The United States is open to studying the possibility of the effectiveness of Solar Radiation Management (SRM).

Key Point

• SRM is one of the strategies that seek to control how much sunlight reaches the Earth.
• It is part of a controversial concept called ‘geoengineering’ that has caught the fancy of some sections as a potential solution to global warming.
• The scientific dimensions of SRM involve new and continued ground-based, airborne, and space-based observations and improving global modelling of SRM approaches and scenarios.
• They can help in the understanding of the physical processes and outcomes associated with SRM.

What is Solar Geoengineering?

• Solar geoengineering- also referred to as solar radiation management– describes a set of proposed approaches to reflect sunlight to rapidly cool the Earth.
• It refers to proposed approaches to cool the Earth by reflecting solar radiation back to space.
• The two main approaches being researched are stratospheric aerosol injection (SAI) and marine cloud brightening (MCB).
• The first- stratospheric aerosol injection, or SAI would involve injecting tiny reflecting particles, known as aerosols, into the upper atmosphere to cool the planet.
• The second-marine cloud brightening, or MCB would use sea salt to stimulate cloud formation over the ocean, which would also help reflect sunlight in the region.

NOTE-

Solar geoengineering is not a substitute for reducing greenhouse gas emissions, but a possible temporary measure to limit warming while emissions are reduced and carbon-dioxide is removed.

Other major approaches within solar geoengineering

High-albedo crops and buildings

• Starting to turn heads is the idea of increasing the albedo of buildings in order to reflect more sunlight. Put simply, this would involve making rooftops and walls brighter.
• Painting roofs and roads in white, covering glaciers and deserts with reflective plastic sheeting, putting white or pale-coloured plastic floating panels over oceans or lakes, and planting genetically engineered paler crops have all been proposed to reflect sunlight into space.

Ocean mirror

• An “ocean mirror” is a less popular choice for reducing the impact of sunlight.
• In theory, this would involve using a fleet of sea vessels to churn up millions of tiny microbubbles on the ocean surface. This seafoam would reflect away sunlight, cooling the planet.

Cloud thinning:

• Another less-explored option for reducing the effects of sunlight at the Earth’s surface would be to “remove” cirrus clouds from the atmosphere.
• Cirrus clouds are thin, wispy clouds made of ice crystals, which form at high altitudes.
• The clouds reflect away some sunlight, but also absorb large amounts of long-wave radiation meaning that, on balance, they warm the planet.
• The overall heat-trapping effect of cirrus clouds is so large that it exceeds that of human-released C02

Space mirrors/sunshades:

• To send into orbit giant mirrors made of wire mesh. or to send trillions of light and small mirrors, to deflect sunlight back to space.
• The size of the mirror would determine how much sunlight it could reflect back towards space and, therefore, its cooling effect.

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 from below.
• 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.

Why is solar geoengineering being considered?

• The Paris Agreement’s target requires limiting global temperature increase well below 2’C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5C.
• For this, nations need to bring net global CO2 emissions to zero by no later than mid-century.
• Despite these ambitious goals, solar geoengineering is being considered to prepare for the possibility that global efforts may fall short.

Solar geoengineering risks

• Solar geoengineering does not remove greenhouse gases from the atmosphere and thus does not reduce other effects from these gases, such as ocean acidification.
• Potential risks with SRM includes potential changes in precipitation patterns, changes in stratospheric temperatures, ozone amounts, sea-level rise, ocean acidification, productivity and mixing, terrestrial vegetation, coral reefs, biodiversity, crop production and ecosystems.
• Research to scope the risks and potential of solar geoengineering has mostly been conducted through computer-based modelling and natural observations (volcanic eruption).
• The technology may become an excuse to slow emissions reductions and nations would stop moving toward a low-carbon economy.