U.S. forests have stored more carbon in the past two decades than at any time in the last century, an increase attributable to a mix of natural factors and human activity. To unravel the cause behind this spike, researchers used nationwide forest data to examine how six environmental factors may have contributed to the increase in carbon sequestered by forests. They found that natural forces such as increasing temperatures, shifting precipitation, and carbon fertilization are among the largest contributors to carbon gains, but human drivers, like letting forests get older and planting trees, are also becoming bigger factors. …this new analysis aims to help researchers better separate what portion of carbon held by forests is related to human action and which portion isn’t. …This work highlights the vast difference in the amount of carbon forests can absorb naturally versus when they are actively managed.