Soils hold 45% more carbon than thought, study finds

The world’s soils may be holding far more carbon than climate models have long assumed. New research released Wednesday finds that topsoils store about 45% more carbon compared to earlier estimates, adding weight to calls to put soil health much closer to the center of climate change planning. The analysis — produced by the International Union for Conservation of Nature, Save Soil, Aurora, and the World Commission on Environmental Law — estimates that the top meter of soil holds about 2,822 gigatons of carbon, which shows how much could be lost if soil degradation accelerates. For context, global greenhouse gas emissions in 2024 were 57.7 gigatons. But scientists say that this carbon reservoir comes with a warning: The system only works if soils remain healthy, but soil health is declining in many parts of the world. Degradation from erosion, nutrient loss, and declining organic matter sharply reduces how much carbon they can retain. Current rates of degradation also risk pushing stored carbon back into the atmosphere, an estimated 4.81 billion metric tons of carbon dioxide each year — roughly the annual emissions of the U.S. in 2023. That raises the stakes for efforts to preserve and restore soils, which underpin food production and biodiversity and now appear even more critical to global carbon management. Without intervention, degradation could weaken this natural sink and accelerate climate impacts by releasing even more carbon. Already, around 30% of the world’s soils are moderately to highly degraded. “For too long, soil has been treated as dirt. However, it is the living skin of the planet. Every handful of healthy, living soil is a microcosm of life and a storehouse of carbon and water,” said Praveena Sridhar, CTO of the Save Soil movement and coauthor of the report, which launched alongside the 30th United Nations Climate Change Conference in Belém, Brazil. “Securing soil is not just an environmental duty,” she added. “It’s a generational responsibility, and essential to climate change mitigation.” Soil as a carbon sink Soils degrade for a number of reasons, many of them tied to land overuse and climate change pressures. Erosion from wind and water strips away topsoil when fields are left bare. Nutrient depletion builds up over years of intensive cultivation without replenishment. Heavy tillage and monocropping accelerate the loss of organic matter, while compaction from machinery or livestock limits the soil’s ability to absorb water. In dry regions, irrigation can drive salinization, and pollution, or chemical overuse disrupts the biological processes that keep soils productive. Together, these forces weaken soil structure and reduce its capacity to store carbon. And degraded soil, although it can recover, takes a long time to do so on its own: “Unless there are timely human interventions to restore degraded soil, it can take up to 500 years to naturally rebuild just 2.5 cm of lost topsoil,” according to the report. Fortunately, there are several human interventions that can help. Among the most effective measures are planting trees, rotating crops and avoiding monocropping, and rotational grazing. Many of the most effective soil restoration efforts focus on supporting farmers so they can manage their land sustainably. It’s also a reminder of why farmers need access to climate finance. They are highly exposed to climate impacts, their farming methods can either increase or reduce emissions, and they play a central role in maintaining soil systems that can store significant amounts of carbon. But policies are also essential, said Anand Ethirajalu, the project director of Save Soil, a group working to improve and transform agriculture in India’s Tamil Nadu state. “Farmers are able to afford industrial farming only because of the subsidies,” Ethirajalu said. Gradually removing these subsidies and using public funds to support regenerative practices would be an effective policy solution, he said. India spent more than $20 billion on fertilizer subsidies in 2023, according to calculations based on IISD data. “A farmer is not here to save the soil or save the planet — he is here to just survive,” Ethirajalu said. “You need to make the solution attractive.” Agroforestry to the rescue One way Save Soil does this is by encouraging agroforestry — integrating trees into cropland and pasture — through sustainable timber production. The system, Ethirajalu says, is sustainable because it uses a mix of tree species with staggered harvest cycles — some ready in seven to eight years, others at 15 to 18 years, and others at 25 to 40 years — giving farmers a predictable sequence of income. Many of these species regenerate from the same root system after harvest, which keeps tree cover in place without the need for constant replanting. The approach also maintains steady carbon storage, since repeated shorter-cycle harvests can store more carbon overall than leaving a single tree to grow for decades. Indeed, government policies are central, the report’s authors note. Despite the scale of the opportunity in healthy soils, 70 percent of countries do not include soil restoration as a climate mitigation measure in their most recent round of nationally determined contributions. They argue that soil needs to be fully counted in climate planning — not only for its risks, but for its potential. Healthy soils represent a path forward: as the world moves past 1.5 degrees Celsius of warming, the threshold laid out in the 2015 Paris Agreement to avert climate disaster, the report estimates that about 27% of the emissions reductions needed to keep temperatures below 2 degrees Celsius could be met through soil sequestration. That amounts to roughly 3.38 gigatons of carbon dioxide each year, achievable only if soils are protected and restored.