Extreme global warming likely by end of century

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Extreme global warming likely by end of century
mongabay.com
May 24, 2006

Climate models predicting a 5.6 degrees Celsius increase in Earth's temperature by the end of the century may have underestimated the increase by as much as 2.3C according to researchers at the University of California at Berkeley.

Analyzing ice cores containing a 360,000-year record of global temperature and levels of carbon dioxide (CO2) and methane, the scientists found that "during periods of warming, greenhouse gas levels rose and created significantly higher temperatures than would be expected solely from the increased intensity of sunlight that triggered these warm periods." The researchers suspect that warming could be amplified by warmer soils -- which decompose faster -- and oceans releasing more CO2 and methane into the atmosphere.

"We are underestimating the magnitude of warming because we are ignoring the extra carbon dioxide dumped into the atmosphere because of warming," said John Harte, UC Berkeley professor of energy and resources and of environmental science, policy & management. "Warming gets an extra kick from CO2 feedback."

Current models predict a doubling of the carbon dioxide in the atmosphere within the next 50 years, an amount that would raise global temperatures between 1.5C and 4.5C. The Berkeley team projects that a doubling of carbon dioxide production would result in natural processes injecting more carbon dioxide into the atmosphere, leading to temperature increases of 1.6C to 6.2C.

Global warming may be worse than predictedClimate change estimates for the next century may have substantially underestimated the potential magnitude of global warming says a new study from a team of European scientists. The paper, published in the May 26 issue of Geophysical Research Letters, says that warming may be 15-to-78 percent higher than estimates that do not consider the feedback mechanism involving carbon dioxide and Earth's temperature.

"The warming caused by our release of CO2 triggers changes in the Earth system that lead to release of more CO2 to the atmosphere," added co-author Margaret Torn, a UC Berkeley adjunct associate professor of energy and resources and staff scientist at Lawrence Berkeley National Laboratory. "If that is the case, then every bit of CO2 release now is actually committing us to a larger CO2 change in the atmosphere."

Harte and Torn conclude "that the upper value of warming that is projected for the end of the 21st century, 5.8ºC [10.4ºF], could be increased to 7.7ºC [13.9ºF], or nearly 2ºC additional warming."

According to a news release from UC Berkeley, the researchers warn "that the large temperature range they predict - 1.6 to 6 degrees Celsius - does not mean that we have an equal chance of ending up with less warming as with greater warming. In other words, it doesn't mean that the uncertainties are symmetric about an average increase of 3.8ºC."

"People see this uncertainty and think that we have an equal probability of dodging a bullet as catching it. That is a fallacy," Torn said.

"By giving the appearance of symmetric feedback, people have an excuse to say, 'Maybe we don't have to worry so much,'" Harte said. "But while there are uncertainties in the feedbacks, all the major feedbacks are positive, meaning they would increase warming, and we know of no significant negative feedbacks that would slow warming."

Harte said that while the future may not look like past periods of global warming, "in the absence of contradictory evidence, we have to assume the future will respond like the past."

"Whatever the mechanisms that cause temperature to create a change in CO2 and methane, they are repeatable again and again and again over many cooling and warming cycles. So, although the world is different today than it was then, we don't have a basis for ignoring them," Torn added.

This article is based on a news release from the UC Berkeley

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