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."