France media agencyJul 16, 2021 12:41:27 PM
Climate change and deforestation have transformed much of the Amazon Basin from ingesting CO2 to emitting the planet, a transformation that could turn mankind’s greatest natural ally into an enemy in the fight against global warming, researchers reported Wednesday.
Hundreds of high altitude air samples collected over the past decade showed that the southeastern Amazon in particular has transformed from a “sink” to a source of carbon dioxide, the main greenhouse gas, they reported in the journal Nature.
Aerial view of the Amazon rainforest, near Manaus, the capital of the Brazilian state of Amazonas, Brazil. Photo credit: Neil Palmer / CIAT / Flickr
Terrestrial ecosystems around the world are vital as the world struggles to curb carbon emissions, which exceeded 40 billion tons in 2019.
Over the past half century, plants and soils have consistently absorbed more than a quarter of these emissions, even though CO2 pollution has increased by 50 percent.
The Amazon basin contains about half of the world’s tropical rainforests, which absorb and store carbon more effectively than other vegetation.
If the Amazon – with 450 billion tons of CO2 in its trees and soil – became a constant source rather than a “sink” of CO2, tackling the climate crisis would be a far greater challenge.
Several factors drove the transition in the eastern Amazon, according to the study.
“Deforestation and forest degradation both reduce the Amazon’s ability to act as a carbon sink,” the authors found.
Since 1970, the region’s tropical forests have declined by 17 percent, mainly to accommodate grazing land for livestock and the plants that feed them.
Forests are generally cleared by fire, which both releases large amounts of CO2 and reduces the number of trees available to absorb CO2.
Climate change itself is also a key factor.
The temperatures in the dry season have risen by almost three degrees Celsius compared to pre-industrial levels, three times the global annual average.
Tipping points
Taken together, these factors “cast doubt on the future ability of tropical forests to store large amounts of CO2 from fossil fuels,” noted Scott Denning, an atmospheric scientist at Colorado State University, in a comment, also in Nature.
To what extent the Amazon basin lost its ability to absorb CO2 has long been a burning question, but satellite data – partly due to the persistent cloud cover – could not provide a complete answer.
To get around this problem, researchers led by Luciana Gatti from the National Institute for Space Research in Sao Jose dos Campos in Brazil used aircraft to collect almost 600 CO2 and carbon monoxide samples at altitudes of up to 4.5 kilometers (2.8) from 2010 to 2018 Miles) above the forest floor.
They found that the northwestern Amazon was in carbon, absorbing as much CO2 into the atmosphere as it was giving off.
But the eastern Amazon – especially during the dry season – emitted far more than it absorbed.
Another recent study using a different methodology found that the Brazilian Amazon released almost 20 percent more CO2 in the past decade than it absorbed from 2010 to 2019.
Above a certain threshold of global warming, global warming could turn the rainforest tip of the continent into a much drier savannah state, as recent research has shown.
This would have devastating consequences both for the region, which is currently home to a significant proportion of global biodiversity, and globally.
The Amazon rainforest is one of a dozen so-called “tipping points” in the climate system.
Ice sheets on Greenland and West Antarctica, Siberian permafrost soils full of CO2 and methane, monsoon rains in South Asia, coral reef ecosystems, the jet stream – all are prone to point-of-no-return transitions that, as we know, would radically change the world.
