A war between India and Pakistan using less than one per cent of nuclear weapons available in the world could lead to the worst global food crisis in modern history, say researchers.

The study, published in the journal Proceedings of the National Academy of Sciences, said that sudden global cooling from a limited nuclear war along with less precipitation and sunlight could disrupt food production and trade worldwide for about a decade -- more than the impact from anthropogenic climate change by late (21st) century.

While the impacts of global warming on agricultural productivity have been studied extensively, the implications of sudden cooling for global crop growth are little understood, according to the researchers.

"Our results add to the reasons that nuclear weapons must be eliminated because if they exist, they can be used with tragic consequences for the world," said study co-author Alan Robock, Professor at Rutgers University in the US.

Robock co-authored a recent study in the journal Science Advances estimating more than 100 million people could die immediately if India and Pakistan wage a nuclear war, followed by global mass starvation.

For the new study, the research team used a scenario of five million tons of black smoke (soot) from massive fires injected into the upper atmosphere that could result from using only 100 nuclear weapons.

That would cool the Earth by 1.8 degrees Celsius (3.2 degrees Fahrenheit) and lead to eight per cent lower precipitation and less sunlight for at least five years.

The researchers included those climate changes in computer simulations by six different crop models for four major crops that account for 90 per cent of global cereal production in terms of calories.

They found that corn calorie production would fall by 13 per cent, wheat by 11 per cent, rice by three per cent and soybeans by 17 per cent over five years.

Total first-year losses of 12 per cent would be four times larger than any food shortage in history, such as those caused by historic droughts and volcanic eruptions, the study said.

Analyses of food trade networks show that domestic reserves and global trade can largely buffer the loss of food production in the first year.

But multiyear losses would reduce domestic food availability, especially in food-insecure countries.

By year five, corn and wheat availability would decrease by 13 per cent globally and by more than 20 per cent in 71 countries with a total of 1.3 billion people. Corn production in the US and Canada -- representing more than 40 per cent of global production -- would drop by 17.5 per cent.

According to the researchers, 16 million tons of smoke could arise from a nuclear war between India and Pakistan since they now have more and bigger weapons and their potential targets are larger.