Nuclear
winter is a hypothetical global
climate condition that was predicted to be a possible outcome of a large-scale nuclear war.
It was thought that severely cold weather would be caused by detonating
large numbers of nuclear
weapons, especially over
flammable targets such as cities, where
large amounts of smoke and soot would be injected into the Earth's
stratosphere.
This layer of
particles would significantly reduce the amount of
sunlight that reached the surface, and could potentially remain in the
stratosphere for weeks or even years (smoke and soot arising from the
burning petroleum fuels and plastics absorbs sunlight much more
effectively than smoke from burning wood). The smoke and soot would be
shepherded by strong west-to-east winds, forming a uniform belt of
particles encircling the northern hemisphere from 30° to 60°
latitude. These thick black clouds could block out much of the sun's
light for a period as long as several weeks, causing surface
temperatures to drop by as much as 20°C for several weeks
The combination
of darkness and killing frosts, combined with high
doses of radiation from nuclear fallout,
would severely damage plant life in the region. The extreme cold, high
radiation levels, and the widespread destruction of industrial,
medical, and transportation infrastructures along with food supplies
and crops would trigger a massive death toll from starvation, exposure,
and disease. It was also thought that nitrogen oxides generated by the
blasts would degrade the ozone layer, as had been observed in the first
thermonuclear blasts, which had unanticipated degrading effects on the
ozone. These effects have since been mitigated by ozone regeneration,
but the effect of a full-scale war would undoubtedly be much greater.
Secondary effects from ozone depletion (and concomitant increases in
ultraviolet radiation) would be significant, with impacts on the
viability of most human staple agricultural crops as well as disruption
of ocean food chains by killing off phytoplankton.
One effort to
predict the metereological effects of a large-scale
nuclear war was the 1983 "TTAPS" study (from the initials of the last
names of its authors, R.P. Turco, O.B. Toon, T.P. Ackerman, J.B.
Pollack, and Carl Sagan). The authors were inspired to write the paper
by cooling effects due to dust storms on Mars and to carry out a
calculation of the effect they used a simplified two dimensional model
of the Earth's atmosphere that assumed that conditions at a given
latitude were constant. The consensus with more sophisticated
calculations is that the atmospheric model used in TTAPS probably
overestimates the degree of cooling although the amount of this
overestimation remains unclear. Although such nuclear war would
undoubtedly be devastating, the degree of damage to life on Earth as a
whole remains controversial.
