"Climatologist Ben Santer on the attribution of extreme weather events to climate change"
“When you warm up the planet, you experience that through changes in weather that makes up the climate,” says Dr. Benjamin Santer at the Lawrence Livermore National Lab. In a video interview with Climate Science Watch, Santer answers the questions: What is the most appropriate way for reporters and scientists to make a distinction between climate and weather when discussing the attribution of specific weather events, such as heat waves, droughts, and intense precipitation to climate change? What do you think is the most important message for the public to take away from witnessing these events?
Reinsurer Munich Re, whose natural catastrophe database is “the most comprehensive of its kind in the world,” has said “The only plausible explanation for the rise in weather-related catastrophes is climate change.” A recent Journal of Climate Study found global warming is driving increased frequency of extreme wet or dry summer weather in southeast, so droughts and deluges are likely to get worse. And it remains an amazing, though clearly little-known, scientific fact: We get more snow storms in warm years!
What follows is re-post from Climate Science Watch, starting with the video interview of Santer:
We conducted the interview on August 27, 2010.
Santer’s written testimony before the House Committee on Science and Technology, Subcommittee on Energy and Environment, held in Washington, D.C. on November 17 includes the following within its 19 pages:
Assessing Risks of Changes in Extreme Events
We are now capable of making informed scientific statements regarding the influence of human activities on the likelihood of extreme events (75, 76, 77).
As noted previously, computer models can be used to perform the control experiment (no human effects on climate) that we cannot perform in the real world. Using the “unforced” climate variability from a multi-century control run, it is possible to determine how many times an extreme event of a given magnitude should have been observed in the absence of human interference. The probability of obtaining the same extreme event is then calculated in a perturbed climate – for example, in a model experiment with historical or future increases in greenhouse gases, or under some specified change in mean climate (78). Comparison of the frequencies of extremes in the control and perturbed experiments allows climate scientists to make probabilistic statements about how human-induced climate change may have altered the likelihood of the extreme event (53, 78, 79). This is sometimes referred to as an assessment of “fractional attributable risk” (78).
Recently, a “fractional attributable risk” study of the 2003 European summer heat wave concluded that “there is a greater than 90% chance that over half the risk of European summer temperatures exceeding a threshold of 1.6 K is attributable to human influence on climate” (78).
This study (and related work) illustrates that the “D&A” [detection and attribution] community has moved beyond analysis of changes in the mean state of the climate. We now apply rigorous statistical methods to the problem of estimating how human activities may alter the probability of occurrence extreme events. The demonstration of human culpability in changing these risks is likely to have significant implications for the debate on policy responses to climate change.
Also see the discussion of climate and weather extremes in the written testimony (pp. 10-13) submitted for the hearing record by Dr. Heidi Cullen and the written testimony (pp. 6-9) of Dr. Gerald Meehl.
- The year of living dangerously. Masters: “The stunning extremes we witnessed gives me concern that our climate is showing the early signs of instability.”
- Russian President Medvedev: “What is happening now in our central regions is evidence of this global climate change, because we have never in our history faced such weather conditions in the past.” NYT: “Russia Bans Grain Exports After Drought Shrivels Crop”
- Another extreme drought hits the Amazon, raising climate change concerns
Exclusive interview: NCAR’s Trenberth on the link between global warming and extreme deluges: “I find it systematically tends to get underplayed and it often gets underplayed by my fellow scientists. Because one of the opening statements, which I’m sure you’ve probably heard is “Well you can’t attribute a single event to climate change.” But there is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapor lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.”