As deforestation and climate change threaten to transform the Amazon, there is growing concern that the ecosystem may be reaching an irreversible tipping point, beyond which self-reinforcing feedback loops would lock the system in a degraded state and lead to the Amazon flipping from a carbon sink to a carbon emitter.
However, a new study , led by Yale School of the Environment scientists, found that there is no evidence of a single, basin-wide tipping point. Instead, there is wide variation in how the ecosystem is responding to human activity, and the more urgent concern in most areas is the repeated "hammer blows" to the system from direct human activities like deforestation, logging, species loss, and burning.
"The biggest concern is not the feedback loops we might have 30 or 50 years from now. It's the sheer size and intensity of direct human impact today," said Paulo Brando, associate professor of ecosystem carbon capture at YSE and the study's lead author. "The forest shows massive resilience to these shocks, but we are, in many places, already surpassing that resilience."
The analysis by the international team of researchers, published in the Annual Review of Environment and Resources, emphasized the impacts of unsustainable land-use on biodiversity, livelihoods, and the global climate.
The Amazon stores an amount of carbon equivalent to about ten years of global carbon dioxide emissions and across the globe, tropical forests account for approximately 55% of global forest above ground-carbon stock and 40% of the total global terrestrial carbon sink. Previous research has suggested some landscapes of tropical forests may be losing their capacity to sequester carbon.
The tipping point idea is increasingly the foundation of a lot of conservation policy in the region, Brando noted. It assumes that, beyond a quantifiable threshold, the forest would be so fundamentally changed that it could no longer sustain itself, driven by cascading feedback loops and lack of regeneration that the authors liken to falling dominos. In some drier regions, these loops include worsening fires that lead to a sparser tree canopy, the accumulation of new growth, and the spread of flammable vegetation, leaving the forest more vulnerable to the next fire.
Yet, there was no scientific consensus of whether a single threshold exists to set off this spiral of total forest collapse. The researchers found many ecological processes in the Amazon that are interacting in different ways in different regions, making it unlikely that a single domino falling could force the entire system to collapse. While some parts of the basin, such as the southeast, may experience climate change-driven tipping points, the primary threat in most areas is more like a hammer, with activities like deforestation chipping away at the health of the ecosystem with each blow.
The study also noted that the Amazon remains surprisingly resilient. Climate change alone appears unlikely to lead to a total collapse, and vast areas of the forest have a high potential to recover — if humans stop the hammering. Brando likens the situation to the difference between a leak slowly eroding the foundation of a house versus a wrecking ball that will demolish it.
"Your house could collapse either way," Brando said. "But if you stop the wrecking ball, you might actually have a chance to fix the leak and save your foundation."
These findings point to the continued need for sustainable land use and local solutions, such as reducing fire activity, promoting ecosystem restoration, and, in particular, curbing deforestation, to ensure the long-term health of the Amazon, he said.
"If we do stop these drivers of change, these hammers, then we still may give the forest a chance to bounce back," Brando said. "Every action — little, big, short-term, long-term — may have a benefit."
