The Planet Earth 

  The 2000 Antarctic Ozone Hole Was Largest Ever 

  The 2000 Antarctic Ozone Hole was the largest ever observed. Earth's wetter
  upper atmosphere may 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.

  Water and ozone. 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.
  The increased transport of water vapor to the stratosphere seems likely to
  have been induced by human activities.

  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. 

  What Is An Ozone Hole?

  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-ever ozone hole was detected 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 is three times larger than the entire land mass of
  the United States, making it the largest such area ever observed.

  The hole had expanded to a record size of 11 million square miles. The
  previous record was 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 many 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 early
  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.

  To learn more: 
  Goddard Institute for Space Studies 
  Upper Atmosphere Research Satellite 
  Halogen Occultation Experiment 
  Largest ozone hole detected by TOMS 
  TOMS ozone data and pictures 
  NASA Says Wet Upper Atmopsphere Delays Ozone Recovery 
  NASA Press Release: Wetter Atmopsphere May Delay Ozone Recovery 

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