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Contact Jim: jdipeso@rep.org (253) 740-2066 / 2008 Archive / 2007 Archive / 2006 Archive / 2005 Archive
It's the Long-Term Record That Counts
March 26, 2008
The latest wheeze trotted out by the climate change denial crowd is an argument that global warming has “stopped.”
That’s progress of sorts. Before, they were arguing that global warming is a hoax. So at least they’re implicitly acknowledging that something has been going on in the atmosphere.
But not anymore, they’re asserting triumphantly. Since 2001, the skeptics say, average temperatures haven’t risen. If greenhouse gas emissions are rising, shouldn’t temperatures rise with them? If not, then the scientists must have screwed up, and it’s time to order up another heapin’ helping of fossil fuels.
Well, they’re wrong about the temperature trend. Eleven of the last 12 years have been the warmest on record.
Even if the deniers were correct about the temps, however, the flaw in their argument is confusion between short-term variability and long-term trends. The onset of global warming does not mean that weather fluctuations will go away. Short-term variability, including cold snaps and spring snowstorms, will still occur. You’ll still be better off booking your beach vacation for the Riviera rather than Greenland.
Climate is a chaotic system, meaning there are many pressure points that can cause short-term variations in the atmosphere’s behavior. An El Nino can heat things up for a bit. A volcanic eruption can cool things down for a time.
Over a longer period, however, variations smooth out and long-term trends can be discerned. But that takes a long data record. Basing conclusions about long-term trends on cherry-picked data from a short time frame is a dangerous game.
The global mean temperature was lower in 1993 than it was in 1990. Does that mean that global warming “stopped” in 1990? No, it means that the Pinatubo volcanic eruption temporarily cooled the climate for a few years. After the volcano's detritus cleared out of the atmosphere, the long-term upward trend became clear again.
If climate is too abstract, let’s try a more prosaic example that illustrates the short-term versus long-term distinction. Like climate, baseball players are chaotic systems whose performance is affected by numerous pressure points from ankle injuries to boo birds. You can’t predict how they will perform on any given day because there are too many variables.
But you can make a reasonable projection how players are likely to do over the course of a season if you look at their lifetime records. If a star slugger’s lifetime batting average is .300, you wouldn’t precipitously trade him just because he’s in a batting slump. That would be confusing short-term variability with long-term trends. Even Babe Ruth had bad days when he couldn’t find the ball.
Likewise, if a journeyman player with a lifetime average of .220 unexpectedly goes on a weeklong home run tear, it wouldn’t be smart to ply him with a 10-year, $100 million contract.
The upshot is that one heat wave is not definitive evidence of global warming, nor is one cold snap proof that it’s a fraud. The long-term record, however, makes for a compelling case that the earth is warming.
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