India's cooling paradox

Aerosols responsible for toxic air pollution could explain India's slower warming—but scientists warn there are no easy solutions

- AKSHIT SANGOMLA NEW DELHI

INDIA HAS warmed significantly over the past several decades—but not as much as the rest of the Northern Hemisphere. Satellite data from the US National Aeronautics and Space Administration (NASA), released on January 10, shows that since the 1950s, the country has warmed about 0.6°C, which is only about half the warming seen in other regions of the hemisphere. At first glance, this might seem like a potential silver lining in the climate crisis. But scientists say it could be a warning sign rather than a cause for comfort.

One possible explanation for this unusual trend lies in the thick blanket of aerosols—fine particulate matter that remain suspended in the air—lingering over large parts of the country, especially the Indo-Gangetic plains.

Aerosols, largely released through fossil fuel combustion, crop burning and industrial activities, act like a massive sunshade. “They reflect sunlight back into space like tiny mirrors or absorb it in the upper atmosphere. Either way, they reduce the amount of solar radiation reaching the surface,” says Loretta J Mickley, senior research fellow and co-lead, Atmospheric Chemistry Modeling Group, Harvard University, US. The result is a net cooling effect at the ground level—even as greenhouse gases continue to accumulate.

However, Mickley says, little has been studied to understand what governs the temperature patterns in India and the role of aerosols in suppressing warming. “In the eastern US, we have historically dealt mostly with reflective sulphate aerosols,” says Mickley. “But India also has a significant presence of black carbon—emitted from industries and crop burning—which makes the aerosol mix much more absorbing,” she adds.