The world is on track to exceed the temperature targets set in the 2015 Paris Agreement. A growing number of scientists and experts say that to achieve long-term climate goals, carbon dioxide (CO₂) will need to be removed from the atmosphere later this century. Governments, energy companies and hundreds of startups around the world are investing billions of dollars in carbon removal strategies. By some estimates, the world could need to remove more than 6 billion tons of CO₂ per year.

There are three main approaches to carbon removal:

1. Direct capture from the air: Large-scale facilities can extract CO₂ directly from thin air. While this is the simplest method on an industrial scale, it is also the most expensive, costing around $600 to $1,000 per ton of CO₂. Several large direct capture facilities are planned in the US. For example, a consortium of Occidental Petroleum and Carbon Engineering plans to launch the world’s largest facility in West Texas, which is expected to capture 500,000 tonnes of CO₂ per year. The captured carbon is often pumped and stored underground.
2. Ocean modifications: The oceans have the potential to absorb more carbon than usual. One approach is to increase the alkalinity of seawater. The $10 million LOC-NESS project, set to begin in the coming months off the coast of Massachusetts, will test this method by pouring a solution of an alkaline material (sodium hydroxide) into the water. The scientists hope to demonstrate that it is possible to monitor and quantify the CO₂ absorbed. If this method could be scaled up even a small fraction, coastal countries could collectively remove a billion tons of CO₂ per year. Other ocean methods include fertilizing the water with iron to promote phytoplankton growth or growing seaweed.
3. Improving carbon removal on land: The cheapest way is to plant more forests, but trees are not a permanent solution due to the risk of logging or fires. More permanent methods include converting plant matter into biochar, a carbon-rich material that is added to the soil. Experiments are also being conducted with applying silicate-rich minerals, such as basalt, to agricultural fields. These minerals react with CO₂ and water to form stable bicarbonate ions that enter the ocean and lock up carbon. Agricultural waste, forest residues, and purpose-grown crops also have the potential to be converted into long-lasting products like building materials. These techniques could potentially eliminate carbon dioxide emissions in the U.S. up to 800 million tons of carbon per year at a price of under $100 per ton of CO₂.

Despite growing investment, the carbon removal industry faces obstacles. These include insufficient international standards, a lack of formal commitments from governments, and policy changes, such as the cuts in US research funding under the Donald Trump administration. There are also scientific questions about whether the technologies can deliver on expectations. In addition, some methods, such as bioenergy with carbon capture and storage (BECCS), can have negative impacts, such as requiring large amounts of fresh water and fertilizer or damaging biodiversity. There are also concerns that carbon removal could lead companies and countries to justify further emissions rather than transitioning to clean energy.

Experts emphasize that while carbon removal technologies are important for the future, there are no easy ways to large-scale carbon removal. This means that global leaders must accelerate efforts to halt emissions now, rather than relying on future generations to solve the problem. It is crucial that science keeps pace with private sector activities and validates the effectiveness and impacts of these new approaches. Spring

The research was published in nature.com