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INVESTIGATING THE CLIMATE IMPACTS OF NUCLEAR WAR  
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Edited by William Burr
October 30, 2024
National Security Archive
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_ 1983 Lawrence Livermore Study Said Nuclear Exchange Could
“Dramatically Affect the Atmosphere’s Temperature” _

Illustration from a 1985 report by Lawrence Livermore National
Laboratory scientist Michael MacCracken, showing smoke and soot lofted
from nuclear detonations on day 1 and the passage of the smoke 5, 10,
and 20 days later , Lawrence Livemore Laboratory

 

WASHINGTON, D.C., OCTOBER 30, 2024 - A 1983 study from scientists at
the Department of Energy’s Lawrence Livermore Laboratory said that a
full-scale nuclear war between the superpowers would “dramatically
affect the atmosphere’s temperature, dynamic, precipitation, and
chemistry,” reduce “the light reaching the surface in the Northern
Hemisphere by 90% or more,” and could cause “a cooling of
continental land areas by up to 30°C.”

The recently released internal study of the “Global-Scale Physical
Effects of a Nuclear Exchange” is featured in an update to the
National Security Archive’s 2022 Electronic Briefing Book on U.S.
government thinking about the possibility of a “nuclear winter,”
in which the fire effects of multiple nuclear detonations would
produce enough smoke and soot to block sunlight and dramatically lower
the Earth’s temperature.

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1983 was a year of increasing tensions between the Cold War
superpowers, highlighted by the Soviet shootdown of a South Korean
airliner (KAL 007) in September, a Soviet false alarm,
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and war scares on the Soviet side. It also saw massive protests
against NATO missile deployments, and the nuclear freeze movement
continued to gain momentum in the United States. At the same time, the
scientific community was beginning to focus more intently on the risks
of nuclear war. At the close of 1983, a group of scientists published
a ground-breaking article in_ Science_ magazine asserting that the
mass fires caused by nuclear war could inject enough smoke and soot
into the atmosphere to obstruct sunlight and dramatically lower
temperatures to freezing levels—nuclear winter.

A longer version of the report published in _Science_ had been
circulating privately for some months when scientists at Lawrence
Livermore National Laboratory (LLNL), one of the two Department of
Energy nuclear weapons labs, did its own internal study of the impact
of nuclear war on the global climate. LLNL’s August 1983 report
focused on the potential cooling effects of a nuclear war, finding
that a superpower conflict involving the detonation of more than 6000
nuclear weapons could produce mass fires, both in urban areas and in
forests. The fires would introduce a large amount of smoke and soot
into the atmosphere, a phenomenon that could “reduce the light
reaching the surface in the Northern Hemisphere by 90% or more” and
that could “lead to a cooling of continental land areas by up to
30°C.”

The “reference scenario” used for the study posited a war where
the total explosive yield of 5300 megatons was spread by some 6300
nuclear warheads. One third of the megatonnage was caused by U.S.
warheads and two thirds by Soviet. About 2500 of the megatons were
surface bursts with 85 percent of them from Soviet weapons. The
authors did not explain why they assumed that the Soviets would
detonate most of the surface bursts; it may have been an arbitrary
assumption. Another scenario that was considered involved a
“significant European theater component” with a total yield of
6500 megatons spread by 10,000 warheads, many of which were
“tactical air burst[s].” The European scenario was not discussed
further.

To analyze the climate impact of the reference scenario, the authors
produced a complex and demanding report covering a wide variety of
issues relating to the impact of thousands of nuclear detonations.
They included the spread of radioactive debris (fission products), the
impact of ultraviolet radiation on the ozone layers, the radiative
effects of dust and nitrogen oxides, the fire effects of the nuclear
detonations, and the effects of soot emissions on the troposphere. At
the heart of the presentation is a section on “Global Climate,”
where the authors suggested that the “burning of 13000 Tg
[teragrams] of fuel in cities, urban areas, and forests” in the mass
fires caused by thousands of nuclear detonations “can dramatically
affect the atmosphere’s temperature, dynamic, precipitation, and
chemistry.” (A teragram is a unit of mass in the metric system.
13000 teragrams is the equivalent of 13,000,000,000,000,000 grams or
over 28 trillion pounds.)

