Decline in Tibetan Glaciers

Context: A study has found that black carbon aerosols have indirectly affected the mass gain of the Tibetan Plateau glaciers.

Decline in Tibetan Glaciers News

• The mass gain of the glacier was affected by changing long-range water vapour transport from the South Asian monsoon region.
• South Asia region, which is adjacent to the Tibetan Plateau, has among the highest levels of black carbon emission in the world.

Black Carbon Aerosols

• Black carbon aerosols are produced by the incomplete combustion of fossil fuels and biomass. They are characterised by strong light absorption capacity.
• Role in climate change: Black Carbon affects the climate through various mechanisms, including heating of the atmosphere, darkening and increased melting of the cryosphere (e.g., glaciers, snow cover, and sea ice) surface, and alteration of the optical and microphysical properties of clouds.

The Study on Decline in Tibetan Glaciers

• Role of South Asian carbon aerosols: Previous studies have found that black carbon aerosols from South Asia can be transported across the Himalayas to the inland region of the Tibetan Plateau.
• These South Asian black carbon aerosols have indirectly affected the mass gain of the Tibetan Plateau glaciers.
• The deposition of black carbon in snow reduces the albedo of surfaces, which may accelerate the melting of glaciers and snow cover, changing the hydrological process and water resources in the region.
• The reduced mass gain by precipitation decrease accounted for 11% of the average glacier mass loss on the Tibetan Plateau and 22.1% in the Himalayas, from 2007 to 2016.

How do Black Carbon Aerosols Reduce the Mass of Tibetan Glaciers?

• Black carbon aerosols in South Asia heat up the middle and upper atmosphere, thus increasing the North­–South temperature gradient.
  • Accordingly, the convective activity in South Asia is enhanced, which causes the convergence of water vapour in South Asia.
• Black carbon also increases the number of cloud condensation nuclei in the atmosphere.
• These changes in meteorological conditions caused by black carbon aerosols make more water vapour form precipitation in South Asia, and the northward transport of water vapour to the Tibetan Plateau is weakened.
• As a consequence, precipitation in the central and the southern Tibetan Plateau decreases during the monsoon, especially on the southern Tibetan Plateau.
  • The decrease in precipitation further leads to a decrease in the mass gain of glaciers.

Albedo

• Albedo is the measurement of reflectivity of solar radiation by any object. It is expressed as a percentage or a decimal value, with 1 being a perfect reflector and 0 absorbing all incoming light.
• A snowy hill, for example, has a high albedo. Whereas, dark objects, like pavement, have a low albedo.
• Albedo and Snow:
  • Because pure snow has a high albedo, it can reflect the majority of solar radiation. With the deposition of black carbon on a snow surface, the albedo decreases.
  • As a result, incoming solar radiation is absorbed, raising the temperature of the snow and causing it to melt.

Importance of Glaciers

Way Forward

• The most important protective measure to counter substantial glacier retreat worldwide is to drastically reduce greenhouse gas emissions.
• If emissions are drastically cut to limit global warming to 1.5°C relative to pre-industrial levels, a significant number of glaciers could be saved.
• Adaptive measures to prevent glacier loss:
  • Identifying knowledge gaps and improving monitoring networks
  • Designing and implementing early warning and disaster risk reduction measures
  • Making glaciers a focus of targeted policy
  • Promoting knowledge exchange, stakeholder engagement, and communication

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