The large contribution of projected HFC emissions to future climate forcing

Abstract

The consumption and emissions of hydrofluorocarbons (HFCs) are projected to increase substantially in the coming decades in response to regulation of ozone depleting gases under the Montreal Protocol. The projected increases result primarily from sustained growth in demand for refrigeration, air-conditioning (AC) and insulating foam products in developing countries assuming no new regulation of HFC consumption or emissions. New HFC scenarios are presented based on current hydrochlorofluorocarbon (HCFC) consumption in leading applications, patterns of replacements of HCFCs by HFCs in developed countries, and gross domestic product (GDP) growth. 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% (CO(2)-eq. basis) of projected global CO(2) emissions in business-as-usual scenarios and contribute a radiative forcing equivalent to that from 6-13 years of CO(2) emissions near 2050. This percentage increases to 28-45% compared with projected CO(2) emissions in a 450-ppm CO(2) stabilization scenario. In a hypothetical scenario based on a global cap followed by 4% annual reductions in consumption, HFC radiative forcing is shown to peak and begin to decline before 2050.

Fig. 1.

CFC and HCFC consumption (A), HFC consumption (B), and HFC RF (C) for 2000–2050 in developing (A5) and developed (non-A5) countries. The CFC and HCFC mass consumption values in A are derived from reported data (1). The shaded regions for GWP-weighted consumption in B and RF in C are bounded by high and low limits as defined by the upper and lower ranges of the baseline scenarios in both developed and developing countries. The consumption values expressed in equivalent GtCO₂ per year in B are sums over the consumption of individual HFC compounds each multiplied by their respective GWP (100-year time horizon) (3).

Fig. 2.

Global ozone-depleting substances (ODSs) and HFC emissions (A), global CO₂ and HFC emissions (B), and ODS, HFC, and CO₂ global RF (C) for the period 2000–2050. Global emissions are the total from developing and developed countries. The CFC data include all principal ODSs in the Montreal Protocol except HCFCs. The emissions of individual gases are multiplied by their respective GWPs (direct, 100-year time horizon) to obtain aggregate emissions expressed in A and B as equivalent GtCO₂ per year (3). The color-shaded regions show emissions and RFs as indicated in the panel legends. The high and low labels identify the upper and lower limits, respectively, in the global baseline scenarios. The dashed lines in A show the HCFC and HFC scenario values calculated without the emission changes caused by the 2007 accelerated HCFC phaseout. Shown for reference in B and C are emissions and RF for the range of SRES CO₂ scenarios and the 450- and 550-ppm CO₂ stabilization scenarios (16, 17). The CO₂ data from 2000 to 2007 are based on reported emissions and observed concentrations. The triangle in C shows the range of HFC RF in 2050 from the baseline scenarios compared with the range in years needed to obtain the same RF change from CO₂ emissions in the SRES scenarios near 2050.

Fig. 3.

Global HFC consumption (A) and RF (B) for the new baseline scenarios and chosen mitigation scenarios for the period 2000–2050. The baseline scenarios (red) represent global HFC values (i.e., the sum of developing and developed country values in Fig. 1). The consumption values in A are multiplied by their GWPs (100-year time horizon) to obtain equivalent GtCO₂ per year (3). Three mitigation scenarios are shown: a freeze in consumption in 2014 for developed countries and in 2024 for developing countries at the previous year's level (green); and 2% per year (blue) and 4% per year (purple) annual decreases relative to the freeze level. The reduction of consumption in the mitigation scenarios has a maximum of 80%.