Last summer, in response to an intense and prolonged drought in the U.S.—the worst, indeed, since 1895—we ran an interview with a climate scientist, Thomas Karl, director of the National Climatic Data Center in Asheville, North Carolina. He said that droughts in general will be exacerbated by climate change, while noting that it’s difficult to link any particular drought to greenhouse gases. “I suspect it will be really difficult to show how much these changing patterns contributed to the drought in the Midwest this year,” he said (see “Is Climate Change to Blame for the Current U.S. Drought?”).
Karl was right about the difficulty of linking a particular event to climate change. A new study from the National Oceanic and Atmospheric Administration provides an assessment of last year’s drought, and concludes that “human-induced climate change” did not play a significant role. It attributes the drought to natural variations, including fewer than normal thunderstorms and a change in the movement of air that redirected moist air from the Gulf of Mexico away from the Midwest, things that can happen without global warming. The report also says that climate models did not predict the drought.
The report concluded that, specifically regarding the impact of global warming on precipitation in the Midwest, “the signal of climate change may be very small compared to the noise of the intrinsic year-to-year variability. Detectability of a global warming signal in the statistics of summertime Great Plains rainfall may thus be very difficult at this time.”
Until the earth warms a lot more than it has already, it’s going to continue to be difficult to read the effects of climate change in the weather. Weather is too variable. There will continue to be very cold weather that will boost the popularity of climate skeptics and very hot or volatile weather—like Hurricane Sandy—that will serve to make global warming seem more plausible. The decision about what to do, or not do, about climate change will ultimately depend on how much people believe climate models’ predictions of a markedly different world in the future that we’ll see only limited—and often ambiguous—evidence of in the present.