A pilot project for filtering climate-damaging greenhouse gases from the atmosphere has been launched in Iceland. According to the Swiss start-up Climeworks, the plant near Reykjavik will capture CO2 and store it in rock. In this way, 4000 tonnes of CO2 are to be absorbed annually in order to slow down climate change.

The technology used for this differs from conventional methods of CO2 sequestration, in which exhaust gases from factories are filtered directly as they are emitted: The Icelandic plant filters the air in the atmosphere, where the concentration of CO2 is much lower.

Mineralisation in two years instead of thousands

Twelve fans powered by an adjacent geothermal power plant suck in the air to capture the greenhouse gas it contains. The CO2 is then mixed with water and injected into basalt at a depth of 1000 metres, where it petrifies. The technique thus reproduces within only two years a natural process, mineralisation, which normally takes several thousand years.

The Intergovernmental Panel on Climate Change lists the process as a possible means of limiting global warming. Critics, however, point to the very high costs and the controversial effectiveness so far. And scientists stress that efforts to reduce CO2 emissions should not be replaced.

Either way, it could be decades before the technology can be used on a large scale.