THE FORMER GLACIATION OF HIGH- AND CENTRAL ASIA AND ITS CLIMATIC IMPACT.- COMMENTS ON THE INQUA-COG-GLACIATION MAP 1:1 MIO

During 33 campaigns the Ice Age glaciation of High- and Central Asia has been reconstructed on the basis of glacigenic forms. Since the INQUA-congress 1999 5 new areas in the Karakorum, Himalaya and Tibet (Xuebao) have been investigated. Sedimentological analyses and flank polishings prove a 2800 m-thick Karakorum icestream network. This is remarkable for mountains which today are semi-arid. The new Glaciation Map (44 sheets) compiles the data obtained since 1973. Data were gathered from the Zagros in the W to the Minya Konka and from the Himalaya to the Sajan in the N.

Absolute datings classify this glaciation as stage 4-2. Radiation balance measurements up to 6650 m asl indicate highest radiation energies on the Plateau, making Tibet today's most important heating surface. At glacial times 70% of the energies were reflected into space by the 2.4 million km²-glacier area, which thus has brought about 32% of the entire global cooling. About 2.5 Ma ago, when Tibet was lifted above the snow line and glaciated, this cooling effect gave rise to the global depression of the snow line and the first Ice Age. The interglacials are explained by the glacio-isostatic lowering of Tibet by 650 m with the effect that the Tibet ice, which had evoked the build- up of the lowland ices, could melt away in a period of positive radiation anomalies. The next Ice Age begins, when the Plateau has again reached the snow line (glacial-isostatic reverse uplift). This explains, why the orbital variations could only have a modifying effect on the Quaternary climate, but were not primarily time-giving: as long as Tibet does not glaciate, the temperature depression is not sufficient for initiating a worldwide Ice Age; if Tibet is glaciated, but not yet lowered isostatically, a warming-up by 4°C causes an important loss in surface but no deglaciation, so that its cooling effect remains in a maximum intensity. Only a glaciation of the Plateau lowered by isostasy can be removed through a warming phase, so that interglacial climate conditions are prevailing until a renewed uplift of Tibet sets in up to the altitude of glaciation.