Was the F5 tornado in Moore, Oklahoma caused by global warming? Probably not. There hasn't been an increase in tornado activity in recent years.
F4 and F5 tornadoes are extremely rare:
Graphs and most images are from Jeff Masters' Wunderblog.
Yes, there is more warm, moist air to power the tornado because of climate change, but there is also less wind shear because of climate change. This is great for hurricane development, but a tornado needs that wind shear. A tornado needs air going at a different direction on the ground vs. in the upper atmosphere in order to create that rolling barrel of air that gets rotated 90 degrees to create the tornado. (See one of Weatherdude's diaries for an excellent description of tornado formation.)
So we have two changes in the climate that are at odds with each other. On the one hand we have warmer, wetter air that helps tornado formation, but on the other hand we have less wind shear that hurts tornado formation.
At this time, we do not have enough data to know which change will have the most effect on tornado formation in the future. One theory is that the distribution over time of strong tornadoes will be less homogeneous. That is, one year will have a lot of tornadoes and another year will have very few. Another change could be to shift the peak tornado activity from June into May.
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