Global Warming?

The newspapers and television are full of stories about “global warming,” so I thought I’d address this term briefly today — and get back to more of the science later.

What does “global warming” mean? “Global warming” is really an unfortunate choice of words. What climate scientists refer to when they talk about temperature changes over decades and centuries is a global average — over the oceans as well as land. And normally, they refer to the air temperature about 1.5 m above the surface, the “surface air temperature.”

So, if someone says that Earth’s temperature has warmed about 1 degree C over the last century, it does not mean that the surface air temperature everywhere has warmed by that amount. In fact, some places — for example, parts of the southeastern United States actually got a little cooler!

A few years ago, as part of a workshop, we asked teachers to plot graphs of average temperature as a function of year for the Weather Service station nearest their schools. All of these teachers lived in the state of Colorado. No one could really see any change from the graphs. Looking at maps of the temperature trends in the “lower 48″ United States, we can see why — Colorado is roughly at the boundary between where there is warming (the northwest U.S.) and the neutral-to cooling southeast U.S.

Can you find out how the temperature has been changing where you live? Have other things (rainfall, amount of snow, number of big snowstorms, seasons, spring thaw, first freeze, last freeze) changed where you live? This would be a good thing for students to ask their grandparents or other senior citizens. Even better — find out what students are observing in other parts of the world.