Natural ice contains approximately 100 p.p.m. (by weight) of enclosed air. This air is mainly located in bubbles. Carbon dioxide is an exception. We estimate the fraction of CO2 present in bubbles to be only about 20%. The remaining part is dissolved in the ice. Measurements of the CO2 content of ice samples from temperate and cold glacier ice as well as of freshly fallen snow and of a laboratory-grown single crystal are presented. Glaciological implications are discussed.