There are few national elections that carry as much environmental weight as Brazil's presidential race. And this one is being watched from far beyond the country's boundaries.
Home to the largest section of the Amazon rainforest, Brazil is guardian of a carbon sink of vital importance, making the country's conservation policies globally relevant.
Environmentalists have already voiced alarm at Flávio Bolsonaro — son of right-wing former president Jair Bolsonaro — coming out 2% ahead of incumbent Luiz Inácio Lula da Silva in the first round of elections.
"It's going to be a second coming of Bolsonaro, therefore a more radical Bolsonaro," said Claudio Angelo, international policy coordinator at Climate Observatory, a network of Brazilian NGOs.
"At the risk of sounding alarmist, I would say Lula's re-election is the only thing standing between us and the end of the Amazon."
One of nature's most powerful defenses
The Amazon rainforest stores huge amounts of the carbon dioxide (CO2) released into the atmosphere from the burning of fossil fuels. As a result, it helps regulate the Earth's climate.
For decades, the tropical forest has acted as one of nature's most powerful defenses against climate change. But it has also suffered from widespread deforestation.
During Jair Bolsonaro's presidency, from 2019 until 2023, environmental agencies were weakened and enforcement efforts curtailed, meaning tropical forest was cleared at unprecedented rates.
"The environment agenda was disregarded and the level of control the government had on pollution overall, but specifically on deforestation, was reversed," said Claudio Forner, head of climate policy at Berlin-based think tank, Climate Analytics.
Over Bolsonaro's four-year term, an estimated 45,586km2 of the Amazon was destroyed, an area bigger than the size of Denmark. And the forest is not as resilient as it once was, with scientists warning that parts of it are now emitting more carbon than they absorb.
Lula came to office with a message of protection for the Amazon. Besides calling for an end to deforestation by 2030, he increased monitoring of the forest and strengthened Brazil's environmental enforcement agency IBAMA.
Deforestation has plummeted under his leadership, with 2026 set to be its lowest level in a decade. That represents a 41% drop overall compared to Jair Bolsonaro's tenure.
Pitting environment against the economy
Experts have already criticized Flávio Bolsonaro's record on forest protection. As a senator in 2019, he authored draft legislation that could have stark impacts for the Amazon. While landowners are currently required to preserve 80% of their property for the growth of native plants, the bill would allow them to use their holdings as they please.
"The signal from the president will say 'now you can deforest' or 'it's harder to deforest'," said Ana Yang, director of the Environment and Society Centre at London-based think tank Chatham House.
"The moment that you decrease enforcement capability, deforestation grows," she told DW.
Bolsonaro has also pledged to end illegal deforestation by 2029, a year before Lula. But Claudio Angelo is critical of that message.
"He will end illegal deforestation not by enforcing the law, but by making it legal," he said.
More generally, environmental experts fear Bolsonaro might dismantle many of the protections strengthened under the current president.
"Unfortunately, climate change has become a partisan issue, so rather than offering a solution from their perspective, the right pictures climate change as an invented problem...that regulation goes against economic growth or it goes against competitiveness, that it's the aim of the left to control the means of production," Forner said.
In an interview with Brazilian media in August, Bolsonaro said he regarded extreme weather events to be cyclical and did not believe they were solely linked to human influence.
No straightforward climate success story
A Bolsonaro win is likely to see Brazil move away from its position as a climate leader, a role the country embraced last year as it hosted the COP30 climate conference in the Amazonian city of Belem.
But even a Lula victory would not represent a straightforward climate success story, say experts. While the current administration has overseen significant reductions in deforestation, it has also backed plans to expand oil production.
Angelo said the decision to allow exploratory drilling was a "betrayal" of Lula's mandate but added that the president's overall record on climate had been "quite impressive".
"Lula is the world's worst climate leader, except for all the others," he told DW.
The current president will face a runoff election with Bolsonaro on October 25th. But while experts say the outcome could determine the fate of the Amazon and the wider efforts to curb global warming, for many Brazilians, climate is not high on their list of priorities.
"Ultimately what people care about is access to education, sanitation and health," said Yang. A road built through the Amazon, to access those services, while criticized from outside Brazil for destroying parts of the rainforest, would be desirable to voters, she added.
"They don't have time to care. Not because they don't want to. They care about their own survival," she said.
Edited by: Tamsin Walker