RUSUTSU, Japan - President Bush and leaders of the world's richest nations pledged yesterday to "move toward a low-carbon society" by cutting greenhouse gas emissions in half by 2050, the latest step in a long evolution by a president who for years played down the threat of global warming.
The declaration by the Group of Eight - the United States, Japan, Germany, Britain, France, Italy, Canada and Russia - was the first time that the Bush White House had publicly backed an explicit long-term target for eliminating the gases that scientists have said are warming the planet. But it failed to set a similar goal for cutting emissions over the next decade, and drew sharp criticism from environmentalists, who called it a missed opportunity.
In a sense, the document represents an environmental quid pro quo. In exchange for agreeing to the "50 by 2050" language, Bush got what he has sought as his price for joining an international accord: a statement from the rest of the Group of Eight that developing nations like China and India, which have declined to accept mandatory caps on carbon emissions, must be included in any climate change treaty.
European leaders, who have long pressed Bush to take a more aggressive stance on global warming, said the declaration could enhance efforts to reach a binding agreement to reduce emissions when negotiators meet in Copenhagen, Denmark, next year under U.N. auspices.
"This is a strong signal to citizens around the world," the president of the European Commission, Jose Manuel Barroso, told reporters at a news conference near here. "The science is clear; the economic case for action is stronger than ever. Now we need to go the extra mile to secure an ambitious global deal in Copenhagen."
Shari Wilson, Maryland's secretary of the environment, applauded the decision by the Bush administration as a step in the right direction, but she said the targets are not aggressive enough to prevent serious disruption of the world's climate. A state task force led by Wilson last year recommended a 90 percent cut by 2050, similar to a goal set by California.
"It's good to see some progress," Wilson said. "But it's not enough, and states like California and Maryland are following the science. And the science is saying we need a minimum of a 90 percent reduction by 2050. ... And we know that our greenhouse gas projections are steadily on the rise, so the earlier we make reductions, the better off we'll be."
The leaders of the eight industrialized countries, who gathered on the northern Japanese island of Hokkaido for their annual meeting, spent months debating the language of yesterday's communique in lower-level negotiations. Critics said it was short on specifics, and that both developed and developing countries would need to make much sharper cuts in emissions to head off the worst effects of global warming.
The statement left unclear, for instance, whether the cuts made by 2050 would be pegged to current emissions levels, or 1990 levels, as many advocates had hoped.
A 50 percent cut from current levels would result in a less significant decrease by 2050 than Japan and European nations had envisioned under the Kyoto Protocol, the international climate agreement that the Bush administration rejected after it took office. Kyoto and earlier agreements had set 1990 as the baseline for future cuts. The United States emitted about 20 percent more carbon dioxide in 2007 than it did in 1990.
"It is one step forward from the U.S. point of view, because President Bush has agreed that the United States, for the first time, must be bound by an international treaty," said Philip E. Clapp, director of the Pew Environmental Group, who is here monitoring the negotiations. "But the emissions reduction goal is extremely weak; the language in the communique is almost meaningless."
The White House painted the document as a victory.
"The G-8 is giving a lot, but the G-8 is also suggesting that others need to be part of that equation," said James L. Connaughton, Bush's top adviser on environmental matters. "And that's a very important shared statement."
Bush did not speak publicly about it, although Chancellor Angela Merkel of Germany raised the issue when she appeared briefly before cameras with the president, before the document was released. Merkel, who has been pushing Bush to take a stronger stance on global warming, pronounced herself "very satisfied."
Yet already, there are signs that the document could produce a rift between rich and poor nations. South Africa's minister of environmental affairs, Marthinus van Schalkwyk, issued a blistering critique of yesterday's communique, calling it a concession to "the lowest common denominator" and expressing concern that it "may, in effect, be a regression from what is required to make meaningful change."
Cutting emissions in half is one step in curtailing warming, climate experts have long said, because the main greenhouse gas generated by human activities, carbon dioxide, can persist for a century or more in the atmosphere once it is released. As long as more is being emitted than the oceans or plants can absorb, its concentration will rise. And fuel emissions are projected to rise relentlessly, driven by quickly expanding economies in Asia.
For Bush, who has just six months left in office, yesterday's declaration was part of an effort to salvage his legacy on climate change before the next administration comes in. His reputation as an outlier on the issue was set in the earliest days of his administration, when he abandoned a campaign promise to restrict carbon dioxide emissions from power plants and refused to join the Kyoto Protocol on the grounds that it did not apply to developing nations.
But over time, Bush's stance has shifted. In 2005, he surprised Europeans when, on a trip to Denmark, he stated unequivocally that humans caused global warming.
Some advocates credit the Group of Eight with Bush's shift. "The peer pressure on issues like climate change has helped," Dennis Howlett, coordinator of the Canadian advocacy group Make Poverty History, told reporters yesterday.
On the way to last year's Group of Eight meeting in Heiligendamm, Germany, Bush proposed his own process for grappling with global warming: a series of meetings involving so-called major emitters, including the developing nations China, India, Brazil, South Africa and Mexico, dubbed the Outreach Five.
Sun reporter Tom Pelton contributed to this article.