EARTHTALK: Was Hurricane Harvey Caused By Global Warming?

Dear EarthTalkWas Hurricane Harvey caused by global warming?

—Tom Dell, Bern, NC

The short answer is no. No single hurricane or weather event can be directly linked to the general phenomena known as climate change. “Climate change does not cause things, because climate change is not a causal agent,” writes David Roberts on “‘Climate change’ is a descriptive term — it describes the fact that the climate is changing.”

That said, global warming likely did contribute to the severity of Harvey, and has created an overall climate more hospitable to the formation of extreme weather events of every stripe. “For hurricanes, we would ask the question as to what are the possible hurricane developments in the world we live in and compare that to the possible hurricane developments in a world without climate change,” Dr Friederike Otto from the University of Oxford tells BBC News.

While global warming didn’t cause Hurricane Harvey, it certainly played a role in how extreme the storm was in terms of high winds and heavy rain. Credit: Texas.713, FlickrCC.

One definite “fingerprint” of global warming on Harvey is the intensity and amount of rainfall. Climatologists cite the Clausius-Clapeyron equation (a hotter atmosphere holds more moisture: for every extra degree Celsius in warming, the atmosphere can hold 7% more water) as one link between global warming and stronger storms. Houstonians have witnessed a 167 percent increase in the frequency of the most intense downpours since the 1950s.

Adam Sobel of Columbia’s Initiative on Extreme Weather and Climate estimates that as much as 10% of Harvey’s rainfall could be blamed on global warming, while Kevin Trenberth of the U.S. National Center for Atmospheric Research pegs the number at closer to 30%. “It may have been a strong storm, and it may have caused a lot of problems anyway—but [human-caused climate change] amplifies the damage considerably,” Trenberth reports in The Atlantic.

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