Nature already removes more than half of the carbon dioxide humans emit each year, split between the ocean and land ecosystems. In 2023, human activities released about 11.1 billion metric tons of carbon into the atmosphere, and natural processes pulled back roughly 5.2 billion tons of that. The remaining 5.9 billion tons stayed in the air, driving up concentrations. Understanding what does the pulling, and how we might boost it, is central to every serious climate strategy.
Land Plants and Photosynthesis
Terrestrial plants are the most visible carbon removal system on Earth. Through photosynthesis, they absorb CO2 and convert the carbon into leaves, wood, roots, and other biomass. Recent estimates from a team led by Cornell University and Oak Ridge National Laboratory put total land plant CO2 uptake at 157 billion metric tons of carbon per year, roughly 30% higher than the figure scientists used for decades. That older number, 120 billion tons, had been the standard for 40 years until improved models better accounted for how CO2 moves from the inside of a leaf into the tiny structures where carbon fixation actually happens.
Most of this carbon cycles back into the atmosphere relatively quickly as plants die and decompose. But a meaningful fraction stays locked away, especially in forests. Global forests currently hold an estimated 374 billion tons of carbon in living trees, and research published in Nature suggests there’s a total natural potential of around 600 billion tons if degraded and deforested areas were restored. That gap of roughly 226 billion tons represents the carbon that reforestation and forest protection could theoretically recover.
The Ocean’s Two Carbon Pumps
The ocean absorbs about one-quarter of the CO2 humans release, making it the single largest active carbon sink. It does this through two distinct mechanisms.
The first is simple chemistry: CO2 from the air dissolves into surface seawater. Cold water absorbs more gas than warm water, so polar and subpolar oceans are especially effective at this. Once dissolved, currents carry carbon-rich water into the deep ocean, where it can stay for centuries to millennia. This is sometimes called the solubility pump, and it operates on very long timescales.
The second is biological. Phytoplankton, tiny photosynthetic organisms at the ocean surface, take up dissolved CO2 as they grow. When they die or are eaten, some of that carbon sinks to the deep ocean floor in the form of dead cells, fecal pellets, and other organic matter. This biological carbon pump plays a huge role in keeping atmospheric CO2 lower than it would otherwise be. As phytoplankton draw down CO2 in surface waters, the water can then absorb more from the air above, creating a continuous cycle.
In 2023, the ocean absorbed about 2.9 billion metric tons of carbon. Over the past decade, it has consistently taken up around 26% of total human emissions.
Soil: The Overlooked Carbon Reservoir
Soil stores roughly three times more carbon than all living vegetation combined, measured down to a depth of one meter. That makes it one of the largest carbon pools on the planet, though it rarely gets the attention forests do.
Carbon enters soil when dead plant material, root secretions, and microorganisms decompose and become incorporated into the ground. How long it stays there depends on physical and chemical protection. Clay-rich soils, for example, bind carbon to mineral surfaces in ways that shield it from microbes that would otherwise break it down and release it as CO2. Waterlogged or compacted soils slow decomposition for similar reasons.
Farming practices have a big influence on soil carbon. Conventional tillage breaks up soil structure and exposes stored carbon to air, accelerating its release. Reduced tillage, cover cropping, and organic management can reverse this. One analysis found a 56% reduction in greenhouse gas emissions under organic management compared to conventional methods. That said, realistic estimates suggest sustainable land management can capture only 50 to 66% of soil’s theoretical carbon storage capacity, because some carbon loss is inevitable under any agricultural system.
Peatlands and Coastal Ecosystems
Peatlands are wetland ecosystems where waterlogged conditions slow decomposition so dramatically that dead plant material accumulates over thousands of years. Northern peatlands alone store around 30 billion tons of carbon, more than all of Canada’s managed boreal forest. Some of that carbon has been locked in place for up to 10,000 years, far longer than the 100 to 500 years typical of tropical forest carbon.
Coastal ecosystems provide another outsized contribution relative to their footprint. Mangroves and salt marshes remove carbon from the atmosphere at a rate 10 times greater than tropical forests and store three to five times more carbon per acre. Their soils, often deep and oxygen-poor, trap organic material much the way peatlands do. These “blue carbon” systems are small in total area but disproportionately powerful per square meter, which makes their protection especially cost-effective as a carbon strategy.
Rock Weathering: The Slowest Sink
Over geological timescales, rocks are one of the planet’s most important carbon sinks. When rain falls through the atmosphere, it picks up CO2 and becomes slightly acidic (carbonic acid). This acidic rain slowly dissolves silicate rocks, releasing calcium and magnesium. Those elements eventually combine with dissolved carbon to form carbonate minerals like limestone, locking the carbon into solid rock.
This process has regulated Earth’s climate for billions of years, but it operates over millions of years. That’s far too slow to counteract today’s emissions on its own. Researchers are experimenting with “enhanced rock weathering,” which involves crushing silicate rocks into fine particles and spreading them on farmland or coastlines to speed up the reaction. The idea is promising but still in relatively early stages of testing at scale.
Biochar: Locking Carbon in Charcoal
Biochar is a form of charcoal made by heating plant waste in a low-oxygen environment. Because the process converts carbon into a highly stable form, burying biochar in soil keeps that carbon out of the atmosphere for a very long time. Modeling studies that simulated 500 years of natural decomposition found that biochar retains roughly 48 to 56% of its original carbon even after five centuries. When you include the additional carbon that accumulates in the surrounding soil through plant-soil interactions, total sequestration reaches 65 to 73% of the original input over that same period.
The recalcitrant components of biochar, which make up 97% or more of its mass, resist microbial breakdown and are physically protected within soil aggregates. This makes biochar one of the more durable carbon removal options available, and it can simultaneously improve soil fertility in degraded cropland.
How the Carbon Budget Adds Up
The Global Carbon Budget, updated annually by an international research consortium, tracks where all human-caused carbon ends up. Over the decade from 2014 to 2023, about 48% of emissions accumulated in the atmosphere, 26% was absorbed by the ocean, and 30% was taken up by land ecosystems. Remarkably, the fraction staying in the atmosphere has remained roughly stable since 1960, meaning natural sinks have been scaling up in pace with rising emissions, absorbing on average 56% of what humans release.
That stability isn’t guaranteed to continue. Warmer oceans absorb less gas. Droughts and wildfires can flip forests from carbon sinks to carbon sources in a single season. Drained peatlands release their ancient carbon stores. The systems currently working in our favor are themselves vulnerable to the climate change they’re helping buffer, which is why both protecting existing sinks and developing new removal methods matter so much.