"As previous work has pointed out, the nuking of a sufficiently large city would be enough to generate a global-scale nuclear autumn. Take Los Angeles, for example, a city that extends for 500 square miles. The explosion and resulting fires would send an estimated 5.5 million tons of ash and soot into the stratosphere, causing sunlight, temperatures, and rainfall to temporarily decrease around the world. Globally, this would result in diminished growing seasons for the next half-decade, and temperatures would be the lowest in a thousand years. In some parts of the world, rainfall would be down by as much as 80 percent. But unlike this earlier work, which focused on relatively small, 15-kiloton nukes exploding over cities, the new study looked at whether today’s more powerful weapons could trigger nuclear autumn all on their own. They can. Liska and his colleagues found that the US, Russia, and China all have weapons that could trigger a nuclear autumn through the detonation of fewer than five bombs."