While the world’s attention is focused on disasters like COVID-19 and the Russian invasion of Ukraine an even bigger danger is sneaking up on us. Scientists warn that three-quarters of the Amazon rainforest is approaching the point where it will burn without the capacity to recover, turning instead to grasslands.
For decades climate models have suggested the combination of local deforestation and global heating was weakening the Amazon’s resilience and putting it in peril. Rainforest trees transpire astonishing amounts of water, most of which falls as rain nearby. When one patch of rainforest is destroyed, less rain falls on the rest.
At some point the reduction in rainfall will be so great large areas will dry out and burn, setting in place a vicious circle that will end with most of the rainforest gone. Although this is widely accepted, it has been hard to confirm empirically, let alone to show how close we are to such a tipping point. A new study published in Nature Climate Change provides strong evidence we are frighteningly close.
Using 25 years of satellite data, University of Exeter researchers measured the resilience of rain forest patches by how local forests responded to changes in weather conditions on a monthly basis.
Resilience represents the capacity of the forest to restore itself in the face of perturbations such as natural disasters, human interventions, and extreme weather effects. When ecosystems approach tipping points they take longer to restore themselves after perturbations. The study found more than three-quarters of the Amazon rainforest has been losing resilience since 2000.
The authors observed resilience loss has been most extreme within 200 kilometers (124 miles) of large farms and settlements, and in naturally drier areas, where any rainfall reduction hits harder. The resilience loss is larger than the loss of biomass the rainforest has experienced, the paper notes.
The authors do not try to predict an exact time at which the forest will reach the tipping point on current trajectories, and any answer would vary between different regions over its vast area. "The Amazon rainforest is a highly complex system, so it's very difficult to predict if and when a tipping point could be reached," Dr Chris Boulton of Exeter University said in a statement.
There is one comforting aspect to this research. ”Our study shows that the Amazon is approaching a tipping point, but also that it has likely not yet crossed it,” Professor Niklas Boers from the Potsdam Institute for Climate Impact Research said. The last part is an important counter to those who fear it may already be too late to stop large areas turning to savannah. In particular, despite severe droughts in 2005 and 2010 overall rainfall has not changed dramatically.
The solutions the authors outline to the problem are familiar: drastic reductions in greenhouse gas emissions, and protection of as much of the Amazon rainforest as possible. The prospects for the latter may improve after October when Brazil's presidential election is held, but until then are greatly hampered by current President Jair Bolsonro's hostility to conservation efforts. There may be more opportunities to protect the 40 percent of the rainforest that lies outside the boundaries of Brazil, for example, through efforts to buy key areas and return them to indigenous control.
The Amazon crossing the tipping point would be a disaster for many who live there. It is larger than every other tropical rainforest on Earth combined. Consequently, along with the loss of coral reefs, its destruction is one of the two nightmare scenarios for the richness of life on Earth, with countless species of plants, animals, and microorganisms likely to go extinct. Moreover, it will be an amplifier of global warming, as well as a consequence, with 90 billion tonnes of carbon dioxide released into the atmosphere as forests burn and are replaced by grasslands that store less carbon.