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Tornado doom then tornado drought: Both linked to climate change?

We are living through the most anemic one-year period for tornadoes in the modern record – a cause for celebration if you dislike human suffering and destruction. The present lull in these violent storms stands in sharp contrast to 2011, one of the most active years for twisters, with devastating consequences for life and property.

What does this tornado pendulum signify about the effect of climate change on twisters? Probably very little – as far as scientists can tell. As we’ve discussed, the latest research shows connections between climate change and tornadoes are neither well-established nor well well-understood – though more is being learned.

Yet it’s exactly this uncertain state of knowledge about tornadoes and climate that has proven fertile ground for debate about how any connections should be conveyed.

(National Weather Service) (National Weather Service)

Before dissecting the latest climate debate tempest, let’s review some statistics:

* In 2011, the second most tornadoes on record (since 1954) touched down. Through the first 4 months of the year, a record number of 586 tornadoes (EF1+) were counted (more information).

* 551 people were killed by tornadoes in 2011, the most since 1950 and third highest on record according to NOAA (more information).

* Over the last 12 months (May 2012-April 2013), just 197 tornadoes (EF1+) touched down nationally, the lowest such number since reliable records began in 1954 (more information). Fewer than half the average of numbers have been observed in the first 4 months of this year.

* Over the last 12 months (May 2012-April 2013), only 7 people died from tornadoes – the fewest number in a 12-month period since just 5 died between September 1899 and August 1900 (more information).

Clearly, 2011 was a catastrophic year for tornado impacts whereas we’ve dodged the bullet pretty much ever since.

During the height of the 2011 tornado swarm, Kevin Trenberth, a climate scientist at NCAR, said it’s “irresponsible not to mention climate change” as a player in the outbreak in an interview posted on the blog Climate Progress. Climate Progress also quoted Penn State climate scientist Michael Mann who said “Climate change is present in every single meteorological event…”

So if climate change was a player in the 2011 tornado boom, is it now also a player in the current tornado bust? New York Times’ science blogger Andrew Revkin posed this question on Twitter:

Penn State’s Mann responded to Revkin’s tweet by accusing him of “concern trolling“, or essentially manufacturing a question to score points with climate change skeptics :

Mann is understandably frustrated that Revkin doesn’t seem to grasp a point that both he and Trenberth have made repeatedly: elevated greenhouse gases have fundamentally changed the environment in which the weather operates. So whether tornado activity is elevated or depressed, climate change is having an effect.

But I can also appreciate where Revkin is coming from. Irrespective of the merits, scientists may walk down a slippery slope when they make strong statements about climate change and fluctuating, short-lived weather phenomena. For their part, tornadoes have so much natural variability and so many different causes, that comments linking a flare-up in activity to climate change can backfire when they hit a lull. Without a convincing explanation, skeptics will criticize and poke fun at such linkages when the apparent linkage vanishes.

Eric Berger, science writer at the Houston Chronicle, put it this way:

…overstating the severity of some consequences (i.e. linking the 2010-2011 tornado outbreak to climate change) only emboldens willful skeptics who would hold the very real uncertainty of some aspects of climate change science as a quarterstaff upon the credibility of its general conclusions.

Ultimately, Mann/Trenberth and Revkin/Berger all have justifiable positions. Yes, the altered environment from rising greenhouse gas concentrations has some effect on all of our weather, and extreme weather events offer good teachable moments to communicate this concept. But, yes, natural variability in climate is a powerful influence that scientists might consider when commenting on the latest whims of the weather.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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