A recent study by polar scientists has supposedly proven that most gases responsible for stratospheric ozone depletion are produced by human activities and are not naturally occurring in the atmosphere. By measuring air trapped in polar snowpack (called firn by those in the know) in Antarctica and Greenland, scientists found that major ozone-depleting gases like chlorofluorocarbons (CFCs), halons and chlorinated solvents were not detectable in the atmosphere in the previous two centuries. These gases are considered major contributors to ozone depletion by the Montreal Protocol on Substances that Deplete the Ozone Layer, an international agreement to reduce the global production of ozone-depleting substances. The recent study, published in the June issue of the journal Nature, was conducted by scientists from several American universities including the Scripps Institution of Oceanography in California, the University of Rhode Island, and Princeton University. “This study demonstrates that the pre-20th century atmosphere was essentially devoid of the long-lived gases currently depleting stratospheric ozone. 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,” said the lead author of the study, James Butler of the National Oceanic and Atmospheric Administration’s Climate Monitoring and Diagnostics Laboratory in Boulder, Colo.