“There is an obvious increase in tornado frequency between 1950-1999. This could be due to increased detection. Also this could be due to changing climatic conditions.”

Joe Romm at Climate Progress makes the connection between extreme weather and climate change. That is what happens when green house gases are pumped in the atmosphere: More extreme heat waves, more intense droughts, and stronger deluges. And, yes, more tornadoes. A top climate scientists says it would be irresponsible not to mention climate change about the tornadoes.



 

Romm has an interesting email exchange with several scientists on the climate-tornado link about their thoughts and asks them to weigh in. Here is an excerpt. Romm's comments are in italics:
 

Best info we have on the relationship between a warmer world and severe convective storms that can produce tornadoes is in the 2008 Synthesis and Assessment Report of the US Global Change Research Program. Chapter three of that Weather and Climate Extremes Assessment indicates that several studies do show that environmental conditions favorable for convection are more likely with more greenhouse gases, but results are not conclusive.

We now have improved resolution models running at our Oak Ridge Supercomputer thanks to the Stimulus funding.  We may be  able to make more definitive statements (one way or the other)after these get analyzed over the next few years. Meanwhile, we know that La Nina years tend to have a greater chance of severe outbreaks.  So as usual, there are natural factors that have to be considered, and any human made factors would be confounded within these naturally occurring events making our attribution much more difficult.

Joe, what we can say with confidence is that heavy and extreme precipitation events often associated with thunderstorms and convection are increasing and have been linked to human induced changes in atmospheric composition.

You can find that 2008 Report here.  I wrote about it here (see Sorry, deniers & delayers, Even Bush Administration says human emissions are changing the climate).

Trenberth made clear to me a year ago in an extended interview that he was dismayed by the media coverage of extreme weather, especially extreme deluges, that made no mention whatsoever of global warming:

I find it systematically tends to get underplayed and it often gets underplayed by my fellow scientists. Because one of the opening statements, which I’m sure you’ve probably heard is “Well you can’t attribute a single event to climate change.” But there is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapor lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.

I emailed Trenberth to check his quote in ThinkProgress. He stands by the quote with a little to clarification of the context:

It is irresponsible not to mention climate change in stories that presume to say something about why all these storms and tornadoes are happening.

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