Russian President Vladimir Putin has surprised the world by promising to move quickly on ratification of the Kyoto climate change treaty.
Putin appears to have ignored advice to reject Kyoto
One environmentalist called it "a very welcome and positive signal" which could breathe life into the protocol.
Mr Putin made the concession after the EU backed Russia's bid to join the WTO.
The EU had made its support dependent on Russia ratifying Kyoto. Since the US rejected the treaty, Russia's backing has been vital to bring it into force.
Mr Putin said: "The EU has met us half way in talks over the WTO (World Trade Organisation) and that cannot but affect positively our position on the Kyoto
Protocol," he said.
"We will speed up Russia's movement toward the Kyoto Protocol's ratification."
His comments were all the more surprising, since two reports he commissioned concluded it would not be in Russia's interest to join.
"I really did not expect this," said Alexei Kokorin, of the WWF environmental group. "He spoke without official advice, but it shows that he is well informed."
Kyoto was signed more than six years ago, and aims to reduce emissions of carbon dioxide and other greenhouse gases.
To come into effect, it needs the support of developed nations responsible for 55% of such emissions.
Since US President George Bush pulled out in 2001, Russia is the only country big enough to carry Kyoto over the 55% threshold.
"It is vital that the Kyoto Protocol enters into force as a first step towards stabilising the global climate," said Klaus Toepfer, head of the UN Environment Programme.
"Ratification by Russia is the last crucial step needed to make Kyoto operational."
Others, though, warned the deal was not yet done.
"I'm cautiously optimistic. It's not a cut and dried promise but it will be much harder for Russia to decide 'no' to Kyoto now," said Steve Sawyer of Greenpeace.
The deal over WTO entry was reached between EU Trade Commissioner Pascal Lamy and Russian Trade Minister German Gref in Moscow.
Russia, the last major economy still outside the WTO bloc, still needs to reach agreements with the US and China.
Mr Putin opened the meeting by saying that Russia and the EU should be equal partners.
Irish Prime Minister Bertie Ahern, whose country holds the current presidency of the newly enlarged EU, said: "We look forward to working closely with you over the next four years and building a strong partnership."