1. From a Huffington Post article yesterday:
Climate change chatter ran rampant after an unusually violent string of twisters in 2011 (see chart above), including a Joplin, Mo., storm that killed 158 people. After tornadoes took at least 24 lives in Moore, Okla., on Monday, headlines are once again raising the question: Will a warming world fuel more tornado strikes?
Michael Mann, a climatologist who directs the Earth System Science Center at Pennsylvania State University said “If you’re a betting person — or the insurance or reinsurance industry, for that matter — you’d probably go with a prediction of greater frequency and intensity of tornadoes as a result of human-caused climate change.”
Gwen Ingram, an artist and yoga instructor, is one of many Oklahomans who have protested Keystone XL in recent weeks. The proposed project has become a poster child in the climate change debate, and Ingram said she does see a potential connection between climate change and the latest string of tornadoes to rip through her state, which boasts a long history of fossil fuel production and transport.
“They seem to be bigger and more intense,” said Ingram of the local tornadoes.”
2. From a Fox News story yesterday:
California Democratic Sen. Barbara Boxer used part of her Monday floor speech to connect the Oklahoma tornadoes to climate change.
“This is climate change,” she said. “We were warned about extreme weather, not just hot weather but extreme weather. … When I had my hearings … scientists all agreed that what we’d start to see was extreme weather. … It’s going to get hot. But you’re also going to see snow in the summer in some places. You’re going have terrible storms. You’re going to have tornadoes.”
MP: There’s just one small, inconvenient problem with making a connection between climate change and an increasing frequency of violent tornadoes – the link doesn’t actually exist. The chart above displays the annual number of “strong to violent tornadoes” (F3 to F5 on the Fujita Scale) in the US from 1954 to 2012 based on data from the National Oceanic and Atmospheric Administration’s National Climatic Data Center. Here are some weather-related facts:
1. Between 1954 and 2012, there has been a downward trend in the frequency of strong to violent tornadoes in the US, and that decline is statistically significant at the 1% level (see red line in chart). On average, there has been a decline of almost 0.40 violent tornadoes every year since 1954, or a decline of almost 4 violent tornadoes every decade.
2. Although there was a significant number (84) of violent tornadoes in 2011 (which generated responses like this in the Washington Post that claimed a link to climate change), there were actually more violent tornadoes in both 1957 (99) and 1965 (98).
3. In the first half of the sample period from 1954 to 1983, there were nine years when there were more than 60 violent tornadoes, and the annual average was 52 during that period. In contrast, in the second half of the sample from 1984 to 2012 there were only two years when there were more than 60 violent tornadoes, and the annual average was only 37.6.
Bottom Line: The statistical evidence on violent tornadoes, although frequently ignored by the media, politicians, and others claiming a link between violent weather and climate change, suggests that the frequency of violent tornadoes like the recent one in Moore, Oklahoma, has been declining over time, not increasing.