Hydrofluorocarbons 

and Climate Change

Summaries of Recent 

Scientific and Policy 

Papers

Nancy H. Akerman, Ph.D.

AAAS Science & Technology Policy 

Fellow, hosted by the Stratospheric 

Protection Division, U.S. 

Environmental Protection Agency
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Hydrofluorocarbons and Climate Change:

Summaries of Recent Scientific and Policy Papers

This memo summarizes recent scientific reports, articles, books, and policy papers

covering the use of hydrofluorocarbons (HFCs) and their role in climate change. 

Hydrofluorocarbons are intentionally made greenhouse gases that have no known natural source. 

They are used in air conditioning, refrigeration, fire retardants, aerosols, solvents, and as blowing 

agents in the foam sector. They have widely been adopted as replacements for 

chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), two classes of ozonedepleting substances (ODS) that are being phased out under the Montreal Protocol on Substances 

that Deplete the Ozone Layer. Although HFCs currently represent a very small portion of the 

total greenhouse gas (GHG) emissions, the studies and papers included here, in addition to other 

studies, indicate that the usage of HFCs is growing steeply, primarily due to increases in the air 

conditioning and refrigeration sectors and as a direct result of the phase out of ozone-depleting 

substances. Because most ODS are also potent GHGs, the actions taken under the Montreal 

Protocol and its amendments and adjustments significantly reduced the contributions these gases 

would have made to global warming by 13.3 billion tons of carbon dioxide equivalent (CO2eq). 

However, if the use of HFCs is left unchecked, these emissions reductions gained under the 

Montreal Protocol may be lost.

Hydrofluorocarbons, with the exception of HFC-23, are short-lived climate pollutants 

(SLCPs). Their atmospheric lifetimes are on the order of a few days to 50 years, with an average 

around 15 years, as compared to CO2 which can stay in the atmosphere for thousands of years. 

Many of the papers summarized here outline a path forward for the United States and other 

countries to move away from the use of HFCs, and the benefits that decreased use of HFCs 

would have for the climate system. Several papers discuss how SLCPs, which include HFCs as 

well as methane, black carbon, and tropospheric ozone, have impacts on the climate which can 

be mitigated through international collaborative treaties or voluntary initiatives. Because of the

more immediate climate benefits that can be made by reductions in SLCP emissions, many 

authors advocate for two separate climate treaties, one that would address short-lived pollutants 

and one that would address the long-lived pollutant CO2. Recent studies have shown that by 

using readily available low-global warming potential (GWP) alternatives to high-GWP HFCs, as 

much as 0.5-degrees Celsius warming can be avoided by the end of the century.

This memo gives one-to-two paragraph summaries of fourteen papers and reports that 

discuss HFCs and climate change, listed in reverse chronological order. This list is not meant to 

be an exhaustive list of all documents related to HFCs and climate change, but instead is a 

starting point from which to consider HFCs and potential policy options to address their role in 

climate change. The scientific findings generally focus on the rapid increases in use and 

emissions of HFCs that are projected to continue. For example, measured atmospheric 

abundances for the commonly used HFCs are on the rise (UNEP, 2011). The policy papers 

suggest that by acting now, we have the opportunity to stem the growth of HFC use and avoid an 

increase in emissions that in three decades could eclipse other climate protection efforts.
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List of Papers Summarized in This Document

Scientific Papers

Xu, Y., D. Zaelke, G. J. M. Velders, V. Ramanathan (2013) The role of HFCs in mitigating 21st century 

climate change. Atmospheric Chemistry and Physics 13: 6083–6089. [doi:10.5194/acp-13-6083-2013]

Hu, A., Y. Xu, C. Tebaldi, W. M. Washington, V. Ramanathan (2013) Mitigation of short-lived climate 

pollutants slows sea-level rise. Nature Climate Change. [doi:10.1038/nclimate1869]

Gschrey B., W. Shwartz, C. Elsner, R. Engelhardt (2011) High increase of global F-gas emissions until 

2050. Greenhouse Gas Measurement & Management 1: 85–92. 

Montzka, S. A., E. J. Dlugokencky, J. H. Butler (2011) Non-CO2 greenhouse gases and climate change. 

Nature 476: 43–50. [doi:10.1038/nature10322]

WMO – World Meteorological Organization (2011) Science Assessment of Ozone Depletion: 2010, 

Global Ozone Research and Monitoring Project - Report No. 52, Geneva, Switzerland.

Miller, B. R., M. Rigby, L. J. M. Kuijpers, P. B. Krummel, L. P. Steele, M. Leist, P. J. Fraser, A. 

