President Vladimir Putin announced on Sunday that he was putting Russian nuclear forces on “high alert”. Alert status probably means little in terms of increasing the risk of escalation in Ukraine. But Putin’s ominous declaration reminded the world that Russia has, among the many destructive tools in its arsenal, many thousands of nuclear weapons.

For most people in the west, the very idea of using nuclear weapons is simply unthinkable — and so they don’t think about it. The cold war, in this view, proved that nuclear weapons are unusable.

But for better or for worse, we now live in a different world. The war in Ukraine, as well as the evolution in Russia’s thinking and its precarious military position, mean that nuclear escalation is a greater possibility than it has been since the early 1980s. It remains unlikely, but we need once again to think about it and consider how to further reduce the chances of it happening.