According to the United Nations’ Intergovernmental Panel on Climate Change, recent years have seen “decreasing deforestation rates and increased afforestation” — and thus, less carbon dioxide pouring into to the atmosphere from this source. Similarly, a 2010 report from the U.N.’s Food and Agriculture Organization found that while 16 million hectares of forest per year were lost in the 1990s, only 13 million per year were lost in the 2000s. It noted in particular that two countries that have seen major tropical deforestation — Brazil and Indonesia — “have significantly reduced their rate of loss.”
But according to a new study just out in the journal Geophysical Research Letters, the U.N. has it wrong. The study, by the University of Maryland, College Park, geographer Do-Hyung Kim and two colleagues, uses satellite imagery to examine how tropical forests in particular are faring. And their answer is far from heartening.
“Our estimates indicate a 62% acceleration in net deforestation in the humid tropics from the 1990s to the 2000s,” write the authors.
The new study used satellite images to examine the tropical forests of 34 countries, including Brazil, Indonesia and Thailand, that collectively house 80 percent of the world’s tropical forest area. Brazil “dominated” tropical forest losses, according to the study, showing a 33 percent acceleration in the amount of forest that was lost over the time period.
So why the big difference with the U.N.’s estimates? According to Kim, it’s because his research uses a fixed satellite algorithm to estimate the extent of forest cover over time, whereas the U.N. “mostly uses country based self-report.”
“We developed a fully automated method to map the forests and non-forests,” says Kim. “We can enforce a consistent definition and method through space and time.”
The new study did find that in the second half of the 2000s, tropical deforestation showed a “small deceleration,” as losses slowed in Brazil even as the Asian tropics saw an increased rate of reforestation.
One of the chief drivers of deforestation is the conversion of forest land into land for agricultural purposes. But the causes vary in different parts of the world, according to Kim. The reason the rate of deforestation increased, he suggests, may be because people were able to use more powerful industrial technologies to clear forests more quickly.
The loss of Amazon rainforest may well be coming back to bite Brazil right now. The country is suffering from a devastating drought, which is threatening water supplies to the megacity of Sao Paulo. Researchers have blamed the drought conditions, in part, on deforestation.
UPDATE: The U.N. Food and Agriculture Organization’s senior forestry officer Kenneth MacDicken sent a response to this story, commenting that “Measuring forests using satellite imagery and measuring and reporting them from ground-based measurements both have value, but comparing them directly should be done with great caution – it’s like comparing apples and oranges.”
MacDicken argued that there are shortcomings to satellite based analyses of forests:
Many tropical or subtropical forests are dry forests, which are very difficult to measure using satellite imagery. For example, dry forests in Africa or central Brazil have great spaces between trees and often have few leaves for large parts of the year. They are still forests according to the international definition, but remote sensing doesn’t capture them – you just can’t see them from space. Those kinds of forests are best measured based on aerial photography and/or ground-based measurements.
The FAO will release a new report on the state of the world’s forests in September of 2015.