Scientists and environmental experts scheduled to attend a UN-sponsored Environment Program in Cancun, Mexico, this month, have warned that "global dimming" is emerging as the latest threat to planet Earth, and added that cities like Beijing and New Delhi lie just beneath atmospheric brown cloud, thought to be caused mainly by the use of wood-burning stoves.
Pollution from soot is now so great that some parts of Asia get a quarter of the sunlight they had 50 years ago - affecting plants' ability to grow, the BBC quotes the experts, as saying.
The soot, also called black carbon, is not only damaging agriculture. The heat it traps may increase climate change problems, like melting ice.
Achim Steiner, head of the UN'S Environment Program, said: "Inefficient cooking stoves are estimated to be responsible for 25 per cent of emissions of black carbon."
Frank Kelly, Professor of Environmental Health at King's College, London, said last night: "It's a real phenomenon. This brown cloud comes from wooden cook stoves - and a lot from when crops are burned at the end of the season.
There is a downside to solving the problem - because soot in the atmosphere absorbs heat, so removing it may actually speed global warming.