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Projections of hydrofluorocarbon (HFC) emissions and the resulting global...

Velders, G. J. M., J. S. Daniel, S. A. Montzka, I. Vimont, M. Rigby, P. B. Krummel, J. Muhle, S. O’Doherty, R. G. Prinn, R. F. Weiss, and D. Young (2022), Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies, Atmos. Chem. Phys., doi:10.5194/acp-22-6087-2022.

The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past 2 decades, primarily as a result of the phaseout of ozone-depleting substances under the Montreal Protocol and the use of HFCs as their replacements. In 2015, large increases were projected in HFC use and emissions in this century in the absence of regulations, contributing up to 0.5 ◦ C to global surface warming by 2100. In 2019, the Kigali Amendment to the Montreal Protocol came into force with the goal of limiting the use of HFCs globally, and currently, regulations to limit the use of HFCs are in effect in several countries. Here, we analyze trends in HFC emissions inferred from observations of atmospheric abundances and compare them with previous projections. Total CO2 eq. inferred HFC emissions continue to increase through 2019 (to about 0.8 Gt CO2 eq. yr−1 ) but are about 20 % lower than previously projected for 2017–2019, mainly because of the lower global emissions of HFC-143a. This indicates that HFCs are used much less in industrial and commercial refrigeration (ICR) applications than previously projected. This is supported by data reported by the developed countries and the lower reported consumption of HFC-143a in China. Because this time period preceded the beginning of the Kigali provisions, this reduction cannot be linked directly to the provisions of the Kigali Amendment. However, it could indicate that companies transitioned away from the HFC-143a with its high global warming potential (GWP) for ICR applications in anticipation of national or global mandates. There are two new HFC scenarios developed based (1) on current trends in HFC use and Kigali-independent (K-I) control policies currently existing in several countries and (2) current HFC trends and compliance with the Kigali Amendment (KA-2022). These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 Gt CO2 eq. yr−1 to 1.9–3.6 Gt CO2 eq. yr−1 . The added provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 Gt CO2 eq. yr−1 in 2050. Without any controls, projections suggest a HFC contribution of 0.28–0.44 ◦ C to global surface warming by 2100, compared to a temperature contribution of 0.14–0.31 ◦ C that is projected considering the national K-I policies current in place. Warming from HFCs is additionally limited by the Kigali Amendment controls to a contribution of about 0.04 ◦ C by 2100.

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Research Program: 
Atmospheric Composition Modeling and Analysis Program (ACMAP)
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The five AGAGE stations from which ambient measurements were used here have been supported by the National Aeronautics and Space Administration (NASA; grant nos. NNX16AC98G (to MIT), NNX16AC97G, and NNX16AC96G (to SIO), and preceding grants). Support also comes from the UK Department for Business, Energy and Industrial Strategy (BEIS; contract no. 1537/06/2018 to the University of Bristol) for Mace Head, the National Oceanic and Atmospheric Administration (NOAA; contract no. 1305M319CNRMJ0028 to the University of Bristol) for Ragged Point, and the Commonwealth Scientific and Industrial Research Organization (CSIRO) and the Bureau of Meteorology (Australia) for Kennaook / Cape Grim. NOAA measurements of HFCs benefited from the technical assistance of Caroline Sico, Bradley Hall, Ben Miller, and Molly Crotwell, who are personnel at remote sampling stations, and funding in part from the NOAA Climate Program Office’s AC4 program (NOAA Coorperative Agreement with CIRES; grant no. NA17OAR4320101).