The Antarctic ozone hole has reached its annual peak size and holds steady, say scientists, trying to determine if the ozone hole trend over the last decade is a result of temperature increases or chorine declines.
 
 The size of this year’s hole was 24.1 million sq km – an area roughly the size of North America.
 
 The single-day maximum area was similar to that in 2013 which reached 24 million sq km, the US space agency said in a statement.
 
 “Year-to-year weather variability significantly impacts Antarctica ozone because warmer stratospheric temperatures can reduce ozone depletion,” said Paul A. Newman, chief scientist for atmospheres at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
 
 “The ozone hole area is smaller than what we saw in the late-1990s and early 2000s, and we know that chlorine levels are decreasing. However, we are still uncertain about whether a long-term Antarctic stratospheric temperature warming might be reducing this ozone depletion,” Newman continued.
 
 The largest single-day ozone hole ever recorded by satellite was 29.9 million sq km Sep 9, 2000.
 
 The Montreal Protocol agreement beginning in 1987 regulated ozone depleting substances, such as chlorine-containing chlorofluorocarbons and bromine-containing halons.
 
 The 2014 level of these substances over Antarctica has declined about nine percent below the record maximum in 2000.
 
 Scientists from NASA and the National Oceanic and Atmospheric Administration (NOAA) have been monitoring the ozone layer and the concentrations of ozone-depleting substances and their breakdown products from the ground and with a variety of instruments on satellites and balloons since the 1970s.
 
 “These observations allow us to provide a continuous long-term record to track the long-term and year-to-year evolution of ozone amounts,” Newman said.
 
 The ozone layer helps shield life on Earth from potentially harmful ultra-violet radiation that can cause skin cancer and damage plants.