terms, the creation of the himalayas and the rising
of the Tibetan plateau are extremely recent events.
The mountains originated less than four million
years ago, making them among the youngest in the
There are three distinct geographical
regions in greater Tibet.
By far the largest natural region
is the Northern Plateau, or Chang Tang, which
covers about half of Tibet's total surface area
and is delineated in the west by the great Karakoram
range, in the north by the wall of the Astin
Tagh, and in the northeast by the Nan Shan range.
The chang tang has one of the
worst climates on earth and therefore most of
the part of this region is never visited by
The second main geographical region
of Tibet, the outer plateau is a relatively
narrow strip, with the Himalayas forming the
southern boundary. It is the most populous part
of Tibet and contains almost all the major human
The outer plateau differs from
the northern plateau in several important ways.
The temperature and climate are milder, and
consequently there is a richer distribution
of flora and fauna. The area around shigatse
and the Lhasa valley are clear examples of this.
Contrary to popular images of Tibet, Lhasa has
a pleasant climate, with nearly all its rainfall
occurring in the summer. For most of the year
the weather is sunny and dry, mild during the
day from April to October, and not unbearably
cold in winter.
The other main geographical region
is the southeastern plateau, comprising only
one-tenth of the total area of Tibet and forests
are very much a characteristic of this region.