Melting Arctic glaciers are releasing ancient methane from rocks beneath the ice, contributing to a self-perpetuating cycle of warming known as a climate 'doom loop,' according to a new study.
Researchers collected 148 water samples from 19 glacier-fed rivers on Svalbard, a Norwegian archipelago in the Arctic Ocean. Every river tested contained higher-than-expected levels of methane, with the most contaminated waterways showing up to 425 times the normal amount. This methane escapes from the rivers into the atmosphere, where it acts as a potent greenhouse gas and contributes to global warming.
The study, published in the journal [Journal Name Placeholder], identified the methane as having a geological origin rather than a biological one. Analysis of carbon types in the water revealed the presence of propane and ethane alongside methane, which is consistent with methane formed over millions of years from organic carbon in shale rock. Heat and pressure beneath the ground can transform this carbon into gases.
"These glaciers are mostly melting on their surfaces, but this meltwater finds its way to the bottom of the glaciers through crevasses and holes," explained lead author Dr. Gabrielle Kleber of the iC3 Polar Research Hub. "This means that it interacts with the rocks underneath, and where those rocks contain ancient gas, the water can flush methane out into rivers."
Scientists estimate that land-terminating glaciers across Svalbard may release between 182 to 368 tonnes of methane annually through meltwater. While Dr. Kleber noted that these amounts are small compared to human-caused emissions, she emphasized their significance.
"But they matter because they reveal a natural feedback loop that is not confined to Svalbard, and that may grow as the Arctic warms," she stated.
Methane is a powerful greenhouse gas; over 100 years, it is 21 times more effective at trapping heat in the Earth's atmosphere than carbon dioxide. The concern is that this additional release of greenhouse gases will accelerate Arctic glacier melt, leading to further methane release and a self-reinforcing cycle.
Researchers used ground-penetrating radar to map ice conditions and identify factors contributing to methane emissions. They found that the highest methane releases occurred where glaciers rested on shale-rich rock formations and experienced specific temperature conditions at their bases. Co-author Leonard Magerl from UiT The Arctic University of Norway noted that "the biggest methane releases happened where the right rocks and the right glacier conditions came together."
Accelerated melting in the Arctic could lead to significant global sea-level rise. The Greenland Ice Sheet alone contains enough fresh water to raise sea levels by approximately 23 feet (7.4 meters) if it were to melt entirely. Such a rise could displace over 100 million people living in low-lying coastal regions worldwide.
However, the researchers acknowledge uncertainty about the future trajectory of this feedback loop. In some cases, shrinking glaciers are becoming colder at their bases. If a glacier freezes to the bedrock, its capacity to flush methane into rivers could decrease.
"Our results show that future methane release will depend on both geology and glacier change," Dr. Kleber said. "That makes it important to know what lies beneath the ice, not only how fast the ice is melting."