Scientists Richard Turco and Carl Sagan made the world cognizant of the effects of a global nuclear war in the early 1980s, and Sagan published a popular book on the subject, The Nuclear Winter, in 1983. While most people were already terrified of the nuclear arms race that had been going on between the United States and the Soviet Union since the 1950s, the idea that ever major city on Earth could be obliterated by atomic and hydrogen bombs was just the beginning. Sagan and Turco showed that it wouldn’t even take all of the then-50,000 nuclear warheads to kick up enough dust and debris to block out the Sun’s warmth. Clouds of irradiated dust would be blown into the stratosphere, where they would circle the planet for months, plunging us into an artificial winter that would destroy crops and lead to a global famine.

Since the publication of The Nuclear Winter, many scientists have come to believe a similar scenario could happen if a large asteroid hit the planet. Indeed, this is one theory about how the dinosaurs may have become extinct 65 million years ago. Another possible cause of a nuclear winter would be planet-wide volcanic eruptions, which some scientists theorize led to a “Snowball Earth” hundreds of millions of years ago. Actually, when volcanoes are involved it would perhaps be more accurate to call these “volcanic winters.”