What happens if there is a nuclear war between Pakistan and India?

In 2018, atmospheric scientist Brian Toon gave a Ted Talk on nuclear war. During the talk, he spoke on the repercussions of a nuclear war between Pakistan and India.

Below is a transcript of his talk on nuclear war between Pakistan and India.

Even a war between India and Pakistan two of the smallest nuclear powers with only a few hundred weapons about the size of the Hiroshima bomb, we might die as unintended consequences that the Indian and Pakistani generals never even gave us a thought about. 

My colleagues Luke Oman and Alan Roubach calculated the spread of smoke [figure 1] after a war between India and Pakistan. It only takes about two weeks for the smoke to cover the entire earth and it would rise to altitudes between 20 to 50 miles above the surface. At those altitudes it never rains, the smoke would stay there for years. 

This farmer [figure 2] maybe in Europe or the United States but many thousand miles from Pakistan and India is looking at the smoky sky above him and down at the crops that have died in his field from lack of light and cold temperatures.

It is estimated that in a war between India and Pakistan that we would lose 10 to 40 per cent of the yields of corn, wheat and rice for years afterward because of the bad weather. The entire world only has enough food to feed the population for 60 days unless agriculture produces more food. Ira Helfand a member of the Noble Peace Prize winning International Physicians for the Prevention of Nuclear War has estimated that one to two billion people would die after a war between India and Pakistan of starvation.