Projections of hydrofluorocarbon (HFC) emissions and the resulting global warming based on recent trends in observed abundances and current policies

Abstract. The emissions of hydrofluorocarbons (HFCs) have increased significantly in the past two decades, primarily as a result of the phaseout of ozone depleting substances under the Montreal Protocol and the use of HFCs as their replacements. Projections from 2015 showed large increases 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 GtCO2-eq yr−1) but are about 20 % lower than previously projected for 2017–2019, mainly because of 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 lower reported consumption of HFC-143a in China. Because this time-period preceded the beginning of the Kigali controls, 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. A new HFC scenario is developed based on current trends in HFC use and current policies in several countries. These current policies reduce projected emissions in 2050 from the previously calculated 4.0–5.3 GtCO2-eq yr−1 to 1.9–3.6 GtCO2-eq yr−1. The provisions of the Kigali Amendment are projected to reduce the emissions further to 0.9–1.0 GtCO2-eq yr−1 in 2050. Without current policies, HFCs would be projected to contribute 0.28–0.44 °C to the global surface warming in 2100, compared to 0.14–0.31 °C with current policies, but without the Kigali Amendment. In contrast, the Kigali Amendment controls are expected to limit surface warming from HFCs to about 0.04 °C in 2100.