In September 2024, biologist Cássio Alencar Nunes was taken aback while heading out for field research in Jaú National Park, a conservation unit in Brazil’s northern state of Amazonas. He had a plan to record bird vocalization samples to estimate the size of certain species’ populations. Early in the morning, alongside his colleagues, Nunes was already at the heart of the park with recorders in hand.

However, instead of hearing the usual noise of the forest at dawn, what researchers found was nothing but silence. No birds, no insects. All quiet.

When measuring the local temperature, the scientist found readings above 30° Celsius (86° Fahrenheit), which is very unusual for that time of the day (normally, he would expect between 24°C and 25°C, or 75-77°F). “We were alarmed,” Nunes said. “[The forest] was very quiet, really different. Animals must have been really stressed by that heat and drought.” According to the expert, everything was as quiet as it usually is at midday, when the scalding, stifling air makes animals hide to save energy. In the morning, on the contrary, one would expect a symphony.

Not on those days.

The researcher had planned last year’s expedition for mid-September, expecting the dry season in that region to be ending with the arrival of the first rains. This, he believed, would make local bird species more active and present. He was not counting on atypical Amazon weather.

A massive, prolonged drought, boosted by higher-than-usual temperatures, led to a record number of wildfires. Considering the entire Amazon, it was the second consecutive year under extreme drought, worsened by climate change, studies show.

Recent reports have warned that deforestation and global warming, when combined, have made the Amazon — a rainforest — much more flammable. Degraded areas, however, are not alone when it comes to the problem: A new WWF-funded study exhibited in the nonprofit platform EarthArXiv revealed that even largely preserved forest areas are being harmed by climate change.

Amazon heats twice as fast in extreme temperatures

In the region where Nunes searched for birdsongs, in the north-central Amazon, an unprecedented surge of extreme temperatures has been noticed. That was one of the conclusions of research conducted by a group of 53 scientists from Brazil and abroad, analyzing the evolution of temperatures and indicators, such as air dryness and the forest’s water deficit, across the entire Amazon basin, between 1981 and 2023.

The EarthArXiv study, in which Nunes participated, indicates that global warming impacts can be better observed when considering extreme temperature-related events in the Amazon, which have increased more rapidly than the average temperature rise — usually the best indicator in Amazon climate studies.

The average pattern is what scientists consider when they say the planet has already warmed by more than 1.2°C (about 2.2°F) since the Industrial Revolution. But the greatest impacts are felt by both people and the environment in the “extremes,” when temperature spikes are much higher.

In the Amazon, according to the study, whose authors are part of the Sustainable Amazon Network, “recent exceptionally hot or dry periods have led to extensive and unprecedented forest fires, large-scale tree mortality and localised animal mortality, and negative outcomes for human access to services and health.”

The group observed that while the average temperature in the Amazon has risen at the same pace as the global rate — 0.2°C (about 0.4°F) per decade since the 1980s — extreme temperatures have climbed much faster: 0.5°C (0.9°F) per decade, or about 2°C (3.6°F) over these 43 years.

In other words, within nearly half a century, the highest temperatures in the Amazon have become 2°C warmer on average.

That figure considers an average of extremes across the entire Amazon. But the study also reveals that this warming of temperatures does not occur uniformly: The scenario becomes much more dramatic when looking at spatial variation.

Scientists divided the Amazon basin map into nearly 58,000 cells (squares of 121 square kilometers, or 46.7 square miles) and analyzed multiple climate variables in each one: temperature changes (minimum, average and maximum), air humidity (or vapor pressure deficit, VPD) and how much more the forest has transpired and evaporated compared with what it has received in rainfall during the 43 years (or maximum cumulative water deficit, MCWD).

The analysis confirmed a trend that was observed in prior studies: Average temperature has increased more in the southern Amazon, in the region known as the “arc of deforestation,” which concentrates native vegetation loss in recent decades.

But the research also found that extreme temperatures have risen at a higher rate in the north-central Amazon, in a broad swath stretching from central Amazonas state to the extreme-northern state of Roraima — precisely where a part of Jaú National Park, studied by Nunes, is located.

In this area, which accounts for 10% of the entire Amazon, extreme temperatures rose by nearly 0.8°C (1.4°F) per decade during the driest period — more than 3.3°C (5.9°F) in 43 years. The historical record of maximum temperatures is particularly concerning among experts because it is still a well-preserved region, with long stretches of continuous forest under protection, such as conservation units like Jaú National Park and Indigenous lands, including Waimiri-Atroari and Yanomami peoples’ territories.

