In 1959, U.S. army engineers began constructing a futuristic project in northwestern Greenland that might as well have been lifted from a Cold War spy movie.

A network of tunnels under the snow contained everything from research facilities to a hospital, a cinema and a church — all powered by a small, portable nuclear reactor. The pollutants left behind include PCBs used in building supplies, tanks of raw sewage and low-level radioactive coolant used in the nuclear reactor that once stood there.

“When the waste was deposited there nobody thought it would get out again,” William Colgan, an assistant professor in the Lassonde School of Engineering at York University in Canada, said.

But a study led by Mr. Colgan, published in August in the journal Geophysical Research Letters , found that higher temperatures could eventually result in toxic waste from the base being released into the environment.

“Neither the U.S. or Denmark has done anything wrong per se, but the world has changed,” he said.

Accommodating up to 200 soldiers, ‘Camp Century’ was officially built to provide a laboratory for Arctic research projects, but it was also home to a secret U.S. effort to deploy nuclear missiles.

Code-named ‘Project Iceworm’, that part of the operation was never mentioned in the treaty between the U.S. and Denmark, once the colonial master of Greenland, a territory that is now largely self-governing.

But the spectacular project — which even included a test railway under the snow — was never fully realised.

Three years later scientists found that the glacier was shifting much faster than previously thought, threatening to crush the tunnels, and the base was abandoned in 1967.

Assuming the site would remain frozen in perpetuity, the US army removed the nuclear reactor but allowed waste — equivalent to the mass of 30 Airbus A320 airplanes — to be entombed under the snow.

Half a century later that decision is being questioned as temperatures in the Arctic rise at a higher pace than in the rest of the world.

Possible leakage

By 2090, the amount of ice melting may no longer be offset by snowfall, meaning the toxic chemicals could start leaking into the environment, the study found.

Before then, fissures in the snow could lead to melt water seeping into the crushed tunnels, currently located around 35 metres below the surface. Since excavating the site would be hugely expensive, Mr. Colgan believes a clean-up operation would have to wait until the camp has been uncovered by the melting ice.

Greenland Foreign Minister VittusQujaukitsoq said the study’s findings were “worrying” and that his government was working to ensure that it was established who would be responsible for cleaning up the site.

The former government in the capital Nuuk had in 2014 requested a report from Copenhagen on possible contamination from Camp Century without receiving “any assessment of the extent or character of the waste” described in the study, he said in a statement.

Danish Foreign Minister Kristian Jensen said in a statement that his government would “now look closer at these aspects together with the relevant expertise... in close dialogue with Greenland.”