Flames are spreading across the Amazon rainforest this summer, spewing millions of tons of carbon dioxide into the atmosphere each day. But scientists say that's not their biggest concern. They're far more worried about what the fires represent: a big increase in illegal deforestation that could deprive the world of a critical buffer against climate change.

More than a soccer field's worth of Amazon forest is falling every minute, according to Brazil's National Institute for Space Research, known as INPE. Preliminary estimates from satellite data revealed that deforestation in June rose nearly 90% compared with the same month last year, and by 280% in July.

The Amazon is a key component of Earth's climate system. It holds about a quarter as much carbon as the entire atmosphere and single-handedly absorbs about 5% of all the CO2 we emit each year.

But if such rapid deforestation continues, it will foil efforts to keep global temperatures in check. Scientists fear parts of the Amazon could pass a critical threshold and transform from a lush rainforest into a dry, woody grassland. And that could bring catastrophic consequences not only for people in South America, but also for everyone on Earth.

"We might be very, very close to the tipping point," said Carlos Nobre, a climate scientist at the University of Sao Paulo. And if we cross it, he said, "it's irreversible."

The trend is particularly alarming because it comes after more than a decade of progress toward preserving the world's largest rainforest. Many blame the anti-environmental rhetoric of Jair Bolsonaro, Brazil's new far-right president, and fear that it will put global climate efforts in jeopardy.

Left to nature, the Amazon rarely burns. But INPE has counted more than 25,000 blazes in the Amazon in August alone.

The fires have sparked an international outcry. But they came as no surprise to those who keep a close watch on the Amazon. Satellite images in May, June and July showed an uptick in deforestation. It was only a matter of time before the flames followed, said Doug Morton, chief of the Biospheric Sciences Laboratory at NASA's Goddard Space Flight Center.

"This is the expected one-two punch," he said.

Instead of axes and machetes, people now use bulldozers and giant tractors with chains to pull down the Amazon's towering trees. A few months later, they torch the trunks. It's the only realistic way to remove such huge amounts of biomass, Morton said. "It's slash and burn, 21st century."

Thousands of acres at a time are being cleared for large-scale agriculture, he added. The land is primarily used as pasture for cattle — one of Brazil's major exports — or for such crops as soybeans.

This marks a troubling reversal in the fight to end deforestation, long a linchpin of global climate policy.

In 2004, the Brazilian government began cracking down on forest destruction by designating more protected areas and reserves for indigenous people. Violators were fined or arrested and forest loss declined 75% by 2012. "It was a big success," he said. "Everybody was happy."

However, deforestation rates have increased sharply since May, a few months after Bolsonaro took office. So far, more than 2,000 square miles of forest have fallen this year.

Bolsonaro has railed against protections for indigenous land and promised to boost the country's economy. He has also weakened the government's capacity for oversight and indicated he would not go after farmers, loggers and miners who seize and clear forest.

If scientists' worst fears come to pass, it could become all but impossible to meet global climate goals aimed at limiting the worst effects of global warming.