UN climate negotiators are meeting amid a welter of reports indicating that concentrations of carbon dioxide in the atmosphere have broken records, while attempts to curb greenhouse gases are not doing enough to avoid dangerous levels of warming. Can technology to remove CO2 from the air could be the answer?
While CO2 concentrations are now higher than they have been in at least 800,000 years, the gas still only accounts for a tiny 0.04% of our atmosphere.
However, extracting carbon dioxide from well mixed air is not just technically difficult, it’s expensive as well.
A half-hour outside Zurich stands one of the frontline attempts to develop a commercial approach to sucking down CO2.
On the roof of a large recycling centre at Hinwil stand 18 metal fans, stacked on top of each, each about the size of a large domestic washing machine.
These fans suck in the surrounding air and chemically coated filters inside absorb the CO2. They become saturated in a few hours so, using the waste heat from the recycling facility, the filters are heated up to 100C and very pure carbon dioxide gas is then collected.
This installation, called a direct-air capture system, has been developed by a Swiss company called Climeworks.
It can capture about 900 tonnes of CO2 every year. It is then pumped to a large greenhouse a few hundred metres away, where it helps grow bigger vegetables.
This is not supposed to be a demonstration of a clever technology – for the developers, making money from CO2 is critical.
"This is the first time we are commercially selling CO2; this is the first of its kind," co-founder Jan Wurzbacher told BBC News.
"It has to be for business; CO2 capture can’t work for free."
Right now Climeworks is selling the gas to the vegetable growers next door for less than $600 per tonne, which is very expensive.
But the company says that this is because it has built its extraction devices from scratch – everything is bespoke. The firm believes that like solar and wind energy, costs will rapidly fall once production is scaled up.
"The magic number we always say is $100 per tonne," said Jan Wurzbacher.
"We have drawn a road down to the region of $100 and that is something we think is feasible. We can do it by scaling up the mass production of our components. I’d say half of the way to go there – we know what to do. We just have to do it over the next two or three years."