According to the authors, the perturbations caused by the injection of
so much soot and smoke into the atmosphere could “lead to
modifications of the weather and climate” that could produce
“reductions in average Northern Hemisphere land temperatures of
5-10° centigrade and perhaps several times more over mid-continental
regions.” The cooling effects could take place within five to 10
days, and the “cooling of mid-continental regions could be
substantially larger.” They also projected a decrease in the
“precipitation rate of 20-30% over the cooled land region and by
5-10% over ocean region, where atmospheric warming has stabilized the
upper troposphere.”

The authors believed that their line of approach involved many
uncertainties and unverified assumptions and they pointed them out.
For example, the degree of cooling would depend on the elevation of
the smoke and the “effect of cloud cover changes.” Moreover,
“unknown parameters” included the scale of the “mass loading [of
soot and smoke] from fires” and how long particulates would reside
in the atmosphere. In addition, the process that filters soot, smoke,
and dust from the atmosphere and the mechanisms that transport them
“are assumed to be those of an unperturbed atmosphere.” That
assumption “was clearly not valid,” according to the study, but
there were no “computational tools” at hand to overcome that
problem. In addition, the “coupling” of the various climate
effects of nuclear war or their “synergistic interactions”
required serious analysis.

The authors noted that what stimulated their study and several related
ones was a 1982 article by Paul J. Crutzen and John W. Birks titled,
“The Atmosphere after a Nuclear War: Twilight at Noon,” that
analyzed the impact of the soot produced by nuclear fire effects. The
Crutzen-Birks article also inspired a report prepared by Richard P.
Turco, Owen Brian Toon, Thomas P. Ackerman, the late James B. Pollack,
and the late Carl Sagan (collectively known as TTAPS), who were
circulating their March 1983 report, the main findings of which were
published later in the year in _Science_. The National Academy of
Sciences also had a study in the works. Although the Livermore report
discussed “cooling” rather than freezing or subfreezing and
emphasized the uncertainties, its authors found that their research
results were in “qualitative accord” with the findings of TTAPS
and the ongoing National Academy investigations.[A]
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Edward Teller [[link removed]], the
founder of LLNL and then its director emeritus, was a major influence
in the nuclear weapons field and in the early 1980s was focused on the
promotion of the Strategic Defense Initiative. The possibility that
nuclear war could have a significant climate impact had never occurred
to Teller, who was surprised by the TTAPS findings and wanted to find
ways to refute or weaken them. Teller would criticize the nuclear
winter concept in an article published in the journal _Nature_ for
which he received assistance from LLNL staffers.[B]
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Yet, Teller, like the LLNL staffers could “not simply discard [the]
theory.” As he wrote, the “possibility of nuclear winter has not
been excluded.”[C]
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Michael MacCracken
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authors of the 1983 LLNL study and a Teller Ph. D student, would move
forward with studies of the cooling impact of nuclear war and the
uncertainties of the nuclear winter thesis, although the latter
remains highly influential.

In the original release, citing privacy grounds, the Department of
Energy withheld the names of the project leaders and participants in
this report. The National Security Archive challenged the excisions
because so much time had passed since the publication of this report,
and DOE duly released the names. The project team leader included
MacCracken along with Joyce Penner
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Tarter [[link removed]], Frederick
Luther, and Joseph Knox
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Lawrence Livermore Laboratory, “LLN Study of the Global-Scale
Physical Effects of a Nuclear Exchange: Preliminary Findings,” 15
August 1983, unclassified  [[link removed]]
AUG 15, 1983

SOURCE: FOIA release by Department of Energy

About the National Security Archive

_Founded in 1985 by journalists and scholars to check rising
government secrecy, the National Security Archive combines a unique
range of functions: investigative journalism center, research
institute on international affairs, library and archive of
declassified U.S. documents ("the world's largest nongovernmental
collection" according to the _Los Angeles Times_), leading non-profit
user of the U.S. Freedom of Information Act, public interest law firm
defending and expanding public access to government information,
global advocate of open government, and indexer and publisher of
former secrets._

* nuclear winter
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* Nuclear war
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* Climate Change
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