Geoscience Reference
In-Depth Information
19
Asian deserts
Let us admit at once that we do not know what are the basic causes of
climatic change.
Richard Foster Flint (1901-1976)
Glacial and Quaternary Geology
(1971, p. 789)
19.1 Introduction
This chapter draws together the disparate strands of evidence relating to climate change
discussed in the earlier specialist chapters and seeks to provide a more integrated
overviewof the Cenozoic climatic history of the Asian deserts. The type of evidence on
which this reconstruction is based includes desert dunes, desert dust and loess deposits,
river and lake sediments and associated fossils, glacial deposits, soils, speleothems,
marine sediments and stable isotope geochemistry. The late Quaternary environments
receive most attention, because they are dated and documented in greater detail than
earlier times. The record of historic floods and droughts is dealt with in
Chapter 23
and
so will not be covered here.
19.2 Present-day climate and causes of aridity
Figure 1.1
(
Chapter 1
) shows the distribution of the arid, semi-arid and dry subhumid
regions of Asia as defined and mapped in the UNEP
World Atlas of Desertification
(UNEP,
1997
). To the north of these dry areas lie the cold temperate grasslands,
woodlands and permafrost regions of Siberia. To the south and east, the woodlands and
grasslands of the seasonally wet tropics give way to the rainforests of the perennially
wet tropics. In contrast to the lowland deserts of Australia, Africa and Arabia, many of
the Asian deserts are flanked by very high mountains, including many of the highest
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