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, 104 (12), 4814-9

The Importance of the Montreal Protocol in Protecting Climate

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The Importance of the Montreal Protocol in Protecting Climate

Guus J M Velders et al. Proc Natl Acad Sci U S A.

Abstract

The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer is a landmark agreement that has successfully reduced the global production, consumption, and emissions of ozone-depleting substances (ODSs). ODSs are also greenhouse gases that contribute to the radiative forcing of climate change. Using historical ODSs emissions and scenarios of potential emissions, we show that the ODS contribution to radiative forcing most likely would have been much larger if the ODS link to stratospheric ozone depletion had not been recognized in 1974 and followed by a series of regulations. 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 that are significant compared with the Kyoto Protocol reduction target 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.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Scenarios for the global production of CFC-11 (Left) and CFC-12 (Center) and mixing ratios [Right; in ppt (part per trillion)] for the period 1960–2020. Scenarios include the baseline scenario and those of the worlds avoided with the early warning of Molina and Rowland (MR74) and with the adoption of the Montreal Protocol (NMP87). The shaded regions for MR74 and NMP87 reflect a range of 3–7% and 2–3%, respectively, for the assumed annual production increases in ODSs. The stripes in the shaded regions indicate the larger uncertainties past 2010. The average annual growth rate in global production between 1960 and 1974 was ≈17% for CFC-11 and 12% for CFC-12. Current total annual emissions of CFCs are <10% of late 1980 values. The baseline scenario represents ODS emissions observed up to 2004 and as projected past 2004 assuming global compliance to the latest provisions of the Montreal Protocol. The emissions up to 2004 are derived primarily from atmospheric observations of ODS concentrations (4) and production records (13). The primary ODS compounds included in the scenarios presented here are CFCs, CCl4, CH3CCl3, HCFCs, CH3Cl, Halons, and CH3Br (see SI Text).
Fig. 2.
Fig. 2.
ODP-weighted emissions (Left), GWP-weighted emissions (Center), and RF (Right) for ODS and CO2 scenarios for the period 1960–2020. Calculated GWP-weighted emissions (100-yr time horizon) and associated RF values are shown for four scenarios: baseline, MR74, NMP87, and SRES CO2. All emissions are normalized by their direct GWPs to equivalent GtCO2·yr−1 (see also Fig. 1 legend). The indirect contribution to the GWP due to ozone depletion, which is thought to be ≈20% (see text), is not included in these figures. The shaded regions for MR74 reflect a range of 3–7% for assumed annual production increases in CFC-11 and CFC-12 starting in 1975 and a 3% annual increase for other ODSs starting in 1987. The shaded regions for NMP87 reflect a range of 2–3% for assumed annual production increases in all ODSs. The stripes in the shaded regions indicate the larger uncertainties past 2010. The CO2 emissions for 1960–2003 are from global fossil fuel and cement production (45). Beyond 2003, the shaded regions for CO2 reflect the maximum (A1B) and minimum (B2) SRES scenarios (25). The CO2 RF data are based on CO2 observations and SRES scenarios (25). All RF values represent net changes from the start of the industrial era (≈1750) to present. Shown for reference is the magnitude of the reduction target of the first commitment period of the Kyoto Protocol, which is based on a 1990–2010 projection of global greenhouse gas emission increases and the average reduction target for participating countries (see text) (36).
Fig. 3.
Fig. 3.
GWP-weighted emissions (Left) and RF (Right) scenarios for all ODSs, HCFCs, and HFCs for the period 1990–2050. Calculated GWP-weighted emissions (100-yr time horizon) and associated RF values for all ODSs from Fig. 2 are shown on an expanded scale. Additional curves show the contribution of the HCFCs and the growth of HFCs according to an IPCC business-as-usual scenario (5) and as in the older and more uncertain SRES A1B and B1 scenarios (25). All emissions are normalized by their GWPs to equivalent GtCO2·yr−1. Under the controls of the current Montreal Protocol, developed countries will step-down HCFC use by 99.5% by 2020, with phase-out in 2030, while developing countries are allowed to increase HCFC use until 2016 and then continue at that level until phase-out in 2040 (8). Shown for reference are the magnitude of the reduction target of the first commitment period of the Kyoto Protocol (see Fig. 2 legend) and the magnitude of possible additional emission reductions in ODSs and HFCs achievable by 2015. All RF values represent net changes from the start of the industrial era (≈1750) to present. The HFC RF contribution is ≈0.02 W·m−2 in 2010, which is small compared with the other scenario differences discussed here. The HFC data before 2000 are based on observed concentrations (5).

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