Tornadoes and Climate Change

Cross-posted from NextGen Journal

It has been a bad season for tornadoes in the United States. In fact, this April shattered the previous record for the most tornadoes ever. Even though the count isn’t finalized yet, nobody doubts that it will come out on top:

In a warming world, many questions are common, and quite reasonable. Is this a sign of climate change? Will we experience more, or stronger, tornadoes as the planet warms further?

In fact, these are very difficult questions to answer. First of all, attributing a specific weather event, or even a series of weather events, to a change in the climate is extremely difficult. Scientists can do statistical analysis to estimate the probability of the event with and without the extra energy available in a warming world, but this kind of study takes years. Even so, nobody can say for certain whether an event wasn’t just a fluke. The recent tornadoes very well might have been caused by climate change, but they also might have happened anyway.

Will tornadoes become more common in the future, as global warming progresses? Tornado formation is complicated, and forecasting them requires an awful lot of calculations. Many processes in the climate system are this way, so scientists simulate them using computer models, which can do detailed calculations at an increasingly impressive speed.

However, individual tornadoes are relatively small compared to other kinds of storms, such as hurricanes or regular rainstorms. They are, in fact, smaller than a single square in the highest-resolution climate models around today. Therefore, it’s just not possible to directly project them using mathematical models.

However, we can project the conditions necessary for tornadoes to form. They don’t always lead to a tornado, but they make one more likely. Two main factors exist: high wind shear and high convective available potential energy (CAPE). Climate change is making the atmosphere warmer, and increasing specific humidity (but not relative humidity): both of these contribute to CAPE, so that factor will increase the likelihood of conditions favourable to tornadoes. However, climate change warms the poles faster than the equator, which will decrease the temperature difference between them, subsequently lowering wind shear. That will make tornadoes less likely (Diffenbaugh et al, 2008). Which factor will win out? Is there another factor involved that climate change could impact? Will we get more tornadoes in some areas and less in others? Will we get weaker tornadoes or stronger tornadoes? It’s very difficult to tell.

In 2007, NASA scientists used a climate model to project changes in severe storms, including tornadoes. (Remember, even though an individual tornado can’t be represented on a model, the conditions likely to cause a tornado can.) They predicted that the future will bring fewer storms overall, but that the ones that do form will be stronger. A plausible solution to the question, although not a very comforting one.

With uncertain knowledge, how should we approach this issue? Should we focus on the comforting possibility that the devastation in the United States might have nothing to do with our species’ actions? Or should we acknowledge that we might bear responsibility? Dr. Kevin Trenberth, a top climate scientist at the National Center for Atmospheric Research (NCAR), thinks that ignoring this possibility until it’s proven is a bad idea. “It’s irresponsible not to mention climate change,” he writes.

4 thoughts on “Tornadoes and Climate Change

  1. What a clear, elegant posting.

    The controversy is more about human psychological denial than it is about climate science or statistics.

    I predict and escalation of cognitive dissonance – consistent with destabilizing weather.

    Thanks for this.

  2. John Hartz asks “Is the advent of tornadoe season in the US occurring earlier now than it has in the past?”.

    I think this is the kind of a good question that could possibly be answered even with current data, though I haven’t seen no one taking a look at it yet. Or possibly tornado researches have looked at it, but wait until they get the results more robust, what ever they are.

    What I’ve gathered of the climate change, as the oceans hold much of the additional heat, this may well produce a sharp temperature difference between coastal areas and the interiors of the continents. F.e. the as the Arctic Ocean (Sea of Northern Lights) warms up the interior of the Siberia still would stay rather cold in the winter, mainly because it’s easier to have a high-pressure area over land than over the ocean (why was that again, anybody? Is it just because of the orographic lift?). This way the potential for more rapid frontal changes over land could be a result, but the difficulty is that a rapid frontal change may as well be relatively easy wrt winds/storm activity.

    I’m not sure that’s correct, as land warms faster than water. The ocean is absorbing much of the heat, but that’s because there’s so much water. Per unit area, continents warm more.

    It’s also difficult to say whether or not there have been trends in tornado occurrence/timing/etc, simply because the record keeping hasn’t been very good until recently. -Kate

    A related question to your question is also “has the end of the tornado season moved earlier?”, which could also be a result of the warmed up globe.

  3. Thanks for the response, I should try to source that bit of info, it was something I recall reading or hearing but not sure if my recollection is accurate. Maybe it was only for some areas on the planet.

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