Elizabeth Barrette (ysabetwordsmith) wrote,
Elizabeth Barrette

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If India and Pakistan start a nuclear war...

... we are all screwed.

Local Nuclear War, Global Suffering
by Alan Robock and Owen Brian Toon
Scientific American
January 2010

[moderator: to view sidebars and other supplementary
material please use the link above]

Worry has focused on the U.S. versus Russia, but a
regional nuclear war between India and Pakistan could
blot out the sun, starving much of the human race

Why Believe It

Some people think that the nuclear winter theory
developed in the 1980s was discredited. And they may
therefore raise their eyebrows at our new assertion that
a regional nuclear war, like one between India and
Pakistan, could also devastate agriculture worldwide.
But the original theory was thoroughly validated. The
science behind it was supported by investigations from
the National Academy of Sciences, by studies sponsored
within the U.S. military, and by the International
Council of Scientific Unions, which included
representatives from 74 national academies of science
and other scientific bodies.

Our current work has appeared in leading peer-reviewed
journals. Still, we seem to be the only ones pursuing
research into the global environmental risks of nuclear
exchanges. We urge others to evaluate and repeat the
calculations both for the effects of a superpower
conflagration and for more regional nuclear wars.

A.R. and O.B.T.

Twenty-five years ago international teams of scientists
showed that a nuclear war between the U.S. and the
Soviet Union could produce a 'nuclear winter.' The smoke
from vast fires started by bombs dropped on cities and
industrial areas would envelop the planet and absorb so
much sunlight that the earth's surface would get cold,
dark and dry, killing plants worldwide and eliminating
our food supply. Surface temperatures would reach winter
values in the summer. International discussion about
this prediction, fueled largely by astronomer Carl
Sagan, forced the leaders of the two superpowers to
confront the possibility that their arms race endangered
not just themselves but the entire human race. Countries
large and small demanded disarmament.

Nuclear winter became an important factor in ending the
nuclear arms race. Looking back later, in 2000, former
Soviet Union leader Mikhail S. Gorbachev observed,
'Models made by Russian and American scientists showed
that a nuclear war would result in a nuclear winter that
would be extremely destructive to all life on earth; the
knowledge of that was a great stimulus to us, to people
of honor and morality, to act.'

Why discuss this topic now that the cold war has ended?
Because as other nations continue to acquire nuclear
weapons, smaller, regional nuclear wars could create a
similar global catastrophe. New analyses reveal that a
conflict between India and Pakistan, for example, in
which 100 nuclear bombs were dropped on cities and
industrial areas - only 0.4 percent of the world's more
than 25,000 warheads - would produce enough smoke to
cripple global agriculture. A regional war could cause
widespread loss of life even in countries far away from
the conflict.

Regional War Threatens the World

By deploying modern computers and modern climate models,
the two of us and our colleagues have shown that not
only were the ideas of the 1980s correct but the effects
would last for at least 10 years, much longer than
previously thought. And by doing calculations that
assess decades of time, only now possible with fast,
current computers, and by including in our calculations
the oceans and the entire atmosphere - also only now
possible - we have found that the smoke from even a
regional war would be heated and lofted by the sun and
remain suspended in the upper atmosphere for years,
continuing to block sunlight and to cool the earth.

India and Pakistan, which together have more than 100
nuclear weapons, may be the most worrisome adversaries
capable of a regional nuclear conflict today. But other
countries besides the U.S. and Russia (which have
thousands) are well endowed: China, France and the U.K.
have hundreds of nuclear warheads; Israel has more than
80, North Korea has about 10 and Iran may well be trying
to make its own. In 2004 this situation prompted one of
us (Toon) and later Rich Turco of the University of
California, Los Angeles, both veterans of the 1980s
investigations, to begin evaluating what the global
environmental effects of a regional nuclear war would be
and to take as our test case an engagement between India
and Pakistan.

The latest estimates by David Albright of the Institute
for Science and International Security and by Robert S.
Norris of the Natural Resources Defense Council are that
India has 50 to 60 assembled weapons (with enough
plutonium for 100) and that Pakistan has 60 weapons.
Both countries continue to increase their arsenals.
Indian and Pakistani nuclear weapons tests indicate that
the yield of the warheads would be similar to the 15-
kiloton explosive yield (equivalent to 15,000 tons of
TNT) of the bomb the U.S. used on Hiroshima.

