Updated estimates of glacier volume changes in the western Chugach Mountains, Alaska, and a comparison of regional extrapolation methods

We used airborne altimetry measurements to determine the volume changes of 23 glaciers in the western Chugach Mountains, Alaska, United States, between 1950/ 1957 and 2001/ 2004. Average net balance rates ranged between - 3.1 to 0.16 m yr(-1) for the tidewater and - 1.5 to -0.02 m yr(-1) for the nontidewater glaciers. We tested several methods for extrapolating these measurements to all the glaciers of the western Chugach Mountains using a process similar to cross validation. Predictions of individual glacier changes appear to be difficult, probably because of the effects of glacier dynamics, which on long ( multidecadal) timescales, complicates the response of glaciers to climate. In contrast, estimates of regional contributions to rising sea level were similar for different methods, mainly because the large glaciers, whose changes dominated the regional total, were among those measured. For instance, the above sea level net balance rate of Columbia glacier ( - 3.1 +/- 0.08 km(3) yr(-1) water equivalent ( weq) or an equivalent rise in sea level ( SLE) of 0.0090 +/- 0.0002 mm yr(-1)) was nearly half of the total regional net balance rate of the western Chugach Mountain glaciers ( -7.4 +/- 1.1 km(3) yr(-1) weq or 0.020 +/- 0.003 mm yr(-1) SLE between 1950/ 1957 and 2001/ 2004). Columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate. Tidewater glaciers should therefore be treated separately when performing regional extrapolations.