Ozone Layer May Be on the Mend, New Data Suggest
for National Geographic News
|August 5, 2003|
Damage to the ozone layer, caused by chlorofluorocarbon (CFC) chemicals and other pollutants, may be starting to reverse itself according to data collected by NASA satellites.
While ozone degradation continues despite global bans on ozone-depleting pollutants imposed more than a decade ago, the rate has slowed markedly enough in one layer of the atmosphere that scientists believe ozone could start to be replenished there within several years.
"There is compelling evidence that we are seeing the very first stages of ozone recovery in the upper atmosphere," said Michael Newchurch, an atmospheric chemist with the National Space Science and Technology Center at the University of Alabama in Huntsville.
Evidence suggests that international efforts to reduce chlorofluorocarbon (CFC) pollution are working. However, Newchurch cautioned that those efforts not be curtailed. "It is absolutely essential that we continue not producing these [ozone-depleting] substances for the rest of the time we want to live on this planet," he said.
Newchurch led the scientific team who will reveal their finding in an upcoming edition of the Journal of Geophysical Research.
Enormous Ozone Hole
Though ozone is only present in tiny quantities in the atmosphere, it is essential to life, as it absorbs harmful ultraviolet (UV-B) light. The ozone layer cuts out up to 95 percent of the sun's UV-B radiation, said Newchurch. Increases in skin cancer cases have been recorded in parallel with ozone depletion. UV-B rays can also cause cataracts and damage crops.
The majority of atmospheric ozone (the "ozone layer") is found in the stratosphere, the region of the atmosphere found six miles (ten kilometers) above the Earth's surface and beyond.
In the mid-1970s, Scientists first noticed that chlorine produced in the atmosphere from human-made CFCs and similar chemicals had the potential to destroy ozone and damage the ozone layer. CFCs were previously used in refrigerators, fire extinguishers, air conditioners, and as aerosol propellants in a wide-range of spray can consumer products, from paint to deodorant to hair spray.
Observations then showed that CFC chemicals were building up in the atmosphere and that the ozone layer was thinning. The most dramatic discovery came in the mid-1980s: Scientists with the British Antarctic Survey discovered the enormous ozone hole which appears seasonally, exposing the entire Antarctic continent to levels of ultraviolet radiation many times greater than natural levels.
As a result of these findings, and their grave implications, governments came together to produce the 1987 United Nations Montreal Protocol. "A life-saving step for the planet," said Newchurch. This treaty and subsequent amendments led to the development of replacement chemicals, and a near-total ban on the use of CFCs and related chemicals.
Reductions in CFCs and chlorine observed at ground level during the 1990s led Newchurch and his team to reassess the effect of these chemicals on the upper stratosphere, the region from 22 to 28 miles (35 to 45 kilometers) above Earth's surface.
Though most ozone is found in the lower stratosphere, the region from 6 to 22 miles (10 to 35 kilometers) above the Earth, ozone depletion in the upper stratosphere is more closely linked to chlorine chemistry alone, said Newchurch. As a result, scientists anticipated that reduced CFC levels and increased ozone levels tied he effect of the global CFC ban would be first observed in the upper stratosphere, Newchurch said.
The team analyzed data from three NASA satellites which have been taking measurements since the late 1970s and from ground-based atmospheric data collection stations in Japan, Switzerland, and the United States.
The results showed that between 1979 and 1997 ozone diminished at a rate of eight percent each decade in the upper stratosphere. However, between 1997 and 2002, the rate of depletion slowed to a projected average of just four percent per decade.
"We are starting to see a turnaround in the upper stratosphere," said Newchurch. "We are within a few years of the point when ozone levels will begin to climb again," he said.
Stephen Montzka, an atmospheric chemist with the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, said the results are significant. "We are seeing the beginnings of a recovery at the edge of the atmosphere," he said.
However, Montzka warned that changes in the upper stratosphere should not yet be interpreted as evidence of recovery in the entire ozone layer.
There is not yet compelling data to indicate that ozone depletion is slowing in the lower stratosphere, "but there's no reason to believe the situation isn't improving," said Newchurch. His team is now looking for hints of ozone layer recovery there also. Ozone depletion is more complicated in the lower stratosphere due to a greater influence of weather effects.
Montzka said the finding in the upper stratosphere is nevertheless important "because we can now have more confidence that the changes to the ozone layer will follow our predictions."
Some predictions suggest that the ozone layer will have recovered to pre-industrial levels by the late 21st century. Though a total recovery could happen within 50 years, Montzka said.
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