date: Thu Feb 28 14:46:03 2002 from: Keith Briffa subject: Re: review of Klok and Oerlemans to: r.braithwaite@man.ac.uk thannnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnkyou Keith At 02:39 PM 2/28/02 +0000, you wrote: Review of: DERIVING A CLIMATE HISTORY FROM A GLACIER LENGTH RECORD BY LINEAR INVERSE MODELLING Klok and Oerlemans Submitted to The Holocene The paper says (p. 3) that a "climate signal" can be extracted from a glacier length record. However, the "climate signal" is obviously a mass balance history or a reconstruction of equilibrium line altitude (ELA). This make me wonder if we are really talking about a "climate signal" or "climate history". I would expect something about temperature and precipitation here. The median elevation of a glacier (p. 3) according to Manley (1959) is not the real median. The simple methods to reconstruct ELA were never intended to consider or include response time. There are certainly more methods than listed here, e.g. see Benn and Lehmkuhl (2000). The author admits that a numerical flowline model (p. 3) would be best but says that their aim is to develop a simple "analytical" model that should be more applicable. I am not sure what they mean with "analytical". Other terminology is a problem. For example, they define "climate sensitivity" in terms of the change in glacier length with a change in the ELA, while this term is already well understood by climate modellers. Equations (1) and (2) look quite scientific but they don't really express much more than the fact that almost any phenomenon can be described by a Taylor series, truncated after the first term. I have real problems calculating time derivatives with fitted polynomials and filtered data (p. 6). On p. 7 and p. 11 they cite an non-existent publication (Oerlemans, 2001) which appears to provide important background. On p. 8, nu (a Greek letter that I can't print in my mail program) is defined as a ratio of mean glacier thickness to glacier length but is taken as zero on p. 9. How can that be? I can't help thinking that the authors make a bit of a mystery about their "analytical" model. A simple conceptual relation between glacier length change and change of ELA was proposed by Callendar (1950). As this relation includes two different glacier widths (at the snout and at the ELA) and slope at the ELA it is a reasonably sophisticated predecessor of their model. The authors should at least reference Callendar's model. The approach is interesting and certainly deserves publication in the Holocene but I don't find this a very reader-friendly paper. Pages 12-17 seem very discursive and approach is rather unsystematic. The authors should tighten up the text and even consider changes of structure. REFERENCE Benn, D. I. and F. Lehmkuhl. 2000. Mass balance and equilibrium-line altitudes of glaciers in high-mountain environments. Quaternary International 65/66, 15-29. Callendar, G. S. 1950. Note on the relation between the height of the firn line and dimensions of a glacier. Journal of Glaciology 1(8), 459-461. ***************************************** * Roger J. Braithwaite Ph.D. * Reader in Physical Geography * School of Geography * The University of Manchester * Oxford Road * Manchester M13 9PL * U.K. * Tel: 0044-161 275 3644 (direct line/answerphone) * Tel: 0044-161 275 3636 (Dept. Office/messages) * Tel: 0044-1663 745 873 (home/answerphone) * Fax: 0044-161 275 7878 * [1]http://www.art.man.ac.uk/geog/home.htm ***************************************** -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [2]http://www.cru.uea.ac.uk/cru/people/briffa[3]/