How much has the amount of CO2 in the atmosphere changed in the past?
Ice cores have been collected from Antarctica and Greenland which contain information stored in the ice that can be used to reconstruct climates thousands of years ago. As snow accumulates on ice caps and ice sheets where temperatures usually remain below freezing year round, it lays down a record of the environmental conditions at the time of its formation. Over time the snow, buried under further accumulations, is compacted to ice, preserving the climatic information. Air bubbles trapped in the ice can be analyzed to reconstruct the atmospheric composition at the time when the ice formed. Measurements of the amount of greenhouse gases in these bubbles show that the “pre-industrial” amount of CO2 in the atmosphere was about 280 parts per million (ppm), about 100 ppm below today’s (2006) value. The figure below show results of CO2 measurements of air trapped in ice cores taken at the Law Dome site in Antarctica, along with present day measurements at the GMD Mauna Loa Observatory in Ha
