South Pacific was below normal. These 
early studies also suggested a Tibet-Pa- 
cific Ocean connection with the Indian 
monsoon. The intriguing linkages did 
not stop there, however. 
Recent research indicates a correla- 
tion between higher than normal air 
pressure in Djakarta, a drier than nor- 
mal Indian monsoon, and more than 
the usual amount of rain in the equato- 
rial Pacific. Under these conditions, the 
usually strong trade winds may be di- 
minished, and the expected upwelling 
of nutrient-rich cold water off the coast 
of Peru, containing plankton on which 
anchovies feed, may be replaced by a 
warm, saline water mass. This infre- 
quent event, which tends to arrive after 
Christmas and has accordingly been 
called el nino (“the child”), kills the 
plankton and drives away the ancho- 
vies, devastating the year’s catch and 
disrupting the world market for those 
who depend on anchovies as their chief 
source of protein. (This disruption is, in 
turn, felt in other protein markets such 
as the soybean market.) 
Thus warm waters off Peru and 
along the equatorial east Pacific occur 
simultaneously with higher than nor- 
mal rainfall in the equatorial Pacific 
and drier than normal Indian monsoon 
weather. But warmer than normal Pe- 
ruvian coastal waters also seem to coin- 
cide with warmer than normal water in 
the usually cold California current, 
which flows north to south, wells up 
along the California beaches, and 
moves water southwest of Baja Califor- 
nia into the tropical Pacific. This pat- 
tern of sea-surface temperatures cor- 
relates with enhanced typhoon activity 
in the North Pacific, which as we have 
shown, tends to coincide with an abnor- 
mally weak Indian summer monsoon. 
Some of the loops and circles of the Ti- 
bet connection can in this fashion be 
seen to close. 
Still another item of more than curi- 
ous coincidence has been found. In win- 
ters with a strong el nino warming of 
the ocean off the coast of Peru, the 
stratosphere (the layer of the atmo- 
sphere directly above the troposphere) 
also warms dramatically over the polar 
regions of the Northern Hemisphere 
and the normal westerly winds in that 
atmospheric layer break up into large, 
wavy patterns. This phenomenon has 
been called sudden stratospheric warm- 
ing. Such major warming events appar- 
ently occur only in the Northern 
Hemisphere and seem to be confined to 
el nino winters when the northeastern 
Pacific also tends to be warmer than 
normal. Warm waters off the Pacific 
coasts of the United States and Canada 
tend to promote the establishment of a 
strong and persistent high-pressure 
ridge in the atmosphere over the west- 
ern seaboard and the Rocky Moun- 
tains. This atmospheric flow pattern 
has a decisive impact on the strato- 
sphere, causing the nearly circular flow 
there to break down into a wavy pattern 
of large amplitudes and further 
strengthening the tropospheric high- 
pressure ridge. Conditions in January 
1977 provided an example of the devel- 
opment of such a ridge, resulting in a 
major stratospheric flow breakdown 
and adjustment and in stratospheric 
warming over the Arctic regions, while 
the eastern United States shivered in 
the grip of arctic air. 
The foregoing discussion demon- 
strates the Tibet plateau’s far-reaching 
effect on large-scale wave patterns in 
the atmospheric airflow over the 
Northern Hemisphere. The connection 
between surface temperatures in Tibet 
and the Indian monsoon has already 
been mentioned. 
Land-surface temperature is, of 
course, dependent on the amount of 
heat energy in the form of solar radi- 
ation absorbed by the plateau. It is in- 
versely proportional to the plateau’s 
albedo, that is, the percentage of energy 
it reflects back to space. Fresh snow has 
an albedo of more than 80 percent, 
which means that only 20 percent of the 
sun’s radiation energy is available to 
melt the snow and heat the underlying 
soil. Dry sand has an albedo of 18 per- 
cent, grass-covered ground ranges be- 
tween 15 and 25 percent, green forests 
between 4 and 6 percent. A rule of 
thumb is that the darker a surface looks 
to the eye, the more radiation energy it 
absorbs, and the lower its albedo, or re- 
flectivity, becomes. 
We know that an increase in the albe- 
do of the Tibet plateau due to extensive 
snow cover tends to diminish the rain- 
fall over India several months later. In 
the past, however, some factor other 
than snow may have affected the albedo 
of Tibet. Traveling through that region 
today one cannot help but notice the 
absence of forests. The Chinese have re- 
cently planted trees in and near the vil- 
lages, but they have to be protected 
from foraging animals by mud walls. 
Everywhere one sees people and beasts 
of burden moving down the mountain- 
sides and across great distances, carry- 
ing huge loads of branches and freshly 
cut junipers for use as firewood. That 
sight raises the question of whether Ti- 
bet’s river valleys have been denuded 
over the centuries by humans in search 
of fuel. Poor soil conditions, made 
worse by erosion, are ubiquitous and 
may have been caused, at least in part, 
by deforestation. 
At present about 1.5 million people 
eke out a living in barren Tibet, but ac- 
cording to some accounts more than 10 
million people inhabited this region 
during the Middle Ages. Was the land 
barren then? If so, how did the inhabit- 
ants keep warm? It does not seem plau- 
sible that the firewood necessary to 
support a population of more than 10 
million could have been carried across 
the Himalayan passes or through the 
river gorges of southeastern Tibet, es- 
pecially since wheeled traffic was hard- 
ly known before the recent arrival of 
the Chinese. Did this large population 
engage in a massive deforestation of the 
Tibetan highlands that drastically in- 
creased the plateau’s albedo? 
The answers to these questions are 
not known, but we can guess that an in- 
crease of albedo over widespread re- 
gions, from the 4 to 6 percent typical of 
forested areas to the 15 to 25 percent of 
grassland terrain that now character- 
izes the valleys of Tibet, could have 
produced noticeable effects in the form 
of decreased summer precipitation over 
India. Because recorded history does 
not provide us with easy answers, we 
have been forced to look for them in 
computer models of the atmosphere’s 
circulation patterns. Mathematical 
models are currently being designed to 
try to establish the Tibet connection in 
the form of a system of equations that 
may be useful in forecasting monsoon 
weather over India. One of the ques- 
tions these models will test is, Would 
the climate in Pakistan, India, South- 
east Asia, and eastern China, where the 
existence of millions of people depends 
on the abundance of monsoon rains, be 
enhanced by bringing the forests back 
to Tibet? □ 
A native of Xigaze, a town almost in 
the center of Tibet, hauls hard-to-find 
juniper, freshly cut to use as fuel. 
Centuries ago, the plateau may have 
been wooded but it has long been 
denuded. To improve the fuel 
situation in Tibet, the government 
of the People's Republic of China 
has an active tree-planting program 
in the province. 
Elmar R Reiter 
70 
