The size of the Antarctic's ozone hole at peak appears to be remaining stable.
The size of last year's hole at peak was 9.3 million square miles (about the size of North America); this year's peak, which occurred on Sept. 11, was about the same size, NASA reported. The largest single-day ozone hole was recorded on Sept. 9, 2000, at 11.5 millions square miles. The ozone hole is generally smaller than it was between 1998 and 2006, but is similar to the size it was in 2010, 2012, and 2013. Since the hole's maximum back in 2000, it has declined by about 9 percent.
The ozone hole formed during the 1980s when there was a dramatic increase in atmospheric chlorine levels. The ozone layer helps shield us from ultraviolet radiation, which can cause skin cancer and devastate plant life. In 1987 the Montreal Protocol was passed in an effort to reduce chlorine-containing chlorofluorocarbons and bromine-containing halons.
"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."
Researchers are working to determine if the ozone hole trend over the last decade is caused be a decrease in chlorine levels or rising temperatures. An increase n temperature would also decrease the ozone hole's area, but stratospheric temperature analyses in that region are not as reliable for determining long-term trends as those that look at chlorine levels.
The researchers determined the minimum thickness of ozone layer was at 114 Dobson units on Sept. 30, 2014, compared to between 250 and 250 units during the 1960s.
