Researchers have known for a long time that the earth has experienced many temperature and carbon dioxide cycles during the past million or more years. These researchers are called Paleoclimatologists, and it is their job to research and reconstruct what the earth’s climate has looked like over time.
The reason ice core samples are important to Paleoclimatologists studying the past history of earth, is that the Northern Hemisphere’s Arctic region and the Southern Hemisphere’s Antarctic region have massive reservoirs of glaciers and ice sheets that took literally hundreds of thousands of years to accumulate.
For ice sheets and glaciers to form, sea ice thickens and expands its coverage, and snow is deposited over these cold northern latitude areas. The glaciers and ice sheets are formed over the course of hundreds or thousands of years during the process in which snow is compacted to form ice, or any rainfall is frozen. During this formation process, bubbles of air from the atmosphere are trapped within the ice. And what is within these air bubbles? Atmospheric gasses such as oxygen, methane and carbon dioxide that comprised the atmosphere at that point in time the air bubbles were trapped.
By drilling ice core samples, then processing and extracting these air bubbles through a complex process, researchers are able to measure the amount of various gases over time in relation to the age of the ice core sample. Once this process is finished, Paleoclimatologists are able to chart past climates of earth, and record temperature and carbon dioxide trends during the past 420,000 years.
One of the most important sites for ice core samples is the Lamont-Doherty Earth Observatory at Lake Vostok in the Antarctic. As seen in Figure 3, scientists have drilled 3,623 meters down to near the bottom of the ice sheet, with ice at that level recorded as 420,000 years old.
Figure 3: A pictorial by Lamont-Doherty Earth Observatory of Antarctic ice core drilling at Lake Vostok. Drilling has reached nearly 3,623 meters down to the bottom of the ice sheet, with the age of the ice at this level 420,000 years old. (click image to enlarge)