A nuclear war between the US and Russia would result in a global famine that would kill more than five billion people — about three quarters of the world's population — a study published in the journal Nature Food predicted on Monday.
Climate scientists at Rutgers University in New Jersey said such a conflict would disrupt food production worldwide and destroy the ozone layer.
“The data tell us one thing: we must prevent a nuclear war from ever happening,” said study-co author Alan Roebuck.
The scientists calculated the levels of sun-blocking soot expelled into the atmosphere by nuclear detonations of six different sizes, the largest based on a war between the US and Russia.
In the smallest scenario, the model showed global average caloric production decreasing by 7 per cent within five years of the conflict, which would be the biggest shortfall ever recorded.
And in the largest scenario, it would decrease by about 90 per cent between three and four years afterwards.
The unprecedented destruction of crop yields would lead to 75 per cent of the world's population dying within two years — partly due to the attendant unavailability of proteins and nutrients humans need to survive.
The effect on climate change would be even more apocalyptic, said study co-author Lili Zia, assistant research professor at Rutgers.
“The ozone layer would be destroyed by the heating of the stratosphere, producing more ultraviolet radiation at the surface, and we need to understand that impact on food supplies,” she said.
UN Secretary General issues desperate plea
The warning came as UN Secretary General Antonio Guterres said “humanity is just one misunderstanding, one miscalculation away from nuclear annihilation” in response to military activity around the Zaporizhzhia nuclear power complex in Ukraine, as Moscow and Kyiv blamed each other for shelling in the area.
Russian troops have occupied the Zaporizhzhia plant in south-eastern Ukraine since March, and Kyiv has accused Moscow of basing hundreds of soldiers and storing weapons there.
The nuclear plant has come under fire repeatedly over the past week, raising fears of a nuclear catastrophe.
“What is happening there is outright nuclear terrorism and it can end unpredictably at any moment,” Dmytro Orlov, mayor of the town of Energodar in the Zaporizhzhia region, told AFP.
Mr Orlov said there was mortar shelling on the plant “every day and night”.
“The situation is hazardous and what causes the most concern is that there is no de-escalation process,” he said.