LONDON (Reuters) - The earth has a fever that could boost temperatures by 8 degrees Celsius making large parts of the surface uninhabitable and threatening billions of peoples' lives, a controversial climate scientist said on Tuesday.

James Lovelock, who angered climate scientists with his Gaia theory of a living planet and then alienated environmentalists by backing nuclear power, said a traumatized earth might only be able to support less than a tenth of it's 6 billion people.

"We are not all doomed. An awful lot of people will die, but I don't see the species dying out," he told a news conference. "A hot earth couldn't support much over 500 million."

"Almost all of the systems that have been looked at are in positive feedback ... and soon those effects will be larger than any of the effects of carbon dioxide emissions from industry and so on around the world," he added.

Scientists say that global warming due to carbon emissions from burning fossil fuels for power and transport could boost average temperatures by up to 6C by the end of the century causing floods, famines and violent storms.

But they also say that tough action now to cut carbon emissions could stop atmospheric concentrations of CO2 hitting 450 parts per million -- equivalent to a temperature rise of 2C from pre-industrial levels -- and save the planet.

Lovelock said temperature rises of up to 8C were already built in and while efforts to curb it were morally commendable, they were wasted.

"It is a bit like if your kidneys fail you can go on dialysis -- and who would refuse dialysis if death is the alternative. We should think of it in that context," he said.

"But remember that all they are doing is buying us time, no more. The problems go on," he added.

REFUGE

Lovelock adopted the name Gaia, the Greek mother earth goddess, in the 1960s to apply to his then revolutionary theory that the earth functions as a single, self-sustaining organism. His theory is now widely accepted.

In London to give a lecture on the environment to the Institution of Chemical Engineers, he said the planet had survived dramatic climate change at least seven times.

"In the change from the last Ice Age to now we lost land equivalent to the continent of Africa beneath the sea," he said. "We are facing things just as bad or worse than that during this century."

"There are refuges, plenty of them. 55 million years ago ... life moved up to the Arctic, stayed there during the course of it and then moved back again as things improved. I fear that this is what we may have to do," he added.

Lovelock said the United States, which has rejected the Kyoto Protocol on cutting carbon emissions, wrongly believed there was a technological solution, while booming economies China and India were out of control.

China is building a coal-fired power station a week to feed rampant demand, and India's economy is likewise surging.

If either suddenly decided to stop their carbon-fuelled development to lift their billions of people out of poverty they would face a revolution, yet if they continued, rising CO2 and temperatures would kill off plants and produce famine, he said.

"If climate change goes on course ... I can't see China being able to produce enough food by the middle of the century to support its people. They will have to move somewhere and Siberia is empty and it will be warmer then," he said.