Cutting emissions may not be enough to avoid a climate catastrophe. Some climate scientists, start-ups, and philanthropists believe that we need to undo the damage already wrought. Geoengineering – the large-scale manipulation of the climate, either by deflecting solar radiation or removing carbon dioxide from the atmosphere – could be a crucial tool to achieving this. It could, experts say, be as flexible as a home thermostat.
Carbon geoengineering is the more developed of the two. Its most low-tech form is afforestation: planting massive numbers of trees and leveraging their photosynthetic power to absorb CO2. But to have a significant impact afforestation requires vast amounts of land, making it both costly and impractical.
A more efficient approach is direct air capture (DAC) which removes CO2 from the air using filtration systems. A Swiss firm, Climeworks, has developed small modular reactors that are improving the energy efficiency of the process by requiring lower temperatures, while also enabling the re-use of waste heat in industrial processes. While DAC is still costly, it is 400 times more space-efficient than afforestation, according to Christoph Gebald, Climeworks’ director. The technique has been known since the second world war; the challenge now, says Gebald, is to “make it cheap and make it big.”
Small-scale sites and modular technology allow Climeworks to choose its physical locations, based on factors like availability of renewable energy and low utility costs. “The concentration of CO2 is roughly the same throughout the atmosphere,” says Gebald. “Within seven days a CO2 molecule travels around the world. We can take it out everywhere. We go where the [CO2] storage is, so we don’t have to transport the CO2, and where cheap renewable electricity is available.”
Others are finding smarter storage solutions. Carbfix, an Icelandic company, has developed a technique to mineralise CO2 into stone, which can be easily and cheaply stored underground. This is in contrast to conventional CO2 sequestration, which pumps CO2 into geological formations like depleted oil and gas reservoirs, but can lead to issues such as leakage and geochemical contamination, thus necessitating continuous monitoring.
“You do not have to carry out monitoring campaigns decades into the future [as with conventional sequestration],” says Edda Sif Aradóttir, Carbfix’s CEO. “We find this is a very elegant way of reducing emissions and reclaiming CO2 that has already been released into the atmosphere”. Carbfix can store 100 kg of CO2 in just 42 cubic metres of rock. The company is currently collaborating with Climeworks on a project called Orca, a commercial demonstration site to capture 4,000 tons of CO2 per year.
Carbon geoengineering is the more developed of the two. Its most low-tech form is afforestation: planting massive numbers of trees and leveraging their photosynthetic power to absorb CO2. But to have a significant impact afforestation requires vast amounts of land, making it both costly and impractical.
A more efficient approach is direct air capture (DAC) which removes CO2 from the air using filtration systems. A Swiss firm, Climeworks, has developed small modular reactors that are improving the energy efficiency of the process by requiring lower temperatures, while also enabling the re-use of waste heat in industrial processes. While DAC is still costly, it is 400 times more space-efficient than afforestation, according to Christoph Gebald, Climeworks’ director. The technique has been known since the second world war; the challenge now, says Gebald, is to “make it cheap and make it big.”
Small-scale sites and modular technology allow Climeworks to choose its physical locations, based on factors like availability of renewable energy and low utility costs. “The concentration of CO2 is roughly the same throughout the atmosphere,” says Gebald. “Within seven days a CO2 molecule travels around the world. We can take it out everywhere. We go where the [CO2] storage is, so we don’t have to transport the CO2, and where cheap renewable electricity is available.”
Others are finding smarter storage solutions. Carbfix, an Icelandic company, has developed a technique to mineralise CO2 into stone, which can be easily and cheaply stored underground. This is in contrast to conventional CO2 sequestration, which pumps CO2 into geological formations like depleted oil and gas reservoirs, but can lead to issues such as leakage and geochemical contamination, thus necessitating continuous monitoring.
“You do not have to carry out monitoring campaigns decades into the future [as with conventional sequestration],” says Edda Sif Aradóttir, Carbfix’s CEO. “We find this is a very elegant way of reducing emissions and reclaiming CO2 that has already been released into the atmosphere”. Carbfix can store 100 kg of CO2 in just 42 cubic metres of rock. The company is currently collaborating with Climeworks on a project called Orca, a commercial demonstration site to capture 4,000 tons of CO2 per year.
