From the Cliff High Volume Weather Blog
Strong, long-lived tornadoes hit western Kentucky, southern Illinois and the surrounding area Friday night. And within hours, major media outlets, national politicians and some climate activists were claiming that global warming was the partial or major cause.
The head of FEMA spoke of recent tornadoes as part of a “new normal” driven by climate change.
As I will demonstrate below, these claims contradict the best of science and are contrary to respected national and international scientific judgment. Many based on simple arguments show a lack of understanding of the components required for severe convection (thunderstorms) or show a lack of understanding of the historical record.
Are powerful tornadoes on the rise in the US?
The first question one must ask when assessing the role of global warming (or “climate change” as some like it), is whether there is a trend. If global warming is contributing to the frequency or intensity of severe tornadoes, one would expect a trend that extends over many decades.
Below you’ll see a graph of the frequency of strong tornadoes (EF 3, 4, 5) over time for the United States (and note that such powerful tornadoes are pretty much limited to the United States). Plains and SE US) from NOAA/NWS Hurricane Prediction Center. Trend is DOWNLOAD for fstrong tornado. So if there is a “new normal” it is a strong LESS.
Some individuals are showing trends all tornadoes over time, but this is problematic because we are now more likely to observe the weakest tornadoes, many of which were missed 40 to 80 years ago.
Tornado trend data provide strong evidence that claims of an increasing number of powerful tornadoes are unfounded. And even if they are increasing, one will have to prove that global warming is the cause.
There have been proposals, based on a piece of paper, that there is a tendency towards change allotment tornadoes of the United States (more east of Mississippi), probably due to global warming,
However, this paper doesn’t really look at changes in tornado frequency, but rather trends in an indirect indicator known as the STP. They do not consider changes in the frequency of strong storms and use the total number of tornadoes at issue as a verification parameter. I could go into more technical details, but this reference is very weak support for any claim that global warming is causing more severe tornadoes around Kentucky.
What do international and national assessments by the scientific community suggest about the link between global warming and tornadoes in the US?
They are pretty clear: there is little evidence to connect global warming to the frequency of severe tornadoes in the US
The Latest IPCC (Intergovernmental Panel on Climate Change) status report:
- “Typonic trends … associated with severe convection storms are not clearly detected”
- “The distribution of certain types of severe weather (e.g. tornadoes) is beyond current modeling and theoretical capabilities”
- “How will tornadoes … change is an open question”
The fourth US National Climate Assessment notes:
“The observed and projected trends in future changes in severe thunderstorms, tornadoes, hail, and high winds are uncertain.”
Claims Not Backed By Science or Data
One of the great frustrations for scientists like me is when lay people make claims that are not supported by rigorous scientific reasoning or facts. Statements related to tornadoes and climate are prime examples.
One common claim is that climate change is making the weather more extreme, and thus one can expect more severe tornadoes. Climate change does NOT make all extreme weather more extreme. And it has different effects on key components of severe thunderstorms in the United States
Others argue that warming temperatures produce more powerful thunderstorms and therefore more tornadoes.
I fear the physical world is not so simple. These individuals and media are making claims without theoretical or observational support.
Tornadic Storm Requires a Complex Chain of Conditions
Strong tornadoes are rare for one reason: a very complex set of simultaneous conditions are needed to create them:
- Strongly unstable atmospheres are essential, with temperatures dropping rapidly with altitude.
- A large variation of winds with altitude (wind shear) is important, both for allowing storms to become intense and to induce rotation in supercell thunderstorms, the parent of events. most severe tornado.
- And one needs upward or upward motion to release instability, and this can be from the strong front or the upper deck trough or the jet trail.
And there are more requirements than I won’t go into here.
Merely warming the surface is not enough to enhance the development of severe thunderstorms.
Good evidence for this is provided by a map showing the climate of tornadoes around the planet. Cyclones do not occur infrequently in warm, humid tropics where large and frequent thunderstorms occur. Essential ingredients are missing.
Therefore, the claim that warming will produce more severe tornadoes should be considered a large grain of salt… Severe tornadoes depend on a range of requirements, some of which can be also weaken with global warming
Finally, let me note that even claims of local warming matter. For example, we’re in for a mild La Nina year, creating warmer-than-normal conditions in the southeastern US Blaming it all on global warming is a big problem. .
Key point
Claims that the severe tornadoes that occurred last Friday night were the result of global warming/climate change have little basis in the scientific literature or in meteorological observations. The observed trends contradict the statements. No such conclusion has been reached by leading scientific groups (eg, IPCC).
Unfortunately, it’s a prime example of the politicization of weather and climate, leading to population fear and lack of action on critical protective technologies, such as improved construction and Better warning.
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