Ozone is a form of oxygen that helps protect the Earth from some damaging ultraviolet radiation at high altitudes in the atmosphere. At lower altitudes it is a pollutant associated with smog. In the 1980s scientists first became aware of the existence of an ozone hole over Antarctica. Depletion of the ozone layer un the upper atmosphere allows more ultraviolet light to penetrate the atmosphere raising the risk of getting skin cancer and cataracts and other problems. It may also harm crop yields and sea life. Scientists who first raised warnings in the early 1970s about ozone damage won a Nobel Prize.

The ozone hole over Antarctica is usually more pronounced on the South American side of the frozen continent. Countries that are affected by it the most are Argentina, Chile, South Africa, New Zealand and Australia.

The largest ozone hole ever observed in the Antarctic was reported by NASA in September 2000. The hole spread out over 28.3 million square miles, more than three times larger than the United States. The ozone hole reached near-record size in 2003 and 2005, raising doubts about whether measures to combat ozone depletion were working.

Causes of the Ozone Hole

The ozone hole and ozone depletion is cause by chlorofluorocarbons (CFC's), chemicals used in aerosols, making Styrofoam and coolants used in refrigerators and air-conditioners. Leakage from refrigerators and air-conditioners are a major source of ozone-depleting gases.

The destruction of ozone comes about because of chemical reactions occurring on the surface of ice crystals in stratospheric clouds, which release reactive chlorine that destroys the ozone. When chlorofluorocarbons are split by ultraviolet light, chlorine is freed, which then spits ozone into oxygen and chlorine monoxide.

Ozone losses occur over the polar regions when temperatures drop below -78 degrees Celsius (-108 Fahrenheit) and iridescent ice clouds form. Sunlight on icy surfaces triggers the ozone-eating reactions in chlorine and bromine that comes from air pollutants such as chlorofluorocarbons, or CFCs, once widely used as refrigerants and flame retardants in household appliances. "As sunlight returns, it all comes together to trigger significant thinning of the ozone," one scientists explained.

The stratospheric ozone layer represents a layer of pure ozone only about 0.1 inch thick. It is spread throughout the stratosphere and is at its greatest concentrations at 10.5 miles above sea level.

The ozone layer can also deeply affected by natural phenomena such as chemicals released by volcanic eruptions as was the case with the eruption of Mount Pinatubo in 1991.

Nitrous oxide has been called the worst greenhouse gas. On top of that it slowly depletes the ozone layer. Better known as laughing gas, nitrous oxide is 296 times more powerful from a global warming perspective than carbon dioxide and has recently replaced chlorofluorocarbons (CFCs) as the primary cause of ozone depletion. About a third of the world’s nitrous oxide emission are caused by human activities, including the use of fertilizer, fossil fuels, livestock manure and industry. One of the primary methane sources is manure from dairy cows, cattle and other animals. The other two thirds come from nature, mostly releases from soil bacteria. A study by the U.S. National Oceanic and Atmospheric Administration published in Science in September 2009, called nitrous oxide emission “the single most important ozone-depleting substance emission and is expect to remain the largest throughout the century.”

Combating the Ozone Problem

The 1987 Montreal Protocol is an international agreement ratified by 196 countries with the intent of saving the Earth's ozone layer by cutting back on CFCs used in air conditioning, aerosol sprays, foam packaging and other products. Ozone-depleting chemicals were cut beginning in 1987 and use of them has largely stopped. The ozone treaty also encourages industries to use replacement chemicals less damaging to ozone.

Ozone-depleting compounds have long atmospheric lifetimes, so it takes decades for their concentrations to subside to the pre-1980 levels agreed to in the Montreal Protocol. The ozone layer outside the polar regions isn't expected to recover to pre-1980 levels until sometime between 2030 and 2040. Some scientists say if that treaty hadn't been adopted, two-thirds of the world's protective ozone layer would be gone about a half-century from now and the CFCs, which also are long-lived potent greenhouse gases, would have pushed the world's temperature up an extra few degrees.

Odin is a Swedish satellite that was launched in 2001 to study the amount of chlorine in the ozone layer and gain some understanding how ozone holes form. It orbits the polls and checks condition above both the Arctic and the Antarctic.

A report from NASA and the University of Alabama in 2003 found evidence that ozone layer depletion has been slowing since 1997 based on measurements taken from satellites and on the ground. The report also stated that the strategy to help the ozone layer was working and the ozone layer was showing signs of recovery although full recover was still decades away. A report from the University of Colorado released in 2006 had similar conclusions.

