🚀 go-pugleaf

R. Bailey wrote:
> 
> eggsoft@sydney.dialix.oz.au (Greig Ebeling) wrote:
> 
> (among many other things)
> >
> >...along with a questionable relationship between ozone depletion and
> >increased surface UVR, and the magnitude of any potential increase
> >relative to natural variations...

SURFACE ULTRAVIOLET RADIATION LEVELS
 HAVE INCREASED FROM 1979 TO 1992 

Douglas Isbell Headquarters,
 Washington, DC August 1, 1996 (Phone: 202/358-1753) 

Allen Kenitzer Goddard Space Flight Center,
 Greenbelt, MD (Phone: 301/286-8955) 

RELEASE: 96-153 

Solar ultraviolet radiation reaching the Earth's surface has
increased over large regions of the planet during the past 15
years, as the amount of total ozone in the atmosphere has
decreased, according to a scientific paper published in the
August 1 issue of Geophysical Research Letters. 

Scientists and others have a keen interest in ozone depletion,
given that the increased amounts of ultraviolet radiation that
reach the Earth's surface because of the ozone loss, have the
potential to increase the incidence of skin cancer and cataracts
in humans, cause harm to some food crops, and interfere with
marine life. 

Ozone, a molecule made up of three atoms of oxygen, is found
in the atmosphere between the ground and about 37 miles in
altitude. Ozone absorbs ultraviolet radiation from the Sun and
shields life on Earth from its harmful effects. 

Because the risks of further increases in ultraviolet radiation
are serious, scientists around the world are working to improve
our current understanding of how much of the ozone-related
change in the atmosphere is caused by humans and how much is
attributable to natural processes, such as shifts in atmospheric
dynamics, variable volcanic activity or long-term cyclical
changes in solar radiation. 

The finding, derived from extensive analysis of data from the
Total Ozone Mapping Spectrometer (TOMS) instrument flown aboard
NASA's Nimbus-7 satellite, is based on the known relationship
between atmospheric ozone depletion and the resulting decrease
in protection from ultraviolet radiation (UV-B, 290 nanometers
to 320 nanometers). The accuracy of the TOMS-derived surface
UV-B values has been validated by comparison with several
ground-based spectrometers in Canada, New Zealand, and South
America. 

"The increases are largest in the middle and high latitudes,
where most people live, and where the majority of the world's
agricultural activity occurs," said Dr. Jay R. Herman, an
atmospheric scientist at NASA's Goddard Space Flight Center,
Greenbelt, MD, and the lead author of the paper, "UV-B increases
(1979-1992) from decreases in total ozone." 

In the paper, Herman finds that annual average UV-B exposure has
increased by 6.8 percent per decade at 55 degrees north latitude,
where major populations in countries such as England, Germany,
Russia and Scandinavia reside. At 55 degrees south latitude,
which includes the southern portions of Argentina and Chile, the
increase has been 9.9 percent per decade. In North America, the
changes are smaller since most of the�population lives below 55
degrees. The UV-B changes for regions near the Canadian border
show about a 4 percent increase per decade. 

"This confirmation that we can use a space-based sensor like
TOMS to measure long-term global surface ultraviolet radiation
levels represents a very powerful new tool for Earth scientists
and others to use both now and in the future," said Dr. Robert
Harriss, director of the science division of NASA's Office of
Mission to Planet Earth, Washington, DC. 

Studies have shown that ozone depletion is caused by complex,
coupled chemical reactions. Emissions of human- manufactured
chlorofluorocarbons (CFCs), which break down into ozone-depleting
forms of chlorine, have led to reduced levels of atmospheric
ozone. If unchecked, the continued build-up of CFCs, historically
used in refrigeration, electronics, and insulating materials,
could lead to additional ozone loss worldwide. However,
international agreements signed in recent years have led to
sharply reduced usage of CFCs, which should lead to the slow
recovery of the ozone layer. Already there are initial
indications that the reduced CFC usage is effective in slowing
the build-up of tropospheric chlorine. 

During its lifetime on the Nimbus-7 satellite, the TOMS helped
make "ozone" a household word through its false-color images of
the Antarctic "ozone hole," which forms from September through
November each year. The NASA-developed instrument, which
measures ozone indirectly by monitoring ultraviolet light
scattered by the atmosphere, produces daily maps of the global
distribution of ozone in Earth's atmosphere and of the surface UV. 

Another Total Ozone Mapping Spectrometer was launched on July
2, 1996, aboard a dedicated NASA Earth Probe satellite called
TOMS/EP.  To ensure that such global ozone data will be available
throughout the next decade, NASA plans to continue the TOMS
program using both U.S. and international spacecraft. Japan's
Advanced Earth Observing Satellite will carry a TOMS into orbit
during its scheduled launch on August 16, and a fifth TOMS
instrument is being prepared for flight in 2000 aboard a Russian
spacecraft. 

TOMS is part of NASA's Mission to Planet Earth, a long-term,
coordinated research effort to study the Earth as a global
system. The TOMS instruments are managed by Goddard for the
Office of Mission to Planet Earth. 

Jay - http://csf.Colorado.EDU/authors/hanson/page1.htm