A new computer modeling study has suggested that a limited nuclear weapons exchange between India and Pakistan using their current arsenals could create a near-global ozone hole, triggering human health problems and wreaking environmental havoc for at least a decade.

The study was led by University of Colorado at Boulder scientists Brian Toon and Michael Mills.

According to Mills, the computer-modeling study showed a nuclear war between the two countries involving 50 Hiroshima-sized nuclear devices on each side would cause massive urban fires and loft as much as 5 million metric tons of soot about 50 miles into the stratosphere.

The soot would absorb enough solar radiation to heat surrounding gases, setting in motion a series of chemical reactions that would break down the stratospheric ozone layer protecting Earth from harmful ultraviolet radiation, he added.

"We would see a dramatic drop in ozone levels that would persist for many years," said Mills.

"At mid- latitudes, the ozone decrease would be up to 40 per cent, which could have huge effects on human health and on terrestrial, aquatic and marine ecosystems," he added.

According to the computer simulations, fires ignited in large cities by nuclear explosions would send several million metric tons of soot into the upper stratosphere, which would be heated by massive smoke injections.

"Higher temperatures would accelerate catalytic reaction cycles in the stratosphere, particularly reactions of nitrogen oxide gases known collectively as NOx that destroy ozone," said Mills.

Human health ailments like cataracts and skin cancer, as well as damage to plants, animals and ecosystems at mid-latitudes would likely rise sharply as ozone levels decreased and allowed more harmful UV light to reach Earth, the study determined.

In addition to ozone losses of 25 per cent to 40 per cent at mid-latitudes, the models show a 50 per cent to 70 per cent ozone loss at northern high latitudes.

"The models show this magnitude of ozone loss would persist for five years, and we would see substantial losses continuing for at least another five years," said Mills.

The ozone losses predicted in the study are much larger than losses estimated in previous "nuclear winter" and "ultraviolet spring" scenario calculations following nuclear conflicts.

"The big surprise is that this study demonstrates that a small-scale, regional nuclear conflict is capable of triggering ozone losses even larger than losses that were predicted following a full-scale nuclear war," said CU-Boulder Professor Brian Toon.