How Big Would a Nuclear War Need to Be to Upend Global Civilization?

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There are 13,865 nuclear warheads presently in existence, but it could only take one hundred of them to set off a "Nuclear Autumn," creating a 10 to 20% shortfall in agricultural production, destabilizing industrial supply chains, and causing widespread starvation, possibly resulting in the deaths of over two billion people.

Scientists Joshua M. Pearce and David C. Denkenberger, respectively from Michigan Tech University and Tennessee State University, arrived at that conclusion last year in a paper published to the journal Safety.

The duo sought to rationally examine the concept of nuclear deterrence.

"Stated simply: no country should have more nuclear weapons than the number necessary for unacceptable levels of environmental blow-back on the nuclear power’s own country if they were used," they wrote.

After all, what's the point in annihilating your enemy if you commit suicide in the process?

So Pearce and Denkenberger simulated the global climatic effects of launching 100, 1,000, or 7,000 nuclear missiles into large cities, then predicted the ramifications for global food supplies.

For nine of the six nuclear powers, launching one hundred weapons would essentially destroy their own societies in the process, Pearce and Denkenberger found. India, Pakistan, the United Kingdom, North Korea, Israel, and China would all likely see half of their citizens perish from starvation in a Nuclear Autumn triggered from the explosions of one hundred warheads over dense urban areas. Residents of France, the United States, and Russia would probably be spared due to those countries' significant swaths of arable land.

Why would such a comparatively small number of nuclear explosions trigger so much global suffering? After all, more than 2,000 nuclear test explosions have been carried out, and yet we haven't experienced a calamitous "Nuclear Winter."

The theorized global effects of a nuclear war actually don't arise from nuclear explosions, themselves, but rather from the all-consuming fires they would ignite. Dropping one hundred nukes on dense urban areas would give rise to firestorms that would send seven trillion grams of soot into the atmosphere. These particles would gradually rise into the stratosphere and linger for years, blocking the sun's rays and lowering global temperatures. Scientists have observed this process on smaller, more localized scales with large wildfires.

According to Pearce and Denkenberger, "This would be more than sufficient to produce the lowest temperatures Earth has experienced in the past 1,000 years—lower than during the post-medieval Little Ice Age or in 1816, the so-called 'Year Without a Summer'. It would result in a 20% drop in sunlight and lead to a 19% drop in global precipitation."

Needless to say, a nuclear exchange of 1,000 missiles would be far more devastating. In this scenario, the authors estimate that 140,000 Americans would perish from global food shortages, in addition to the direct deaths from nuclear strikes and billions more starvation deaths around the world.

While Pearce and Denkenberger's analysis solely focused on Nuclear Autumn's effects on food production, they acknowledge that there would be many more deleterious effects, "including disruption of the economic system, reduction of medical supplies and personnel, high levels of pollution, psychological stress, increased diseases and epidemics, and enhanced UV radiation causing increased rates of skin cancer."

These unaccounted for figures likely makes their dire estimates somewhat conservative. Let's hope we never find out.

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