Russian scientists have discovered that volcanic particles can help cool the Earth, a leading environmental scientist said yesterday.

The world's temperature can drop 0.5 to 1 C a year if 1 million tons of volcanic particles are sprinkled across the globe from 10 to 14 km in the sky, said Yuri Israel, deputy head of the UN Inter-governmental Panel on Climate Change (IPCC), which won this year's Nobel Peace Prize with former US vice-president Al Gore.

"Our experiments have shown it's effective, and actually it's more effective than some methods stipulated in the Kyoto Protocol to mitigate global warming," Israel said during a Moscow-Beijing video-conference on climate change. The conference was part of an exchange program between Russia and China.

The floating particles will not stay in the sky forever. They will fall to earth in two to three years, said Israel, who is also Russian Academy of Science's chief climatologist.

The volcanic particles are "not harmful" in that their impact on the environment is only a fraction of industrial discharges.

A Russian scientist discovered the volcanic particles' resistance against solar radiation as early as 1974 when he noticed that the ground temperature around a volcano dropped remarkably after an eruption, Israel said. After a recent volcanic eruption in the Philippines, Russian scientists noticed the global temperature temporarily dropped 0.3 to 0.5 C.

Chinese Academy of Sciences' senior climatologist Huang Yao said the Russians' volcanic finding is "interesting and correct in principle".

"I also noticed the temporary drop in global temperature after the Philippines volcano eruption. So I think the new method may play an important role in research to fight on climate change."

But Huang said the possible impact of the volcanic particles on the environment and people's health is not known. "I look forward to seeing the data (of the Russian scientists)."