The Amazon rainforest, one of the planet's green lungs, is slowly entering a new, much more extreme climate scenarioRecent research warns that this large tropical forest, adapted to classic tropical climate, it is heading towards a regime called hypertropical climate, marked by very high temperatures and a longer and more intense drought than usual.
This change is not a mere nuance within the classic tropical climate, but a fundamental alteration that, according to scientists, It hadn't been seen on Earth for tens of millions of years.The combination of heat and lack of water is subjecting the trees of the Amazon to a severe physiological stress, with a clear increase in mortality and a direct impact on the planet's capacity to absorb carbon dioxide.
What is a hypertropical climate and why is it a concern for the scientific community?
Experts have coined the term “hypertropic” to describe this new climate regime that is beginning to emerge in the Amazon rainforest. These are areas that are becoming warmer than 99% of historical tropical climates, exceeding the limits within which equatorial forests traditionally operated.
Under these conditions, the typical Amazonian dry season, which is usually concentrated between July and September, becomes It lengthens and becomes more rigorousThe global temperature increase intensifies heat waves, so that drought episodes cease to be isolated incidents and become periods of... extremely hot drought, much more damaging to vegetation.
Until now, this hypertropical environment only occurred sporadically, during a few days or weeks in exceptional droughts. However, climate models indicate that if current levels of greenhouse gas emissions are maintained, These conditions could normalize over the course of the century, progressively transforming the landscape and ecological functioning of the Amazon.
The study, led by the University of California, Berkeley, was published in the journal NatureIt presents a scenario in which the climate we currently consider tropical could be displaced by this new hypertropical biome, absent from the planet since remote geological eras and with consequences that are difficult to reverse on a human scale.
More heat, less water: how the Amazon rainforest is stressed
The crux of the problem lies in the combination of increased temperature and water deficitDuring the most severe droughts recorded in recent decades, soil moisture in some areas of the Amazon has dropped to as low as... a third of its usual contentBeyond that threshold, trees practically stop absorbing carbon and enter a critical phase.
When the soil dries out excessively, the root systems cannot supply enough water to the canopy, leading to a hydraulic collapseAir bubbles appear in the sap, a phenomenon comparable to an embolism, which impedes the transport of water and nutrients. If these embolisms accumulate, the tree eventually diesalthough in some cases the plant tries to "sacrifice" branches to keep the trunk and the most important parts alive.
This process is aggravated by the abnormally high temperatureswhich increase evaporation and transpiration from the leaves. In a hypertropical climate, the atmosphere's demand for water is so high that trees cannot compensate for it, even in areas that were once considered relatively humid year-round.
Sensors installed in observation towers, about 50 meters high, have allowed recordings to be made for more than three decades. temperature, humidity, solar radiation and soil water contentBased on this data, the research team has verified that, after extraordinary droughts such as those associated with the El Niño episodes of 2015 and 2023, there is a clear increase in tree mortality.
Continuous monitoring of sap flow, leaf temperature, and transpiration has revealed that once soil moisture falls below a certain value, around 0,32 by volume, Perspiration rates plummetFor researchers, this behavior marks a critical boundary beyond which the forest ceases to function as it has until now and approaches the hypertropical threshold.
A 55% increase in tree mortality and a carbon cycle in jeopardy
One of the most disturbing conclusions of the study is that hypertropical climate conditions cause a approximate 55% increase in the mortality rate of the trees during episodes of extreme drought. Although annual mortality in a mature forest is usually just over 1%, an increase of this magnitude has a notable cumulative effect over decades.
Tropical forests, and the Amazon in particular, are a key carbon sinkThey absorb more carbon dioxide from human activities than any other type of terrestrial ecosystem. When rainforests lose trees on a large scale, not only does their capacity to capture CO2 decrease, but so does their ability to absorb carbon dioxide.2but some of the carbon stored in dead biomass ends up returning to the atmosphere.
