Changing Glaciers and Hydrology in Asia - Environmental Health at ...

SECTION 2GLACIERS AND HYDROLOGIC CHANGES/IMPACTSThe high mountains of Asia were a “white spot” in the Intergovernmental Panel on ClimateChange’s (IPCC’s) 2007 Assessment Report—meaning that little to no data existed. Therefore,before developing programmatic approaches for addressing possible impacts of glacier melt, asummary of existing scientific knowledge was required. This section describes the state ofknowledge about glacier melt in the heavily glaciated areas of the Himalayan region, including thevarious ways to measure glacier health, glacier dynamics, and current studies of the potentialimpacts of accelerated glacier melt.The main conclusion of this assessment is that scientific studies and evidence are currentlyinadequate to assess how much melt is occurring across High Asia and what the rates of changeare under various conditions. Different studies show the retreat of some glacier termini, loss ofmass in some areas, and a few indications that excess melt (that is, more melting thanaccumulation) is not occurring in some areas. However, the data and studies in High Asia arenot extensive enough to provide a general assessment or projections of impacts. The lack ofdata should not encourage complacency but presents a critical risk in effective preparations foradaptation to climate change.2.1 BACKGROUNDGlacier retreat did not start with recent climate change, but with the more gradual climatewarming since the Little Ice Age (LIA), which occurred from approximately 1650 to 1850(Oerlemans 2005). Throughout the world, including the Himalaya, evidence left by glaciermoraines shows the maximum extent of these glaciers during the LIA and quantifies the fact thatglaciers have been retreating since this period in response to a warmer climate.What is new is the clear evidence of the accelerated pace of that change in recent decades(Zemp et al. 2008). Many glaciers all over the world are retreating—but differences exist, mostnotably because of different elevations. Glacier systems at the highest elevations, 4,000-7,000meters (m), have not responded to recent climate warming in the same way as glaciers thatextend to lower elevations, simply because glaciers at higher elevations remain below freezingduring much of the year, even in the presence of a warmer climate. Therefore, although glaciersare retreating both in the European Alps and in the Himalaya, one cannot always make directcomparisons and extrapolations from the well-studied lower elevation glaciers to the morepoorly observed higher elevations of the Himalaya.2.2 MEASUREMENTS OF GLACIER TERMINUS FLUCTUATIONSPerhaps the simplest method to monitor mountain glacier change is by recording the annuallocation of the glacier terminus—the location at which the glacier extends furthest down valley.Abundant terminus histories are available from several regions of the world, Europe inparticular. Comparative pictures show rapid retreat of some glaciers. But terminusmeasurements are misleading in the following ways:13