Mr. Bolsonaro has called his own government’s information “lies,” stripped the environment ministry of authorities and slashed the environmental budget. When eight former environment ministers protested in May, current environment minister Ricardo Salles alleged that there is a “permanent and well-orchestrated defamation campaign by [nongovernmental organizations] and supposed experts, within and outside of Brazil.”

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In its reality denial, Mr. Bolsonaro’s brand of right-wing populism closely resembles that of President Trump. Both leaders stoke unfounded suspicions that environmental concerns represent foreign plots to undermine the domestic economy. Both are committed to breakneck resource extraction while dismissing expert warnings. And both lead nations with special responsibilities in the global fight against climate change. Global warming cannot be successfully addressed without the engagement of the United States, the world’s largest historical emitter of greenhouse gases and erstwhile leader. The Brazilian Amazon, meanwhile, is a unique natural treasure, its abundance of plant life inhaling and storing loads of planet-warming carbon dioxide day and night. Without “the world’s lungs,” life on the planet is doomed.

Earlier this month, the journal Science published a paper finding that, if world leaders made reforestation a priority, the planet’s ecosystems could accommodate massive numbers of new trees — perhaps hundreds of billions more. True, reforestation advocates would no doubt have to compete with those who would use land for other purposes, particularly as the world population increases. Even so, the paper’s authors note, their work “highlights global tree restoration as our most effective climate change solution to date.”

This is not to say that the fight against global warming is as easy as planting a few, or even billions, of trees, if such a thing were politically or logistically feasible. As long as humans depend on carbon-emitting sources of fuel for energy, the atmosphere’s chemistry will continue to change and the climate will be in peril. But it does suggest that leaders such as Mr. Bolsonaro, who are leading in the opposite direction, can do particularly extreme damage to the effort to restrain climate change.