"We estimate that climate change may already be causing in the region of 160,000 deaths...a year," Professor Andrew Haines of the London School of Hygiene and Tropical Medicine told a climate change conference in Moscow.

"The disease burden caused by climate change could almost double by 2020," he added, even taking account of factors like improvements in health care. He said the estimates had not been previously published.

Most deaths would be in developing nations in Africa, Latin America and Southeast Asia, which would be hardest hit by the spread of malnutrition, diarrhea and malaria in the wake of warmer temperatures, floods and droughts.

"These diseases mainly affect younger age groups, so that the total burden of disease due to climate change appears to be borne mainly by children in developing countries," Haines said.

Milder winters, however, might mean that people would live longer on average in Europe or North America despite risks from heatwaves this summer in which about 15,000 people died in France alone.

Haines said the study suggested climate change could "bring some health benefits, such as lower cold-related mortality and greater crop yields in temperate zones, but (that) these will be greatly outweighed by increased rates of other diseases."

Russia is hosting a World Climate Change Conference this week to discuss how to rein in emissions of gases like carbon dioxide from factories and cars that scientists blame for blanketing the planet and nudging up temperatures.

Russian President Vladimir Putin, who opened the conference on Monday, suggested in jest that global warming could benefit countries like Russia as people "would spend less money on fur coats and other warm things."

But Putin also backed away from Russia's earlier pledge to swiftly ratify the key Kyoto pact on curbing global warming, a plan that will collapse without Moscow's backing.

He told 940 delegates to the conference Russia was closely studying the issue of Kyoto. "A decision will be taken when this work is finished," he said, giving no timetable.