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When to Blame the Rain (or Lack Thereof) on Climate Change
A series of new reports studies global warming's role in extreme weather.

According to a bevy of studies released Monday, we can point the finger at climate change for much of last year’s extreme weather. (And there was a lot of it.) In a report published by the Bulletin of the American Meteorological Society, scientists from 22 research groups looked at 16 separate extreme weather events from 2013 and asked—in their best Steve Urkel voice—“Did climate change do that?”

In half of those cases, the answer is a resounding yes. The teams found that climate change increased both the likelihood and severity of a range of weather events last year—particularly heat waves, such as those experienced by Europe, China, Japan, and South Korea. But sometimes, a rainy day is still just … well, a rainy day. The researchers cleared climate change of blame for other freaky storms—like the abnormally high snowfall in the Pyrenees and Cyclone Christian, which slammed Europe with 120-mph winds last October. In still other cases, the climate connection remains uncertain.

The science of attributing any weather event to climate change is complex, and since 2011, the American Meteorological Society has been trying to clear the air over whether global warming influenced the previous year’s major storms, droughts, and other weather phenomena. The latest report is the organization’s most extensive to date. Here are three examples of how the scientists answered the question: “Did climate change do that?”

Australian Heat Wave: YES!

In what the New York Times calls “perhaps the most definitive statement climate scientists have made tying a specific weather event to global warming,” five teams linked the 2013 Australian heat wave to human-driven climate change. Using a computer model, the researchers determined that such extreme temperatures—which reached 120 degrees in some places, melted roads, and halted play at the Australian Open—would not have been possible without the help of humans burning fossil fuels.

Ironically, the finding comes just months after the country’s government repealed a carbon tax that would have required large companies to pay for every metric ton of carbon dioxide they emitted. (The nation's prime minister, Tony Abbott, is notorious for denying climate science.)

Colorado Flooding: NOPE.

In September 2013, up to 17 inches of rain falling over five days triggered catastrophic flooding across Colorado’s Front Range. The natural disaster affected nearly 2,000 square miles of the state, claiming 10 lives and racking up $2 billion in damages. Although a warmer atmosphere holds greater moisture and can cause more frequent extreme rainfalls, researchers concluded that climate change has actually made it less likely for these types of deluges to occur in northeastern Colorado at that time of year (one of the few places in the world where that is true, according to one of the study's authors). Not all climatologists agree with those results, but for now, we'll have to give climate change the benefit of the doubt.

California Drought: MAYBE?

A “ridiculously resilient ridge,” a stubborn pattern of high pressure over the northeastern Pacific Ocean, has been blocking rain clouds from reaching California. But researchers disagree over the cause. “The picture that emerged Monday of climate change’s potential role in condemning California to drought was as murky as muddy water in a nearly parched lakebed,” writes Climate Central’s John Upton. One study found that such a ridge was more likely to form under current emissions scenarios. A second study agreed, but it argued that climate change would also increase humidity over the state, which would counteract the drying effects of the high-pressure system. And yet a third study found no evidence that climate change has increased the chances of long-term drought in California.

So the jury may still be out on what role greenhouse gases played in triggering the state’s debilitating mega-drought, but one thing scientists do agree on is that warmer temperatures are making the drought worse, whatever its original cause.

* * *

Playing whodunit with weather is no simple task, and scientists don’t have all the answers of how climate change will continue to unfold across the globe. What we do know is that we have altered the planet’s atmosphere, and now and then, the heavens respond. It’s not just angels bowling up there—we’re playing our part down here, too.

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image of Clara Chaisson
Clara Chaisson is a Boston-based writer and OnEarth.org's associate producer. She previously reported for Audubon magazine, and recently graduated from Boston University with an M.S. in science journalism. MORE STORIES ➔