Record warm start to 2002
UK scientists say the last three months were globally the warmest January, February and March since records began.
They are also the second-warmest consecutive three months ever recorded.
Worldwide temperatures were 0.71 Celsius above the 1961-1990 average.
The scientists say it is significant that the record was broken in the absence of any warming influence from El Nino, the climate disturbance that originates in the Pacific. El Ninos, which occur roughly every four years, are associated with increases in global temperatures.
Dr. Geoff Jenkins, of the UK Government's Hadley Centre for Climate Prediction and Research, said: "These three months were the warmest January, February and March since records began in 1860. Proxy records, for instance from tree rings, suggest they are in fact the warmest for a thousand years. Previous records have chiefly been broken during an El Nino, but this has happened in a slightly cool period."
The only consecutive three months warmer than the last three were February, March and April 1998, during a marked El Nino.
El Ninos occur when a huge mass of warm water builds up in the western Pacific and moves eastwards to the normally colder waters off the coast of South America, with widespread effects on weather in many parts of the world.
Dr. Jenkins was speaking at the launch of a report, Climate Change Scenarios for the United Kingdom, prepared by the Hadley Centre and the Tyndall Centre for Climate Change Research.
The report refines an earlier set of predictions published four years ago.
It explores four possible impact scenarios, based on low, medium-low, medium-high and high emissions of the gases many scientists believe are exacerbating the climate's natural variability.
Snow a distant memory
Some scientists argue that human activities are irrelevant to climate change, and that attempts to reduce any impact are misconceived.
The report includes predictions that by the 2080s:
Introducing the report, the Environment Secretary, Margaret Beckett, said: "We've known for some time that we have to worry about the impacts of climate change on our children's and grandchildren's generations. But we now have to worry about ourselves as well.
"Some of the impacts we will not be able to avert. The changes are already locked into the climate system and cannot be reversed," she added.
Dr. Jenkins told BBC News Online: "We believe there's an inbuilt temperature rise of 0.5-1C still to come.
"With sea level rise, there's even more of an inbuilt commitment there over the next 30 or 40 years, because the oceans take so long to warm."
Dr. Mike Hulme, of the Tyndall Centre, said temperatures over the UK lowlands could exceed 40 C within 80 years.
Barbara Young, chief executive of the Environment Agency, said: "The ultimate challenge is going to be the Thames.
"We need to start planning now all along the Thames estuary if London is going to be safe for the future."