The large contribution of projected HFC emissions to future climate forcing
By 2050, the effect of hydrofluorocarbons (HFCs) on global warming will be as large as that of 14% of global CO2 emissions, in business-as-usual scenarios. HFCs are strong greenhouse gases, and are used more and more in refrigeration and air conditioning. HFCs are used as substitutes for ozone-depleting gases.Over the past decades, the reduction in ozone-depleting gases – which are also greenhouse gases – has limited the effects of global warming. The use of HFCs could significantly undo this effect.
Shift from CFCs to HCFCs and to HFCs
Emissions of chlorofluorocarbons (CFCs) are globally recognised to be the main cause of the observed depletion of the ozone layer. The Montreal Protocol on Substances that Deplete the Ozone Layer has provided a mechanism for reducing and phasing out the global production and use of these compounds. With a global phase out of CFCs by 2010, the use of hydrochlorofluorocarbons (HCFCs) as transitional substitutes will have increased even further. HCFCs are, per kilogram of emission, about 10 to 20 times less harmful to the ozone layer than CFCs. HCFCs are also regulated by the Montreal Protocol with a phase out; in developed countries by 2020 and in developing countries by 2030. A global phase out of CFCs and HCFCs will mean that much of the application demand for refrigeration, air conditioning, heating and thermal-insulating foam production will be met by HFCs. Although HFCs do not deplete the ozone layer, they are greenhouse gases, as are their predecessors, and contribute to the radiative forcing of climate.
HFCs can undo climate benefits of the Montreal Protocol
Previous research showed that the Montreal Protocol provides a dual benefit: it helps both to protect the ozone layer and to reduce global warming. According to new research led by the Netherlands Environmental Assessment Agency, increased use and emission of HFCs could largely undo the climate benefits already achieved by the Montreal Protocol. HFC emissions are projected to reach between 5.5 and 8.8 GtCO2 eq/yr (CO2 basis), by 2050. In comparison, emissions of ozone-depleting substances peaked at 9.4 GtCO2 eq/yr in 1988, and in the absence of Montreal Protocol regulations would have reached over 15 GtCO2 eq/yr after 2010.
HFC emissions significant in comparison with CO2 emissions
The demand for HFCs is expected to increase globally, and especially in the developing world (mainly Asia), in the absence of new regulations. The use and emission of HFCs in developing countries is projected to be 800% greater than in developed countries, by 2050. Global HFC emissions in 2050 are projected to be between 9 and 19% of the total global CO2 emissions in business-as-usual scenarios. HFCs will contribute a radiative forcing of 0.25 to 0.40 W/m2, in 2050, compared to CO2 values of 2.9 to 3.5 W/m2. This global radiative forcing from HFCs is equivalent to that from 6 to 13 years of CO2 emissions.
HFC mitigation scenarios
In a scenario based on a global freeze in HFC consumption, followed by a 4% annual reduction in consumption, the radiative forcing from HFCs will peak near 2040 and then begin to decline. In this scenario, projected total HFC emissions will reduce, from now up to 2050, by 70 to 113 GtCO2-eq, and, by 2050, their radiative forcing will have reduced by 0.18 to 0.30 W/m2 (equivalent to 4 to 10 years of CO2 emissions).
The significance of energy use during HFC lifespan
Comparisons between the climate contribution of HFCs in various applications requires an analysis of their lifespan. Indirect climate forcings associated with HFCs or other halocarbons are based, for example, on the energy used or saved during their application or product lifespan, and on energy used in the manufacturing of the product. These and other effects need to be considered when evaluating the total climate forcing impact of HFCs.
Related publication on the PNAS Webstie: The importance of the Montreal Protocol in protecting climate
|Author(s)||Velders GJM ; Fahey DW ; Daniel JS ; McFarland M ; Andersen SO|
|Publication||Proc Nat Acad Sci 2009; in press|