Ozone destruction slows; refrigerant ban credited
- Published Wednesday, July 30, 2003, by the San Francisco Chronicle
Ozone hole's growth rate slows down
Scientists credit refrigerant ban
By David Perlman
Chronicle Science Editor
Almost 30 years after scientists discovered that common industrial
gases were destroying Earth's protective ozone layer, satellite
readings and ground observations show for the first time that the
dangerous rate of ozone loss is finally slowing.
Colorless compounds known as chlorinated fluorocarbons (CFCs), such
as the Freon once used in refrigerators and common spray cans, have
accumulated in the stratosphere to cause a growing "hole" in the
ozone layer. That layer normally acts to screen out much of the sun's
harmful ultraviolet radiation, which can cause skin cancer and damage
Alarm has grown over the years as satellite observations found that
an ozone hole was spreading over thousands of square miles in the
Southern Hemisphere while high-flying NASA missions discovered
evidence that a similar hole was growing over far northern latitudes.
Now, atmospheric researchers are reporting "compelling evidence" that
the rate of ozone depletion in the highest levels of the stratosphere
is slowing down as a result of an international treaty known as the
Montreal Protocol that began banning CFCs in 1987 and has been made
even stronger in subsequent years.
"This is proof that the treaty is working," said Michael Newchurch,
an atmospheric chemist at the University of Alabama in Huntsville and
lead author of the study, in a phone interview Tuesday. "We had a
monumental problem on a global scale that we have started to solve,
and we're finally seeing the beginning of the recovery in the upper
The ozone problem caused by CFCs was first noticed as early as the
1960s, but was largely ignored until 1974, when Sherwood Rowland of
UC Irvine and Mario Molina of MIT published the first powerful
evidence of the impending danger in the journal Nature. Paul Crutzen
of Germany's Max Planck Institute in Mainz added to the research, and
the three atmospheric scientists won the Nobel Prize in chemistry in
It was in 1985, after Australian scientists began fearing an epidemic
of skin cancer as a result of the fast-spreading ozone hole, that
international efforts began to limit the spread of CFCs. Despite
powerful resistance by industry lobbyists, the first treaty banning
the compounds was signed two years later. It has since been
strengthened several times.
The report by Newchurch and his colleagues, to be published in the
Journal of Geophysical Research, is based on ozone measurements made
by three NASA satellites and by scientists at ground stations in
Boulder, Colo.; Arosa, Switzerland, and Tateno, Japan. All are
maintained by government meteorological agencies.
Although the scientists measured only the slowing rate of ozone
depletion in the high stratosphere -- some 22 to 28 miles above the
Earth -- it is reasonable to assume, he said, that the same process
is occurring at lower levels of the stratosphere where the bulk of
the ozone layer exists and its destruction has been most noticeable.
"We're not gaining ozone, we're just losing it less quickly," he
said. Between 1997 and 2000, the average growth rate of the ozone
hole has slowed by approximately 7 percent per decade, according to
their calculations. It will take at least 40 or 50 years before all
the ozone depletion stops and recovery begins, Newchurch said.
Rowland voiced enormous satisfaction at the results of the Newchurch
team's work in a phone interview Tuesday.
"It shows clearly that the Montreal Protocol is working as it
should," he said. "It also shows that when people and industries
won't voluntarily change the way they operate and are forced to
change by a treaty, then they'll find that changing is much easier
than they thought. The industries that produced and used CFCs have
plenty of very smart people, and they quickly found substitutes for
the compounds once the treaty required them to."
To Rowland that lesson also applies to the increasing evidence that
industrial emissions of greenhouse gases are the major cause of the
current global warming trend.
"The Kyoto Protocol could work as powerfully as the Montreal treaty,"
he said, referring to the agreement to limit greenhouse gas emissions
that the Bush administration has refused to sign. He praised the
renewed effort by Sens.
John McCain, R-Ariz., and Joe Lieberman, D-Conn., to force a vote on
an effort to control global warming when the Senate takes up an
energy bill this week.
Both Rowland and Newchurch warned, however, that this first report of
success against the ozone hole is only the beginning: The chlorinated
fluorocarbons last from 45 to 100 years in the atmosphere, they
noted, so that even if the rate of growth in the ozone holes
continues slowing, "the CFCs will still be around a for long time
after we're all gone," Rowland said.
E-mail David Perlman at dperlman@...