Ice core records of atmospheric carbon dioxide

Beneath the surface of Antarctica lies a near perfect record of changes in the atmosphere composition over hundreds of thousands of years. This unique archive allows us to reconstruct atmospheric CO2 prior to the onset of modern atmospheric monitoring in the 1950s, with accuracies down to just a few parts per million. The data reveal natural variations in atmospheric CO2 on glacial-interglacial, millennial, and centennial time scales and thus provide highly accurate reconstructions of the radiative forcing over time. Additionally, the stable isotopes of CO2 can be measured at accuracies that can quantify the sources and sinks of CO2 over these same timescales. In combination, the concentration and isotope composition of CO2 allow us to constrain both the past climate sensitivity (i.e., how climate responds to a change in CO2) and carbon-climate feedbacks (i.e., how the carbon cycle responds to a change in climate).