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Explained: Why Amazon rainforest is reaching a dangerous tipping point

The Amazon basin is the world’s largest repository of biodiversity and produces about 20 per cent of the world’s flow of freshwater into the oceans. In the recent few years, the rainforest has been under threat from deforestation and burning.

Written by Mehr Gill , Edited by Explained Desk | New Delhi |
Updated: December 21, 2019 11:03:54 pm
Earlier this year, fires in the Amazon that were visible from space made headlines. (Reuters/File)

In an editorial published in the journal Science Advances on Friday, researchers Thomas E Lovejoy and Carlos Nobre have said that while 2019 was not the worst year for fire or deforestation in the Amazon— the world’s largest tropical rainforest—“the precious Amazon is teetering on the edge of functional destruction and, with it, so are we.”

Why is the Amazon rainforest in danger?

The Amazon basin is the world’s largest repository of biodiversity and produces about 20 per cent of the world’s flow of freshwater into the oceans. In the recent few years, the rainforest has been under threat from deforestation and burning. Earlier this year, fires in the Amazon that were visible from space made headlines. According to Brazil’s National Institute for Space Research (INPE), forest fires in the Brazilian part of the rainforests have doubled since 2013. It estimates an increase of over 84 per cent since last year. Until August this year, over 72,000 fires were recorded. June to December is considered to be burning season when farmers want to clear land for farming.

Deforestation in the Brazilian Amazon, which comprises about two-thirds of the area of the rainforest, started in the 1970s and 1980s when large-scale forest conversion for cattle ranching and soy cultivation began. NASA’s Earth Observatory notes that state policies that encourage economic development, such as railway and road expansion projects have led to “unintentional deforestation” in the Amazon and Central America. Furthermore, forest clearing has been encouraged by agricultural subsidies, timber concessions and tax breaks have encouraged forest clearing in the Amazon.

What the researchers have said?

In the editorial, the researchers mention that when it rains on the landscape of the Amazon forest, it returns at least 75 per cent of the moisture to the westward-moving air mass. Furthermore, over the whole Amazon basin, the air rises, cools and precipitates out close to 20 per cent of the world’s river water in the Amazon river system. Significantly, they write that the moisture of the Amazon is crucial for the continental climate system and has specific benefits for Brazilian agriculture practised in the south. “In fact, every country in South America other than Chile (blocked from this moisture by the Andes) benefits from Amazon moisture,” they write.

Essentially, when forests are cut, the land is rendered barren, which means that potentially more than 50 per cent of the rainforest runs off and not much water is left for recycling. The researchers predict that if the deforestation continues to happen at the going rate, the rainforest, which they have likened in size to that of 48 states of the continental US, could soon not have enough moisture for the rainforests to sustain, eventually leading to the development of savannahs in the eastern and southern portions of the Amazon, “perhaps extending into central and southwestern areas, because these zones are naturally close to the minimum amount of rainfall required for the rain forest to thrive.” The situation may exacerbate further due to “negative synergies” induced by man-made global warming.

Eventually, the loss of forests will lead to loss of biodiversity, carbon and human well being. “In addition, although deforestation anywhere in the Amazon diminishes its hydrological cycle, what happens in the Brazilian Amazon is particularly important because of the sensitivity of that part of the forest to incremental and cumulative impacts of vegetative decline from dieback.” The researchers have estimated that 17 per cent of the entire rainforest and about 20 per cent of the Brazilian rainforest has been deforested. They refer to these figures as “substantial and frightening”.

“Bluntly put, the Amazon not only cannot withstand further deforestation but also now requires rebuilding as the underpinning base of the hydrological cycle if the Amazon is to continue to serve as a flywheel of continental climate for the planet and an essential part of the global carbon cycle as it has for millennia,” they’ve said.

What is dieback?

When the Amazon rainforest reaches its tipping point, which is to say when the level of deforestation has led to there not being enough water for recycling and as result, moisture to induce rainfall, the rainforests will be unable to sustain themselves. This will lead to a situation when the trees, and in turn, the forest will start to “dieback”. In other words, some trees and eventually the forests will reach the physiological limits of dryness probably induced by droughts and heat stress. Because of this dehydration, the affected trees will begin to die from the tip of their leaves or roots backwards.

According to a report in The New York Times, the first time that an Amazon dieback scenario was suggested was in 2000 by Peter M Cox who published his findings about running large-scale computer simulations that showed how forests were affected by a changing climate scenario throughout the 21st century. As per Cox’s analysis, forests would continue to take up carbon until about 2050, post which, warmer temperatures and water-related stress could cause dieback of the Amazon rainforest. Essentially this means that instead of being a carbon sink, the rainforest would start emitting carbon.

The way forward

Lovejoy and Nobre suggest that “immediate, active, and ambitious” reforestation, particularly in the deforested regions can help save the rainforests from reaching their tipping point. Through reforestation, Brazil should help to reach its goals under the Paris Agreement and a “new vision” for the Amazon must be created by the citizens and leaders of South America and the world, they say.

“Today, we stand exactly in a moment of destiny: The tipping point is here, it is now. The peoples and leaders of the Amazon countries together have the power, the science, and the tools to avoid a continental-scale, indeed, a global environmental disaster. Together, we need the will and imagination to tip the direction of change in favor of a sustainable Amazon.”

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