If this project is completed, it will open the central Amazon basin to even more deforestation.

I believe this should cause alarm. Research shows too much deforestation could push the forest over a tipping point from which it can’t recover. No one knows exactly where the line is, but the vast Amazon that people picture today with its extraordinary biodiversity and dense forests would be no more. Such a catastrophe once seemed the bad dream of doomsayers, but there is mounting evidence that the forest is in trouble.

The tropical rainforest sustains itself by recycling rain to the atmosphere through evapotranspiration, which makes more moisture available. Rainfall recycling accounts for about 50% of the basin’s precipitation today.

Too much deforestation could leave too little rainfall recycling to sustain the forest.

Scientists initially estimated the tipping point would occur once about 40% of the Amazon was deforested. That estimate has slipped downward over time given the intensification of fires and the onset of observable climate change in the basin itself. Moreover, the forest shows diminishing resilience, meaning it is less able to recover from climate extremes. Scientists have already observed widespread shifts to more drought-tolerant tree species.

Given the evidence, scientists have revised the tipping point to deforestation as low as 20% to 25%. Even if only a fifth of the forest is lost, the remainder could quickly degrade into an ecosystem of fire-adapted grasses and shrubby trees that look nothing like the massive ones native to the rainforest.

Deforestation across all the Amazonian nations now stands at a little over 16%. In my view, this is far too close for comfort, especially with the momentum of the IIRSA program.

The deforestation problem isn’t the only pressure on the forest – the Amazon is also dealing with the heat and drought of global warming.

Evidence suggests that global climate change may be enough to push large parts of the rainforest to the brink. One concern is that the dry season is getting longer, a shift that appears to be driven by global warming. This affects annual precipitation by reducing the number of rainy days and makes fire more damaging by extending the season when trees can easily burn.

Currently, dry season lengthening is most pronounced in the Southern Basin. However, changes in the southern rainfall pattern can reduce precipitation in the wettest parts of the basin to the west. One estimate suggests dry season lengthening could cause a tipping point transition by 2064.

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