On the attribution of extreme weather events

"Finally, a comment on frequently asked questions of the sort: Was global warming the cause of the 2010 heat wave in Moscow, the 2003 heat wave in Europe, the all-time record high temperatures reached in many Asian nations in 2010, the incredible Pakistan flood in 2010? The standard scientist answer is 'you cannot blame a specific weather/climate event on global warming'. That answer, to the public, translates as 'no'.

"However, if the question were posed as 'would these events have occurred if atmospheric carbon dioxide had remained at its pre-industrial level of 280 ppm?', an appropriate answer in that case is 'almost certainly not'. That answer, to the public, translates as 'yes', i.e., humans probably bear a responsibility for the extreme event."

- James Hansen, "How Warm Was This Summer?" from NASA Goddard Institute for Space Studies.

The whole piece is worth reading, not least for the prediction that 2012 is "likely" to reach "record high global temperatures", after 2010 has already repeatedly broken the twelve month running average (temperatures in 2011 are likely to be slightly suppressed from record levels by the La Niña that has developed in recent months). I also talked about the difference between weather and climate back here.

Dr James Hansen is the head of NASA GISS and was the first academic to bring climate change into mainstream awareness at his US congressional testimony on 23rd June 1988, which became front page news when he claimed there was sufficient evidence to give 99% certainty that "It is already happening now".

As you may have noticed, Hansen takes his duties as a citizen (and grandfather), as well as a scientist, seriously. Last week Dr Hansen was arrested (once again) for civil disobedience while protesting coal mining through mountaintop removal, which manages to combine a whole raft of destructive effects on the way to disrupting the climate.

Here is another quote on attribution worth pondering:

"The point is that while it is a perfectly reasonable question to ask: “Was this event due to climate change?” it would more useful to ask a related question: “are we putting ourselves at greater risk of experiencing this kind of event?” And to that scientists can answer with high confidence: yes!

"Now, you might think this question is less interesting or useful, and perhaps not as worth asking than the first one. But we would argue that, in fact, it is very important to pose this question, and to carefully consider its answers.

"Think of smoking, sun bathing without sunscreen, eating lots of junk food and so on. You may not be able – ever – to unequivocally attribute one person’s problem to the effects of these activities: people develop lung cancer without smoking, for example, but as a population we know we are better off wearing sunscreen, watching our cholesterol, and not smoking, since all of these actions have been shown to make the chances of harm to our health lower."

- Nicole Heller, Claudia Tebaldi, and Phil Duffy, "Why Can’t Scientists Say the Recent Extreme Weather Events Are ‘Proof’ of Climate Change?" at Climate Central.