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Tropical forests are absorbing less carbon dioxide from the air, reducing their ability to act as "carbon sinks" and bringing closer the possibility of accelerating climatic decomposition.
Research has found that the Amazon could become a source of carbon in the atmosphere, rather than one of the largest absorbers of gas, starting in the next decade, due to damage caused by loggers and agricultural interests and impacts. of the climate crisis.
If that happens, climate decay is likely to become much more severe in its impacts, and the world will have to reduce carbon-producing activities much faster to counter the loss of carbon sinks.
"We have found that one of the most worrisome impacts of climate change has already begun," said Simon Lewis, professor at the University of Leeds School of Geography, one of the lead authors of the research. "This is decades before even climate models. most pessimistic ”.
Over the past three decades, the amount of carbon absorbed by the world's intact tropical forests has decreased, according to a study by nearly 100 scientific institutions. They are now absorbing a third less carbon than in the 1990s, due to the impacts of higher temperatures, droughts and deforestation. This downward trend is likely to continue as forests are threatened by climate change and exploitation. The typical rainforest can become a carbon source in the 2060s, according to Lewis.
"Humans have been lucky so far, as tropical forests are removing much of our pollution, but they cannot continue to do so indefinitely," he said in a note with The Guardian, explaining: may the global carbon cycle begin to work against us. The time for action is now ”.
At this year's UN climate talks, known as COP26 in Glasgow in November, many countries are expected to come forward with plans to reach net zero emissions by mid-century. But some wealthy countries and many companies plan to cut their emissions. emissions through offsetting, often by preserving, replanting or cultivating new forests.
This research shows that relying on tropical forests is unlikely to be enough to offset emissions on a large scale. “There's a lot of talk about offsetting, but the reality is that every country and every sector needs to achieve zero emissions, and any small amount of residual emissions. It needs to be removed from the atmosphere, "Lewis said." Using forests as compensation is very much a marketing tool for companies to try to continue business as usual. "
Carbon removal from the atmosphere by tropical forests peaked in the 1990s when approximately 46 billion tonnes were removed from the air, which is equivalent to about 17% of carbon dioxide emissions from human activities. In the last decade, that amount had dropped to about 25 billion tons, or just 6% of global emissions.
The difference is about the same as a decade of fossil fuel emissions from the UK, Germany, France and Canada combined.
Climate scientists have long feared the existence of "tipping points" in the climate system, which when passed will doom the world to runaway global warming. There are many known feedback mechanisms: for example, the melting of Arctic ice leaves more sea uncovered, and because it is darker than reflective ice, it absorbs more heat, leading to further melting.
These feedback mechanisms have the potential to accelerate the climate crisis well ahead of current projections. If forests start to become sources of carbon rather than absorb it, it would be a powerful positive response leading to much greater warming that would be difficult to stop.
Forests lose their ability to absorb carbon as trees die and dry out from drought and higher temperatures, but loss of forest area through logging, burning and other forms of exploitation is also a major factor in the loss of sinkholes. carbon.
Tom Crowther, founder of the Crowther Lab, who was not involved in the research, told TheGuardian: “This analysis provides worrying evidence that, along with ongoing deforestation rates, the rate of carbon sequestration of tropical forests could also be threatened by increasing the mortality of trees. This is very important information, since the capacity of tropical forests to capture anthropogenic carbon emissions could be seriously affected ”.
The study, published in the journal Nature, tracked 300,000 trees over 30 years, providing the first large-scale evidence of the decline in carbon uptake by the world's tropical forests. The researchers combined data from two large forest observation research networks in Africa and the Amazon, as well as years spent traveling to remote field sites, including a week in a dug out canoe to reach Salonga National Park in the troubled Republic. Democratic of the Congo.
They used aluminum nails to label individual trees, measured the diameter and height of each tree within 565 patches of forest, and returned every few years to repeat the process. This allowed them to calculate the carbon stored in the trees that survived and those that died. They found that the Amazon sinkhole began to weaken first, but that the African forests are now rapidly following. Amazonian forests are exposed to higher temperatures, faster temperature increases, and more frequent and severe droughts than African forests.
His projection that the Amazon forest will become a carbon source in the mid-2030s is based on his observations and a statistical model and trends in emissions, temperature and rainfall to forecast changes in the way forests will store carbon until 2040.
Doug Parr, the UK Greenpeace chief scientist, said governments should pay attention to science and make a strong commitment to reduce greenhouse gases at the COP26 summit, and agree on measures to protect and restore forests. "For years, we have received scientific warnings about tipping points in the Earth system and have been largely ignored by decision makers and policy makers," he said.
“Forests now apparently losing their ability to absorb pollution is alarming. What other wake-up call do we need?