Drought. Fire. Mass illegal logging.
Now, researchers warn another “Super” El Niño could doom the Amazon rainforest.
“The southern Amazon is close to a tipping point,” Brazilian Earth system scientist Carlos Nobre tells the science journal Nature.
He’s been flying over the dense landscape for two decades, measuring its health.
It’s been shrinking.
It’s been browning.
Now, sensors show the highly stressed “lungs of the planet” have begun to emit more carbon dioxide than they can absorb.
The plants are essentially overworked and overtired.
“This is exactly how a tipping point will actually happen,” adds Earth-system analyst Nico Wunderling.
“We will see more extreme events — due to El Niño, for instance. They will become more severe. And then the recovery time for the trees is just not enough.”
Now, another El Niño is brewing.
A vast patch of the Pacific Ocean is heating up.
The US National Oceanic and Atmospheric Administration (NOAA) says there’s an 80 per cent chance it will burst historic boundaries to become “Super” – the most powerful in 150 years – by November.
The last one – a regular-sized event in 2023 – dried up rivers and killed off undergrowth. This produced the most devastating fire season in a quarter of a century.
The rainforest is yet to recover.
Now, it faces another.
“If this next El Niño really is as strong as we think it will be, it might result in things like huge wildfires in the Amazon, spreading across areas that were unimaginable before,” warns Brazilian environmentalist Bernardo Flores.
Nature reports the trend threatens to transform the landscape. Once the moisture tipping point is reached, it would take a few short decades for 80 per cent of the Amazon’s remaining trees and undergrowth to be replaced by grassy savannah.
Changing times
Like Europe, North America and Australia, the Amazon – one of the New 7 Wonders of Nature – is heating up.
The tropical rainforest used to experience just a few hot, dry days each year.
That’s now measured in weeks.
By the end of the century, researchers warn the dry season could grow to a solid five months.
“When these hot droughts occur, that’s the climate … beyond the boundary of what we consider to be tropical forest now,” says researcher Jeff Chambers.
These are conditions not experienced on the planet for the past 10 million years, researchers note. That’s when temperatures were, on average 14C greater than they are today.
The scientists have been measuring water and sap densities in trees, humidity levels and soil moisture for the past 30 years.
Low moisture prompts the trees to close the pores in their leaves. This halts evaporation. But it also stops the CO2 absorption that produces healing and growth.
Fast-growing tropical rainforest trees cannot sustain this abnormal strain for long.
Researchers say such events cause the rainforest’s “stress hormone” to be released into the air 122 per cent more than normal: a distinctly peppery-smelling compound of sesquiterpene.
And dehydrated tree sap can quickly develop “blood clots”.
“If there are enough embolisms, the tree just dies,” Chambers explains.
This happened in 2015.
Then 2023 produced the most intense drought ever recorded for the region.
Now, 2026 is trending to become even worse.
“Between El Niño events, which occur every two to seven years, the rainforest can revert to the original non-stressed emissions,” says Max Planck Institute for Chemistry researcher Jonathan Willians.
“However, climate models suggest that El Niño events will increase in frequency and intensity in this century, so these emissions may become a permanent feature of the region.”
The Amazon rainforest’s “tipping point” is when the trees no longer have enough time between drying events to heal sufficiently.
“We may have already crossed the tipping point,” Flores tells Nature.
“We don’t know. But the thing is, if we have crossed it, or we might cross it very soon, this is very concerning.”
Rewind to fast forward
Forest researchers are striving to determine what comes next.
Can forests recover? Can the damage be mitigated? How do we know what’s happening?
The best prophet of the future is the past.
Which is why the fossilised forests of Wyoming have become the focus of intense study.
It reached a tipping point some 56 million years ago.
That’s when the planet’s average temperature appears to have gradually warmed by 6C. Likely thanks to greater-than-average volcanic activity.
“Those Wyoming forests lost 60 per cent of their canopy during this period,” says Professor Regan Dunn.
“It took them well over 100,000 years to recover.”
That epoch, known as the Paleocene-Eocene Thermal Maximum (PETM), is the closest known natural event to loosely parallel what’s happening now.
“Although humans are releasing carbon dioxide roughly 10 times faster than the planet’s natural processes did then,” Professor Dunn adds.
But the natural historic record may help researchers recognise what a tipping point looks like.
So they’ve been studying fragments of fossilised leaf litter.
It’s all about their cells.
“Leaves that grow in shade develop longer, more elongated cells as they stretch out seeking sunlight. Those exposed to more sun develop shorter, rounder ones,” Professor Dunn explains.
At first, the forest thrived. Higher C02 levels meant more plant food.
“That flourishing forest did not last, however,” she adds. “As temperatures climbed, heat and drought overwhelmed the benefits of higher carbon dioxide levels. The canopy rapidly thinned as trees died, and it remained much thinner for over 100,000 years.”
The entire landscape changed.
Open plains expanded. Rivers, their banks now free to be eroded, changed course.
“Higher carbon dioxide levels like the world is experiencing now can stimulate plant growth, but only while temperatures and water remain within the limits that trees can tolerate,” Professor Dunn concludes.
“Beyond those limits, heat, drought, insects, pathogens and wildfire can overwhelm any fertilisation effect.”
Jamie Seidel is a freelance writer
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