THE Earth faces a new environmental threat, scientists have warned - global DIMMING.
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.
Cities like Beijing and New Delhi lie beneath atmospheric brown cloud, thought to be caused mainly by the use of wood-burning stoves.
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 Programme, will call for action at a conference this month in Cancun, Mexico.
He 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.
"You see reports of schools being closed in Singapore after clouds drift over from Indonesia."
There is a downside to solving the problem - because soot in the atmosphere absorbs heat, so removing it may actually speed global warming.