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Reply to the comments of H. Slupetzky on “Mass balance of glaciers other than the ice sheets” by Cogley and Adams

Published online by Cambridge University Press:  20 January 2017

J. Graham Cogley  and
W. P. Adams
J. Graham Cogley
Affiliation:
Department of Geography, Trent University, Peterborough, Ontario K9J 7B8, Canada
W. P. Adams
Affiliation:
Department of Geography, Trent University, Peterborough, Ontario K9J 7B8, Canada
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Abstract

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Type
Correspondence
Information
Journal of Glaciology , Volume 45 , Issue 150 , 1999 , pp. 400
Copyright
Copyright © The Author(s) 1999 

Sir,

We agree with nearly all the points made by Slupetzky. However, he writes that his indirect method of estimation of the mass balance of Stubacher Sonnblickkees, based on measurements of accumulation-area ratio (AAR), is “certainly as accurate as ‘direct’ mass-balance measurements”. From information given by Reference SlupetzkySlupetzky (1991) in connection with his equations 5 and 7, the standard error of his regression of mass balance B on AAR, measured concurrently from 1964 to 1980, is ±1l8 mm a1. The total error in his indirect estimate of B is the geometric sum (Reference Cogley, Adams., Ecclestone., Jung-Rothenhäusler and Ommanney.Cogley and others, 1996) of the standard error of the regression and the standard error of B. The latter is not given by Reference SlupetzkySlupetzky (1991), but if we choose Reference Cogley and Adams.Cogley and Adams’ (1998) nominal figure of ±200 mm a−1 the total error in Slupetzky’s indirect estimate is about ±230 mm a−1 (that is, ). Here we assume no correlation between errors in B and in AAR. If these measurement errors are correlated, the error in the indirect estimate will be greater (up to ±318 mm a−1, the arithmetic sum of the errors).

In short, an indirect estimate of mass balance must in practice be less accurate than the direct measurements against which it is calibrated. Methods such as Slupetzky’s serve vital functions, for example in regional extrapolation, and we did not mean to discount such work. But the uncertainty of the direct measurements is itself a serious problem. Reference Cogley, Adams., Ecclestone., Jung-Rothenhäusler and Ommanney.Cogley and others (1996) note that, quite apart from the systematic errors which they discuss, a tenfold reduction in random errors will be needed if climatically expectable trends are to be identified in mass-balance time series. Reducing the measurement errors, for example through better control of the biases and better calibration by periodic geodetic surveys, should be a more urgent priority than enlarging the global network of balance estimates in ways which risk blurring the distinction between measurement and inference.

References

Cogley, J. G. and Adams., W. P. 1998. Mass balance of glaciers other than the ice sheets. J. Glaciol., 44(147), 315–325.CrossRefGoogle Scholar
Cogley, J. G. Adams., W. P. Ecclestone., M. A. Jung-Rothenhäusler, F. and Ommanney., C. S. L. 1996. Mass balance of White Glacier, Axel Heiberg Island, N.W.T., Canada, 1960 91. J. Glaciol., 42(142), 548–563.CrossRefGoogle Scholar
Slupetzky, H. 1991. Die Massenbilanzmessreihe vom Stubacher Sonnblickkees 1958/59 bis 1987/88: die Berechnung der Massenbilanz 1980/81 bis 1987/88 und 1958/59 bis 1962/63. Z. Gletscherkd. Glazialgeol., 25(1), 1989, 69–89.Google Scholar