Ozone levels down as much as 66%
losses of over 66% have occurred in the Arctic stratosphere near 18km altitude
during one of the coldest stratospheric winters on record. These losses are
likely to affect the ozone levels over Europe during spring. This is one of the
most substantial ozone losses at this altitude in the Arctic.
The Arctic ozone hole first
appeared in the mid-1990s, more than a decade after the Antarctic hole. Like its
southern cousin, it forms as the Sun rises after the midwinter night. Solar
radiation triggers reactions between ozone in the stratosphere and chemicals
containing chlorine or bromine. These occur fastest on the surface of ice
particles in clouds, which only form in the polar stratosphere at temperatures
below 80 °C.
"This year is most
unusual. Temperatures have been consistently as low as ever recorded in the
Arctic stratosphere," says Neil Harris, head of the European Ozone Research
Coordinating Unit in Cambridge. "There have been polar stratospheric clouds
since the end of November and we are already seeing ozone destruction."
Scientists are warning that the biggest hole in the ozone layer over the
northern hemisphere will appear this spring. It is likely to trigger public
alerts against going out in the sun without protective clothing across Europe.
The development of the hole, which could extend from the Arctic to the British
Midlands, follows a period of unusually low temperatures combined with high
levels of pollutants in the stratosphere - the ideal formula for ozone
Ozone blocks the harmful ultraviolet rays that cause ageing and skin cancer in
humans and can damage crops and wildlife.
Maps of deviations represent total ozone deviations from the 1978-1988 level
estimated using TOMS data.
Significant reductions in the column ozone content over the mid- and polar
latitudes of the Northern Hemisphere have been observed during the winter-spring
seasons of seven of the last eleven years. These reductions usually reached 20
to 30% of the pre-1976 averages. They appeared within and/or at the boundary of
the polar stratospheric vortex, and last continuously over the same region
usually for a few weeks. By contrast, over the Antarctica even greater
reductions last continuously for nearly three months.
losses are likely to affect the ozone levels over Europe during spring. This is
one of the most substantial ozone losses at this altitude in the Arctic,"
said Scientists taking part in the ozone experiment, a joint
initiative by America's National Aeronautics and Space Administration (NASA),
the European Ozone Research Coordinating Unit, based in Cambridge, and the
European Union's research directorate in a statement issued 4April2000. An
Arctic " low ozone event" could easily be blown south by high-altitude
winds, and appear over populated areas of The United States, Canada, Europe and
the northern regions of Britain.The ozone layer in the upper atmosphere is the
key filter for damaging ultraviolet-B (UV-B) radiation in the Sun's rays.
Without it, organisms suffer extensive DNA damage, which in humans results in a
greater increase in the risk of skin cancer, eye cataracts and defects in the
body's immune system.
Severe stratospheric ozone depletion in the Arctic
Recovery of ozone layer delayed
due to climate change?
Ozone losses of over 60% have occurred
in the Arctic stratosphere near 18km altitude during one of the coldest
stratospheric winters on record. These losses are likely to affect the ozone
levels over Europe during spring. This is one of the most substantial ozone
losses at this altitude in the Arctic. Measurements from the largest
international campaign ever investigating stratospheric ozone depletion have
provided more insight into the processes that control stratospheric ozone. They
have also reinforced concerns that the Arctic ozone may continue to decline
despite the benefits of reductions in stratospheric chlorine levels (a result of
the Montreal Protocol), due to the global climate change. Research Commissioner
Philippe Busquin points out that "European cooperation within an
international team has made it possible to achieve these research results. They
will provide the best possible scientific advice to the regulatory process
concerning ozone depleting substances in the framework of the Montreal Protocol
and, equally important, to the citizens".
During the 1999/2000 winter, the Third
European Stratospheric Experiment on Ozone (THESEO 2000) sponsored by European
Union and the NASA sponsored SAGE III Ozone Loss and Validation Experiment
(SOLVE) obtained measurements of ozone and other atmospheric gases and particles
using satellites and aircrafts, large, small and long duration balloons, and
Scientists from Europe, the United
States, Canada, Russia and Japan joined forces in mounting the biggest field
measurement campaign yet to measure ozone amounts and changes in the Arctic
stratosphere. The total amount of information collected by the THESEO 2000/SOLVE
campaign is more extensive than any information collected by past polar
measurement campaigns. Most of the measurements were made near Kiruna, Sweden,
with additional measurements being made from satellites and through a network of
stations at mid and high northern latitudes.
During the winter of 1999-2000 large
ozone losses were observed inside the Arctic stratospheric polar vortex. These
ozone losses in the lower stratosphere have been observed by a number of
European techniques based on ozonesondes and ground-based measurements developed
in the past decade. At altitudes around 18km cumulative losses of over 60% have
occurred between January and March. These are among the largest chemical losses
at this altitude observed during the 1990s. The effect on column ozone was
slightly mitigated by the fact that ozone loss was less dramatic above 20 km
altitude. Satellite observations (eg. by the ESA Global Ozone Monitoring
Experiment GOME) showed a clear ozone minimum over the polar region during
February and March. The average polar column amount of ozone for the first 2
weeks of March was 16% lower than observed in the 1980's.
