Our Extraordinary Tornado Year

Tornadoes are the new hurricanes.

That's what I can't help thinking as I read blog posts like Jeff Masters' recent offering discussing the "record early season onslaught of tornadoes" we've seen thus far in 2008.

There were 368 documented U.S. tornadoes in January and February of this year. The previous record for that two month span? 243, in 1999.

February 2008's 232 tornadoes was also a record.

The number of tornadoes in 2008 so far far outpaces that of any of the past three years. However, Tornado numbers for 2008 are likely to be overestimated at this point, due to duplicate reports for the same tornado.
Storm Prediction Center - Warning Coordination Meteorologist

All this reminds me of the 2004 and especially the 2005 Atlantic hurricane seasons – when our weather started breaking every record in sight, and we suddenly got 4 Category 5 hurricanes in a single year and 28 total storms, vastly surpassing the previous record of 21.

Inevitably, this all this tornado activity sparks global warming talk; inevitably, it's complicated. Masters writes, "It will be at least 10 more years before we can say with any confidence that a warming climate is leading to an earlier peak in tornado season." He adds that the current La Nina in the Pacific is probably helping prompt this record early year tornadic activity – and nobody that I know of thinks the current La Nina has anything to do with human induced-climate change.

In a previous, more thorough post, Masters is even more pessimistic about reaching reliable conclusions on the relationship between tornadoes and climate change. The trouble is that tornadoes are ephemeral, hard to detect, easy to miss if there's no one around. As Masters notes:

Until a technology is developed that can reliably detect all tornadoes, there is no hope of determining how tornadoes might be changing in response to a changing climate. According to Doswell (2007): I see no near-term solution to the problem of detecting detailed spatial and temporal trends in the occurrence of tornadoes by using the observed data in its current form or in any form likely to evolve in the near future.

Still, it is certainly possible at least to anatomize the problem. If we want to know if tornadoes are changing as a result of climate change, it helps to think about precisely what sorts of changes we might see.

Consider: Tornadoes might change in number. Alas, since we can't detect all tornadoes, it will be very hard to prove this.

Or tornadoes might become more intense on average. The strongest tornadoes, EF4s and EF5s, are the least likely to go undetected, for obvious reasons – but currently, we do not see a trend in these storms.

But still, that's not all. In addition to changes in storm numbers or intensities, tornado season might change – e.g., we might get more storms earlier in the year, so more years will be like this year. Or, there might be other types of changes as well – tornado distribution, etc.

It's all exceedingly complicated, and unlikely to find resolution soon.

But as Masters points out, peering at the data isn't our only way of looking at tornadoes and how they might change. Climate model simulations can also project how global warming will change the conditions that cause tornadoes, and thus provide plausible, if hardly definitive, answers about future severe storm activity – just so stories, if you will, showing particular results for particular assumptions.

Right now, these type of studies do suggest that we may see "an increase in the number of severe storms capable of producing tornadoes over the U.S. late this century." But there's much more work to be done before that conclusion can be considered a very solid one; this is pretty new field.

So if you want to know what global warming is doing to tornadoes ... well, I'd say spend some time with your kids. Watch them grow up. Then, check back in a few years.