Four decades on ice
With thinning hair, a sandy beard and a predilection for a pipe, Steffensen is in his fourth decade drilling holes in polar ice.
His first trip to Greenland, in 1980, came on short notice.
It was a July afternoon shortly after Steffensen graduated from college. The head of an ice-drilling mission called to offer him a job.
It was a Friday. The eight-week expedition was leaving Tuesday. The caller gave Steffensen a half-hour to cancel any plans he had for the summer.
Steffensen did. Because the caller was Willi Dansgaard, the Danish scientist who essentially invented ice-core drilling as a way to study past climates.
In the early 1950s, Dansgaard discovered that rain carries a record of the temperature at which it fell encoded in its chemical makeup. He figured that he could read temperatures deep into the past if he could find a supply of “old water.”
“Where do you find old water? In glacier ice. And where do you find old glacier ice? In Greenland,” he wrote in a 2005 memoir (PDF).
The snow that falls on central Greenland rarely melts. For roughly 100,000 years, snowstorm after snowstorm piled up the snow, forming an ice sheet more than 3 kilometers thick in spots.
That ice contains an encyclopedic record of the climate in which it formed.
Temperature data is just the beginning. Frozen inside the cores are tiny bubbles of ancient air that can reveal concentrations of greenhouse gases from the distant past. Trapped dust particles tell of the force and frequency of storms that blew particles onto Greenland’s snowy face from far away. Volcanic eruptions left their mark in acidic ash.
Ice cores have provided some of the most valuable data about past climates to scientists seeking answers about the causes and impacts of today’s global warming.