Climate Less Sensitive to Greenhouse Gases Than Predicted, Study Says

April 19, 2006

How sensitive is Earth's climate? Sufficient to warm by at least several degrees in response to greenhouse gas pollution but perhaps not as sensitive as some scientists have feared, according to a new study.

Climate sensitivity is a measure of how much the global temperature will warm in response to greenhouse gas emissions, explained Gabriele Hegerl, a climate scientist at Duke University in Durham, North Carolina.

The measure specifically estimates how the climate might respond to a doubling of the amount of carbon dioxide in the atmosphere. Carbon dioxide is a greenhouse gas that humans release by burning fossil fuels in cars and power plants.

"If [climate sensitivity is] high, we have a strong response not only to carbon dioxide but to any greenhouse gas. If it's low, we have a weak response. So we would really like to know what it is," Hegerl said.

Hegerl and her team measured climate sensitivity by studying temperature changes in the Northern Hemisphere over the past 700 years.

The study's results refute recent research suggesting that the climate may be susceptible to extreme increases in temperature. But Hegerl cautions that the findings do not diminish the threat of global warming.

"[The finding] means the climate does react significantly to greenhouse gases," she said.

"In other words," she added, "we have really detected greenhouse warming, and we are really concerned it is not small."

(See National Geographic magazine's "Global Warning: Signs From Earth.")

Climate Sensitivity

In 1979 meteorologist Jules Charney made the first modern estimate of climate sensitivity using two climate models. He concluded that the Earth would warm within a range of 2.7º to 8.1ºF (1.5º to 4.5ºC) if carbon dioxide in the atmosphere doubled.

That range has become the generally accepted value of climate sensitivity and is used in international climate-change research.

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