The Nuclear Winter

Carl Sagan / The Nuclear Winter.

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The Nuclear Winter

Carl Sagan

Carl Sagan, a modern-day Renaissance man of science, was horn in 1934 in New York. After graduating with both a B.A. and a B.S.

degree from the University of Chicago, Sagan completed his M.S.

in

physics and earned a Ph.D. in astronomy and astro-physics in 1960.

Sagan was nominated to join the Smithsonian Astrophysical Observatory in 1962. At the same time, he also worked with the Nobel-prize winner Joshna Lederberg, investigating the origins of life on earth, and taught genetics at Stanford. Sagan then taught astronomy at Harvard until 1968, when he became profossor of astronomy and space sciences at Cornell University. He was then appointed director of the laboratoy for Planetary Studies. Sagan was

awarded the NASA medal for exceptional scientific achievement in 1972, after his hypotheses about Mars were validated by data obtained from the 1971 Mars Mariner expedition. Beginning in 1968,

Sagan was editor of Icarus, the international journal of astronomy,

and wrote many distinguished books. His works include The Cosmic Connection (1973), which received the Campbell Award for best science book; the Pulitzer-prize winning Dragons of Eden (1977); Broca's Brain (1979), on developments in neurophysiology; and Cosmos

(1980), which accompanied his widety-acclaimed television series.

In

"The Nuclear Winter" (1983), Sagan explored the unforeseen and devastating physical and chemical effects of even a small-scale nuclear war on the earth's biosphere and life on earth.

Except for fools and madmen, everyone knows that nuclear war would he an

unprecedented human catastrophe. A more or less typical strategic warhead

has a yield of 2 megatons, the explosive equivalent of 2 million tons of

TNT. But 2 million tons of TNT is about the same as all the bombs exploded

in World War II -- a single bomb with the explosive power of the entire Second World War but compressed into a few seconds of time and an area 30

or 40 miles across …

In a 2-megaton explosion over a fairly large city, buildings would be vaporized, people reduced to atoms and shadows, outlying structures blown

down like matchsticks and raging fires ignited. And if the bomb were exploded on the ground, an enormous crater, like those that can be seen through a telescope on the surface of the Moon, would be all that remained

where midtown once had been. There are now more than 50,000 nuclear weapons, more than 13,000 megatons of yield, deployed in the arsenals of

the United States and the Soviet Union -- enough to obliterate a million

Hiroshimas.

But there are fewer than 3000 cities on the Earth with populations of 100,000 or more. You cannot find anything like a million Hiroshimas to obliterate. Prime military and industrial targets that are far from cities

are comparatively rare. Thus, there are vastly more nuclear weapons than

are needed for any plausible deterrence of a potential adversary.

Nobody knows, of course, how many megatons would be exploded in a real nuclear war. There are some who think that a nuclear war can be

"contained," bottled up before it runs away to involve much of the world's

arsenals. But a number of detailed analyses, war games run by the U.S.

Department of Defense, and official Soviet pronouncements all indicate that this containment may be too much to hope for: Once the bombs begin exploding, communications failures, disorganization, fear, the necessity

of making in minutes decisions affecting the fates of millions, and the immense psychological burden of knowing that your own loved ones may already have been destroyed are likely to result in a nuclear paroxysm.

Many investigations, including a number of studies for the U.S.

government, envision the explosion of 5,000 to 10,000 megatons -- the detonation of tens of thousands of nuclear weapons that now sit quietly,

inconspicuously, in missile silos, submarines and long-range bombers, faithful servants awaiting orders.