Following the recent major Amazonian droughts, a specific phenomenon has been observed. rebound in atmospheric carbon dioxide concentrationsThis indicates that the carbon balance may shift towards net emissions rather than absorption. If this pattern solidifies with an increasingly hypertropical climate, the Amazon's buffering role against global warming could be compromised. to weaken structurally.
The study also focuses on the difference in response between tree types. The species of rapid growth and low-density wood They are significantly more vulnerable to extreme drought than those with slow growth and denser wood. In practice, this means that secondary forests and regenerated areas, very common in deforested zones, They could suffer an even greater impact under hypertropical conditions.
This selective shift in mortality can alter species composition, favoring more resilient trees but perhaps less efficient at carbon sequestration. In the long term, the very ecological functioning of the Amazon rainforest It could be transformed, with consequences that go beyond the region and affect the global climate balance.
Projections for 2100: from the tropics to the hypertropics
The simulations carried out by the international team of researchers, in a scenario of greenhouse gas emissions without major cutsThey suggest that by the end of the century, extremely hot droughts could reach up to about 150 days a year in large areas of the Amazon.
In such a context, the days of heat and severe drought would no longer be concentrated solely at the peak of the dry season. Models indicate that They could even extend into the traditionally rainiest monthsThis represents a break with the climatic pattern to which tropical vegetation has adapted for millennia.
The authors of the study warn that if CO2 emissions are not drastically reduced, the situation will worsen.2 and other greenhouse gases, the transition to a hypertropical climate could accelerateUnder that scenario, many areas of the Amazon would experience recurring water and heat stress conditions, with a increasing risk of mass mortality of trees and forest degradation.
This change would not necessarily imply an instant disappearance of the rainforest, but rather a progressive transformation towards less dense ecosystems, with biodiversity loss and biomass.
Scientists emphasize that this scenario is not set in stone: the outcome depends largely on the decisions that will be made in the coming decades In terms of climate, both globally and regionally, drastically reducing emissions and protecting the remaining forests are considered essential steps to limit the expansion of hypertropics.
A phenomenon with echoes beyond the Amazon: Africa and Southeast Asia in the spotlight
Although the research focuses on the Amazon, the conclusions have direct implications for other large tropical rainforestsClimate projections suggest that rainforests of West Africa and Southeast Asia They could also begin to experience hypertropical conditions as global warming progresses.
These ecosystems share key features with the Amazon: high biodiversity, a large capacity for carbon storage, and a very strong dependence on a delicate balance between rain and temperatureIf this balance is disrupted, the pattern of increased tree mortality, biomass loss, and reduced CO2 uptake will continue.2 It could be replicated in other tropical regions critical to the global climate system.
For Europe, and particularly for countries like Spain, this potential expansion of the hypertropical climate is not a distant issue. The deterioration of large tropical forests It affects global atmospheric circulation and the evolution of warming, which in turn influences heat waves, droughts and climate impacts over the Mediterranean and the European continent.
In fact, climate science has already shown that extreme events in the tropics, such as severe Amazonian droughts, can be related to alterations in rainfall patterns and in the intensity of phenomena such as El Niñowhich have indirect effects on the weather in Europe. The advance of the hypertropics, therefore, is part of a chain of processes that ultimately impact the daily lives of regions far from the rainforest.
Therefore, the authors insist that The protection of tropical forests must be understood as a central element of the global response to the climate crisis. Not only for its intrinsic ecological value, but also because its stability helps to mitigate changes that could otherwise be even more abrupt on a planetary scale.
The photograph that studies on the new hypertropical climate in the Amazon It is the case of a natural system pushed to its limits by global warming. Through field data collected over more than 30 years and models projecting climate evolution until the end of the century, researchers show that the combination of extreme heat and prolonged drought is already increasing tree mortality, reducing the capacity of forests to absorb CO2.2 and opening the door to a biome unknown in recent times on Earth. The decisions that will be made in the coming decades They will largely determine whether the Amazon, and other large tropical rainforests, become established as hypertropics or whether this drift towards a much more hostile climate for the forests themselves, and ultimately for the planet as a whole, can be stopped.
