STUDY: Tropical Forests Are Now Releasing More Carbon Than Oxygen Into the Atmosphere

Tropical rainforests are emitting more carbon than they take in due to deforestation and loss of crucial biodiversity.

We learned in elementary school that trees are good for the atmosphere because they take in harmful carbon dioxide (as well as carbon monoxide and sulfur dioxide) and release oxygen. Rainforests, those dense, rich, species-diverse forests, have historically been so good at this, they’ve been dubbed “the lungs of the planet.” Tropical forests store carbon, known as carbon sequestration, in their stems, leaves and roots, rather than releasing it to the atmosphere where it contributes to global warming and climate change. Unfortunately, these natural lungs appear to be losing their function, releasing more carbon dioxide into the atmosphere than they take in, according to a new study in the journal Science. Given that tropical forests store 25 percent of the global carbon and are home to 96 percent of the world’s tree species, this new research reveals a potentially huge impact.

After analyzing satellite imagery of Asia, Africa and the Americas, researchers determined that deforestation, in which forests are torn down and replaced with urban spaces, farms or roads, is stealing the atmosphere-purifying power of these forests. However, it’s not just the sheer loss of numbers of trees that are responsible for the shift, the researchers say, so much as it is a decline in diversity of the kinds of trees that remain.

A 2015 study in the journal Global Ecology and Biodiversity found that there are good ecological reasons why biodiversity matters when it comes to carbon uptake. Lead author Professor Lourens Poorter said: “Ecological theories indicate that species richness can enhance carbon uptake; species have different strategies to acquire and use resources, and they are therefore more efficient together.” A multitude of tree species allows for a variety of responses to climatic fluctuations, he said, “which means that a high biodiversity buffers the carbon uptake and storage of the ecosystem against climatic variation.

Even forests that appear to be thriving are seeing diversity loss caused by logging, changes to their environment, wildfires and other diseases.

The most common causes of deforestation and severe forest degradation, according to the World Wildlife Fund (WWF), which advocates for declining forests and the creatures that inhabit them, “are agriculture, unsustainable forest management, mining, infrastructure projects and increased fire incidence and intensity.

In addition, road building has “a large indirect effect” by making forests accessible to settlers and agriculture. In addition, poor forest management and unsustainable methods at collecting wood for fuel create a “death by a thousand cuts” form of deforestation, WWF describes.

To put deforestation in perspective, a 2011 study which pointed out that “extensive tropical deforestation is a relatively modern event, that gained momentum in the 20th century and particularly in the last half of the 20th century.” These researchers found that deforestation has occurred at the rate of 9.2 million hectares per year from 1980 to 1990, 16 million hectares per year from 1990 to 2000, and 13 million hectares per year from 2000 to 2010. “Some smaller countries have very high losses per year and they are in risk of virtually losing all their forests within the next decade if current rates of deforestation are maintained,” the authors write.

While deforestation is fairly easy to spot on a satellite image, the loss of diversity is not so evident to the naked eye (or lens, for that matter), according to lead study other Alessandro Baccini, a forest ecologist and remote sensing specialist at the Woods Hole Research Center in Falmouth, Massachusetts. This “degraded forest,” as they call this, stores less carbon biomass, however.

The data is more than alarming to him. “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.”

“Carbon density is a weight,” Baccini said. “The problem is that there is no satellite in space that can give an estimate of weight.”

Study co-author Wayne Walker said, “It can be a challenge to map the forests that have been completely lost. However, it’s even more difficult to measure small and more subtle losses of forest.”

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