Scientists say they have invented a machine that can suck carbon dioxide out of the air – potentially creating a vital weapon in the war against global warming.

The blueprint for the CO2 'scrubber' raises the prospect of a generation of machines which would help reduce the billions of tonnes of greenhouse gases being pumped into the atmosphere by the use of fossil fuels.

The team of US scientists now plans to build a prototype which would capture one tonne of CO2 from the air every day.

Holy grail? How one of the CO2-scrubbing machines would look

Though the idea is considered a holy grail in the battle against climate change – and Sir Richard Branson has put up £12.6 million for anyone who makes it a reality – the machines would fall far short of a quick fix.

The prototype, being built at a laboratory in Tucson, Arizona, by a company called Global Research Technologies, will cost about £100,000 and take about two years to construct.

The devices – each nearly the size of a shipping container - would have to be produced in their millions to soak up human carbon emissions.

Inventor: US physicist Klaus Lackner says his machine offers more hope than attempts to cut down carbon emissions

The idea is bound to be controversial, with environmentalists seeing so-called technological solutions to global warming as undermining attempts to promote greener lifestyles and industries.

But physicist Klaus Lackner, who led the U.S. team behind the invention, said the CO2 scrubber offered more hope than current efforts to cut carbon emissions by reducing fossil fuel use.

' I'd rather have a technology that allows us to use fossil fuels without destroying the planet, because people are going to use them anyway,' he said.

Scientists say it is not difficult to remove carbon dioxide from the atmosphere by absorbing it in various chemical filters. But the problem has been how to clean those filters of CO2 so they can then be reused to carry on the job.

Professor Lackner, of New York's Columbia University, says the solution lies in a newly discovered property of absorbent plastic sheets known as 'ion exchange membranes' which are routinely used to purify water.

It turns out that humid air can make these membranes 'exhale' the CO2 they have trapped – leaving them clean and ready to absorb another load.

The Lackner team says the captured carbon dioxide could then be pumped into greenhouses to boost plant growth.