Thursday, December 29, 2011

1440.txt

cc: Jonathan Overpeck <jtoatXYZxyzrizona.edu>,Eystein Jansen <Eystein.JansenatXYZxyz.uib.no>
date: Mon Aug 14 10:24:19 2006
from: Keith Briffa <k.briffaatXYZxyz.ac.uk>
subject: Re: Oerlemans in IPCC
to: olgasolominaatXYZxyzdex.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/

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