A single Russian nuclear strike in Ukraine causes existential devastation across the world quickly

Few nations on earth are unaffected. If the strike happens in a country like Ukraine, among the largest grain-exporting nations in the world, the impact spreads quickly. The attack prompts an agricultural embargo to contain potentially contaminated crops, creating a domino effect of food shortages that spread across the Middle East, South Asia, North Africa and West Africa. Fear is as dangerous as contamination itself: Panic over radiation exposure and its long-term effects drives people from their homes, regardless of whether the threat in their community is real or not. Border crossings are quickly overrun. Anxieties over a wider nuclear war immediately spike, causing the New York Stock Exchange to plunge. Lockdown orders trigger a rush on groceries, wiping markets’ shelves clean. No one can say what would happen next. If it was Vladimir Putin who launched an attack on Ukraine, the U.S. has warned there would be “catastrophic consequences.” But the response might not be nuclear. It could be a devastating aerial bombardment aimed at Russia’s naval fleet, or Washington could decide to target a base in Belarus, where Russia has recently deployed nuclear weapons, avoiding a direct attack on Russian territory. A tit-for-tat escalation, once touched off, is difficult to stop. If the end result was a thermonuclear exchange between nuclear powers, like the U.S. and Russia, the impact on humanity would be swift and long-lasting. Even a limited nuclear war could be catastrophic. A 2022 scientific study found that if 100 Hiroshima-size bombs — less than 1 percent of the estimated global nuclear arsenal — were detonated in certain cities, they could generate more than five million tons of airborne soot, darkening the skies, lowering global temperatures and creating the largest worldwide famine in history. An estimated 27 million people could immediately die, and as many as 255 million people may starve within two years.