The mixing of polar air into middle
latitudes, both during the winter and as the polar vortex broke down in late
March, influences ozone levels over the populated middle latitudes. Dilution of
ozone-depleted air into middle latitudes is a major contributor to the long-term
mid-latitude ozone decline, along with other chemical and dynamical processes.
In March 2000, the World Meteorological Organisation Mapping Centre at the
University of Thessaloniki reported that the mean column ozone amounts over
Europe were 15 % below the pre-1976 average.
Results from THESEO 2000/SOLVE have
reinforced the scientific concern that the recovery of the ozone layer may be
delayed. Cooling of the stratosphere could be caused by increasing
concentrations of greenhouse gases, by reduced concentrations of ozone in the
stratosphere, or by changes in the dynamics of the stratosphere. Even as the
stratospheric concentrations of chlorine and bromine decline, such a cooling
and, possibly, a more stable Arctic vortex are currently predicted to prolong
Arctic ozone depletion.
For further information
More information, including a list of
participating institutions, can be found at the Theseo 2000 and Solve web sites:
You may also contact the following
Dr Georgios Amanatidis,
Scientific Officer, Environment and Sustainable Development Programme,
tel: + 32-2-295.88.15, fax: + 32-2-296.30.24,
Dr Neil Harris, European
Ozone Research Coordinating Unit
tel: + 44-1223-31.17.72, fax: + 44-1223-31.17.50,
- Piia Huusela, Press and Information Officer,
tel: +32-2-299.21.38, fax: +32-2-295.82.20,
NASA Press Release
NASA Goddard Space Flight Center
Jet Propulsion Laboratory, Pasadena, Calif.
|Apr. 5, 2000
RELEASE NO: 00-39
OBSERVES SIGNIFICANT ARCTIC OZONE LOSS
Ozone losses of over 60 percent have occurred
in the Arctic stratosphere near 60,000 feet (18 km) in one of the coldest
winters on record. This is one of the worst ozone losses at this altitude in the
Investigations into the Arctic stratosphere
have provided better insights into the processes that control polar ozone. These
insights considerably add to our ability to predict ozone levels in the future
as chlorine levels decline as a result of the Montreal Protocol, and as
greenhouse gases increase. Climate change in the stratosphere will likely
enhance ozone losses in the Arctic winter in the coming decades as chlorine
During the 1999/2000 winter, the NASA
sponsored SAGE III Ozone Loss and Validation Experiment (SOLVE) and European
Union sponsored Third European Stratospheric Experiment on Ozone (THESEO-2000)
obtained measurements of ozone, other atmospheric gases, and particles using
satellites, airplanes, large, small and long duration balloons, and ground-based
instruments. NASA, along with the National Oceanic and Atmospheric
Administration (NOAA), the National Science Foundation (NSF), and several
universities, worked jointly on the SOLVE mission.
Scientists from the United States joined with
scientists from Europe, Canada, Russia and Japan in mounting the biggest field
measurement campaign yet to measure ozone amounts and changes in the Arctic
stratosphere. The activities were conducted from November 1999 through March
2000. The total amount of information collected by the SOLVE/THESEO 2000
campaign is greater than the information collected in any past polar measurement
campaign. Most of the measurements were made near Kiruna, Sweden with additional
measurements being made from satellites and a network of stations at mid and
high northern latitudes.
During the winter of 1999-2000 large ozone
losses were observed in the Arctic stratosphere. These lower stratospheric ozone
losses were observed by a number of instruments and techniques, including a
National Oceanic and Atmospheric Administration ozone instrument aboard the high
altitude NASA ER-2 aircraft. "Measurements from the NASA ER-2 show ozone in
the Arctic region decreasing by about 60 percent between January and
mid-March," said ER-2 co-project scientist Dr. Paul A. Newman of NASA’s
Goddard Space Flight Center, Greenbelt, Md.
These measurements are comparable to the large
chemical losses at this altitude observed in several winters in the mid-1990s.
The effect on total column ozone was slightly mitigated by the fact that
reductions in ozone were smaller above 66,000 feet (20 kilometers). Spacecraft
observations by NASA's Total Ozone Mapping Spectrometer-Earth Probe showed a
clear ozone minimum over the polar region during February and March. The average
polar column amounts of ozone for the first two weeks of March were 16 percent
lower than observed in the early 1980's.
Polar stratospheric clouds (PSCs) are
necessary for the conversion of chlorine from benign molecular forms into the
chlorine monoxide molecule which directly destroy ozone. PSCs were observed over
very extensive portions of the Arctic region from early December to early-March.
