Some of the substances that are helping to avert the destruction of theozone layer could increasingly contribute to climate warming, accordingto scientists from NOAA's Earth System Research Laboratory and theircolleagues in a new study published today in the journal Proceedings ofthe National Academy of Sciences.
The authors took a fresh look at how the global use ofhydrofluorocarbons (HFCs) is expected to grow in coming decades. Usingupdated usage estimates and looking farther ahead than past projections(to the year 2050), they found that HFCs—especially from developingcountries—will become an increasingly larger factor in future climatewarming.
"HFCs are good for protecting the ozone layer, but they are not climatefriendly," said David W. Fahey, a scientist at NOAA and second author ofthe new study. "Our research shows that their effect on climate couldbecome significantly larger than we expected, if we continue along abusiness-as-usual path."
HFCs currently have a climate change contribution that is small (lessthan 1 percent) in comparison to the contribution of carbon dioxide(CO2) emissions. The authors have shown that by 2050 the HFCscontribution could rise to 7 to 12 percent of what CO2 contributes. Andif international efforts succeed in stabilizing CO2 emissions, therelative climate contribution from HFCs would increase further.
HFCs, which do not contain ozone-destroying chlorine or bromine atoms,are used as substitutes for ozone-depleting compounds such aschlorofluorocarbons (CFCs) in such uses as refrigeration, airconditioning, and the production of insulating foams. The MontrealProtocol, a 1987 international agreement, has gradually phased out theuse of CFCs and other ozone-depleting substances, leading to thedevelopment of long-term replacements such as HFCs.
Though the HFCs do not deplete the ozone layer, they are potentgreenhouse gases. Molecule for molecule, all HFCs are more potentwarming agents than CO2 and some are thousands of times more effective.HFCs are in the "basket of gases" regulated under the 1997 KyotoProtocol, an international treaty to reduce emissions of greenhouse gases.
The new study factored in the expected growth in demand for airconditioning, refrigerants, and other technology in developed anddeveloping countries. The Montreal Protocol's gradual phasing out of theconsumption of ozone-depleting substances in developing countries after2012, along with the complete phase-out in developed countries in 2020,are other factors that will lead to increased usage of HFCs and otheralternatives.
Decision-makers in Europe and the United States have begun to considerpossible steps to limit the potential climate consequences of HFCs. ThePNAS study examined several hypothetical scenarios to mitigate HFCconsumption. For example, a global consumption limit followed by a 4percent annual reduction would cause HFC-induced climate forcing to peakin the year 2040 and then begin to decrease before the year 2050.
"While unrestrained growth of HFC use could lead to significant climateimplications by 2050, we have shown some examples of global limits thatcan effectively reduce the HFCs' impact," said John S. Daniel, a NOAAcoauthor of the study.
Source: NOAA Headquarters