Scientists in the US have found a way to take carbon dioxide (CO2) from the air and make carbon nanofibres, a valuable manufacturing material.
Their solar-powered system runs just a few volts of electricity through a vat full of a hot, molten salt; CO2 is absorbed and the nanofibres gradually assemble at one of the electrodes.
It currently produces 10g in an hour.
The team suggests it could be scaled up and make an impact on CO2 emissions, but other researchers are unsure.
Nonetheless, it could offer a cheaper way of making carbon nanofibres than existing methods.
Carbon nanofibres are already used in high-end applications such as electronic components and batteries, and if costs came down they could be used more extensively - improving the strong, lightweight carbon composites used in aircraft and car components, for example.
The question is whether the "one-pot" reaction demonstrated by the team could help to drop that cost.
The idea of turning CO2 from the air into useful products is a popular one, and the field is strewn with many more unfulfilled promises than success stories.
Dr. Katy Armstrong, a chemical engineer at the University of Sheffield, said the process was "promising and very interesting on a lab scale" but that the bigger vision might be problematic.
"As they are capturing CO2 from the air, the process will need to deal with huge volumes of gas to collect the required amount of carbon, which could increase process costs when scaled up," she said.
Dr. Paul Fennell, a chemical engineer and clean energy researcher at Imperial College London, said: "If they can make carbon nanofibres, that is a laudable aim and they're a worthwhile product to have.
"But if your idea is to take CO2 out of the atmosphere and produce so many carbon nanofibres that you make a difference to climate change - I'd be extremely surprised if you could do that."
Meanwhile, other chemists were impressed by the simple fact that the team had produced nanofibres from atmospheric carbon.