The world’s forests double as the planet’s lungs. So when it comes to a natural solution to sequestering carbon emissions, a pressing question is exactly how much air those lungs can hold. The answer is better than expected–and the unlikely reason may have to do with our increased urban living.
Last month, Science published a study led by U.S. Forest Service researcher Yude Pan that found the world’s established forests absorb 2.4 billion tons of carbon dioxide each year, or about a third of the total released by burning fossil fuels. This carbon sink was not only higher than expected, but actually increased between 1990 and 2007. Tropical deforestation in places like Indonesia and Brazil appears to be the only thing holding forests back from even greater sequestration–net deforestation (i.e. the difference between gross deforestation and forest re-growth) emits 1.3 billion tons annually. And deforestation is getting worse, right? Not necessarily.
Deforestation rates in Brazil’s Amazonian rainforest have actually fallen by more than 75% off their recent peak in 2004, according to a report published last year by Hector Maletta, an economist at the Universidad del Salvador in Buenos Aires. A crackdown on illegal logging and designating 273,000 additional square miles as protected areas have helped, he says. But the real rates are even lower, he says, because much of the land being chopped at the edges was already cut down once and has since grown back. “A significant part is taking place on the re-grown forest that has been deforested twice,” he says. “So the net change is about one-half or two-thirds as much” as the official figure.
Once you factor in reforestation, the carbon sink of the world’s forests practically doubles from a third of all human emissions to 60%. While Maletta says deforestation in the Amazon will never fully cease, although he does believe the net change will continue to shrink, the world’s forests may grow back faster than our need to chop them down.
Scientists Joseph Wright and Helene Muller-Landau of the Smithsonian Tropical Research Institute have made waves by suggesting that secondary growth forests are expanding at a phenomenal rate–for every acre of land deforested each year, more than 50 acres are waiting to take their place, according to the United Nations’ Food and Agriculture Organization 2005 “State of the World’s Forests” report. Wright estimates reforestation rates are more than double deforestation ones.
The reasons are simple, Wright has argued: migration and urbanization. In the Amazon, Maletta notes, the majority of deforestation is caused by subsistence farmers clearing land for cattle pasture, not by agribusiness. (They have cultivated vast swaths of the savannah instead, which is problematic, but doesn’t affect carbon levels.) As those farmers, now out of business, migrate to cities in search of work, the jungle quickly reclaims their land. With the world’s urbanization rate expected to climb from a little more than 50% today toward 80% by the end of the century, the planet’s forests appear poised to gain even more breathing room.