By Paul Homewood
As regulars will be well aware, I have been reporting the decline in severe tornadoes for a long time now.
This new paper from Roy Spencer and Joe D’Aleo confirms the trend:
Key Takeaways
There has been a 50 percent reduction in strong tornadoes in the U.S. since the 1950s; weak tornado counts increased until 1990 due to better reporting.
When tornadoes do occur, growing population and infrastructure put more property and lives at risk, but growth-normalized tornado damage has decreased since 1950.
These facts do not support claims that increasing greenhouse gas emissions are causing storms to intensify. Modest warming has reduced tornado activity.
This is a particularly interesting graph:
This is the conclusion:
Conclusion
Despite a modest warming trend, the claim that climate change is causing more and stronger tornadoes in the U.S. is unsupported by the relevant trend data. Most notably, tornado frequency has elicited a decline of at least 50 percent in all but the weakest tornadoes since the inception of these statistics in 1950. Although the number of weak tornadoes increased from 1950 to 1990, this increase may be in part explained due to an expanding, weather-conscious population increasingly armed with cameras—and that increase stopped more than 30 years ago. Fluctuations in these trends do indeed occur, as can be seen in Charts 3 and 4; however, the fluctuations are largely manifestations of natural climactic cycles, such as El Niño and La Niña.
Tornadoes that once roared through mostly open fields now more frequently devastate areas that have since experienced significant population growth and urbanization. As a result, tornadoes that have struck such areas have indeed resulted in increased damages. But when these damages are normalized with respect to the growing and maturing economy, these increases disappear.
Taken together, these results refute the implication of the Fifth National Climate Assessment that severe storms are becoming more frequent and stronger and causing more damage across the United States. Indeed, the frequency and intensity of tornadoes varies over time, but not due to CO2 emissions. If anything, modest warming in the U.S. has been accompanied by a decrease in strong to violent tornado activity.