One way to combat global warming is by sequestering the carbon dioxide belched out by power stations, locking it away in buried vaults. A big problem, though, is that only about a tenth of the gas produced by burning fossil fuels is CO2. Most of the rest is nitrogen, which is not a greenhouse gas and would needlessly take up space in the vault. But separating the two gases can be a costly affair. Now a team led by Maciej Radosz at the University of Wyoming in Laramie say they have designed a cheap filter that could capture 90 per cent or more of the CO2 emitted by power stations.