Bengaluru: Giant sunshades in the sky to block out sunlight and save a rapidly heating Earth?
This may sound like something straight out of a sci-fi novel, but solar radiation management (SRM) — strategies that seek to control how much sunlight reaches the Earth — is part of a controversial concept called ‘geoengineering’ that has caught the fancy of some sections as a potential solution to global warming.
‘Geoengineering’ literally means interventions that change the way the Earth’s systems work.
A White House report released last week suggested the Biden administration is open to studying the possibility of SRM’s effectiveness, once more bringing the issue to the forefront of the climate debate.
Just days before, a draft EU report had flagged the risks associated with geoengineering and called for talks towards an international framework to govern such technologies.
Ideas associated with geoengineering have not been tested or executed yet.
The call to pursue geoengineering is spurred by the urgency of tackling the fallout of climate change. As the world continues to heat, with no end in sight for fossil fuel emissions, solar and other forms of geoengineering are starting to occupy more mainstream space in climate discussions.
Proponents include investors, business magnates, and government and military agencies. British businessman Richard Branson is among the founders of the Royal Society’s geoengineering programme, which is a big cheerleader for SRM. Research funding has also come from Silicon Valley, the Pentagon, CIA, and billionaires such as Bill Gates.
Carbon-capture technologies — that form the other vertical of geoengineering — also have the backing of the fossil-fuel industry.
Geoengineering proponents have been accused of “technological fetishism” and wanting to maintain the current social order of “capital accumulation and profit maximisation”.
Critics say a shift towards geoengineering may slow down efforts towards emission cuts and adoption of renewable energy, while pointing out that its consequences — difficult to predict now — could be potentially catastrophic.
Nations such as Mexico have banned experimental solar geoengineering, and the United Nations Convention on Biological Diversity (2010) instituted a moratorium on geoengineering.
Multiple experts and institutions have called for a complete ban on geoengineering projects.
However, many scientists who support the concept say they want geoengineering to supplement ongoing efforts centred on emission cuts, and not replace them altogether. They point to the urgency of the situation to argue that geoengineering may well be the only way out of the climate crisis at this point.
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Understanding geoengineering
Geoengineering is broadly divided into two categories — technologies for capturing carbon (carbon dioxide removal) and methods for managing how much of the Sun’s heat reaches the Earth.
For the latter, proposed solutions target preventing the Sun from heating up the Earth (solar radiation management), or removing heat from the Earth’s atmosphere into space (Earth radiation management).
Popular theoretical ideas for SRM include modifying cloud structures, and spraying aerosols into the stratosphere.
Clouds are our natural umbrella — being white, they reflect sunlight, keeping the Earth cool. Clouds that are present above the oceans cool the surface below substantially. There are proposals to further “whiten” these clouds and expand their cover, through a process called marine cloud brightening (MCB).
This can be theoretically achieved by seeding the region with smaller particles that can induce condensation and create water droplets. These particles are smaller than natural aerosols that float above the ocean. Hence, when water condenses and aggregates around these particles high up in the atmosphere, smaller droplets of water are produced.
Smaller droplets of water have a larger surface area than larger, natural droplets. Hence, clouds with smaller droplets are lighter and more reflective, as compared to natural clouds above the ocean, which are darker (for example, thunderstorm clouds).
Releasing reflective particles into the upper atmosphere is more complex to execute. This is called stratospheric aerosol injection (SAI). At stratospheric latitudes, higher than clouds, lighter coloured particles such as polluting sulphur particles, can reflect sunlight.
This idea is inspired by volcanic eruptions, like that of the Philippines’ Mount Pinatubo in 1991. The eruption released millions of tonnes of sulphur dioxide — which reacts with other substances to form suplhate aerosols.
The eruption led to a drop of 0.6°C in global temperatures for about 2 years. However, it also caused a temporary shift in Asian rain patterns.
Solar geoengineering with clouds also includes ERM. Cirrus clouds in the upper layers of the atmosphere can theoretically be thinned, causing heat from the atmosphere to escape into space.
This project is being considered by the US National Academies of Sciences, Engineering, and Medicine’s new solar geoengineering committee, which in 2021 advocated for researching and experimenting with these ideas cautiously.
Not everyone is convinced, however.
Unknown consequences
The biggest impediment, ideologically, in evaluating and implementing geoengineered climate interventions is that their consequences are unknown. Climate systems are notoriously difficult to model because of chaos — even a small change can have cascading and unforeseen effects that can’t be predicted.
Studies have recommended negative emissions as the last resort. This is beyond the net-zero and zero-emissions scenario. However, researchers are mainly concerned that there is no knowledge yet on how to implement these solutions safely, without affecting other Earth systems or worsening problems.
Research into geoengineering so far has been difficult to quantify, carry out, and is ethically contentious, because of which experiments with results have not really taken place.
Just like volcanic particles, which can remain in the atmosphere for several months, researchers think that engineered aerosols could be around for over two years — with unknown consequences for the rest of the atmosphere, including the ozone layer.
Resulting events could potentially include droughts and floods, which cannot be predicted.
Geoengineering on a planetary scale today is impossible. Only certain regions and territories can be experimented with. SRM in one part of the Earth could have devastating consequences elsewhere. What’s more, these solutions could give rise to dependency on them in the future to keep climate and heating in control.
Some experts also worry that climate-altering technology could be weaponised, like it was in the Vietnam War, where “rainmaking” was used as a weapon by the US.
‘Achievable targets’
There are programmes around the world in works for geoengineering — specifically solar geoengineering.
There are two major processes of natural SRM that are considered achievable — planting more plants, especially suitable ones with lighter coloured leaves, and increasing the coverage of water ice.
While sea water is a darker, deeper blue, absorbing nearly 94 percent of sunlight, sea ice is perhaps the best known natural surface for reflecting light and heat, sending back nearly 90 percent of energy.
It is estimated that nearly 30 percent of sunlight that reaches Earth is reflected back by sea ice that covers the Arctic and Antarctic regions, which are today facing irrecoverable glacial ice melt, threatening major sea-level rise.
(Edited by Sunanda Ranjan)
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