"We were somewhat surprised to see PSCs so early in December," said
Dr. Mark Schoeberl, who was the SOLVE co-project scientist for observations made
from NASA’s DC-8 aircraft. "Some of the PSC types and their locations
which we observed in December did not fit within our current
understanding." The last PSCs were observed on March 8 by instruments
aboard the DC-8, and on March 15 by satellite.
The polar stratosphere temperatures were
extremely low over the course of this last winter. PSCs can only form in these
low temperature regions. At 66,000 feet on Jan. 28, the area covered by
temperatures low enough to form PSCs was 5.7 million square miles (14.8 million
square kilometers), which is larger than the United States. This is the largest
area coverage recorded in over 40 years of Northern Hemisphere stratospheric
"The polar stratospheric clouds covered a
larger area, and persisted for a longer period of time, than for any other
Arctic winter during the past 20 years. These conditions heighten our concern
regarding possible couplings between climate change and stratospheric ozone
depletion," said ozone researcher Dr. Ross Salawitch of NASA's Jet
Propulsion Laboratory, Pasadena, Calif.
The mixing of polar air into middle latitudes,
both during the winter and as the polar circulation broke down in late March,
influences ozone levels over the populated middle latitudes. Dilution of ozone
depleted air into latitudes is a major contributor to the long-term mid-latitude
decline. These mixing processes have been studied during SOLVE/THESEO-2000 and
detailed analysis of these processes continues.
For further information visit the SOLVE web
site at: http://cloud1.arc.nasa.gov/solve/
For supporting images visit the web site at: http://svs.gsfc.nasa.gov/imagewall/solve.html
Scientific background information
The ozone loss is directly related to
the high concentrations of chlorine compounds that exist in the stratosphere.
The principal chlorine compound involved in ozone loss is the chlorine monoxide
molecule (ClO). Complementary measurements of ClO were made by instruments on
aircraft, balloons, a satellite, and from the ground so that good spatial and
temporal coverage was obtained. These instruments showed high ClO concentrations
from January to March consistent with the large ozone loss measurements, as did
measurements of other important chemical species such as bromine monoxide (BrO).
Polar stratospheric clouds (PSCs) are
directly involved in the conversion of chlorine from benign molecular forms into
the ClO molecule. PSCs were observed in very extensive portions over the Arctic
region from early December to early-March. The last PSCs were observed around 10
The temperatures in the polar
stratosphere were extremely low over the course of this last winter, which
increases ozone losses. Polar stratospheric clouds can only form in these low
temperature regions. At 20 km on January 28, the area covered by temperatures
low enough to form these clouds was 14.8 million km2 – as compared
with the total surface area of Europe: just over 10 million km2.
This is the largest areal coverage recorded in over 40 years of
stratospheric analyses. The low temperatures first appeared in mid-November at
about 24 km, and persisted at lower altitudes into mid-March. The low
temperatures generally resulted from a stratosphere that has been relatively
undisturbed by large-scale tropospheric weather systems over the course of the
Measurements in THESEO 2000/SOLVE were
made using a large suite of instruments aboard several European aircraft – the
German DLR Falcon, the French ARAT and Mystère 20 and a Swiss Air Force Lear
Jet - and on NASA's DC-8 and ER-2. Most of these planes were based in Kiruna
during the campaign. Nearly 30 research balloons, carrying payloads weighing up
to several hundred kilogrammes were launched from Esrange (The Swedish Space
Research Centre), Kiruna, by teams from CNES, Esrange and NASA. Atmospheric
readings made at the European network of over 30 stations of ground-based
instruments have shown how the Arctic stratosphere evolved through the winter
and measurements of ozone have been made at the WMO Global Atmospheric Watch
network. In addition, ozone losses have been derived from over 600 ozonesondes
launched from an international experiment coordinated by the Alfred Wegener
Institute in Germany. All these measurements were complemented by observations
from a number of satellite instruments including GOME.
In all, more than 500 international
scientists, technicians and support workers were involved in the THESEO
2000/SOLVE experiment. The THESEO 2000/SOLVE campaign represents a new level of
active cooperation between European, US and other national research scientists.
This cooperation will be continued during the analysis of the measurements and
there will be a joint science meeting held in Palermo, Italy, in September 2000.
Such scientific collaboration has been encouraged under the 1998 European
Union/United States Science and Technology Cooperation Agreement.
THESEO 2000 consists of a core of 12
major EU funded projects within the Environment programmes of both Fourth and
Fifth Framework programmes for Research and Technological Development. The EU
has a major research programme on stratospheric ozone and UV-B which includes
laboratory based research into the fundamental principles of stratospheric
chemistry, the ozone-climate interactions, the development of new devices to
measure the atmosphere’s composition, research into improving atmospheric
chemical models and UV-B radiation field measurements. The research funded by
the EC Research DG in THESEO 2000 is closely coordinated with, and substantially
increased by, the national research programmes. European research on
stratospheric ozone and UV-B makes a valuable contribution to the international
research which underpins the Montreal Protocol.