More than a billion people around the world would face starvation if India and Pakistan unleash nuclear weapons -- even if that war is regionally limited, a study released Tuesday warned.

That's because the deadly and polluting weapons would cause major worldwide climate disruption that would dramatically drive down food production in China, the United States and other countries.

"The grim prospect of nuclear famine requires a fundamental change in our thinking about nuclear weapons," said study author Dr. Ira Helfand of the International Physicians for the Prevention of Nuclear War.

"The new evidence that even the relatively small nuclear arsenals of countries such as India and Pakistan could cause long lasting, global damage to the Earth's ecosystems and threaten hundreds of millions of already malnourished people demands that action be taken," Helfand said in a statement.

"The needless and preventable deaths of one billion people over a decade would be a disaster unprecedented in human history. It would not cause the extinction of the human race, but it would bring an end to modern civilization as we know it."

The study, set to be published in the peer-reviewed journal Climate Change, was released at the World Summit of Nobel Laureates in Chicago.

It found that corn production in the United States would decline by an average of 10 percent for an entire decade and soybean production would drop by about 10 percent, with the most severe decline occurring five years after the nuclear war.

It also determined that rice production in China would drop by an average of 21 percent for the first four years and 10 percent for the next six years.

The resulting increase in food prices and agricultural shortfalls would almost certainly lead to panic and hoarding on an international scale, further reducing access to food.