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Mar 11, 2009

Danish glaciologist Dorthe Dahl-Jensen looks for clues about the Earth’s future deep under the Arctic ice sheet.

By Anna-Katarina Gravgaard

“From the Earth’s point of view, [climate change] isn’t a problem at all,” says scientist Dorthe Dahl-Jensen, director of the Center for Ice and Climate at the Niels Bohr Institute in Copenhagen, Denmark. “The problem is people.”
Dahl-Jensen, one of the world’s leading ice and climate specialists, is pointing out that the planet has survived many cycles of dramatic warming and cooling—but man has not. She and other scientists are studying ice cores drawn from far under the ice sheets that cover Greenland and Antarctica to understand how the planet’s climate has changed over the past 500,000 years.
Like most researchers, Dahl-Jensen and her fellow glaciologists spend a considerable amount of time in the library. Their library, in the basement of the Center for Ice and Climate, houses 80 tons of ice core samples, some of which are 120,000 years old.
That explains why the temperature is kept at 20 degrees Fahrenheit below zero. Dahl-Jensen opens an even colder freezer and takes out three tube-like ice core samples. She explains that the Greenland ice sheet is almost 2 miles thick.
“When you drill down through the ice, first you have snow and gradually the snow is compressed into ice. Layers and layers of ice, reaching back in time.”
She holds an ice core wrapped in protective plastic to the light, revealing the ancient air bubbles and dust that is trapped inside. Dahl-Jensen marvels—these bubbles hold greenhouse gases and the ice contains volcanic dust and bits of organic matter.
They may hold the keys to mankind’s future on the planet.

Dahl-Jensen has always been fascinated and interested by ice. When she was just 11 years old, she joined the Danish scouts and learned to ice climb and ski, but it wasn’t until her last year in high school (when her father brought home a catalog from the University of Copenhagen), that she learned about glaciology as a discipline.
“You had to go into the field while you were studying,” she remembers. “And I decided: ‘wow, this is just for me.’”
In 1981, she got her first practical experience drilling for ice cores in Greenland. Since then, she has spent considerable time studying the ice sheets of both Greenland and Antarctica and is now widely recognized as one of the leaders in her highly specialized field of research.
Her husband is also an ice and climate researcher, and they often work together in Greenland. During the summer, when the temperatures are comfortable enough, the couple takes turns living in the field and watching their four children at the nearest town, more than 600 miles away.
“Spending so much time in Greenland has its costs, but it also has given the family plenty of joy.” One bit of proof: her two eldest sons have decided they, too, want to be scientists.

Dahl-Jensen spent much of last summer roughly 600 miles from the North Pole at the newest drilling site, nicknamed NEEM for North Greenland Eemian Ice Drilling.
Why “Eemian?” During the so-called Eemian period (115 to 130 thousand years ago), the temperature on Greenland rose five degrees centigrade. That, says Dahl-Jensen, is “a perfect analogy to our time.” She and other scientists are increasingly convinced that greenhouse gas concentrations are triggering another period of global warming, which is likely to be about the same magnitude as during the Eemian.
North Greenland wasn’t chosen for its scenic beauty or temperate climate. In the summer, it warms to 15 or 20 degrees Fahrenheit, while in the winter temperatures can reach minus 100 with winds in excess of 125 miles per hour. NEEM sits on a flat plateau, with only snow as far as the eye can see.
What it lacks in beauty, the isolated camp makes up for by offering the possibility of drilling through 1.5 miles of ice to the Greenland bedrock. That should be deep enough to develop a picture of the climate stretching back 150,000 years, since that’s how long it took for the ice to form.
Last summer, Dahl-Jensen and scientists from 15 countries began to build their camp. Today—or, at least, when the scientists return to shovel off the winter snows in May—it consists of a large geodesic dome with baths, toilets, a kitchen, laundry room and offices. There, the scientists will sleep in insulated sleeping bags, typically in tents raised directly on the ice.
But the center of the action is a research laboratory.
The lab hosts the ice drill, testing equipment and—of course—ice cores before they are shipped back to the Ice Library.
“The ice cores themselves have a diameter of around four inches…and we drill them up in bits of up to four meters,” Dahl-Jensen explains. “In that way, we drill to a depth of more than 2.5 kilometers where we will hit bedrock.”
They expect to produce 800 to 1,000 cores over the next three summers. By analyzing them, scientists can construct a profile of the climate as it ebbed and flowed through pre-history: everything from snowfall amounts and temperature changes to atmospheric CO2 and the temperature of the nearest ocean.
For Dahl-Jensen, climate change isn’t a theory, but a fact that has been demonstrated time and time again over the centuries, with a record etched literally in the ice.
She has high hopes for the NEEM project, since it is the first effort to map the entire Eemian period. One of the biggest questions she wants to answer is how much of the Greenland ice sheet melted back then, and how much the seas rose as a result.
Her goal is to produce a snapshot of a period similar to the present and, especially, to understand how it ended. “Then we can say, ‘hey, this is what happened last time.’ And we will know what is likely to happen in our future.”

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