Frozen Crystal Balls

Ice Cores Offer Clues to the Climate

At a site called Dome C on the eastern side of the Antarctic continent, the European Project for Ice Coring in the Antarctic (EPICA) recently removed cylinders of ice from a depth of nearly two miles. When the crew returns in December to finish the five-year project and remove the last 328 feet of ice, they will uncover a bedrock layer that has not been touched by light or air in more than 900,000 years.

John Rhoades examines a core in the National Ice Core Laboratory. Ancient ice gives clues to atmospheric conditions hundreds of thousands of years ago.©USGS/National Ice Core Labratory

But why is old ice so interesting to the scientific community? "What you see in this record, combined with earlier data, are the rules by which climate works, and these are the rules that go into climate models for prediction of the future," says Eric Wolff, chief scientist of the EPICA program, and member of the British Antarctic Survey.

Ice coring began in the 1950s, and since then researchers have been removing samples from the Arctic, Antarctic, and any other location where ice accumulates unhindered by melting. A trove of information about the atmosphere and environment waits inside, gleaned from the physical properties of the ice itself, and from the antique air bubbles within it. "It is a direct link to the atmosphere," says Mark Twickler, director of the National Ice Core Laboratory. "With all other ways of getting data, you have a water surface in the way. Even tree rings have some mediation."

Researchers have discovered several things about the planet through ice coring. We know that for the last 800,000 years or so, the Earth’s climate has shifted back and forth between ice age conditions and warm, inter-glacial periods, such as the one we’re in right now. Dust in the ice hints at events that influenced climate, such as volcanic eruption and the circulatory power of the Earth’s winds.

Researchers are also able to watch the ebb and flow of elements through the environment. Lead levels in the ice increased measurably in the layers corresponding to the introduction of leaded gasoline, and decreased just as sharply in layers corresponding to its removal from the market.

Ice coring allows scientists to gain perspective on our atmosphere and greenhouse gases. "Maybe the most important thing we can see in respect to human activity, [is that] we can show the atmospheric composition we have now is really unlike anything we’ve had for the last 100,000 years," says Kurt Cuffey, an earth sciences professor at the University of California, Berkeley. "Fossil-fuel burning and agricultural practices have all had an effect. Right now, atmospheric levels of [the global warming gas] carbon dioxide (CO2) are about 30 percent higher than their pre-industrial levels."

Climate models are now being constructed to look 100, 200 and even 300 years into the future. These complex computer models take in such variables as predicted international economic growth, population size and projected dependence on fossil fuels. The models must also realistically render the myriad systems that the Earth employs to regulate itself. Data from ice cores is used both to create these representations, and to check the accuracy of the model.

Modelers can run the simulation backward in time to see if it predicts the actual data. "The models do a pretty good job explaining why world temperatures for the last 10,000 years have been 10 to 15 degrees higher than in the ice age," says Cuffey. "It seems to answer the critical question that if you change carbon dioxide by such and such an amount how much will you change the temperature."

The major problems with the models lie in how accurately they depict the feedback systems of the Earth. Models failed to predict a series of sudden climate change events that happened during the period of the ice ages, but there is hope for their improvement.

"Given more information about the past, we hope we can make better predictions about the future," says Twickler. Before the EPICA project, climate records only dated back 400,000 years or so. EPICA more than doubled the scope of climate data.

Wolff says that at a recent conference of field experts "there was general support to look for somewhere in Antarctica to find even older ice, more than one million years old. This will require a lot of survey and modeling work, and we agreed that it should be a truly international effort."

Another expedition may also be underway next year. Kendrick Taylor, research professor at the Desert Research Institute in Nevada and leader of a possible U.S.-fronted trip to the Antarctic, says there are plans to drill a core reaching back only the last 100,000 years. "EPICA focused on long time scales. It’s really a great tool," says Taylor. "We’re taking a slightly different tactic, and looking at only the last 100,000 years. There’s better time resolution."

As researchers probe deeper and deeper down in the ice sheet, the layers of ice tend to become thinner, sometimes only fractions of an inch thick. These layers inevitably lack the year-to-year information of more recent, thicker layers, and span larger periods of time. This is why the EPICA core falls short. "We want to see what the last warm period was like, and how it shifted from warm to cold," Twickler says. "This should help us understand the time scale of change, and see what is happening. We need to see conditions of the past atmosphere to see how activity has altered it."