Ten years ago, the world's premier group of earth, atmospheric, and planetary scientists declined to wade into the debate over global warming.
Yesterday, it jumped in with both feet. Citing advances in research and in modeling Earth's past and present climate, the American Geophysical Union (AGU) agreed that public concern about climate change is justified. Remaining scientific uncertainties, it said, fail to support a do-nothing approach.
While it tops short of detailed steps and timetables, the AGU recommends that policymakers develop and evaluate strategies such as reducing carbon-dioxide emissions, removing CO2 from the atmosphere, and adapting to the effects of climate change.
The AGU is by no means leading the charge among scientific groups. Nor do all its 35,000 members agree with the new position statement. Still, from the standpoint of scientific credibility, the statement could rank among the most influential yet.
"This is very significant," says Dan Becker, director of the Sierra Club's global warming and energy program, based in Washington. "This is one of the last groups of scientists to speak out; and it's a large body of respected, thoughtful scientists."
The position statement, drafted by the group's governing council, appears at a time when the Clinton administration is trying to raise the profile of global warming. The White House reportedly is sending a budget to Congress that includes a sizable package of spending and tax breaks to spur climate research and use of energy-efficient technologies.
The move also follows last November's international climate meeting in Buenos Aires, where United States representatives signed the 1997 Kyoto Protocol. It requires the US to cut energy use by more than 30 percent over the next 12 years. But the protocol, which the Senate must ratify to take effect, has drawn sharp criticism from key senators and industry. They argue such cuts would seriously undermine the US economy, particularly if countries such as China and India refuse to sign on to the agreement. And even supporters acknowledge that the treaty's targets fall short of what's needed to strike a significant blow against CO2 buildup.
Against this backdrop and in the face of advances in scientific understanding of the phenomenon, "the AGU felt it was important to go on record in a way that could be supported scientifically," says Timothy Killeen, a professor of atmospheric, oceanic, and space science at the University of Michigan in Ann Arbor and a member of the AGU's governing council. "Silence on this issue makes a statement of its own."
In making its case for action, the AGU acknowledges that at several periods during the past few thousand years, average global temperatures rose for reasons that had nothing to do with burning fuels such as coal, oil, and wood.
It also notes that temperature increases during the past 150 years fall within the range of such natural variations. But the same record also shows that when CO2 has been pumped into the atmosphere in quantities similar to those deposited by human activities during the past century, it has eventually altered the climate.
S. Fred Singer, an AGU fellow and outspoken critic of the notion that humans are altering Earth's climate, holds that key parts of the statement are misleading or inaccurate in laying out the scientific rationale - overstating the length of time CO2 remains in the atmosphere, for example, and ignoring recent results that he says show CO2 building up after warming episodes, not before. He says the council did not follow procedures.
The AGU's executive director, A. Frederick Spilhaus, replies that in pulling the statement together, the group "followed all of its procedures ... and went beyond what we normally do" to get members' input.
As for the science, "a lot more work needs to be done," says Dr. Killeen, "but the bottom line is we're not at the starting line any more."