CO2 can be removed from the air through a range of methods, from planting trees to industrial machines that chemically filter it out of the atmosphere. Some approaches are simple enough for a landowner to start tomorrow; others require billions of dollars in infrastructure. Each works at a different scale, speed, and cost, and most climate strategies call for using several of them together.
Direct Air Capture: Machines That Filter CO2
Direct air capture (DAC) is the most engineered approach. Large fans pull ambient air across materials that selectively grab CO2 molecules, then release them in a concentrated stream that can be stored underground or used in manufacturing. Two main types of DAC exist, and they differ significantly in how much energy they need.
Liquid solvent systems pass air through a solution of strong alkaline chemicals that react with CO2. The captured carbon is then released by heating the solution to extremely high temperatures, between 800 and 1,000°C. That makes liquid DAC very energy-intensive, typically powered by natural gas or industrial heat sources.
Solid sorbent systems use materials coated with chemicals (often amines) that bond with CO2 at ambient temperatures. To release the captured gas, the sorbent only needs to be heated to around 80–120°C, and some newer materials work at temperatures as low as 60°C. This dramatically reduces energy demand. One experimental sorbent, COF-999, consumes just 0.8 gigajoules of energy per ton of CO2 removed, a fraction of what liquid systems require.
The tradeoff is cost. Current estimates put DAC at $400 to $1,000 per metric ton of CO2, though government tax credits can reduce that by up to $180 per ton. For context, humanity emits roughly 37 billion tons of CO2 annually. Scaling DAC to make a meaningful dent requires not just cheaper sorbents but enormous amounts of clean energy to power the process.
Forests and Reforestation
Trees remain one of the most effective and accessible ways to pull CO2 from the air. Through photosynthesis, they convert atmospheric carbon into wood, roots, and leaf litter, locking it away for decades or centuries. The rate varies enormously by climate. Tropical forests sequester 4 to 8 metric tons of carbon per hectare per year in their biomass. Temperate forests capture 1.5 to 4.5 tons, and boreal forests in colder regions store just 0.4 to 1.2 tons, according to IPCC data.
Those numbers represent carbon, not CO2. Since each ton of carbon corresponds to about 3.67 tons of CO2, a hectare of new tropical forest could remove roughly 15 to 29 tons of CO2 annually during its growth phase. That rate slows as forests mature and reach a carbon equilibrium. Reforestation works best on degraded land that was recently cleared, where fast-growing species can maximize early uptake. The limitation is land: large-scale reforestation competes with agriculture, and forests are vulnerable to wildfires, disease, and future deforestation that would release stored carbon back into the atmosphere.
Soil Carbon Through Farming Practices
Agricultural soils hold enormous quantities of carbon, and certain farming practices can increase that storage. Cover cropping, conservation tillage, crop rotation, and applying compost or manure all help build organic matter in soil. Switching pastures from continuous grazing to intensive rotational grazing is particularly effective. A modeling study of Vermont’s agricultural land found that converting cropland to well-managed perennial pastures could increase total soil carbon stocks by 11% over 50 years, compared to just 5% from adopting regenerative practices on existing cropland.
Interestingly, no-till farming, often promoted as a carbon storage strategy, appears to mostly redistribute carbon between soil layers rather than increasing the total amount stored. The real gains come from keeping living roots in the ground year-round and adding organic inputs. Soil carbon storage is slow, measured in fractions of a ton per hectare per year, but it applies across hundreds of millions of hectares of farmland worldwide, which adds up.
Enhanced Weathering: Crushing Rocks to Absorb CO2
When certain rocks like basalt are exposed to air and water, they naturally react with CO2 and lock it into stable mineral forms. This process happens over thousands of years in nature, but crushing the rock into fine powder and spreading it on farmland accelerates it dramatically by increasing the surface area available for the reaction.
A 2024 study published in Nature modeled what would happen if crushed basalt were applied annually at 40 tons per hectare across U.S. agricultural land. The result: a net removal of 0.16 to 0.30 billion tons of CO2 per year by 2050, rising to 0.25 to 0.49 billion tons by 2070. The upper estimate equals about 6% of current U.S. emissions. The study’s authors estimate this could deliver 16 to 30% of the carbon removal needed from engineered technologies by mid-century.
The appeal of enhanced weathering is that it piggybacks on existing farming infrastructure and can improve soil health by adding minerals. The challenge is the sheer volume of rock that needs to be mined, crushed, and transported, along with remaining uncertainties about how permanently the carbon stays locked away as dissolved minerals move through rivers and into the ocean.
Ocean Alkalinity Enhancement
The ocean already absorbs about a quarter of human CO2 emissions, but that absorption is making seawater more acidic. Ocean alkalinity enhancement aims to speed up CO2 uptake while reversing acidification by adding alkaline minerals to seawater.
The process works by dissolving pulverized silicate or carbonate rock (or their chemical byproducts) into the surface ocean. The added alkalinity converts dissolved CO2 into bicarbonate and carbonate ions, which are stable forms that remain in seawater for thousands of years. This chemical shift lowers the CO2 concentration in surface water, causing more atmospheric CO2 to flow into the ocean to restore equilibrium. For every mole of dissolved magnesium- or calcium-based silicate mineral, at least 1.5 moles of atmospheric CO2 are removed.
Beyond carbon removal, this approach could help restore marine ecosystems damaged by acidification, since the added alkalinity raises ocean pH. The risks include ecological disruption from increased shipping traffic needed to distribute minerals, potential introduction of invasive species via vessels, and the difficulty of monitoring carbon uptake across vast stretches of open ocean.
What Happens to Captured CO2
Removing CO2 is only half the equation. What you do with it determines whether the removal is temporary or permanent. There are two main paths.
Geological storage injects concentrated CO2 deep underground into rock formations where it mineralizes over time. In the U.S., this requires a Class VI injection well, a category created by the EPA specifically for long-term CO2 storage. These wells must meet strict requirements for site characterization, monitoring, and post-injection care to protect underground drinking water sources. When done properly, geological storage locks carbon away for millennia.
Utilization turns captured CO2 into products: synthetic fuels, building materials, carbonated beverages, or chemical feedstocks. This offsets some of the cost of capture, but many uses are temporary. CO2 put into a synthetic fuel gets released again when that fuel is burned. CO2 mineralized into concrete, on the other hand, stays locked in for the life of the structure. The climate value depends entirely on whether the carbon stays out of the atmosphere.
Comparing the Options
- Speed: DAC and ocean alkalinity enhancement can ramp up as fast as infrastructure allows. Forests take decades to reach peak absorption. Soil carbon builds slowly over years.
- Permanence: Geological storage and mineralization last thousands of years. Forest carbon can be released by fire or logging. Soil carbon can be lost if farming practices change.
- Cost: Reforestation and regenerative farming cost tens of dollars per ton of CO2. Enhanced weathering falls in the mid-range. DAC currently runs $400 to $1,000 per ton.
- Scale potential: Enhanced weathering on U.S. farmland alone could remove up to half a billion tons of CO2 per year by 2070. Tropical reforestation could remove billions of tons annually if enough land were available. DAC is currently negligible in volume but has no theoretical ceiling if powered by clean energy.
No single method can handle the roughly 10 billion tons of CO2 that climate models say we need to remove annually by mid-century. The realistic path forward involves deploying all of these approaches simultaneously, matching each to the geography, economics, and timeline where it works best.