Despite a decade of efforts worldwide to curb its release into the atmosphere, NOAA and university scientists have measured increased emissions of a greenhouse gas that is thousands of times more efficient at trapping heat than carbon dioxide and persists in the atmosphere for nearly 300 years.
The substance HFC-23, or trifluoromethane, is a byproduct of chlorodifluoromethane, or HCFC-22, a refrigerant in air conditioners and refrigerators and a starting material for producing heat and chemical-resistant products, cables and coatings.
"Without the international effort to reduce emissions of HFC-23, its emissions and atmospheric abundance would have been even larger in recent years," said Stephen Montzka, a NOAA research chemist and lead author of the collaborative study between NOAA and university scientists. "As it was, emissions in 2006-2008 were about 50 percent above the 1990-2000 average."
HFC-23 is one of the most potent greenhouse gases emitted as a result of human activities. Over a 100-year time span, one pound of HFC-23 released into the atmosphere traps heat 14,800 times more effectively than one pound of carbon dioxide. To date, the total accumulated emission of HFC-23 is small relative to other greenhouse gases, making this gas a minor (less than one percent) contributor to climate change at present.
Because HFC-23 is such a potent greenhouse gas, the United Nations Framework Convention on Climate Change (UNFCCC) has facilitated the destruction of substantial quantities of HFC-23 in developing countries since 2003. The study by Montzka and colleagues shows for the first time that even with these actions HFC-23 emissions from developing countries remained substantial compared to recent years.
The Montreal Protocol, which is the international agreement that phases out ozone-depleting substances, requires the end of HCFC-22 production by 2020 in developed countries and 2030 in developing counties for uses that result in the HCFC-22 escaping to the atmosphere. This Protocol does not restrict HCFC-22 production in the synthesis of fluoropolymers or the HFC-23 that is co-produced. The future atmospheric abundance of HFC-23 and its contribution to future climate change depends on amounts of HCFC-22 produced and the success of programs to reduce emissions of the co-generated HFC-23.
Scientists measured air collected from above the snow surface and down to 380 feet below the snow surface during field studies in Antarctica in 2001, 2005 and 2009. Using these results, they were able to determine how amounts of HFC-23 and other gases affecting climate and stratospheric ozone have changed in the recent past. The first published measurements of HFC-23 appeared in 1998 but this was the first time scientists examined how HFC-23 emissions have changed since 1996, particularly in developing nations and since the UNFCCC's projects to reduce emissions began in 2003.
This study was supported in part by NOAA's Climate Program Office and the National Science Foundation.
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