Ice cores taken from glaciers can also provide a reliable record of past El Niño episodes. Seasonal variations in precipitation and chemical composition (CO₂ and O¹⁸/O¹⁶ data) produces laminations in both polar and alpine glaciers which can be precisely dated from ice core samples. Two ice cores of this type were taken in 1983 from the Quelccaya ice cap in the Andes mountains in Peru. One ice core, taken from the summit contained a record of 1350 years while the other ice core contained a record of 1500 years. This information was compared with that from the subtropical Dunde ice cap in China. Even though these two locations are considerably far apart, the information was remarkably similar, indicating that the climatic changes were in fact affecting more than just the Peruvian area.

(Taken from El Nino. Historical and Paleoclimatic Aspects of the Southern Oscillation, p.297)