Watch: Earth's climate history frozen in a warehouse

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Locked in a warehouse-size freezer in suburban Denver is a detailed sample of thousands of years of the earth's climate history trapped in gasses, acids, dust, water molecules and atoms.

It's the National Ice Core Laboratory where 17,000 meters of ice collected from around the world is stored at -36 degrees Celsius.

Geoffrey Hargreaves is the curator of the laboratory.

"It doesn't hit me like some people see it, it's like, 'Wow, this piece of ice is 400,000 years old.' Well, to me it's a very valuable piece of ice and it's my job to make sure it stays that way," he says.

Researchers working in -24 Celsius conditions process ice cores collected from the South Pole.

They cut it, catalogue the depth, photograph it and conduct preliminary tests.

The tests include shooting a jolt of electricity though meter long pieces of ice, which on this occasion detects a layer of acid deposited by a volcanic eruption - seen here as a spike on the graph.

"Hey, we've got a volcano," says T.J. Fudge, a researcher from the University of Washington. "That is a big volcanic event that occurred about 8,000 years ago. So by looking for these volcanoes through the cores we can actually figure out how much volcanic activity there's been through time and help understand how the climate system has worked and responds to these large forcing that are the volcanic events.''

Once the ice is processed, it is shipped to other labs across the United States where further studies are carried out.

"Ice cores are a great proving ground for models that can predict climate in the future. If we run them backwards with the parameters that we measure in the ice core and they get it right that gives us a lot more confidence in the climate models going forward,'' says Bruce Vaughn, manager of the Stable Isotope Lab at the Institute of Arctic and Alpine Research (INSTAAR) in Boulder, Colorado.

Vaughn melts the ice millimeter by millimeter to study the molecules inside that were formed by ancient snow storms.

Heavier oxygen molecules indicate warmer temperatures.

"What we have is a really pretty accurate historical thermometer. It's as if we were standing on the ice sheet writing down the temperature for the last 800,000 years. It's that good," says Vaughn.

Scientists continue to find new ways to study the past, including analyzing trace gasses in the ice to learn about previous plant life on earth.

Each piece of ice holding the history of the earth's climate frozen in time.