CLIMATE DRIVERS OF EQUILIBRIUM LINE ALTITUDE CHANGES AT 4 LOW-LATITUDE ANDEAN GLACIERS FROM 1980 TO 2010: DIFFERENT DRIVERS, BUT LIKELY CONTINUED RETREAT IN A WARMING WORLD

Low-latitude Andean glaciers are vital water resources and invaluable terrestrial paleoclimate records. However, the dominant climate drivers for their past and future changes are not fully understood. We explore climate drivers of glacier change at 4 outer tropical glaciers: Huascarán, Quelccaya, Illimani, and Sajama, by calculating the thermal year (July – June) equilibrium line altitude (ELA) from 1980 to 2010 using a numerical energy balance ELA model forced with monthly mean reanalysis and gridded data products.

Huascarán, Quelccaya, and Illimani are in the wet outer tropics, and their ELA fluctuations correlate almost one-to-one (r > 0.9; p < 0.001) with peak accumulation season (January, February, March) freezing level heights (FLHs). Huascarán ELA fluctuations are the smallest (-150 m to +180 m), followed by the Quelccaya Ice Cap (-185 m to +212 m) and Illimani (-178 m to 228 m). Sajama is in the dry outer tropics, and its ELA fluctuations correlate most strongly with precipitiation rate (r ≈ -0.7; p < 0.001). It also correlate significantly (|r| > 0.4; p < 0.05) with climate variables important in sublimation, including wind speed, relative humidity, incident shortwave radiation, and mean air temperature. Sajama ELA fluctuations are the largest (-754 m to +1938 m).

Wet outer tropical ELAs roughly track Austral summer (accumulation season) FLHs. FLH trends in the region are linked to tropical sea surface temperature (SST) trends and the El Nino Southern Oscillation (ENSO). Thus, past and future variations in these glaciers likely reflect trends in tropical SSTs and the magnitude and/or frequency of ENSO. Dry outer tropical ELAs depend on different and more numerous climate variables than wet outer tropical ELAs, and some of these variables do not have intuitive linkages to regional-scale changes. However, some of these variables have regional-scale linkages, and there is a significant (p < 0.05) linear trend of ELA increase between 1980 and 2009. Our results identify dominant climate drivers for changes in outer tropical ELAs and highlight the tenuous future of these glaciers in a warming world.