A Swiss company says it has certifiably extracted CO2 from the air and permanently stored it in the ground -- for the first time on behalf of paying customers, including Microsoft.
Climeworks, a startup created in 2009 by two Swiss engineers, said its facility in Iceland had successfully removed carbon dioxide from the atmosphere and injected it into the ground, where it would very gradually be transformed into rock.
The potential for scaling up remains to be proven.
In its announcement on Thursday, Climeworks said its process had been certified in September by DNV, a Norwegian independent auditor, marking the first time carbon had been permanently captured on behalf of paying corporate clients.
Climeworks counts companies including Microsoft, Stripe and Shopify among the clients who have already bought into its future carbon removal services, to compensate for their greenhouse gas emissions.
The startup said it hoped "to lead as an example for peers, customers and policymakers alike that are committed to climate action".
The Paris Agreement, agreed by nearly all the world's nations in 2015, called for the rise in the Earth's average temperature to be limited at 1.5 degrees Celsius, which scientists say would keep the impact of climate change at manageable levels.
Many businesses, including fossil fuel companies, rely heavily on carbon offset schemes based on afforestation to compensate for continuing carbon emissions.
But there has been growing interest in the newest carbon dioxide removal (CDR) method, of which Climeworks is the industry leader -- a chemical process known as direct air carbon capture and storage (DACCS).
In its report last year, the United Nations' Intergovernmental Panel on Climate Change (IPCC) warned that regardless of how quickly the world slashes greenhouse gas emissions, it will still need to suck CO2 from the atmosphere to avoid climate catastrophe.
But it remains to be seen whether this can be done at scale.
So far, Climeworks's direct air capture facility in Iceland -- the largest in the world -- removes in a year what humanity emits in three to four seconds.
The company has not divulged how much its clients are paying for the service, and how much CO2 each client wants extracted.