Impact on the Global Energy Budget and Ice Volume

At subtropical latitudes and high altitudes, insolation levels on the Tibetan plateau are close to the solar constant (Kuhle and Jacobsen 1988). They are four times higher than in the areas formerly occupied by the Nordic ice sheets. An ice-free plateau surface absorbs 80% of incoming solar radiation, converts it into longwave radiation, and thus contributes substantially to warming the Earth's atmosphere. Our measurements have shown that snow-covered glaciers directly reflect 75-95% of insolation, which is therefore lost to the global heat budget (Kuhle and Jacobsen 1988). Calculations indicate that during the LGM as much as 32% of the albedo-induced energy loss of the Earth's atmosphere was due to the ice sheet of the Tibetan plateau (Bielefeld 1997).

As a result of the albedo of a winter snow cover at high subtropical insolation levels, the Tibetan plateau was able to influence the absolute heat balance of the Earth. The respective altitude of the Tibet-Plateau and the expansion of the Nordic ice-sheets appear to be contemporaneous. Because its elevation was lower than it is today, the plateau had only a 2550% ice cover at most, even during cold phases. Sensitivity experiments conducted by Marsiat (1994) have shown that under conditions of a reduced glaciation of Tibet the Nordic lowland glaciers also remained rudimentary. This correlates with marine S18O records according to which global ice volumes between 2.5 and 1 MaB.P. were only half those during the late Pleistocene (Shackleton et al. 1988; Morley and Dworetsky 1991; Tiedemann et al. 1994).

Glaciation of the Tibetan plateau could only reach its proven LGM extension of 2.4 million km2 when today's average elevation of at least 4600 m had been attained, i.e. from ~1 MaB.P. onwards, then inducing maximum global ice volumes.

This effect must have been a strong promoter of ice build-up on a global scale. Thus if for example an extended and/or long-term snow cover occurs today on the Tibet-Plateau it is expected to have a measurable effect on the temperatures of the region and possibly a large part of the northern hemisphere.

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