[♪ INTRO].

In 1959, the US Army started building a town in Greenland. It was named Camp Century.

And while science wasn't its primary goal,. Camp Century was the source of the first long ice core ever acquired -- an ice core that opened the door to the history of Earth's climate. Oh, also: Camp Century wasn't built on the ice sheet -- but inside it.

Camp Century wasn't the only US base in Greenland, but it was the only one completely underground. And this was no cramped, one-room burrow, either. Camp Century had a barbershop and a theater and everything you'd expect from a small city.

All inside the ice -- generally around eight meters beneath the surface. All that ice meant that even after the tunnels were completed in 1960,. Camp Century was plagued by construction issues.

Between the weight of the ice pressing down on every ceiling, the heat generated by both buildings and humans, and the movement of the ice itself, the whole base required constant upkeep. By the time it was just a few years old, about fifty people spent their days cutting through ice with chainsaws to maintain the tunnels and avoid collapse — in a base that only ever had about 200 occupants at most. And then there was the nuclear reactor.

Camp Century was powered by the world's first portable nuclear reactor. It was designed off-site and built almost IKEA-style in Greenland so that the people in the camp didn't have to spend too much time tinkering. The reactor produced plenty of electricity, but it also made a lot of heat -- compounding the problem of melting walls.

Plus, it made radioactive waste, which was left in the ice when the camp was abandoned. But we'll come back to that. To the outside world, Camp Century was for research.

The Army wanted to study how to live and build in such an extreme, remote environment -- because this was the Cold War, and everyone thought that the Army might end up somewhere with famously murderous winters. But a team of scientists got to tag along, too. It was, after all, the perfect chance to study Greenland's ice sheet.

Ice sheets are made of years of snow piled on top of each other, with deeper ice being made of older snow. Air gets trapped between the snowflakes -- air that scientists can use to find out what the atmosphere was like when the snow first fell. They can see how much carbon dioxide there was at the time, for instance, or even if a volcano erupted and threw a bunch of ash into the air.

But global temperatures also affect the amounts of certain isotopes (or atomic variants) of hydrogen and oxygen. So scientists can use those elements to understand global temperatures when that snow fell and became part of the ice sheet. We've used ice this way since the 1930s, but Camp Century provided the first opportunity to dig more than a kilometer down into an ice sheet.

And that ice core is its most lasting scientific legacy. It showed Earth's climate evolving over the last hundred thousand years, with ice ages and warm periods right where scientists expected them based on other kinds of evidence. Because it's one long, continuous sample of the past, the Camp Century ice core showed that these other, more piecemeal sources of data were accurate pictures of Earth's climate.

The data weren't quite detailed enough to show the effects of climate change, which also wasn't as pronounced then as it is now. But Camp Century's ice helped provide a baseline for future research. We now know from it and other ice cores that what's happening now is not part of any natural cycle; it's our fault.

The core keeps giving, too. In 2019, one researcher used mud trapped in the ice to figure out that Greenland's ice sheet is probably around one million years old. But science wasn't Camp Century's main goal -- because, again: Cold War.

Camp Century was really built to test out a plan to dig hundreds of tunnels throughout Greenland and fill each one with a nuclear missile. Luckily for the world in general, the ice didn't cooperate. They'd dig and reinforce a tunnel to fit a missile, but then the ice would shift or melt and change the shape of the tunnel.

And you don't want that happening with missiles in there. Once the Army realized that, Camp Century was on borrowed time. With its tunnels falling apart around them, the tiny city was abandoned by 1967.

They'd removed the nuclear reactor a few years earlier, but they left behind buildings and diesel fuel and nuclear waste -- to be encased in ice forever. But the very climate change that Camp Century helped reveal has also put a much shorter timeline on that “forever” bit. Greenland's ice is on the move; radar has shown that Camp Century is a couple hundred meters west of where it used to be.

And while it's currently under even thicker ice than it was back in the day, that's changing, too. In 2016, a team calculated that as Greenland's ice melts,. Camp Century's waste will be exposed to the elements by around the year 2090 —maybe sooner, if climate change keeps getting worse.

That's not just nuclear waste, but other hazardous materials as well. The ice is too thick for us to retrieve anything right now. But we'll need to do it eventually.

It's up to us to learn from this city buried under the ice. Because as Camp Century helped teach us, that ice might not last forever. Thanks for watching this episode of SciShow.

If you want to help us make videos about everything from bees to nuclear disasters in waiting, check out patreon.com/scishow. [♪ OUTRO].