The hole in the ozone layer has shrunk to its smallest size since its discovery in 1982, NASA announced on Monday.

"It's great news for the ozone in the Southern Hemisphere," said NASA's chief earth scientist Paul Newman.

"But it's important to recognise that what we're seeing this year is due to warmer stratospheric temperatures. It's not a sign that atmospheric ozone is suddenly on a fast track to recovery," he said in a statement.

According to NASA, the hole reached its largest size of 10.1 million kilometres on September 8 before shrinking to less than 6.3 million during the remainder of September and October.

The shrinking hole is attributed to unusually warm temperatures in the Antarctic.

In normal weather conditions polar clouds high in the stratosphere interact with man-made chemicals such as chlorine and create a byproduct which destroys the ozone layer.

In warmer temperatures, not as many of these clouds form and they don't last as long, minimising the depletion of the ozone layer.

"During years with normal weather conditions, the ozone hole typically grows to a maximum of about 8 million square miles [12.9 million km]" it said in a press release.

The shrinking event has occurred twice in the last 40 years due to unusual weather systems causing warmer temperatures.

Similar weather patterns occurred in 1988 and 2002.

"It's a rare event we're trying to understand," NASA atmospheric scientist Susan Strahan said.

"If the warming hadn't happened we'd likely be looking at a much more typical ozone hole."

This year's warming temperatures were unusually strong - about 16 degrees Celsius warmer than usual.

"[This] was the warmest in the 40-year historical for September by a wide margin," NASA said.

There is no identified connection between the unique weather patterns and climate change the organisation says.

It's expected the ozone hole will gradually return to normal in the coming weeks.

Newshub.