Greenland's ancient methane reveals a dangerous climate weakness. For years, scientists have been sampling meltwater streams at Greenland's glacier margins, finding methane dissolved in the water. This methane was barely a global concern, as the fluxes seemed small, localized, and dependent on site-specific conditions. However, an international team decided to test this picture across the entire western edge of Greenland. What they discovered - the age of the gas - suggested that the ice had once pulled back far further than anyone assumed. This finding has significant implications for our understanding of climate change and the role of methane in the greenhouse effect.
The gas in question is methane, a potent greenhouse driver even more powerful than carbon dioxide. Researchers had previously spotted it leaking from glacier fronts at scattered sites worldwide. An earlier paper confirmed methane streaming out of one Greenland outlet. But no one had checked whether this was an isolated incident or a phenomenon occurring along the entire edge of the ice sheet. That's where Jade Hatton and her team from Charles University in Prague came in.
Hatton's team sampled 26 streams of meltwater flowing from the western flank of Greenland's ice, covering a transect of over 1,200 miles from the northwest to the southwest. Each meltwater stream provided the team with dissolved subglacial methane and chemical fingerprints of its source. Field crews drilled over 3,900 feet through the ice to reach the bed, collecting sediment cores and water samples.
In the lab, the team ran two main tests. First, they analyzed the chemical signature of the gas to determine whether it came from microbes or deep geological sources. Second, they used radiocarbon dating to determine its age. The isotopes pointed to microbes as the source of the methane. This methane was produced by anaerobic microbes breaking down decaying plant material in oxygen-starved sediments, not gas seeping up from deep rock formations.
The radiocarbon results were a surprise. Those samples returned ages of 1,500 to 4,400 years old. This age tells a story of the past. The radiocarbon clock implies that microbes have been producing the gas from buried organic matter under the ice for millennia. For this to have happened, vegetation must have once grown on land now covered by ice. The math points to a known warm stretch in Earth's recent past, the Holocene Thermal Maximum, when the Arctic ran warmer than usual, similar to today's conditions.
During this warm period, Greenland's ice sheet was smaller, allowing plants to take root. Boreal forest and tundra crept onto the exposed land, with plants dying and leaving carbon-rich material in the sediment. As the climate cooled, ice readvanced, overriding the exposed land and sealing plant remains under thousands of feet of frozen weight. Down in the dark, microbes continued to break down the buried carbon, century after century.
Modern glacial retreat is replaying this earlier turn. As the ice margin pulls back, meltwater finds new paths through the bed, flushing out the methane produced by those long-buried microbes. Western Greenland's land-based glaciers now release approximately 790 tons of dissolved methane annually. This buried organic matter could sustain the flow for at least another 200 years.
A feedback loop is emerging. As Greenland melts, more pathways open beneath the ice, allowing methane to escape. This gas carries its own warming effect, which could push the melt even further. The same setup likely exists at the other pole, Antarctica, on a much larger scale. An older study flagged the possibility of vast methane reservoirs beneath Antarctica, where buried organic matter is far greater than Greenland's.
If Antarctic ice continues to thin and its bed becomes more connected by meltwater, the same kind of slow methane transport could amplify, dwarfing Greenland's contribution. The survey covered western Greenland's margin, leaving eastern and northern sectors uncharted, meaning total flux could be higher than estimated. The 200-year projection also relies on a degradation model, not direct measurement, and carries a wide uncertainty range.
The ultimate irony is that as Greenland retreats, the ice sheet itself further contributes to methane emissions. Existing ice sheet models don't yet capture this dynamism. A separate study estimates that Greenland is locked into roughly a foot of sea-level rise from melt already committed. The methane evidence suggests that this floor is too low. Greenland's ice has shown it can swing farther than the models forecast, and as it pulls back, it feeds the warming that drives more retreat.
"The ultimate irony is that as it retreats, the ice sheet itself further contributes to those methane emissions," said Alun Hubbard, a professor at the University of Oulu and co-author of the study. The study is published in the journal Nature Geoscience. This research highlights the urgent need to improve our understanding of methane's role in climate change and the potential consequences of its release from melting ice sheets.
