Controlled pollution of the atmosphere could be a way to fight global warming, researchers say.

Nobel prize winner Paul Crutzen from Germany's Max Planck Institute for Chemistry raised the idea in a recent article in Climatic Change, which he wrote to try to get governments to take action on the problem.

He suggested introducing sulphur dioxide into the stratosphere using balloons or big guns. Sulphur dioxide reflects the sun's rays, which would help reduce the heating of the Earth.

The idea was picked up by U.S. government climatologist Tom Wigley, who wrote that Crutzen's idea would work.

Both scientists relied on evidence from the 1991 eruption of Mount Pinatubo in the Philippines. Debris containing sulphur from the eruption cooled the Earth by 0.5 degrees C for a year.

And a NASA research arm will be holding a workshop on the idea and other  "methods to ameliorate the likelihood of progressively rising temperatures over the next decades" this weekend.

While Crutzen's idea may work, the sulphur dioxide will come back to Earth as acid rain, posing its own risks. And because the chemicals will come back to Earth, more pollutants would have to be released every year or so.

Crutzen said he's not enthusiatic about the idea, but if governments do not act to cut emissions of carbon dioxide, which contribute to global warming, "then in the end we have to do experiments like this."

The idea is circulating at the UN climate change conference at Nairobi, where the reaction ranged from caution to concern about side effects.

"Yes, by all means, do all the research," Indian climatologist Rajendra Pachauri, who heads the UN network on climate change, told the Associated Press.

The delegates at the conference are struggling to determine what to do after the Kyoto accord ends in 2012.

Crutzen shared the 1995 Nobel prize for chemistry for work on the ozone layer with two other scientists.