The rise of far-right authoritarian Jair Bolsonaro in Brazils presidential race has caused concerns about what he could mean for the health of the worlds fourth-largest democracy and its most marginalized communities especially black Brazilians, the indigenous, women and LGBTQ people who are the targets of his most violent rhetoric .

But a Bolsonaro victory, which polls suggest is almost assured on Oct. 28, would also have a major global implication: It could spell doom for the worldwide fight against climate change.

Few countries are more important to stemming climate change than Brazil, which is home to the Amazon rainforest and the Cerrado savanna two of the most crucial environmental defenses against global warming.

And over the last two decades, no country as large as Brazil has assumed more of a leadership role in addressing the crisis. While many large nations dawdled in addressing the threat, Brazil made dramatic reductions in greenhouse gas emissions since 2004. It has emerged as one of the planets leading producers of sustainable biofuels, and in 2017 it launched an ambitious effort to plant more than 70 million trees to help reforest the Amazon and thus increase absorption of carbon dioxide.

Bolsonaro, however, could threaten much, if not all, of that progress.

He has acknowledged the threat of climate change. But on the campaign trail, he has promised to shutter Brazils Ministry of the Environment and put many of its administrative and regulatory duties under the charge of other agencies. He has said he would seek to withdraw Brazil from the Paris climate accord (following the lead of U.S. President Donald Trump ).

Bolsonaro has committed to stop demarcating indigenous lands in the Amazon and further open the forest to mining interests. And he has pledged to loosen regulatory regimes over land-use and deforestation in the worlds largest tropical rainforest.

A move by Brazil to absolve its leadership role on climate change through the election of Bolsonaro would have huge consequences for the rest of the world, said Steve Schwartzman, the senior director of tropical forest policy at the New York-based Environmental Defense Fund.

The kinds of policies Bolsonaro has talked about could be catastrophic, Schwartzman said. Brazil is still the world leader in reducing greenhouse gas pollution. If that changes, its exactly what Brazil doesnt need, and exactly what the world doesnt need.