For most of the industrial era, spreading crushed limestone across farmland has been treated as a carbon problem. The rock contains carbon; it ends up in contact with air and water, and by the most conservative accounting conventions, carbon is assumed to escape as carbon dioxide. Regulators and major climate assessments have baked that assumption into their default rules for decades.

A study published in Nature now argues that the opposite is true and that the error came from asking the wrong question. Across more than 120 years of records from the Mississippi River Basin, the researchers, including study co-author Chris Reinhard, conclude that agricultural liming has removed somewhere between 300 and 400 million metric tons of carbon dioxide from the atmosphere since 1900.