Can carbon removal solve climate change?

Posted: October 4, 2024

Just outside Akhfennir, Morocco, on a remote and rugged coast where the Sahara desert meets the sea, fields of algae are blooming across shallow man-made pools that hug the shore. At harvest, a slurry of the stuff will be sprayed into the hot, dry desert air and float back to the ground as salty powder, before being buried deep in the sand. Brilliant Planet, a UK start-up, is behind this design to grow and bury algae in the desert, which could lock away its biomass – and the carbon stored therein – for thousands of years.

Meanwhile, in the southwest corner of England, SeaCURE, a research organization based at the University of Exeter, is drafting plans for an industrial plant that will take in seawater and treat it to draw out the dissolved carbon within. Once treated, the low-carbon water will be released back into the ocean, where it will draw down even more CO2 from the air to restore the natural equilibrium.

These are just some of the many innovations that companies around the world are pursuing in the rapidly growing field of carbon removal. Taking inspiration from nature, companies and scientists have tried everything from simulating how mollusks form seashells to using microbes to increase carbon storage in agricultural fields. Sequestering CO2 emissions has long been a seductive fix to the climate crisis, offering a seemingly simple solution to avoid the worst effects of global warming. That promise has kicked off a race to find the most viable solutions and build them to a meaningful scale before we run out of time.

Carbon capture vs. carbon removal

Carbon management usually breaks down into two buckets: industrial carbon capture, which involves directly trapping carbon dioxide emitted from power plants and industrial facilities, and the removal of emissions directly from the air through either natural methods or technological fixes.

Climate scientists now broadly agree that carbon removal, in particular, has become a necessity: the Intergovernmental Panel on Climate Change says that, without it, we won’t be able to limit global warming to below 2 °C by the end of the century. Even if temperatures rise beyond that point, carbon removal could help achieve net-negative emissions and reduce warming in the long run.

As a result, various methods to capture carbon – from planting trees, to enriching the soil with minerals to store more carbon in the ground, to direct air capture – are now central to governments’ climate strategies. The same goes for carbon capture and removal technologies, even if their rollout has been slow and mired in controversy.

But many of these solutions are still prohibitively expensive and unproven at scale. Engineered carbon removal, for example through direct air capture plants, still costs hundreds of dollars per ton of CO2 – meaning countries would need to spend hundreds of billions a year for them at current prices to reach their targets.

That’s why they are increasingly funding innovation in this space: the U.S. Department of Energy last year launched a call for new solutions to store carbon at gigaton scales for less than $100 per ton, and the EU recently announced a €30 million funding round for removal projects. Philanthropies have also started putting more money into carbon removal, although most funding is still focused on nature-based solutions.

Carbon capture picking up pace

The most commonly understood form of carbon removal is still carbon capture, utilization and storage (CCUS), which involves trapping gas directly at the smokestack. The captured CO2 can be used on site or compressed and shipped to serve as feedstock for a range of applications, from concrete to fuels and even fizzy drinks. It can also be injected into rock formations or aquifers for long-term storage, or – most controversially – used to enhance oil and gas production through a technique called enhanced oil recovery.

Leaving aside enhanced oil recovery, proponents of CCUS say it’s the best way to eliminate hard-to-abate emissions from heavy industry and long-haul transport; cement, chemicals and iron and steel production alone account for at least 12% of global emissions, and have few alternatives for decarbonization. But how much we should rely on CCUS is a contentious topic. Critics argue it merely keeps big emitters in operation and distracts from the vital work of actually reducing emissions-intensive activities – a ‘moral hazard’ argument also lobbed at other carbon removal methods – by switching from fossil fuels to renewable energy, for example.

Amidst this debate, actual deployment of industrial carbon capture has long trailed expectations. There are just over 40 commercial facilities now operating around the world, capturing around 50 million tonnes of CO2 per year – a fraction of the world’s annual emissions, which reached 35.8 billion tonnes last year. But the industry is picking up pace: some 700 projects are in various stages of development and could bring global capture capacity to 435 million tonnes by 2030.

Out of thin air

The past few years have also seen an explosion in innovative solutions to draw down carbon directly from the air. There is now a dizzying array of different approaches, which blur the line between nature-based and technological methods. They include:

• Planting trees, restoring wetlands and sequestering carbon in soils. Generally known as conventional carbon removal, this makes up most of the 2 billion tons of annual carbon removal taking place already.
• Direct air capture (DAC). This method, which has drawn outsize interest, requires purpose-built facilities that filter CO2 out of the air with giant fans. By far the largest plant commissioned to date is Climeworks’ Mammoth project in Iceland, drawing 36,000 tons per year from the atmosphere. The 27 other DAC plants in operation are far smaller, but the US is already planning to build two with a capacity of more than 1 million tons each. (Learn more about the role of software in industrial design and engineering)
• Marine carbon dioxide removal (mCDR). There is a whole host of ocean-based removal methods, from increasing the sea’s alkalinity to draw carbon from the air, to adding nutrients such as iron to boost phytoplankton growth.

All of these methods, and many more besides, have varying levels of readiness, potential and durability – as well as tradeoffs that range from cost and resource needs to the extent of negative side-effects. Still, consensus is growing that we need to explore all of them to identify the most promising solutions.

With so much innovation taking place, it’s easy to forget that carbon removal still has a long way to go: around 7 to 9 billion tons of CO2 per year need to be removed by mid-century to meet the 1.5°C Paris Agreement target – requiring at least a fourfold increase from current levels. Nevertheless, while reducing emissions remains the most important tool to achieve net-zero, removing carbon has turned from a luxury into a necessity.