Toon and Turco, along with Charles Bardeen, now at the
National Center for Atmospheric Research, modeled what
would happen if 50 Hiroshima- size bombs were dropped
across the highest population-density targets in
Pakistan and if 50 similar bombs were also dropped
across India. Some people maintain that nuclear weapons
would be used in only a measured way. But in the wake of
chaos, fear and broken communications that would occur
once a nuclear war began, we doubt leaders would limit
attacks in any rational manner. This likelihood is
particularly true for Pakistan, which is small and could
be quickly overrun in a conventional conflict. Peter R.
La- voy of the Naval Postgraduate School, for example,
has analyzed the ways in which a conflict between India
and Pakistan might occur and argues that Pakistan could
face a decision to use all its nuclear arsenal quickly
before India swamps its military bases with traditional

Obviously, we hope the number of nuclear targets in any
future war will be zero, but policy makers and voters
should know what is possible. Toon and Turco found that
more than 20 million people in the two countries could
die from the blasts, fires and radioactivity -a horrible

But the investigators were shocked to discover that a
tremendous amount of smoke would be generated, given the
megacities in the two countries, assuming each fire
would burn the same area that actually did burn in
Hiroshima and assuming an amount of burnable material
per person based on various studies. They calculated
that the 50 bombs exploded in Pakistan would produce
three teragrams of smoke, and the 50 bombs hitting India
would generate four (one teragram equals a million
metric tons).

Satellite observations of actual forest fires have shown
that smoke can be lofted up through the troposphere (the
bottom layer of the atmosphere) and sometimes then into
the lower stratosphere (the layer just above, extending
to about 30 miles). Toon and Turco also did some 'back
of the envelope' calculations of the possible climate
impact of the smoke should it enter the stratosphere.
The large magnitude of such effects made them realize
they needed help from a climate modeler.

It turned out that one of us (Robock) was already
working with Luke Oman, now at the NASA Goddard Space
Flight Center, who was finishing his Ph.D. at Rutgers
University on the climatic effects of volcanic
eruptions, and with Georgiy L. Stenchikov, also at
Rutgers and an author of the first Russian work on
nuclear winter. They developed a climate model that
could be used fairly easily for the nuclear blast

Robock and his colleagues, being conservative, put five
teragrams of smoke into their modeled upper troposphere
over India and Pakistan on an imaginary May 15. The
model calculated how winds would blow the smoke around
the world and how the smoke particles would settle out
from the atmosphere. The smoke covered all the
continents within two weeks. The black, sooty smoke
absorbed sunlight, warmed and rose into the
stratosphere. Rain never falls there, so the air is
never cleansed by precipitation; particles very slowly
settle out by falling, with air resisting them. Soot
particles are small, with an average diameter of only
0.1 micron (µm), and so drift down very slowly. They
also rise during the daytime as they are heated by the
sun, repeatedly delaying their elimination. The
calculations showed that the smoke would reach far
higher into the upper stratosphere than the sulfate
particles that are produced by episodic volcanic
eruptions. Sulfate particles are transparent and absorb
much less sunlight than soot and are also bigger,
typically 0.5 µm. The volcanic particles remain airborne
for about two years, but smoke from nuclear fires would
last a decade.

Killing Frosts in Summer

The climatic response to the smoke was surprising.
Sunlight was immediately reduced, cooling the planet to
temperatures lower than any experienced for the past
1,000 years. The global average cooling, of about 1.25
degrees Celsius (2.3 degrees Fahrenheit), lasted for
several years, and even after 10 years the temperature
was still 0.5 degree C colder than normal. The models
also showed a 10 percent reduction in precipitation
worldwide. Precipitation, river flow and soil moisture
all decreased because blocking sun-light reduces
evaporation and weakens the hydrologic cycle. Drought
was largely concentrated in the lower latitudes,
however, because global cooling would retard the Hadley
air circulation pattern in the tropics, which produces a
large fraction of global precipitation. In critical
areas such as the Asian monsoon regions, rainfall
dropped by as much as 40 percent.

