This week NPRasks:
When can a big storm or drought be blamed on climate change?
If you have been nodding in approval to everything that Bill McKibben and his fellow climate concerned advocates say on this subject, then you already have your answer. And if you are familiar with the "new normal" meme, which I have written on previously, then you also know that nearly every severe weather event is now associated in some way with climate change. It's been interesting to watch this play out in the media the past few years. For example, plug into Google 's search engine "climate change" and "Typhoon Haiyan" (the tropical cyclone that devastated portions of the Philippines last year) and see all the stories that come up. A quick sampling of headlines: "Is Climate Change to Blame for Typhoon Haiyan?"--Guardian "Did Climate Change Cause Super Typhoon Haiyan?"--Time "Super Typhoon Haiyan: A hint of What's to Come?"--Climate Central A definitive answer is impossible in the immediate aftermath of such an event, but many outlets still made a connection along these lines:
Hurricane researchers contacted by Climate Central said Haiyan is an example of the type of extreme storm that may become more frequent as the climate continues to warm.
This sets the stage for every major storm to be discussed in the context of climate change. And indeed, this is often what ends up happening with every heat wave, every drought, every big flood, and every unseasonable cold spell or blizzard. That is the whole point of the "new normal" meme, which by the way, may be counterproductive, Dawn Stover recently argued in the Bulletin of the Atomic Scientists. In the last couple of years, scientists have tried to bring some clarity to these discussions. This has resulted in dozens of studies assessing whether or not severe weather events from around the world can be linked to global warming. The latest batch of research was published earlier this week in a special Bulletin of the American Meteorological Societyreport. The results were covered widely in the media--most with a particular slant. I found NPR's summary of the findings to be among the most accurate:
Dozens of these researchers just published an analysis of 16 weather events from 2013 in the Bulletin of the American Meteorological Society, and what they found was a mixed bag.
As Justin Gillis explained in his New York Times write-up:
The findings relied on computer analyses of what the climate would have been like in the absence of human-caused greenhouse emissions, a type of research widely acknowledged to be imperfect, and which often produces conflicting findings from different groups.
That was the case with an assessment of California's drought, with two groups of researchers not finding a a linkage to a warming climate (from rising concentrations of greenhouse gases) and a third group finding such a connection. Other studies in the report determined that catastrophic floods in Boulder, Colorado could not be attributed to human caused global warming but that a heat wave in Australia had such a connection. (Oddly, there was no assessment of typhoon Haiyan.) In his NYT summary of the findings, Gillis included a helpful perspective from one UK scientist:
Myles R. Allen, a researcher at Oxford whose group conducted the study on the European rains, noted in an interview that the science of attributing specific events to human emissions was still contentious and difficult, so any answers given today must be regarded as provisional.
His group has found a measure of human influence on several weather events over the years. But with the science still emerging, he cautioned against the tendency to cite global warming as a cause of almost any kind of severe weather.
“If we don’t have evidence, I don’t think we should hint darkly all the time that human influence must be to blame somehow,” Dr. Allen said.
I doubt that Bill McKibben, whose twitter stream often resembles an extension of the weather channel, will be taking that advice to heart. It would be difficult for many others, as well, to stop hinting darkly about a relationship between global warming and severe weather. But McKibben and company might come to regret this if people start to shrug their shoulders and say, "oh well, I guess this is the new normal."
UPDATE: See this related 2013 Dot Earth post by Andy Revkin, which makes some excellent points about how the emphasis on weather disasters can boomerang. An excerpt:
According to the latest science, in most cases (outside of extreme heat waves) the connections between today’s extreme weather events and human-driven climate change range from weak (hurricanes) to nil (tornadoes) — and the dominant driver of losses in such events is fast-paced development or settlement in places with fundamental climatic or coastal vulnerability.
So “here and now” arguments take the policy fight on global warming into the terrain favored by those who recoil at environmental regulation or profit from fossil fuels — an arena where there’s lots of real scientific uncertainty. All they have to do is sprinkle just a little of that uncertainty dust and the public disengages. Job done.
