A university study has found that the rate of deforestation in the humid tropics, including rainforests of critical biomass and biodiversity, has accelerated drastically throughout the past decade, contradicting previous beliefs that the situation was improving.
Using satellite data, a university study announced today and published in Geophysical Research Letters, found forests in the humid tropics — areas near the equator in South America, Africa and Asia — shrunk at a faster rate in the 2000s than they did in the 1990s. Previous data from the United Nations Food and Agriculture Organization suggested the rate decelerated by 25 percent throughout the past decade.
“Our results show the opposite,” said Do-Hyung Kim, a remote sensing scientist for the geographical sciences department and the lead author of the study. “Our results show the acceleration of the deforestation by 62 percent.”
Joseph Sexton, a professor in the geographical sciences department and co-author of the study, said the areas studied are those of “most concern” with regard to deforestation’s effect on global climate change.
“These are the ecosystems that hold the most biomass,” Sexton said, “so when we lose that forest, that biomass is released as carbon dioxide into the atmosphere.”
These forests also tend to be hot spots for biodiversity, he said, as many types of species thrive in rainforests.
Kim, a geographical sciences doctoral candidate at this university, said this new NASA-funded study could better reveal the reality of deforestation.
“Our findings will greatly enhance our ability to evaluate the efficacy of policies and to infer the driving forces of deforestation,” Kim said.
Kim said he and his colleagues could compare this deforestation data with policies in place to see which methods of tree protection produce better results. For instance, he said, other researchers in the department found the Soy Moratorium in Brazil was effective in decreasing deforestation in the Amazon.
Kim said they couldn’t be sure why these research results were so different from those in the previous Food and Agriculture Organization research but said they used a consistent definition of forestland and found a clear acceleration of data from 1990 to 2000, and the data from 2000 to 2010.
Sexton, who led the algorithm development in the study, said the researchers analyzed 8,500 images from each decade collected by NASA satellites. They then used algorithms to estimate the tree coverage areas by looking at the shades of pixels in the images and by taking into account how trees can look different in some areas.
“Once we did that and we had a machine-learning model that was able to identify trees,” Sexton said, “we were able to look at that at multiple points in time and we can apply a threshold that says whether or not it meets the criterion for being a forest.”
Different countries often have different definitions of what is or is not a forest, so it is beneficial to have consistent data on forest loss around the world, Sexton said. The researchers used the definition of forests established by the United Nations Food and Agriculture Organization at the U.N. Framework Convention on Climate Change in Kyoto, Japan.
Doug Morton, a research scientist at NASA and a university alumnus, was not involved in this study, but said the data could reveal more information about climate change and the effect deforestation has on it.
“The global carbon budget is one of the toughest problems for climate scientists,” Morton wrote in an email. “This paper will have carbon cycle and Earth system scientists reviewing estimates of global carbon sources and sinks for the 1990s and 2000s.”
Though deforestation has accelerated in the past decade as a whole, the study found some slight deceleration in the years after 2005, Kim said. Though forests are still depleting fast, he said, the deceleration could be a sign for some hope that policies can further slow the forest decline.
“I want these results to encourage people to care more about the increase in deforestation,” he said.
