The UK government's chief scientist has said that there is already enough CO2 in the atmosphere for there to be more floods and droughts over the next 25 years.
Prof Sir John Beddington said there was a "need for urgency" in tackling climate change.
He said that the later governments left it, the harder it would be to combat. Prof Beddington made his comments in the final week of his tenure as the government's chief scientific adviser.
"The current variation we are seeing in temperature or rainfall is double the rate of the average. That suggests that we are going to have more droughts, we are going to have more floods, we are going to have more sea surges and we are going to have more storms.
"These are the sort of changes that are going to affect us in quite a short timescale," he warned.
Prof Beddington's comments come at a time when "climate sceptics" have been challenging claims by scientists that the release of CO2 into the atmosphere is increasing global temperatures.
Other critics have argued that even if the burning of fossil fuels is changing the planet's climate, the reduction of CO2 levels by the world's emerging nations is unrealistic, impractical and undesirable.
Prof Beddington's blunt response is: "The evidence that climate change is happening is completely unequivocal."
But the issue, he says, has been clouded by the fact that the planet's climate system operates slowly to changes and so there are long delays in CO2 level rises in the atmosphere resulting in changes to weather patterns. "So the next 20 or 30 years are going to be determined by what's up there now."
Governments have agreed to try to keep the rise in average global temperatures to below 2C. Given the slow progress in attempts to curb CO2 emissions at successive climate change talks, many experts believe that target to be unrealistic.
From the BBC News