The Amazon Is Entering A "Hypertropical" Climate For The First Time In 10 Million Years

A new type of climate regime is emerging in the Amazon rainforest as intense heat and drought continue to push the region beyond the tolerable limits for a tropical ecosystem. According to researchers, the escalating conditions have reached the point of becoming “hypertropical”, recreating an environment that hasn’t been seen anywhere on Earth for around 10 million years.

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And while the prolonged hot droughts associated with this regime are still relatively rare in the Amazon, the authors of a new study predict that these conditions could occur on 150 days a year by the end of this century, with devastating consequences. For instance, by analyzing 30 years' worth of forest demographic data, the researchers showed that tree mortality increases by 55 percent whenever such a drought occurs.

“When these hot droughts occur, that’s the climate that we associate with a hypertropical forest, because it’s beyond the boundary of what we consider to be tropical forest now,” said lead study author Jeff Chambers in a statement. Hypertropical biomes were last present on Earth between 10 and 40 million years ago, when the planet was considerably hotter than it is today.

However, Chambers insists that a return to these scorching conditions is not inevitable, and can be avoided if we take the necessary measures. “It’s up to us to what extent we’re actually going to create this hypertropical climate,” he says. “If we’re just going to emit greenhouse gasses as much as we want, without any control, then we’re going to create this hypertropical climate sooner.”

To understand how hot droughts cause such catastrophic tree die-offs, the researchers observed transpiration rates at two different Amazonian sites during the warm El Niño events of 2015 and 2023. At both sites, and on both occasions, they found that when soil moisture content dropped below a threshold of about one-third of its capacity, transpiration plummeted as trees closed the pores in their leaves to prevent water loss.

This, in turn, led to carbon starvation, as leaves became unable to capture the carbon dioxide they require for photosynthesis. Eventually, trees experienced hydraulic collapse as air bubbles – called embolisms – formed in their sap.

“[I]f there are enough embolisms, the tree just dies,” says Chambers.

Overall, the combined effect of a mass die-off and reduced carbon uptake by surviving trees could have a major impact on the global climate, as the Amazon – like other rainforests around the world – plays an essential role in regulating the planet’s carbon budget. Analyzing five different climate models to try and simulate future changes, the researchers concluded that hypertropical conditions are likely to become common in the Amazon during the dry season within the next two to four decades, and could be present year-round by 2100.

Sounding a warning to the world and urging policymakers to take note, the researchers write that “present-day hot droughts are harbingers of this emerging climate, offering a window for studying tropical forests under expected extreme future conditions.”

The study is published in the journal Nature.