Ozone Depletion’s Lessons for Global Warming

Published October 1, 2003

Depletion of the Earth’s ozone layer is slowing, according to a study scheduled for publication in the Journal of Geophysical Research.

At a press conference, the scientists who conducted the study hailed their findings as evidence the 1987 Montreal Protocol, the international treaty banning ozone-destroying chemicals, is successfully addressing the threat. “This is proof that the treaty is working,” said lead scientist Michael Newchurch.

Others have trumpeted the findings as evidence the Kyoto Protocol, a similarly designed treaty targeting carbon dioxide and other global warming gases, could be equally successful. “The Kyoto Protocol could work as powerfully as the Montreal treaty,” said Nobel-laureate Sherwood Rowland, who coauthored the ozone depletion hypothesis in 1974.

No Cause-and-Effect

Stratospheric ozone depletion and the Montreal Protocol do in fact offer lessons that apply to global warming and the Kyoto Protocol … but those lessons differ from what Newchurch, Rowland, and others have drawn.

The Newchurch study concludes ozone depletion in the uppermost portion of the stratosphere is still occurring, but at a rate somewhat slower than was taking place before 1997. While this trend may be due to the Montreal Protocol, as Newchurch and his colleagues assert, more significant ozone trends unreported by Newchurch lead to a very different conclusion.

The overall news on global ozone levels has been surprisingly good since the early 1990s. According to the World Meteorological Organization’s comprehensive Scientific Assessment of Ozone Depletion: 1998, “since 1991, the linear [downward] trend observed during the 1980s has not continued, but rather total column ozone has been almost constant at midlatitudes in both hemispheres since the recovery from the 1991 Mt. Pinatubo eruption.”

A 2002 update of the WMO report concluded, “global mean total column ozone for the period 1997-2001 was approximately 3 percent below the pre-1980 average values,” considerably less severe than the 5 percent depletion observed in the early 1990s.

The ozone layer has not returned to the historical average level (which itself is an estimate and may be incorrect), but it has been considerably less damaged over the past decade than had been predicted. This trend largely predates any declines in stratospheric concentrations of the compounds banned by the Montreal Protocol. In 1998, the WMO determined “the peak had not occurred” for the chlorine-containing molecules believed to attack the ozone layer. Only in 2002 did WMO report, “observations in the stratosphere indicated that the total chlorine abundance is at or near a peak.”

“Ozone depleting chemicals are still increasing slowly in the stratosphere but ozone is no longer depleting–not since 1992,” notes Dr. S. Fred Singer, president of the Science and Environmental Policy Project and longtime critic of ozone alarmism.

According to Singer and others, no cause and effect has been established between the past decade’s improvements in the ozone layer and the Montreal Protocol. The natural variability of atmospheric ozone concentrations is much greater and considerably less well understood than originally thought. Singer and others suggest the role of man-made compounds is more modest than earlier believed, especially in relation to this natural variability.

Drawing a Different Lesson

Natural variability and the role of man-made emissions are also key elements of the current debate over global warming theory.

The relationship between carbon dioxide emitted during fossil fuel combustion and global temperatures is poorly understood. Extensive research into the global warming phenomenon has raised more questions than it has addressed.

Past assumptions about the planet’s “normal” temperatures, on which predictions of man-made warming were based, have given way to a flood of work showing large and unpredictable temperature fluctuations over periods of time both long and short. The National Academy of Sciences has concluded, “the evidence of natural variations in the climate system–which was once assumed to be relatively stable–clearly reveals that climate has changed, is changing, and will continue to do so with or without anthropogenic influences.”

For both ozone depletion and global warming, the evidence points to at least some anthropogenic contribution, but we mainly see changes that cannot easily be correlated with man-made emissions and are more plausibly attributable to natural causes.

What some are touting as evidence of a solution to the ozone depletion problem may actually be evidence it wasn’t a great problem in the first place. This may prove to be the real lesson for the global warming debate.

Ben Lieberman is director of clean air policy for the Competitive Enterprise Institute in Washington, DC. His email address is [email protected].