Polar ice caps preserve information about atmospheric composition over the past tens of thousands to hundreds of thousands of years. They contain a rich history of the Earth's volcanic activity, terrestrial dust sources, sea ice location, terrestrial and marine biological activity, pollution, and atmospheric oxidation capacity. Differences in concentrations of CO2 and CH4 in air extracted from ice of various ages, changes in temperature inferred from d18O in ice, and differences in the dust or acid loading of ice are all used to deduce major changes in the global environment [Oeschger and Langway, 1989]. These temporal patterns of physical properties and chemical species that are recorded in ice offer an opportunity to study the cause and effect relationships of environmental change.