Impact of ELA Depressions on Global Climate

The high altitude of the Tibet Plaeau implies that a large area can get glaciated with a low amount of ELA depression. About 70% of incoming solar radiation is then reflected into space after an ELA depression of 500 m. This supports further cooling. If the radiation-deficit equivalates a further temperature drop a cooling of 1-1.5°C can be inferred (Kuhle 1989, p.279). This implies that an initial temperature drop of 3.5°C based on orbital parameters might be amplified by further 1-1.5°C through the Tibet Plateau. For warm times the reverse magnitude applies.

An ELA depression on the Tibet-Plateau may or may not have counterparts in other regions of the world. If - which needs to be tested - various regions on earth are coupled such that an ELA depression in one region might, with or without a time-lag, appear in other regions as well, then respective ELA depressions in other regions, such as Scandinavia, might be expected as a consequence. There an ELA depression of 500-700m implies the coverage of a large region with ice and a subsequent further feedback through backscattered radiation. This is outlined in Kuhle 1998 Fig.25. If the link between various continents is not that close the glaciation of the Tibet-Plateau is one of several important factors that contributed to glacials/interglacials. This needs to be tested quantitatively by future long transient coupled GCM runs.

The earliest time for additional amplifications of glaciations through the Tibet-Plateau is due to the necessary uplift during the late Neogene.

In this context attention ought to be drawn to the fact that a 1000 to over 2000 m thick burden of inland ice has existed. The Vostok ice-core shows that Pleistocene interglacials have been characterized by temperatures between 2.5 and 3.5 C above pre-industrial values. As today the Tibet-Plateau is generally unglaciated it is inferred that during Pleistocene interglacials it was ice-free as well. Consequently the isostatic depression during glacials was replaced by isostatic uplift during the short times of Pleistocene interglacials. Whether during these short warm times the Tibet-Plateau was able to uplift considerable amounts (viscosity of the mantle) or whether it factually remained generally depressed needs to be tested. If during Pleistocene warm times it uplifted only slightly then since the Holocene considerable uplift can be expected.

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