreak in the United States may be increasing and that weather extremes associated with severe thunderstorms are similarly on the rise.[1][2] Climate change has been proposed as contributing to these increases; however, the scientific literature is not yet robust enough to link changes in tornado activity to climate change.

Climate model projections indicate that convective available potential energy (CAPE)—a measure of the amount of energy available for convection—would increase in a warmer climate leading to more frequent environments favorable to severe thunderstorms in the United States.[3][4]

However, a December 2016 study links recent increases in the number of tornadoes per outbreak, not to CAPE, but to trends in storm relative helicity,[1] a quantity related to vertical wind shear previously identified as a factor in increased year-to-year variability of US tornado numbers.[2]

The 5 largest U.S. winter tornado outbreaks on record have all hit since 1999 and the uncertainty about the climate change connection translates as an increase risk due to climate change.