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सेमिनार: अंग्रेज़ी सीखने का अवसर (23 सितंबर: दोपहर 3 बजे)
Using Geoengineering to combat Global Warming
Aug 18, 2017

[GS Paper III: (Conservation, environmental pollution and degradation, EIA, Disaster and Disaster Management)]

Why in news?

A collaborative study by researchers from India, China and the U.S. published in Geophysical Research Letters has offered a combination of two dominant geoengineering methods — stratospheric sulphate aerosol increase and cirrus cloud thinning — to reduce global warming and precipitation rates to pre-industrial levels.

What is Geoengineering?

  • Geoengineering is the technique designed to tackle the effects of climate change directly, usually by removing carbon dioxide (CO2) from the air or limiting the amount of sunlight reaching the planet's surface. It involves deliberate planet-scale interventions to counteract global warming. 
  • Techniques suggested include placing mirrors in space that reflect sunlight away from the Earth and fertilising the oceans with iron to encourage the growth of algae that can soak up atmospheric carbon dioxide.

Stratospheric sulphate aerosol injection

  • Fine, light-coloured particles designed to reflect back part of the solar radiation before it reaches and warms the earth would be sprayed into the stratosphere.  
  • This would not only reduce the global warming to pre-industrial levels, but also reduce the precipitation at a much higher rate than required to balance the effect of carbon dioxide.
  • The 1991 volcanic eruption of Mount Pinatubo in the Philippines is a natural precedent of the technique. It had injected 20 megatonnes of sulphur dioxide (SO2) into the stratosphere, cooling the earth significantly for a couple of years.

Cirrus cloud thinning

  • Cirrus clouds, which are at a height of 10 km above the Earth’s surface also trap the heat and thinning them could cool down the Earth. 
  • Greenhouse gases and cirrus clouds regulate outgoing longwave radiation (OLR) and cirrus cloud coverage is predicted to be sensitive to the ice fall speed which depends on ice crystal size. The higher the cirrus, the greater their impact is on OLR. Thus by changing ice crystal size in the coldest cirrus, OLR and climate might be modified. 
  • Deliberate depletion of cirrus clouds increases outgoing longwave radiation, reduces the upper tropospheric water vapor, and cools the climate. 

Types of clouds 

According to their height, expanse, density and transparency or opaqueness clouds are grouped under four types:

(i) Cirrus- Cirrus clouds are formed at high altitudes (8,000 - 12,000m). They are thin and detatched clouds having a feathery appearance. They are always white in colour.
(ii) Cumulus- Cumulus clouds look like cotton wool. They are formed at a height of 4,000 - 7,000 m. They exist in patches and can be seen scattered here and there. They have a flat base.
(iii) Stratus- These are layered clouds covering large portions of the sky. These clouds are generally formed either due to loss of heat or due to the mixing of air masses with different temperatures.
(iv) Nimbus- Nimbus clouds are black or dark gray. They form at middle levels or very near to the surface of the earth. These are extremely dense and opaque to the rays of the sun. 

A combination of these four basic types can give rise to the following types of clouds: 

  • high clouds – cirrus, cirrostratus, cirrocumulus; 
  • middle clouds – altostratus and altocumulus; 
  • low clouds – stratocumulus and nimbostratus and clouds with extensive vertical development – cumulus and cumulonimbus.


  • The technique could result in reduced precipitation, soil moisture and river flow in many regions.
  • Thinning cirrus cloud will also reduce the rate of precipitation to less than the required amount.
  • Injection of sulphur compounds into the stratosphere is likely to increase acid deposition on the ground and also contribute to ozone layer depletion.
  • Once the aerosol has been injected into the atmosphere, it cannot be removed.

Way Forward 

  • As nations struggle to reduce emissions even further, alternative solutions using geoengineering innovations will become more attractive.
  • However, geoengineering techniques carry the risk of causing unintended environmental damage by upsetting earth's natural cycles.
  • There must be a strict regulatory framework at global level to explore these options, as the consequences of such interventions can affect entire humanity. 


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