THE AMAZON RAINFOREST is reaching a “tipping point” where large swathes will begin to transform into savannah, according to a study.
The authors of the new paper said three-quarters of the Amazon is showing dwindling resilience against droughts and other adverse weather events, meaning it is less able to recover.
The loss of the forest would mean billions of tons of CO2 would be released into the atmosphere, as well as a reduction in the planet’s ability to recycle the greenhouse gas – leading to the acceleration of global climate change, researchers say.
While they admit it is “highly uncertain” when the tipping point will be reached, once the process begins they predict it could be a matter of decades before a “significant chunk” – possibly “well over” 50% – is transformed into savannah.
Around a fifth of the rainforest has already been lost compared with pre-industrial levels, they said.
Dr Chris Boulton, from the University of Exeter, said: “We’ve found a pronounced loss of Amazon rainforest resilience over the last 20 years.
“What we do find over the Amazon is that, particularly since the early 2000s, 75% coverage of the Amazon rainforest appears to show some sense of a loss of resilience.
“And what we also find is that areas which are closer to human land use, such as urban areas or crop lands, they tend to be losing resilience faster, as do areas which receive less rainfall.”
Professor Tim Lenton, also from the University of Exeter, gave a stark reminder of the consequences of rainforest loss.
He said: “The reason we’re focused on the Amazon rainforest is because we think this is one of the parts of the climate system that could pass a tipping point – by which we mean there’s another possible state for vegetation and the land surface in this part of South America could switch perhaps to something more like savannah.
Having got this evidence that’s consistent with the forest heading towards a tipping point it’s worth reminding ourselves that if it gets to that tipping point, and we commit to losing the Amazon rainforest, then we get a significant feedback to global climate change.
“It will lose about 90 billion tons of carbon dioxide – mostly from the trees and some from the soil – and that’s several years of emissions.
“And also past studies have shown, you lose the forest, it affects the whole circulation of the atmosphere so it has knock-on, we call them teleconnections, potentially to the climate elsewhere in the world.”
The findings, published in the journal Springer Nature, were reached with the use of satellite data from 1991 to 2016, which include measurements of the density of life in the forest, which is closely linked to water levels, and vegetation greenness.
Professor Niklas Boers, from Technical University Munich, said: “The resilience loss that we observed means we have likely moved closer to that particular point, or that tipping point, but we also suggest we haven’t crossed that tipping point yet so there’s still hope.”
Climate models have suggested that global heating – which has on average warmed Earth’s surface 1.1 degrees Celsius above preindustrial levels – could by itself push the Amazon past a point of no return into a far drier savannah-like state.
If carbon pollution continues unabated, that scenario could be locked in by mid-century, according to some models.
“But of course it’s not just climate change – people are busy chopping or burning the forest down, which is a second pressure point,” said Lenton.
“Those two things interact, so there are concerns the transition could happen even earlier.”
Besides the Amazon, ice sheets on Greenland and the West Antarctic, Siberian permafrost loaded with CO2 and methane, monsoon rains in South Asia, coral reef ecosystems, and the Atlantic ocean current are all are vulnerable to tipping points that could radically alter the world as we know it.
Global fallout
Deforestation in Brazil has surged since far-right President Jair Bolsonaro took office in 2019, hitting a 15-year high last year.
Scientists reported recently that Brazil’s rainforest – 60% of the Amazon basin’s total – has shifted from a “sink” to a “source” of CO2, releasing 20% more of the greenhouse gas into the atmosphere over the last decade than it absorbed.
Terrestrial ecosystems worldwide have been a crucial ally as the world struggles to curb CO2 emissions. Vegetation and soil globally have consistently absorbed about 30% of carbon pollution since 1960, even as emissions increased by half.
“Savannification” of the Amazon would be hugely disruptive, in South America and across the globe.
Some 90 billion tonnes of CO2 stored in its rainforest – twice worldwide annual emissions from all sources – could be released into the atmosphere, pushing global temperatures up even faster.
Regionally, “it’s not just the forests that take a hit”, said Lenton. “If you lose the recycling of rainfall from the Amazon, you get knock-on effects in central Brazil, the country’s agricultural heartland.”
Ominously, the new findings marshall data pointing in the same direction.
“Many researchers have theorised that a tipping point could be reached,” said co-author Niklas Boers, a professor at the Potsdam Institute for Climate Impact Research in Germany.
“Our study provides vital empirical evidence that we are approaching that threshold.”
Saving grace?
To assess change in the resilience of the rainforest, Lenton, Boers and lead author Chris Boulton from Exeter University analysed two satellite data sets, one measuring biomass and the other the “greenness” of the canopy.
“If too much resilience is lost, dieback may become inevitable – but that won’t become obvious until the major event that tips the system is over,” said Boers.
There may be a “saving grace” that could pull the Amazon back from the brink.
“The rainforest naturally has a lot of resilience – this is a biome that weathered the ice ages, after all,” said Lenton.
“If you could bring the temperature back down again even after passing the tipping point, you might be able to rescue the situation.”
“But that still puts you in the realm of massive carbon dioxide removal, or geoengineering, which has its own risks.”
Just under 20% of the Amazon rainforest – straddling nine nations and covering more than five million square kilometres – has been destroyed or degraded since 1970, mostly for the production of lumber, soy, palm oil, biofuels and beef.
Additional reporting from AFP
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