Here's why carbon capture is no easy solution to climate change.
Carbon capture technology is central to the climate strategies of many world governments.
It is also expensive, unproven at scale, and can be hard to sell to a nervous public.
This currently makes the model of capturing carbon dioxide emissions from the air and storing them for money unworkable.
As nations gather for COP28 - the 28th United Nations climate change conference - in Dubai at the end of November, the question of carbon capture’s future role in a climate-friendly world will be in focus.
So where are we up to with carbon capture and what stands in the way of its widespread deployment?
What is carbon capture?
Carbon capture is a way of reducing carbon emissions by capturing them at the source or removing them from the atmosphere.
The most common form of carbon capture technology involves capturing the gas from a point source like an industrial smokestack.
From there, the carbon can either be moved directly to permanent underground storage (CSS) or it can be used in another industrial purpose first - a process known as carbon capture, utilisation and storage (CCUS).
Another form of carbon capture is direct air capture (DAC), in which carbon emissions are captured from the air.
How many carbon capture projects currently exist?
There are currently 42 operational commercial CCS and CCUS projects across the world with the capacity to store 49 million tonnes of carbon dioxide annually, according to the Global CCS Institute, which tracks the industry.
That is about 0.13 per cent of the world’s roughly 37 billion tonnes of annual energy and industry-related carbon dioxide emissions.
Some 30 of those projects, accounting for 78 per cent of all captured carbon from the group, use the carbon for enhanced oil recovery (EOR), in which carbon is injected into oil wells to free trapped oil. Drillers say EOR can make petroleum more climate-friendly, but environmentalists say the practice is counter-productive.
The other 12 projects, which permanently store carbon in underground formations without using them to boost oil output, are in the US, Norway, Iceland, China, Canada, Qatar and Australia, according to the Global CCS Institute.
It is unclear how many of these projects, if any, turn a profit.
About 130 direct air capture facilities are being planned around the world, according to the International Energy Agency (IEA), though just 27 have been commissioned and they capture just 10,000 tonnes of carbon dioxide annually.
The US in August announced $1.2 billion (€1.1b) in grants for two DAC hubs in Texas and Louisiana that promise to capture two million tonnes of carbon per year, though a final investment decision on the projects has not been made.
High cost of carbon capture is a setback
One stumbling block to rapid deployment of carbon capture technology is cost.
CCS costs range from €14 to €110 per tonne of captured carbon depending on the emissions source. DAC projects are even more expensive, between €550 and €916 per tonne, because of the amount of energy needed to capture carbon from the atmosphere, according to the IEA.
Some CCS projects in countries like Norway and Canada have been paused for financial reasons.
Developers say they need a carbon price, either in the form of a carbon tax, trading scheme or tax break, that makes it profitable to capture and store the carbon. Without that, only carbon capture projects that increase revenue in a different way - like through increased oil output - are profitable.
Countries including the US have rolled out public subsidies for carbon capture projects. The Inflation Reduction Act, passed in 2022, offers a $50 (€46) tax credit per tonne of carbon captured for CCUS and $85 (€78) per tonne captured for CCS, and $180 (€165) per tonne captured through DAC.
Though those are meaningful incentives, companies may still need to take on some added costs to move CCS and DAC projects ahead, says Benjamin Longstreth, global director of carbon capture at the Clean Air Task Force.
Some CCS projects have also failed to prove out the technology's readiness. A $1 billion (€1.15b) project to harness carbon dioxide emissions from a Texas coal plant, for example, had chronic mechanical problems and routinely missed its targets before it was shut down in 2020, according to a report submitted by the project’s owners to the US Department of Energy.
The Petra Nova project restarted in September.
Problems with where to store captured carbon
Where captured carbon can be stored is limited by geology. This reality would become more pronounced if and when carbon capture is deployed at the kind of massive scale that would be needed to make a difference to the climate.
The best storage sites for carbon are in portions of North America, East Africa and the North Sea, according to the Global CCS Institute.
That means getting captured carbon to storage sites could require extensive pipeline networks or even shipping fleets - posing potential new obstacles.
In October, for example, a $3 billion (€3.5b) CCS pipeline project proposed by Navigator CO2 Ventures in the US Midwest - meant to move carbon from heartland ethanol plants to good storage sites - was cancelled due to concerns from residents about potential leaks and construction damage.
Companies investing in carbon removal need to take seriously community concerns about new infrastructure projects, says Simone Stewart, industrial policy specialist at the National Wildlife Federation.
"Not all technologies are going to be possible in all locations," Stewart says.