Weather Is Not Climate

Nov. 16, 2006 — -- "Choosing shorts or long underwear on a particular day is about weather; the ratio of shorts to long underwear in the drawer is about climate."

-- Charles Wohlforth, "The Whale and the Supercomputer"

You probably noticed there were fewer Atlantic hurricanes this year. Melting Arctic sea ice came extremely close to but didn't break the record minimum of summer 2005. And today, the National Oceanic and Atmospheric Administration, or NOAA, announced two months of cooler-than-average temperatures across the United States.

So what happened to global warming?

Scientists who study climate say they get that question every time there's a cold spell. Their answer: It's important to keep in mind an important concept.

Weather is not climate.

Weather, as we all know, is what we see in the day-to-day, often unpredictable fluctuations in local temperature, humidity, precipitation and wind.

"The fact that we had a couple of cool months doesn't say anything at all about long-term trends," said Mark Serreze, a research scientist at the National Snow and Ice Data Center. "It's just a clear example of natural variability on the climate system. The long-term averages are decidedly toward a warming planet."

Kevin Trenberth, a scientist at the National Center for Atmospheric Research, agreed.

"Weather is chaotic. It has an infinite amount of variability, and that's just the nature of weather," he said. "Weather dominates on a day-to-day basis, and there will be warmer period and cooler periods. But it's the overall pattern that gives you the climate."

And that, said climate scientists, means the occasional cold snap is not inconsistent with global warming, just as a heat wave may not by itself indicate global warming.

Long-term trends in the data tell scientists that the planet is getting warmer. Weather events that suggest otherwise are to be expected, they said.

"We have a gradual warming of Earth's system, but that is interspersed with a strong natural variability in the system," Serreze said. "This is just the way the system works."