As thousands of intentional fires continued to burn up swaths of the world's largest and most biodiverse rainforest Tuesday, the National Aeronautics and Space Administration warned that based on 20 years of ground and satellite data, "human activities are drying out the Amazon" and jeopardizing its ability to sustain itself.

The findings have experts at NASA and beyond concerned about the implications for the Amazon, a rainforest that annually pulls billions of tons of carbon dioxide out of the atmosphere, which helps to limit global temperature rise and prevent more catastrophic climate change.

New NASA study finds climate change and logging are rapidly drying out the world's greatest rainforest--setting it up to burnhttps://t.co/Oy1xSL386m — Bill McKibben (@billmckibben) November 6, 2019

"We observed that in the last two decades, there has been a significant increase in dryness in the atmosphere as well as in the atmospheric demand for water above the rainforest," said Armineh Barkhordarian, a researcher at NASA's Jet Propulsion Laboratory and lead author of the study published last month in Scientific Reports.

"In comparing this trend to data from models that estimate climate variability over thousands of years," she continued, "we determined that the change in atmospheric aridity is well beyond what would be expected from natural climate variability."

Barkhordarian pointed to elevated greenhouse gas levels and ongoing human activity—specifically, fires set to clear forest land for agriculture and other uses—as key drivers of the increase in dryness, or what the study described as a "recent increasing trend in vapor pressure deficit (VPD) over tropical South America in dry months."

As for how the drying trend impacts the rainforest's ability to sustain itself and help regulate the global climate, NASA researcher and study co-author Sassan Saatchi explained that "it's a matter of supply and demand."

"With the increase in temperature and drying of the air above the trees, the trees need to transpire to cool themselves and to add more water vapor into the atmosphere. But the soil doesn't have extra water for the trees to pull in," Saatchi said. "Our study shows that the demand is increasing, the supply is decreasing and if this continues, the forest may no longer be able to sustain itself."

Over the last 20 years, the atmosphere above the Amazon rainforest has been drying out, leaving ecosystems vulnerable to fires and drought, and it's primarily the result of human activities. Here's how we know and why it matters. https://t.co/ShQZ40oJgc — NASA Climate (@NASAClimate) November 5, 2019

Biologist and activist Sandra Steingraber, who was not involved in the NASA study, told Newsweek that "fully half of the the carbon dioxide that is pulled out of atmosphere by the biosphere on land is pulled out by tropical forests."

"The Amazon is a big carbon sink but its ability to scrub carbon dioxide from the atmosphere is declining," Steingraber warned. "This will contribute to climate chaos, turning tropical forests from a global carbon sink to a global carbon source."

NASA's findings come amid rising concerns about human destruction of the Amazon—particularly under Brazil's far-right president, Jair Bolsonaro, who took office in January. Although Brazil, home to the majority of the Amazon, has made strides in protecting the rainforest in recent decades, Bolsonaro's government has "scaled back efforts to fight illegal logging, ranching, and mining."

In a speech to the United Nations General Assembly in September, Bolsonaro claimed that his government "is solemnly committed to environmental preservation" and dismissed international criticism about this summer's spike in deforestation and corresponding fires in the Brazilian Amazon as "sensationalist attacks."

However, critics such as Márcio Astrini, public policy coordinator at Greenpeace Brazil, said that "the president's speech about the environment was a scam" and "Bolsonaro is trying to convince the world that he is protecting the Amazon, when in reality he is promoting the dismantlement of the environment."