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If you've ever walked past a drying lakebed in the peak of summer, you might have noticed some very unpleasant smells emanating from the mud.
That pungent odor is a mix of gases being released from the soil, as enormous quantities of organic matter – a rich sludge of poop, algae, plants, decaying bodies, and other pondy things – dry out.
On a larger scale, that phenomenon stinks much worse than a bad smell.
In many parts of the world, lakes are drying out at a scale so massive that scientists are warning they may be emitting enough greenhouse gases to rival our fossil fuel habit.
In a new study published in Science, scientists say the Aral Sea – the world's largest desiccated lake – has emitted a whopping 204 megatons (~225 million US tons) of carbon dioxide since it was drained in the 1960s.
But it might not be too late to turn the tide.
Today, the Aral Sea is a salty wasteland, more a desert than a sea. But it wasn't always that way.
Its water levels only began to fall rapidly when its tributary rivers – the Amu Darya and the Syr Darya – were diverted to feed Uzbekistan's rapidly expanding cotton industry.
By the 1990s, the lake – once the fourth-largest in the world – was depleted beyond recognition.
In its place now stretches a wheezing, salty desert, a giant lakebed rotting in the sun.
The study estimates that between 1960 and 2022, the evaporating sea has released 204 megatons of carbon dioxide into the atmosphere, based on site surveys and core samples collected from across the dry lakebed.
There are some signs of recovery in the north, where the Kazakhstan government has adopted water usage laws to ensure the Syr Darya continues to flow into the North Aral.
The new study suggests that rehydrating the entire basin could come with enormous benefits to the environment, not just within the sea itself, but at a global level.
"There is a hidden carbon treasure beneath the Aral Sea," says biochemist Rafael Marcé from the Spanish National Research Council.
"If these sediments remain exposed, carbon will continue to be released into the atmosphere. If the sea is re-flooded, that same carbon could shift from being a source of emissions to becoming part of the climate solution."
According to the researchers' calculations, re-flooding the lakebed could prevent the release of the estimated 165 megatons of carbon that remain.
The study also revealed that nearly one-fifth of the Aral Sea's carbon emissions are actually being released as wind blows away sediment on the lakebed, a factor that researchers had not accounted for in the past.
"When a lake dries up, we are not only facing a hydrological, ecological or socio-economic problem," says ecologist Núria Catalán from the Spanish National Research Council.
"The carbon cycle is also altered in ways that have so far remained largely absent from climate accounting."
Meanwhile, climate change looms large over concerns about the future of the Aral Sea's water supply.
The Amu Darya and Syr Darya are fed by melting glaciers in the Tienshan and Pamir mountains. As those glaciers are depleted in a warming climate driven by fossil fuels, the supply is likely to dwindle, with water evaporating long before it has a chance to rehydrate the Aral.
Ironically, reallocating water to lakes across Earth that have been dried by human activity could be a major part of preventing that glacier loss.
The Aral Sea is not the only inland body of water that humans have drained in the pursuit of profit. There's the Great Salt Lake, and the Salton Sea in the United States; the transcontinental Caspian Sea; Lake Urmia in Iran; Lake Poopó in Bolivia; and many more.
All of these lost lakes are potentially contributing to carbon emissions.
Related: Droughts Are The Ideal Breeding Ground For Antibiotic-Resistant Bacteria, Study Warns
"Our study shows that protecting these vast stores of carbon buried in sediments also has a climate value that could be incorporated into carbon-based financing mechanisms," the study's authors note.
"This provides a new perspective, expressed in a language familiar to climate finance and carbon markets, and opens up a new conversation about how re-flooding could be funded."
This research was published in Science.
This article was fact-checked by Michael Irving and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
