WASHINGTON, DC, November 17, 2008 (ENS) - The emissions of ozone-depleting substances should have "a negligible effect on ozone in all regions beyond 2070," as long as governments continue to comply with the Montreal Protocol, according to a new assessment of the global ozone layer led by the National Oceanic and Atmospheric Administration, NOAA.
The report shows that the United States has cut the production of ozone-damaging substances by 98 percent since the late 1980s.
The assessment offers the first detailed look at the role of the United States in emitting and reducing the emissions of chemicals containing chlorine and bromine that deplete the ozone layer. These include chlorofluorocarbons, or CFCs, that were used as coolants in refrigerators and air conditioning systems before the damage they do to the ozone layer was discovered in the 1970s.
Emissions of ozone-depleting substances arise from their use not only as coolants, but also as fire-extinguishing chemicals, electronics cleaning agents, and in foam blowing and other applications.
The ozone layer, which surrounds the globe about nine to 28 miles above the surface, protects living things from the Sun’s harmful ultraviolet rays, but springtime holes in the ozone layer over the South Pole and over the Arctic have appeared annually due to the release of these substances into the atmosphere.
"With the efforts of the U.S. and the over 190 nations in the Montreal Protocol, we have avoided a future world of higher ozone depletion and exposure of humans and other living things to unhealthy levels of ultraviolet radiation," said A.R. Ravishankara, NOAA atmospheric chemist and lead author on the new report.
The 1987 Montreal Protocol and its subsequent amendments established limits and eventual phase-outs for production and consumption of several ozone-depleting substances.
One in a series of reports coordinated by the U.S. Climate Change Science Program, this ozone report was written by a team of 16 scientists from six different federal agencies. They developed information for and about the United States and drew material from two recent international scientific assessment reports to which the U.S. contributed, to distill a U.S.-specific perspective on this global issue.
The contributions of the United States to the emission of ozone-depleting substances to date have accounted for between 15 and 39 percent of the overall atmospheric abundance of ozone-depleting substances measured between 1994 and 2004, the report finds.
The United States has also contributed significantly to emission reductions of ozone-depleting substances, thereby helping efforts to achieve the expected recovery of the ozone layer and prevent large surface changes in ultra-violet radiation.
The U.S. percentage of the global total production has fallen to 10 percent in recent years.
As the report notes, without the Montreal Protocol, the levels of ozone-depleting substances in the “world we avoided” would likely have been 50 percent larger in 2010 than currently predicted.
Since the 1980s, global ozone sustained a depletion of about five percent in the midlatitudes of both the Northern Hemisphere and Southern Hemisphere, where most of the Earth’s population resides; it is now showing signs of turning the corner towards increasing ozone, the report states.
"The large seasonal depletions in the polar regions are likely to continue over the next decade but are expected to subside over the next few decades," the report predicts.
There is a relationship between ozone concentrations in the atmosphere at climate change. Ozone-depleting substances and many of the chemicals being used to replace them are potent greenhouse gases that influence the Earth’s climate by trapping heat radiation that would otherwise escape to space.
Ozone is itself a greenhouse gas. The stratospheric ozone layer heats the stratosphere and, indirectly, the lower atmosphere so stratospheric ozone is a key component that affects climate. Depletion of the ozone layer has a cooling effect on climate, though large uncertainties exist regarding this effect, which is a combination of multiple contributing factors.
The full Climate Change Science Program report, "Trends in Emissions of Ozone-Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet Radiation Exposure," and a summary brochure are available online at: http://www.climatescience.gov/Library/sap/sap2-4/final-report/default.htm
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