Nuclear weapons are the only devices ever created with the capacity to destroy all complex life forms on Earth.

If tens or hundreds of them were used against cities, the soot and smoke from the ensuing firestorms would blanket the planet and block out sunlight for a decade or more, leading to a dramatic drop in global temperatures – an effect known as nuclear winter.

Plunged into darkness, the world would experience freezing conditions even in what are now tropical environments. Food crops would be decimated and global agricultural production would collapse, leading to widespread famine and societal breakdown.

Infectious disease epidemics and conflict over scarce resources would become rife. People who are already malnourished would be at greatest risk of death.

Even a so-called “limited” nuclear war – involving a small fraction of the global inventory of nuclear weapons – would place much of the world’s population at risk of starvation.

Such a war would severely deplete the ozone layer, leading to a major increase in certain cancers and devastating loss of marine life. Many plant and animal species would face extinction, and the damage to the planet would be irreversible.