Ozone Treaty Taking a Bite Out of US Greenhouse Gas Emissions

The Montreal Protocol, the international treaty adopted to restore Earth's protective ozone layer in 1989, has significantly reduced emissions of ozone-depleting chemicals from the United States.  In a twist, a new study shows the 30-year old treaty has had a major side benefit of reducing climate-altering greenhouse gas emissions from the U.S.

That's because the ozone-depleting substances controlled by the treaty are also potent greenhouse gases, with heat-trapping abilities up to 10,000 times greater than carbon dioxide over 100 years.

The new study is the first to quantify the impact of the Montreal Protocol on U.S. greenhouse gas emissions with atmospheric observations.  The study's results show that reducing the use of ozone-depleting substances from 2008 to 2014 eliminated the equivalent of 170 million tons of carbon dioxide emissions each year.  That's roughly the equivalent of 50 percent of the reductions achieved by the U.S. for carbon dioxide and other greenhouse gases over the same period.  The study was published today in Geophysical Research Letters, a journal of the American Geophysical Union.

"We were surprised by the size of the decline, especially compared with other greenhouse gases," said Lei Hu, a researcher with the Cooperative Institute for Research in Environmental Sciences (CIRES) working at NOAA and lead author of the new study.

Hu added that the benefits of the Montreal Protocol on greenhouse gas emissions would likely grow in the future.  By 2025, she projects that the effect of the Montreal Protocol will be to reduce U.S. greenhouse gas emissions by the equivalent of 500 million tons of carbon dioxide per year compared with 2005 levels.  This reduction would be equivalent to about 10 percent of the current U.S. emissions of carbon dioxide.

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