Rare, mother-of-pearl coloured clouds caused by extreme weather conditions above Antarctica are a possible indication of global warming, Australian scientists have announced.

Known as nacreous clouds, the spectacular formations showing delicate wisps of colours were photographed in the sky over an Australian meteorological base at Mawson Station on July 25.

The clouds can only form in temperatures lower than minus 80 degrees Celsius (minus 112 Fahrenheit). Meteorologist Renae Baker who photographed the clouds, said a weather balloon sent up about 12 miles above the Earth's surface measured temperatures as low as minus 87 Centigrade (minus 124.6 F).

"They reveal extreme conditions in the atmosphere, and promote chemical changes that lead to destruction of vital stratospheric ozone," Baker said.

Australian scientist Andrew Klekociuk said said temperatures in the stratosphere, between 5 and 31 miles above Earth, would be expected to drop as global warming increases. Data collected over the past 25 years had reflected this.

"Over that time there has been a small decrease in temperature and that change is actually occurring faster than the warming at the surface of the Earth," he said.

The delicate cloud colours are created at sunset when fading light passes through tiny water-ice crystals blown along on strong jets of stratospheric air.