AGU Releases New Statement Addressing Human Impacts on Climate

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Publication date: 
30 January 2008

Scientists representing the American Geophysical Union released a new statement on climate change on January 24th, that says, “Earth’s climate is now clearly out of balance and is warming.”The statement, an update of the AGU’s 2003 climate change position statement, says that when the scientific data related to warming is studied, “the human footprint on Earth is apparent.”  In releasing Human Impacts on Climate Change, the organization’s strongest statement to date on the impact of global warming, AGU president Timothy Killeen said, “the changes we’re seeing are best explained by greenhouse gas emissions and aerosol loading in the atmosphere caused by human activity.”

The statement says that “as of 2006, eleven of the previous twelve years were warmer than any others since 1850 [when official weather record-keeping began in the U.S.].” The statement, approved unanimously in December by the Council of AGU, goes on to say that, “Many components of the climate system - including the temperatures of the atmosphere, land and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons - are now changing at rates and in patterns that are not natural and are best explained [by the increase in greenhouse gas emissions] generated by human activity during the 20th Century.”

The statement differed in several ways from past statements, said Killeen, who is also the director of the federal government’s National Center for Atmospheric Research in Boulder, Colorado. First, he said, the AGU is making “a declarative statement” about the threats of global warming.  “There are fewer caveats that might have appeared in previous statements,” he said.

“Second, the AGU is now saying that we need to do something about [global warming].”  The statement says that “warming greater than 2 degrees Celsius (3.6 degrees Fahrenheit) above 19th century levels is projected to be disruptive, reducing global agricultural productivity, causing widespread loss of biodiversity, and - if sustained over centuries - melting much of the Greenland ice sheet with ensuing rise in sea level of several meters.”

If the 2 degrees Celsius warming is to be avoided, the statement continues, annual emissions of CO2 “must be reduced by more than 50 percent within this century.” And while there is scientific uncertainty in the long-range projections of climate change, “none are known that could make the impact of climate change inconsequential.”

And unlike past AGU global warming statements, Killeen said, the new one calls for “collaborations across science, technology, industry, and government,” to find ways to lessen the emission of greenhouse gases and to prepare for the changes that are already inevitable.  The statement says AGU’s 50,000 members have “special responsibilities” to pursue climate change research and educate the public “on the causes, risks, and hazards.”

Killeen was joined in releasing the statement by Michael Prather, an Earth scientist from the University of California, Irvine, and chair of the AGU committee that drafted that statement, and Bette Otto-Bliesner, an NCAR senior scientist who models past climates,.

The full statement is available at:

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