Hurricanes, droughts, and other extreme weather raise the question: Was that related to global warming?
The provocative answer that Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research, proposed in 2012 can be roughly summarized as yes. All weather events are related to climate change, he argued, because the atmosphere is hotter and moister than it was before humans started filling it with greenhouse gases. "The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question," Trenberth wrote in the journal Climatic Change.
Allowed more than one word, the answer is considerably more complicated.
This short video looks at what scientists call climate attribution studies, which use heavy-duty computation to gauge how big an influence humanity may have had on weather. Using powerful computer models, researchers can simulate extreme events, in scenarios with and without greenhouse gas pollution. The differences between the results help them understand how the warming is altering the odds or magnitude of different phenomena.
Among the findings:
- The deadly 2003 European heat wave, which killed more than 20,000 people, was the first major focus of an attribution study. The lead scientist reanalyzed the data in 2011. The heat wave is now thought to have been responsible for about 64 deaths in London and 506 in Paris.
- Heavy rain in southern Louisiana last August was studied by the World Weather Attribution project, which concluded that global warming had upped the odds considerably. By contrast, the central European flooding of May and June 2013 showed no such human fingerprints [see page S69 here: pdf].
- An April 2015 study in Nature Climate Change found that about 75 percent of major heat events and 18 percent of heavy precipitation events are attributable to global warming.
The World Meteorological Organization releases a thick annual report, "Explaining Extreme Events From a Climate Perspective," with analysis of destructive weather.