Global warming has not stalled

Suggestions that global warming has stalled are a "diversionary tactic" from "deniers" who want the public to be confused over climate change, according to the world's best-known climate scientist. Prof James Hansen.

Since 1998, when the NiƱo climate phenomenon caused global temperatures to soar, the rate of increase in warming has slowed, causing some sceptics to suggest climate change has stopped or that the effect of rising carbon dioxide levels on climate is not as great as previously thought.

Speaking to BBC Radio 4's Today programme, he rejected both arguments. "In the last decade it has warmed only a tenth of a degree compared to two-tenths of a degree in the preceeding decade, but that's just natural variability. There is no reason to be surprised by that at all," he said. "If you look over a 30-40 year period the expected warming is two-tenths of a degree per decade, but that doesn't mean each decade is going to warm two-tenths of a degree."

"Our understanding of sensitivity is based on the Earth's history, not on climate models, and we have good data on how the Earth responded in the past when carbon dioxide changed."

On 9 May, a new study of lake sediments from a remote meteorite crater in Siberia showed temperatures in the region were 8C higher the last time CO2 levels were as high as they are today.

Last week, atmospheric CO2 concentrations reached the milestone 400 parts per million, for the first time in millions of years.