sius, hence the term “nuclear winter.” Critics of the
nuclear arms race used these scenarios to under-
score the folly of the use of nuclear weapons.
Climatic Impact of Nuclear War Using computer
simulations of the debris thrown into the atmo-
sphere, soot from extensive fires, and wind patterns,
TTAPS demonstrated, in an article published in the
leading scientific journalScience, that various levels
of nuclear exchanges between the United States and
the Soviet Union would produce negative climatic
impacts. The material thrown into the atmosphere
would circle the globe, first in the Northern Hemi-
sphere, then spreading to the Southern Hemisphere
particularly with high-level conflicts. This material
would inhibit sunlight from reaching the earth, pro-
ducing a cooling effect. TTAPS cited the impact of
the explosion of the volcano Tambora in 1815 on the
world climate the next year as empirical evidence for
their hypothesis, indicating that a nuclear war could
produce a much more severe and long-lived impact
than a simple volcanic eruption. With the expansion
of nuclear arsenals, both superpowers, the United
States and the Soviet Union, had moved some of
their nuclear weapons capacity from targeting what
were called counterforce targets (military sites) to
targeting countervalue targets (industrial sites and
cities that affected a country’s ability to wage and
survive nuclear war), so a nuclear conflict was likely
to produce numerous fires and substantial debris.
TTAPS produced six scenarios depending on the
intensity of the conflict and the targets of the weap-
ons. Their first scenario, based on the use of few weap-
ons on military targets, produced no climatic impact.
Their second, called “marginal nuclear winter,” de-
creased temperatures by a few degrees Celsius in the
Northern Hemisphere, producing severe famines.
The third, “nominal nuclear winter,” came from a
full-scale exchange of nuclear weapons, producing
a drop in average land temperature of 10 degrees
Celsius for several months, followed by a return of
sunlight enhanced by depletion of the ozone layer.
Worldwide, one to two billion people could be ex-
pected to die in addition to those already killed in the
conflict and its direct aftermath. The “substantial nu-
clear winter scenario” would lead to the deaths of sev-
eral billion people in both hemispheres. The “severe”
scenario could produce temperature declines of 20
degrees Celsius and a decrease in sunlight so severe as
to inhibit photosynthesis for several years. This sce-
nario could imperil everyone on earth. The sixth and
“extreme” scenario would produce darkness at noon
at about the level of a moonlit night and would be
likely to extinguish most life on the planet. TTAPS in-
dicated that scenario three was the most likely one to
result from a nuclear conflict and continued to refine
their models through the 1980’s.
Various other scientists around the world entered
the nuclear winter debate, producing scenarios based
on different manipulations of the data. One major
challenge by Stephen H. Schneider and Starley L.
Thompson labeled the impact of nuclear war as “nu-
clear autumn.” Although indicating that nuclear war
would be likely to produce a less severe impact than
the TTAPS models, these authors still posited a no-
ticeable climatic impact that might be quite severe in
some places. Although members of the scientific
community differed somewhat in terms of how se-
vere a nuclear winter might be, they agreed that
nuclear war would be likely to produce a negative cli-
matic impact that went beyond the immediate im-
pact of the blasts and radioactive fallout.Political Implications of Nuclear Winter The impact
of nuclear weapons through blast damage, fires, and
radiation had already been shown to be quite severe.
As Carl Sagan indicated, the additional impact on
global climate made nuclear war nearly unthink-
able. During the 1980’s, the United States and the
Soviet Union were experiencing the last stages of the
Cold War, in which both sides engaged in a continu-
ally escalating arms race. Some of the policy debate
surrounding the nuclear winter scenario centered
on whether the possibility of nuclear winter made a
nuclear exchange more or less likely. A few staunch
cold warriors dismissed the possibility of nuclear
winter, but most policy makers seem to have ac-
cepted its possibility. Several opponents of the nu-
clear arms race used the nuclear winter scenario as
further evidence that at least some degree of nuclear
disarmament was essential.Impact With the fall of the Soviet Union and a de-
cline in the tensions of the Cold War, a nuclear war
scenario seemed to become less likely. Today, it is
rarely mentioned. Nonetheless, the science of the
nuclear war scenarios remains sound. An exchange
of nuclear weapons, particularly if targets such as oil
refineries were hit, could produce a negative impact
on the climate.The Eighties in America Nuclear winter scenario 717