THE EARTH’S natural systems are so complex that it can be hard to prove links between specific instances of extreme weather and the long-term shifting of global temperatures that humans are causing. But that does not suggest there are no links, or that warming is not happening. In fact, experts are getting better at the science of “climate attribution,” as a new report from the American Meteorological Society shows.
The society collected papers from a large number of researchers in its report, " Explaining Extreme Events of 2015 From a Climate Perspective." As in past years, scientists associated climate change with extreme heat, investigating a variety of temperature blips last year. Though 2015 saw a significant El Niño, which is a recurring oscillation in Pacific Ocean water temperature that tends to affect a variety of weather events, the researchers were able to distinguish the effects of El Niño and other instances of natural variability from climate change's potential influence. Among other things, they found that global warming made an unexpectedly hot summer in Japan 1.5 to 1.7 times more likely.
Scientists are investigating the climate change connection to an increasing variety of natural events, finding that global warming enhanced the odds of extreme cyclones in the Pacific and highlighting “sunny-day” flooding in Miami. “Even without a cloud in the sky or a storm on the horizon, the Miami, Florida, region is more likely to experience tidal flooding because of long-term sea level rise caused by global warming,” the report noted. Experts are using the recent climatic past to predict future conditions: Last year’s “snowpack drought” in the Cascade Mountains, for example, occurred because hot temperatures encouraged rain instead of snow to fall on the mountains, the sort of thing that could happen more often as the world warms.
Researchers are also trying to be more specific, when possible, about the impacts of the events they associate with climate change. The report noted that investigators consulted with public-health experts this year to determine the link between climate change and direct impacts on human beings, finding that several hundred deaths in London and Paris during a 2003 summer heat wave were attributable to climate change. This sort of research comes with uncertainties, but as it gets better and becomes more common, it should underscore that global warming will result in more than merely a few inconveniently hot days.
To be sure, researchers were not always able to discern a clear connection between climate change and the events they examined. They also admitted that some of the effects they investigated might be welcomed — for example, more wintertime sunshine in the United Kingdom.
The overall picture is of an expert community just beginning to grapple with a new scientific frontier — documenting in near-real time how human-caused changes in atmospheric chemistry affect a wide variety of natural systems that are best left alone. Sadly, this is likely to be a burgeoning field for the foreseeable future.
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