Glaciers in the Andes are particularly important natural archives of present and past climatic and environmental changes, in significant part because of the N-S trend of this topographic barrier and its influence on the atmospheric circulation of the southern hemisphere. Strong gradients in the seasonality and amount of precipitation exist between the equator and 30° S. Large differences in amount east and west of the Andean divide also occur, as well as a change from tropical summer precipitation (additionally modified by the seasonal shift of the circulation belts) to winter precipitation in the west wind belt (e. g. , Yuille, 1999; Garraud and Aceituno, 2001). The so-called 'dry axis' lies between the tropical and extra­ tropical precipitation regimes (Figure 1). The high mountain desert within this axis responds most sensitively to the smallest changes in effective moisture. An important hydro-meteorological feature on a seasonal to inter-annual time-scale is the occurrence of EN SO events, which strongly control the mass balance of glaciers in this area (e. g. , Wagnon et ai. , 2001; Francou et ai. , in press). The precipitation pattern is an important factor for the interpretation of climatic and environmental records extracted from ice cores, because much of this information is related to conditions at the actual time of precipitation, and this is especially so for stable isotope records. Several ice cores have recently been drilled to bedrock in this area. From Huascanin (Thompson et ai. , 1995), Sajama (Thompson et ai.

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1. Climate Variability and Change in High Elevation Regions: Past, Present and Future; H.F. Diaz, et al. 2. Climatic Change in Mountain Regions: A Review of Possible Impacts; Beniston, Martin. 3. Variability of Freezing Levels, Melting Season Indicators, and Snow Cover for Selected High-Elevation and Continental Regions in the Last 50 Years; H.F. Diaz, et al. 4. Comparison of Radiosonde Temperature Climatologies and Trends at High and Low Elevation Sites; D. Seidel, M. Free. 5. 20th Century Climate Change in the Tropical Andes; M. Vuille, et al. 6. The Impact that Elevation Has on ENSO-Related Signal in Precipitation Records from the Gulf of Alaska Region; G.W.K. Moore, et al. 7. The Health of Glaciers: Recent Changes in Glacier Regime; M.F. Meier, et al. 8. Tropical Glacier and Ice Core Evidence of Climatic Change on Annual to Millennial Time Scales; L.G. Thompson, et al. 9. Climate Variability and Environmental Changes as Recorded in Glaciers from the Central Andes; U.M. Schotterer, et al. 10. Large-Scale Temperature Changes across the Southern Andes: 20th Century Variations in the Context of the Past 400 Years; R.A. Villalba, et al. 11. Frequency-Dependent Climate Signal in Upper and Lower Forest Border Trees in the Mountains of the Great Basin; M.K. Hughes, G. Funkhouser. 12. Multi-Decadal Variability of Precipitation in the Greater Yellowstone Region as Inferred from Tree Rings; L. Graumlich, J. Littell. 13. Taking the Pulse of Mountains: Ecosystem Responses to Climatic Variability; D.B. Fagre, et al.