The ozone hole over Antarctica expanded this month to one of the largest sizes on record due to unusually cold temperatures in the stratosphere, which could lead to more harmful ultraviolet rays reaching the Earth, according to NASA.
The 2015 Antarctic ozone hole area was larger and formed later than in recent years, reaching a peak of 28.2 million square kilometres, an area larger than North America, said scientists from NASA and the National Oceanic and Atmospheric Administration (NOAA).
The large size of this year's ozone hole will likely result in increases of harmful ultraviolet rays at Earth's surface, particularly in Antarctica and the Southern Hemisphere in the coming months, researchers said.
The hole reached its peak on October 2 and remained large and set many area daily records throughout. Unusually cold temperature and weak dynamics in the Antarctic stratosphere this year resulted in this larger ozone hole.
In comparison, last year the ozone hole peaked at 24.1 million square kilometres on September 11. Compared to the 1991-2014 period, the 2015 ozone hole average area was the fourth largest.
"While the current ozone hole is larger than in recent years, the area occupied by this year's hole is consistent with our understanding of ozone depletion chemistry and consistent with colder than average weather conditions in Earth's stratosphere, which help drive ozone depletion," said Paul A Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Centre in US.
The Antarctic ozone hole forms and expands during the Southern Hemisphere spring (August and September) because of the high levels of chemically active forms of chlorine and bromine in the stratosphere.
These chlorine- and bromine-containing molecules are largely derived from human-made chemicals that steadily increased in Earth's atmosphere up through the early 1990s.
"This year, our balloon-borne instruments measured nearly 100 per cent ozone depletion in the layer above South Pole Station, Antarctica, that was 14 to 19 kilometres above Earth's surface," said Bryan Johnson, a researcher at NOAA's Earth System Research Laboratory in US.
"During September we typically see a rapid ozone decline, ending with about 95 per cent depletion in that layer by October 1. This year the depletion held on an extra two weeks resulting in nearly 100 per cent depletion by October 15," said Johnson.
The ozone layer helps shield Earth from potentially harmful ultraviolet radiation that can cause skin cancer, cataracts, and suppress immune systems, as well as damage plants.
Ozone depletion is primarily caused by human-made compounds that release chlorine and bromine gases in the stratosphere.
The ozone hole is expected to recover back to 1980 levels in approximately 2070.