A new study led by Yale University suggests that adding limestone to farmlands in the Mississippi River Basin acts as a significant carbon sink. The research found that farmers in this region are storing more carbon dioxide (CO2) in the soil than they emit when they apply limestone, a common agricultural practice called "liming." This discovery could influence how soil is managed in the American heartland and beyond, offering a potential strategy for reducing atmospheric CO2 levels. Liming works similarly to a climate change mitigation technique called "enhanced weathering." This process involves adding crushed rock—like limestone or silicate—to soil, which helps neutralize acidity. As the rock interacts with CO2 in the soil, it forms stable bicarbonate ions. These ions can move through the soil, groundwater, and rivers, eventually reaching the ocean, where the carbon can remain stored for long periods. A key contribution of the study is its consideration of what would happen without liming. Researchers noted that even without the addition of lime, soil acidity from fertilizer use and air pollution would still cause reactions that release CO2. When comparing liming to this scenario, the study found that it results in a net removal of carbon over time. This insight challenges current greenhouse gas accounting methods, such as those used by the Intergovernmental Panel on Climate Change (IPCC), which typically treat the carbon in lime as emitted CO2 rather than stored. The researchers caution that the benefits of liming seen in the Mississippi River Basin might not apply universally. The effectiveness of liming in reducing CO2 levels can vary based on local conditions, such as the existing acidity of the soil, its ability to buffer pH changes, and the region's hydrology. However, since 1900, liming in the Mississippi River Basin is estimated to have removed between 300 million and 400 million metric tons of CO2. These findings suggest that promoting agricultural liming could be a viable way to scale up enhanced weathering and contribute to global efforts to combat climate change.