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Scientists See Leveling off of Hole Size, Predict Slow Recovery

NOAA's latest total ozone analysis done Oct. 15, 2001.October 16, 2001 — NOAA and NASA scientists report that satellite data show the area of the Antarctic ozone hole peaked at about 26 million square kilometers (about 10 million square miles), making this year's ozone hole the same size as North America, and similar in size to those of the past three years. (Click image for NOAA's latest total ozone analysis.)

Over the past several years the annual ozone hole over Antarctica has remained roughly the same in both area and minimum total column ozone amount. "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 NOAA scientist Samuel Oltmans. 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. 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. "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 (EPTOMS) 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 the low 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 NOAA's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo. 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. The amount of chlorine in the stratosphere from CFCs has reached a maximum due to regulations on emissions as dictated by the Montreal Protocol on substances that deplete the ozone layer and subsequent amendments.

NOAA and NASA scientists report that this year's ozone hole is not cause for alarm, and is within the bounds of what was expected. The thinning of the ozone layer is a matter of concern because the ozone layer protects the Earth from the harmful effects of the sun's ultraviolet radiation, which affects life on Earth and contributes to skin cancer and cataracts in humans. Total recovery of the ozone hole back to levels observed before 1980 will take at least 50 years, and expected changes in climate, including a cooler stratosphere, could cause a delay in the recovery of the ozone layer.

NASA and NOAA satellite instruments have been measuring Antarctic ozone levels for more than 20 years. Continued monitoring by satellite instruments over the next two months will establish how long-lived the current year's ozone hole will be, and a summary report will be issued by NOAA in December.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of our nation's coastal and marine resources.

Relevant Web Sites
NOAA's Ozone Online

NOAA's Climate Monitoring and Diagnostics Laboratory

NOAA's Polar-orbiting Operational Environmental Satellites

NOAA's Climate Prediction Center

NASA's Total Ozone Mapping Spectrometer (TOMS)

Media Contact:
Patricia Viets, NOAA Satellite Service, (301) 457-5005