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Extreme heat and drought are already stressing some central Amazon forests, and a 2025 Nature study suggests that today’s hot droughts may preview conditions tropical forests could face more often in a hotter climate. But “new normal” needs a qualification: the study’s direct field evidence comes from central Amazon sites, while its projections extend across tropical forest regions. It does not show that every tropical forest has already shifted into one uniform new state.
What the study examined
Jeffrey Q. Chambers and co-authors combined more than 30 years of annually resolved forest-demography records with field measurements of tree physiology during the 2015 and 2023 El Niño droughts. They also analyzed climate-model projections to assess how tropical forest climates could change under future warming.
The evidence has two distinct scales. Tree mortality and physiological responses were observed at central Amazon field sites; projections about future tropical forest climates come from climate models. The observations help explain how trees respond to hot drought, but they are not measurements from every tropical forest.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors| Evidence | What it covers | What it can show |
|---|---|---|
| Forest-demography record | More than 30 years of records synthesized in the 2025 study | How tree survival and mortality varied over time at the study sites |
| Physiological field measurements | Central Amazon observations during the 2015 and 2023 El Niño droughts | How tree water use responded as soil moisture declined |
| CMIP6 climate projections | Future tropical forest climates, including high-emissions scenarios through 2100 | How extensive hotter, drier climate conditions could become; these are projections, not observations |
Which El Niño droughts are involved?
The study analyzes field measurements from two events, rather than an unspecified “last El Niño.” The IPCC dates the Amazon drought of 2015–16 from September 2015 to May 2016. The 2023 Amazon drought had a different climate context: the Science Panel for the Amazon describes it as involving El Niño along with a warmer Tropical North Atlantic.
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| Event | Relevant context | Evidence cited here |
|---|---|---|
| 2015–16 | The IPCC identifies the Amazon drought as lasting from September 2015 to May 2016. | Field measurements in the 2025 Nature study; regional timing from the IPCC. |
| 2023 | The Science Panel for the Amazon links the drought to El Niño and a warmer Tropical North Atlantic. | Field measurements in the 2025 Nature study; regional climate context from the Science Panel. |
The Science Panel also identifies severe Amazon droughts in 2005 and 2010. It says the 2023 event could be representative of a new normal if climate change is not stopped. That is regional context from the panel, distinct from the Nature study’s site measurements and projections.
What happens to trees during a hot drought?
Heat and lack of rain can combine to increase water stress. In the central Amazon measurements, transpiration—the movement of water through a tree and its release from leaves—fell rapidly after soil moisture passed a threshold identified at the study site. The study does not establish that threshold as a universal value for other forests.
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When rainless conditions persist beyond that point, stress can intensify. The authors identify hydraulic failure, when a tree’s water-transport system can no longer function adequately, and carbon starvation, when it cannot maintain the carbon supply needed for essential processes, as potential pathways to mortality. These are risks that rise with stress, not a claim that every tree dies by either mechanism.
Which trees showed higher mortality?
The study reports elevated mortality during intense droughts, with a stronger effect among fast-growing pioneer trees with low wood density. This indicates that drought impacts vary across tree types; the result does not support a simple ranking of all tropical forests by vulnerability.
That variation matters because a forest is not a uniform collection of equally drought-resistant trees. The finding identifies a pattern in the study’s demographic record, but it should not be turned into a prediction about the fate of every species or location.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What do the projections say about a “new normal”?
Under high-emissions scenarios, the study’s CMIP6 analysis projects that a large area of tropical forest could move toward hotter “hypertropical” conditions by 2100. The authors describe present-day hot droughts as “harbingers” of this emerging climate: current events can offer a window into conditions that models suggest may become more relevant in the future.
A Nature commentary describes the projected hypertropical conditions as involving dangerous heat and water stress on more than 40% of days. That figure belongs to the commentary’s account of modeled conditions; it is not a direct measurement of current drought frequency across tropical forests.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →“New normal” can also mean something more specific in climate science: a proposed framework for identifying when an extreme that was once unusual becomes common in model projections. A 2017 Bulletin of the American Meteorological Society paper applied that framework to global temperatures in 2015. That global-temperature result is not evidence that Amazon drought has already become normal.
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What the findings do—and do not—establish
- Established by the study: central Amazon trees experienced physiological stress during the 2015 and 2023 drought measurements, and the long-term record showed higher mortality during intense droughts, particularly among fast-growing, low-wood-density pioneers.
- Projected, not observed across all forests: high-emissions climate scenarios point toward a large tropical forest area facing hotter “hypertropical” conditions by 2100.
- Not established: one universal soil-moisture threshold, a uniform response across tropical forests, or proof that every forest has already entered a permanent new climate state.
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