McCulloch, C. Harth, P. Slameh, J. Mühle, R. F. Weiss, R. G. Prinn, R. H. J. Wang, S. O’Doherty, B. 

R. Greally, P. G. Simmonds (2010) HFC-23 (CHF3) emission trend response to HCFC-22 (CHClF2) 

production and recent HFC-23 abatement measures. Atmospheric Chemistry and Physics 10: 7875–

7890. [doi:10.5194/acp-10-7875-2010]

National Research Council (2010) Climate Stabilization Targets: Emissions, Concentrations, and Impacts 

Over Decades to Millennia. 298pp.

Velders, G. J. M., D. W. Fahey, J. S. Daniel, M. McFarland, S. O. Andersen (2009) The large 

contribution of projected HFC emissions to future climate forcing. Proceedings of the National 

Academy of Sciences USA 106: 10949–10954. 

IPCC (2007) Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the 

Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Core Writing Team, 

R. K. Pachauri and A. Reisinger, eds.) IPCC, Geneva, Switzerland, 104 pp.

Policy Papers

Bianco, N., K. Meek, R. Gasper, F. Litz (2013) Can the U.S. get there from here? Using existing federal 

laws and state action to reduce greenhouse gas emissions. World Resources Institute.

Seidel, S., and J. Bachmann (2013) Domestic policies to reduce the near-term risks of climate change. 

C2ES Center for Climate and Energy Solutions.

Velders, G. J. M., A. R. Ravishankara, M. K. Miller, M. J. Molina, J. Alcamo, J. S. Daniel, D. W. Fahey, 

S. A. Montzka, S. Reimann (2012) Preserving Montreal Protocol climate benefits by limiting HFCs. 

Science 335 (6071), 922-923. [doi:10.1126/science.1216414]

Victor, D. G., C. F. Kennel, V. Ramanathan (2012) The climate threat we can beat. Foreign Affairs.

UNEP – United Nations Environment Programme (2011) HFCs: A Critical Link in Protecting Climate 

and the Ozone Layer. 36pp.

Jackson, S.C. (2009) Parallel pursuit of near-term and long-term climate mitigation. Science 326: 526–

527.

Molina, M. J., D. Zaelke, K. M. Sarma, S. O. Andersen, V. R. Ramanathan, D. Kaniaru (2009) Reducing 

abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement 

cuts in CO2 emissions. Proceedings of the National Academies of Science USA 106: 20616–20621. 

[doi: 10.1073/pnas.0902568106]
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Scientific Papers

Xu, Y., D. Zaelke, G. J. M. Velders, V. Ramanathan (2013) The role of HFCs in mitigating 21st

century climate change. Atmospheric Chemistry and Physics 13: 6083–6089. [doi:10.5194/acp-13-

6083-2013]

This paper discusses how the use of low-GWP substitutes that are as energy efficient as the 

HFCs they are replacing can avoid as much as 0.5-degrees Celsius (°C) of warming of the global 

climate system by 2100. By decreasing the use and emissions of high-GWP HFCs, the radiative 

forcing (RF) of these SLCPs decreases significantly, in a matter of weeks to decades. This paper 

models the impacts of HFCs on radiative forcing, including recently developed projections of 

HFC emissions towards the end of the century. It shows that replacing high-GWP HFCs with 

already available low-GWP substitutes that have atmospheric lifetimes of one month or less, or 

with other materials or technologies, can provide 0.35– 0.5°C of avoided warming. This avoided 

warming can be in addition to the potential 1°C avoided warming from other SLCP reductions.

Hu, A., Y. Xu, C. Tebaldi, W. M. Washington, V. Ramanathan (2013) Mitigation of shortlived climate pollutants slows sea-level rise. Nature Climate Change. 

[doi:10.1038/nclimate1869]

This study investigated the impact of mitigating short-lived climate pollutants, including HFCs, 

on global sea-level rise. Models showed that reducing both CO2 and SLCP emissions beginning 

in 2015 would help global temperatures stay below a 2°C rise from pre-industrial temperatures, 

half of which would be due to SLCP reductions. HFCs have the smallest impact on sea level rise 

behind methane, CO2, and black carbon, but reducing SLCPs has a significant impact on sealevel rise, with the rate of sea-level rise being reduced 24 – 50%, or up to 35 centimeters. 

However, by delaying SLCP mitigation by 25 years, the global temperature will rise more than 

2°C above pre-industrial temperatures and the rate of sea-level rise will be three to six times 

higher.