The study demonstrates that even in areas without deforestation, the Amazon is at risk due to climate change.

Led by Sustainable Amazon Network co-founder and conservation science professor Jos Barlow and remote sensing specialist Nathália Carvalho, both from Lancaster University in the United Kingdom, and of which Cássio Alencar Nunes is one of the main authors, the study is still undergoing peer review for publication in a scientific journal but is already available in preprint form on EarthArXiv.

The release was brought forward to draw attention to the changes that climate alteration poses to the forest ahead of the COP30 climate summit in Belém, which will happen Nov. 10-21.

Changes call for public action beyond combating deforestation

“The work shows that the southern Amazon area is not the only one we need to worry about. The focus on that region is valid due to the extensive deforestation it has already suffered, but we saw that the northern part of the forest is also fragile. It is changing very quickly, and it may not be adapted to this level of heat and drought,” Barlow said.

According to him, “In many studies, the north is presented as a refuge to which animals can move because the south will become too hot. But perhaps it won’t be a valid refuge [because it is also warming significantly].” Indeed, the first mass mortality of terrestrial mammals was observed in this exact area in 2023.

Report authors note that further investigation will be necessary to understand why this specific part of the north-central Amazon is experiencing the highest rates of increase in extreme temperatures. In any case, they already state that it is necessary to develop public policies that factor in that “climate change in the Amazon is neither gradual nor homogeneous.”

“The spatial dissociation [of the rapid increase in extreme temperatures in the north-central region] with forest loss — the main local driver of climate change — demonstrates that the world’s highest greenhouse [gas] emitting countries bear a strong responsibility for Amazonia’s rapidly changing socioecological condition,” the authors wrote.

“This underscores once again the urgent need for rapid reductions in greenhouse gas emissions and strengthens arguments that high-emitting countries should contribute to adaptation and conservation interventions in tropical forest regions through mechanisms such as the Fund for responding to Loss and Damage or novel initiatives like the Tropical Forest Forever Facility.”

Also, according to the research, it is necessary to prevent deforestation from advancing into this region. Cutting down the forest “would amplify temperature changes and expose the remaining forests to greater risks of fire.” That is what another study, published by a part of the same group of researchers in August in the journal Annual Review of Environment and Resources, called “hammer effect.”

“Climate change is already a pressure in that region. If you add deforestation, it’s like hammering on an area that is already very fragile,” said ecologist Joice Ferreira, a researcher at Brazil’s eastern Amazon agricultural research agency, Embrapa, and one of the founders of the Sustainable Amazon Network. She also co-authored both studies.

Ferreira said the new results brought in October add concerns because experts assumed that the north-central region would be relatively safeguarded, since it had not been deforested. “We always thought that the south-southeast of the Amazon was the most affected, and it really is. And we thought that if we saved that region from deforestation, which we thought was more or less safe, everything would be fine. And now we see that it’s not.”

In addition, many traditional and Indigenous populations live in this north-central region, relying on forest products to survive, like the açaí (Euterpe oleracea), Brazil nuts (Bertholletia excelsa) and local fish. “All of this is harmed in this context of higher temperatures,” Ferreira said. “We predict that, as temperatures rise, there will be forest degradation, which enters a physiological stress process and leads to more tree mortality. Fruit production declines.”

And this, she warned, could have an impact on the much-heralded bioeconomy. “What is currently put on the table as a solution for the Amazon — stronger socio-bioeconomies and forest restoration, alongside conservation, of course — becomes compromised. The window of opportunity is reduced.”

“It’s necessary to design public policies focused on the social dimension, because the changes are primarily affecting traditional peoples in this region,” Carvalho said.

“And it’s no use only talking about this in years when we have extreme events, because if someone loses their harvest, how will they manage to survive in the following years after the impact? It has to be long-term support, because the effects also come in a long term,” she said.

‘We can no longer predict tomorrow’

Locals feel they have lost even the predictability needed to plan crops or any other income-generating activity. “We can’t say, ‘Come at such a time and it will be dry.’ We can’t predict it, because you know that the climate has changed. There is a difference from one year to the next; one year is dry, another year is wet, and we don’t know anymore,” said Eduardo Elisio de Souza, known as Sibá, a resident of the Cachoeira community, located inside Jaú National Park.

Sibá earns part of his income from tourism and he was the guide who led Cássio Nunes and colleagues during their field research last year. His community is named after a waterfall on the Jaú River that only appears in the driest season, when the river drops to its lowest levels and the cascade becomes visible. That used to happen around Oct. 10; last year, however, it was already visible in September due to the extreme drought.

