The ozone hole in 2003 was almost as big...
 Click to enlarge NASA depiction of Ozone hole |
- The area of the hole in September 2000 was 11.4 million square miles.
- The second largest hole formed in 2003 and covered 11.1 million square miles.
Years of data. The first satellite measurement by satellite of ozone over Earth was recorded by NASA in 1979.
1998. A very large ozone hole in September 1998 covered some 10.5 million square miles. It was the record size before 2000.
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2001. In September 2001, the Antarctic ozone hole covered about 10 million square miles. That was smaller than 2000, yet larger in area than the United States, Canada and Mexico combined.
2002. The ozone hole receded and in September 2002 was the smallest since 1988. Not only was the 2002 hole over Antarctica much smaller than in 2000 and 2001, but it had split into two separate holes. The small size may have been due to unusually warm conditions and the split may have been due to peculiar stratospheric weather patterns.
2003. The 2003 ozone hole covered 11.1 million square miles, making it the second largest ever recorded. The year 2000 was largest. Its growth was helped by calm winds and very cold weather.
2004. In September 2004, the ozone hole was 9.4 million square miles. That was smaller than 2003, possibly due to a relatively warm Antarctic winter.
2005. The winter hole in the ozone layer above Antarctica appears to have grown from last year but is still smaller than in 2003, when it was at its largest, according to the World Meteorological Organization. The 2005 hole will cover about 10 million square miles. WMO weather data showed that winter 2005 was warmer than 2003, but colder than 2004.
The size of the hole in 2005 was near the average across the years 1995-2004. It was bigger than 2004, but smaller than 2003
Danger zone. The layer of ozone in our planet's stratosphere shields Earth from the Sun's ultraviolet-B radiation that promotes skin cancer and cataracts, and can harm plants and animals including marine life.
Historically, the continuously spinning ozone hole over Antarctica was discovered only recently, in 1985. Since then, researchers have noticed that its expansion peaks each year in the second week of September.
After the hole was discovered, many industries stopped releasing ozone-depleting chemicals into the atmosphere. An international agreement known as the Montreal Treaty intends to reduce the emission of ozone depleting chemicals. The annual output of such chemicals is down six percent since 1994. Scientists hope that the reduction of chemicals spewing into the upper atmosphere will stop the expansion of the ozone hole.
What causes it? Industrial chemicals floating up in the atmosphere – including chlorine and bromine – are thought to cause the thinning of the ozone layer by breaking down ozone molecules so their components fall apart. Many chemicals have been banned to protect the ozone layer.
While the ozone hole may appear for as much as 40 more years, it is expected to improve. It probably will take decades for the depleting chemicals to disappear completely from the atmosphere, according to the WMO.
Watchers. The ozone over Antarctica is watched by numerous Global Atmosphere Watch (GAW) stations in Antarctica. They include Australia's Davis and Mawson bases and the Marambio and Vernadsky stations along the Antarctic Peninsula and the DuMont D¼Urville and Syowa stations around the Antarctic perimeter.
Among their techniques is the release of balloons carrying instruments up where the ozone is depleted around 9 to 16 miles altitude. Satellites in space looking down on the ozone layer also record data that reveals the condition of the atmosphere. In 2003, more than 50 million tons of ozone were found to be missing from the atmosphere over Antarctica.
The ozone hole is influenced by changes in weather, which causes the size, depth and persistence of the ozone hole to vary substantially from year to year. Scientists point out that data from any one year can't be used to conclude there is a general trend in the ozone hole.
CFCs in the clouds. Clouds usually don't form in the dry stratosphere. However, sometimes winters temperatures are low enough to allow clouds to form.
Inert man-made chemicals known as chlorofluorocarbons – CFCs – are used by human beings as propellants in spray cans. High up in the stratospheric clouds, chemical reactions convert CFCs to ozone. The earlier in the year the clouds form, the larger will be the ozone hole later in that year.
August and September are the coldest months for the South Pole. As temperatures warm in October, the ozone layer starts to rebuild.
Water and ozone. Scientists wonder if a wetter upper atmosphere might delay global ozone recovery.
NASA researchers have found that an increase in water vapor in the stratosphere, stemming partially from greenhouse gases, may delay ozone recovery and increase the rate of climate change.
To check on the long-term stratospheric cooling and ozone depletion, NASA put data from satellites and other remote sensors into its GISS global climate model. It was the first study to link greenhouse gases to increased ozone depletion over populated areas.
Climate models show cooler stratospheric temperatures happen when there is more water vapor present. Water vapor also leads to the breakdown of ozone molecules.
The stratosphere is the dry layer of the atmosphere above the troposphere, where temperatures increase with height.
According to satellite data, upper atmospheric temperatures around the world - at altitudes of 20 to 35 miles high -- have cooled between 5.4 and 10.8 degrees Fahrenheit over recent decades.
Driving forces. NASA found two driving forces behind the change in stratospheric moisture:
- Increased emissions of the greenhouse gas methane are transformed into water in the stratosphere, accounting for about a third of the observed increase in moisture there.
