—
“Our baseline case, as in many other studies, was a 5000-megaton war with only a modest fraction of the yield (20 percent) expended on urban or industrial targets… In the baseline case, the amount of sunlight at the ground was reduced to… too dark for plants to make a living from photosynthesis.
“Land temperatures, except for narrow strips of coastline, dropped to minus 25 Celsius (minus 13 degrees Fahrenheit) and stayed below freezing for months -- even for a summer war... virtually all crops and farm animals, at least in the Northern Hemisphere, would be destroyed, as would most varieties of uncultivated or domesticated food supplies. Most of the human survivors would starve.
“But what if nuclear wars can be contained, and much less than 5000 megatons is detonated? Perhaps the greatest surprise in our work was that even small nuclear wars can have devastating climatic effects. We considered a war in which a mere 100 megatons were exploded, less than one percent of the world arsenals, and only in low-yield airbursts over cities. This scenario, we found, would ignite thousands of fires, and the smoke from these fires alone would be enough to generate an epoch of cold and dark almost as severe as in the 5000 megaton case. The threshold for what Richard Turco has called The Nuclear Winter is very low.
—
I think the reason the Carl Sagan was widely panned afterwords is that the science was just plain bad. The scale of the predictions he made were so off the charts from almost forty years of previous nuclear experience, that he was obviously was wrong. He predicted essentially the end of the humanity from a mere 100 megatons of nuclear explosions, and yet twenty years before article, the Soviet Union had tested a 50 megaton bomb with no more than the usual local effects.
Using bad science to advance a public policy goal is exactly what got us to the current "distrust of science"