“A month earlier, it was already as dry as it should have been at its driest [point]. We even had to carry the voadeira [motorized canoe] over the waterfall because boats couldn’t get through anymore. It was very critical,” Nunes said.

This year, around the same time, Sibá said the rocks were still underwater. “We can still pass them over with the boat,” he said by mid-September. “It leaves us with this terrible uncertainty, because we can no longer say what tomorrow will be like. When the climate was normal, we could define it.”

Tourism is not the only activity that has been affected. Sibá complained that Brazil nut trees in the region are producing less and that the fish are dying.

These are profound changes in the ways of life of these populations, which demand specific adaptation measures. One of the most urgent issues, researchers pointed out, is preventing forest fires, which also involves controlling the community’s own traditional use of fire.

The importance of preventing forest fires 

Rising temperatures and the resulting loss of air humidity have made the forest much more flammable. The past two years have seen widespread and severe fires, and in 2024, the Amazon set a record for burned area since 1985, according to data from the collaborative monitoring initiative MapBiomas.

A total of 15.6 million hectares (38.5 million acres) burned — an area 117% above the historical average. A notable change occurred: For the first time, most of the Amazon’s burned area was standing vegetation (43%). Historically, what burned most were pastures and newly deforested regions (to finish the “clearing process” of the land). In that procedure, fire would occasionally escape into the forest.

In 2024, the scenario was completely different and alarming. First, because deforestation has been decreasing since 2023, reducing the amount of organic material to be “cleared” with fire. Looking at the historical series, normally when deforestation goes down, fires also decrease.

But that was not the case in the last two years.

“Large areas of forest burned across the Brazilian Amazon,” said Érika Berenguer, a researcher at the British University of Oxford and one of the leading fire behavior researchers in Brazil. “We had flooded biome areas catching fire. We had underground fires. It was a calamitous situation that shows that fire is the Amazon’s current problem.”

Berenguer, a co-author of the study on extreme temperatures, said that in 2023, she even saw fire reach the tree canopy, which is unusual in the region. Fires in the Amazon — precisely because it is a tropical, humid forest — are typically ground fires, 30-50 centimeters (12-20 inches) high at most, but long — with some blaze lines stretching for kilometers.

The expert witnessed that in a region that had already burned in 2015 — a particularly dry year, also marked by many wildfires — with the flames climbing up young trees, about 15 meters (50 feet) tall, which had grown after that previous fire, and leaping from one canopy to another.

As someone who studies fire behavior, the researcher had often found herself helping to contain flames throughout her years of fieldwork. “But that was the first time I ran. It was the first time I was truly afraid of the fire.”

Berenguer recalled that global warming brings new challenges and requires additional caution with fire management in the main environmental public policy for the Amazon, the Action Plan for Prevention and Control of Deforestation in the Amazon.

“Deforestation remains a problem. We know that efforts to combat it vary greatly depending on who is in the government. So it’s not as if deforestation has been solved. However, when there is a solid foundation of enforcement, we see impressive drops, like what happened in 2023 and 2024. Now, despite that decline, there was an absurd increase in forest fires. So, unfortunately, it’s no longer enough to fight only deforestation. Public policies must change because the world has changed,” the researcher said.

In the context of the upcoming COP30, Berenguer and other researchers stressed that reducing greenhouse gas emissions worldwide is essential to save the forest. “It’s not just about reducing deforestation. To preserve the Amazon, we need countries in the Global North, as well as China, to cut their emissions and help curb global warming.” Internally, however, she said it is also important to focus on adaptation strategies to strengthen the resilience of affected regions and to rethink fire-use practices in the Amazon.

Berenguer added that an important step was taken with the approval of a law creating the National Policy for Integrated Fire Management, to implement targeted actions in this regard.

But she called for special attention to fire prevention. “Hiring more firefighters is important, but the Amazon makes up 60% of Brazil’s territory — it’s a vast area to fight fires in. We need a list of multiple solutions to prevent the fire from even starting, because once it starts, it’s much harder to control.”

Banner image: A researcher measures fire behavior during the 2023 dry season in the Tapajós National Forest (PA). Image courtesy of Marizilda Cruppe/Rede Amazônia Sustentável.

This story was first published by Agência Pública here in Portuguese on Oct. 2, 2025.

With half its surface water area lost, an Amazonian state runs dry

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