In a recent study, climate and weather researchers found that the number of more intense or higher rated tornadoes - EF1-EF5 - tornadoes has not changed, but the number of tornadoes that occur per severe weather outbreak has increased.
Since the 1950s, the number of tornadoes per outbreak has grown from 10 to 15.
2011 Tornado Outbreak
A recent example of such an outbreak occurred in 2011, when 363 tornadoes touched down with many crossing state lines, while others also moved over the border into Canada. Total damages exceeded $11 billion dollars and caused the deaths of 350 people.
There are dozens of tornadoes and tornado outbreaks each year, and their level of intensity varies. The lower the rating of a tornado, the less damage that occurs. The most intense tornadoes, such as the one that occurred in Joplin, Missouri during the 2011 super outbreak, can completely demolish buildings, destroy infrastructure, and hurl heavy objects such as vehicles through the air, turning them into missiles.
Citing these types of outbreaks as tornado factories, the authors indicate that not only has the number of tornadoes increased during the outbreaks, but the chances of such outbreaks taking place has also grown.
— Science (@scienmag) March 3, 2016
Climate Change Impacts on Increased Outbreaks
When asked if the increase in outbreaks and occurrences were related to climate change, lead author Michael Tippett, a climate and weather researcher at Columbia University's School of Applied Science and Engineering and Columbia's Data Science Institute, said researchers are still studying the different ways in which climate change can alter tornado events.
"The scientific community has thought a great deal about how the frequency of future weather and climate extremes may change in a warming climate. The simplest change to understand is a shift of the entire distribution, but increases in variability, or variance, are possible as well. With tornadoes, we're seeing both of those mechanisms at play." -- Michael Tippett
Tippett said he is also curious about what specific elements in the climate system are driving these changes, and indicated that he is still researching that topic, as well.