As Sandy continues to batter most of the northeast, people have jumped to conclusions about what caused–or didn’t cause– the storm. Predictably, President Bill Clinton and environmental activist Bill McKibben have both used the storm to highlight the importance of action on climate change, while Fox News host Sean Hannity interviewed meteorologist Joe Bastardi, who rejects current science that suggests climate change is real and exacerbated by human activity.
But whether Sandy was caused—or made worse—by a gradual human-induced warming of the planet isn’t quite as simple.
When I interviewed NASA climatologist Gavin Schmidt last month, his take was that climate change (while real, and happening) can really only be measured when looking at trends, like average monthly temperatures. Extreme weather events like tornadoes are trickier, he said, because there’s really no way of knowing whether they did happen before, but weren’t accurately recorded.
The more thoughtful media coverage of the links between Sandy and climate change tends to agree. The concensus? Sandy may have been made worse by climate change, but there’s not really concrete evidence to suggest that the storm was caused by climate change.
From the New York Times’ Green blog:
But in interviews on Tuesday, several climate scientists made some initial points. A likely contributor to the intensity of Sandy, they said, was that surface temperatures in the western Atlantic Ocean were remarkably high just ahead of the storm — in places, about five degrees Fahrenheit higher than normal for this time of year. In fact, part of the ocean was warmer than it would normally be in September, when accumulated summer heat tends to peak.
Kevin E. Trenberth, a scientist with the National Center for Atmospheric Research in Boulder, Colo., said that natural variability very likely accounted for the bulk of that temperature extreme. And many of Sandy’s odd features derived from its origin as a “hybrid” storm — a merger of several weather systems, including a hurricane and a midlatitude storm that had earlier dumped snow in Colorado.
“My view is that a lot of this is chance,” Dr. Trenberth said. “It relates to weather, and the juxtaposition of weather systems. A hybrid storm is certainly one which is always in the cards and it’s one we’ve always worried about.”
But, he added, human-induced global warming has been raising the overall temperature of the surface ocean, by about one degree Fahrenheit since the 1970s. So global warming very likely contributed a notable fraction of the energy on which the storm thrived — perhaps as much as 10 percent, he said.
And NPR agrees:
Here the waters get muddied. There is a hierarchy of weather events which scientists feel they understand well enough for establishing climate change links. Global temperature rises and extreme heat rank high on that list, but Hurricanes rank low. As the IPCC special report on extreme events put it “There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities.”
The reasons for “low confidence” are manifold. Some part of the caution comes from the complexity of the problem, and some part comes from the lack of good data before the satellite era (about 1970). Thus, many climate scientists will not want to go out on a limb for hurricanes. They just don’t have the tools to make strong inferences.
Climate change is complicated, and so is its role in huge storms like this one. But at the very least, there’s a chance Sandy will convince one or both of the presidential candidates that climate change is worth discussing before the election next week.