Hydrofluorocarbon (HFC) refrigerants are factory-made chemicals produced for use in refrigeration, air conditioning, insulating foams, fire extinguishers, solvents and aerosol propellants. Since their introduction emissions of HFCs have grown rapidly as they are the primary replacement for ozone-depleting substances (ODSs) currently managed under the Montreal Protocol1,2,3. HFCs are not ODSs but powerful greenhouse gases (GHGs) and account for about 1.5% of global anthropogenic GHG emissions2. Without any controls, HFC emissions are expected to double by 2030 and nearly quadruple by 2050 over the 2015 level3,4.
Even though HFCs are not ODSs, an international consensus was achieved that HFCs could be most effectively controlled through the phase-down of their production and consumption under the Montreal Protocol5, complementary to mitigation under the UN Framework Convention on Climate Change (UNFCCC). The Montreal Protocol has the experience and expertise to ensure a fast, effective, and efficient phase-down of HFCs, which are in the same family of gases, have similar chemical properties and are used in the same sectors as the ODSs that they are replacing. The Montreal Protocol also utilizes a ‘start and strengthen’ approach wherein controlled substances are phased out in an orderly and transparent schedule which is regularly evaluated and strengthened, through amendments, as markets innovate and adjust (Fig S1). Furthermore, unlike the Paris Agreement to the UNFCCC, the Montreal Protocol and its amendments are legally binding for countries that ratify them.
The Kigali Amendment (KA) to the Montreal Protocol (in force since 1 January 2019) is a global agreement to phase down consumption of HFCs by 80-85% by the late 2040s (See: Table S2). Unlike previous Montreal Protocol amendments, which managed ODSs, the KA is primarily a climate treaty, therefore it is appropriate to evaluate the sufficiency of its ambition based on its consistency with climate mitigation targets. The 2015 Paris Agreement established an ambitious target of limiting global temperature rise this century to well below 2°C preferably to 1.5°C, compared to pre-industrial levels, but did so in the context of broader international goals of sustainable development and poverty eradication. The 1.5°C-consistent scenarios used in IPCC’s Special Report on Global Warming of 1.5ºC (SR1.5) include a 70-80% reduction in HFC emissions by 2050 compared to 2010 levels6 along with deep and simultaneous reductions of CO2 and all non-CO2 climate-forcing emissions.
A recent IIASA study7 use the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model8 framework to develop a range of long-term scenarios for HFC emissions under varying degrees of stringency in climate policy and assess co-benefits in the form of electricity savings and associated reductions in GHG and air pollutant emissions. Full compliance with the KA (Fig. 1 (a)) is expected to achieve a 56% reduction in HFC emissions by 2050, compared to 2010 levels7,9. This will not surpass the 70-80% threshold set by 1.5°C consistent scenarios6. Full compliance with the KA phase-down schedule is estimated to avoid 0.2 to 0.4°C additional warming by the end of this century3,10 which is significant, but insufficient to achieve a 1.5°C-consistent pathway6. Despite the widely recognized success of the Montreal Protocol for phasing out ODSs faster11 and at a lower cost than originally assumed, some observers question whether the HFC-reduction process under KA is taking place quickly enough to adequately address the urgency of the climate crisis12. Considering the role HFC mitigation plays in 1.5°C consistent scenarios6, enhancing the ambition of mitigation efforts by all Parties to the Montreal Protocol is called for. In this study, we develop a series of alternative HFC phase-down scenarios (Fig. 1) consistent with the Montreal Protocol’s history and experience of a gradual increase in ambition.
The Kigali Amendment defines HFC phase-down schedules for four different Party groups. The first group (Article 5-Group 1) includes 136 primarily developing countries that make up all Article 5 countries with the exception of ten countries characterized by high ambient air temperatures forming a second group (Article 5-Group 2) and allowed less ambitious timing of targets. Non-article 5 countries are primarily developed countries and under KA divided into two groups with 45 countries in a first group (non-Article 5-Earlier start) and five in a second group allowed to start somewhat later (non-Article 5-Later start).
