Scientific Colloquium
January 28, 2015, 3:30 p.m., Building 3 Auditorium
OWEN BRIAN
TOON
UNIVERSITY OF COLORADO
"Dead Dinosaurs and Nuclear
Wars"
Sixty six million years ago a
mountain sized chunk of rock traveling at more than 10 times the
muzzle velocity of an assault rifle, slammed into the shallow
sea covering what is now the Yucatan Peninsula of Mexico.
Shortly thereafter the 5th of the Earth’s great mass extinctions
occurred. The energy released by the impact was comparable to
having a 1-megaton nuclear explosion spaced every 5 km over the
Earth’s surface. Massive tidal waves and earthquakes swept the
Gulf of Mexico, and rock ejected from the crater carpeted the
land as far away as Wyoming. However, a greater danger lay in
the vaporized asteroid and coral from the bottom of the sea,
which flew back into space in a massive fireball. After the
material in the fireball recondensed into drizzle-sized droplets
of rock it reentered the atmosphere over the entire Earth as a
massive swarm of shooting stars. The shooting stars heated the
upper atmosphere until it glowed like the heating bar in an
electric broiler oven. The radiation from this hot gas and rock
ignited all the land biomass on Earth, creating firestorms on a
global scale, and broiled the dinosaurs alive. Then it became
pitch-black, to dark even for cats to see, and much too dark for
photosynthesis. Temperatures on the land fell below freezing. In
the few years before the Earth recovered many species of plants
and animals that were not broiled alive were driven to
extinction by the cold weather. The food chain in the ocean
collapsed because phytoplankton could no longer metabolize
without sunlight, and the fish, ammonites and other larger
creatures that depended on plankton starved to death. Many of
these same phenomena may occur if there is a nuclear war.
Nuclear explosions in cities would cause urban firestorms,
killing large numbers of people. For example, 20 million Indians
and Pakistanis might die directly from nuclear bomb blasts in a
war involving half of their current arsenals. North Korea could
cause as many casualties as the U.S. experienced in World War
II, by exploding only 3 small atomic weapons over U.S. cities.
The smoke from these firestorms would rise into the upper
atmosphere, block sunlight, and cool the planet. The resulting
cold temperatures would reduce or eliminate food production.
Even a war between smaller powers, such as India and Pakistan,
could cool the Earth to lower temperatures than any in thousands
of years, damaging agriculture and triggering mass starvation,
perhaps killing a billion people. A war between Russia and the
US would likely create sub-ice age temperatures and kill the
majority of the human population by starvation. Destruction of
agriculture, starvation and large losses of life would sweep the
planet even in places not attacked. Unfortunately, at present,
we are not capable of stopping an asteroid from hitting the
planet. It remains to be seen if we can prevent a nuclear
conflict.
About the Speaker:
Owen Brian Toon is a Professor in the Department of Atmospheric
and Oceanic Sciences for which he was the founding Chair, and a
Research Associate in the Laboratory for Atmospheric and Space
Physics at the University of Colorado at Boulder. He received an
A. B. in physics at the University of California at Berkeley in
1969 and a Ph.D. in physics at Cornell University in 1975. He
was a Research Scientist at NASA’s Ames Research Center from
1975 until 1997 when he moved to Colorado.
Brian’s research group studies radiative transfer, aerosol and
cloud physics, atmospheric chemistry and parallels between the
Earth and planets. Brian has helped conceive, develop and lead
many NASA airborne field missions aimed at understanding
stratospheric volcanic clouds, stratospheric ozone loss, the
effects of aircraft on the atmosphere, and the role of
convective and cirrus clouds in Earth’s climate system. He has
been involved in numerous satellite missions for both Earth and
the planets.
He has published more than 300 papers in refereed scientific
journals, and is one of the most highly cited researchers in
Geoscience. He received NASA’s 1983 and 1989 medals for
Exceptional Scientific Achievement for studies of the climates
of Earth and the planets, and of the ozone hole. He won the
American Physical Society's 1985 Leo Szilard Award for Physics
in the Public Interest for his work on nuclear winter. He was
recognized by UNEP in 2007 for contributions to the Nobel Peace
Prize winning IPCC reports. In 2011 he received the American
Geophysical Union’s Roger Revelle Medal. In 2014 he received the
American Meteorological Society’s Carl-Gustaf Rossby Medal “for
fundamental contributions toward understanding the role of
clouds and aerosols in the climates of Earth and other planets”.
Return to Schedule