SOME schemes to save the Earth just might cost the Earth. Back-of-the-envelope calculations suggest that scaling up proposals to scrub the atmosphere of carbon dioxide would mean creating the biggest industry there has ever been.
You can strip CO2 from the air with chemical filters or by boosting reactions occurring as rocks weather. Colin Axon of Brunel University in Uxbridge, UK, and Alex Lubansky at the University of Oxford estimated what it would take to remove the 30 gigatonnes of CO2 we emit every year.
That would mean processing 75,000 Gt of dry air. Scaling up proposals to filter air would use 180 Gt of clean water per year, depriving 53 million people of water, on top of the 66 per cent of the world's population who will face water shortages by 2025.
Enhancing rock weathering is no better. It would call for 100 Gt of olivine, a common mineral. This is 12,500 times more than is produced worldwide. To deal with 30 Gt of CO2 we would need to spread the olivine 1 centimetre thick over 3.6 billion square kilometres of dry land, 1000 times more than Earth has available.
Axon says his calculations are rough. "Still, I'm confident that a CO2 removal scheme would have to be in the order of 1000 times larger than any existing industry." He presented the estimates at the Planet Under Pressure conference in London last week.
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