When is it OK to blame climate change for a heat wave?
As Washington, D.C. endures a record eighth straight day of near-triple-digit temperatures, it might be hard for the city's residents to remember that just two years ago, when the capital was blanketed with record snowfall, Republican senator and noted climate change skeptic James Inhofe and his family were building an igloo on the national mall to mock former vice president and leading environmentalist Al Gore. That winter, Matt Drudge and Rush Limbaugh gleefully noted that a Senate conference on climate change had to be canceled due to snow. Scientists and environmentalists pointed out at the time that a record snowfall is in no way inconsistent with a warming planet -- in fact many models predict that heavy snow could become more common because a warmer atmosphere will hold more water vapor. But the larger point is that, as Jane Lubchenco, the head of the National Oceanic and Atmospheric Administration (NOAA), put it in 2010, "It is important that people recognize that weather is not the same thing as climate." Large variations in temperature and humidity will occur even as global temperatures rise.
But in this record-breaking heat wave, it can sometimes seem like the weather-climate distinction is being lost on the other side. "This is what global warming looks like at the regional or personal level," University of Arizona professor Jonathan Overpeck told the AP of this summer's heat waves, wild fires, and brutal storms. The liberal news watchdog Media Matters has blasted outlets that fail to mention climate change in the coverage of the wildfires sweeping across western U.S. states. Some commentators have also attributed the derecho storm that left 23 dead and 1.4 million without power to climate change. The public might be forgiven for wondering if the mantra "weather is not climate" only applies when the weather is politically inconvenient for the person discussing it. So when is it OK to chalk up unusual weather conditions to climate change, and when is it just normal weird weather?
"It's OK to talk about events when you discuss them in a proper scientific context," says Michael Mann, director of the Earth Science Center at Penn State and creator of the famous "hockey stick" graph. "The climate models have predicted what we've now seen, which is a doubling in the rate at which we break all-time warmth records in the U.S. We're breaking those records, over the past decade, at a rate of almost twice what we would expect from chance alone."
In fact, more than 2,000 U.S. heat records were broken just in the past week. Climatologists argue that while there's certainly nothing unexpected in periodic record-breaking temperatures, the rate at which these records are being broken year after year can't be explained away by coincidence.
"There's a randomness to weather, but what we're seeing is loading of the weather dice to the point where sixes are coming up 10 times more often," says Mann. "If you were gambling and you saw sixes coming up 10 times more often you'd start to notice. We are seeing climate change now in the statistical loading of these dice."
Mann also notes with some satisfaction that the year after Inhofe's igloo stunt, his home state of Oklahoma had the hottest month of any state in U.S. history, with an average temperature of 88.9 degrees in July 2011. The senator himself became ill after swimming in a lake that suffered from unexpected algae growth, likely due to the hotter temperatures.
But while the planet is undoubtedly getting warmer, attributing a particular weather phenomenon to this shift is a bit problematic. Although the science may be on the side of climate change, blaming one particular weather incident on global warming is just as misleading as saying that a cold winter disproves it. "I don't think anybody in the climate change community had even heard the word 'derecho' before last week," says Gavin Schmidt, a climate modeler at NASA's Goddard Institute for Space Studies.
"If you really want the nation to be aware of climate change, severe weather outbreaks are certainly a way to get people's attention. But to attribute a specific one to climate change is, at this stage of the game, impossible," says Otis Brown of NOAA's National Climatic Data Center. According to Brown, by 2100 Chicago is projected to have the kind of temperatures we now associate with Dallas, but the change will be gradual and far more difficult for the public to comprehend than a two-week spell of 100-degree days that may or may not have anything to do with global warming.
As the late science fiction author Robert Heinlein famously put it, "climate is what you expect, weather is what you get." But that's often unsatisfying for a public that wants tangible evidence of climate change before they're willing to fully buy into the concept or support policies aimed at mitigating it.
"Most people don't assimilate global statistics or long-term trends -- you feel what's going on by the weather," says NASA's Schmidt. "When weird weather happens, a lot of people just instinctively think its climate change."
Observations over time show that heat waves are getting more frequent and longer, while severe rainstorms are becoming more intense, but that's not the same thing as saying that this week's D.C. heat in particular is the result of global warming. "That kind of statement doesn't make any sense at all," says Schmidt.
Similarly, when it comes to Colorado's wildfires, it's true that a warmer winter led to earlier snow melt, lower precipitation, and an infestation of pine beetles, creating conditions conducive to severe fire. But, of course, wildfires took place long before the planet began warming and most scientists are cautious about stating an unambiguous causal link.
That ambiguity can often create some tension between a media and public looking for explanations for bizarre weather occurrences and a climate science community that, as Schmidt puts it, is often "playing catch-up," trying to establish a causal link between climate and weather after the weather occurs. Says Schmidt, "We don't have a rapid-response climate services team that can tell people what they want to know."
David McNew/Getty Images