By Alex Kirby
BBC News Online environment correspondent
Europe can still save the Kyoto Protocol, the international climate treaty, a US environmental leader says.
Can Europe entice Russia to come in out of the cold?
Jonathan Lash, president of the World Resources Institute, told BBC News Online the Europeans held "the trump card" in making the treaty a reality.
He said Europe should offer Russia the diplomatic and economic gains it was seeking if it ratified the protocol.
The treaty will remain a dead letter unless Russia agrees to ratify it, and so far there is no clear sign it will.
To come into effect, the protocol requires the ratification of countries representing at least 55% of the global total of carbon dioxide emissions.
With the US and Australia refusing to take part, all the other major industrial powers must ratify the agreement for the quota to be reached, and Russia is the only country which has still not signed.
Mr Lash told BBC News Online: "The protocol is hanging in the balance: if the Russians don't ratify it in 2004, it will probably never be ratified.
"People thought originally the Russians could earn about $20bn by selling their unused emission credits.
"But now the US and the Australians have pulled out that's probably worth less than $1bn, because there's far less demand for the credits.
"So Europe holds the trump card, and it can save Kyoto if it wants to. It's not a question of renegotiating the protocol, but of offering the Russians what they want in other areas.
"First, they very badly want to join the World Trade Organisation. The Americans have no objections, but the Europeans do, and for them to agree to let Russia in would be very attractive to Moscow.
High-level kick start needed
"Then Europe could offer the Russians enhanced investment guarantees, especially in the energy sector. That would help a lot to reassure them.
"Finally, perhaps you could have a debt-for-cleanup swap, offering the Russians debt reductions if they spent roubles on reducing pollution.
"I can't imagine that happening at the level of environment ministers, and I think it would need a signal from 10 Downing Street.
"And if there's some competition between Europe and the US over which way Russia will be looking in the future, this could help to swing things Europe's way."
Mr Lash said the world should pursue attempts to store the main greenhouse gas covered by the protocol, carbon dioxide, where it could not add to atmospheric levels, a process known as sequestration.
He said he did not rule out an expansion of nuclear power to combat climate change: "I have a great sense of urgency about this. We don't have the luxury of being ideological."