Gschrey B., W. Shwartz, C. Elsner, R. Engelhardt (2011) High increase of global F-gas 

emissions until 2050. Greenhouse Gas Measurement & Management 1: 85–92.

This paper presents tables showing the amounts of fluorinated GHGs, or F-gases, emitted and in 

banks through 2050, based on data and projections from the Intergovernmental Panel on Climate 

Change (IPCC) and the United Nations Environment Programme (UNEP) Technology and 

Economic Assessment Panel (TEAP). Emissions of F-gases, which include HFCs, 

perfluorocarbons (PFCs), and sulfur hexafluoride, have increased significantly in recent years 

and are estimated to rise further. Steep increases in emissions are mostly due to the refrigeration 

and air conditioning sectors where HFCs are being deployed to replace ozone-depleting 

refrigerants. By 2050, total global emissions of F-gases will amount to 4 gigatons (Gt) CO2eq if 

no mitigation measures are taken. F-gases will comprise 7.9% of projected total anthropogenic 

CO2 emissions in 2050, up from ~1.3% in 2004. For significant reductions in future emissions of 

F-gases, additional efforts from both developed and developing countries are needed.

Montzka, S. A., E. J. Dlugokencky, J. H. Butler (2011) Non-CO2 greenhouse gases and 

climate change. Nature 476:43–50. [doi: 10.1038/nature10322]
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This review paper summarizes human activities and natural processes that emit non-CO2 GHGs, 

and explores the impact of these chemicals on radiative forcing and climate change. In 2008, the 

15 Gt CO2eq per year contribution from non-CO2 GHGs accounted for 30% of all humanrelated, long-lived GHG emissions, with HFCs contributing 0.5 Gt CO2eq per year. Large cuts in 

anthropogenic emissions of both long- and short-lived GHGs could stabilize climate forcing 

fairly rapidly, because non-CO2 GHGs account for about one-third of total CO2eq emissions and 

35 – 45% of total climate forcing from all long-lived GHGs. Mitigating non-CO2 GHG 

emissions could also reduce costs for overall climate mitigation, improve air and water quality, 

reduce acid deposition, and decrease eutrophication of aquatic ecosystems.

WMO – World Meteorological Organization (2011) Science Assessment of Ozone 

Depletion: 2010, Global Ozone Research and Monitoring Project - Report No. 52, Geneva, 

Switzerland.

This report contains the most up-to-date understanding of ozone depletion, including in-depth 

information on HFCs and their effect on the climate system. It reflects the thinking of hundreds 

of international scientific experts who contributed to its preparation and review. Tropospheric 

abundances and emissions of HFCs increased from 2006 levels. HFC emissions were mainly 

from Europe, Asia, and North America. HFCs contributed about 0.4 gigatonnes of CO2eq per 

year to total global CO2eq emissions, and the CO2eq emissions of HFCs are increasing by about 

8% per year and are expected to continue to grow.

Miller, B. R., M. Rigby, L. J. M. Kuijpers, P. B. Krummel, L. P. Steele, M. Leist, P. J. 

Fraser, A. McCulloch, C. Harth, P. Slameh, J. Mühle, R. F. Weiss, R. G. Prinn, R. H. J. 

Wang, S. O’Doherty, B. R. Greally, P. G. Simmonds (2010) HFC-23 (CHF3) emission trend 

response to HCFC-22 (CHClF2) production and recent HFC-23 abatement measures. 

Atmospheric Chemistry and Physics 10:7875 – 7890. [doi:10.5194/acp-10-7875-2010]

This paper reports observed atmospheric concentrations of HFC-23, based on global 

measurements and air samples taken from 1978–2009. By using these observations in models, an 

emission history for HFC-23 was produced and compared with emissions data reported to the 

United Nations Framework Convention on Climate Change (UNFCCC) and UNEP. Both the 

models and the reported data agree that HFC-23 emissions from developed countries dominated 

all other sources in the 1990s, then began to decline and became constant from 2003–2008. 

Developing countries use of HCFC-22 peaked in 2007, along with HFC-23 emissions. From 

2007–2009, HFC-23 emissions were reduced largely due to incineration through projects of the 

Clean Development Mechanism (CDM) of the UNFCCC. 

National Research Council (2010) Climate Stabilization Targets: Emissions, 

Concentrations, and Impacts Over Decades to Millennia. 298pp.

This report quantifies the outcomes of different stabilization targets for greenhouse gas 

concentrations using scientific analyses, and provides important scientific insights into the 

relationships between emissions, greenhouse gas concentrations, temperatures, and impacts.

