"Climate Change and Land Ice" In: the International Encyclopedia Of
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especially as influenced by ocean temperatures Climate change and land and position of the jet stream. Glacier response ice also depends on the distribution of glacier area with elevation. As climate warms, the elevation of the snow line will progressively experience Andrés Rivera upstream migration, shifting precipitation from Centro de Estudios Científicos, Chile solid to liquid on low-altitude glaciers. In this Universidad de Chile context, a small mountain glacier with most Claudio Bravo of its area at lower elevations will experience Giulia Buob retreat and thinning due to rain. However, a Centro de Estudios Científicos, Chile valley glacier with an important accumulation area at higher elevations will experience stability Glaciers provide excellent records of climate or even thickening if the maximum snowfall change. Samples of particulates and gases can is also migrating upstream. Thus, glaciers with be extracted from ice cores, from which the bigger and higher elevation accumulation areas past composition of the atmosphere can be may advance during periods of climate warming, reconstructed. Ice cores also record temperature whilst small glaciers without high-altitude areas and moisture, and all of this information is will more likely tend to disappear if ongoing stored in dateable, consecutive layers. The posi- climate trends persist over time. tion of end moraines, past and present, can be Scientists have incomplete geographic coverage used to discern past glacier positions, and these for monitoring long-term glacier changes, espe- deposits can be dated with radiogenic isotopes cially for cold-ice glaciers in the high latitudes. to reveal the timing of past shifts in climate. The The Fifth Assessment Report of the Intergov- response of a glacier to climate change may be ernmental Panel on Climate Change (IPCC) fairly immediate for alpine cirque glaciers, but a provided enough evidence of human-induced response time is usually involved, ranging from climate change, especially in connection to the decades for valley glaciers to thousands of years generation of greenhouse gases such as CO2, for ice sheets. Long-narrow glaciers will have which has increased 40% since 1750 (IPCC a longer response time than will compact ice 2013). According to the same IPCC report, caps of the same area. A negative mass balance worldwide glaciers continued to shrink in the may cause an immediate response in the position past decade, as revealed by time series of changes of the glacier snout, but a positive regime may in glacier length, area, volume, and mass. In not be detected at the snout for many years. a global context of glacier area reduction, an Weekly, monthly, and seasonal variations in outline of glacier changes taking place in the glaciers are especially sensitive to ablation rates extra-tropical Andes of Chile and Argentina and meltwater lubrication. Glacier response since 1985 is presented. over years and decades is tied to mass balance, The selected glaciers are located from the which reflects a range of climate conditions, northern arid zone down to the humid and cold The International Encyclopedia of Geography. Edited by Douglas Richardson, Noel Castree, Michael F. Goodchild, Audrey Kobayashi, Weidong Liu, and Richard A. Marston. © 2017 John Wiley & Sons, Ltd. Published 2017 by John Wiley & Sons, Ltd. DOI: 10.1002/9781118786352.wbieg0538 CLIMATE CHANGE AND LAND ICE southern tip of South America (Figure 1), and charge of updating the Chilean glacier inventory. their areal changes have been mapped between Recent figures they have for the total number 1985/1986 and the most recent cloud-free of Chilean glaciers is 24 114 with a total area available satellite image (Table 1). of 23 460 km2 (2013). This inventory includes any ice body bigger than 0.01 km2, including rock glaciers, glaciarets, debris-covered ice, and Methods clean ice. These glaciers are distributed from 18○ Sdownto55○ S and experience a contrast of Variations in glacial areas have been obtained climatic conditions, from areas with only a few through a comparison of several satellite images, millimeters of precipitation per year along the acquired for all the selected glaciers. The glacier Atacama Desert in northern Chile, to more than outlines have been obtained by analyzing false 3000 mm along the islands facing the Pacific in color composite scenes produced from Landsat the southern part of the country (Quintana and Multispectral Scanner (MSS), Thematic Mapper Aceituno 2012). (TM), Enhanced Thematic Mapper (ETM), and Glaciers located in northern Chile, at high Advanced Spaceborne Thermal Emission and altitude, are characterized by cold ice, little Reflection Radiometer (ASTER) bands. The summer melting, high sublimation, and very low outlines were manually digitalized using ArcGIS ice velocities. Located in a dry environment, commercial software. these glaciers are more sensitive to precipitation The error of the glacial