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| Titel |
Strong Alpine glacier melt in the 1940s due to enhanced solar radiation |
| VerfasserIn |
Matthias Huss, Martin Funk, Atsumu Ohmura |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034133
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| Zusammenfassung |
| Changes in climatic forcing are directly reflected by the mass budget of snow and ice
surfaces. Observed strong glacier wastage throughout the 20th century was mainly attributed
to changes in air temperature. However, changes in solar radiation at the earth’s surface were
rarely considered to explain cryospheric variability on decadal time scales. This is due to the
scarcity of both long-term radiation measurements and unbiased time series of snow and ice
melt.
We present a 94-year time series of annual glacier melt rates at four high elevation sites in
the Swiss Alps derived from the longest direct observations of glacier surface mass
balance worldwide. Since 1914 winter snow accumulation and summer ablation
were observed almost every year at two sites on Claridenfirn, and one site each on
Aletschgletscher and Silvrettagletscher located at elevations between 2700 and
3350 m a.s.l. Using a statistical model the field data are homogenized and the mass balance
components – accumulation and melt – are separated. Records of global solar radiation
since the late 1930s are available for the inner Alpine station at Davos. It could
be shown that the time series is spatially representative for the Alpine mountain
range.
Melting conditions have undergone strong temporal variations throughout the last century.
Snow and ice melt at the four high elevation sites was stronger by 4% in the 1940s compared
to the last decade. This is intriguing because air temperatures during the 20th century never
were as high as today. The radiation time series reflects the tendency towards a dimming of
global radiation between 1950 and 1980 and brightening during the last two decades, both
recognizable on a global scale and related to the aerosol content of the atmosphere. Maximal
global radiation was recorded during the 1940s. Summer (JJA) radiation was 8% above the
long-term average and 18 W m-2 higher than over the last decade. The positive
summer radiation anomalies between 1940 and 1960 provide evidence that the
extreme glacier melt rates in the 1940s were favored by above average incoming
global radiation and only to a lesser extent by high air temperatures. Between 1960
and 1980 high cloudiness, low global radiation and low air temperatures in the
European Alps are in line with strongly reduced melt rates, resulting in a short
period of balanced mass budget of alpine glaciers. The data set also indicates a
prolongation of the melting season at high elevations by almost one month since the 1970s.
Simultaneously, the calculated fraction of snowfall relative to the total annual precipitation
has decreased by 12% on average at the study sites. These processes have the potential to
considerably accelerate future glacier wastage, have strong impacts on the hydrological
cycle and could offset the effect of currently lower global radiation compared to the
1940s.
We provide evidence that the extraordinary melt rates in the 1940s can be attributed to
enhanced global radiation in summertime. Models for past and future glacier changes should
take into account the effect of decadal variations in radiation at the earth’s surface as
they significantly alter the relationship between glacier melt and air temperature. |
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