How would the world react if Russia launched a nuclear attack?

Russia’s assault on Ukraine and its veiled threats of using nuclear arms have policymakers, past and present, thinking the unthinkable: How should the rest of world respond to a Russian battlefield explosion of a nuclear bomb?

The default US policy answer, say some architects of the post-Cold War nuclear order, is with discipline and restraint. That could entail stepping up sanctions and isolation for Russian President Vladimir Putin, said Rose Gottemoeller, deputy secretary general of Nato from 2016 to 2019.

But no one can count on calm minds to prevail in such a moment, and real life seldom goes to plan. World leaders would be angry, affronted, fearful. Miscommunication and confusion could be rife. Hackers could add to the chaos. Demands would be great for tough retaliation – the kind that can be done with nuclear-loaded missiles capable of moving faster than the speed of sound.

When military and civilian officials and experts have war-gamed Russian-US nuclear tensions in the past, the tabletop exercises sometimes end with nuclear missiles arcing across continents and oceans, striking the capitals of Europe and North America, killing millions within hours, said Olga Oliker, programme director for Europe and Central Asia at the International Crisis Group.

“And, you know, soon enough, you’ve just had a global thermonuclear war,” Oliker said. It’s a scenario officials hope to avoid, even if Russia targets Ukraine with a nuclear bomb.

Gottemoeller, a chief US nuclear negotiator with Russia for the Obama administration, said that the outlines that President Joe Biden has provided so far of his nuclear policy stick with those of past administrations in using atomic weapons only in “extreme circumstances.”