The World Health Organization, in a recent detailed study chaired by Sune

K. Bergstrom (the 1982 Nobel laureate in physiology and medicine), concludes that 1.1 billion people would be killed outright in such a nuclear war, mainly in the United States, the Soviet Union, Europe, China

and Japan. An additional 1.1 billion people would suffer serious injufles

and radiation sickness, for which medical help would be unavailable. It thus seems possible that more than 2 billion people-almost half of all the

humans on Earth-would be destroyed in the immediate aftermath of a global

thermonuclear war. This would represent by far the greatest disaster in the history of the human species and, with no other adverse effects, would

probably be enough to reduce at least the Northern Hemisphere to a state

of prolonged agony and barbarism. Unfortunately, the real situation would

be much worse. In technical studies of the consequences of nuclear weapons

explosions, there has been a dangerous tendency to underestimate the results. This is partly due to a tradition of conservatism which generally

works well in science but which is of more dubious applicability when the

lives of billions of people are at stake. In the Bravo test of March 1, 1954, a 15-megaton thermonuclear bomb was exploded on Bikini Atoll. It had

about double the yield expected, and there was an unanticipated last-minute shift in the wind direction. As a result, deadly radioactive

fallout came down on Rongelap in the Marshall Islands, more than 200

kilometers away. Most all the children on Rongelap subsequently developed

thyroid nodules and lesions, and other long-term medical problems, due to

the radioactive fallout.

Likewise, in 1973, it was discovered that high-yield airbursts will chemically burn the nitrogen in the upper air, converting it into oxides

of nitrogen; these, in turn, combine with and destroy the protective ozone

in the Earth's stratosphere. The surface of the Earth is shielded from deadly solar ultraviolet radiation by a layer of ozone so tenuous that, were it brought down to sea level, it would be only 3 millimeters thick.

Partial destruction of this ozone layer can have serious consequences for

the biology of the entire planet.

These discoveries, and others like them, were made by chance. They were largely unexpected. And now another consequence -- by far the most dire

--

has been uncovered, again more or less by accident.

The U.S. Mariner 9 spacecraft, the first vehicle to orbit another planet,

arrived at Mars in late 1971. The planet was enveloped in a global dust storm. As the fine particles slowly fell out, we were able to measure temperature changes in the atmosphere and on the surface. Soon it became

clear what had happened:

The dust, lofted by high winds off the desert into the upper Martian atmosphere, had absorbed the incoming sunlight and prevented much of it from reaching the ground. Heated by the sunlight, the dust warmed the adjacent air. But the surface, enveloped in partial darkness, became much

chillier than usual. Months later, after the dust fell out of the atmosphere, the upper air cooled and the surface warmed, both returning to

their normal conditions. We were able to calculate accurately, from how much dust there was in the atmosphere, how cool the Martian surface ought

to have been.

Afterwards, I and my colleagues, James B. Pollack and Brian Toon of NASA's

Ames Research Center, were eager to apply these insights to the Earth.

In

a volcanic explosion, dust aerosols are lofted into the high atmosphere.

We calculated by how much the Earth's global temperature should decline after a major volcanic explosion and found that our results (generally a

fraction of a degree) were in good accor4 with actual measurements.

Joining forces with Richard Turco, who has studied the effects of nuclear

weapons for many years, we then began to turn our attention to the climatic effects of nuclear war. [The scientific paper, "Global Atmospheric Consequences of Nuclear War," was written by R. P. Turco, 0.

B. Toon, T. P. Ackerman, J. B. Pollack and Carl Sagan. From the last names

of the authors, this work is generally referred to as "TTAPS."]

We knew that nuclear explosions, particularly groundbursts, would lift an

enormous quantity of fine soil particles into the atmosphere (more than 100,000 tons of fine dust for every megaton exploded in a surface burst).

Our work was further spurred by Paul Crutzen of the Max Planck Institute

for Chemistry in Mainz, West Germany, and by John Birks of the University

of Colorado, who pointed out that huge quantities of smoke would be generated in the burning of cities and forests following a nuclear war.

