Even a limited nuclear war would inject enough smoke and dust into the atmosphere to threaten the survival of our species.
The impact of the Cretaceous-Paleocene asteroid 66 million years ago released enough dust and debris to cloud large parts of the planet, causing the mass extinction of some 80 per cent of animal species. When Turco et al. (1983) and Carl Sagan (1983) warned the world about the climatic effects of a nuclear war, they pointed out that the amount of carbon stored in a large city was sufficient to release enough aerosols, smoke, soot and dust to block sunlight over large regions, leading to a widespread failure of crops and extensive starvation.
The current nuclear arsenals of the United States and Russia could potentially inject 150 teragrams of soot from fires ignited by nuclear explosions into the upper troposphere and lower stratosphere (Coupe et al., 2019), lasting for a period of 10 years or longer, followed by a period of intense radioactive radiation over large areas.
Even a “limited” nuclear war, such as between India and Pakistan, would release enough aerosols to affect large regions, killing millions or billions through starvation. As stated by Robock et al. (2007):
“The casualties from the direct effects of blast, radioactivity, and fires resulting from the massive use of nuclear weapons by the superpowers would be so catastrophic … the ensuing nuclear winter would produce famine for billions of people far from the target zones.”
With the global arsenal of nuclear warheads at around 13,000 – 90 per cent of which are held by Russia and the US – a regional conflict such as in Ukraine or Taiwan would threaten to spill worldwide. As the clock of atomic scientists is set at 100 seconds to doomsday, the rising probability of an intended or inadvertent nuclear war, against the background of rising global warming, indicates an hour of truth for our species – a choice between the defence of life on earth and global suicide.
While the inhabitants of the planet are preoccupied with the 24-hour news cycle, media hype, a deadly virus, economic issues and sports games, the hair-trigger nuclear gun loaded by the powers-that-be, east and west, is threatening all life on earth.
A release of 5 teragrams of smoke from nuclear explosions has been modelled to lower the average global temperature by about 1.5 degrees Celsius (Robock et al. 2007), although over the continents the cooling is likely to be more abrupt.
Inherent in nuclear war strategy is a “use them or lose them” approach, namely hitting the enemy’s air and missile launch pads before the weapons can be launched, which virtually ensures that many or most nuclear warheads would be potentially used. Given the size of the world’s nuclear warheads inventory, this would guarantee a global catastrophe.
Such an extreme event would arrest global warming for 10 years or longer, possibly in part analogous to the consequences of a less abrupt flow of polar ice melt into the oceans, as modelled by Bronselaer et al. (2018).
When Sagan and colleagues published their nuclear winter scenario as a warning to humanity, Sagan was painted as an alarmist by many and he faced extensive criticism not just from pro-nuclear conservatives but also from scientists who resented him leveraging his fame to advocate what some regarded as political views. A similar situation occurs today in regard to accelerating global warming and the nuclear threat, as confirmed by the warning by the Bulletin of the Atomic Scientists. Time is running out.