Climate change and tropical Andean glaciers: Past, present and future

Abstract

International audienceObservations on glacier extent from Ecuador, Peru and Bolivia give a detailed and unequivocal account of rapid shrinkage of tropical Andean glaciers since the Little Ice Age (LIA). This retreat however, was not continuous but interrupted by several periods of stagnant or even advancing glaciers, most recently around the end of the 20th century. New data from mass balance networks established on over a dozen glaciers allows comparison of the glacier behavior in the inner and outer tropics. It appears that glacier variations are quite coherent throughout the region, despite different sensitivities to climatic forcing such as temperature, precipitation, humidity, etc. In parallel with the glacier retreat, climate in the tropical Andes has changed significantly over the past 50–60 years. Temperature in the Andes has increased by approximately 0.1 °C/decade, with only two of the last 20 years being below the 1961–90 average. Precipitation has slightly increased in the second half of the 20th century in the inner tropics and decreased in the outer tropics. The general pattern of moistening in the inner tropics and drying in the subtropical Andes is dynamically consistent with observed changes in the large-scale circulation, suggesting a strengthening of the tropical atmospheric circulation. Model projections of future climate change in the tropical Andes indicate a continued warming of the tropical troposphere throughout the 21st century, with a temperature increase that is enhanced at higher elevations. By the end of the 21st century, following the SRES A2 emission scenario, the tropical Andes may experience a massive warming on the order of 4.5–5 °C. Predicted changes in precipitation include an increase in precipitation during the wet season and a decrease during the dry season, which would effectively enhance the seasonal hydrological cycle in the tropical Andes. These observed and predicted changes in climate affect the tropical glacier energy balance through its sensitivity to changes in atmospheric humidity (which governs sublimation), precipitation (whose variability induces a positive feedback on albedo) and cloudiness (which controls the incoming long-wave radiation). In the inner tropics air temperature also significantly influences the energy balance, albeit not through the sensible heat flux, but indirectly through fluctuations in the rain–snow line and hence changes in albedo and net radiation receipts. Given the projected changes in climate, based on different IPCC scenarios for 2050 and 2080, simulations with a tropical glacier–climate model indicate that glaciers will continue to retreat. Many smaller, low-lying glaciers are already completely out of equilibrium with current climate and will disappear within a few decades. But even in catchments where glaciers do not completely disappear, the change in streamflow seasonality, due to the reduction of the glacial buffer during the dry season, will significantly affect the water availability downstream. In the short-term, as glaciers...

Lake Fluctuations, Plant Productivity, and Long-Term Variability in High-Elevation Tropical Andean Ecosystems

“…Drier conditions were also identified in an aridity reconstruction for the central Andes region from southern South America (Boucher et al, 2011). Consistently, a sustained shrinking of small glaciers from the tropical Andes have been recorded since the second half of the 20th century (Ramirez et al, 2001;Francou et al, 2003;Vuille et al, 2008), which was associated with the increasing trend in temperature for JULIETA CARILLA ET AL. / 187 the last decades across the region (Vuille andBradley, 2000, Urrutia andVuille, 2009).…”

The last deglaciation of Peru and Bolivia

“…Modern temperature values and radiosonde observations indicate that ELA's in the central Andes have risen by at least 70 m since A.D. 1962, as a consequence of warming temperatures (Mark and Seltzer, 2005). At the same time, precipitation has decreased, accelerating the rate of recent glacial retreat (Vuille et al, 2008a). Strong gradients in precipitation exist across the Andes in this region, with wetter conditions to the east given predominant precipitation sources of the easterly trade winds.…”

“…The freezing height of precipitation and relative amount of snowfall are determinative for glacier mass balance. Ablation is more intensely focused below the equilibrium line elevation (ELA) and occurs all year round, while accumulation is restricted seasonally to regions above elevations dividing snow and rain, and this tends to persist at a constant altitude throughout the year (Vuille et al, 2008a). Tropical glaciers have high mass accumulation area ratios , and are thus fundamentally constrained by landscape hypsometry (area to elevation) and precipitation.…”

“…For example, the warm phase of the El Niño Southern Oscillation (ENSO) typically produces higher wet season rainfall amounts at low elevations along the Pacific coast of the central Andes, and the opposite during cold phases (Coelho et al, 2002). At altitude, glaciers are affected by ENSO through large-scale circulation dynamics and zonal flow anomalies in the upper troposphere that affect snowfall (Vuille et al, 2008a). Although the relationship varies geographically and breaks down during certain years, El Niño events generally cause warm and dry conditions, whereas La Niña events are cold and wet in alpine regions of the southern tropical Andes (Vuille et al, 2008b).…”

Climate change and crop diversity: farmers’ perceptions and adaptation on the Bolivian Altiplano

“…Rising temperatures, glacial retreat, and shifts in the frequency and intensity of precipitation and frost events have been documented in the Andean highlands over the last 30 years (Bradley et al 2006;Vuille et al 2008;Perez et al 2010;Thibeault et al 2010;Valdivia et al 2010). Further increase in temperature and variability are projected that will impact water supplies and crop yields (Bradley et al 2006;Valdivia et al 2010;Seiler et al 2013).…”