Croundburst -- at hardened missile silos, for example -- generate fine dust. Airbursts -- over cities and unhardened military installations --

make fires and therefore smoke. The amount of dust and soot generated depends on the conduct of the war, the yields of the weapons employed and

the ratio of groundbursts to airbursts. So we ran computer models for several dozen different nuclear war scenarios. Our baseline case, as in many other studies, was a 5000-megaton war with only a modest fraction of

the yield (20 percent) expended on urban or industrial targets. Our job,

for each case, was to follow the dust and smoke generated, see how much sunlight was absorbed and by how much the temperatures changed, figure out

how the particles spread in longitude and latitude, and calculate how long

before it all fell out in the air back onto the surface. Since the radioactivity would be attached to these same fine particles, our calculations also revealed the extent and timing of the subsequent radioactive fallout.

Some of what I am about to describe is horrifying. I know, because it horrifies me. There is a tendency -- psychiatrists call it "denial" --

to

put it out of our minds, not to think about it. But if we are to deal intelligently, wisely, with the nuclear arms race, then we must steel ourselves to contemplate the horrors of nuclear war.

The results of our calculations astonished us. In the baseline case, the

amount of sunlight at the ground was reduced to a few percent of normal-much darker, in daylight, than in a heavy overcast and too dark for

plants to make a living from photosynthesis. At least in the Northern Hemisphere, where the great preponderance of strategic targets lies, an unbroken and deadly gloom would persist for weeks.

Even more unexpected were the temperatures calculated. In the baseline case, land temperatures, except for narrow strips of coastline, dropped to

minus 250 Celsius (minus 13 degrees Fahrenheit) and stayed below freezing

for months -- even for a summer war. (Because the atmospheric structure becomes much more stable as the upper atmosphere is heated and the low air

is cooled, we may have severely underestimated how long the cold and the

dark would last.) The oceans, a significant heat reservoir, would not freeze, however, and a major ice age would probably not be triggered.

But

because the temperatures would drop so catastrophically, virtually all crops and farm animals, at least in the Northern Hemisphere, would be destroyed, as would most varieties of uncultivated or domesticated food supplies. Most of the human survivors would starve.

In addition, the amount of radioactive fallout is much more than expected.

Many previous calculations simply ignored the intermediate time-scale fallout. That is, calculations were made for the prompt fallout -- the plumes of radioactive debris blown downwind from each target-and for the

long-term fallout, the fine radioactive particles lofted into the stratosphere that would descend about a year later, after most of the radioactivity had decayed. However, the radioactivity carried into the upper atmosphere (but not as high as the stratosphere) seems to have been

largely forgotten. We found for the baseline case that roughly 30

percent

of the land at northern midlatitudes could receive a radioactive dose greater than 250 rads, and that about 50 percent of northern midlatitudes

could receive a dose greater than 100 rads. A 100-rad dose is the equivalent of about 1000 medical X-rays. A 400-rad dose will, more likely

than not, kill you.

The cold, the dark and the intense radioactivity, together lasting for months, represent a severe assault on our civilization and our species.

Civil and sanitary services would be wiped out. Medical facilities, drugs,

the most rudimentary means for relieving the vast human suffering, would

be unavailable. Any but the most elaborate shelters would be useless, quite apart from the question of what good it might be to emerge a few months later. Synthetics burned in the destruction of the cities would produce a wide variety of toxic gases, including carbon monoxide, cyanides, dioxins and furans. After the dust and soot settled out, the solar ultraviolet flux would be much larger than its present value.

Immunity to disease would decline. Epidemics and pandemics would be rampant, especially after the billion or so unburied bodies began to thaw.

Moreover, the combined influence of these severe and simultaneous stresses

on life are likely to produce even more adverse consequences --

biologists

call them synergisms -- that we are not yet wise enough to foresee.

So far, we have talked only of the Northern Hemisphere. But it now seems

-

unlike the case of a single nuclear weapons test -- that in a real nuclear

war, the heating of the vast quantities of atmospheric dust and soot in northern midlatitudes will transport these fine particles toward and across the Equator. We see just this happening in Martian dust storms.