Pictorial Parade/Getty Images

During the Cold War, the U.S. Army devised a secret plan to hide nuclear missiles inside of Greenland's ice sheet. While the missiles never actually arrived, scientists found something more interesting below the surface: sediments that could teach us more about Greenland's history with climate change. A new study published in Climate of the Past found that the site of the plan was completely free of ice around 416,000 years ago. Back then, the Greenland summers were about 8.5 degrees Fahrenheit (4.7 degrees Celsius) warmer than they are today.

For the location, known as Camp Century, to be ice-free, the study says that the Greenland Ice Sheet would have had to retreat more than 60 miles (97 kilometers) from where its edge sits in that part of Greenland today.…