area calculation was changes, with sublimation being the main pro- estimated by multiplying the pixel size, or image cess defining ablation; therefore, these glaciers are resolution, by the perimeter of the digitized particularly sensitive to changes in atmospheric polygon. The average relative error for each humidity which affect the ratio between subli- zone varies between ±0.2% and ±12%. mation and melting at the ice surface. Conversely, Finally, the temperature reanalysis data from glaciers located in southern Chile, under wet and NCEP-NCAR (National Centers for Envi- cold conditions, are more sensitive to temper- ronmental Prediction-National Center for ature changes because ablation is mostly dom- Atmospheric Research) is compared with the inated by melting. These characteristics of the observed glacier area changes. NCEP-NCAR ablation process define somewhat the different reanalysis data corresponds to monthly mean sensitivity of glaciers located at the same latitudes values at the pressure level close to the altitude in the Andes in response to orographic effects. of each glacier area (Table 1). The annual mean Changes in temperature have a double influ- and anomalies estimations have been calculated ence on glacier mass balance: first, they affect the with respect to the 1977–2006 mean. amount of energy available for the melting pro- cess; and second, the air temperature determines General overview of Chilean glaciers, whether precipitation falls as snow or rain, defining the amount of accumulation during the climate, and climate changes hydrological year. However, the effect of changes in air temperature depends on the 0○ C isotherm The water cadastre (Dirección General de position, since an increase in air temperature will Aguas) of the public works ministry (DGA not affect the mass balance of a glacier until the 2013) of Chile is the governmental institution in freezing line reaches the elevation of that glacier. 2 CLIMATE CHANGE AND LAND ICE Marancelos and Tronquitos glaciers Marmolejo and San José volcanoes Sierra Velluda Tolhuaca volcano Michinmahuida volcano Los Moscos and Narváez Norte glaciers Campo de Hielo Sur Cordillera Darwin Figure 1 Location map of selected glaciers. 3 CLIMATE CHANGE AND LAND ICE Table 1 Glacier areas. Glacier areas Region Glacier type Area changes Mean altitude Studied Total % of (number of studied Initial Final (m asl) period area change glaciers per area) (km2) (km2) Maranceles and Northern Mountain 15.9 9.4 5263 1985–2013 −41 Tronquitos (7) Chile Volcán Marmolejo Central Chile Ice-capped 22.3 21.1 4653 1986–2013 −5 and San José (5) volcanoes Sierra Velluda (8) Chilean Lake Mountain 19.0 11.4 2666 1985–2014 −40 District Volcán Tolhuaca (3) Chilean Lake Ice-capped 3.1 1.5 2424 1985–2014 −50 District volcano Volcán Michinmahuida Northern Ice-capped 39.7 36.2 1758 1985–2013 −9 (4) Patagonia volcano Los Moscos and Central Valley 21.5 18.9 1483 1985–2014 −12 Narváez Norte (3) Patagonia Torres del Paine (5) Southern Freshwater 423.1 380.4 1284 1986–2014 −11 Patagonia calving Cordillera Darwin (6) Tierra del Tidewater 129.9 118.6 1044 1986–2014 −10 Fuego calving For instance, in northern Chile, where glaciers over the Andean slope (Falvey and Garreaud are far above the 0○ C isotherm, an increase or 2009). In southern Chile (38○ Sto48○ S), tem- decrease in temperature probably would have a perature trends over land are weak and do not scarce effect on the mass balance; by comparison, show a clear identifiable spatial pattern (Falvey a change in precipitation is likely to strongly and Garreaud 2009). By comparison, in the affect the net mass balance of such glaciers. Chilean Lake District (38–42○ S) the surface tem- perature trend exhibits a cooling in the second half of the twentieth century; nevertheless, in Recent climate change in Chile the middle to upper troposphere, radiosonde Several studies indicate that air temperatures in data from Puerto Montt show a warming trend Chile have warmed in recent decades. How- between 0.019○ Ca−1 and 0.031○ Ca−1 (Bown ever, the spatial pattern of these temperature and Rivera 2007). This warming is demonstrated changes exhibits a considerable variability. bytheincreaseofthe0○ C isotherm elevation in In situ radiosonde and satellite information central Chile, both in summer (200 ± 6m)and from 1979 onwards indicates a marked cooling in winter (122 ± 8 m) (Carrasco, Casassa, and (−0.20○ C/decade) along the coast of north- Quintana 2005). All these observed data suggest central Chile between 17○ Sand37○ S, and a that mid-troposphere warming is the main cause marked warming (0.25○ C/decade) inland and of glacier retreat along the Chilean Andes. 4 CLIMATE CHANGE AND LAND ICE In Chile, precipitation trend changes are altitude from 4800 to almost 5800 m asl. These clearer south of 30○ S. For instance, Quintana mountain glaciers have suffered important areal and Aceituno (2012) detected a negative trend reductions, with a total loss of 41% since 1985. in annual precipitation between 30○ Sand43○ S from the beginning of the twentieth century.