Amazon’s southeast moves from carbon sink to carbon source, according to research published in Nature magazine in June.
the research was written up for Yaleclimateconnections.org by Bob Henson and published Aug. 26. The following are excerpts from Henson’s article.
“The sixth major assessment of climate science from the Intergovernmental Panel on Climate Change (IPCC) – which landed with an existential thud on our collective doorstep in August – confirms why we need to be profoundly concerned about parts of the Amazon shifting from a carbon sink to a carbon source, a finding reported in the journal Nature in June.
”Just under half of the carbon dioxide (CO2) pumped out by human activity each year accumulates in Earth’s atmosphere. The other 56% is dutifully soaked up by the planet’s oceans and vegetation. That absorption has grown in remarkable sync with emissions themselves, the IPCC noted. There are year-to-year ups and downs, largely associated with El Niño and La Niña, but the average fraction of emitted CO2 going into ocean and land sinks has remained nearly constant for the past six decades.
“Ecologists and climate scientists have marveled at the planet’s ever-growing carbon sink even as they’ve worried about its ability to keep up with fossil fuel use.
“Now, a new Amazon study has yielded the starkest evidence to date of a region where the tide has turned and the landscape is consistently giving up more carbon than it can absorb. If additional land areas become sources instead of sinks over time, it could hobble our ability to slow and eventually reverse the nonstop buildup of CO2 in the atmosphere.
”The transition from sink to source in the southeast Amazon became evident through monthly sampling via aircraft from 2010 through 2018: at four sites across the Amazon, as documented in the Nature study led by researcher Luciana Gatti of Brazil’s National Institute for Space Research (INPE). The southeast Amazon falls squarely in the long-time “arc of deforestation” that’s been pushing relentlessly toward the central Amazon.
“The other three areas, where forests are less depleted, were found to be either carbon-neutral or serving as weak carbon sinks. But in the southeast Amazon, deforestation and heating are pouring carbon into the atmosphere while cutting back on the region’s carbon absorption.“Emissions come from fire initially, and later from the decomposition,” said Gatti in an interview.
“The region is a welter of vicious circles. As trees are cut down or burned, the fragmented landscape heats up more readily. Deforestation and biomass burning means less moisture to be pumped from forests back into the atmosphere by evapotranspiration. All this has helped boost regional temperatures during the dry season, already longer and more distinct here than in other parts of the Amazon. The hotter, drier, and more prolonged fire season, in turn, only enhances blazes and contributes to further tree loss.
“According to Gatti, average temperatures for the August-to-September period across the southeast Amazon climbed by 3.1°C (5.6°F) from 1979 to 2019. “This is more than in regions where the glaciers are melting,” she said. “It’s unbelievable.”
“Britt Stephens of the National Center for Atmospheric Research in Boulder, Colo. pointed out that most of the planet remains a carbon sink, a fact that can get lost amid the intense (and well-justified) attention to the Amazon’s deforestation crisis.
“”Northern mid-latitude forests are taking up a lot more [net carbon] than the tropics,” Stephens said. The new IPCC report asserts that Earth system models underestimate the Northern Hemisphere carbon sink.
”There’s been active debate on why the planet-wide carbon sink has managed to grow in lockstep with emissions. The main factor seems to be CO2 fertilization, the ability of trees and plants to grow more rapidly in an atmosphere with more CO2.
”There’s already some evidence that the CO2 fertilization effect may be starting to weaken.”
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Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance venues, and has authored several books. In 2018 Henson began a three-year elected term on the AMS Council, the governing body of the American Meteorological Society.
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