The possibility of a nuclear exchange is enhanced by the disparity between India and Pakistan's military forces. One does not have to be Karl von Clausewitz to predict the likely outcome of a conventional war between a country of 200 million people and a country of 1.3 billion people.
Pakistan reserves the right to use nuclear weapons first. India has a "no first use" p olicy, but with so many caveats that it is essentially meaningless. In brief, it wouldn't take much to ignite a nuclear war between them.
If that happens, its effects will not be just regional. According to a study by the University of Colorado, Rutgers University and UCLA, if Pakistan and India exchanged 100 Hiroshima sized nuclear warheads (15 kilotons), they would not only kill or injure 45 million people, but also generate enough smoke to plunge the world into a 25-year long nuclear winter.
Both countries have between 130 and 150 warheads apiece.
Temperatures would drop to Ice Age levels and worldwide rainfall would decline by 6 percent, triggering major droughts. The Asian Monsoon could be reduced by between 20 and 80 percent, causing widespread regional starvation.
Between the cold and the drought, global grain production could fall by 20 percent in the first half decade, and by 10 to 15 percent over the following half decade.
Besides cold and drought, the ozone loss would be between 20 and 50 percent, which would not only further damage crops, but harm sea life, in particular plankton. The reduction of the ozone layer would also increase the rate of skin cancers.
The study estimates that "two billion people who are now only marginally fed might die from starvation and disease in the aftermath of a nuclear conflict between Pakistan and India."