Brazil’s stretch of the Amazon lost more than 1,330 square miles of forest cover during the first seven months of the year, a 39 percent increase over the same period last year.

Experts say that spike appears to be the main driver of the fires in the Amazon this year.

The number of fires in the Amazon so far this year, 40,341, is the highest since 2010, and roughly 35 percent higher than the average for the first eight months of the year, according to Brazil’s National Institute of Space Research agency, which tracks deforestation and forest fires using satellite images.

Most of the fires are set intentionally to clear land for agriculture and cattle grazing. But the fire season got off to an early start this year, and blazes set along the edges of the rain forest are unusually potent, raising the risk that some will spread beyond the intended areas, according to Doug Morton, a scientist at NASA’s Goddard Space Flight Center who tracks deforestation and fires in the Amazon.

“This is a critical time,” he said in an interview. “Part of the international attention to what is going on comes from the fact that Brazil has been such a pioneer and leader on environmental protection and it has shown the world it’s possible to have economic development while protecting the rain forest.”

That hard-earned reputation has been crumbling in the Bolsonaro era.

Global outrage over the fires has spurred calls to boycott Brazilian products and led European leaders to threaten to walk away from a trade agreement that the European Union struck with Brazil and a handful of neighboring countries in June.

In what has become an unusually nasty exchange among leaders of major democracies, President Emmanuel Macron of France went so far as to accuse Mr. Bolsonaro of lying about being committed to fighting climate change and protecting the Amazon. “Our house is burning. Literally.” Mr. Macron wrote on Twitter on Thursday.