Aerosols fast heating up Himalayas, will have severe impact on monsoon and snow melt: Study

Tribune News Service

Vijay Mohan

Chandigarh, October 11

Aerosols are heating up the Himalayas at a high rate and will remain a key factor driving climate change over the Hindu Kush–Himalaya–Tibetan Plateau (HKHTP) region, altering atmospheric stability and influencing the hydrological cycle and precipitation patterns,with severe consequences for the Asian summer monsoon and glacial snow melt, a new study by Indian and German scientists has revealed.

“This is a first-time analysis of its kind, including ground-based observations, satellite data, and model simulations, which reveals that the Aerosol Radiative Forcing Efficiency (ARFE) in the atmosphere is clearly high over the Indo-Gangetic Plains (IGP) and the Himalayan foothills, with values being greater at higher elevations,” researchers have claimed.

The mean ARFE is 2–4 times higher here than over other polluted sites in South and East Asia, the study observed. Further, the observed annual mean aerosol-induced atmospheric heating rates are significantly higher than previously reported values for the region. Aerosol is a suspension of fine solid particles or liquid droplets, which could be natural or anthropogenic.

“The significant, regionally coherent aerosol-induced warming that we observe in the high altitudes of the region, is a significant factor contributing to increasing air temperature, observed accelerated retreat of the glaciers and changes in the hydrological cycle and precipitation patterns over this region,” the researchers said.

Titles “Aerosols Heat up the Himalayan Climate,” the study, carried out by experts at the Physical Research Laboratory, Ahmedabad, Research Institute for Sustainability – Helmholtz Centre, Potsdam, Leipzig Institute for Meteorology, University of Leipzig, Leipzig, and Institute for Environmental Sciences and Geography, University of Potsdam, Potsdam, all three in Germany, has been published this month.

They closely examined ground-based high-quality observations of aerosol characteristics, including radiative forcing from several locations, in the IGP, the Himalayan foothills and the Tibetan Plateau, which are relatively poorly studied regions with several sensitive ecosystems of global importance, as well as highly vulnerable large population.

The IGP, which covers parts of Pakistan, India, Bangladesh and Nepal, is a densely populated, industrialised and heavily polluted region in South Asia. Diverse aerosol emissions from natural and anthropogenic sources give rise to a persistent blanket of haze characterised by heavy aerosol loading over the IGP and downwind regions throughout nearly the whole year, the study observed.

High ARFE and aerosol heating rate observed over the Himalayas have significant implications. The near surface air temperature trend over the Himalayas during the past decades has increased to between 0.2 and 0.3 degree Celsius per decade since the mid-1950s, which is significantly higher than the global average.

In addition, there is a tendency for the warming rate to increase at higher elevations in the Tibetan Plateau and its surrounding regions. The atmospheric warming due to aerosols can alter regional atmospheric stability and vertical motions, affect large-scale circulation and the hydrological cycle, and thus be accompanied with significant regional climate effects and consequent impacts, the study observed.

Pointing out that the HKHTP region, containing the largest ice mass outside Antarctic and Arctic polar regions, has witnessed a pronounced retreat in glaciers that feed into major rivers of Asia, the researchers said that aerosol-induced atmospheric warming and deposition of light-absorbing carbonaceous aerosols on snow and ice are expected to accelerate glacier and snow melt.

Stating that the consistent ice loss observed along the entire 2000-km transect of the Himalayas could dominantly be the result of direct heating of the atmosphere by absorbing aerosols, the researchers have cautioned that rapid retreat of glaciers is expected to negatively affect water supply in southern and eastern Asia, with significant consequences for the regional hydrological cycle.

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