CBC Science What on Earth? James Westman 4vAug 23
"....................................................... One potential effect of the atom bomb wasn't understood until years after the death of J. Robert Oppenheimer, the director of the Manhattan Project. Specifically, the concept of nuclear winter, which was first brought to the world's attention by astrophysicist and author Carl Sagan in 1983.
Virtually every modern climate model has confirmed the initial findings: nuclear war would cool the planet.
"Nuclear weapons dropped on cities and industrial areas would produce fires, the fires would produce smoke, and that smoke would be lofted up into the stratosphere in a giant thunderstorm," Alan Robock, a climate scientist at Rutgers University in New Jersey, said in a recent interview.
................... "The basic physics are very simple: if you block out the sun, it gets cold at the ground," Robock said. "We have analogues of that. We have nighttime, we have winter."
.......................... Why has the smoke from wildfires not caused global cooling? Unless smoke particles reach the stratosphere, they get washed out of the lower atmosphere by precipitation.
.............................According to a 2007 paper, a nuclear war between the U.S. and Russia would send 150 million tonnes of black soot into the stratosphere, resulting in global average surface cooling of 7 C to 8 C that would persist for years. Even after a decade, the world would still be 4 C cooler.
This would be a massive problem for global food production. Countries at higher latitudes, like Canada, would be particularly hard hit by nuclear winter, since much of the country is already too cold for significant agriculture.
If you're wondering if nuclear winter would stop global warming, you're not alone. It's a question Robock gets all the time. A full-scale nuclear war and a global famine resulting from nuclear winter would lead to the collapse of industrial society and human civilization. Robock said that if the U.S. and Russia had a nuclear war, it would largely halt carbon emissions, since most human activities would have ceased.................
Human-caused climate change poses the threat of an average global temperature change of several degrees on the timescale of decades. Nuclear winter, on the other hand, poses that danger on the timescale of years — even within a year.
"A nuclear war's impact on global food systems comes as a shock. It basically comes overnight. There's no way to adapt," said Jonas Jaegermeyr, a climate scientist and crop modeller who studies nuclear winter at Columbia University in New York.
A paper released last year in Nature Food found that up to 5.3 billion people would die from starvation two years after a full-scale nuclear exchange between the U.S. and Russia and the ensuing nuclear winter. (The paper also found 99 per cent of Canadians would starve to death.)
Clearly, nuclear winter is just about the worst way imaginable to stop global warming. It would replace steady planetary warming with abrupt planetary cooling.
"If you want to solve the global warming problem, the first answer is to just leave the fossil fuels in the ground and stop and use the sun and the wind [for power]," said Robock. "We have enough to power the world." https://www.cbc.ca/news/science/what-on-earth-oppenheimer-nuclear-winter-climate-change-1.6926861
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