The cooling might not seem like much, but even a small
dip can cause severe consequences. Cooling and
diminished sunlight would, for example, shorten growing
seasons in the midlatitudes. More insight into the
effects of cooling came from analyses of the aftermaths
of massive volcanic eruptions. Every once in a while
such eruptions produce temporary cooling for a year or
two. The largest of the past 500 years, the 1815 Tambora
eruption in Indonesia, blotted the sun and produced
global cooling of about 0.5 degree C for a year; 1816
became known as "The Year without a Summer" or "Eighteen
Hundred and Froze to Death." In New England, although
the average summer temperature was lowered only a few
degrees, crop-killing frosts occurred in every month.
After the first frost, farmers replanted crops, only to
see them killed by the next frost. The price of grain
skyrocketed, the price of livestock plummeted as farmers
sold the animals they could not feed, and a mass
migration began from New England to the Midwest, as
people followed reports of fertile land there. In Europe
the weather was so cold and gloomy that the stock market
collapsed, widespread famines occurred and 18-year-old
Mary Shelley was inspired to write Frankenstein.

Certain strains of crops, such as winter wheat, can
withstand lower temperatures, but a lack of sunlight
inhibits their ability to grow. In our scenario,
daylight would filter through the high smoky haze, but
on the ground every day would seem to be fully overcast.
Agronomists and farmers could not develop the necessary
seeds or adjust agricultural practices for the radically
different conditions unless they knew ahead of time what
to expect.

In addition to the cooling, drying and darkness,
extensive ozone depletion would result as the smoke
heated the stratosphere; reactions that create and
destroy ozone are temperature-dependent. Michael J.
Mills of the University of Colorado at Boulder ran a
completely separate climate model from Robock's but
found similar results for smoke lofting and
stratospheric temperature changes. He concluded that
although surface temperatures would cool by a small
amount, the stratosphere would be heated by more than 50
degrees C, because the black smoke particles absorb
sunlight. This heating, in turn, would modify winds in
the stratosphere, which would carry ozone-destroying
nitrogen oxides into its upper reaches. Together the
high temperatures and nitrogen oxides would reduce ozone
to the same dangerous levels we now experience below the
ozone hole above Antarctica every spring. Ultraviolet
radiation on the ground would increase significantly
because of the diminished ozone.

Less sunlight and precipitation, cold spells, shorter
growing seasons and more ultraviolet radiation would all
reduce or eliminate agricultural production. Notably,
cooling and ozone loss would be most profound in middle
and high latitudes in both hemispheres, whereas
precipitation declines would be greatest in the tropics.

The specific damage inflicted by each of these
environmental changes would depend on particular crops,
soils, agricultural practices and regional weather
patterns, and no researchers have completed detailed
analyses of such agricultural responses. Even in normal
times, however, feeding the growing human population
depends on transferring food across the globe to make up
for regional farming deficiencies caused by drought and
seasonal weather changes. The total amount of grain
stored on the planet today would feed the earth's
population for only about two months [see "Could Food
Shortages Bring Down Civilization?" by Lester R. Brown;
Scientific American, May]. Most cities and countries
have stockpiled food supplies for just a very short
period, and food shortages (as well as rising prices)
have increased in recent years. A nuclear war could
trigger declines in yield nearly everywhere at once, and
a worldwide panic could bring the global agricultural
trading system to a halt, with severe shortages in many
places. Around one billion people worldwide who now live
on marginal food supplies would be directly threatened
with starvation by a nuclear war between India and
Pakistan or between other regional nuclear powers.

Independent Evidence Needed

Typically scientists test models and theories by doing
experiments, but we obviously cannot experiment in this
case. Thus, we look for analogues that can verify our

Burned cities. Unfortunately, firestorms created by
intense releases of energy have pumped vast quantities
of smoke into the upper atmosphere. San Francisco burned
as a result of the 1906 earthquake, and whole cities
were incinerated during World War II, including Dresden,
Hamburg, Tokyo, Hiroshima and Nagasaki. These events
confirm that smoke from intense urban fires rises into
the upper atmosphere.

The seasonal cycle. In actual winter the climate is
cooler because the days are shorter and sunlight is less
intense; the simple change of seasons helps us quantify
the effects of less solar radiation. Our climate models
re-create the seasonal cycle well, confirming that they
properly reflect changes in sunlight.

Eruptions. Explosive volcanic eruptions, such as those
of Tambora in 1815, Krakatau in 1883 and Pinatubo in
1991 provide several lessons. The resulting sulfate
aerosol clouds that formed in the stratosphere were
transported around the world by winds. The surface
temperature plummeted after each eruption in proportion
to the thickness of the particulate cloud. After the
Pinatubo eruption, the global average surface
temperature dropped by about 0.25 degree C. Global
precipitation, river flow and soil moisture all
decreased. Our models reproduce these effects.

