It is hot outside. I’ll bet it’s hot where you live too. The United States is experiencing one of the hottest summers on record, with more than 40,000 new records set for daily high temperatures.
Inevitably, unusual weather, and especially unusually hot weather, brings widespread discussion of the specter of global warming. Often, these discussions focus on the wrong data, namely, local weather.
Perhaps you believe in global climate change, or perhaps you don’t, but in either case, it is important to recognize the differences between “climate” and “weather,” and between “global” and “local.” A Yahoo news article this week looks at this-summer’s weather in the United States, and quotes several climate scientists saying the trend toward extremes – heat, drought, severe storms – is consistent with predicted effects of global warming. But even these scientists who support theories of global climate change point out the difficulty in drawing any correlation between our current conditions and larger climate trends. This might not be global warming, they say, but this is what it looks like.
People on both sides of the argument tend to hold their local conditions up as evidence. When the winter weather in your town is unusually cold and snowy, how many times have you heard the sarcastic jokes from climate-change deniers: “Hey look, it’s global warming in action,” they say while shoveling mounds of snow from their driveways. “Where’s Al Gore when we need him?”
Then, during a summer like this, the climate-change believers have their moment. “See, told you so. Hope you enjoy 105 and the smell of smoke.”
Global climate change will (or would?) influence local weather, but local weather alone does not prove or disprove its existence. Scientists quoted in the Yahoo News article are reluctant to link U.S. conditions this summer with global climate change, but suggest it could be a glimpse of the future. Michael Oppenheimer, a Princeton University geosciences and international affairs professor, says “What we're seeing really is a window into what global warming really looks like. It looks like heat. It looks like fires. It looks like this kind of environmental disasters."
And while we tend to focus on our local weather, this year actually has been pretty hot globally. According to the National Oceanographic and Atmospheric Administration (NOAA), the combined global land and ocean average surface temperature for May 2012 was 1.19°F above the 20th century average of 58.6°F. This is the second warmest May since records began in 1880, behind only 2010. In the Northern Hemisphere, the land and ocean average surface temperature for May 2012 was the all-time warmest May on record, as was the globally-averaged land-surface temperature.
For January through May 2012, the combined global land and ocean average surface temperature was the 11th warmest on record, 0.90°F above the 20th century average.
So whether you choose to believe global climate change is occurring, or whether human activities play a role, the reading on your window thermometer doesn’t prove much either way.