As snow falls, it picks up the chemicals and dust in the atmosphere. Over time, the snow is covered by more snow, and the pressure from the weight of the snow turns it into ice. This process traps air bubbles which can be tested for carbon levels, different gases and chemicals, among other things. Each year of snowfall adds another layer to the snow, creating a record similar to tree rings, only one that goes much further back into history. Studying this evidence, which is stacked up in many years of snow fall, allows scientists to see how the climate has responded to changes in greenhouse gases in the past.
Scientists access this data by drilling deep into the ice and drawing out ice cores, which are cylinders of ice about 10cm in diameter. The cores are brought to the surface a few metres at a time. Scientists then catalogue and carefully store the ice cores for further study. Ice cores are the only records that preserve so much information about changes in the earth's climate and atmosphere. This core is like opening a big history book about one small spot of the earth.
Scientists with the North Greenland Eemian Ice Drilling team have just finished drilling all the way through the Greenland ice cap to bedrock, creating a hole that is 2537.36 metres deep. The project has taken about 300 researchers more than five years to complete. The drilling alone has taken two years to finish. The scientists are now able to study the earth's climate during a period called the Eemian, which was between 115,000 and 130,000 years ago.
During the Eemian, global temperatures were 2-3 degrees Celsius higher than they are today. Sea levels were five metres higher, but ice still existed on Greenland. Scientists believe studying records from that time may be useful for predictions of future climates.
The ice cores they have drilled have not seen the light of day for hundreds of thousands of years. Scientists will now analyse them for DNA or pollen which can offer clues to what existed on Greenland before it became covered by ice more than 3 million years ago.
You can learn more about the Greenland ice core project by visiting http://neem.nbi.ku.dk/