- More water is transported from the lower atmosphere. Warmer air holds more water vapor than colder air, so the amount of water vapor in the lower atmosphere increases as it is warmed by the greenhouse effect. Greenhouse gases, such as carbon dioxide and methane, may enhance the transport of water into the stratosphere.
Ozone destruction. Rising greenhouse gas emissions account for all or part of the water vapor increase, which causes stratospheric ozone destruction.
When more water vapor works its way into the stratosphere, the water molecules can be broken down, releasing reactive molecules that can destroy ozone. If the trend of increasing stratospheric water vapor continues, it could increase future global warming and impede ozone stratospheric recovery.
The impact on global warming comes about because both water vapor and ozone are greenhouse gases, which trap heat leaving the Earth. When they change, the Earth's energy balance changes too, altering the surface climate.
Warmer ground. Increased water vapor in the stratosphere makes it warmer on the ground by trapping heat, while the ozone loss makes it colder on the ground.
Water vapor has a much larger effect, so that overall the changes increase global warming.
Although ozone depletion cools the Earth's surface, repairing stratospheric ozone is important to block harmful ultraviolet radiation. Other greenhouse gas emissions also need to be reduced.
UARS satellite. NASA combined seven years of data from the Upper Atmosphere Research Satellite (UARS) Halogen Occultation Experiment (HALOE) with data collected on the ground to paint a complete picture of the upper atmosphere.
NASA's HALOE was aboard the UARS spacecraft when it was launched September 12, 1991 as part of the Earth Science Enterprise Program. The spacecraft's mission at launch was to improve understanding of stratospheric ozone depletion by analyzing vertical profiles of ozone, hydrogen chloride, hydrogen fluoride, methane, water vapor, nitric oxide, nitrogen dioxide, and aerosols.
Fourteen years of lower stratospheric measurements have revealed large increases in water vapor. Though some older studies conflict with lower stratospheric observations of water vapor trends, new studies agree with the increases, showing they have been taking place for more than four decades.
Ozone molecules are made up of three atoms of oxygen. They comprise a thin layer of the atmosphere that absorbs harmful ultraviolet radiation from the Sun.
Most atmospheric ozone is found between approximately six miles and 18 miles above the Earth's surface.
An ozone "hole" is what scientists call an "ozone depletion area" of in that region of Earth's atmosphere.
Really big hole. The largest ozone hole ever detected was spotted on September 6, 2000, by the Total Ozone Mapping Spectrometer (TOMS) aboard a NASA satellite known as Earth Probe (TOMS-EP).
The Antarctic ozone hole was three times larger than the entire land mass of the United States, making it the largest such area ever observed.
The hole expanded to a record size of 11.4 million square miles. The previous record had been 10.5 million square miles in September 1998.
Scientists were surprised by its enormous size. The lowest readings in the Antarctic ozone hole usually are observed in late September or early October each year.
Frail layer. The year 2000 observations reinforced concerns about the frailty of Earth's ozone layer. Although production of ozone-destroying gases had been curtailed under international agreements, concentrations of the gases in the stratosphere have been reaching their peak.
Due to their long persistence in the atmosphere, it will be decades before the ozone hole is no longer an annual occurrence.
Antarctic vortex. The year 2000 saw an extremely intense Antarctic vortex -- an upper-altitude stratospheric air current that sweeps around the Antarctic continent, confining the Antarctic ozone hole.
Variations in the size of the ozone hole and of ozone depletion accompanying it from one year to the next are not unexpected.
NASA instruments have been measuring Antarctic ozone levels since the 1970s. Since the discovery of the ozone hole in 1985, TOMS has been a key tool for monitoring ozone levels above Earth.
TOMS-EP and other ozone-measurement programs are important parts of a global environmental effort of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice and life as a total integrated system.
The World Meteorological Organization (WMO) has 181 member nations and is headquartered at Geneva, Switzerland. It analyzes data collected by satellites, balloons launched into the atmosphere, and ground observations.
Learn more:
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NOAA:
NOAA ozone facts
NASA:
Goddard Institute for Space Studies
Visible Earth
Upper Atmosphere Research Satellite
Halogen Occultation Experiment
NASA Says Wet Upper Atmopsphere Delays Ozone Recovery
NASA Press Release: Wetter Atmopsphere May Delay Ozone Recovery
TOMS:
NASA TOMS Total Ozone Mapping Spectrometer
NASA TOMS Ozone Hole Monitoring Page
Largest ozone hole detected by TOMS
TOMS ozone data and pictures
Earth Observatory:
NASA Earth Observatory
Ozone in the Stratosphere
United Nations:
World Meteorological Organization (WMO)
World Meteorological Organization (WMO)
WMO Global Atmosphere Watch (GAW)
World Ozone and UV Radiation Data Centre (WOUDC)
Canada:
Select Ozone Maps
Meteorological Service of Canada (MSC) Ozone and Ultraviolet Research and Monitoring
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