The UN and the US scientists have said that the Antarctic ozone hole has this month enlarged to one of its biggest sizes on record. They have insisted that the Earth-shielding ozone layer is still on track to long-term recovery but the southern hemisphere’s residents must stay alert and be on watch for high UV levels in the coming weeks.

In a regular bulletin released on Thursday, the World Meteorological Organization said that seasonal and year-to-year variations are often faced by the Antarctic ozone hole, but has said that this year’s expansion has shown that ‘they need to remain vigilant’.

On October 2, the Geneva-based UN agency pointed towards NASA data and showed that the hole had reached 28.2 million square kilometers (10.9 million square miles), which is bigger than the size of Russia and Canada put together. WMO said that it was the biggest recorded on that date, and the hole has stayed at a record size on the dates since.

As per NASA, the record biggest ozone hole dates to September 9, 2000. On that day, it was 29.9 million square kilometers.

The chief scientist for earth sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland, Paul Newman, said that prolonged wintertime conditions in the Antarctic area were continuing longer than usual. Paul Newman said that the strangely weak vertical energy flows is one of the main contributors to the exceptionally large hole.