Two-thirds of people on the planet would die from starvation within two years of a nuclear war between the US and Russia, researchers have concluded.
Modelling by Rutgers University, in the US, suggested nuclear weapon detonation would cause massive fires and inject soot into the atmosphere, blocking sunlight from reaching the surface and devastating crops.
The biggest war would bring starvation to three-quarters of people and kill up to five billion within two years.
But even a smaller nuclear skirmish - such as between India and Pakistan - would likely lead to 2.5 billion deaths within 24 months, the team has estimated.
To judge the global devastation, researchers calculated how much Sun-blocking soot would enter the atmosphere from firestorms ignited by the detonation of nuclear weapons.
Under even the smallest nuclear scenario, food production based on total calorie content would reduce by seven per cent, but a full-scale conflict between US and Russia would see a fall of 90 per cent within three to four years of fighting.
‘Banning nuclear weapons is the only long-term solution’
“The data tell us one thing - we must prevent a nuclear war from ever happening,” said Alan Robock, distinguished professor of climate science in the department of environmental sciences at Rutgers.
“The world has come close to nuclear war several times. Banning nuclear weapons is the only long-term solution.”
The demise of crops in major exporting countries such as Russia and the US would cause major food shortages elsewhere, the study in the journal Nature Food found.
The team said the outcome could be even worse, because they have yet to factor in the damage caused by ultraviolet radiation to the surface of the planet, once the ozone layer had been destroyed by the heating of the stratosphere.
The team has called on the nine nuclear powers - the UK, France, the US, Israel, Russia, China, India, Pakistan, North Korea - to sign up to the UN Treaty on the Prohibition of Nuclear Weapons.
“Our work makes clear that it is time for those nine states to listen to science and the rest of the world and sign this treaty,” added Prof Robock.