The greenhouse effect is not all about carbon dioxide. Several other substances, such as water vapor and methane, also play a key part in trapping radiation. Recently, a family of relatively obscure chemicals called hydrofluorocarbons, or HFCs, has entered the spotlight due to its role in global warming. HFCs are highly potent greenhouse warmers – and we wouldn’t be talking about them today if not for global policy to heal the ozone layer.
Most HFCs were relatively undetectable in the atmosphere prior to 1989, when the Montreal Protocol on Substances That Deplete the Ozone Layer entered into force. The internationally negotiated Protocol aimed to phase out substances that were known to deplete the ozone layer by replacing them with safer alternatives. The agreement primarily targeted chlorofluorocarbons (CFCs), but also regulated substances such as carbon tetrachloride and halons. From the start, the Protocol recognized hydrochlorofluorocarbons (HCFCs) and HFCs as suitable CFC substitutes. Since HCFCs also deplete the ozone layer, they were used as a transitional substitute to be phased out starting in 2004.
Today, the Protocol is seen as one of the most successful international environmental agreements of all time. It is expected that damage to the ozone layer will be fixed by mid-century. Yet despite its success, the Montreal Protocol’s phaseout of CFCs and HCFCs came with its share of unintended consequences.
Early on, HFCs became the primary CFC alternative. The man-made chemicals were ozone-friendly substitutes that could be used in consumer, commercial and industrial products (such as refrigeration, air conditioning, insulating foams, aerosols and fire extinguishers). HFCs, however, have one major shortcoming: their high global warming potential (GWP). A substance’s GWP is defined as the degree to which it contributes to global warming, relative to an equivalent amount of carbon dioxide (CO2). Since CO2 is the dominant greenhouse gas by volume, other gases are converted into CO2-equivalents according to their GWP; a substance with GWP of 10, for example, contributes to global warming 10 times as much as the same amount of CO2.
The dozen or so substances in the HFC family have GWPs ranging from 140 to 11,700. The lifespan of these chemicals also varies: the less harmful compounds stay in the atmosphere for just over one year, while the most damaging ones can last up to 260 years.
HFC-23 – with a GWP of 11,700 and a 260-year lifespan – has been analyzed extensively due to its significant contribution to global warming. Prior to 1989, the primary source of HFC-23 was the combustion of HCFC-22 (one of the most widely used HCFCs, typically found in refrigerants). According to the EPA, the atmospheric concentration of HFC-23 increased from 3 to 10 parts per trillion (ppt) between 1978 and 1995. The global average concentration of the second most abundant form, HFC-134a, is about 10ppt; in 1990, HFC-134a was virtually untraceable.
Converted to CO2-equivalents, HFCs account for about one percent of total heat-trapping emissions. However, a June 2009 paper published by the Proceedings of the National Academy of Sciences (PNAS) showed that at current growth rates, this contribution could rise to 7 to 12 percent. The authors, from the Netherlands Environmental Assessment Agency, the National Oceanic and Atmospheric Administration, DuPont Fluoroproducts and the EPA, highlighted the importance of HFCs as a factor in climate change. HFC consumption, they showed, will rise with increasing global demand for refrigeration, air conditioning and insulation, especially as countries comply with the Montreal Protocol by phasing out CFCs.
The PNAS article noted that new estimates of projected HFC growth exceeded prior expectations. Due to population growth, HFC emissions in developing countries could be as much as 800 percent greater than in developed countries by 2050. At that time, HFC emissions, when measured by their CO2-equivalent, would account for roughly 9 to 19 percent of carbon dioxide emissions (in business-as-usual scenarios). As a result of this higher-than-expected atmospheric concentration, the impact of HFC emissions on the climate is slated to be about three times greater than what the Intergovernmental Panel on Climate Change (IPCC) had anticipated.
The paper concluded that international collaboration would be the only effective way to mitigate such drastic rises in HFC emissions: “a global freeze followed by modest annual reductions in both developed and developing countries is more effective in limiting the [radiative forcing] contribution from HFCs than is a single regional cap and reduction of HFCs.”
Recognizing HFCs’ contribution to climate change, several nations have called for international action to reduce HFC emissions. They argue that since the framework for regulation already exists in the Montreal Protocol, the global community has the tools to efficiently and equitably reduce HFC consumption. And given that HFCs are one of six gases regulated by the 1997 Kyoto Protocol (the global agreement to reduce greenhouse gases emissions), consensus already exists that HFCs pose a danger to human health and the environment.
In May 2009, the Federated States of Micronesia and Mauritius proposed an amendment to the Montreal Protocol addressing HFC emissions. Citing the urgency of the climate crisis and relative ease with which HFC emissions can be mitigated, the proposal called for a phasedown (rather than phaseout) of HFC consumption in both developed and developing countries. The plan would reduce consumption to roughly 10 percent of current levels.
The United States, Mexico and Canada in May 2010 presented a trilateral proposal that would yield “environmental benefits equal to removing greenhouse gas emissions from 59 million passenger cars each year through 2020, and 420 million cars each year through 2050.” According to a press release from the U.S. Department of State, “Phasing down consumption and production of HFCs will encourage the development of innovative alternatives that do not harm the ozone layer or the climate system.”
The North American amendment establishes phasedown deadlines for developed and developing countries. By mid-century, global HFC emissions would plateau at 15 percent of baseline levels. The EPA estimated that the plan – if enacted globally – would curb HFC reductions by 3,100 million metric tons of CO2-equivalent (MMTCO2eq) through 2020 and almost 88,000 MMTCO2eq through 2050.
EPA research has shown that the proposed phasedown is both feasible and affordable, since low-GWP alternatives to HFCs are readily available and additional substitutes are in the pipeline.
As the international community struggles to address climate change in a post-Kyoto world, it is critical that countries reach for the low-hanging fruit. The Montreal Protocol, in particular, has great potential to protect the climate. As noted in a 2007 PNAS paper,
“The climate protection already achieved by the Montreal Protocol alone is far larger than the reduction target of the first commitment period of the Kyoto Protocol. Additional climate benefits…could be achieved by actions under the Montreal Protocol, by managing the emissions of substitute fluorocarbon gases and/or implementing alternative gases with lower global warming potentials.”
While plans to collectively curb CO2 emissions seem to be in limbo, alternative strategies to reduce our impact on the climate must be considered. The proposal to regulate HFCs under the Montreal Protocol is a sensible and important step that should quickly be embraced by developed and developing nations alike.
Additional information on ozone depletion can be found here.
Additional information on the proposals to Montreal Protocol can be found here.