Shan Jiang

Climate change, former US Secretary of State Rex Tillerson once said, is “an engineering problem, and it has engineering solutions.” Following President Trump’s withdrawal from the Paris Agreement on climate, an idea has been catching on among Republican politicians and climate researchers alike – geoengineering. In other words: What if we reversed global warming simply by redesigning the atmosphere?

There are two main forms of geoengineering: sucking CO2 out of the air, and reducing heat. Some climate scientists are uncomfortable with comparing the former, carbon capture — expensive but with no substantial side effects — with the latter, solar radiation management (SRM), which aims to reflect more sunlight back into space and could affect the planet in unpredictable ways.


Some types of SRM could be relatively cheap and easy. In 2009, London's Royal Society estimated that, for tens of billions of pounds a year — on a global scale, a steal — reducing solar radiation by about two per cent could rebalance the heating caused by a doubling of CO2 emissions. The hack would provide a grace period of around 20 years to hit emissions targets.

But while it may cool down the planet, SRM is not a cure-all: it would not reverse the ocean acidification caused by excess CO2; would likely interfere with the global water cycle; may deplete ozone; and, if it were suddenly stopped, warming would return. And there are fears that climate-change deniers and fossil-fuel corporations would hijack the technique as an excuse for not tackling the real task of curbing emissions.

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Even in the rosiest of scenarios, though, purely reducing emissions will not halt the warming of the planet. Here’s WIRED’s guide to the technologies being proposed.

Balloon

Aerosols released during the 1991 eruption of the Philippines’ Mount Pinatubo volcano resulted in a localised sunlight reduction of ten per cent, and cooling of 0.5 per cent to 0.6 per cent. In spring 2019, a team at Harvard University will try to mimic that event by releasing a high-altitude balloon 20 kilometres up into the atmosphere to drop a smattering (100g to 1kg) of calcium carbonate, followed by sulphates, into the air. They will then observe how much radiation is reflected back.




Clouds

Marine stratus clouds cool the Earth by reflecting some sunlight back. It might be possible to make these clouds brighter, and more reflective, by using rotor ships to spray seawater into the lower atmosphere, stimulating cloud droplet formation. Deployed widely, cloud brightening could reverse the warming caused by double atmospheric CO2. As it relies on seawater, the technique could be relatively safe – but it could alter weather patterns. The technology to produce this fine mist is still in development.

Shade

Space-based geoengineering aims at blocking the Sun’s rays before they reach Earth. One of the most detailed projects of this kind involves building a space shade. A 1,000-kilometre-wide lens only a few millimetres thick — floating like a satellite between the Sun and Earth —would disperse the Sun’s light before it reaches Earth, reducing solar energy by between 0.5 per cent and one per cent. Sadly, the Royal Society has cautioned that a space shade would not be cost- or time-effective, requiring decades and trillions to be completed.

Sand

A Silicon Valley startup called Ice911 has run experiments in Utqiaġvik, Alaska, to investigate whether tiny grains of reflective silica sand can keep at bay the effects of global warming. Should these shards be able to stave off melting in Alaska’s North Meadow Lake, the same idea could be rolled out to 49,000km2 of Arctic ice – roughly the size of Costa Rica – and mitigate projected sea level rises.

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Carbon capture

Despite the difficulty of deploying it at scale, direct air capture of CO2 for storage or repurposing will certainly form a part of the global response to climate change. Methods to do so vary: Canadian company Carbon Engineering, for instance, is using "air conductors" with an alkaline hydroxide solution to capture CO2 and convert it into new fuels. Research suggests a tonne of CO2 could be captured for less than $200 (£154), were existing technologies implemented on an industrial scale.

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