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Let's Look at the Evidence on Tipping Points in the Amazon Rainforest



In the face of mounting scientific evidence that the Amazon rainforest is at grave risk because of climate change, President Jair Bolsonaro’s government continues to deny reality. The most recent example came in October with a letter from the Brazilian embassy in Washington to the Peterson Institute for International Economics, challenging the facts presented in its Policy Brief citing expert conclusions that the Amazon rainforest is nearer than generally realized to a “tipping point” beyond which it may be impossible to save it from destruction. That evidence is reviewed in this posting.

The tipping point is a threshold beyond which the rainforest can no longer produce the rainfall it needs to sustain itself. Once the threshold is crossed, climatic and environmental changes develop rapidly, turning the moist rainforest into dry savanna. The first paper to calculate the tipping point was published in 2007 and showed that at about 40 percent deforestation, the Amazon would experience diminished rainfall and a lengthier dry season, predicting a shift to savanna vegetation to the east. About a decade later, the tipping point calculations were revised to 20 to 25 percent of total deforested area, as new factors had seemed to impinge on the rainforest’s hydrological cycle, namely climate change and the widespread use of fire to eliminate felled trees and clear weedy vegetation.

The authors of the second study—Carlos Nobre, one of Brazil's leading climate change scientists, and Thomas Lovejoy, the prominent US environmental scientist who coined the term "biodiversity"—argued that widespread fires in the rainforest, often set by cattle ranchers and farmers but abetted by the effects of climate change, led the surrounding forest to become dry and more vulnerable to fire. They pointed to the severe droughts occurring in 2005, 2010, and 2015–16 as evidence of what they called “the first flickers of the ecological tipping point.” At the time, one of the authors (Nobre) estimated that reaching the tipping point could take 20 to 25 years. In the years since their research was published, however, Nobre has said that the tipping point might be much closer, perhaps 15 years out. The other author (Lovejoy) believes that the forest may already be at the cusp of the tipping point: In a recent interview for the PBS NewsHour, he said that President Bolsonaro would “go down in history as being the equivalent of the person who created the Dust Bowl in the United States.” He added: “The difference between the Dust Bowl and the situation in the Amazon and in Brazil is that we actually scientifically understand what’s going on and can avoid those tipping points.”

The Bolsonaro government has not only denied these concerns but has contributed to the problem by reducing the funding for environmental agencies responsible for monitoring deforestation and law enforcement, as my Policy Brief notes. The Brazilian embassy does not dispute this fact. It merely asserts that spending cuts in these programs are in line with other budget cuts ordered by authorities in Brasília. President Bolsonaro has also criticized the Amazon Fund established by Norway and Germany, sparking fears over the future of the fund, and has emboldened illegal exploitation of the rainforest by his words and actions.

While the embassy in Washington maintains that the Bolsonaro government seeks to protect the rainforest, Bolsonaro himself spoke more honestly at a recent investor conference in Saudi Arabia. He told that audience that the Amazon fires that have raged since July-August 2019 were “powered by me because I do not agree with previous policies that were adopted for the development of the Amazon.” With this statement, the Brazilian leader has buried the narrative pushed by members of his own government that he stands behind the conservation of the rainforest, and that he is doing everything at his disposal to fight deforestation. With one fell swoop, he undercut his supporters' attacks on his critics.

We have published a PIIE Chart reflecting calculations of the time it would likely take to reach the Amazon’s tipping point if current rates of deforestation are extrapolated into the future. Of course, these scenarios are based on assumptions and are inherently unpredictable. The dynamics of nonlinear processes that characterize climate change and deforestation are very difficult to model with precision. But it is simply wrong to deny the calculations of respected scientists like Lovejoy: The tipping point may in fact be reached during Bolsonaro’s tenure, making him the equivalent of those responsible for the Dust Bowl disaster.

The findings also mean that because the tipping point may be closer than many estimate, the time for action is now.

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