The ozone layer normally absorbs ultraviolet light, which can cause skin cancer and be hazardous in other ways to creatures living on the surface.

Ozone depletion has occurred annually over the past few decades mainly due to the release of chlorine and bromine gases into the atmosphere by human activity.

The gases become trapped by a band of high winds around Antarctica in winter and react to the brightening sunlight of spring, destroying the ozone in the process.

When warmer temperatures return aloft over Antarctica later in the spring, the vortex of winds that has isolated the chlorine and bromine weakens, allowing the ozone killers to disperse throughout the rests of the atmosphere.

The ozone hole then gradually fills in over the summer.

The image to the upper right shows how large this year’s ozone hole became, covering more than 10 million square miles (27 million square kilometres). While larger than last year's, the current ozone hole is smaller than the record size that developed in 2006.

Image: NASA