Forests are a great bulwark against climate change, so programs to reduce deforestation are important. Those efforts usually focus on stopping the destruction in areas where it is already occurring.

But a new study suggests these programs would do well to also preserve forests where deforestation and degradation haven’t begun. Gradual loss of these largely pristine, intact forests has a much greater climate impact than previously accounted for, the researchers said.

Globally, forests take more than a quarter of the carbon emissions from human activities out of the atmosphere every year. Intact forests are especially effective at storing carbon — although only about 20 percent of tropical forests are considered relatively pristine, they are responsible for about 40 percent of carbon storage in the tropics.

The study, by researchers from the Wildlife Conservation Society, the University of Queensland in Australia and other institutions, analyzed carbon emissions from the loss of intact tropical forests worldwide from 2000 to 2013.