Monday, May 2, 2011

Tornadoes and climate change

One of my friends wanted to know what I thought about tornadoes and global warming. Here's my basic line; this applies to any kind of extreme weather.

Temperature is a measure of energy. So higher average temperatures mean that there's more energy in the global system. The function of the climate system is to balance incoming solar radiation and outgoing heat. It does that by moving energy from the equator (where the most radiation comes in) to the poles (where the most heat goes out). Winds — including the winds that cause tornadoes — are one manifestation of moving energy.

Now - you can never attribute any particular weather event, or even a series of apparently related events like these tornadoes, directly to climate change, because weather is so highly variable and chaotic. Only changes in averages are actually climatic.

The relationship between tornadoes and climate is especially hard to analyze since they're highly local phenomena (unlike hurricanes, which occur on a much larger physical scale). This year's tornado series may or may not be the beginning of a trend — we don't know, and we can't know for a number of years. On the other hand, it's certainly plausible that they are part of a trend. Same thing for hurricanes, snowstorms, and other extreme phenomena: we don't know for sure yet, but there's an obvious intuitive connection between higher numbers of more energetic events and increasing energy in the overall climate system.

Laura Gottesdiener did a nice report on this at Huffington Post Green.  Here's an extract:
A 2008 report from the U.S. Global Change and Research Program, a federal interagency research program overseen by the White House Office of Science and Technology Policy, found that more greenhouse gases in the atmosphere could lead to an increase in severe storm conditions that make tornadoes possible. "We can’t say there is a correlation between a specific tornado and global change," said program director Thomas Armstrong. "But the reports do indicate that there is a positive correlation between climate change and the frequency of conditions favorable to the formation" of tornadoes, he said, while stressing that the research is still preliminary.
Sound about right to me. Basically, if you like making bets on low odds, this could be a good one to get in on.

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