"You can win a nuclear war for two weeks, until the Nuclear Winter grabs you," Carl Sagan told an overflow audience at the Institute of Politics forum last night.

Sagan, the David Duncan Professor of Physical Science at Cornell, emphasized the "absolutely devastating" climatic effects on earth after a thermonuclear war.

Sagan based his arguments on a study he worked on with other scientists, including Professor of Geology Steven Jay Gould, that will be published later this month.

Using slides to illustrate his 90 minute presentation, Sagan said that following a nuclear war the earth would experience a dramatic drop in intercontinental temperatures, the partial destruction of the ozone layer, and the virtual ceasing of photosynthesis of green plants in the northern hemisphere.

He added that a nuclear war would result in radioactive fallout, possibly reaching lethal doses for human beings, and poisonous toxins being released into the air from burning cities. Medical facilities would be unavailable to deal with these crises, he said adding. "The extinction of Homo Sapiens cannot be excluded."

Sagan said that a nuclear exchange between the U.S. and the USSR would also "utterly destroy" developing countries and neutral countries, adding, "the fate of these nations depends profoundly on what the U.S. and Soviet Union do."

Sagan concluded his speech by saying that he found it "considerable" that the U.S. and the Soviet Union had been making decisions since the 1940s effecting all people, with no idea of the climatic consequences of a nuclear war.