Figure 2 (a) presents the HFC emissions (CO2eq using GWP100 from IPCC/AR513) for all analyzed scenarios. In a pre-KA baseline, HFC emissions increase to about 4.2 Gt CO2eq by 2050, which is within the range of previous estimates (4.0–5.3 Gt CO2eq) by Velders et al.14 With full KA compliance, global HFC emissions drop to 0.32 Gt CO2eq by 2050, achieving 56% reduction compared to 2010 levels. Technology exists that if deployed globally to a maximum extent could achieve near-complete mitigation of HFC emissions one-decade sooner than the KA phase-down schedule, resulting in a cumulative reduction of approximately 77 Gt CO2eq HFC emissions until 2050 (Table S2). Such a rapid reduction is however infeasible on practical grounds and also inconsistent with the Montreal Protocol’s history of a phased step-wise approach to refrigerant management. Instead, we have analyzed a set of more realistic reduction scenarios.
First, we analyze whether aligning Article 5-Group 2 countries with the higher ambition level of the Article 5-Group 1 (A5-Groups 1&2-alignment scenario) would result in achieving the Paris Agreement targets, however found that this would not be the case, as shown in Fig. 2 (b), where the orange box indicates the 70-80% threshold set by 1.5°C consistent scenarios6. In a second set of three scenarios, we increased the ambitions of both Article 5 and non-Article 5 parties, resulting in achieving the Paris Agreement targets globally by 2050, however with different cumulative emissions until 2050 due to variations in the timing of adapted KA targets. If Article 5 and non-Article 5 party groups follow the KA phase-down schedules but step-up ambitions in their final phase-down step (starting in 2036 for non-Article 5 with Article 5 following only in year 2050) to 95% below baseline in 2050 (95% scenario), then the resulting cumulative reduction is 61 Gt CO2eq (Table S2). If the A5-Groups 1&2-alignment scenario and 95% scenario are combined (Combined scenario), the resulting cumulative reduction is 63 Gt CO2eq. Finally, if the combined scenario is accelerated with a more ambitious target timeline (Accelerated combined scenario), with non-Article 5 countries achieving 95% reduction already in 2036 and Article 5 countries starting earlier and achieving 95% in 2045, then a cumulative HFC reduction potential of 69 Gt CO2eq can be achieved. The latter scenario follows the example of the accelerated phaseout of HCFCs under the Montreal Protocol from 2007. In particular for the period 2021-2030, the cumulative emissions are lower in the Accelerated combined scenario compared to other scenarios.
The developing countries are less than three years away from the first HFC consumption compliance obligation of the Kigali Amendment applicable to Article 5-Group 1 countries. Much still needs to be done to ensure that all these countries are ready to comply with the 2024 HFC freeze. In countries where HFC consumption is projected to exceed their baselines by 2024, there is an urgent need to implement actions towards a rapid transition to low-GWP refrigerants. In countries where HFC consumption is projected lower than their baselines by the agreed freeze year, there are opportunities for faster implementation of the Kigali Amendment to achieve HFC emission reductions earlier than strictly required under Kigali.
The Kigali Amendment provides an important opportunity and framework to control the production and consumption of HFCs resulting in reductions of both direct and indirect emissions from the cooling sector. Combining benefits from energy efficiency and climate-friendly cooling is vital to developing markets with rising cooling demand. Harnessing such opportunities by ensuring the transition to low-GWP refrigerants is combined with adoption of energy efficient cooling equipment can potentially double the climate benefits of the HFC phase-down3 and save as much as 20% of the expected future global electricity consumption7. Lower electricity consumption also offsets the need to build new power plants and increases energy access across emerging economies. For example, transitioning to low-GWP refrigerants with enhanced energy efficiency in room air-conditioners in China could avoid the construction of approximately 300 coal-fired power plants (500 MW each) by 205015. Therefore, an early HFC phase-down will foster sustainable growth with energy-efficient, innovative technologies that provide jobs, increase energy access, and reduce air pollution while reducing consumer energy bills.
The Kigali Amendment is a work in progress, but one that needs to be embraced and expanded upon in the global interests of mitigating climate change, just as the original Montreal Protocol has been instrumental in the recovery of the stratospheric ozone layer. An example of progressive legislation could be the HFC reduction steps under the EU F-gas regulation that are more ambitious than what is included in the Kigali Amendment16. Finally, if parties to the Montreal Protocol do not align early HFC phase-down policies with their economic transformation plans in the post-COVID era, they might not only become more vulnerable to climate shocks but also miss out on new technologies, investment and market access in a rapidly shifting global economy.