"We need to put a price on carbon, everything else is secondary," said Dan Reicher, a former Energy Department official who is now president of New Energy Capital, which invests in renewable energy projects.

Greenhouse gas emissions have risen steeply over the past century and many scientists see a connection between that and an increase in global average temperatures and a related increase in extreme weather, wildfires, melting glaciers and other damage to the environment.

President Bush's administration has consistently rejected capping greenhouse gas emissions as bad for business and US workers.

In his first year in office in 2001, Bush withdrew from the Kyoto Protocol, an international agreement aimed at cutting greenhouse gases by setting limits on emissions from industrialized nations. He offered an alternative plan offering incentives for voluntary emissions cuts.

Reicher was part of a panel that included Stanford University climatologist Stephen Schneider, Sierra Club President Carl Pope and Duke Energy Chairman Paul Anderson.

Former Vice President Al Gore, who has become a vigorous campaigner in the fight against global warming, endorsed the panel's findings and said, "We have to overcome inertia and that's difficult."

Earlier Thursday, Gore urged more than 4,000 scientists at a meeting of the American Geophysical Union scientific group to become more active in explaining the dangers of global warming to the public.

"It is time, in my opinion, for scientists to play a different role in asserting the value of scientific insight, in defending the integrity of the scientific process and becoming far more active in communicating directly to the American people," he said. "Get involved, because so much is at stake."

Anderson said the lack of a clear signal over what form government action may take could delay plans among energy companies to invest in new technologies.