Long-term global climatic changes may also have been caused by Cenozoic plateau uplift (especially of the Himalaya-Tibetan- and the N-American plateaus), inducing a change of zonal wind and precipitation patterns and a steepening of the climatic south-north gradient (Ruddiman and Kutzbach 1992). However, uplift of the Tibetan plateau started 20 MaB.P. ago (Harrison et al. 1992; Copeland 1997). For the summer monsoon to occur, a plateau elevation of 2000-2500 m is required. This was attained around 8 Ma B.P. (Prell and Kutzbach 1992; Tiedemann et al. 1994). The winter monsoon additionally needs the albedo effect of a seasonal snow cover (Flohn 1981; Ding et al. 1995; Xiao et al. 1995). This requires plateau elevations of 4000-4300 m. Data on the onset of the summer monsoon suggest, the Tibet-Plateau began to act as a climate-effective barrier some 8 Ma ago already (Manabe and Broccoli 1985; Quade et al. 1989; Prell and Kutzbach 1992; Tiedemann et al. 1994; De Menocal 1995). This is well before the large northern hemisphere glaciations.
In addition, the monsoon chronology reveals the start of the Tibetan plateau's impact on the climate (Fig.4c).
This implies that the uplift of the Tibet Plateau is one of several co-factors for climate change. It supports boundary conditions, such as for ice-formation and melting.
Data on the existence of a Tibetan inland ice are presented in detail above. These data show that once the Tibet-Plateau reached LGP altitudes around 4600 m glaciations are possible and proven by data. At this altitude even small temperature changes, such as 2-3°C can lead to extensive ice-sheets. Other studies show that the Tibetan plateau produces similar effects on wind patterns to those observed at the present time when average elevations of 2000-2500 m are attained (Manabe and Broccoli 1985; Prell and Kutzbach 1992). Thus the above-mentioned stabilizing effect on global climate can be expected at least since the Pliocene. In non-glaciated times the Tibet-Plateau delays a glaciation; in glaciated times it delays a deglaciation.
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