Photosynthesis and respiration occur widely on Earth's surface, and the 18O/16O ratio of the oxygen produced and consumed varies with climatic conditions. As a consequence, the history of climate is reflected in the deviation of the 18O/16O of air (delta18Oatm) from seawater delta18O (known as the Dole effect). We report variations in delta18Oatm over the past 60,000 years related to Heinrich and Dansgaard-Oeschger events, two modes of abrupt climate change observed during the last ice age. Correlations with cave records support the hypothesis that the Dole effect is primarily governed by the strength of the Asian and North African monsoons and confirm that widespread changes in low-latitude terrestrial rainfall accompanied abrupt climate change. The rapid delta18Oatm changes can also be used to synchronize ice records by providing global time markers.