MOSCOW, Sept. 30 - The long-delayed Kyoto Protocol on global warming overcame its last critical hurdle to taking effect around the world on Thursday when Russia's cabinet endorsed the treaty and sent it to Parliament. The treaty, the first to require cuts in emissions linked to global warming, would take effect 90 days after Parliament's approval, a formality that was widely expected.
The United States has rejected the treaty and will not be bound by its restrictions. But the treaty, which has already been ratified by 120 countries will take effect if supporters include nations accounting for at least 55 percent of all industrialized countries' 1990-level emissions. The only way for it to cross that threshold was with ratification by Russia. In 1990, the United States accounted for 36.1 percent of emissions from industrialized countries, and Russia 17.4 percent.
The protocol was dormant over the last two years as Russia considered its merits and sought concessions from the European Union, the treaty's main proponent.
The treaty is widely considered a milestone of international environmental diplomacy. It is the first agreement that sets binding restrictions on emissions of heat-trapping gases that, for now, remain an unavoidable result of almost any facet of modern life, including driving a car and running a power plant. The main source of the dominant gas, carbon dioxide, is burning coal and oil.
But many specialists say that, at the same time, the protocol is just the tiniest initial step toward limiting the human influence on the climate, given that its targets are small and that the United States will not be bound by its terms. China, a major polluter that did sign the treaty, is not bound by its restrictions because it is considered a developing country.
The treaty would require 36 industrialized countries to reduce their collective emissions of six greenhouse gases by 2012 to more than five percent below 1990 levels, with different targets negotiated for individual countries.
By one calculation, it would take more than 40 times the emissions reductions required under the treaty to prevent a doubling of the pre-industrial concentration of carbon dioxide in the atmosphere in this century.
Still, the decision by the government of President Vladimir V. Putin to endorse the treaty was "cause for celebration," said Klaus Toepfer, the executive director of the United Nations Environment Program.
He acknowledged that the Kyoto accord was "only the first step in a long journey towards stabilizing greenhouse gas emissions." But Mr. Toepfer added that Russia's move sent a vital signal to developing countries, which supported the treaty only if it excused them from reductions, and the small number of wealthy nations that still oppose curbs on the gases that cause global warming, most notably the United States.
"I hope other nations, some of whom, like Russia, have maybe been in the past reluctant to ratify, will now join us in this truly global endeavor," he said.
In Washington, Harlan L. Watson, the chief State Department negotiator on climate issues, said Russia's decision would not change the Bush administration's rejection of the treaty. Mr. Watson said the United States would continue to focus on long-term research to find new nonpolluting sources of energy or ways to limit the buildup of carbon dioxide.
A spokesman for Senator John Kerry, the Democratic presidential candidate, who has criticized the Bush administration's position on global warming, was quick to seize on Russia's decision. "George Bush made a catastrophic mistake when he declared a decade's work of 160 nations dead on arrival instead of working with our allies to fix the treaty and lead on global warming,'' said the spokesman, David Wade. "We're still paying a heavy price for his unilateralism."
One more step is required in Russia for the pact to take effect - approval by the Parliament, or Duma. But the body is dominated by supporters of Mr. Putin, so approval is expected, even though Prime Minister Mikhail Fradkov predicted a "difficult debate." The treaty would take effect 90 days after the Duma approval.
Mr. Putin made no public statement on Thursday. His top economic adviser, Andrei Illarionov, who had opposed the pact, said that the decision to endorse it had been made for political reasons and that the task now would be to try to minimize what he called the treaty's negative consequences for Russia.
He said compliance would slow Russia's economic growth and make it impossible to meet Mr. Putin's stated goal of doubling the gross domestic product within a decade.
"It's not a decision we are making with pleasure," Mr. Illarionov said, the Interfax news agency reported.
The European Union had pressed Russia for more than a year to accept the pact. In Brussels, Romano Prodi, the president of the European Commission, said "President Putin has sent a strong signal of his commitment and sense of responsibility."
