"We understand that without Russia's participation in the protocol, it cannot begin to work," he said last week.

Russian ratification will push the 126-nation U.N. accord, aimed at battling global warming, over the threshold of 55 percent of developed nations' greenhouse gas emissions needed to make it internationally binding after a U.S. pullout in 2001.

After Duma approval last week, the bill still has to go through the upper house and be signed into law by its key advocate, President Vladimir Putin.

Environmentalists are confident of ratification but say the pact is only the start of a lot of hard work needed to counter the dangers of climate change.

"We must build on the Kyoto Protocol, and seek agreement for the much deeper emissions reductions required to put us on a path towards a real solution to the threat of dangerous climate change," Greenpeace climate policy adviser Steve Sawyer said in a statement ahead of the vote.

Klaus Toepfer, executive director of the United Nations Environment Programme (UNEP), said a positive vote would be a milestone that "will concentrate the efforts of governments, business and industry on meeting the Kyoto targets and concentrate efforts on how we can deliver the even deeper cuts."

Rising global temperatures have been linked to extreme weather patterns, including droughts and flooding which are seen by some as a spark for regional conflicts.

Moscow signed the 1997 Kyoto Protocol in 1999, but delayed ratifying it until May this year in exchange for EU agreement on the terms of Moscow's admission to the World Trade Organisation.

Russia, which accounts for 17 percent of world greenhouse gas emissions, became the key to Kyoto's future after the United States pulled out of the agreement.

Proponents of Kyoto say that apart from improving the environment worldwide, the pact would force Russia to upgrade its industry to new standards.

They also believe Russia, whose smokestack industries have cut emissions by about 30 percent since the collapse of the Soviet Union, could earn billions of dollars by selling excess quotas for gas emissions to polluters abroad.

But opponents insist new emission limits could constrain Russia's economic growth and undermine Putin's plan to double gross domestic product in 10 years.

Russian debates reflect worldwide arguments over the pact.

Supporters of Kyoto believe Russia's ratification could help Europe's cause of persuading the United States to reconsider its rejection of the pact.

"We have a completely new momentum in the debate," said European Environment Commissioner Margot Wallstrom. "This will continue to raise the debate level in the U.S."

Gryzlov told Itar-Tass news agency last week he expected no problems with Kyoto ratification and suggested that if the assessment of the pact's impact on Russia proved wrong, things could be fixed later.