Reconciling melting glaciers and falling temperatures in the
By Lykke E. Andersen*,
Bolivia’s rapidly diminishing
Chacaltaya glacier has been widely used as a symbol of
Anthropogenic Global Warming (1).
However, it is an unfortunate choice of symbol, because the
retreat of this specific glacier is demonstrably not due
to increasing temperatures caused by CO2 emissions.
Figure 1: Retreat of the
Chacaltaya glacier, Bolivia, 1940 – 2005.
Source: IPCC Working Group II
Fourth Assessment Report 2007, Figure 1.1.
monthly temperature series for the Bolivian highlands, including
the La Paz/El Alto station, which is located near Chacaltaya,
show cooling trends over the last six decades of about -0.2ºC/decade
(2). This is confirmed by more recent
daily temperature anomalies from the University of Dayton Daily
Temperature Archive since 1995 (see Figure 2). There is a
statistically significant negative trend of -0.11ºC/decade since
1/1/1995 (98% confidence). The average anomaly for the 1995-2009
period is -0.6ºC, suggesting that the recent negative trend is a
continuation of a longer trend, as suggested by the monthly
Daily temperature anomalies for La Paz/El Alto, 1 January 1995 –
12 March 2009
Source: Author’s elaboration based on data from the University
of Dayton Daily Temperature Archive (http://www.engr.udayton.edu/weather/).
Note: Green is summer temperature anomalies and blue is winter
temperature anomalies. The black slightly downward sloping line
is the linear trend.
negative temperature trends in the Bolivian highlands beg two
1. How can the
falling temperatures in the Bolivian highlands be reconciled
with the visibly diminishing glaciers?
2. Why are
temperatures falling, when they are supposed to be increasing?
The answers to
these questions are quite complex and involve many different
First, it is
important to understand that changes in glaciers do not only
depend on temperatures, but also on precipitation, cloud cover,
relative humidity and the intensity of solar irradiation. And in
the case of temperatures, summer temperatures (rainy season) are
more important than winter temperatures (dry season), and
daytime temperatures are more important than night time
In Figure 2
above, we see that winter temperatures have fallen more strongly
than summer temperatures (the average winter anomaly is -0.9ºC
while average summer anomaly is -0.4ºC). Since winter is the dry
season in this region, colder winter temperatures will have
little effect on the glaciers because temperatures are already
well below freezing. In contrast, warmer summer temperatures can
have a dramatic effect. It was the unusually hot and dry summer
of 1998 (the Mega-El Niño) which caused the permanent closing of
the Chacaltaya ski-resort, and the four consecutive warm summers
of 2002, 2003, 2004 and 2005 almost completely eliminated the
meteorologist from the Hadley Climate Research Centre suggested
to me that the likely explanation for the observed decrease in
temperatures in the Bolivian highlands is a decrease in low
level clouds. With fewer low level clouds, night time
temperatures would tend to fall substantially (due to increased
outgoing infra-red radiation), which would pull down average
temperatures. During the day, fewer clouds would have a positive
effect on temperatures, increase solar irradiation reaching the
ice, and decrease air humidity and precipitation, all of which
would contribute to speed up melting, despite stronger night
I could not
find specific data on cloud cover in the Bolivian highlands, but
worldwide low level cloud cover has clearly decreased since
about 1987 (see Figure 3). According to NASA/GISS the decrease
is particularly strong in the tropics, including Bolivia
(3), so the meteorologist’s hunch is
likely to be correct.
Global low level cloud cover, 1983-2007
http://www.climate4you.com/. (Look under the topic: “Climate
The decrease in cloud cover is
related to decreases in precipitation, which has had a large
influence on the fate of the Chacaltaya glacier. The increase in
the glacier regression rate since the end of the 1970s appears
to coincide with the Great Pacific Shift of 1976, after which
precipitation has decreased systematically, both according to
direct measurements at the La Paz/El Alto station, and according
to precipitation proxy series generated from ice cores from two
other Bolivian glaciers (4).
If the rapid melting of
Chacaltaya since the mid 1970s were caused by increasing
temperatures due to increased CO2 in the atmosphere,
we would have observed increased night time temperatures,
increased average temperatures, and increases in cloud cover and
precipitation (that is what CO2 driven climate models
would suggest). But instead we have observed decreasing cloud
cover, decreasing average temperatures (likely the result of
night time temperatures falling more than day time temperatures
increased), and decreasing precipitation, all of which conspired
to melt the glacier.
The observed evidence from
Chacaltaya is thus inconsistent with the Anthropogenic
Greenhouse Warming (AGW) theory, or, at least, if there is an
AGW signal, it is completely drowned by other climatic changes
unrelated to AGW.
It is ironic that the melting
Chacaltaya glacier has become such an important symbol of the
AGW theory, when in fact the evidence from Chacaltaya seems to
refute this theory. (In contrast, the evidence from Chacaltaya
is fully consistent with Svensmark’s cosmic ray theory
(5), but that is another story).
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(*) Director, Institute for Advanced Development Studies, La
Paz, Bolivia. The author happily receives comments at the
Figure 1 of this newsletter is a
reproduction of Figure 1.1 of the IPCC Fourth Assessment Report
from Working Group 2. It has been reproduced countless times
before in climate change studies and presentations all over the
According to the NCDC Monthly
Climatic Data for the World Data Base, which starts in 1948 (http://www7.ncdc.noaa.gov/IPS/mcdw/mcdw.html).
For NASA cloud data, see:
See Hoffmann, G., E. Ramirez, J. D.
Taupin, B. Francou, P. Ribstein, R. Delmas, H. Dürr, R. Gallaire,
J. Simões, U. Schotterer, M. Stievenard & M. Werner (2003)
“Coherent isotope history of Andean ice cores over the last
century.” Geophysical Research Letters, 30(4):
See Svensmark, H. & N. Calder (2007)
The Chilling Stars: The New Theory of Climate Change.
Institute for Advanced Development Studies 2009.
The opinions expressed in this Newsletter are those of the
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