7,000 years ago, Greenland’s giant ice dome disappeared as temperatures climbed. Today, scientists say the ancient melting occurred at temperatures close to those now threatening the island’s remaining ice

There is something unsettling about standing on top of a 1,600-foot-thick wall of ice and knowing that the same ground beneath your feet was once completely exposed. That is what researchers have now established at Prudhoe Dome in northwestern Greenland. About 7,000 years ago, this frozen landscape disappeared, leaving sediment at the surface before the ice eventually returned.

The discovery matters because the temperatures associated with that ancient melt were not impossibly different from conditions scientists expect later this century. Researchers estimate that summer temperatures around Prudhoe Dome were roughly 3 to 5 degrees Celsius warmer than today when the ice dome disappeared. Some projections indicate similar warming could occur there by 2100.

That does not mean Prudhoe Dome will simply vanish by 2100. The study does not establish how quickly the ice would retreat under future warming. What it provides is something climate models cannot get from equations alone: direct evidence that this part of Greenland has already responded dramatically to comparable warmth.

What did scientists find beneath the ice?

Today, Prudhoe Dome is a roughly 500-meter-thick ice-covered high point of the Greenland Ice Sheet, covering about 2,500 square kilometers. In 2023, the GreenDrill team established a camp on the dome and drilled through 509 meters of firn and ice to reach material buried underneath it.

The researchers were looking for sediment because it can preserve a record of the last time the surface was exposed. The core from the summit contained sediment that had been exposed to daylight sometime between about 6,000 and 8,200 years ago. Other evidence from the ice above the sediment supports the conclusion that the dome had melted completely rather than simply thinning during that period.

That is the unusual part. Scientists did not infer the ancient ice loss simply from computer simulations or distant climate records. They reached through the modern ice and found the ground that had been exposed when the ice was gone.

How can a layer of sediment reveal an ancient melt?

The team used a technique called luminescence dating. It works a little like a natural clock hidden inside mineral grains. While sediment is buried, radiation causes electrons to become trapped within those grains. When the sediment is exposed to sunlight again, that stored energy is released, producing a measurable signal.

The strength of that signal helped researchers determine when the sediment last saw daylight. In this case, the evidence points to exposure during the early or middle Holocene, after the last ice age. The result provides a direct geological marker showing that Prudhoe Dome was ice-free during a period when Greenland was warmer than it is today.

Why does the discovery matter for the United States?

Greenland is thousands of miles from the U.S. mainland, but what happens to its ice does not stay in Greenland. The Greenland Ice Sheet contains enough ice to raise average global sea level by about 7.3 meters, or 24 feet, if it were completely lost. That is not a prediction for this century. It is the maximum long-term consequence of losing the entire ice sheet.

The more immediate value of the Prudhoe Dome research is different. Scientists want to learn which parts of Greenland are most vulnerable and how the ice responds when temperatures rise. That information can improve estimates of future sea-level change, including risks facing coastal communities in the United States.

American scientists helped make the deep drilling possible

The project also has a strong U.S. research connection. GreenDrill is funded by the National Science Foundation and is co-led by researchers at the University at Buffalo and Columbia University’s Lamont-Doherty Earth Observatory. Lead author Caleb Walcott-George is now an assistant professor at the University of Kentucky.

Getting the sample was not straightforward. The team worked in remote Greenland conditions, dealing with snow, drilling logistics and a fracture in the ice near the end of the operation. Researchers ultimately used a drill bit normally intended for rock to complete the final section and reach the bed before the equipment had to be removed.

That difficult fieldwork is important because the sediment beneath Greenland is unusually valuable. Much of the evidence showing how far the ice sheet retreated in the past remains buried beneath today's ice. GreenDrill is designed specifically to recover that hidden history.

What could happen next?

The Prudhoe Dome study is only the beginning. Researchers also collected material from a second site near the edge of the dome, where the ice is much thinner. Those samples could reveal more about the area's most vulnerable zones, while traces of ancient plants may provide clues about what the landscape looked like when the ice disappeared.

The larger goal is to collect similar evidence from other parts of Greenland. Models can estimate how an ice sheet might behave as temperatures rise, but buried rocks and sediment provide something more concrete: evidence of what Greenland actually did during past warm periods.

That is why the most important discovery at Prudhoe Dome may not be that an ice dome vanished 7,000 years ago. It is that scientists can now look directly at the ground it left behind. The ice preserved that evidence for thousands of years, and the drilling finally brought the record back to the surface. For researchers trying to understand Greenland's future, that ancient landscape may be one of the clearest warnings the ice has ever kept hidden.