It has long been the holy grail for those who believe that technology can save us from catastrophic climate change: a device that can "suck" carbon dioxide (CO2) from the air, reducing the warming effect of the billions of tonnes of greenhouse gas produced each year.

Now a group of US scientists say they have made a breakthrough towards creating such a machine. Led by Klaus Lackner, a physicist at Columbia University in New York, they plan to build and demonstrate a prototype within two years that could economically capture a tonne of CO2 a day from the air, about the same per passenger as a flight from London to New York.

The prototype so-called scrubber will be small enough to fit inside a shipping container. Lackner estimates it will initially cost around £100,000 to build, but the carbon cost of making each device would be "small potatoes" compared with the amount each would capture, he said.

The scientists stress their invention is not a magic bullet to solve climate change. It would take millions of the devices to soak up the world's carbon emissions, and the CO2 trapped would still need to be disposed of. But the team says the technology may be the best way to avert dangerous temperature rises, as fossil fuel use is predicted to increase sharply in coming decades despite international efforts. Climate experts at a monitoring station in Hawaii this month reported CO2 levels in the atmosphere have reached a record 387 parts per million (ppm) - 40% higher than before the industrial revolution.

The team is working to build a prototype at a laboratory in Tuscon, Arizona. Run by a company called Global Research Technologies (GRT), of which Lackner is vice president of research, the laboratory unveiled a "pre-prototype" air capture machine last year, based on a different technique -rinsing trapped CO2 off the membrane with liquid sodium carbonate, and then using electricity to liberate the CO2 from the fluid.

The team is also working on ways to dispose of the pure CO2 gas produced by each scrubber.

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