In 1967, the U.S. decommissioned a military base that had been constructed underneath the Greenland Ice Sheet. In doing so, the military removed a portable nuclear reactor that had helped power the 200-person base, but left the rest of the waste there, from gasoline to PCBs and nuclear coolant water.

At the time, the U.S., along with their Danish partners who had authority over Greenland, assumed the waste would be entombed for eternity beneath a perpetually deepening snow cover.

However, what once was buried, global warming is poised to unearth. According to a new study published Wednesday in the journal Geophysical Research Letters, the melting ice sheet could begin spreading the hazardous waste across the surface of the ice sheet and into the ocean in as little as 75 years from now.

SEE ALSO: Greenland ice melt goes into overdrive after record heat wave

Such waste poses a threat to ecosystems and human populations, the study found. More importantly, though, the research calls attention to an issue that could complicate relations between the U.S., Denmark and the newly autonomous territory of Greenland.

The waste, says Liam Colgan, a climate scientist at York University in Toronto and lead author of the study, is "... An unexpected liability due to climate change that potentially undermines the goodwill between the U.S., Denmark and Greenland."

That goodwill, in turn, allows the U.S. to still maintain one U.S. air base on Greenland, and potentially build more as the planet's largest island opens up as the climate warms.

A crane lowers a hatch into a lateral trench of the permanent camp at Camp Century in Greenland. Image: Pictorial Parade/Archive Photos/Getty Images

"No one realized that there was a climate assumption buried in that treaty, which was that it would keep snowing there,” Colgan told Mashable in an interview, referring to the agreement between the U.S. and Denmark regarding the based, called Camp Century.

Evaluating the "city under the ice"

The scientists examined documents from the U.S. Army Corps of Engineers to determine roughly how much waste is buried beneath the ice sheet, and across how large an area.

They estimated that Camp Century, located 125 miles inland from the west coast of Greenland, hosts approximately 9,200 tonnes of physical waste associated with abandoned infrastructure — equivalent to the mass of 33 Airbus A380s super jumbo jets, along with 20,000 liters of chemical waste associated with base fuel. This is about equivalent to the volume of a full-size tanker truck.

The depth of the solid waste is estimated at about 36 meters, or 118 feet beneath the ice sheet surface, the study found.

Part of the glacial ice sheet that covers about 80 percent of Greenland is seen on July 17, 2013 . Image: Joe Raedle/Getty Images

In addition, they calculated that there is likely about 24 million liters of biological waste (mainly sewage), along with radioactive coolant water from the reactor.

The total area of the facility sprawls across about 136 acres, the study found, or about 100 football fields.

The study indicates that the most significant threat to the Arctic environment from the buried waste are polychlorinated biphenyls, or PCBs, which do not break down naturally in the environment and can build up in plants and animals, potentially causing cancer in humans.

“I am sure there’s tons of PCBs up at Camp Century. Literally tons,” Colgan said.

The researchers, who applied for funding from NATO and the Danish government but were turned down, also examined climate simulations to determine when the Camp Century site could become part of what is known as the ablation zone, where instead of net snowfall per year, there is net melt occurring.

Studies show that the Greenland ice sheet lost 262 billion tons of ice per year between 2007 and 2011, with most of this due to enhanced surface melt.

Meltwater can percolate down into the subsurface of the ice sheet, up to about 10 meters, or 33 feet, per season, and may persist under the surface while sinking further, the study found. This means that buried wastes will be vulnerable to both the long-term melting of the surface and subsurface flow of meltwater.

The model simulations showed this may happen before the end of this century, given the steady advance of the melt zone inland and upward from the Greenland coast as rapid warming occurs.

Project Iceworm

The little-known Camp Century base was one of five ice sheet bases that the Army constructed near Thule Air Force Base, in northwest Greenland.

The base had a secret mission, in addition to its stated purpose of testing Arctic construction techniques and conducting scientific research.

Camp Century was also designed to carry out a proof of concept for a far more expansive plan that would have built a nuclear missile base underneath the ice sheet.

Water is seen on part of the Glacial Ice Sheet in Greenland. Image: Joe Raedle/Getty Images

The waste at Camp Century could be far worse, Colgan says, if the U.S. Army had gone through with its secret plan to bury up to 600 intermediate range ballistic missiles under the ice. That secret project, codenamed Project Iceworm, was nixed by the Joint Chiefs of Staff in 1963.

Waste constitutes political risk

According to James White, a climate scientist at the University of Colorado at Boulder who was not involved in the study, the waste cannot be viewed as being buried for eternity in an area that is transforming so quickly.

"This stuff was going to come out anyway, but what climate change did was press the gas pedal to the floor and say, 'it's going to come out a lot faster than you thought,'" he said in a press release.

Managing the waste problem at Camp Century could become a model for figuring out how to deal with similar unexpected pollution issues around the world, as ice sheets melt and ecosystems shift in response to the warming climate.

“All of a sudden the world has shifted beneath our feet and now we have a multinational and multigenerational problem beneath our hands,” Colgan said.

“This is probably going to happen more around the world as climate change goes on.”