FROM: THE SCIENCE & ENVIRONMENTAL POLICY PROJECT
Fairfax, Virginia
December 8, 1998Editor, The Washington Post
I read with some amusement the contention by paleoclimatologist Jonathan Overpeck of the National Oceanic and Atmospheric Administration that current global temperatures are the warmest in 1200 years because the "Medieval Warm Period" a thousand years ago was merely a regional phenomenon ("Earth at Its Warmest in Past 12 Centuries," Washington Post, December 8, 1998)
As any scientist who has examined a map of current temperatures around the world can tell you, what we are now experiencing is also a regional phenomenon--and that is true whether temperatures are taken by satellites or surface temperature stations.
Both sets of data show "hot spots" at northern mid-latitudes (i.e., over the United States and Western Europe) that skew global averages. I am certain this would even show up in Dr. Overpeck's low-tech tree-ring data.
Because these "hot spots" are so striking, some scientists have speculated that these temperature readings are either badly tainted by things like the urban "heat island" effect or indicate a regional influence of other kinds of human activities. For example, one theory is that contrails from commercial airline traffic (which has been increasing at the rate of 5 percent per year) are creating high cirrus clouds and a regional enhancement of the greenhouse effect. That, of course, would be completely unrelated to any build-up of carbon dioxide in the atmosphere.
As your reporter notes, Dr. James Hansen of NASA, so certain--only a decade ago--that a human-induced global warming was upon us, now says "The forcings that drive long-term climate change are not known with an accuracy sufficient to define future climate change."
Many scientists have been saying that same thing for years.
Candace Crandall
Policy Research Associate
The Science & Environmental Policy Project
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