Forest fires. Smoke from large forest fires sometimes is
injected into the troposphere and lower stratosphere and
is transported great distances, producing cooling. Our
models perform well against these effects, too.

Extinction of the dinosaurs. An asteroid smashed into
Mexico's Yucatán Peninsula 65 million years ago. The
resulting dust cloud, mixed with smoke from fires,
blocked the Sun, killing the dinosaurs. Massive
volcanism in India at the same time may have exacerbated
the effects. The events teach us that large amounts of
aerosols in the earth's atmosphere can change climate
drastically enough to kill robust species.

We have used such analogues to test and improve our
models in the past. But we hope more people will do
further work. Independent models that either verify or
contradict ours would be very instructive. Agricultural
impact studies, which we have not conducted, would be
particularly welcomed.

Abolition: The Only Policy

People have several incorrect impressions about nuclear
winter. One is that the climatic effects were disproved;
this is just not true [see sidebar on page 78]. Another
is that the world would experience "nuclear autumn"
instead of winter. But our new calculations show that
the climate effects even of a regional conflict would be
widespread and severe. The models and computers used in
the 1980s were not able to simulate the lofting and
persistence of the smoke or the long time it would take
oceans to warm back up as the smoke eventually
dissipated; current models of a full-scale nuclear
exchange predict a nuclear winter, not a nuclear fall.

Another misimpression is that the problem, even if it
existed, has been solved by the end of the nuclear arms
race. In fact, a nuclear winter could readily be
produced by the American and Russian nuclear arsenals
that are slated to remain in 2012. Furthermore, the
increasing number of nuclear states raises the chances
of a war starting deliberately or by accident. For
example, North Korea has threatened war should the world
stop its ships and inspect them for transporting nuclear
materials. Fortunately, North Korea does not now have a
usable nuclear arsenal, but it may have one capable of
global reach in the near future. Some extremist leaders
in India advocated attacking Pakistan with nuclear
weapons following recent terrorist attacks on India.
Because India could rapidly overrun Pakistan with
conventional forces, it would be conceivable for
Pakistan to attack India with nuclear weapons if it
thought that India was about to go on the offensive.
Iran has threatened to destroy Israel, already a nuclear
power, which in turn has vowed never to allow Iran to
become a nuclear state. Each of these examples represent
countries that imagine their existence to be threatened
completely and with little warning. These points of
conflict have the potential to erupt suddenly.

The first nuclear war so shocked the world that in spite
of the massive buildup of these weapons since then, they
have never been used again. But the only way to
eliminate the possibility of climatic catastrophe is to
eliminate the weapons. Rapid reduction of the American
and Russian arsenals would set an example for the rest
of the world that nuclear weapons cannot be used and are
not needed.

Under the Strategic Offensive Reductions Treaty, the
U.S. and Russia both committed to reduce deployed
strategic nuclear warheads down to between 1,700 to
2,200 apiece by the end of 2012. In July 2009 President
Barack Obama and Russian president Dmitry Medvedev
agreed to drop that range further, to 1,500 to 1,675 by
2016. Although smaller strategic arsenals are to be
commended, our new results show that even the lower
counts are far more than enough to destroy agriculture
worldwide, as is a regional nuclear war. If this mother
lode of weapons were used against urban targets,
hundreds of millions of people would be killed and a
whoppping 180 Tg of smoke would be sent into the global
stratosphere. Average temperatures would remain below
freezing even in the summer for several years in major
agricultural regions. Even the warheads on one missile-
carrying submarine could produce enough smoke to create
a global environmental disaster.

The combination of nuclear proliferation, political
instability and urban demographics may constitute one of
the greatest dangers to the stability of society since
the dawn of humans. Only abolition of nuclear weapons
will prevent a potential nightmare. Immediate reduction
of U.S. and Russian arsenals to the same levels as other
nuclear powers (a few hundred) would maintain their
deterrence, reduce the possibility of nuclear winter and
encourage the rest of the world to continue to work
toward the goal of elimination.

President Obama understands this logic. In his first
press conference as president, on February 9, 2009, he
said, 'It is important for the United States, in concert
with Russia ... to restart the conversations about how
we can start reducing our nuclear arsenals in an
effective way so that we then have the standing to go to
other countries and start stitching back together the
nonproliferation treaties.' Then, on September 24, the
president led the United Nations Security Council to
approve a draft resolution that would step up efforts to
rid the world of nuclear weapons. Our modeling results
only strengthen the reasons to support further progress
on such policy.

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