A new study has found that in the rainforests of equatorial Asia, a link between drought and deforestation is fueling global warming.
The study, analyzing six years of climate and fire observations from satellites, shows that in dry years, the practice of using fire to clear forests and remove organic soil increases substantially, releasing huge amounts of climate-warming carbon dioxide into the atmosphere.
In 2006, the climate on the fast-developing islands of Borneo and Sumatra and in New Guinea and other parts of equatorial Asia was three times drier than in 2000, but carbon emissions from deforestation were 30 times greater - exceeding emissions from fossil fuel burning.
"Land managers respond to the drought by using fire to clear more land. In dry years, they burn deeper into the forest, which in turn releases more carbon dioxide," said James Randerson, climate scientist at UCI (University of California Irvine) and co-author of the study.
The findings, according to Randerson, illustrate why limits on deforestation should be a critical part of future climate agreements.
Global warming modelers typically consider climate and land use separately when assessing how changes will affect greenhouse gas emissions.
The results also indicate that forecasting drought may be important when countries in this region allocate resources to combat illegally set fires and clearing.
"The link between drought and deforestation is very sensitive," Randerson said. "If the climate warms and there are more droughts, it potentially makes the forest and its stored carbon more vulnerable," he added.
Randerson and his colleagues used several kinds of satellite data to develop and refine their emission estimates.
First, they used satellite images of fire areas and additional information about carbon pools to estimate emissions from the region.
Next, they sharpened their estimate using measurements of atmospheric carbon monoxide levels, which can be a strong signal of fire activity.
In a final step, they used both carbon monoxide and satellite data to determine total carbon emissions.
"Deforestation and carbon emissions are substantial and important contributors to the buildup of greenhouse gases in the atmosphere," Randerson said. "We should not neglect this flux in developing comprehensive approaches for stabilizing climate," he added.