(CN) – As nations across the world consider strategies for battling climate change, forests have become unlikely adversaries of such efforts: Instead of being our carbon filters, they’ve become emitters themselves.
While previous measurements of carbon density in aboveground forests have focused primarily on deforestation, subtle human-caused and natural losses stemming from degradation and disturbance also play key roles in reducing the ability of tropical forests to trap greenhouse gas emissions.
Rather than serving as environmentally friendly carbon “sinks,” forests now produce about 8 percent of CO2 emissions worldwide, according to a study published Thursday in the journal Science.
“Forests are the only carbon capture and storage ‘technology’ we have in our grasp that is safe, proven, inexpensive, immediately available at scale, and capable of providing beneficial ripple effects – from regulating rainfall patterns to providing livelihoods to indigenous communities,” said lead author Alessandro Baccini, a scientist at the Woods Hole Research Center.
“If we’re to keep global temperatures from rising to dangerous levels, we need to drastically reduce emissions and greatly increase forests’ ability to absorb and store carbon.”
Using satellite imagery captured between 2003 and 2014, Baccini and his team were able to measure losses in forest carbon caused by fine-scale degradation and disturbance, which have been proven difficult to quantify over large areas. The team also calculated the impact of deforestation.
“It can be a challenge to map the forests that have been completely lost,” said Wayne Walker, a scientist at WHRC and co-author of the study. “However, it’s even more difficult to measure small and more subtle losses of forest.”
Walked explained that in many cases, these losses are the result of selective logging – small-scale farming operations remove individual trees, which are then used for fuel wood. While such activities are relatively insignificant at any one location, when added up, the effect of these losses is considerable.
Based on their calculations, the team found that forests now produce a net total about 425 teragrams of carbon annually – more than the emissions from all cars and trucks in the United States each year. Gross yearly carbon losses were roughly 862 teragrams, while gains were about 437 teragrams.
The majority of carbon losses – almost 60 percent – occurred in Latin America. Africa experienced nearly 24 percent of carbon losses, while Asia accounted for 16 percent.
Besides Asia, degradation and disturbance were the primary driver of continental carbon losses. In the Americas and Africa, these factors contributed to 70 percent and 81 percent of losses, respectively.
“With this study, countries are now able not only to identify where degradation is taking place, but also, given the potential to now measure gains from growth, they can demonstrate their contribution to returning tropical forests to their more beneficial role as a carbon sink,” Baccini said.
The United Nation’s Reducing Emissions from Deforestation and Forest Degradation program, or REDD+, provides incentives for nations to keep forests intact – provided the organization has consistent access to accurate measurements of forest carbon density.
The team hopes their findings can be used to guide new, efficient approaches to mitigating climate change based on forest conservation.
“These findings provide the world with a wakeup call on forests,” Baccini said.