The world’s boreal forests are absorbing carbon dioxide from the atmosphere at faster rates, at the same time that tropical forests are becoming less effective as a carbon sink, according to a new study in the journal Nature Ecology and Evolution.
The detailed review of carbon loss and gain across all the Earth’s land types between 1992 and 2015 showed a billion-tonne increase in the land carbon sink, Carbon Brief reports, largely thanks to the boreal. By combining remote sensing data with modelling, the research team identified deforestation as the primary culprit driving carbon loss in tropical forests, particularly in the Amazon, Indonesia, and southeast Asia.
“We can clearly see that the anthropogenic land use and land cover change have a big impact for the contribution of tropical forests,” said lead author Dr. Torben Tagesson, a researcher at Sweden’s Lund University.
“It is not fully clear what is driving carbon gains in boreal forests,” although “one likely driver is the ‘CO2 fertilization effect’—a term describing how increasing CO2 levels in the atmosphere can boost plant growth,” Carbon Brief adds, citing Prof. Anja Rammig of the Technical University of Munich, who studies land-surface interactions and wasn’t involved in the latest study. But “overall, the findings paint a comprehensive picture of a ‘worrying’ shift in the ability of tropical forests to absorb CO2 emissions.”
Carbon Brief adds that the study data cut out in 2015—and deforestation has increased in the five years since. “Late last year, deforestation of the Brazilian Amazon reached its highest level in a decade, while central and west Africa also saw a spike in forest loss,” the online publication notes.
This week, the BBC reported on a separate study that shows the deforested parts of the Amazon emitting more CO2 than they absorb. “Carbon loss in tropical regions was also affected by ‘meteorological factors’ such as droughts—which cause tree deaths and worsen the risk of wildfires,” Carbon Brief adds, citing a paper published late last month in the journal Nature Sustainability.
Meanwhile, the factors driving increased carbon uptake in the boreal are not yet fully understood, and Rammig said the effect could slow down or even reverse over the next couple of decades.
“The question is: How long will this carbon stay in forests?” she told science writer Daisy Dunne. “It could be that this carbon gets lost earlier because if trees are growing faster, they could die younger. If trees are dying younger, we could expect to see a completely reversed picture in 10 or 20 years.”