“This is climate change. We were warned about extreme weather. Not just hot weather. But extreme weather."That's not a scientifically justifiable statement. But the fact remains that no one really knows the extent to which these storms are affected by climate change -- it's not something science can yet determine, which is very different from saying there is no influence.
Kevin Trenberth said a few years ago, "The environment in which all of these storms and the tornadoes are occurring has changed from human influences."
This is true, by the way, even if the number and types of storms were decreasing. A world with 40% more carbon dioxide is simply not the same world our ancestors lived in.
Jeff Masters said the other day, on PRI:
Every weather event is substantially changed now by climate change. There is more heat in the atmosphere. There is more moisture. And something I've been seeing the last three years is the jet stream patterns have been getting very extreme. I've never seen, in my 30 years as a meteorologist, the sort of unusual sorts of jet stream patterns where we get these large loops, where they tend to get stuck in place, contributing to extreme weather. Whether we're going to be seeing more tornadoes because of that, I don't really know, because when you do change a jet stream like that, you are actually going to slow the winds down of the jet stream. And when you have slower winds, you get less of a twisting motion to get tornadoes spinning. So, in theory, that should decrease tornadoes. But on the other hand, when you have a warmer atmosphere, the air is more unstable, and that's the other key ingredient we need to make tornadoes. How those two factors are going to interplay in the future, we don't know. But I think Dr. Trenberth is right: We have to look at the changed environment that all these sorts of weather systems are in now to look forward to what we're going to see in coming decades.