The Amazon Rainforest Is Entering a Scary New Phase Called a “Hypertropical Climate”

The rainforest is drifting toward a hotter, drier state last seen tens of millions of years ago.

Parts of the Amazon are drifting into uncharted territory. According to a concerning new study published in Nature, the rainforest is approaching a climate state that scientists are calling “hypertropical.”

This new reality could expose the forest to prolonged stress, drive widespread tree death, and shatter its ability to act as a shield against climate change.

By the end of this century, the Amazon could experience up to 150 days each year of “hot drought” conditions, the study finds. These are periods when extreme heat intensifies dryness, sharply increasing water loss from soils and leaves. Some of these hot droughts could occur during months that are now part of the wet season.

Jeff Chambers, a geographer at the University of California, Berkeley, put it bluntly: “When these hot droughts occur, that’s the climate that we associate with a hypertropical forest. It’s beyond the boundary of what we consider to be a tropical forest now.”

The Struggle to Survive

The warning comes from an unusually deep look at how Amazon trees respond to heat and water stress. Chambers and his colleagues drew on more than 30 years of detailed measurements from forest plots north of Manaus, in central Brazil. The data track temperature, humidity, soil moisture, sunlight, and the life and death of individual trees.

During recent El Niño–driven droughts in 2015 and 2023, the researchers observed sharp increases in tree mortality. To understand why, they turned to sensors embedded inside tree trunks that measure sap flow—the movement of water that keeps trees alive.

As droughts intensified, trees began to struggle. When soil moisture dropped to roughly one-third of normal levels, many trees sharply reduced transpiration. They closed microscopic pores in their leaves to conserve water. That response slowed dehydration but also blocked carbon dioxide uptake, which trees need to grow and repair damage.

At the same time, extreme heat increased evaporation, pushing trees toward hydraulic failure. Air bubbles formed inside their water-conducting tissues, disrupting circulation.

What stood out was how consistent the tipping point proved to be. Across different drought years and even different study sites, trees began to fail at nearly the same soil moisture threshold. Fast-growing species were especially vulnerable, while slower-growing, dense-wooded trees were more resistant.

Today, annual tree mortality across the Amazon is just over 1%. The study projects that rate could rise to about 1.55% by 2100. Spread across a forest of continental scale, that increase represents a profound ecological shift.

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The Implications

The Amazon is one of our planet’s vital organs. It pulls carbon dioxide from the atmosphere and locks it away in wood and soil. But that role is already faltering.

Previous research has shown that parts of the southeastern Amazon now emit more carbon than they absorb, due to a combination of deforestation, fire, and drought. The new study suggests that climate stress alone could push larger areas of rainforest in the same direction.

Hot droughts suppress photosynthesis almost immediately, reducing carbon uptake even before trees die. Over time, increased mortality adds another blow, releasing carbon as dead wood decomposes. Together, these effects risk turning a major carbon sink into a source.

The implications extend beyond South America. Using global climate models, the researchers found that tropical forests in western Africa and Southeast Asia may also face hypertropical conditions this century, depending on how quickly greenhouse gas emissions are reduced.

The last time Earth experienced similar tropical climates was during the Eocene and Miocene epochs, when global temperatures were far higher than today and forests near the equator looked very different. The crucial difference now is speed. The projected changes are unfolding over decades, not geological ages.

The authors emphasize that the outcome is not fixed. Their most extreme projections assume little to no reduction in emissions.

“It all depends on what we do,” Chambers said. “If we’re just going to emit greenhouse gases as much as we want, without any control, then we’re going to create this hypertropical climate sooner.”