1246. Three Ways to Absorb Carbon from the Atmosphere and Cool the Planet

It is estimated that the world will need to remove more than 6 billion tons of CO2 per year from the atmosphere by the middle of this century to meet long-term climate change goals. With the world on track to significantly exceed the temperature goal set by the 2015 Paris Agreement, governments, utility companies, and hundreds of startups around the world are investing in carbon removal strategies based on three main approaches: absorbing carbon directly from the atmosphere, modifying the oceans to absorb more carbon than usual, and enhancing land-based carbon removal. Meanwhile, the carbon removal industry faces headwinds, including a lack of international standards and formal government commitments on the technology, and scientific doubts about whether the technology can meet the expectations of the emerging carbon removal market. Here are some key points from an editorial in Nature magazine:

Capturing carbon from the atmosphere

The cheapest way to capture carbon from the atmosphere is to increase forestation, but trees can be cut down or burned in fires, and these threats are growing. That's why many scientists and industry leaders are focusing on more permanent, but more expensive, solutions. The simplest method is industrial-scale direct air capture, but it is also the most expensive, costing $600–1,000 per ton of CO2, roughly 10 times the price of carbon credits under the European Union (EU) Emissions Trading Scheme. Several projects are planned, including the world's largest direct air capture facility, which will capture 500,000 tons of CO2 per year and bury it underground, due to begin operation in West Texas later this year, but there is growing uncertainty about continued support for these projects following the transition of U.S. administrations.

Ocean alchemy

It is estimated that with only a small increase in ocean alkalinity, coastal countries around the world could collectively capture 1 billion tons of CO2 per year from the atmosphere, roughly equivalent to Japan's annual carbon emissions and about 3% of global emissions. Most cost estimates for methods to change ocean chemistry to capture carbon indicate that they are likely to be cheaper than direct air capture. The project, funded through the Public-Private Collaborative Research Program coordinated by the National Oceanic and Atmospheric Administration (NOAA), focuses on various methods of CO2 absorption in the ocean. One of these, if final permits are granted, will release 50 tons of a solution containing sodium hydroxide and an inert tracer dye off the coast of Massachusetts in August to monitor and quantify how it reduces the acidity of seawater and increases the absorption of CO2 from the atmosphere, and to evaluate the biological impacts to demonstrate the possibility of scaling up. Other NOAA-funded projects have so far moved forward, including research into fertilizing seawater with iron to increase phytoplankton and cultivating seaweed.

Greening the land

Similar efforts at carbon removal are underway on land, with many scientists and entrepreneurs around the world researching ways to help cropland capture and store more carbon. First, biochar, a carbon-rich material made by converting plant matter into a charcoal-like substance, prevents carbon from being released into the atmosphere for long periods of time. Also, silicate-rich minerals such as basalt can be applied to agricultural land, where they react with carbon dioxide and water to form stable bicarbonate ions that dissolve and flow into the ocean, trapping carbon. The most promising strategies for carbon removal could come from agricultural waste, forest residues, and possibly specialized crops that can be converted into long-life products such as building materials. It has been estimated that such technologies could achieve the equivalent of about 17% of annual U.S. carbon emissions for less than $100 per ton of CO2, but the challenge lies in figuring out the logistics of deploying them at scale, involving everyone from farmers to transporters to energy producers.

Achieving net-zero emissions will require a variety of options in the coming decades. Separate targets for emissions reduction and carbon removal will be necessary to prevent companies and countries from giving themselves an excuse to simply offset fossil fuel emissions rather than transitioning to truly clean energy. Growing crops to fuel bioenergy plants also involves large amounts of freshwater and fertilizer use as well as negative impacts on biodiversity. There is no easy path to a large-scale carbon removal future, and world leaders need to accelerate efforts to stop emissions now, rather than assume that future generations will clean up after themselves.

(Reference)
Jeff Tollefson Three ways to cool Earth by pulling carbon from the sky. NEWS FEATURE 23 April 2025. Nature 640, 872-874 (2025) doi: https://doi.org/10.1038/d41586-025-01233-6

Contributor: IIYAMA Miyuki, Information Program