A nuclear war between India and Pakistan could kill up to 125 million people in a week and send the planet into ecological freefall with plummeting temperatures leading to mass starvation, a new study has claimed.
The study, published in Science Advances, looks at a war scenario that could play out between India and Pakistan in 2025 when it is predicted that the two nuclear powers could have a combined 500 nuclear weapons.
Co-author Alan Robock, a Distinguished Professor in the Department of Environmental Sciences at Rutgers University, said that "such a war would threaten not only the locations where bombs might be targeted but the entire world".
The report details how, if nuclear weapons were used, up to 125 million people could be killed in one week in the crowded cities of India and Pakistan. For context, 50 million people were killed in the whole of World War II.
The world's annual death rate from all causes is about 56 million people per year, meaning this scenario would see the global death rate increase by a factor of 50.
And that's just the local and immediate effects.
Researchers found that the resulting nuclear fires could release 16 million to 36 million tons of soot (black carbon) that would rise into the upper atmosphere, spreading around the world within weeks.
The cloud would block the sunlight reaching the surface by up to 35 per cent, cooling temperatures by up to 5C and reducing precipitation by 15 to 30 per cent.
Those sorts of temperatures haven't been seen on earth since the last ice age and would cause "severe disruption to natural ecosystems", according to the report.
This would have a huge impact on global food production, triggering mass starvation.
The report states that recovery from all these impacts would take over a decade as smoke lingers in the upper atmosphere.
"Nine countries have nuclear weapons, but Pakistan and India are the only ones rapidly increasing their arsenals," said Robock.
"Because of the continuing unrest between these two nuclear-armed countries, particularly over Kashmir, it is important to understand the consequences of a nuclear war.
"Nuclear weapons cannot be used in any rational scenario but could be used by accident or as a result of hacking, panic or deranged world leaders.
"The only way to prevent this is to eliminate them."
The growing tension between India and Pakistan over the disputed region of Kashmir was brought to a head last week, when Pakistani leader Imran Khan made a chilling speech at the UN that warned of "consequences far beyond the borders".
"When a nuclear-armed country fights to the end, it will have consequences far beyond the borders. It will have consequences for the world.
Khan called India PM Narendra Modi's actions in Kashmir "stupid" and "cruel".
"That's not a threat," he said of his war comments. "It's a fair worry. Where are we headed?"