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Recommendations for Research
The uncertainties that impede an accurate quantification of the
atmospheric degradation implied by a nuclear exchange are numerous and
are large. Nevertheless, despite the limited understanding of these
matters, it is clear that the hazard posed by a large nuclear exchange
is of serious concern and deserves continuing attention.
Accordingly, investigations should be initiated
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to narrow the
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accurate estimates of the atmospheric modifications. To that end the
committee makes the recommendations below. These recommendations are
not intended to define precisely designed studies, but rather to
indicate the general areas in which it appears that the uncertainties
can most probably be narrowed. Because further uncertainties and even
new causal mechanisms could emerge, research programs that address this
problem should be flexible enough to accommodate changing scientific
information needs.
1. Our ability to predict the climatic consequences of prescribed
injections of smoke and dust into the atmosphere is not well developed
at this time, but it can advance substantially in the next few years.
Problems that deserve special emphasis are (a) the transport of smoke
and dust by the atmosphere and the subsequent feedback effects of this
transport on the circulation, (b) the lifetime of smoke particles in
the perturbed atmosphere, (c) the transient response of the surface
temperature and near-surface meteorology to fluctuating light levels on
day to week time scales, (d) the regional influence of ocean-continent
climate interaction, (e) the radiative, optical, and infrared
properties of smoke aerosols and their evolution with time, and (f) the
implications of changes ~ ~
in precipitation and cloud structure.
One-dimensional radiative-convective climate models have proven
very useful in the initial phase of study, but, except for problem (c),
are severely limited in their ability to address these problems.
Two-dimensional zonally symmetric circulation models can be used to
study areas (a) and (b), but the limitations imposed by not easily
validated parameterizations of large-scale atmospheric eddies must be
kept in mind. Three-dimensional general circulation models (GCMs)
could be used to address all of the problems above, although existing
models are not properly designed for the task. The groups that have
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such models should be encouraged to use their resources in an effort to
decrease the current level of climate modeling uncertainty. Additional
supporting research will be needed to improve the treatment of those
processes in GCMs that influence aerosol lifetime and surface
conditions.
2. There is a need to develop a better understanding of the
following phenomena related to the fires induced by nuclear war: (a)
the dynamics of large-scale fires, including fire spread, the effects
of prompt water condensation, and the implications for smoke injection
heights, optical properties, and removal rates; (b) inventories of
urban fuels by type and density; (c) seasonal variations in, and areal
extents of, wildland fuel burdens :(using existing surveys and Landsat
data, for example); (d) the efficiency of ignition of both urban and
natural fuel arrays by nuclear bursts; (e) the quantity, composition,
and size distribution of smoke produced by different fuels in
large-scale fires, and the extent of fine per ticulates other than smoke
swept into fire plumes; (f) the microphysical processes that remove
smoke particles from the atmosphere in the long term; and (g) the
mesoscale transport and mixing of smoke, including the coupling of
smoke heating and microphysics to dynamics and precipitation.
These recommendations concerning fires and smoke are only generally
spelled out, as it was not the objective of the committee to design
specific research programs. However, it is worth emphasizing that a
particularly important subject that is amenable to both experimental
and theoretical study is the microphysical processing (by coagulation
and water scavenging) of smoke particles in large fire plumes, and the
implication for radiative properties of the smoke layer. Because of
the complexity of the fire/smoke problem, research planning and
management in this area should be carefully coordinated.
3. An important effect of nuclear war is radioactive fallout.
This topic does not lie within the scope of the present study, and the
committee has not addressed it; but the committee does believe that the
radioactivity problem should be reexamined in appropriate detail.
Earlier studies estimated that the globally averaged long-term
radiation hazard would not be large. However, these studies depended
on an analysis of strontium-90 fallout from atmospheric nuclear tests,
which were dominated by multimegaton bursts that resulted in
stratospheric injection of the radioactive debris, and thus avoided
early rainout. Current arsenals comprise mainly submegaton warheads,
which would inject a major share of their radioactivity into the
mid-latitude troposphere. Thus widespread fallout and precipitation on
intermediate time scales (days to weeks) might pose a more serious
problem. New preliminary estimates suggest that low-yield scenarios
significantly increase the globally averaged radiation hazard per
megaton released (Knox, 1983; Turco et al., 1983~.
4. Although the committee's conclusions on dust seem well
constrained, they are largely based on a small body of empirical data
derived from nuclear tests that in some respects are imperfect analogs
of 0.5- to 1.0-Mt continental surface bursts. The data come from
either high-yield tests at the Pacific Proving Ground or from Johnie
Boy, a very low yield, partially buried test in Nevada. More detailed
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theoretical treatments (especially, detailed numerical simulations) of
fireball mass loading (i.e., vaporized and melted rock and ejected,
lofting, and recondensation processes that lead to the
distribution of dust particles in the stabilized cloud
estimates on a firmer footing.
5. With the exception of one study using a two-dimensional model,
all of the published calculations of ozone decreases from nuclear
explosions (including the present set) have come from one-dimensional
models of chemistry and transport. Present-day scenarios of nuclear
war involve the injection of nitrogen oxides in the lower stratosphere,
where the chemical processes and the transport processes both have
similar characteristic times. Suitable two- and three-dimensional
models potentially can represent the ozone space-time variations more
realistically than a one-dimensional model. The committee recommends
the development and application of higher-dimensional models to this
problem. Included in the work should be appropriate sensitivity tests
and a degree of verification of the model.
6. Geologists and paleoclimatologists should make joint
investigations on the local and global scales of the possible climatic
effects of well-dated great volcanic explosions that have occurred in
the past few million years. The errors in dating volcanic eruption
products increase with increasing age: hence the youngest great
volcanic explosions offer the best opportunity to correlate climate
changes with particular explosions. Research is also needed to
quantify adequately the character and amount of material injected into
the atmosphere by large volcanic explosions.
Recent work suggests that the occurrence of regional to global
effects of meteorite impacts in the energy range 106 to 107 Mt may
~ Multidisciplinary
investigations of identifiable events should be carried out to assess
the effects of large impacts on climate and on the biology.
final
could put these
be recognizable in marine and continental sediments
REFERENCES
Knox, J.B. (1983) Global scale deposition of radioactivity from a large
scale exchange. Paper presented at the International Seminar on
Nuclear War, 3rd Session: The Technical Basis for Peace. Ettore
Majorana Centre for Scientific Culture, Erice, Sicily, August
19-24, 1983.
Turco, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, and C. Sagan (1983)
Global Atmospheric Consequences of Nuclear War. Interim Report.
Marina del Rey, Calif.: R&D Associates. 144 pp.
Representative terms from entire chapter:
nuclear war
