Asia's brown clouds warm planet

BBC NEWS | Science/Nature | Asias brown clouds warm planet

Clouds of pollution over the Indian Ocean appear to cause as much warming as greenhouse gases released by human activity, a study has suggested. US researchers used unmanned aircraft to measure the effects of the “brown clouds” on the surrounding area. Writing in Nature, they said the tiny particles increased the solar heating of the lower atmosphere by about 50%.

The warming could be enough to explain the retreat of glaciers in the Himalayas, the scientists proposed. The clouds contain a mixture of light absorbing aerosols and light scattering aerosols, which cause the atmosphere to warm and the surface of the Earth to cool.

Wow, I’ll have to read the paper later today to confirm, but when I was doing aerosol work in India back in the mid ’90s, the Indian Ocean cloud was unknown. 1995 through 1998, there was an experiment called INDOEX (my thesis advisor in Bombay participated in the later phases) which first observed this brown cloud. At that time, it was assumed that the light scattering (hence “cooling”) effects of this aerosol would dominate the absorbing (or “heating”) effects, and initial model estimates seemed to agree.

Turns out that it has a significant warming effect because the soot particles (dark, therefore heat absorbing) predominate. And, you had to measure it.

For their study, the team of researchers used three unmanned aircraft, fitted with miniaturised instruments that were able to measure aerosol concentrations, soot amounts and the flow of energy from the Sun.

The crafts flew over the polluted region of the Indian Ocean at varying heights between 500m (1,640ft) and 3,000m (9,840ft).

“During 18 flight missions, the three unmanned aerial vehicles were flown with a separation of tens of metres or less and less than 10 seconds (apart), which made it possible to measure the atmospheric solar heating rates directly,” they wrote.

If true, we can reduce the size of this “cloud” by reducing biomass combustion, installing particle controls on power plants, cleaning up other combustion sources, etc, and reduce global warming effects without worrying that this cloud was somehow mitigating temperature rise as previously thought. So, a win-win!

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