The study, co-authored by researchers at Rutgers University, quantifies just how catastrophic a nuclear conflict between the two nations would be. In addition to the 100 million-plus death toll in the immediate aftermath, the study authors warn we could expect global vegetation growth to decline 20 to 35 percent as ocean productivity fell 5 to 15 percent⁠—a result that would cause mass starvation, ecosystem disruption and more deaths. It could take over a decade to fully recover from the impacts, they say.

“Nine countries have nuclear weapons, but Pakistan and India are the only ones rapidly increasing their arsenals,” said Alan Robock, a Distinguished Professor in the Department of Environmental Sciences at Rutgers University—New Brunswick.

“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.”

Indeed, only last week in an address to the United Nations General Assembly in New York, Pakistani Prime Minister Imran Khan appealed for international support against India’s decision to remove semi-autonomous status from its share of Kashmir last month and impose a lockdown on the majority Muslim population—stressing the threat of nuclear war.

“If a conventional war starts between the two countries, anything could happen,” said Khan. “But supposing a country seven times smaller than its neighbor is faced with the choice: either you surrender, or you fight for your freedom till death, what will we do?”

“I ask myself this question and my belief is la ilaha illallah, there is no god but one, and we will fight. And when a nuclear-armed country fights to the end, it will consequence far beyond the borders.”

Robock et al.’s calculations are based on a potential war scenario for 2025, when it is estimated the two countries could have 400 to 500 nuclear weapons between them. Each nuke could have an explosive power between 15 kilotons—equivalent to 15,000 tons of TNT, i.e. the same size as the “Little Boy” that fell on Hiroshima in 1945—and a few hundred kilotons, the researchers say. The largest known nuclear weapon in existence today, the Tsar Bomba, far exceeds those considered in the study with an explosive power of 50 megatons.

The researchers conclude that were India to release 100 strategic weapons in a nuclear conflict and Pakistan 150, the number of fatalities caused by the initial effects could total 50 million to 125 million people—the exact size depends on the size of the weapons used. For context, an estimated 50 million people were killed in the Second World War, although that number excludes those who died from disease and starvation. Many more would die from the mass starvation that would almost certainly follow, they add.

Starvation is likely because the explosions would cause fires that could, between them, release 16 million to 35 million tons of soot into the atmosphere. This soot would absorb solar radiation and heat the air, which would then cause the smoke to rise further, blocking our sun’s light so that 20 to 35 percent less would fall on the Earth. This would trigger a period of global cooling—resulting in a nuclear winter—that would see surface temperatures drop 3.6 F to 9 F to levels not seen on Earth since the last ice age. We could also see global precipitation levels plummet 15 to 30 percent, affecting some regions more than others, the study’s authors conclude.

As a result, they predict 15 to 30 percent less vegetation growth and a 5 to 15 percent decline in ocean productivity worldwide.

“Such a war would threaten not only the locations where bombs might be targeted but the entire world,” said Robock.

“I think we have been lucky in the 74 years since that last nuclear war that we have not had another due to mistakes, panic, misunderstanding, technical failures or hacking,” Robock told Newsweek.

“If the weapons exist, they can be used. And the ongoing conflict in Kashmir has the potential to escalate.”

Neither party is likely to initiate a nuclear conflict without major provocation, the study’s authors wrote. However, they did warn of a new Cold War.

“India and Pakistan may be repeating the unfortunate example set by the United States and Russia during the ‘Cold War’ era: that is, building destructive nuclear forces far out of proportion to their role in deterrence,” they write.

While India and Pakistan do not have anything like the nuke-power of the US or Russia—nations that, combined, possess 93 percent of the world’s estimated 13,900 nuclear weapons—both are continuing to grow, rather than stabilize, their arsenal. India, for example, is thought to have a stockpile of 130 to 140 nuclear warheads. By 2025, they could have 200.

“The only way to prevent [nuclear conflict] is to eliminate them,” said Robock.