Ozone hole's growth rate slows down

Scientists credit refrigerant ban

San Francisco Chronicle

by David Perlman

July 30, 2003

Almost 30 yeaers 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 ecosystems.

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 "complelling 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 atmosphere."

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 1995.

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 caculations. 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 sgin. 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, "CFCs will still be around for a long time after we're all gone," Rowland said.