Shining back
A more radical – and controversial – climatic engineering approach is solar geoengineering, a still hypothetical solution which would alter the Earth’s temperature by reflecting the sun’s heat.Minute scale innovations of this kind already exist, such as high-albedo surfaces, which are designed to reflect heat radiation, on buildings in warm climates. But solar geoengineering can have much bigger scope.
The most well-understood approach, according to Peter Irvine, a lecturer in climate change at University College London, is stratospheric aerosol geoengineering, which entails spraying large quantities of inorganic particles, like sulphur dioxide, into the upper layers of atmosphere.
Dispersed at altitudes above 20 km, these would create a barrier against incoming sunlight, similar to the effects of volcanic eruptions, which spew sulphur aerosols into the stratosphere. There, after reacting to form sulfuric acid, they mix with water to form tiny droplets that scatter light.
Worries that such geoengineering might accidentally turn down the temperature too far and create a frozen apocalypse, as in the movie Snowpiercer, are unfounded, according to Irvine. By adjusting aerosol injections as needed, “You could run the climate like the thermostat in your house,” he says.
But there are reasons for caution. Aerosols have a limited lifespan, and, if not carefully sustained, solar geoengineering could cause rapid rebounds in temperatures, leaving some species unable to adapt. Researchers have also shown that temperature manipulation could significantly increase the number and intensity of naturally occurring climate phenomena like the El Niño Southern Oscillation, a warming of ocean temperatures that impacts weather and precipitation patterns.
However, modelling work led by Irvine indicates that if geoengineering was applied with the aim of halving global warming, rather than eradicating it altogether, adding aerosols into the stratosphere would deliver planetary gains with low risks.
There are more localised solar engineering strategies too. Marine cloud brightening, for instance, involves seeding coastal-based stratocumulus clouds with seawater aerosols, which increases the concentration of cloud droplets and creates an albedo effect to reflect solar energy. This could be useful in tackling temperature-sensitive areas like ice cover or coral reefs. However, marine cloud brightening has risks of its own. It could create large, localised differences that interact in unpredictable ways with ocean circulation, weather patterns and local biology.
Solar geoengineering is yet to reach any scale. Funding is miniscule, estimated at just USD8m in 2017 and 2018, compared with USD3.5bn spent annually on climate-change research. It also faces pushback.
Weather manipulation, while distinct from planetary geoengineering, has an unseemly military history: Operation Popeye, for example, was a US military cloud-seeding initiative designed to extend monsoon season to disrupt North Vietnamese military logistics. In 1978 a UN convention was initiated, banning environmental modification for military purposes.
A more pervasive critique of all forms of geoengineering is that of moral hazard and complacency – that a vague hope that we can re-engineer the climate could incentivise decision-makers to avoid the tough actions needed to cut emissions. Advocates, though, see geoengineering as one among many tools needed and argue that without it we may not be able to avoid a climate catastrophe – particularly because, given the lag of climate physics, global temperatures will peak as the world reaches net zero emissions.
“Solar geoengineering can reduce temperatures we see at net zero,” says Irvine. “I think we’ve made enormous progress [on emissions reduction] in developed countries. The technology is here and competitive on solar and wind; this transition is well underway. But this progress is in the context of a global economy that is growing every year, so we are only just now approaching peak emissions”.
There are differences of opinion among the public, with indications that people in developing countries, who are more exposed to the effects of climate change, are more open to geoengineering, according to Masahiro Sugiyama, an associate professor at the Policy Alternatives Research Institute of the University of Tokyo. He led an online survey of college students in six Asia Pacific countries, and found more positive attitudes among those from emerging economies (China, India and the Philippines) compared with those from the high-income nations of Australia, Japan and South Korea. “They are on the front line of climate change and are more concerned. They might be feeling more desperate, and want to know every possible action that could save the damage from climate change.”
Yet there is broad agreement among survey respondents, Sugiyama notes, on the need for international governance. Researchers are promoting principles and frameworks that could guide the incubation of solar geoengineering, the most controversial intervention, including requiring public participation, “governance before deployment” and independent impact assessment.
