The nuclear arsenals of Britain, France, China, Israel, India, and Pakistan are thought to lie in the range of 100 to 300 warheads each. Although the use of these weapons by any of these countries could produce a regional, and likely global disaster, India, and Pakistan are of special concern because of a long history of military clashes including serious recent ones, lack of progress in resolving territorial issues, densely populated urban areas, and ongoing rapid expansion of their respective nuclear arsenals. India’s and Pakistan’s nuclear forces in 2019 each may contain 140 to 150 warheads, with a possible expansion to 200 to 250 warheads in each country by 2025. Britain (215), France (300), China (270), and Israel (80) have a similar number of weapons but have been maintaining relatively constant arsenals.
Estimates of the numbers of warheads possessed by India and Pakistan are based on the capacity of delivery systems that can be observed from remote sensing, rather than on the amount of enriched uranium and plutonium fuel that the countries may have produced. Pakistan has nuclear-capable aircraft (F-16A/B and Mirage III/V) with ranges up to 2100 km, eight types of land-based ballistic missiles with possible ranges up to 2750 km, and two types of cruise missiles with ranges up to 350 km. All of India can be reached by the longest range delivery systems. Since India has about 400 cities with more than 100,000 people, Pakistan could potentially attack slightly more than one-third of all moderate- and large-sized cities in India with its current arsenal and more than two thirds by 2025. Pakistan has produced tactical nuclear weapons for use on battlefields to counter the conventional weapons advantage of an invading Indian army. The current arsenal probably includes 24 tactical weapons of unknown yield, but perhaps in the range of 5 to 12 kt. Tactical and strategic weapons (which are used to attack targets distant from a battlefield) can overlap in yield. The yields of advanced boosted fission weapons can be adjusted across a large range from sub-kilotons to more than 100 kt. Tactical weapons may be less secure than strategic ones and may lower the threshold for nuclear weapons use. The 2018 arsenal of India is thought to contain 130 to 140 nuclear warheads, which may expand to 200 by 2025. India has nuclear-capable aircraft including Mirage 2000H and Jaguar IS/IB, with ranges up to 1850 km. It has four types of land-based ballistic missiles that have been deployed with ranges up to 3200 km and two others that are under development with ranges up to 5200 km. The range of these missiles allows India to reach all of Pakistan now, as well as all of China when its new missiles are deployed. India also has one deployed ship-based ballistic missile and two submarine-based missiles in development.
Since Pakistan has about 60 cities with more than 100,000 people, India could potentially attack each moderate- or large-sized city in Pakistan with two nuclear warheads using its current arsenal and four warheads if its arsenal grows to 250 weapons by 2025. Neither Pakistan nor India is likely to initiate a nuclear conflict without substantial provocation. India has declared a policy of no first use of nuclear weapons, except in response to an attack with biological or chemical weapons. Pakistan has declared that it would only use nuclear weapons if it could not stop an invasion by conventional means or if it were attacked by nuclear weapons. Unfortunately, the two countries have had four conventional wars 1947, 1965, 1971,1999 and many skirmishes with substantial loss of life since the partition of 1947. Therefore, the possibility of conventional war becoming nuclear is of concern. Even one nuclear weapon exploded in a city can do a great deal of damage. For example, in the most densely populated urban area in Pakistan, a 15 kt airburst at the optimum height to maximize blast damage could kill about 700,000 people and injure another 300,000. With a 100 kt airburst over the same region, roughly 2 million fatalities and an additional 1.5 million nonfatal casualties could occur.
Similar numbers would result in nuclear explosions over large Indian cities. A war between India and Pakistan involving 50 nuclear weapons with 15 kt yield detonated as airbursts over the most densely populated cities of each nation would lead to about 22 million immediate fatalities and 44 million total casualties. India would suffer two to three times more fatalities and casualties than Pakistan because Pakistan uses more weapons than India and because India has a much larger population and more densely populated cities. However, as a percentage of the urban population, Pakistan’s losses would be about twice those of India. In general, the fatalities and casualties increase rapidly even up to the 250th explosion due to the high population in India, whereas the rate of increase for Pakistan is much lower even for the 50th explosion. 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. Should a war between India and Pakistan ever occur, these countries alone could suffer 50 to 125 million fatalities, a regional catastrophe. Also, severe short-term climate perturbations, with temperatures declining to values not seen on Earth since the middle of the last Ice Age, would be triggered by the smoke from burning cities, a global disaster threatening food production worldwide and mass starvation, as well as severe disruption to natural ecosystems.
Compounding the devastation brought upon their own countries, decisions by Indian and Pakistani military leaders and politicians to use nuclear weapons could severely affect every other nation on Earth. Pakistan and India may have 400 to 500 nuclear weapons by 2025 with yields from tested 12- to 45-kt values to a few hundred kilotons. If India uses 100 strategic weapons to attack urban centers and Pakistan uses 150, fatalities could reach 50 to 125 million people and nuclear ignited fires could release 16 to 36 Tg of black carbon in smoke, depending on yield. The smoke will rise into the upper troposphere, be self-lofted into the stratosphere, and spread globally within weeks. Surface sunlight will decline by 20 to 35%, cooling the global surface by 2° to 5°C and reducing precipitation by 15 to 30%, with larger regional impacts. Recovery takes more than 10 years.