Two ice cores from the col of Huascarán in the northcentral Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Würm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear as much as 8-12^oC cooler, the atmosphere was 200 times dustier, and the Amazon Basin forest cover may have been 40 to 50% less extensive. Differences in both ¹⁸O (8 per mil) and deuterium excess (4.5 per mil) from the Late Glacial Stage (LGS) to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5-6^oC cooler during the LGS, that the climate was warmest from 8400 to 5200 yr BP, and that it cooled gradually culminating with the Little Ice Age (200-500 yr BP). A strong warming has dominated the last two centuries.