October 21, 2013
Encouraging information from this year’s observations of the ozone hole
NOAA, CIRES, international scientists expect improvement in upcoming years
For nearly 50 years, scientists with NOAA have launched high-altitude balloons from the South Pole, to understand why a hole was forming in the protective ozone layer high in the atmosphere. Now, organizations around the world track the infamous ozone hole through these ballon-sondes, satellite measurements and ground instruments.
This year, the ozone hole was a little smaller than in years past, those measurements showed, and ozone levels in a critical region of the atmosphere did not drop as low.
“We cannot say that this represents recovery, but it is certainly good news to see this year on the higher side of the average ozone range,” said NOAA’s Bryan Johnson, with the Earth System Research Laboratory (ESRL) in Boulder, Colo.
Johnson works with colleagues at NOAA and the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder to track and understand trends in seasonal ozone from measurements made by a two-person NOAA crew at South Pole Station. Earth’s ozone layer shields life on the planet’s surface from ultraviolet radiation that can cause skin cancer and damage plants.
The Antarctic ozone hole began making a yearly appearance in the early 1980s, caused by chlorine released from man-made chemicals called chlorofluorocarbons, or CFCs. Under the the Montreal Protocol of 1987 and its later amendments, countries agreed to phase out most ozone-depleting substances, which were used in fire extinguishers and as other foams, sprays, as solvents, refrigerants and in other industries. According to NOAA global observations, chlorine levels at the poles reached a maximum at the beginning of this century and are now on the decline.
“It takes the atmosphere a while to break down these long-lived chemicals, and some can remain in the atmosphere for about 100 years,” said NOAA ESRL atmospheric scientist Steve Montzka, who is also a CIRES Fellow.
When conditions are right—as they are in the Antarctic spring—chlorine from ozone-depleting gases can rapidly break apart ozone molecules, reducing ozone over Antarctica by one half in just a couple of weeks. The World Meteorological Organization reports that this year’s ozone hole stretched about 8 million square miles (21 million square kilometers) in late September, about the size of the United States, Canada and Mexico combined. For comparison, the Antarctic ozone hole stretched to more than 10 million square miles in the record year of 2006.
Of particular interest is the region between 7 and 12 miles altitude (12-20 kilometers). There, ozone levels are more strongly influenced by man-made ozone-depleting chemicals than by natural variations in meteorology. This year, ozone levels in this region of the atmosphere only dropped to about 25 Dobson Units (DUs) in late September; in previous years, they plummeted to less than 10 DUs.
In a sign of the effectiveness of the Montreal Protocol, the ozone hole over Antarctica is likely to show signs of recovery within the next decade. NOAA and CIRES scientists will continue their long-term atmospheric measurements of ozone and ozone-depleting gases not only to capture evidence of recovery, though. Some chemicals used as substitutes for ozone-depleting gases are potent greenhouse gases, too, and pose a potentially significant climate threat.
“The need for observations will remain paramount,” said Jim Butler, director of the Global Monitoring Division of NOAA’s ESRL.
CIRES is a joint institute of the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado Boulder.
Science teams from NASA and the National Oceanic and Atmospheric Administration (NOAA) have been monitoring the ozone layer from the ground and with a variety of instruments on satellites and balloons since the 1970s. These ozone instruments capture different aspects of ozone depletion. The independent analyses ensure that the international community understands the trends in this critical part of Earth's atmosphere. The resulting views of the ozone hole have differences in the computation of the size of the ozone hole, its depth, and record dates. More from NOAA here; and from NASA here.