You can now see an excellent visualization of global catastrophic risks estimates produced in the Ragnarök series here.
A nuclear exchange could cause a nuclear winter – a release of black carbon into the atmosphere which would according to some studies, result in the blocking the Sun’s thermal energy. This would lower temperatures regionally and globally for several years, and open up new holes in the ozone layer protecting the Earth from harmful radiation, reduce global precipitation by about 10%, trigger crop failures, and result in widespread food shortages.
According to some models, the smoke would rapidly engulf the Earth and form a dense stratospheric smoke layer. The smoke from a war fought with strategic nuclear weapons would quickly prevent up to 70% of sunlight from reaching the surface of the Northern Hemisphere and 35% of sunlight from reaching the surface of the Southern Hemisphere. Such an enormous loss of warming sunlight would produce Ice Age weather conditions on Earth in a matter of weeks. For a period of 1-3 years following the war, temperatures would fall below freezing every day in the central agricultural zones of North America and Eurasia.
This could leave some survivors in parts of Australia and New Zealand, but they would be in a very precarious situation and the threat of extinction from other sources would be great. Whether a nuclear winter could cause extinction is currently unclear. Some models consider total extinction very unlikely, and suggest parts of the world would remain habitable.
These studies consider what is currently the worst-case nuclear exchange, namely, that between the US and Russia. However, It is possible that a future nuclear arms race someday leads to larger stockpiles or more dangerous nuclear weapons than existed at the height of the Cold War. In this case, chances of a nuclear extinction might be higher than they currently are.
In the first part of the Ragnarök Question Series, we asked the question If a global catastrophe happens before 2100, will it be principally due to the deployment of nuclear weapons?. Now it is asked,
Given that nuclear catastrophe occurs that results in the reduction of global population of at least 10% by 2100, will the global population decline by more than 95% relative to the pre-catastrophe population?
The question resolves ambiguous if a global nuclear catastrophe that claims at least 10% (in any period of 5 years or less) does not occur. It resolves positively if such a catastrophe does occur, and the global population is less than 5% of the pre-catastrophe population at any point within 25 years of the catastrophe. The question resolves negative if a global nuclear catastrophe occurs that claims at least 10% (in any period of 5 years or less) but the post-catastrophe population remains above 5%.
This question is part of the Ragnarök Question Series. Check out the other questions in the series:
Also, please check out our questions on whether a global catastrophe will occur by 2100, and if so, which?:
All results are analysed here, and will be updated periodically.