Tropical forests aren’t the carbon sponges they once were.
In a role reversal, today’s jungles lose more carbon to the atmosphere each year than they soak up, according to a study published Thursday in Science. The carbon released by these forested areas amounts to 425 million metric tons per year, which is more than all the emissions from U.S. cars and trucks combined.
But, the researchers said there is still time to reverse these trends.
“We actually have a lot of room to improve this,” said Alessandro Baccini, a forest ecologist at the Woods Hole Research Center, who co-led study. “The old story of ‘planting trees and stop chopping them down’ is exactly what needs to happen long term.”
For this study, Baccini and his fellow forest ecologist Wayne Walker strapped on their backpacks, laced up their hiking boots and trudged through forests in 22 countries across three continents. They were on a mission to measure the dry weight, or biomass, of the world’s tropical forests.
Biomass, as it turns out, is directly related to forests’ ability to absorb carbon, reduce global warming and prevent climate change. Unlike cars, which are a one-way source of carbon to the atmosphere, plants both absorb carbon and release it.
Tropical forests were known for soaking up excess carbon dioxide from the atmosphere. The bigger the forest, the more it can hold, but every sponge has a limit as to how much it can store. Plus, thinning forests begin to release carbon into the atmosphere, as the fallen and dead trees decompose.
Tromping deep into thick forests on tough terrain, the team collected tree height and diameter data and used it to calculate biomass. Unlike past studies that examined single factors like deforestation, the researchers wanted to estimate harder-to-measure changes, such as small-scale tree loss through drought or rising temperatures. These changes lead to thinner forests with more dead trees.