Mr. Illarionov had said the treaty was based on false and even deceptive scientific assumptions.
His views conflict with a broad international scientific consensus that the buildup of long-lived gases, which act like the panes in a greenhouse roof, is likely to disrupt weather patterns and water supplies and threaten coasts by raising sea levels.
German Gref, Russia's economic development minister, called the treaty "a progressive step" but said, "It will hardly be decisive in radically improving the environmental situation."
Breaking with Mr. Illarionov, Mr. Gref added that the treaty was unlikely to undermine Russia's economic growth.
In Washington, some lobbyists for American industries opposed to the treaty suggested there was a chance that Mr. Putin still opposed it and was planning for Parliament to reject it - as proof that he was not consolidating power.
But in Moscow, the mood among environmental activists was cautiously upbeat.
Vladimir Azkharov, director of the Center for Russian Environmental Policy, a lobbying group, said the treaty "very, very probably" would be approved in parliament, although he said, "there is no guarantee."
President Bush summarily rejected the treaty in 2001, saying it would burden the economy by limiting use of fossil fuels and would unfairly exclude big developing countries from curbs on emissions. The Senate had long ago signaled its opposition for the same reasons.
China and other developing countries, while signing the treaty, only did so because it obligated established industrial powers to act first.
Last December, in what seemed a definitive rejection, Mr. Illarionov said Russia would not sign the treaty. In May, however, Mr. Putin promised to speed ratification, in a move widely interpreted as a concession to gain support from the European Union for Russia's bid to join the World Trade Organization. International environmental groups expressed satisfaction at the news.
"As the Earth is battered by increasing storms, floods and droughts, President Putin has brought us to a pivotal point in human history," Steve Sawyer, a climate campaigner for Greenpeace International, said. "The Bush administration is out in the cold and the rest of the world can move forward."
In a telephone interview, Fred Krupp, the president of Environmental Defense, said, "What is significant is that it will be a market signal heard around the world, a signal that we are moving into a carbon-constrained future."
The treaty, named for the Japanese city of Kyoto where it was negotiated in 1997, is an outgrowth of a 1992 pact, the United Nations Framework Convention on Climate Change, that was signed by Mr. Bush's father and under which countries agreed to strive to bring their emissions of the gases to 1990 levels by 2000.
By the mid-1990s, however, it was clear that the targets would not be met, leading to a new round of talks toward a binding protocol with firm targets and penalties.
Its basic architecture and targets were hastily negotiated in December 1997 in Kyoto. But momentum was lost after Mr. Bush rejected it and after the attacks of Sept. 11, 2001.
Some of its biggest weaknesses now stem from the long delays. Subsequent economic activity and rising emissions have threatened to put Europe and Japan, its main backers, out of compliance.
The treaty provides various strategies through which countries can reach their targets without actually reducing emissions at home. Investments can be made in poor countries to save forests, which absorb carbon dioxide, or introduce efficient technologies, which use less fuel.
It permits emissions trading, in which one country buys the right to emit from another that has already exceeded its targets for reducing emissions and has extra credits.
Prof. David G. Victor, a political scientist at Stanford and longtime student of the protocol, said Russia had nothing to lose by moving ahead, since it surpassed its Kyoto targets before they were set.
After the Russian economy collapsed with the fall of Communism, the country's greenhouse gas emissions fell far below 1990 levels, leaving it with a bonanza of tradable credits earned when it surpassed its targets for reducing emissions. For Europe this bundle of credits is a mixed blessing now, Mr. Victor said.
The European Union recently passed legislation creating an internal trading market under the protocol's terms, so that richer member states, like Britain, could get credit toward targets by investing in emissions-cutting projects in poorer, more polluted, ones, like Spain. But under the treaty's terms, Europe, Japan, and other industrialized participants can buy credits from Russia as well. If Russia now starts selling its credits to Europe, there will be little incentive for companies within the European Union to push ahead with plans to cut emissions that would be more costly, Mr. Victor said.