Wednesday, October 06, 2010

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.

15 comments:

byron smith said...

Evidence for anthropogenic climate change behind aspects of Pakistani floods.

byron smith said...

Monbiot: Two new studies on climate attribution, making a strong case for increased severity being linked to human carbon emissions.

byron smith said...

Richard Brenne: “Every weather event is now influenced by global warming in one way or another, and this trend is intensifying. In approximate order, record high temperatures of all kinds are increasing, as are heat waves, droughts and dramatic precipitation events of all kinds, including snow where and when it is cold enough to snow. Hurricanes and tornadoes are more complex, but when conditions are right higher sea surface temperatures alone are enough to intensify them. This combined with 4% additional water vapor in the atmosphere and far greater energy in the system has created storms like those we’ve seen within the last year in Pakistan and Australia that are unprecedented in the human written record. With 40% more water vapor in the atmosphere possible by 2100, this century would see storms no human can now imagine, dwarfing every storm of every kind we’ve seen so far.”

byron smith said...

Scientific American: a three part series on the links between climate change and extreme weather. Part One. Part Two. Part Three (not yet up, but should soon be linked from the other two).

byron smith said...

Guardian summary of a new IPCC report on the links between extreme weather and climate change. The full report is here.

byron smith said...

Kevin Trenberth: The wrong question.

byron smith said...

That previous link is a very good summary of the links between extreme weather and climate change from an expert in the field, available under creative commons license.

byron smith said...

CP: New attribution study in Nature.

byron smith said...

Guardian: Is it now possible to blame extreme weather on climate change? Leo Hickman gathers some very useful quotes from top attribution researchers.

byron smith said...

David Roberts: Journalists and CC disclaimers.

Why "no one extreme weather event can be blamed on climate change" is trivially true, but quite misleading to put in every article about them.

byron smith said...

Grist: Smoking causes cancer, carbon pollution causes extreme weather. If we don't have a problem using the former, which is a shorthand that doesn't feel the need to nuance the various complexities of the links between tobacco smoke inhalation and carcinomas of the respiratory tract and mouth, then why are we so hesitant to use the latter shorthand, which is just as accurate?

byron smith said...

Guardian: New Hansen study published. Study is not yet available in its final form online, but a draft version is here.

This study does not use models, but is a statistical study based on observed changes that argues that the increase in what used to be extreme events (three standard deviations above the 1950-80 average) to now cover something like 10% of the globe's surface at any given time (rather than about 0.1% during 1950-80), is strong evidence that such events are vanishingly unlikely to not be related to climate change.

byron smith said...

Ignore previous link to draft (this was the wrong study). Here is the study.

byron smith said...

CP: How to relate climate extremes to climate change by Gavin Schmidt.

byron smith said...

ABC Catalyst: Excellent 20 summary of links between warming and extreme weather.