How do they do it? - Looking back in time to understand climate changes. Scientists have drilled as deep as 3 kilometers (about 2 miles) into the earth’s ancient ice in Antarctica and Greenland to remove and examine ice core layers formed over thousands of years. The ice layers appear as bands that can be counted like tree rings with small air pockets frozen in time that contain samples of the gases that made up the atmosphere.
The layers include carbon dioxide and the hydrogen isotope deuterium. The amount of deuterium in the ice corresponds to atmospheric temperature when the ice was formed. A change of 1 degree Celsius (1.8º F) leads to a change of 9 parts per million in deuterium levels. By comparing and analyzing these levels, climatologists look back at the historical relationship between carbon dioxide levels in the atmosphere and temperatures.