The Secrets In Ice Cores
by Daniel Grossman

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NASA scientist James Hansen first sounded the alarm about global warming in 1988 - photo courtesy National Aeronautics and Space Administration

Uncharted Territory

Changes like these won't notably alter the lives of these people at the top of the world, but they could be a prelude to more serious problems. NASA scientist James Hansen says the two tiny light bulbs worth of heat that humans have added to each square meter of Earth's surface has brought the planet to the brink of a completely new chapter of climate history.

He says, "We're becoming as warm as it has been in the last million years, and soon it will be warmer than it has been in the last million years. So we're really going into territory that hasn't been charted for a long time."

For the last million years, the Earth has alternated between ice ages, which last about 80,000 years and warm periods, called interglacials, which are much shorter. We're currently about 11,000 years into an interglacial. We probably should be sliding toward the next ice age. Instead it's getting warmer.

Heinz Miller, a professor at Germany's Alfred Wegner Institute, is a glaciologist, an expert on glaciers. He says in order to figure out what happens next, scientists study what happened before.

German glaciologist Heinz Miller - photo by Daniel Grossman

At a base camp on Greenland's windswept ice, he says researchers have only measured the climate systematically with precise scientific instruments like thermometers for about 150 years. Those measurements represent only a fleeting snapshot of Earth's past. However researchers do have other ways to gauge climate further back in time by examining the evidence

"And we find those," says Miller, "in sediments of the deep sea and we find them in tree rings or we find them lake sediments."

Tree rings, for instance, tend to be thicker in wetter years. Lake sediments store pollen that shows what plants were growing. Cave stalactites hold evidence of past temperatures in fine rock layers. Cylinders, or cores, of glacier ice contain climate records trapped in frozen water molecules.

Miller continues, "Ice cores are a very special climate archive because they will tell us about past temperatures and at the same time they will tell us about atmospheric composition."

Glacier cores give scientists some of the most detailed pictures of past changes in climate because researchers can distinguish annual layers of ice like tree rings and count tens of thousands of years back in time.

Next - Measuring History on a Giant Glacier