Our Greatest Libraries are Melting Away

In the mid-1960s, scientists working at a secret U.S. nuclear base in Greenland made an astonishing discovery: Ice has memory.

As they excavated a nearly mile-long core of ice from Camp Century, the name of the secret nuclear base, U.S. scientists were puzzled by the discovery of light and dark bands in the ice. They turned to Willi Dansgaard, a Danish scientist who had devised a method to date ice that fell as snow thousands of years ago by measuring the density of isotopes in each layer of snowfall. Water molecules that fall in winter have more of the heavier oxygen-18 isotopes than those that fall in summer. Dansgaard deduced that the core retrieved from Camp Century was stratified with 100,000 years of snowfall, arranged in seasonal layers that could be read like lines on a calendar.

As fallen snow solidifies into ice, it traps microscopic bubbles of air along with traces of past climates. Ash from ancient forest fires, or pollen, can help scientists reconstruct what life on Earth was like thousands of years ago.

The world’s frozen places are an immense library of our planet’s history.

The Camp Century ice core caused a sensation. It was the first to reach bedrock; the New York Times called it “the most rewarding hole ever drilled.” But until recently, no one had examined the soil sample that came up with it. As The Post reported last month, Andrew Christ, a geologist at the University of Vermont, has determined that the soil — full of the frozen remains of ancient plants — was last exposed to the air less than 1 million years ago. If Greenland had been ice-free that recently (geologically speaking), then surely it could become so again.

Christ’s discovery is a warning. The mechanisms that could cause the ice sheet’s collapse are extremely delicate. The Camp Century core not only tells us about the world as it once was, but also it foreshadows the world to come if our efforts to mitigate climate change fail.