Climate history forces action -- after decades

US President Lyndon Johnson and British Prime Minister Margaret Thatcher made stark warnings about global warming decades ago, but convincing evidence for action only amassed in recent years, experts say.

A 190-nation U.N. conference in Copenhagen in December is due to agree a new U.N. pact to curbgreenhouse gas emissions to slow a rise in temperatures to prevent floods, droughts, wildfires or rising sea levels.

Scientists have known for a century that greenhouse gases, for instance from burning coal, can warm the planet. But most experts say the evidence was thin until about the past decade.

"I don't think it (the world reaction) was too slow -- I think we have a very solid foundation for action now," said Yvo de Boer, head of the U.N. Climate Change Secretariat. "The sceptics are no longer derailing the process."

He noted it was only in 1995 that the U.N's Intergovernmental Panel on Climate Change blamed mankind for global warming, saying cautiously that the "balance of evidence suggests a discernible human influence on global climate".

"In recent years we've managed to move light years beyond that" level of certainty, he told Reuters during talks on the new U.N. treaty in Barcelona. The panel says it is at least 90 percent certain that global warming is man-made.