Context

With intensified debate on climate change, alternate methods like geo-engineering can be considered.

About

• Also known as “climate engineering”, geo-engineering is the intentional large-scale intervention in the Earth’s climate system to counter climate change.
• It includes techniques to remove carbon dioxide from the atmosphere, and technologies to rapidly cool the Earth by reflecting solar energy back to space.

Types of geo-engineering proposals

• Carbon dioxide removal techniques (CDR): techniques to remove carbon dioxide from the atmosphere.
• Ocean fertilisation using phytoplankton and iron:
  • Phytoplankton in the ocean use photosynthesis to capture CO2.
  • When they die, they sink deep into the ocean, taking all that CO2 with them.
  • Phytoplankton needs iron to grow.
  • Increasing the ocean’s iron content will cause the phytoplankton population to increase, thereby removing more CO2.
• Biochar production:
  • Biochar is a type of charcoal made from animal wastes and plant residues (such as wood chips, leaves, and husks) which can sequester carbon by circumventing the normal decomposition process or acting as a fertilizer to enhance the sequestration rate of growing biomass.
• Artificial trees:
  • Artificial trees essentially would be a series of sticky, resin-covered filters that would convert captured CO2 to a carbonate called soda ash.
  • Periodically, the soda ash would be washed off the filters and collected for storage.
• Carbon filtering:
  • Carbon burial: For example; burning large quantities of wood in power plants with carbon-capture technology, grazing cattle in a way designed to turn grasslands into giant carbon sinks, or converting C02 into stones.
  • Direct Air Capture: This technology uses huge fans to suck air through a filter to which CO2 chemically bonds. When heated, the filter releases the CO2, which can then be sold for other uses, such as growing vegetables in greenhouses, making carbonated drinks or even fuel.
  • Solar geo-engineering, or “solar radiation management” (SRM); technologies to rapidly cool the Earth by reflecting solar energy back to space.
• Stratospheric aerosol injection:
  • The idea is to simulate the cooling effects of volcanic eruptions, and enhancing the reflectivity of marine clouds.
  • When volcanoes erupt, they spread into the atmosphere tiny particles, commonly known as "aerosols."
  • Light-coloured aerosol particles can reflect incoming energy from the sun in cloud-free air, and dark particles can absorb it.
  • A small fleet of aircraft, for example, could conceivably inject sulphate-aerosols or other reflecting particles into the stratosphere and drive large-scale cooling.

• Marine cloud brightening:
  • Another idea is to increase the Earth’s ‘albedo’, which is the measure of amount of solar radiation the planet reflects back than it absorbs.
  • Because whiter surfaces reflect more light than darker ones, a whiter Earth will reflect more of the Sun’s energy back into space, helping to keep temperatures cooler.
  • One way to do this is to make clouds brighter and whiter.
  • This can be done by spraying sea water into clouds over the ocean. The salt water will cause them to grow bigger and brighter.
  • Other proposals to increase the Earth’s albedo include painting houses white, planting crops that are pale and perhaps even laying out reflective sheets in deserts.

• Cirrus cloud thinning (CCT):
  • CCT is almost the opposite of marine cloud brightening. High-altitude Cirrus clouds are thin and whispy, so they don't reflect much solar radiation back into space, and instead trap long-wave radiation on earth.
  • CCT proposes thinning them further through cloud seeding, letting more long-wave radiation escape.
  • The problem with CCT is that the cloud seeding can have the exact opposite effect, thickening the Cirrus formations.

• Space reflectors:
  • Technologies like giant mirrors in space or umbrellas in orbit can be built to reflect sunlight away and keep the planet cooler.
  • All these ideas have been proposed, but would be so expensive that no one really thinks we could afford them.