Half of the Amazon may be pushed to climate tipping point by 2050

Large portions of the Amazon rainforest are threatened by the compounding effects of drought, heat and deforestation, which could push some ecosystems past a tipping point. But the potential for a wider scale collapse remains uncertain.

“The forest as a whole is very resilient, and that’s why we still have a window to act,” says Marina Hirota at the Federal University of Santa Catarina in Brazil.

Researchers have warned for decades that rising temperatures and deforestation could push the Amazon past a tipping point beyond which runaway feedbacks lead to a rapid transition from forest to savannah. Drought and heat driven by the ongoing El Niño and warming with climate change have again raised the alarm.

But climate and ecological models representing the enormous complexity of the Amazon disagree on when or where such a tipping point might occur.

To understand which regions of the Amazon are most acutely at risk, Hirota and her colleagues looked at satellite data to assess how several different ecosystem stressors might change in the coming decades. These included temperature during the dry season, exposure to drought and the risk of fire and deforestation.

They found 10 per cent of the Amazon basin is at risk of being exposed to at least two of these stressors by 2050, and therefore has a higher potential of transitioning to degraded forest or to a savannah-like ecosystem. As much as 47 per cent of the basin is predicted to be exposed to at least one stressor – meaning it is also in some danger.

“Some forests are going to be lost because of ongoing changes, but there are things we can do to avoid going to 47 per cent,” says Hirota. She points out most of the forest not exposed to stressors is located inside protected areas and Indigenous territories, which are associated with low rates of deforestation. Deforestation rates in Brazil have also plummeted under the administration of president Luiz Inácio Lula da Silva, although they have increased in other parts of the Amazon.

Dominick Spracklen at the University of Leeds in the UK says the study is a strong survey of the different threats facing the Amazon. However, he says it doesn’t resolve the differences between models projecting a potential tipping point.

For instance, models project some of the negative effects of warming may be offset by increasing concentrations of atmospheric CO2, which should boost plant growth. But other factors, like nutrient and water availability, vary widely across the basin and influence the strength of this effect, leading to considerable uncertainty for modelling the future of the Amazon.

“For such an important ecosystem, that’s quite a scary place to be,” he says.

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