Under a complex weighting system, Russian ratification is the key to whether the 1997 Kyoto pact on limiting climate change will enter into force. Only if nations accounting for 55 percent of emissions sign up can the protocol take effect.

The United States, the world's biggest polluter, accounts for about one-third of all emissions, but U.S. President George W. Bush withdrew from the pact in 2001.

Russian Prime Minister Mikhail Kasyanov told an Earth Summit in Johannesburg last September that Moscow would ratify Kyoto "in the near future".

"I'm afraid that if Kyoto is not ratified we will have lost about eight or nine years chasing what might turn out to be a mirage," said Pachauri, chairman of the Intergovernmental Panel on Climate Change.

Asked if he had any idea when Russia might ratify the agreement Pachauri, speaking on the sidelines of an environmental conference in the Norwegian capital, replied "God knows."

"If you talk to 10 different people you get 10 different views of what Russia is likely to do...I don't know why it's taking so long," he said.

The Kyoto pact aims to cut emissions of gases like carbon dioxide, blamed for blanketing the planet and pushing up temperatures, to about five percent below 1990 levels.

Pachauri said Russian ratification would allow the world to move on and act more strongly to curb global warming, blamed by many scientists for phenomena ranging from rising sea levels to more extreme weather like floods and droughts.

"The whole world has been consumed with Kyoto and we've not looked at the longer term," he said. "The sooner we get the Kyoto protocol out of the way the better."

"The Kyoto Protocol is in a sense only going to scratch the surface," he said, adding that the world needed to do far more to reduce reliance on fossil fuels, for instance by shifting to renewable energy and raising energy efficiency.