The Aral Sea isn’t just an ecological nightmare – it’s a carbon bomb

The Aral Sea sits between Kazakhstan and Uzbekistan and was once the fourth-largest inland body of water on Earth. For the past 60 years, though, humans have bled it nearly dry irrigating cotton crops, leaving behind a salty plain the size of Ireland. Its loss has long been seen as an ecological and humanitarian problem, but new research shows that it has also been a significant driver of climate change.

The Aral Sea is technically a lake. But when nearly any body of water is full and works as it should, organic matter collects on the bottom, where it remains trapped, often for centuries or millennia. “They accumulate carbon in the sediment,” explained Rafael Marcé, a research scientist at the Centre for Advanced Studies in Blanes, Spain and the lead author of the study, which was published today in the journal Science. “They are carbon sinks.”

If the water dries up, however, stored carbon is released, turning sinks into sources. It’s something that Marcé has seen in smaller lakes he’s studied, but even he was surprised by what his team found during its 2022 expedition to Central Asia. “We didn’t go to the Aral Sea blind. We had some previous evidence,” he said. “We had no idea about the potential magnitude.”

The Aral Sea has left behind a timeline of sorts. The edges dried out decades back, while some areas were wet until just a few years ago. Marcé and his colleagues collected samples along this gradation. The technique allowed them to reconstruct how much carbon the lake had emitted as it evaporated. The figure is staggering. Between 1960 and 2022, they found, the Aral Sea had pumped a remarkable 748 million metric tons of carbon dioxide into the atmosphere. That’s three times the annual emissions of Spain.

“At the beginning it goes pretty fast, then it slowly decays,” said Marcé, noting that about half of the carbon dioxide is released in the first 15 years after a section of the lake is exposed. The paper also found that nearly a fifth of emissions came fr…