The world’s biggest carbon-removal plant switches on

SHORTLY AFTER 6pm on September 9th, the Orca carbon-capture plant, just outside Reykjavik in Iceland, switched on its fans and began sucking carbon dioxide from the air. The sound was subtle—a bit like a gurgling stream. But the plant’s creators hope it will mark a big shift in humanity’s interaction with the climate.

Orca is, for now, the largest installation in the infant “direct air capture” industry, which aims to remove CO₂ from the atmosphere. When sealed underground such CO₂ counts as “negative emissions”—an essential but underdeveloped method for tackling global warming. To stop temperatures rising by 1.5°C or even 2°C above pre-industrial averages, as per the Paris climate agreement, hundreds or thousands of billions of tonnes of CO₂ will have to be removed from the atmosphere in the second half of the century.

Currently, the only means of doing that is planting trees, an option that is not entirely without drawbacks. Trees burn in wildfires and can be cut down. When this happens, much of the carbon they store escapes. The Orca plant shows another way. Climeworks, the company that owns it, has developed chemical filters which snag CO₂ when air passes through them. When heated they release the CO₂again, generating a stream of gas that is handed to another...