Above it was shown that the Tibet-Plateau contributes to stabilizing global climate. Glaciated it serves as stabilizer for glacial conditions; non-glaciated the low albedo together with the high, close to the solar-constant, insolation, prevents a glaciation. Large volcanic eruptions can cause the global climate to react accordingly. Following the eruptions of Laki in Iceland around 1783 the next year was in Europe known as the "year without summer".
If short-term extreme conditions lead to a permanent snow-cover of the Tibet-Plateau, it is not excluded that this snow-cover contributes to stabilizing these conditions.
At present the Tibet-Plateau is not glaciated. It contributes thus to stabilizing the non-glaciated state.
The following lines focus on the duration of potential future warmer climates.
As has been discussed, Tibet's uplift above the snowline will continue as long as the plate-tectonic boundary conditions and isostatic uplift are not overcompensated by the erosion of the plateau. Due to the minor relief energy on the high plateau, the fluvial erosion during interglacial periods and the glacial denudation during high glacial periods is very insignificant. For this reason, the insignificant erosion, the level of the high plateau will exceed 5000 m in average for several hundred ka. The center will exceed an altitude of 54005600 m.
Conservatively calculated, at present an uplift of 400 m would be necessary to reach altitudes that permit a permanent snow-cover. This corresponds to a cooling of ca. 2.4°C at a gradient of 0.6°C per 100 m of uplift measured in High Asia (Kuhle 1994). At the current uplift velocity of 12 mm/a (Hsu et al. 1998) the surface of Tibet needs ca. 33 ka to reach 5400-5600 m asl..
The predicted time interval to trigger an ice age may be delayed by an unforseeable global warming. A future warming of the atmosphere by 1°C requires an additional uplift by 160 m up to 5160, i.e. 5560-5760 m. At the assumed constant uplift velocity, about 13.35 (13.333) ka would be necessary to reach this altitude. Accordingly, the next Quaternary High Glacial would start ca. 46.35 ka from today, i.e. delayed by 13.35 ka.
These predictions apply to the impact of the Tibet-Plateau on global climate. If other parameters change, different time-scales apply. Such parameters are for example the deep ocean circulation or the formation of pronounced latitudinal temperature gradients. In case such changes will not be observed the Tibet-Plateau is expected to contribute to stabilizing the current climate in its non-glaciated state.
The author thanks PD. Dr. Peter Paul Smolka for a very careful review of the manuscript.
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