By Alex Kirby
BBC News Online environment correspondent
source: [
news.bbc.co.uk]
A British researcher says there are simple technical solutions to the huge problems caused by pollution in southern Asia.
United Nations scientists say the pollution is both a regional and a global menace.
They say the Asian brown haze affects rainfall and farming, and puts hundreds of thousands of people in jeopardy.
They fear the pollution's impacts will worsen over the next 30 years.
It has a direct effect on human health, they say, causing more respiratory disease.
The British scientist is Dr David Viner, of the Climatic Research Unit, University of East Anglia, UK.
He told BBC News Online: "The London smogs of the last century were a comparable problem, though the Asian haze is more widespread, more persistent, and thicker.
Not so easy
"There are solutions - stop burning the forests, switch to less polluting fuels, and introduce clean air technology, like scrubbers on power station chimneys.
"They're simple to work out. Unfortunately, they're rather more difficult to implement."
The scientists, working for the UN Environment Programme (Unep), have based their work on data gathered by the Indian Ocean Experiment (Indoex), supplemented by satellite readings and computer modelling.
The team includes Professors V Ramanathan of the Scripps Institution of Oceanography, US, Paul Crutzen, of the Max Planck Institute for Chemistry, Germany, and A P Mitra, of India's National Physical Laboratory.
The head of Unep, Dr Klaus Toepfer, told journalists in London the threat was real.
He said: "The haze is the result of forest fires, the burning of agricultural wastes, dramatic increases in the burning of fossil fuels in vehicles, industries and power stations, and emissions from millions of inefficient cookers burning wood, cow dung and other 'bio-fuels'.
"These initial findings clearly indicate that this growing cocktail of soot, particles, aerosols and other pollutants is becoming a major environmental hazard for Asia.
"There are also global implications, not least because a pollution parcel like this, which stretches three kilometres (two miles) high, can travel halfway round the globe in a week."
The UN says about two billion people in south and southeast Asia use wood or similar "biomass" fuels. Clean energy will be one of the preoccupations of the sustainable development summit starting in Johannesburg in late August.
Drier summers
The scientists say the haze is reducing the amount of solar energy reaching the Earth's surface by up to 15%. But it also absorbs heat, and they estimate that it is not only cooling the Earth's surface but warming the lower atmosphere appreciably.
They believe this is altering the winter monsoon, sharply cutting rainfall over north-western Asia and increasing it further east.
The models they used suggest the haze may reduce rain and snow over parts of western central Asia by between 20% and 40%.
Researchers at the Hadley Centre for Climate Prediction and Research, UK, say the overall cooling of the northern hemisphere, where aerosol concentrations are higher than south of the Equator, may also weaken the summer monsoon and reduce rainfall in south Asia.
They say most rain falls during the summer monsoon, and it helps to wash pollution out of the atmosphere.
Sick and hungry
The report's authors say the reduction in solar energy reaching the Earth's surface means less oceanic evaporation of the moisture which controls summer rainfall.
They estimate that the haze could be reducing India's winter rice harvest by up to 10%. And they fear "several hundreds of thousands" of premature deaths from haze-related respiratory diseases.
The report, commissioned by Unep, was prepared by the Center for Clouds, Chemistry and Climate.