If we can find cost-effective ways to drawn down carbon dioxide from the air - as plants do - our journey towards net zero will be much easier

Pulling carbon dioxide directly out of the air and safely storing it in perpetuity is the holy grail of negative emissions technologies. It is the only (man-made) carbon capture technology that can work for distributed carbon emissions, such as those from transport.

There have been pilot-scale operations in this space for the past 5 years. These are now being scaled up. Key issues include the cost of the process, the amounts of energy required given the low concentrations of CO2 in the air, the availability of the sorbents used in the process, and how the carbon dioxide that is extracted is used or stored.

The leading companies operating in this space include Canada's Carbon Engineering and Switzerland's Climeworks. Both aim to permanently store the carbon that they extract, either deep underground or in rock formations.

Carbon Engineering claims that its current costs are around $100/tonne of CO2 while Climeworks is looking to a longer-term $100-200/tonne cost for carbon removed. It is unclear what the scope for reducing these costs are as the process is scaled.