Reliable meteorological observations for climate reconstruction are limited or absent prior to A.D. 1850 for much of the Earth and particularly in the Tibetan Plateau region of central Asia and in tropical South America. Over 50 percent of the Earth's surface lies between 30 N and 30 S and 75 percent of the world's inhabitants live and conduct their activities in these tropical regions. Thus, much of the climatic activity of significance to humanity, such as variations in the occurrence and intensity of the El Nino-Southern Oscillation and Monsoons, are largely confined to lower latitudes. Moreover, the variability of these tropical systems and particularly that of the tropical hydrological system in response to regional and globalclimate forcing are not well understood.
Ice core records are available from selected high altitude, low and mid-latitude ice caps. The ice core studies described here were undertaken as part of a long-term program to acquire the global-scale, high resolution climatic and environmental history essential for understanding more fully the linkages between low and the high latitudes. Comparisons are made between two ice core climatic records spanning the last 30,000 years from the Tibetan Plateau: the Guliya ice cap, (China,35 N; 6200 m asl) and the new Dasuopu, Himalayan site (China, 28 N; 7200 m asl). The Tibetan records are compared and contrasted with the two recent tropical ice core records from Huascaran (Peru, 9 S; 6050 m asl) and Sajama (Bolivia, 18 S; 6550 m asl). Cooling of approximately 8 degrees C as measured in the oxygen isotopic ratios contributes to a growing body of evidence that the tropical climate was cooler and more variable during the last glacial cycle and has renewed interest in the tropical water vapor cycle. The ice core evidence for past changes in the tropical hydrological cycle are presented as well as a discussion evidence of recent warming and potential linkages to recent increases in high altitude water vapor