New Delhi, April 7: A devastating nuclear war between India and Pakistan would also tear open a giant hole in the Earth’s protective blanket of ozone, endangering human health and crops worldwide, a study predicted today.

Scientists in the US simulated a hypothetical war involving 100 Hiroshima-size bombs to predict that soot from firestorms in the subcontinent’s cities would rise high in the atmosphere, triggering ozone loss that would affect all continents.

Indian researchers have dubbed the scenario “outlandish” and cautioned that simulations of the atmosphere need to be validated through multiple models.

“I’m amazed they simulated this scenario. The chances of 100 weapons being used in the subcontinent are very unrealistic,” said Roddam Narasimha, a senior faculty member at the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, and former member of the national security advisory board.

The ozone layer, densest at about 25km high in the atmosphere is a natural shield against ultraviolet radiation from the sun. But it is itself vulnerable to destruction by chemical reactions.

Research scientist Michael Mills at the University of Colorado and his colleagues found that loss of ozone after a regional nuclear war could reach up to 45 per cent in the mid latitudes and 70 per cent in the upper latitudes. Their findings will be published on Tuesday in the Proceedings of the National Academy of Sciences.

“It will be a near-global ozone hole, affecting places as far away as North America, Europe, and Africa,” Mills told The Telegraph over the phone.

The simulation showed that soot from the fires would rise up to 60-km high, penetrating the ozone layer where it would absorb heat from the sun and trigger chemical destruction of ozone.

The ozone loss is likely to increase ultraviolet radiation that can cause genetic damage to humans, plants, and animals. Previous studies have shown that a 40 per cent loss of ozone would increase damage to DNA believed to be related to carcinogenesis by 213 per cent, the researchers said.

“Such ozone depletion could elevate the risk of skin cancer and cataracts in humans, and cause damage to crops and aquatic ecosystems,” Mills said.

The first studies of the impact of nuclear war on the atmosphere conducted in the 1980s had shown that a global nuclear exchange of 6500 Mt would deplete 17 per cent of ozone that would recover to 8.5 per cent loss within a year.

But the new study suggests that even a regional nuclear war with only 1.5 Mt (100 Hiroshima-type 15 kT bombs) would lead to 25 per cent to 70 per cent ozone loss that would persist for more than five years, posing a hazard to the biosphere worldwide.

“The soot appears to have a long-lasting impact,” said William Selvamurthy, chief controller of research with India’s Defence Research and Development Organisation. “But I would say the scenario it has examined is quite exaggerated.”

One scientist who requested anonymity told The Telegraph that the concept of neighbouring countries throwing dozens of nuclear weapons at each other is “outlandish”.

Narasimha pointed out that India and Pakistan have the smallest arsenals in the world. “It’s odd that they pick on a country with the smallest arsenals,” he said.

But Mills said the simulation examined a scenario where “things get out of hand”. “It’s easier to have faith in predictions when several models produce smilar results,” said J. Srinivasan, a senior atmospheric scientist at the Indian Institute of Science, Bangalore.