Does bitter winter weather refute climate-change claims?

Q: Don’t all these huge snow and ice storms across the country mean that the globe isn’t really warming? I’ve never seen such a winter!
– Mark Franklin, Helena, Mont.

A: On the surface, it certainly can appear that way. But just because some of us are experiencing a particularly cold and snowy winter, doesn’t refute the fact that the globe is warming as we continue to pump carbon dioxide and other greenhouse gases into the atmosphere.

According to the National Aeronautics and Space Administration (NASA), the 10 warmest years on record have occurred since 1997. The National Oceanographic and Atmospheric Administration (NOAA) reports that recent decades have been the warmest since at least around AD 1000, and that the warming we’ve seen since the late 19th century is unprecedented over the last 1,000 years.

“You can’t tell much about the climate or where it’s headed by focusing on a particularly frigid day, or season, or year, even,” writes Eoin O’Carroll in an online blog for The Christian Science Monitor. “It’s all in the long-term trends,” concurs Gavin Schmidt, a climatologist at NASA’s Goddard Institute for Space Studies.

Most scientists agree that we need to differentiate between weather and climate. NOAA defines climate as the average of weather over at least a 30-year period. So periodic aberrations – like the harsh winter storms across many parts of the country this winter – do not call the science of human-induced global warming into question.

The flip side of the question is whether global warming is partly to blame for especially harsh winter weather. As was pointed out in a previous EarthTalk column, warmer temperatures in the winter of 2006 caused Lake Erie to not freeze for the first time in its history. This led to increased snowfalls because more evaporating water from the lake was available for precipitation.

But while more extreme weather events of all kinds – from snowstorms to hurricanes to droughts – are likely side effects of a climate in transition, most scientists maintain that any year-to-year variation in weather cannot be linked directly to either a warming or cooling climate.

Even most global warming skeptics agree that a specific cold snap or freak storm doesn’t have any bearing on whether or not the climate problem is real. One such skeptic,

Jimmy Hogan of the Rational Environmentalist website writes, “If we are throwing out anecdotal evidence that refutes global warming, we must at the same time throw out anecdotal evidence that supports it.” He points to environmental groups that hold up hurricane Katrina as “proof” of global warming as one example of the latter.

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