Climate change was the primary driver of a massive drought in the Amazon basin in 2023 and will likely cause future extreme droughts, with potentially dire consequences for global efforts to cut greenhouse gas emissions, according to a new report from World Weather Attribution.

The group, which assembles teams of scientists to rapidly assess if climate change had an impact on recent weather events, released a report Wednesday saying that the “exceptional” Amazon drought was 30 times more likely to have occurred because of climate change.

“We’ve never seen anything like this before,” said Regina Rodrigues, professor of physical oceanography and climate at the Federal University of Santa Catarina in Brazil and a lead author of the new report. “And it was widespread in the whole basin.”

The Amazon basin, which extends into parts of nine countries but lies mostly in Brazil, is the single biggest land-based sink of carbon on the planet—storing up to five times the world’s annual greenhouse gas emissions. Its survival as an intact ecosystem is critical to stabilizing Earth’s atmosphere. 

The recent drought, brought on by excessive temperatures and a lack of rain, triggered forest-destroying fires, pushed river levels in some areas to their lowest points on record and overheated waters that killed at least 150 Amazonian river dolphins.

Low waters meant that people who depend on the basin’s river system for transportation were trapped and that goods that travel along the many rivers in the basin, including the Amazon River, were unable to reach markets.

“Small-holder farmers and indigenous river and rural communities were among the most vulnerable and will continue to be,” said Simphiwe Stewart of the Red Cross Red Crescent Climate Centre, based in the Netherlands. 

Previous reports have shown that parts of the Amazon, mainly in the southeast—a region known as the “arc of deforestation”—has become a source of carbon, rather than a sink, because so much of the rainforest there has been felled for grazing lands and soybean fields.

Now, researchers are concerned that the latest drought could turn more untouched and vulnerable parts of the Amazon basin into carbon sources. Rodrigues explained that northwestern parts of the Amazon, which are less impacted by human activity, are especially fragile because they haven’t adapted to the damage caused by human interference in the southern part of the region. 

“Genetically speaking, that is more diverse and resilient, but ecologically speaking, is more vulnerable to physical drought,” Rodrigues said. “This is very problematic for the tipping point … The forest might not be able to cope.” 

Even if there’s adequate rain in the future, it might not make a difference.

“If it gets too dry, it can actually trigger a die-back and become a savannah,” Rodrigues said. “Some projections show that even if you have precipitation, you might not get the Amazon back.”

Rodrigues said that this dieback could continue even if fossil fuel use is slashed and the world meets targets for cutting greenhouse gas emissions. “It might be too late,” she said. 

The group of scientists set out to determine if the El Niño weather phenomenon, which is linked to drought in parts of the region, was behind this particular event, which lasted from June to November. They determined that El Niño led to less rain in the region, but the high temperatures that led to the drying out of vegetation were entirely due to higher global temperatures.

They concluded that the drought, consisting of both a meteorological drought, which considers only rainfall, and an agricultural drought, which looks at rainfall and evapotranspiration, was more likely because of climate change. Climate change made the meteorological drought 10 times more likely; the agricultural drought 30 times more likely.

The agricultural drought, which they classified as “exceptional” based on the United States drought monitoring system, would only have been a “severe” drought without climate change.

Though rates of deforestation in the Brazilian Amazon have dropped under the administration of the current president, Luiz Inácio Lula da Silva, consecutive years of high deforestation rates, driven mostly by agriculture, have made the rainforest drier over time. 

That, combined with rising temperatures, could spell disaster for the region. The researchers found that, in a world that’s 2 degrees Celsius warmer than preindustrial temperatures, agricultural droughts will be four times more likely and meteorological droughts, three times more likely.

“This result is very worrying. Climate change and deforestation is already wrecking parts of the most important ecosystems in the world.” said Friederike Otto, a member of the research team and a senior lecturer in Climate Science at the Grantham Institute, in a press release issued Wednesday. “If we continue burning oil, gas and coal, very soon, we’ll reach 2 degrees of warming and we’ll see similar droughts about once every 13 years.”