Web Extra Friday, December 19, 2003

Humans impact the climate, says AGU

The American Geophysical Union (AGU) has adopted a new position statement on climate change that recognizes the increasing alteration of the Earth's climate by human activities. "Scientific evidence strongly indicates that natural influences cannot explain the rapid increase in global near-surface temperatures observed during the second half of the 20th century," the statement says.

"We're not reporting on startling new science," said Marvin Geller, an atmospheric scientist at Stony Brook University in New York and chair of the committee that drafted the statement, at a press conference on Monday in Washington, D.C. But the new statement, he said, reflects the current scientific understanding of the effects of humans on the climate, as is reported in the peer-reviewed science literature. "Human-induced global warming is happening," Geller said, "and now we need to do something."

According to Geller, the AGU statement is consistent with the reports issued by the Intergovernmental Panel on Climate Change and the National Academies of Science, and also with the Bush administration's climate change science plan released this year. It is also consistent with the most reputable science out there, he said.

The unprecedented increase in greenhouse gas concentrations has, and will continue, to change the global climate — that is a certainty, the statement says. It also expresses confidence that climate change will mean higher sea levels, melting glaciers and more droughts and floods. What is less certain is the impact of climate change on a regional, rather than global, scale. For example, while the scientists are confident that mid-continent temperatures will rise, mid-ocean surface temperatures may not be as affected.

Another point that should be made, Geller said, is that scientists have not defined any single threshold for when greenhouse gas concentration becomes dangerous. The scientists notably left out any language about abrupt climate change because the trigger mechanisms are not well established. "But the more you push on something, the more likely it is to break," Geller said.

The statement calls upon the scientific community to increase the research to further understanding of climate change and future impacts, and to educate policy-makers and the public about the changes. Scientists need to use their best knowledge to determine what's happening and how to deal with it.

The new position statement replaces the society's previous statement on climate change that was adopted in 1998 and reaffirmed in 2002. Whereas the previous statement dealt primarily with greenhouse gases and the associated climatic effects, this one mentions other human influences as well. It reflects the evolution of scientific thinking about climate change, he said. The scientists involved in the rewrite said that because so much information is published about climate change, it was time to take another look at their position. AGU alone publishes roughly 90 peer-reviewed papers per month that deal with climate change.

When asked at the press conference how AGU's new statement might affect the Bush administration's overall climate policy, Geller answered, "I don't know." The statement suggests several ways to mitigate the impacts humans have on the environment, including slowing greenhouse gas emissions, improving land management practices and removing carbon from the atmosphere. The scientists said that their job is to present the most accurate scientific information available. "We all hope our statements are useful in formulating policy," said Bob Dickinson, an atmospheric scientist at Georgia Tech and current AGU president. But the scientists were reluctant to say any more.

Part of scientists' job is to differentiate between research that has undergone rigorous scientific peer review processes from that that has been published by "any Joe with a computer," Geller said. The researchers recognize that there will always be nay-sayers, but they hope to help policy-makers sort through the vast amount of information out there to arrive at the best scientific conclusions. They stressed the importance of broad scientific assessments.

AGU is an international scientific society with more than 41,000 members. Part of AGU's mission is to inform the public on issues that affect them, and to make the best science available to the public and to policy-makers, Dickinson said. The AGU governing council unanimously passed the new position statement at its meeting last Friday at the AGU annual fall meeting in San Francisco.

Megan Sever


American Geophysical Union's Climate Change Position Statement
Intergovernmental Panel on Climate Change

"Climate Change Report Reexamined," Geotimes, Aug. 28, 2003
AGI Government Affairs Climate Change Overview

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