A hole larger than Russia, Canada together found in ozone layer. Why aren't scientists worried?

How did the hole came about?

This is the same hole that in the 1980s caused fears of exposure to ultraviolet radiation. Excessive exposure to UV rays raises the risk of skin cancer and cause cataracts.

The excess depletion of ozone was caused by gases called chlorofluorocarbons or CFCs. Once widely used in refrigerators and spray cans, CFCs were banned in 1987 under the Montreal protocol. The UN Environment Programme has said that by 2030 the treaty would have prevented 2 million cases of skin cancer annually.

False-colour view of total ozone over the Antarctic pole on 26 October 2015. The purple and blue colorus are where there is the least ozone, and the yellows and reds are where there is more. (Photo: NASA)

The ozone hole fluctuates in size during the season in polar regions and typically becomes bigger in September. Extreme cold temperatures in the stratosphere and the return of sunlight unleash chlorine-based chemicals, which destroy the ozone.

This year, the depletion has continued longer than expected because the weather over Antarctica was colder than usual.

As a result, the hole has widened to a peak 28.2 million square kilometres on 2 October.

While the hole has remained since the 1980s, according to data from Nasa, its current size is the third largest hole (after 2000 and 2006).

No reason to worry

The United Nations' weather and climate agency has said that there no reason to worry as the hole should shrink again.

"This shows us that the ozone hole problem is still with us and we need to remain vigilant. But there is no reason for undue alarm," World Meteorological Organisation (WMO)'s senior scientist Geir Braathen said in a statement. "Overall, however, this does not reverse the projected long-term recovery in the coming decades," the statement said.

Last year, the WMO had said that it detected the first signs of ozone recovery. However, the meteorologists believe that it could be a decade before the hole starts shrinking. Some scientists estimate that the ozone hole of Antarctica will completely recover by 2070.

Meanwhile, large Antarctic ozone holes will continue to be seen until about 2025 because of weather conditions in the stratosphere, also because ozone depleting chemicals linger in the atmosphere for several decades after they have been phased out.