Ozone Hole Linked to Climate Changes and Southern Rain Increases

In 2011, AFP reported; “The hole in the ozone layer over Antarctica is a significant driver of climate change and rain increases in the southern hemisphere over the past 50 years according to findings by a team at Columbia University's School of Engineering and Applied Science, who are the first to link ozone depletion in the polar region to climate change all the way to the equator. [Source: AFP, April 21, 2011]

Researchers said the analysis should lead policy-makers to consider the ozone layer along with other environmental factors such as Arctic ice melt and greenhouse gas emissions when considering how to tackle climate change. "It's really amazing that the ozone hole, located so high up in the atmosphere over Antarctica, can have an impact all the way to the tropics and affect rainfall there," Sarah Kang, lead author of the study in the journal Science, told AFP. "It's just like a domino effect," she said.

"While the ozone hole has been considered as a solved problem, we're now finding it has caused a great deal of the climate change that's been observed," said co-author Lorenzo Polvani, senior research scientist at the Lamont-Doherty Earth Observatory. The study used two independently drawn climate models -- the Canadian Middle Atmosphere Model and the United States' National Center for Atmospheric Research (NCAR) Community Atmosphere Model.

In four experiments comparing data on sea ice, surface temperatures, precipitation and the ozone hole, the analysis showed the hole was the main driver of heavy summer rains across eastern Australia, the southwestern Indian Ocean and the Southern Pacific Convergence Zone. "We show in this study that it has large and far-reaching impacts. The ozone hole is a big player in the climate system," said Polvani. "This could be a real game-changer." Next, the researchers plan to look at "extreme precipitation events," the sort that cause devastating floods and landslides. "We really want to know if and how the closing of the ozone hole will affect these," said Kang.

Ozone Hole in the Arctic

An ozone hole is also forming above the Arctic. A large hole was observed there in the winter of 1999-2000. The hole there often forms when temperatures in the stratosphere drop to unusually low levels. An ozone hole over the northern latitudes many think is probably more the result of natural causes, particularly strong polar stratospheric vortex winds, than man-made ones.

In April 2011, AP reported, “The protective ozone layer in the Arctic has thinned about 40 percent in the winter of 2010-2011, a record drop, the U.N. weather agency said. But the Arctic's situation is due to similar causes: ozone-munching compounds in air pollutants that are chemically triggered by a combination of extremely cold temperatures and sunlight. [Source: John Heilprin, Associated Press, April 5, 2011]

The losses this winter in the Arctic's fragile ozone atmospheric layer strongly exceeded the previous seasonal loss of about 30 percent, the U.N.'s World Meteorological Organization in Geneva said. It blamed the combination of very cold temperatures in the stratosphere, the second major layer of the Earth's atmosphere, just above the troposphere, and ozone-eating CFCs from aerosol sprays and refrigeration. "This is pretty sudden and unusual," said Bryan Johnson, an atmospheric chemist who works in the U.S. National Oceanic and Atmospheric Administration's Earth System Laboratory in Boulder, Colorado.

Atmospheric scientists concerned about global warming focus on the Arctic because that is a region where the effects are expected to be felt first. "The Arctic stratosphere continues to be vulnerable to ozone destruction caused by ozone-depleting substances linked to human activities," the U.N. weather agency's secretary-general Michel Jarraud said.

Although the thinner ozone means more radiation can hit Earth's surface, the ozone levels in the Arctic remain higher than in other regions such as in the equatorial regions, said the National Oceanic and Atmospheric Administration, whose recent Arctic findings mirror those of the U.N. agency.

"Mostly the concern, for the Arctic ozone depletion, is for people that live in northern regions, more towards Iceland, northern Norway, the northern coast of Russia," Johnson added, saying they should be more careful outside, wearing sunscreen and sunglasses. In March 2011, the U.N. said, the thinning ozone was shifting away from the pole and was covering Greenland and Scandinavia.

For the planet, Johnson said, there's the concern that "if this were to happen every year --- even though the ozone naturally regenerates itself --- you might see a trending downward of the atmospheric ozone layer."

Arctic ozone conditions vary more than the seasonal ozone "hole" that forms high in the stratosphere near the South Pole each winter and spring, and the temperatures are always warmer in the Arctic than over Antarctica. Because of the changing weather and temperatures that some Arctic winters experience, there have been times where there is almost no ozone loss, and others when the exceptionally cold stratospheric conditions has led to substantial ozone depletion, U.N. scientists say.

In 2010-2011, the Arctic winter was warmer than average at ground level but colder in the stratosphere than normal. Average Arctic temperatures in January range from about -40 to 0 C (-40 to 32 F) and in July from about -10 to 10 C (14 to 50 F). U.N. officials say the latest losses --- unprecedented, but not entirely unexpected --- were detected in satellite observations and weather balloons that show at what altitudes the ozone loss is occurring.

Image Sources: World Meteorological Organization; National Oceanic and Atmospheric Administration (NOAA), Wikimedia Commons

Text Sources: World Meteorological Organization; National Oceanic and Atmospheric Administration (NOAA), New York Times, Washington Post, Los Angeles Times, Times of London, Yomiuri Shimbun, The Guardian, National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated January 2012

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