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Geoengineering means manipulating the earth’s climate to lower its temperature in a bid to counter global warming. Solar geoengineering, also called solar radiation modification, involves cooling the earth by radiating absorbed sunlight back into space. It is a subset of geoengineering.
The basic idea behind solar geoengineering
The temperature of the earth’s surface rises by absorbing heat energy from the sun (short wave radiation). The warm surface of the earth emits part of this heat back as infrared radiation (long wave radiation). This outgoing radiation heats the atmosphere. At higher altitudes, the heat escapes into outer space without raising the temperature of the earth’s atmosphere. The temperature of the atmosphere at the altitude of emission determines the total outgoing energy.
Greenhouse gases like carbon dioxide make it difficult for infrared radiation to escape the earth’s atmosphere, causing an imbalance between the incoming and outgoing energies. As the total incoming energy exceeds the total outgoing energy, the surface of the earth warms up.
Solar geoengineering aims at increasing the amount of heat radiated back into the space using artificial methods. This will, in turn, reduce the temperature of the earth’s surface.
Types of solar geoengineering
Currently, the two commonly proposed methods of solar geoengineering are stratospheric aerosol injection (SAI), and marine cloud brightening.
SAI includes spraying large quantities of tiny particles into the earth’s stratosphere to reflect sunlight and keep the earth cooler. Scientists have proposed using compounds with reflective properties, like sulphur dioxides or finely powdered calcium carbonate, as aerosols.
The concept of SAI is derived from sulphur clouds released during volcanic eruptions. Powerful volcano eruptions emit a sulphur-rich dust cloud that can reach the stratosphere. It has particles that reflect sunlight and cause a cooling effect.
Marine cloud brightening proposes spraying sea salt into low-lying clouds to increase their brightness and the ability to reflect sunlight. This could increase the concentration of droplets at the base of a cloud, which in turn will reflect more sunlight before it reaches the surface of the earth.
Why is it controversial?
Solar geoengineering is not a permanent solution to global warming or climate change.
SAI is particularly controversial because the reflective effect of aerosols wears off after some time, leading to a net heating effect.
According to the Union of Concerned Scientists, solar geoengineering can be a “moral hazard” and slow efforts towards emission reduction as it does not address the root cause of climate change. There is also not enough evidence to show how altering the atmosphere can affect regional as well as global precipitation cycles.
According to Geoengineering Monitor, it is possible that the scale of geoengineering proposals can have an unpredictable impact on environmental elements like air, land, and sea, and these negative outcomes of the exercise would be borne by the global south.
In January 2022, an international group of scientists and scholars launched an initiative that called for a moratorium on the study and development of solar geoengineering. According to the experts, risks of the concept are poorly misunderstood, and the global governance system is unfit to maintain a fair and inclusive control over the technology.
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