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Imagine a machine that sucks carbon dioxide out of the air. It may sound like the perfect solution to global warming and there are machines that can do it. Dozens are already operating on several continents, but the process is complex because the atmosphere is only 0.04 per cent carbon dioxide.
The most common method is to use large fans to pull air across a chemical substance which binds with the CO2 molecules. Then the CO2 is separated from the chemical agent using heat, purified, and stored. Another method is best described as a mechanical tree. The wind simply blows across the structure and the CO2 in the breeze is absorbed by discs soaked in chemicals.
The collected CO2 has a variety of uses. One Swiss company is selling some in gas form to nearby greenhouses, where it acts as fertiliser. But it can also be used in fizzy drinks and for energy, fuels, and material. Right now it costs as much as $600 per tonne to extract CO2 from the air, which is expensive. Over time, start-ups are targeting a cost of around $100 per tonne. But other methods of sequestering carbon, such as planting a tree, cost as little as $10 per tonne.
In 2022, construction is expected to start in Texas on the world's biggest direct air capture plant capable of pulling a million tonnes of carbon dioxide out of the atmosphere every year, the equivalent of 40m trees. But the Intergovernmental Panel on Climate Change estimates that we might need to extract more than 100bn tonnes of CO2 from the atmosphere by the end of this century to limit warming to less than 1.5 degrees Celsius.
We still have a very long way to go.