Regional nuclear war would create near-global ozone hole

The astronomer Carl Sagan
is remembered for his lucid and edifying presentations on public television
science program “Cosmos,” in which he would discuss the origins of
the universe, the fate of stars, and similar topics. He is forever associated with
the phrase “billions and billions” (as in: “The universe
comprises billions and billions of stars”). In fact, Sagan never used the
phrase. The public’s association of the phrase and Sagan came from a Tonight
Show skit. Parodying Sagan’s affect, Johnny Carson quipped “billions and
billions.” Carson’s mimicking of Sagan’s voice and manner
was so compelling that the phrase not only became inextricably associated with
Sagan, but it also gave rise to a humorous fictitious number — the Sagan. A
Sagan is a (humorous) unit of measurement equal to at least four billion. The
unit is derived from the phrase “billions and billions.” The lower
bound of a number conforming to the constraint of billions and billions must be
two billion plus two billion, or four billion. Assuming one uses the short
scale definition for billion, there are nearly 100 Sagan (400,000,000,000)
stars in the Milky Way galaxy. Note that Sagan, who had a sense of humor about
the myth, titled his final book Billions and Billions: Thoughts on Life and
Death at the Brink of the Millennium

Sagan was also a major
scientific force behind the Nuclear Winter argument, which was hotly debated in
the 1980s. A group of scientists argued that even a limited nuclear exchange
between the United States and the Soviet Union would create large fires which
would send so much smoke and soot into the atmosphere, that the light of the
sun would be blocked for months, leading to massive extinction of animals and
plants (see the Sagan’s essay on the “Nuclear
Winter”).

We were reminded of Sagan
by two researchers at the University of Colorado at Boulder, whose
computer-modeling study showed that a nuclear war between the two countries
involving fifty Hiroshima-sized nuclear devices on each side would cause
massive urban fires and loft as much as five million metric tons of soot about
fifty miles into the stratosphere. Research Associate Michael Mills, chief
study author, said the soot would absorb enough solar radiation to heat surrounding gases, setting
in motion a series of chemical reactions which would break down the
stratospheric ozone layer protecting Earth from harmful ultraviolet radiation.
“We would see a dramatic drop in ozone levels that would persist for many
years,” said Mills of CU-Boulder’s Laboratory for Atmospheric and Space
Physics. “At mid- latitudes the ozone decrease would be up to 40 percent, which
could have huge effects on