Enviornment Prelims cum Mains

Black carbon travelling from Mediterranean polluting Himalayas in Uttarakhand, contributing to receding snowline, reveals study

The News

  • According to a study, black carbon travelling from Mediterranean countries during the western disturbance may be one of the important factors leading to the receding snowline in the Himalayas.

 

Key Highlights

  • The data was recorded at Gangotri Glacier Valley in Chirbasa between January and December 2016.
  • It was found that the black carbon concentration was high even in winter months, January and February, having no human activity like burning of fossil fuels or influx of tourists.
  • Thus, it was concluded that black carbon aerosols were being transported during western disturbances and wind trajectories.
  • Further, the concentration of black carbon during the months of January and February was fourth and fifth highest respectively among the 12 months recorded.

 

Background

  • The Hindu Kush-Himalayan-Tibetan region is considered as the “Third Pole” of the world.
  • 14 mountain ranges run in parallel from east to west, including the Altay, Tien Shan, Pamirs, Kunlun Shan, Karakoram, and Himalaya.
  • Global warming is having dramatic effects on the climate system in this region.
  • As a result, the majority of the glaciers in the region are retreating, and the monsoon rains are becoming less predictable.
  • It has been found in earlier studies that one of the leading causes of Climate Change at the third pole is Black Carbon.

 

 

Movement of pollutants to the region

  • The Tibetan Plateau is at the crossroads of influence between maritime air masses from the Indian Oceans (monsoons) and continental air masses from central Asia (westerlies).
  • During the winter and pre-monsoon season (October to April), large-scale circulation patterns (predominantly westerlies) transport air masses to the Plateau.
  • It was till now thought that Westerlies do not bring large quantities of pollutants with them.
  • However in summer (June to September), low pressure over the plateau induces a supply of moist, warm air from the Indian Oceans to the continent (summer monsoon).
  • These masses bring considerable pollution from South Asia.
  • The current study has shown that the pollutants in the atmosphere get transported during the western disturbance also.

 

 

Black Carbon 

  • Black carbon, a component of soot, is a by-product of incomplete combustion.
  • Unlike other aerosols, black carbon absorbs solar radiation.
  • It mixes with other aerosols like sulfates, nitrates, and carbon to form called as Atmospheric Brown Clouds.
  • The Atmospheric Brown Clouds leads to both warming of the lower atmosphere and surface dimming (due to the presence of sulfates).
  • Besides increasing amounts of soot in atmospheric brown clouds have accelerated snowmelt.

 

Effect of Black Carbon on snow

  • Snow is the most reflective natural surface on earth, with an albedo of almost 90%. Snow albedo can be reduced by very small amounts of impurities, like dust or black carbon.
  • Black Carbon is estimated to be fifty times more efficient than dust in reducing snow albedo.
  • One part-per-billion of black carbon (BC) on the surface can reduce snow albedo by 1-2%.

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