5 March 2007
NOAA scientists at the Chemical Sciences Division of ESRL and colleagues have found that the international Montreal Protocol agreement that protects the ozone layer has had an additional effect: it has helped slow global warming by an amount equivalent to 7 to 12 years of rise in carbon dioxide in the atmosphere. The double effect occurred because the gases that deplete the ozone layer are also greenhouse gases. The results are presented in a paper published March 5 in the Proceedings of the National Academy of Sciences.
The authors found that the Montreal Protocol halved the amount of greenhouse warming caused by ODSs that would have occurred by 2010, if the use of these substances had not been controlled. Put in another context, the amount of warming reduced through controlling the ODSs is about five times the reduction target for the first phase of the Kyoto Protocol agreement, a climate agreement initiated in 1997 and entered into force in 2005. The Kyoto Protocol did not regulate ODSs, largely because the prior agreements of the 1987 Montreal Protocol had already dealt with them.
Background: The Montreal Protocol protects the ozone layer by controlling the production and use of ozone-depleting substances (ODSs) such as chlorofluorocarbons (CFCs) used in refrigeration and air conditioning and halons used in fire extinguishers. Those same gases also have significant Global Warming Potentials, a yardstick used to compare the relative ability of compounds to absorb infrared radiation, thereby warming the atmosphere.
Significance: The paper gives an updated evaluation of the climate impacts of past actions to curtail the use of ozone-depleting substances. In addition, the paper explores other ideas for reducing future uses of ODSs and assesses the associated climate benefits. Examples of options listed in the paper include collecting and destroying storage "banks" of ODSs in old refrigerators and air conditioners, and choosing substitute chemicals that have low climate warming impacts. The paper thus gives timely scientific information to inform current policy discussions related to climate change. The research contributes to the Climate Forcing Program of NOAA's Climate Goal, and addresses NOAA's mission to provide policy-relevant scientific information to decisionmakers.