Rising ‘black carbon’ heating Himalayan snow: Study

Rising black carbon levels in the Himalayas contribute to warmer snow, increasing flood risk, according to Climate Trends study.

Levels of black carbon — ultra-fine particles of carbon that come from vehicles, stoves and wood-fire — in the Himalayas have been rising for most of the past two decades, according to a study by the think-tank Climate Trends. This is contributing to warmer snow, increasing the risk of unseasonal flooding by glacier-fed rivers, it said.

While not a peer-reviewed analysis, the study analysed satellite-based measurements of black carbon and changes in the temperature of snow between 2000 and 2023. Climate science says that aerosols — particulate matter emissions from a variety of sources, from fertiliser to vehicle exhaust — clog the atmosphere, deflecting sunlight away from the carbon and are known to mask the heating effect of greenhouse gases.

Black carbon is different, in that it absorbs sunlight and if it settles on the surface can thus heat the ground. This is one reason climatologists consider black carbon as a catalyst to global warming, even though it is relatively short-lived in the atmosphere unlike carbon dioxide, the most pervasive greenhouse gas.

“The snow surface temperature in the Himalayas has shown a consistent warming trend over the past two decades, which may have serious implications for snow and glacier stability,” the study notes. The average snow-surface temperature has increased from -11.27°C from 2000–2009 to -7.13°C during 2020–2023, with an overall mean of -8.57°C for the 23-year period.

Among the three major regions, the Eastern Himalayas record the warmest snow surfaces, followed by the Central and Western Himalayas. This warming was “likely driven,” the study surmised, in part by the deposition of light-absorbing particles like black carbon, which lowers snow albedo — the ability to reflect sunlight — and accelerates surface heating. The decadal average for 2010–2019 showed the highest warming in the Eastern Himalayas at -5.69°C.

“Continued temperature rise in snow-covered areas can shorten snow season duration and advance melting onset, impacting hydrological systems and water security for millions downstream. Thus, temperature increases, in conjunction with [black carbon] BC presence, are significantly altering the snow thermal regime in the Himalayas,” the study underlined.

“Glacier melt is accelerating, threatening freshwater resources to nearly two billion people downstream,” Palak Baliyan, lead author of the study, said in a statement.