AGU Releases Statement Addressing Human Impacts on Climate

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Publication date: 
22 December 2003

Human activities - including adding to the concentrations of carbon dioxide and other greenhouse gases in the atmosphere - are "altering the Earth's climate," according to a new position statement by the American Geophysical Union. The increased levels of atmospheric carbon dioxide are likely to "remain in the atmosphere for hundreds to thousands of years," the statement continues, and "it is virtually certain that increasing atmospheric concentrations of carbon dioxide and other greenhouse gases will cause global surface climate to be warmer."

The statement, "Human Impacts on Climate," was endorsed unanimously by the Council of AGU this month, and released on December 16 with a series of briefings to the media and congressional staffers. The release of the AGU statement comes less than two months after an historic vote in the Senate on legislation to regulate carbon dioxide and other greenhouse gases (see FYI #152). Although the bill, "The Climate Stewardship Act of 2003," was defeated this time around, its key sponsors, Senators Joseph Lieberman (D-CT) and John McCain (R-AZ) vowed not to give up the fight. Also, within the past month, the Department of Energy released an inventory of the federal government's current climate change technology activities, and a report on technology options for the future. Both documents are available on DOE's climate change technology program web site at .

The AGU statement is an attempt to communicate to the public and policymakers the current state of scientific understanding about human influences on the Earth's climate, AGU president Robert Dickinson explained. The new statement replaces one first issued in December 1998 and, according to Marvin Geller of SUNY Stony Brook, is intended to reflect the scientific progress made in the intervening time. While the new statement does not reveal any "startling" new research results, he said, it summarizes the peer-reviewed literature and is consistent with studies by the Intergovernmental Panel on Climate Change and the National Research Council.

Geller summarized the main points of the statement: In order to explain the observed temperature record, climate models must include human activity; increasing atmospheric concentrations of greenhouse gases are "virtually certain" to cause warming of the global surface climate; predictions about the global-scale impacts of warming are more certain than predictions about regional impacts; while more can be learned from additional research, short-term actions can help mitigate the situation without major societal disruptions; AGU believes no single threshold can be defined above which interference is "dangerous;" and peer-reviewed science should be the basis for all policy decisions.

A number of congressional staffers sought an AGU opinion on what climate change policies should be implemented, but Geller explained that it was not the society's role to recommend policy; many other socio-political factors outside the expertise of the AGU membership needed to be considered in formulating a policy. But he said that policymakers could use the statement to assess the scientific basis for policy alternatives: "If people are using science to make policy arguments, and it differs much from what you read here, be careful!" he said.

The representatives of AGU were also asked how long the U.S. could safely wait to implement policies on climate change. Geller pointed out that some scientists believe the Earth is already experiencing dangerous impacts. "It's highly unlikely you'll ever get perfect certainty," he said; political decisions will have to be made "in the presence of scientific uncertainties." Geller cautioned that the consequences of decisions made now will still be felt "hundreds of years from now," and Dickinson added that not taking action "is a policy."

The AGU statement will be reproduced in its entirety in FYI #164.

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