2001 Ozone Hole About the Same as Past Three Years
Satellite data show the area of this year’s Antarctic
ozone hole peaked at about 26 million square kilometers —
roughly the size of North America — making the hole similar
in size to those of the past three years, according to
scientists from NASA and the National Oceanic and Atmospheric
Administration (NOAA). Researchers have observed a leveling-
off of the hole size and predict a slow recovery.
Over the past several years the annual ozone hole over
Antarctica has remained about the same in both its size and
in the thickness of the ozone layer. “This is consistent with
human-produced chlorine compounds that destroy ozone reaching
their peak concentrations in the atmosphere, leveling off,
and now beginning a very slow decline,” said Samuel Oltmans
of NOAA’s Climate Monitoring and Diagnostics Laboratory,
Boulder, Colo.
In the near future — barring unusual events such as
explosive volcanic eruptions — the severity of the ozone
hole will likely remain similar to what has been seen in
recent years, with year-to-year differences associated with
meteorological variability. Over the longer term (30-50
years) the severity of the ozone hole in Antarctica is
expected to decrease as chlorine levels in the atmosphere
decline.
The total area of the ozone hole is one measure of its
severity. The ozone hole area is defined as the size of the
region with total ozone below 220 Dobson units. A Dobson unit
is a unit of measurement that describes the thickness of the
ozone layer in a column directly above the location being
measured, a quantity called the “total column ozone amount.”
Prior to the springtime period in Antarctica, when ozone
depletion occurs, the normal ozone reading is around 275
Dobson units. “Last year the ozone hole was of record size,
but it formed very early and then collapsed quickly,” said
NASA scientist R.D. McPeters of the Goddard Space Flight
Center, Greenbelt, Md. “This year the hole was about 10
percent smaller.”
Data from NOAA’s polar-orbiting operational environmental
satellites and estimates of the area made by NASA scientists
using measurements from the Total Ozone Mapping Spectrometer
aboard NASA’s Earth Probe satellite give similar sizes.
Each spring when the Sun rises over Antarctica, chemical
reactions involving chlorine and bromine from man-made CFCs
(chlorofluorocarbons) and bromine-containing compounds occur
in the stratosphere and destroy ozone, causing the “ozone
hole.” Measurements of this year’s ozone hole made at the
South Pole and above the Antarctic show that atmospheric
ozone depletion reached levels typical of the past 10 years.
Using instrumented balloons to make ozone-profile
measurements at the South Pole, researchers from NOAA
reported that the September decline in ozone was similar to
recent years with almost all of the ozone in the 15-20
kilometer (9-12 mile) altitude region destroyed.
“Total column ozone over the South Pole reached a minimum
reading of 100 Dobson units on Sept. 28, 2001, compared to a
minimum of 98 Dobson units in 2000,” said Bryan Johnson, a
scientist with the Climate Monitoring and Diagnostics
Laboratory. The record low of 88 Dobson units was observed in
1993.
“The severity of the ozone depletion within the hole reached
about the same levels as the past few years and the highly
depleted region filled about three-fourths of the Antarctic
polar vortex,” said Jim Miller, a scientist with NOAA’s
Climate Prediction Center in Camp Springs, Md. “This year the
vortex has been more stable and somewhat colder than
average.” Year-to-year fluctuations in the geographical size
of the polar vortex and the size of the region with low
temperatures will alter the size of the ozone hole over the
next decade during the period that levels of ozone-destroying
chemicals in the atmosphere begin a slow decline.
Thinning of the ozone layer is a concern because the ozone
layer protects the Earth from harmful effects of the Sun’s
ultraviolet radiation, which contributes to skin cancer and
cataracts in humans. Total recovery of the ozone layer to
levels observed before 1980 will take at least 50 years, and
expected changes in climate, including a cooler stratosphere,
could delay this process. NASA is committed to obtaining
critically important observations to examine and document the
recovery of this life-protecting atmospheric gas.
More information is available at:
http://www.gsfc.nasa.gov/topstory/20011016ozonelayer.html
http://www.cpc.ncep.noaa.gov/products/stratosphere/polar/pola
r.html
