Clouded verdict

A new analysis of satellite data, collected over a decade, has identified the concentration, distribution, and composition of aerosol pollution over the Indian subcontinent. Using the multi-angle imaging spectroradiometer (MISR) from NASA’s Terra spacecraft, researchers at the University of Illinois at Urbana-Champaign, were able to document high levels of natural and human-caused pollution and reveal unexpected seasonal shifts in pollution.

Aerosol pollution across much of the country was two to five times higher than World Health Organization standards, with levels fluctuating during the seasons as monsoon rains wash away much of the smog and particulate matter, according to the study published in the Journal of Geophysical Research.

Black carbon particles, commonly called soot, are dark and light-absorbing and therefore warm the climate. Soot comes from combustion of fossil and biofuels, especially burning of diesel, coal and wood. Due to its warming effects, reduction of soot could help cool climate. However, soot absorption also affects cloud distributions and the verdict on how the clouds change is unclear. Because clouds mostly cool the climate, the possibility that soot absorption could increase cloud cover needs to be considered. And that means reducing BC may not be the silver bullet solution many thought.

Global model studies of soot effects on clouds do indeed find a variety of cloud responses, with increased clouds in some regions and decreased clouds in others. Most of the global model studies indicate that the net cloud response to absorbing particles is cooling. This suggests the need for caution when pursuing mitigation of soot in order to cool climate.