The hole in the ozone layer over Antarctica and New Zealand this year is the ninth largest on record.
Scientists at NASA and the United States' National Oceanic and Atmospheric Administration say the hole is particularly large at the moment because unusually cold temperatures in the stratosphere have caused the man-made chemicals which destroy ozone to work more efficiently.
They say the hole reached its annual peak in September with an area of more than 26 million square kilometres.
In the Northern Hemisphere, scientists writing in the journal Nature say ozone loss over the Arctic this year has been so severe that the lack of ozone there could be called an ozone hole for the first time.
