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.

While some see the scrubber as an efficient and economical way to reduce atmospheric carbon dioxide, many environmentalists oppose the technology because it allows people to use fossil fuels and emit carbon in the first place.

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