The Amazon rainforest is nearing a tipping point (临界点), according to researchers from the University of Exeter, UK.
Previous studies have warned that the world's largest rainforest, which acts as the lung of the Earth, is approaching a critical threshold (限度). But most past research has depended on projections using models, not real-world observations.
Now, Tim Lenton and his colleagues have used two sets of satellite data covering between 1996 and 2016 to measure the greenness of the Amazon over time, watching for how it recovered after impacts such as drought and fires.
They found that since the early 2000s, 76 per cent of the region had become less resilient. Importantly, says Lenton, the signal of this growing trouble was picked up without immediately obvious changes such as huge drops in the forest's biomass (生物量) or tree cover.
"Why do we care about it? It's worth reminding ourselves that if it gets to that tipping point and we lose the Amazon rainforest then we get a significant feedback to global climate change," says Lenton. He says a change into savannah (稀树草原) would unlock about 90 billion tons of carbon dioxide stored in the trees and soil.
Lenton says he cannot put an exact date on how far off the rainforest's tipping point might be, but he expects it to be a process that would take in a few years. Other Amazon experts say the research adds to a growing body of evidence that the rainforest is approaching a tipping point.
The changes aren't the same throughout the rainforest. The south-eastern part of the Amazon has already changed to the point at which it is now a carbon emitter (释放者) rather than a carbon sink.
Matt Finer at the Amazon Conservation non-profit organization says the research could help decide which remaining parts of the forest to prioritize (优先) for protection. "The western and north-east Amazon appear the most resilient, showing the need to protect these areas now and in the future from any more damages," he says.
