A groundbreaking new study has challenged a long-standing belief in conservation science, revealing that climate change, intensified by increasingly extreme El Niño events, is the true force accelerating the extinction and decline of Brazil’s amphibians. Contrary to decades of assumptions, researchers have found that the aquatic fungus Batrachochytrium dendrobatidis (Bd), once blamed as the main cause, plays only a secondary role in the crisis.
Climate change and El Niño: the extinction of Brazil’s amphibians
The study delivers a striking revelation: while Bd is undeniably harmful, it acts not as the trigger but as an opportunistic invader, targeting amphibian populations already weakened by climate stress, loss of immunity, and reduced genetic diversity.
Rather than causing mass deaths directly, Bd outbreaks tend to emerge years after populations have already declined, revealing the real danger: environmental instability. Intense droughts, rising temperatures, and erratic weather patterns fuelled by El Niño have severely damaged amphibian habitats, stripping species of their ability to adapt and survive.
The research also highlights a surprising twist, Brazilian amphibians, through generations of exposure, have developed herd immunity to Bd. Their vulnerability originates not from the fungus itself, but from a changing environment.
Shifts in temperature and rainfall have disrupted ecosystems and damaged the skin microbiomes that amphibians rely on for defence. As water sources dry up, frogs and other species are forced into smaller, crowded areas, perfect conditions for disease to spread.
This study marks a critical turning point in our understanding of amphibian decline, redirecting attention from disease to the broader and more urgent threat of a destabilised climate.
Loss of Brazil’s amphibians: a blow to global conservation efforts
Célio Fernando Baptista Haddad, biologist in the department of biodiversity and CBioClima centre at São Paulo State University (UNESP), and one of the authors of the study, mentioned that adapting conservation strategies to address human-induced climate change is a multifaceted challenge that requires profound changes in our way of life. He further explained:
We must urgently transition to cleaner energy sources, but this is obstructed by powerful oil and coal lobbies that resist ending the exploitation of polluting resources – resources that are not only heating the planet but also pushing wildlife and ecosystems toward extinction.
Haddad also emphasised that deforestation remains a major concern, driven by a growing global population, now over eight billion, exceeding the Earth’s carrying capacity and prompting land clearing for agriculture and livestock.
From 1923 to 2014, scientists documented the extinction or decline of 90 Brazilian frog species, with at least eight possibly extinct. One species was classified as critically endangered, while another was deemed endangered. This trend began in the 1970s and shows no signs of stopping, driven by a combination of factors: loss of biodiversity, agricultural expansion, pesticide use, disruption of aquatic and terrestrial ecosystems, and, most significantly, climate change.
A hotspot of biodiversity hurtling towards collapse
The lead author of the study, Lucas Ferrante, said:
Our research refutes the hypothesis that the decline of Brazilian amphibians was primarily caused by the Bd fungus. Using causal effect equations, we demonstrate that climate change, extreme weather events, and rising temperatures are in fact the main culprits. This is particularly important because the declines began after the Industrial Revolution – the same period during which humans began significantly altering the planet’s climate.
He further stressed that current mitigation targets are no longer sufficient. Brazil plays a significant role in this scenario: when deforestation alone is considered, the country ranks as the fourth-largest global emitter of greenhouse gases.
Moreover, emissions from wildfires – which have increased under the current government – have yet to be fully accounted for. The situation is further worsened by President Lula’s plans to expand oil exploration, including in environmentally sensitive areas such as the Amazon River mouth, as well as in several other sites within the Amazon rainforest.
Brazil is home to the world’s largest number of amphibian species, the majority of which are found nowhere else on Earth. This makes the country a critical hotspot for biodiversity, and the ongoing amphibian crisis is a blow to global conservation efforts.
Zoonotic spillovers
Adding another layer of concern, climate change and extreme weather events, such as the severe droughts and rising temperatures linked to El Niño, are also accelerating the spread of zoonotic diseases, which pose significant risks to both wildlife and human populations.
In the Amazon region, record-breaking temperatures and unusual weather patterns – combined with deforestation driven by road projects like the BR-319 highway and the expansion of cattle farming into conservation areas – are amplifying the risk of disease spillover. As ecosystems are disrupted and human activities encroach deeper into wildlife habitats, the likelihood of disease transmission increases, posing a growing threat to both animals and humans.
Haddad highlighted how deforestation and infrastructure projects not only disrupt ecosystem, but also contribute to the spread of infectious diseases and climate instability:
Human-driven environmental degradation is a key driver of climate change, with deforestation altering critical abiotic factors like temperature, humidity, and light, often making habitats uninhabitable for many species. While the link between deforestation and diseases like chytridiomycosis is complex and context-dependent, one principle holds true: the more intact and undisturbed an ecosystem is, the greater the resilience of its wildlife, including against disease.
Infrastructure such as roads not only accelerates deforestation by enabling easier access for logging and agriculture but also serves as a vector for the spread of infectious agents. In regions like the Amazon, a moratorium on deforestation, highway and dam construction, and extractive industries is urgently needed. Sustainable, economically viable alternatives for local communities are not only possible, but they’re also essential for the survival of both the forest and the planet.
Research indicates that intensified agriculture and the conversion of forests into farmland and cattle pastures increase interactions between humans and pathogens, thereby facilitating the emergence of viral, bacterial, fungal, and parasitic infections.
An unmistakable signal of ecological crisis
The rising frequency of these extreme climate events not only strains the survival of amphibians but also compromises the overall health of the Amazon’s delicate ecosystem.
Haddad warns that human disruption of ecosystems not only threatens wildlife but also increases our own vulnerability to future pandemics:
Human-induced environmental degradation increases the exposure of wildlife to infections and parasites, often introducing pathogens into species that have never encountered them before.
While Bd is unlikely to infect humans, diseases affecting birds and mammals, species with physiologies closer to ours, pose a much greater risk. As we’ve seen with COVID-19, environmental disruption can bring humans into contact with novel pathogens capable of adapting to our bodies and causing serious public health crises.
As the situation grows more dire, the study highlights the urgency of addressing climate change and its cascading effects. The decline of amphibians, once considered a silent environmental crisis, is now an unmistakable signal that broader ecological changes are underway.
Haddad underscored that environmental restoration, and systemic change must occur simultaneously, despite the political and economic challenges. He said:
We need immediate local actions like halting deforestation, road and dam construction, and extractive projects, alongside global measures such as transitioning away from fossil fuels and restoring degraded ecosystems.
Forest restoration can help absorb excess carbon, but implementing these solutions in a world driven by economic power and home to over 8 billion people is far more difficult than it sounds.
The extinction of amphibians, especially in a biodiversity-rich country like Brazil, serves as a clear warning of the broader environmental challenges confronting humanity. If we fail to take meaningful action to combat climate change and safeguard ecosystems, the planet’s vulnerable species, particularly those that rely on fragile habitats, will continue to suffer the consequences of our collective neglect.
Featured image via the Canary
