WASHINGTON, April 7: A nuclear war between Pakistan and India would cause more than slaughter and destruction -- it would knock a big hole in the ozone layer, affecting crops, animals and people worldwide, US researchers said on Monday.

Fires from burning cities would send five million metric tons of soot or more into the lowest part of Earth’s atmosphere known as the troposphere, and heat from the sun would carry these blackened particles into the stratosphere, the team at the University of Colorado reported.

“The sunlight really heats it up and sends it up to the top of the stratosphere,” said Michael Mills of the Laboratory for Atmospheric and Space Physics, who chose Pakistan and India as one of several possible examples. Up there, the soot would absorb radiation from the sun and heat surrounding gases, causing chemical reactions that break down ozone.

“We find column ozone losses in excess of 20 per cent globally, 25 per cent to 45 percent at midlatitudes, and 50 per cent to 70 per cent at northern high latitudes persisting for five years, with substantial losses continuing for five additional years,” the team wrote in the Proceedings of the National Academy of Sciences. This would let in enough ultraviolet radiation to cause cancer, damage eyes and skin, damage crops and other plants and injure animals.

Michael Mills and colleagues based their computer model on other research on how much fire would be produced by a regional nuclear conflict.

“Certainly there is a growing number of large nuclear-armed states that have a growing number of weapons. This could be typical of what you might see,” Mr Mills said in a telephone interview.

SMOKE IS KEY: Eight nations are known to have nuclear weapons, and Pakistan and India are believed to have at least 50 weapons apiece, each with the power of the weapon the United States used to destroy Hiroshima in 1945.