Secular glacier mass balances derived from cumulative glacier length changes M. Hoelzle a,b, * , W. Haeberli a , M. Dischl a , W. Peschke b a Department of Geography, Glaciology and Geomorphodynamics Group, University of Zurich, Winterthurerstr. 190, CH-8057 Zurich, Switzerland b Laboratory of Hydraulics, Hydrology and Glaciology, Federal Institute of Technology, Gloriastr. 37/39, CH-8092 Zurich, Switzerland Received 5 April 2002; accepted 17 September 2002 Abstract Glacier mass changes are considered to represent natural key variables with respect to strategies for early detection of enhanced greenhouse effects on climate. The main problem, however, with interpreting worldwide glacier mass balance evolution concerns the question of representativity. One important key to deal with such uncertainties and to assess the spatio- temporal representativity of the few available measurements is the long-term change in cumulative glacier length. The mean specific mass balance determined from glacier length change data since 1900 shows considerable regional variability but centers around a mean value of about  0.25 m year  1 water equivalent. D 2003 Elsevier Science B.V. All rights reserved. Keywords: Glacier fluctuations; Glacier length changes; Glacier mass changes; Climate change 1. Introduction Observation of worldwide glacier changes as com- piled by the World Glacier Monitoring Service (WGMS) are presently being built into Global Climate Observing Systems (GCOS, WMO, 1997; Haeberli et al., 2000). Especially glacier mass changes are consid- ered to represent natural key variables with respect to strategies for early detection of enhanced greenhouse effects on climate (Kuhn, 1980; Haeberli et al., 1999). The latent heat required to cause the measured glacier wastage can be compared with the estimated excess radiation income and with changes in sensible heat as calculated by numerical climate models. Several attempts have recently been undertaken to regionally or globally summarize the available data using various approaches such as area-weighting with glacier inven- tory data, spatial interpolation based on global ice extent and correlations between mass balance time series, comparison with integrated geometric changes as determined by laser altimetry flights and GPS surveys on selected flowlines, or cumulative length changes as combined with glacier inventory data (Cog- ley and Adams, 1998; Dyurgerov and Meier, 1997a,b, 2000; Dyurgerov, 2002; Echelmeyer et al., 1996; Gregory and Oerlemans, 1998; IAHS, 1999; Kuhn, 0921-8181/03/$ - see front matter D 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-8181(02)00223-0 * Corresponding author. Department of Geography, Glaciology and Geomorphodynamics Group, University of Zurich, Winter- thurerstr. 190, CH-8057 Zurich, Switzerland. Tel.: +41-16355139; fax: +41-16356848. E-mail address: hoelzle@geo.unizh.ch (M. Hoelzle). www.elsevier.com/locate/gloplacha Global and Planetary Change 36 (2003) 295 – 306