Scientific Colloquium
January 28, 2015, 3:30 p.m., Building 3 Auditorium

"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”.

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