cc: Jonathan Overpeck ,Eystein Jansen date: Mon Aug 14 10:24:19 2006 from: Keith Briffa subject: Re: Oerlemans in IPCC to: olgasolomina@yandex.ru Olga thanks for this - I suggest we simply remove the last sentence only from our section (6-30-43-55) "In southern Norway,.......temperatures (Nesje and Dahl, 2003)." The rest is consistent but not repetitive , with our discussion relating to the temperature interpretation only. Cheers Keith At 06:04 14/08/2006, olgasolomina wrote: Dear Georg and Keith, We discuss Oerlemans paper two times in Ch 6 and Ch 4. I copied here the sections from both chapters. I guess you have to decide what to keep and where. I also copied a paragraph from ch6 concerning the glacier retreat Georg might be interested to see it. We decided to write Little Ice Age and Medieval Warm Period in quotes. Shall we correct it now? This should be consistent though the whole Assessment we probably have to draw attention of TSU to this point. Cheers, olga From SOD ch 4 4-14-2-12 4.5.2. Large and Global Scale Analyses Records of glacier length changes go far back in time (written reports as far back as 1600 in a few cases) and are directly related to low-frequency climate change. From 169 glacier-length records, Oerlemans (2005) has compiled mean length variations of glacier tongues for large scale regions from 1700 to 2000 (Figure 4.5.1). Although much local to regional and high-frequency variability is superimposed, the smoothed series give an apparently homogeneous signal. General retreat of glacier termini started after 1800, with considerable mean retreat rates in all regions after 1850 lasting throughout the 20th century. A slowdown of retreats between about 1970 and 1990 is more evident in the raw data. Retreats were again generally rapid in the 1990s; the Atlantic and the Southern Hemisphere curves reflect precipitation driven advances of glaciers in Western Scandinavia and New Zealand (Chinn et al., 2005). 4-18-32-41 The surface mass balance of snow and ice is determined by a complex interaction of energy fluxes toward and away from the surface, and the occurrence of solid precipitation. Nevertheless, glacier fluctuations show a strong statistical correlation with air temperature at least on a large spatial scale throughout the 20th century (Greene, 2005), and a strong physical basis exists to explain why warming would cause mass loss. Changes in snow accumulation also matter, and may dominate in response to strong circulation changes or when temperature is not changing greatly. For example, analyses of glacier mass balances, volume changes, length variations and homogenized temperature records for the western portion of the European Alps (Vincent et al., 2005) clearly indicate the role of precipitation changes in glacier variations in the 18th and 19th centuries. Similarly, Nesje and Dahl (2003) explained glacier advances in southern Norway in the early 18th century based on increased winter precipitation rather than cold temperatures. FROM TOD ch 6 6-30-43-55 Oerlemans (2005) constructed a temperature history for the globe based on 169 glacier-length records. He used simplified glacier dynamics that incorporate specific response time and climate sensitivity estimates for each glacier. The reconstruction suggests that moderate global warming occurred after the middle of the 19th century, with about 0.6°C warming by the middle of the 20th century. Following a 25-year cooling, temperatures rose again after 1970, though much regional and high-frequency variability is superimposed on this overall interpretation. However, this approach does not allow for changing glacier sensitivity over time, which may limit the information before 1900. For example, analyses of glacier mass balances, volume changes, and length variations along with temperature records in the western European Alps (Vincent et al., 2005) indicate that between 1760 and 1830, glacier advance was driven by precipitation that was 25% above the 20th century average, while there was little difference in average temperatures. Glacier retreat after 1830 was related to reduced winter precipitation and the influence of summer warming only became effective at the beginning of the 20th century. In southern Norway, early 18th century glacier advances can be attributed to increased winter precipitation rather than cold temperatures (Nesje and Dahl, 2003). I also copy here a paragraph from ch 6 that you might want to take into account. FROM TOD ch 6 6-32-40-48 Stable isotope data from high-elevation ice cores provide long records and have been interpreted in terms of past temperature variability (Thompson, 2000), but recent calibration and modelling studies, in South America and southern Tibet (Hoffmann et al., 2003; Vuille and Werner, 2005; Vuille et al., 2005), indicate a dominant sensitivity to precipitation changes, at least on seasonal to decadal timescales, in these regions. Very rapid and apparently unprecedented melting of tropical ice caps has been observed in recent decades (Thompson et al., 2000; Thompson, 2001) (see Box 6.3), likely associated with enhanced warming at high elevations (Gaffen et al., 2000), but other factors besides temperature can strongly influence tropical glacier mass balance (see Chapter 4). -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [1]http://www.cru.uea.ac.uk/cru/people/briffa/