Under a business-as-usual scenario, emissions of HFCs could reach about 6 Gt CO2eq in 2050, 

representing as much as one-third of the emissions of CO2 itself required for a stabilization target 

of 450 parts per million of CO2. The authors note that the emission of HFCs from all uses, 
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sectors, and nations should be seriously considered when outlining future strategies and for 

climate stabilization.

Velders, G. J. M., D. W. Fahey, J. S. Daniel, M. McFarland, S. O. Andersen (2009) The 

large contribution of projected HFC emissions to future climate forcing. Proceedings of the 

National Academy of Sciences USA 106: 10949–10954. [Accessible at: 

http://www.pnas.org/content/early/2009/06/19/0902817106.full.pdf+html]

This paper presents baseline scenarios for HFC consumption and emissions to 2050, based on 

existing policies. These scenarios show that global HFC emissions significantly exceed previous 

estimates after 2025, with developing country emissions as much as 800% greater than in 

developed countries in 2050. Global HFC emissions in 2050 are equivalent to 9–19% of 

projected global CO2 emissions, and contribute an RF equivalent to that from 6–13 years of CO2

emissions near 2050. In a hypothetical scenario based on a global cap followed by 4% annual 

reductions in consumption, HFC RF is shown to peak and begin to decline before 2050.

IPCC (2007) Climate Change 2007: Synthesis Report. Contribution of Working Groups I, 

II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate 

Change [Core Writing Team, R. K. Pachauri and A. Reisinger (eds.)]. IPCC, Geneva, 

Switzerland, 104 pp.

This Synthesis Report, commonly known as AR4, is the most recent report from the IPCC on 

climate change. The 100-year time horizon GWP values in this report for HFCs and other 

substances are used by EPA. This report provided a scientific assessment of climate change, its 

effects, and options for mitigating and adapting to climate change. It includes citations of over 

6,000 peer-reviewed scientific documents. The report found that the warming of the climate 

system is unequivocal, based on observations of increases in global average air and ocean 

temperatures, as well as widespread melting of snow and ice and rising of the global average sea 

level. These changes were found to be very likely due to the observed increases in anthropogenic 

greenhouse gas concentrations, including HFCs, which have increased above a near-zero preindustrial background concentration.

Policy Papers

Bianco, N., K. Meek, R. Gasper, F. Litz (2013) Can the U.S. get there from here? Using 

existing federal laws and state action to reduce greenhouse gas emissions. World Resources 

Institute.

This report discusses greenhouse gas (GHG) emissions in the United States and the projected 

future emissions to 2035. It surmises that the United States will not reach its target to reduce 

GHG emissions in the range of 17% below 2005 levels by the year 2020 without taking 

additional actions. It considers what legal and policy tools exist under the current U. S. federal 

laws that could be used to achieve emissions reductions and what actions could be taken by 

states. Among the different scenarios explored for meeting the U. S. reduction target are specific 

recommendations that the United States pursue HFC reductions under both the Montreal 
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Protocol and under the domestic Clean Air Act. World Resources Institute indicates that HFCs 

represent the second largest opportunity for GHG emissions reductions in the United States.

Seidel, S., and J. Bachmann (2013) Domestic policies to reduce the near-term risks of 

climate change. C2ES Center for Climate and Energy Solutions.

This paper discusses a domestic policy agenda that the United States could implement to cut 

domestic emissions of SLCPs (HFCs, methane, and black carbon). The paper advocates U. S. 

federal government leadership through directed actions by federal agencies to reduce their 

emissions of SLCPs in addition to new regulatory actions and programs. Federal leadership on 

HFCs would take the form of a Presidential Executive Order directing agency procurement 

practices to avoid products with HFCs. 

Automobile air conditioning is currently the largest source of HFC emissions in the United 

States, and HFC-134a currently is the predominately used coolant for motor vehicle air 

conditioning. The authors suggest that the U. S. Environmental Protection Agency (EPA) should 

move forward immediately with the removal of HFC-134a from the list of acceptable 

alternatives in the motor vehicle air-conditioning sector under the EPA’s Significant New 

Alternatives Policy (SNAP) program, because HFC-134a has a GWP of 1430, and other 

alternatives that have lower GWPs are now available in this sector. The removal of HFC-134a 

from acceptable use in motor vehicle air conditioning, and from other sectors such as refrigerants 

and foams as new alternatives become available, would have environmentally beneficial impacts. 

The authors also suggest the EPA should evaluate the costs and benefits of implementing 

mandatory recycling and other HFC management practices under the domestic Clean Air Act.

