Climate tech explained: carbon capture and removal

Large polluters, tech start-ups, and governments are all moving swiftly to work out how best to remove carbon dioxide from the air — as well as stopping it from getting there in the first place.

And “large-scale deployment” of their solutions will be needed if the world is to limit warming to 1.5C above pre-industrial levels — the preferred goal of the 2015 Paris agreement — according to the UN’s climate science body, the Intergovernmental Panel on Climate Change.

But efforts to cut CO₂ are dogged by questions over the effectiveness and cost of the various carbon capture techniques available.

How does it work?

The term carbon capture is typically used for technologies that catch CO₂ at the point of emission, while the greenhouse gas can also be removed after it has dispersed into the atmosphere.

With carbon capture, large polluters — such as steel and cement factories, oil refineries, and power plants — trap some of the CO₂ they produce before it enters the atmosphere.

Plants are typically fitted with equipment that separates CO₂ from other gases, before or after combustion, using chemical solvents and other methods.

The CO₂ is compressed into a liquid and pumped underground, sometimes into depleted oil and gas reservoirs. Some of it can also be put to use — applications include making plastics, concrete, or fuel.

When it comes to removing the CO₂ already in the air, growing more trees on land, or kelp forests at sea, harnesses the natural process that converts CO₂ into biomass.

There are also chemical and mineralogical processes under development that aim to remove CO₂ from the atmosphere for longer than plant-matter stores carbon — ideally, thousands of years.

One example is when agricultural and forestry waste is heated in the absence of oxygen to create biochar, a type of charcoal rich in carbon that is then buried in the ground.

Another technique, known as enhanced weathering, involves spreading minerals on agricultural land or in oceans, to speed up their natural absorption of CO₂.

What are the pros and cons?

Carbon capture is seen as beneficial as it appears to be a direct solution to the problem of CO₂ concentration in the atmosphere being too high.

However, not all capture, storage and removal projects lock CO₂ away for long enough to make a dent in rising global temperatures.

“The main issue is that every carbon dioxide molecule in the atmosphere has a [warming] impact over thousands and thousands of years, and we’re pretty bad at planning multiple millennia ahead,” says Wijnand Stoefs, a policy lead from the non-profit Carbon Market Watch.

CO₂ pumped underground could well stay there for hundreds of years. But trees and other plants have finite lives and, when they decompose, they return carbon to the atmosphere in a matter of months or years. Depending on the rate at which other plants regrow in their place, this could mean the CO₂ is returned to the atmosphere relatively quickly.

There are opportunity costs, too — capture technologies use up power and money that could otherwise be used for cutting emissions at source, such as in transport, energy and buildings.

Debate over benefits and drawbacks is particularly sharp when biomass is used to generate electricity, with carbon capture applied to the resulting emissions. Advocates say the wood used is typically a byproduct of other industries, while critics say the process could be linked to unsustainable deforestation.

Will it save the planet?

Record-breaking temperatures over the past year make it increasingly likely that some of the goals countries committed to as part of the 2015 Paris agreement will be missed, scientists say. This potentially creates the need for more CO₂ capture, or removal, as a form of damage limitation. 

Carbon capture technology is also considered critical to helping decarbonise heavy industries, such as those that produce cement, iron and steel, which cannot easily reduce their emissions. But it is controversial when used to justify the continued supply of oil, gas and coal.

At the COP28 climate summit in December 2023, about 50 of the world’s top fossil fuel producers committed to eliminate emissions from their own operations, which will partly rely on equipping refineries with carbon capture. But none agreed to drastically reduce production of fossil fuels, the use of which generates much more of the sector’s emissions.

A set of principles for the responsible use of carbon removal has been set out by a group of universities, non-profits, and companies under the banner of the EU-funded Negem “negative emissions” project. They include the principle that carbon removal should be used only alongside ambitious decarbonisation targets, and should lead to CO₂ being stored for several centuries, while not harming the environment.

Has it arrived yet?

Industrial carbon capture and storage has been around since the 1970s, when natural gas processing plants in Texas started capturing CO₂ to sell it on.

But the story of the technology since then “has largely been one of unmet expectations”, the International Energy Agency said in 2020. “Its potential to mitigate climate change has been recognised for decades, but deployment has been slow.”

This may be changing rapidly. The IEA anticipates that, by 2030, there will be enough capacity to capture 435mn tonnes and store 615mn tonnes of CO₂ a year. However, both figures are short of the 1bn tonnes a year of carbon capture and storage that the IEA says would probably be needed to hit net zero emissions in 2050.

This does not include tree planting initiatives, which are estimated to account for most of the 2bn tonnes of CO₂ currently removed per year, according to a report led by Oxford’s Smith School of Enterprise and the Environment.

Who is investing in it?

Annual investment in carbon capture, utilisation and storage could reach $175bn by 2035, mostly in hard-to-decarbonise sectors such as cement and steel making, according to a McKinsey report from earlier this year. It predicted this investment would be concentrated in south-east Asia, China, India and North America.

The US government is among the most significant backers of carbon removal, having offered $3.5bn in grants for facilities that can directly capture carbon from the air, and $35mn in prizes for proposals for a range of removal techniques. 

Governments can provide an incentive to invest in carbon capture through tax credits, carbon taxes, and cap-and-trade schemes, where industrial polluters must buy permits giving them the right to pollute.

Another incentive comes via the voluntary carbon market, where instruments representing a tonne of CO₂ captured or avoided are traded. Polluters can buy the credits and record these in their non-financial accounts to help hit their climate goals. They typically pay more — up to $1,608 per tonne last year — for the promise that CO₂ will be locked away for longer.

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