ozone_11sept2014USA: Scientists are trying to determine whether the diminishing ozone hole trend is more a result of temperature increases than chlorine declines.

NASA and the National Oceanic and Atmospheric Administration (NOAA) report that the Antarctic ozone hole reached its annual peak size on September 11 when it was recorded at 24.1 million km² – an area roughly the size of North America. 

The single-day maximum area was similar to that in 2013, which reached 24.0 million km², and comparable to 2010 and 2012.

The largest single-day ozone hole ever recorded by satellite was 29.9 million km² on September 9, 2000. Overall, the 2014 ozone hole is smaller than the large holes of the 1998–2006 period.

The Montreal Protocol agreement, which began regulating ozone depleting substances in 1987, has seen levels of these substances over Antarctica decline by about 9% below the peak maximum in 2000. But scientists are working to determine if the diminishing ozone hole trend over the last decade is a result of temperature increases or chorine declines. An increase of stratospheric temperature over Antarctica would decrease the ozone hole’s area. Satellite and ground-based measurements show that chlorine levels are declining, but stratospheric temperature analyses in that region are said to be less reliable for determining long-term trends.

“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.”