Velders, G.J.M., A. R. Ravishankara, M.K. Miller, M. J. Molina, J. Alcamo, J. S. Daniel, D. 

W. Fahey, S. A. Montzka, S. Reimann (2012) Preserving Montreal Protocol Climate 

Benefits by Limiting HFCs. Science 335 (6071), 922-923. [DOI:10.1126/science.1216414]

This article proposes using the Montreal Protocol to regulate HFCs in order to preserve the 

climate benefits already gained from phasing out ODS under the Montreal Protocol. 

Atmospheric abundances of major HFCs have increased 10 to 15% per year in recent years, and 

could increase substantially due to demand, particularly in developing countries, if no regulations 

are put in place. In an upper-range business-as-usual scenario, global RF from HFCs increases 

from approximately 0.012 W/m2in 2010 to 0.25 – 0.40 W/m2in 2050, which corresponds to 14 

to 27% of the increase in CO2 forcing. However, if the current mix of HFCs (average lifetime of 

15 years and average GWP of 1600) were replaced by HFOs and other alternatives with lifetimes 

less than 1 month and GWP less than approximately 20, the total HFC RF contribution in 2050, 

even under the high-emission scenario, would be less than the current forcing from HFCs. 

The two main areas where HFC use can be reduced are (a) through the use of alternative 

technologies and lower-GWP alternatives to HFCs, and (b) the reduction of HFC emissions 

through better containment and end-of-life practices. The authors suggest that the Montreal 

Protocol, with its infrastructure such as the Multilateral Fund, is an ideal institution through 

which HFCs can be regulated.
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Victor, D. G., Kennel, C. F., Ramanathan, V. (2012) The Climate Threat We Can Beat. 

Foreign Affairs.

This essay discusses the climate benefits of addressing SLCPs, such as methane, black carbon, 

and HFCs. It includes a few brief examples of adopting existing technology, regulation, and 

market-based incentives that have led to decreases in emissions in various sectors. The authors 

also stress the importance of how international organizations can fund networks so that local 

authorities and experts around the world can share information with each other about how to 

assess and best respond to growing climate change.

United Nations Environment Programme (UNEP), HFCs: A Critical Link in Protecting 

Climate and the Ozone Layer, 2011. 36pp.

This Synthesis Report discusses the current contribution to climate forcing by HFCs and the 

linkages to the ODS phaseout. From 2004 to 2008, HFC emissions (excluding HFC-23) 

increased by approximately 8% per year. The consumption of HFCs is projected to exceed by 

2050 the peak consumption level of CFCs in the 1980s and will offset much of the climate 

benefits gained by the phase-out of CFCs and other ODS under the Montreal Protocol. The 

authors note the importance of the projected HFC emissions growth, which would be equivalent 

to 7 to 19% of the CO2 emissions in 2050 based on the IPCC’s Special Report on Emissions 

Scenarios (SRES) and equivalent to 18-45% of the CO2 emissions based on the IPCC’s 450 ppm 

CO2 emissions scenario. This report also notes that there are options available to minimize 

climate impacts from HFCs including the use of alternative methods and processes, and use of 

more climate-friendly alternatives.

Jackson, S.C. (2009) Parallel pursuit of near-term and long-term climate mitigation. 

Science 326: 526–527.

This paper advocates two separate treaties to deal with climate pollutants: one treaty for shortand medium-lived climate pollutants, and one treaty to focus exclusively on reduction of longterm climate pollutants. Short-lived pollutants, such as HFCs, black carbon, and tropospheric 

ozone, and medium-lived pollutants such as methane will account for 57 to 60% of the positive 

RF generated in the next 20 years, and 7 of the top 10 pollution-generating activities create shortor medium-lived pollutants that would be overlooked by mitigation strategies that focus solely 

on long-lived pollutants.

Molina, M. J., D. Zaelke, K. M. Sarma, S. O. Andersen, V. R. Ramanathan, D. Kaniaru

(2009) Reducing abrupt climate change risk using the Montreal Protocol and other 

regulatory actions to complement cuts in CO2 emissions. Proceedings of the National 

Academies of Science USA 106: 20616–20621. [doi: 10.1073/pnas.0902568106]

This article urges “fast action” regulatory measures that can begin within 2–3 years, be 

implemented in 5–10 years, and produce a climate response within decades. These fast actions 

would mostly cover SLCPs, and be enacted in addition to long-term CO2 policies. HFCs, black 

carbon, tropospheric ozone, and other SLCPs can be addressed through existing treaties and local 

air pollution policies, along with funding and technology transfer through existing institutions.