If India and Pakistan fought a war detonating 100 nuclear warheads (around half of their combined arsenal), each equivalent to a 15-kiloton Hiroshima bomb, more than 21 million people will be directly killed, about half the world’s protective ozone layer would be destroyed, and a “nuclear winter” would cripple monsoons and agriculture worldwide.

As the Indian Army considers armed options, and a Bharatiya Janata Party (BJP) MP urges a nuclear attack, even as the Pakistan Defence Minister threatens to “annihilate” India in return, the following projections, made by researchers from three US universities in 2007, are a reminder of the costs of nuclear war.

According to the study by researchers from Rutgers University, University of Colorado-Boulder and University of California, Los Angeles, about 21 million people — half the death toll of World War II — would perish within the first week from blast effects, burns and acute radiation in India and Pakistan.

This death toll would be 2,221 times the number of civilians and security forces killed by terrorists in India over nine years to 2015, according to an IndiaSpend analysis of South Asia Terrorism Portal data.

Another two billion people worldwide would face risks of severe starvation due to the climatic effects of the nuclear-weapon use in the subcontinent, according to a 2013 assessment by the International Physicians for the Prevention of Nuclear War, a global federation of physicians.

Pakistan has an estimated 110 to 130 nuclear warheads as of 2015 — an increase from an estimated 90 to 110 warheads in 2011 — according to a report from the Bulletin of the Atomic Scientists, a global disarmament advocacy. India is estimated to have 110 to 120 nuclear warheads.

Talk of war began after a terrorist attack on an army garrison in the Kashmir town of Uri claimed the lives of 18 Indian soldiers. The Indian Army said the attack was carried out by four terrorists from the Jaish-e-Mohammed (Army of Mohammed) group, based in Pakistan.

Pakistan’s nuclear weapons capability has previously deterred India from responding to previous attacks.

“At the end of the day, India has to ensure that the options it exercises — particularly the military ones — do not leave it worse off than before in terms of casualties and costs,” wrote analyst Manoj Joshi in The Wire.

As many as 66 per cent of Pakistani nuclear warheads are mounted on 86 land-based ballistic missiles, according to Bulletin of the Atomic Scientists data estimates. Pakistan’s Hatf series of ballistic missiles has been developed — and is still under development — keeping India in mind.

A major attack by Pakistan’s nuclear-tipped medium-range ballistic missiles (MRBMs) would likely target India’s four major metropolitan cities — New Delhi, Mumbai, Bengaluru and Chennai (depending on where the missile is fired from), according to Sameer Patil, fellow, national security, ethnic conflict and terrorism at Gateway House, a think tank in Mumbai.

The MRBMs would also target “the major commands of the Indian Army,” Patil told IndiaSpend.

Nearly half (40) of Pakistan’s ballistic missile warheads could be mated to Ghauri MRBMs. The missile has a claimed range of 1,300 km and can target Delhi, Jaipur, Ahmedabad, Mumbai, Pune, Nagpur, Bhopal and Lucknow, according to a 2006 report on Pakistan’s ballistic missile programme by the National Institute of Advanced Studies (NIAS), Bengaluru.

Pakistan has an estimated eight warheads which could be mated to the Shaheen (Falcon) II. This MRBM has a range of 2,500 km and can target most major Indian cities, including Kolkata on the east coast.

An estimated 16 warheads could be fired atop the short-range Ghaznavi ballistic missile. With a range of 270 km to 350 km, it can target Ludhiana, Ahmedabad and the outer perimeter of Delhi.

Pakistan has an estimated 16 nuclear-tipped Shaheen1 (Falcon), short-range ballistic missiles (IRBM), having a 750 km range which can reach Ludhiana, Delhi, Jaipur and Ahmedabad.

Pakistan has an estimated six 60-km range Nasr missiles, which could be mated to nuclear weapons. These tactical nuclear missiles could target “advancing battle formations of the Indian Army”, according to Patil.

Pakistan also has eight nuclear-tipped 350-km Babur cruise missiles with nuclear warheads.

An estimated 36 nuclear warheads, accounting for 28 per cent of Pakistan’s total, can be delivered using aircraft. US-made F-16 A/B aircraft can deliver 24 nuclear bombs while the French-made Mirage III/V can deliver 12.

India has deployed 56 Prithvi (earth) and Agni (fire) series of surface-to-surface ballistic missiles, which carry 53 per cent of India’s 106 estimated warheads, according to the Bulletin of Atomic Scientists.

This doesn’t take into account the estimated 12 warheads for the K-15 Sagarika submarine-launched ballistic missiles (SLBMs), which India has possibly produced for the nuclear-powered ballistic missile submarine INS Arihant. Once commissioned, Arihant would give India a strategic nuclear triad and second-strike capability.

“Given the smaller geographical size of Pakistan,” said Patil, India would likely target “Islamabad, Rawalpindi, Lahore and Karachi and the Pakistani Army Armed Corps headquarters at Nowshera”.

However, he cautioned: “The fallout of the nuclear attacks on Lahore and Karachi, for instance, would not just be restricted to the Pakistani territory, and depending on the wind directions, can affect both Indian and Afghan border territories.”

The 250 km-range Prithvi SRBM acts as a delivery system for 24 of India’s warheads. These are capable of hitting major Pakistani cities, such as Lahore, Sialkot, the capital Islamabad, and Rawalpindi, according to an IndiaSpend analysis.

India has 20 nuclear-tipped Agni I SRBM and eight Agni II intermediate range ballistic missiles (IRBMs), with ranges of 700 km and 2,000 km, respectively. These are capable of covering almost all Pakistani cities, including Lahore, Islamabad, Rawalpindi, Multan, Peshawar, Karachi, Quetta and Gwadar.

Agni III, IV and V, with their longer ranges, might be able to reach all of Pakistan, but it can be safely said that they are directed more towards China.

India also possesses an estimated two ship-launched 350-km range Dhanush SRBMs, which could be fitted with nuclear warheads.

India’s aircraft can deliver an estimated 45 per cent of 106 warheads. The Indian Air Force’s Jaguar fighter bombers can deliver about 16 nuclear warheads, while the French-built Mirage-2000 fleet can deliver 32.