A double whammy of climate
change and deforestation could double the area burned by wildfires in the
southern Brazilian Amazon forest, simulations suggest. That increase in fires
could burn up to 16 percent of the region by 2050 and release enough carbon dioxide to flip parts of the
forest from carbon dioxide sponge to source
— exacerbating greenhouse gas warming rather than combating it.
Avoiding new deforestation, however, could slow or prevent that transition,
researchers report January 10 in Science

Scientists previously have warned
that these two effects — climate change and deforestation — may already be drying out parts of the Amazon, reducing its ability to soak up atmospheric carbon
dioxide and making it more susceptible to wildfires (SN: 8/23/19).

How the wildfires themselves
might exacerbate the problem and increase emissions isn’t usually included in
climate simulations. But the blazes play a role: Combusting trees and
underbrush releases CO2 directly to the atmosphere. And the
heat-driven breakdown of plant matter can add other climate-warming gases such
as methane, nitrogen oxides and carbon monoxide. Trees felled by fire and slowly
decomposing also emit CO2 for years. 

In the new study,
researchers led by forest ecologist Paulo Brando of the University of
California, Irvine, simulated how several different climate and deforestation
scenarios would alter the future area, intensity and greenhouse gas emissions
of fires in the southern Brazilian Amazon. When it comes to burned area and
fire intensity, the most important variable, the team found, was drought — in
particular, the dampness of the understory layer of plants and soil. Even under
moderate future greenhouse gas emissions, fires in the region will be
more severe due to shifting climate patterns that will tend to dry out the

But avoiding new
deforestation could greatly reduce the fire danger, even under the highest-emissions
scenario, the team found. By midcentury, preventing new deforestation reduced
the area burned by 30 percent, and shrank emissions of carbon dioxide and other
gases by 56 percent. That could help the forest maintain its status as a carbon
storehouse, the researchers say.