NOAA, NASA: Antarctic ozone hole second smallest in 20 years
October 24, 2012-NOAA
Warmer air temperatures high above the Antarctic led to the second smallest seasonal ozone hole in 20 years, according to NOAA and NASA satellite measurements. This year, the average size of the ozone hole was 6.9 million square miles (17.9 million square kilometers). The ozone layer helps shield life on Earth from potentially harmful ultraviolet (UV) radiation that can cause skin cancer and damage plants.
The Antarctic ozone hole forms in September and October, and this year, the hole reached its maximum size for the season on Sept. 22, stretching to 8.2 million square miles (21.2 million square kilometers), roughly the area of the United States, Canada and Mexico combined. In comparison, the largest ozone hole recorded to date was in 2000 at 11.5 million square miles (29.9 million square kilometers).
The Antarctic ozone hole began making a yearly appearance in the early 1980s, caused by chlorine released by manmade chemicals called chlorofluorocarbons or CFCs. The chlorine can rapidly break apart ozone molecules in certain conditions, and the temperature of the lower stratosphere plays an important role.
“It happened to be a bit warmer this year high in the atmosphere above Antarctica, and that meant we didn’t see quite as much ozone depletion as we saw last year, when it was colder,” said Jim Butler with NOAA’s Earth System Research Laboratory in Boulder, Colo.
Even 25 years after an international agreement was signed to regulate production of ozone-depleting chemicals, the ozone hole still forms each year. In fact, it could be another decade before scientists can detect early signs of Antarctic ozone layer recovery, according to a paper by NOAA researchers and colleagues published last year. The ozone layer above Antarctica likely will not return to its early 1980s state until about 2060, noted NASA atmospheric scientist Paul Newman.
Ozone levels at the South Pole continue to plummet every Antarctic spring, when a coincidence of environmental factors and manmade chemicals still in the atmosphere promote reactions that eat away at the protective ozone layer. This year (in yellow) ozone levels did not drop as low as they have in recent years
The length of time needed for this full recovery is due in part to the large quantity and long lifetime of ozone-depleting substances in the atmosphere. Climate change may also affect the rate of ozone recovery by cooling the stratosphere, which has several competing effects on ozone depletion.
Monitoring the ozone’s state remains important because the ozone layer acts as Earth’s natural shield from DNA-mutating UV radiation. Under the mandate of the Clean Air Act, NOAA and NASA scientists keep a close eye on the ozone layer’s health with satellite data, ground-based measurements and balloon-borne instruments.
A new ozone-monitoring instrument on Suomi-NPP weather satellite, the Ozone Mapping Profiler Suite (OMPS), will be key to that effort. OMPS will extend the satellite record of ozone hole extent, which dates back to the early 1970s, and will provide more detail about ozone levels at various layers in the atmosphere and around the globe.
“OMPS Limb instrument looks sideways, and it can measure
ozone as a function of height,” says Pawan Bhartia, NASA atmospheric physicist
and OMPS instrument lead.
Balloon-borne and ground-based instruments provide ozone
data when darkness prevents satellite observations. “The sun doesn’t rise above
the South Pole horizon until about Sept. 22, by which time ozone depletion has
already begun,” said NOAA atmospheric scientist Irina Petropavlovskikh.