The Effect of Climate Change on Tornado Frequency and Magnitude

Michael Pateman and Drew Vankat



Our research project concerns the phenomena of tornadoes, their frequency and magnitude, and possible correlations between that and climate. Investigations will be made into the effect of events such as El Nino and La Nina in regards to tornado occurrence and strength. Research will be conducted with data from 1950 to 1999, and in several geographic regions: Texas, Nebraska, and Ohio. We hope this will give us both a broad overview of the topic, as well as more localized data showing what happens to locations regularly experiencing tornadoes, and those that lack much pronounced tornado activity. Relationships in our data could assist authorities in preparation for aid to families and businesses, as well as further strengthen the belief that we must reduce emission of harmful pollutants into the environment.

Results from data show a stronger correlation in tornado magnitudes by state over the 1950-1999 time period, as well as in El-Nino and La-Nina years. This suggests that those events affect our three states in similar manners.

Results pertaining to frequency are less conclusive, as p-values tend to either be split a slight tendency to show a significant difference in data sets and rank orders, as detailed in our report. This means that there is a lack of strong evidence to relate tornado frequency to El-Nino or La-Nina years. Variations in this generalized conclusion are detailed in the results and conclusion sections.


Tornadoes have struck every U.S. state, including Alaska and Hawaii. But most tornadoes form in a belt from Nebraska southward through central Texas known as Tornado Alley and in the Southeast. Wind speeds in tornadoes can vary from 72 to almost 300 mph.

When the El Nino/Southern Oscillation peaked in 1997 and 1998, much talk was given to the theory of global warming and its possible connection to an increase in extreme weather. In some areas of the United States, tornadoes are and have been a serious risk to property and lives. Are tornadoes a part of this web of phenomena possibly related to the theory of global warming? Could a possible increase or decrease (depending on the area) be an indicator of global warming?

Our hypothesis is that the increase in greenhouse gases plays a role in the formation of tornadoes. This means that we are experiencing more tornadoes and tornadoes of greater magnitude as a result of both global warming and strengthened cycles such as El Nino and La Nina. We are cautious, however, not to underestimate the advances in forecasting and detection technology which may have led to an increase especially in the number of tornadoes reported.