Climate Change and ‘Balanced’ Coverage
By JUSTIN GILLIS, Green blog, The New York Times, December 23, 2010
In an article this week on the relentless rise of carbon dioxide in the atmosphere, I outlined one of the canonical projections of climate science: if the amount of carbon dioxide doubles, the average surface temperature of the earth is likely to increase by 5 or 6 °F, a whopping change. I contrasted that with a prediction from skeptics of climate change who contend that the increase is likely to be less than 2 degrees.
One major voice on climate science, Richard B. Alley of the Pennsylvania State University, told me he gets annoyed by the way this contrast is often presented in news accounts. The higher estimate is often put forward as a worst case, he pointed out, while the skeptic number is presented as the best case.
In fact, as Dr. Alley reminds anyone who will listen, and as he recently told aCongressional committee, the estimate of 5 or 6 degrees is actually mildly optimistic. Computer programs used to forecast future climate show it as the most likely outcome from a doubling of carbon dioxide, but those programs also show substantial probabilities that the warming will be much greater.
The true worst case from doubled carbon dioxide is closer to 16 degrees of warming, Dr. Alley said — an addition of heat so radical that it would render the planet unrecognizable to its present-day inhabitants.
Dr. Alley calls the usual news media presentation of the issue a form of “false balance.” In his view, mainstream climate science should be seen as coming down on the conservative side of a range of numbers that runs from 2 to 16 °F. And in setting public policy, he said, lawmakers need to entertain the possibility that any of these numbers is correct.
In climate science, the problem of how the earth will react to extra greenhouse gases is known as “climate sensitivity,” and it is classically formulated as the average temperature increase that can be expected to occur if carbon dioxide doubles from its preindustrial value of 280 parts per million (ppm). By itself, this is a hard problem, one that consumes the lives of thousands of scientists. But projecting the actual future temperature of the earth involves even greater complexities.
For instance, there is no reason to assume that the increase of carbon dioxide will stop at a doubling, to 560 ppm. So scientists are simultaneously trying to project the earth’s response to a given future level of carbon dioxide, and to project how high the carbon dioxide will actually go before emissions are brought under control.
Myles R. Allen, a leading British climate scientist, pointed out to me that a business-as-usual scenario would take the carbon dioxide level well beyond a doubling.
Myles R. Allen, a leading British climate scientist, pointed out to me that a business-as-usual scenario would take the carbon dioxide level well beyond a doubling.
“There is plenty of fossil carbon underground (mostly in the form of coal and unconventional sources like tar sands) to push atmospheric concentrations well above 1,000 ppm if we simply burn everything that it makes economic sense to burn,” he said by e-mail. “And then even the most likely warming would be in the double figures in Fahrenheit.”
Climate science does have optimists in its ranks, and they tend to think that society will get a grip on emissions in time to head off a real catastrophe. But as I reported in my article, the recent global climate conference in Cancún, Mexico, did not provide much succor for the optimists. For the 18th year running, countries talked a big game while making only weak commitments that no one believes will bring emissions under control.
Meantime, the carbon dioxide level in the atmosphere keeps ticking upward, with 400 ppm now only a few years away.
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