The Antarctic ozone hole, which yawns wide every Southern Hemisphere
spring, reached its annual peak on Sept. 12. It stretched to 10.05 million
square miles, the ninth largest ozone hole on record. Above the South
Pole, the ozone hole reached its deepest point of the season on Oct. 9,
tying this year for the 10th lowest in this 26-year record.
Data Show Significant Antarctic Ozone Hole Remains
NASA and the National Oceanic and
Atmospheric Administration (NOAA) use balloon-borne instruments, ground-based
instruments and satellites to monitor the annual Antarctic ozone hole, global
levels of ozone in the stratosphere and the manmade chemicals that contribute to
"The colder than average temperatures in the stratosphere this year caused a
larger than average ozone hole," said Paul Newman, chief scientist for
atmospheres at NASA's Goddard Space Flight Center in Greenbelt, Md. "Even though
it was relatively large, the area of this year's ozone hole was within the range
we'd expect given the levels of manmade ozone-depleting chemicals that continue
to persist in the atmosphere."
The ozone layer helps protect the planet's surface from harmful ultraviolet
radiation. Ozone depletion results in more incoming radiation that can hit the
surface, elevating the risk of skin cancer and other harmful effects.
"The manmade chemicals known to destroy ozone are slowly declining because of
international action, but there are still large amounts of these chemicals doing
damage," said James Butler, director of NOAA's Global Monitoring Division in
In the Antarctic spring (August and September) the sun begins rising again after
several months of darkness and polar-circling winds keep cold air trapped above
the continent. Sunlight-sparked reactions involving ice clouds and manmade
chemicals begin eating away at the ozone. Most years, the conditions for ozone
depletion ease before early December when the seasonal hole closes.
Levels of most ozone-depleting chemicals in the atmosphere have been gradually
declining as the result of the 1987 Montreal Protocol, an international treaty
to protect the ozone layer. That international treaty caused the phase-out of
ozone-depleting chemicals, which had been used widely in refrigeration, as
solvents and in aerosol spray cans.
However, most of those chemicals remain in the atmosphere for decades. Global
atmospheric computer models predict that stratospheric ozone could recover by
midcentury, but the ozone hole in the Antarctic will likely persist one to two
decades longer, according to the latest analysis in the 2010 Quadrennial Ozone
Assessment issued by the World Meteorological Organization and United Nations
Environment Programme, with co-authors from NASA and NOAA.
NASA currently measures ozone in the stratosphere with the Dutch-Finnish Ozone
Monitoring Instrument, or OMI, on board the Aura satellite. OMI continues a NASA
legacy of monitoring the ozone layer from space that dates back to 1972 with
launch of the Nimbus-4 satellite. The instrument measured the 2011 ozone hole at
its deepest at 95 Dobson units on Oct. 8 this year. This differs slightly from
NOAA's balloon-borne ozone observations from the South Pole (102 Dobson units)
because OMI measures ozone across the entire Antarctic region.
That satellite-monitoring legacy will continue with the launch of NASA's
National Polar-orbiting Operational Environmental Satellite System Preparatory
Project, known as NPP, on Oct. 28. The satellite will carry a new
ozone-monitoring instrument, the Ozone Mapping and Profiler Suite. The
instruments will provide more detailed daily, global ozone measurements than
ever before to continue observing the ozone layer's gradual recovery.
It will take a few years of averaging yearly lows in Antarctic ozone to discern
evidence of recovery in ozone levels because seasonal cycles and other variable
natural factors -- from the temperature of the atmosphere to the stability of
atmospheric layers -- can make ozone levels dip and soar from day to day and
year to year.
NOAA has been tracking ozone depletion around the globe, including the South
Pole, from several perspectives. NOAA researchers have used balloons to loft
instruments 18 miles into the atmosphere for more than 24 years to collect
detailed profiles of ozone levels from the surface up. NOAA also tracks ozone
with ground-based instruments and from space.
Goddard Release No. 11-069 (co-issued as HQ Release No. 11-357)