Geoscience Reference
In-Depth Information
Great Basin
Mojave/Sonoran
Gobi
Kara
Kum
Taklimakan
30 o
Iranian
Thar
Sahara
Arabian
0 o
Sechura
Atacama
Namib
Kalahari
Western Australia
Central
Australia
30 o
Patagonia
Hyperarid
Arid
Semiarid
Dry subhumid
120 o
90 o
60 o
30 o
0 o
30 o
60 o
90 o
120 o
150 o
180 o
Figure 1.1. Distribution of deserts and their semi-arid and dry subhumid margins.
(Adapted from UNEP, 1997 , fig. 6.)
aridity, given that they are the results of weathering and erosion processes that are
seldom active today. These observations invite us to ask when and why the deserts
were once green and why are they no longer able to support much life. A further
question is: How might they respond to future change?
Against this background, this volume has three main aims. One is to examine
critically the various lines of evidence from geology, biology and archaeology that
have been used to reconstruct climatic change within the hyper-arid, arid and semi-arid
lands that presently occupy more than one-third of the land area of the globe. If we
include the dry subhumid regions, that proportion increases to nearly one-half of the
land area (see Figure 1.1 ). We also discuss both the Arctic - a region associated with
globally important changes in ocean circulation initiated in the North Atlantic - and
Antarctica - the largest and driest of our cold deserts - because Antarctica has long
exerted a powerful influence on the global climate. The second aim, which follows
logically from the first, is to trace systematically the climatic history of the deserts
from the inception of Cenozoic aridity through the fluctuations of the Quaternary until
the droughts and floods of the present day. (The Cenozoic covers the last 65 million
years of geological time, with the final 2.6 million years being termed the Quaternary.)
Our last aim is inherently more speculative, but nevertheless worthwhile, because it
seeks to use the insights from our study of past events to envisage how human societies
are likely to interact with possible future climatic changes in the desert world.
This introductory chapter enlarges on these aims, defines what is meant by a desert,
outlines the approach adopted in this work, discusses briefly the scope and limitations
 
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