New results from climate research using ice cores
8 January 2009
A 139m long ice core drilled in the Siberian Altai has now provided new findings in climate research. Oxygen isotopes in the ice were used to reconstruct the temperatures in the Altai over the past 750 years. The scientists discovered a strong link between regional temperatures and the solar activity in the period 1250-1850, concluding that the sun was an important driver of preindustrial temperature changes in the Altai.
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The observation that the reconstructed temperatures followed the solar forcing with a delay of 10 to 30 years is particularly interesting. The strong rise in temperature in the Altai since 1850 can not be explained by solar activity changes, but rather by the increased concentration of the greenhouse gas CO2 in the atmosphere. The Swiss-Russian project was carried out under the leadership of the Paul Scherrer Institute (PSI). Eawag scientists analyzed the cosmogenic radio-nuclide 10Be from polar ice cores |
The Altai mountains lie on the border between Russia,
Kazakhstan, Mongolia, and China, in a region with a particularly pronounced
continental climate. In 2001, an international research team under the
leadership of Margit Schwikowski (PSI) drilled a 139 m-long ice core at the
Belukha glacier, near the highest mountain of the Altai. Following extensive
work in the laboratory, this core has now revealed its secrets.
Ice core acting as a thermometer
The ice core was cut into 3600 samples at -20°C in the PSI’s cold room, and
the 16O and 18O oxygen isotope content determined with an isotope mass
spectrometer. It was demonstrated that the behaviour of the stable oxygen
isotope ratio has closely followed the record of the temperature measured at a
nearby weather station over the past 130 years. This parameter can therefore be
used as a measure for temperature in the past. The deepest sample was dated to
the year 1250, which means that the ice core contains climate information
covering the past 750 years.
Solar activity influences temperature
The total solar irradiance is not a constant factor. It fluctuates
periodically around a value of 1365 watts per square metre. The best-known
cycle has an average duration of 11 years. It has only been possible to measure
solar activity directly since 1978, but the number of sun spots – a measure of
solar activity – has been observed through telescopes from as far back as the
year 1610. Information about the solar activity before that time can be
provided by other indirect methods: analysis of the cosmogenic radio-nuclides
10Be from polar ice cores, and 14C from tree rings, which are also dependent on
solar activity. In the period between 1250 and 1850, the regional temperatures
in the Altai showed a high correlation with the reconstructed solar activity. This
indicates that the changes in solar activity during this time were a main
driver of temperature changes.
The temperature follows the sun
Interestingly, the regional temperatures followed the solar forcing with a
time lag of 10 to 30 years. The PSI researchers’ study is the first in which
such a delay has been observed over a period of more than 500 years. Since the
influence of solar activity on climate has not yet been fully resolved, such
observations provide an important contribution to its understanding. One
possible mechanism discussed by various authors, which might explain this
average lag of 20 years, is the indirect effect of the sun on temperature
changes involving ocean-induced changes in atmospheric circulation. Ocean water
warms up to a higher level in places where the solar radiation is most
powerful, i.e. in the sub-tropics and the tropics. The heat energy is carried
from the lower to the higher latitudes by the ocean, then released back into
the atmosphere. Because of the high thermal capacity of the oceans and the
variable velocities of their currents, these processes are subject to
considerable delay. Changes in the North Atlantic atmospheric circulation
system, which is responsible for temperature changes in the Altai, may be
initiated 20 years earlier by changes of solar radiation in the tropical
oceans.
Strong temperature increase in the 20th century can not be explained by the sun
“Our study distinguishes between the pre-industrial era (1250-1850) and the
period covered by the past 150 years”, emphasises Anja Eichler, scientist at
the PSI. “While changes in the solar activity were a main driver of temperature
variations in the pre-industrial period, the temperatures in the Altai have
shown a much higher rate of increase than that of solar activity during the
past 150 years. The strong increase in the industrial period, however,
correlates with the increase in the concentration of the greenhouse gas CO2
over this time. The results of our regional study indicate that changes in
solar activity explain less than half of the increase in temperature in the
Altai since 1850. This agrees with global studies, based on reconstructed
northern hemispheric temperatures”, says the researcher.
This work was undertaken in a collaborative project between the Paul Scherrer
Institute and the Eawag, the Oeschger Centre for Climate Change Research, and
the Department of Chemistry and Biochemistry at the University of Bern,
together with the Institute for Water and Environmental Problems at Barnaul
(Russia).
Original publication: A. Eichler, S. Olivier, K. Henderson, A. Laube, J.
Beer, T. Papina, H.W. Gäggeler, and M. Schwikowski, Temperature response in the
Altai region lags solar forcing, Geophysical Research Letters,
doi:10.1029/2008GL035930.