Britain's top government scientist warns current global warming will raise temperatures enough to put 400 million more people at risk of hunger.

Professor David King, using computer predictions, said worldwide temperatures will soar more than 3 degrees Celsius(5.4 F) over the next decades, causing worldwide cereal crops to drop up to 400 million tons.

King's government report said a 3 degree Celsius rise would also create water stress among 1.2 billion to 3 billion people. The report said few ecosystems can adapt, while a fifth of coastal wetlands would be lost, reports the BBC.

Britain's Prime Minster Tony Blair has called for a global consensus on stabilizing greenhouse gas emissions, but the United States has refused to cut them, the report said.

King told the BBC: "What we are talking about here is something that will play through over decades -- we are talking 100 years or so. We need to begin that process of investment."

"If you ask me where do we feel the temperature is likely to end up if we move to a level of carbon dioxide of 500 parts per million -- which is roughly twice the pre-industrial level and the level at which we would be optimistically hoping we could settle -- the temperature rise could be in excess of 3 C and yet we are saying 500 parts per million in the atmosphere is probably the best we can achieve through global agreement," he said.

King, a physical chemist, has served as head of the Office of Science and Technology and the government's chief science advisor since 2000.

Copyright 2006 by United Press International