The Amazon rainforest may be nearing a tipping point

The Amazon rainforest may be nearing a tipping point

In 2020, the Covid-19 pandemic slowed virtually everything, except for the deforestation of the Amazon rainforest. During 2020, Brazil lost nearly thirty-eight square kilometers of vegetation per day, equivalent to twenty-four trees every second. The phenomenon is largely attributable to ranchers and farmers, who clear the forest and burn the debris to make way for crops and livestock. Fires can in turn ignite peat, the organic matter concentrated in the soil that releases large amounts of carbon into the atmosphere. The Amazon is transforming from a huge basin capable of capturing CO 2 into a source of gas that warms the planet.

"The Amazon is in an emergency situation - explains Luciana Vanni Gatti, who studies the rainforest at Brazil's National Space Research Institute - Deforestation increases year on year: 2020 was worse than 2019, 2021 worse than 2020, and we are sure 2022 will be even more negative. "

Scientists are now rushing to try to figure out if and when the Amazon will reach a feared irreversible tipping point, a kind of tipping point where Earth's largest rainforest could dry out, turning into an extensive savannah. The extreme consequence would be the loss of an irreplaceable ecosystem and a fundamental factor in global climatic dynamics.

Loss of resilience Cities can become a key ally in the fight against climate change The latest IPCC report highlights the risks to urban areas dictated by the climate crisis, but also suggests how they could become one very useful tool to help humanity face the threat. Read the article An article published on 7 March in the journal Nature Climate Change tries to shed more light on this critical point, which could be rapidly approaching. While previous research relied on complicated models to predict how the decline of the Amazon rainforest might have occurred, this new study builds on satellite data, which shows that seventy-five percent of the Amazon has become less resilient to adverse events such as drought. .

One way to determine the resilience of a forest is to employ a satellite measurement called vegetation optical depth, which can penetrate into the forest and detect the amount of biomass. wooded present (other satellite techniques only analyze the treetops, while the Vod is able to provide a better picture of what is hidden below). The scientists also looked at a range of other data that track changes in land cover types - comparing forest and farms, for example - to pinpoint where urban areas and farmland had infiltrated rainforest. With data available as far back as 1991, scientists were able to observe how long it took a particular area of ​​the Amazon to regrow its biomass after an adverse advent. This regrowth represents resilience, and the Amazon is losing it. Researchers divided the rainforest into a virtual grid to track the vegetation within each cell and determine correlations with stressors such as drought or nearby building development.

Scientists have found that vegetation in over three-quarters of the Amazon has been losing resilience since the early 2000s, experiencing a slower regrowth rate. By also having land cover data available, the researchers were able to further demonstrate how areas that receive less rainfall or that are closer to human-caused disturbances, such as agricultural land, are losing resilience faster than areas. more humid and pristine lands.

The Amazon is taking longer to recover from factors such as meteorological events, which have a duration that extends over weeks or months, as well as the most long periods of drought. "This indicates that the system is slowing down - says the climatologist Chris Boulton of the University of Exeter, lead author of the new article -. [The Amazon rainforest, ed.] Is taking longer to recover from short-term fluctuations".

It would not be possible to arrive at this conclusion by relying on a more simplistic measurement of the Amazon, such as that provided by satellite images that show only rainforest ground cover, i.e. where the forest is present or not. Vod allowed Boulton and his colleagues to analyze biomass in much more detail, offering a more complete picture of how the Amazon reacted to periods of extreme drought. Not good, it would seem: the loss of resilience worsens when the landscape dries up. “There have been three periods of drought in the Amazon recently as they generally happen once every century,” explains Boulton.

The risks of deforestation WiredLeaks, how to send us an anonymous report Read the article Another great threat is represented by deforestation, including what is done by selecting the trees to be cut and saving others. Even if you don't completely clear an area, it is still possible to destabilize the forest. forest degradation, in which biomass is stolen from the forest - explains environmental scientist Pontus Olofsson, who studies the Amazon but was not involved in the new study -. They are cutting the trees, but not to the point of changing the land cover, which it is still forest, but with fewer trees ".

The farmers also contribute to the weakening of the Amazonian landscape, albeit in a less evident way, by cutting down the trees but leaving part of the forest intact. Since they find themselves surrounded by barren land, however, the animals left inside that patch of forest don't dare venture out. Even birds are not in danger of flying out of the area. Also, the boundaries of that part of the rainforest are exposed to the open air, and they degrade rapidly. In theory, a rainforest should remain humid, but in some areas its outer edges bake in the sun. Over time, rainforest vegetation dies off, as savanna-like vegetation creeps into it.

This can happen on a smaller scale even when Amazonian biomass is cut down to build roads or power lines . "The effects of what happens in a cleared area are not limited to that area," says tropical ecologist Paulo Brando of the University of California, Irvine, who studies the Amazon but was not involved in the new research. >
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Arrow The new study found that the Amazon loses resilience when it collides with human activity. Brando's research found that about seventeen percent of southeastern Amazon, where deforestation is particularly acute, is within 100 meters of one of these dry areas. It is a huge problem, because the Amazon is an extremely sensitive hydrological machine: trees absorb rain and release water vapor with photosynthesis, a quantity of water sufficient to allow the Amazon rainforest to independently generate rain. "In the water cycle, evapotranspiration is essential to produce precipitation - explains Gatti -. The Amazon can release into the air a quantity comparable to that which the Amazon River discharges into the ocean. It is an enormous quantity of vapor. water in the atmosphere ".

All this additional atmospheric water goes to hydrate every other country in South America, except Chile, where the Andes locks in moisture. Losing the Amazon River would mean drying up the continent. It's a vicious circle: deforestation involves fewer trees, which means less moisture in the atmosphere, which equates to less rain, which results in more trees dying. Evapotranspiration, then, also serves to cool the forest - with a functioning similar to that of sweating - and without it the Amazon not only dries up, but heats up. "Destroying enough forest changes the climate enough to create a perpetual vicious circle - says Brando -. I think there is enough evidence to argue that some parts of the Amazon have been pushed over the edge. That's where it happens. most deforestation, most droughts, most warming and most animal losses. "

A dry rainforest also burns more easily, thus emitting more carbon into the atmosphere. If the forest continues to lose water and turns into a savannah, it will become a much drier and grassy ecosystem, significantly more flammable than a rainforest.

Scientists are still unable to tell when the The Amazon as a whole could reach the point of no return, as there are a myriad of variables at play, such as the rate of deforestation and how droughts could intensify. But the situation in the southeastern rainforest is perhaps providing a preview of what it might be like to get to that point. In this area, as the forest fragments and its edges are more exposed to the sun, the large trees that need a lot of water are dying. Those that tend to survive are similar to those seen in a savannah and may even lose their leaves during the dry season, unlike the evergreens characteristic of a rainforest.

Brando points out that not all the Amazon reaches this critical point: "A reduction in resilience does not mean that there is no more - he explains -. These forests, especially if they are left alone, have a very high resilience". If enough of the tallest trees remained standing, if the animals still managed to move seeds and nutrients, and if large patches of vegetation remained connected, adds Brando, "all these elements would contribute to the resilience of the system."
Gatti is less optimistic, as the threat of deforestation does not seem to subside: "It's really a nightmare time in Brazil - he says -, nightmare".

This article originally appeared on Us.

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