Ozone-depleting gases are not natural

The data, obtained at two sites in Antarctica and one site in Greenland from depths of up to 120 meters, are consistent with suggested human-caused emission histories of ozone-depleting gases.

July 2, 1999
Web posted at: 12:13 p.m. EDT (1613 GMT)

Most of the gases responsible for stratospheric ozone depletion are produced by human activities and are not naturally occurring in the atmosphere, according to measurements of air trapped in the polar snowpack.

Federal and university scientists measured firn — the air stuck in the polar snowpack in Antarctica and Greenland — and found major ozone-depleting gases were not present in detectable amounts in the atmosphere in the late 19th or early 20th centuries.

The data, obtained at two sites in Antarctica and one site in Greenland from depths of up to 120 meters, are consistent with suggested human-caused emission histories of these gases. This indicates that human emissions can account entirely for their presence in the atmosphere, according to an article in the June 23 issue of the journal Nature.

Lead author James Butler of the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory in Boulder, Colo., said that the data confirm that these major chlorofluorocarbons, halons, and chlorinated solvents in the atmosphere are entirely produced from human emissions and that contributions from volcanoes or the biosphere are negligible or non-existent.

Suggestions that volcanoes, biota or other natural sources could be contributing significantly to the atmospheric burden of these ozone-depleting gases were considered plausible by some, because measurements were not available to confirm the absence of these gases in the atmosphere before their human-caused emission began in the mid-20th century.

The gases measured in the study are all listed as significant ozone-depleting substances in the Montreal Protocol on Substances that Deplete the Ozone Layer. The Montreal Protocol is an international agreement to reduce the global production of ozone-depleting substances.

"This study demonstrates that the pre-20th century atmosphere was essentially devoid of the long-lived gases currently depleting stratospheric ozone," said Butler. "It underscores the human contribution to these gases in the atmosphere and the need for compliance with current international agreements to bring the atmosphere back to pre-ozone hole conditions."

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