ENVIRONMENTAL POLICY ANALYSIS
STRATOSPHERIC OZONE
Potential Environmental Impacts of Future Halocarbon Emissions K. JOHN HOLMES, J. HUGH ELLIS Department of Geography and Environmental Engineering The Johns Hopkins University Baltimore, MD 21218 An integrated analysis of future halocarbon emissions and their environmental impacts shows that strict global compliance is required if the Montreal Protocol is to accomplish the goal of eliminating the lower stratospheric ozone hole. This analysis is integrated in the sense that demographic, economic, and regulatory processes controlling future production were linked explicitly to the technological factors translating production into emissions and the environmental processes transforming emissions into environmental impacts. Given current models of halocarbon transformation and atmospheric response, this research suggests that if a small percentage of nations continues to expand production at modest rates, the ozone hole will not be eliminated. In addition, high growth rate assumptions for halocarbon production by noncompliance nations will result in significantly increased ozone depletion. This research also shows that the continued use of small amounts of ozone-depleting substances for essential uses and the failure to adequately replace all ozonedepleting substances can eliminate the possibility of returning the atmosphere to pre-ozone hole conditions. The global climate change potential of halocarbons is fairly small if growth rates for chlorofluorocarbon substitutes remain low. If growth rates return to precontrol levels, these substitutes could contribute significantly to global climate change.
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Halocarbons play a significant role in several critical environmental processes. Increased emissions of several halocarbons—chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl chloroform, and carbon tetrachloride—are implicated in depletion of lower stratospheric ozone. Although most pronounced over the Antarctic, statistically significant decreases in ozone concentrations in mid- and high latitudes of both the Northern and Southern Hemispheres have been observed by the World Meteorological Organization (WMO) (1). Halocarbons including hydroffuorocarbons (HFCs) also alter the radiative forcing in the atmosphere. Although their role is not fully understood, research shows that halocarbons have a direct positive (increasing) impact on radiative forcing and, except for HFCs, an indirect negative (decreasing) impact through their role in reducing ozone concentrations. Recent research indicates that the indirect negative impact from cooling in the lower stratosphere due to ozone depletion may be of the same magnitude as the positive forcing due to the presence of CFCs (2). Ozone depletion may exert an additional negative influence on climate forcing by clouds through perturbation of the atmosphere's oxidation state (3). Background We analyzed future halocarbon production and emissions and their environmental impacts by linking simplified representations of demographic, economic, and regulatory processes controlling future production explicitly to the technological factors that transform production into emissions and the environmental processes that transform emissions into environmental impacts. This analysis is similar to other models of the integrated assessment of climate change described in a review paper by Dowlatabadi (4). The model that formed the basis of our work is shown in the highlighted portion of Figure 1. A simple computational model represented the major processes that control future halocarbon production and emissions. In Table 1, we show the substances included in this analysis and their primary uses. The model simulates future demands and emissions for selected CFCs, HCFCs, HFCs, halons, methyl chloroform, and carbon tetrachloride similar to modeling efforts described in references 8-13. A more detailed version of this approach was used to develop the Intergovernmental Panel on Climate Change (IPCC) future halocarbon emission scenarios {14,15). Projections of future emissions resulting from changes in the overall economy were accomplished by linking the growth rates for future demands for products that use halocarbons to global economic growth. 0013-936X/96/0930-348AS12.00/0 © 1996 American Chemical Society
The Edmonds and Reilly energy-economic model (ERM) simulates the overall economy and energyeconomic processes (16). In most cases, demand for products using halocarbons grows at the same rate as the global gross national product (GNP). Incorporating components that simulate atmospheric chemistry and thermodynamic processes allowed us to simulate global climate change and stratospheric ozone depletion. These critical environmental processes were simulated using an atmospheric composition assessment model (17) and a climate model (18). Within this analysis, we used radiative balance and transient temperature changes as measures of global climate change, and the chlorine loading and free halogen concentrations (1) as the measures of ozone depletion. Our work links the effects of halocarbons on ozone depletion and global warming in an integrated assessment of the impact of several Montreal Protocol future compliance strategies. It adds to the conclusions in the literature (1,13,15,19-22) about future environmental impacts of halocarbons by focusing on long-term growth of halocarbon demand in compliance and noncompliance nations and on the effects of legal exemptions to the protocol. Critical to our analysis was the coupling of future demand for goods and services that use halocarbons in all nations to economic activity as measured by global GNP (7). This assumption is plausible given that halocarbon use for solvents, refrigeration, air conditioning, and insulation is linked closely to economic activity. Data on uncontrolled halocarbon growth rates suggest this assumption may be conservative given that growth of halocarbon use can be much larger than economic growth. Examples of historical and current growth rates include 23% and 16% average annual growth rates for global CFC-11 and CFC-12 (1934-1974) production, respectively, occurring before the aerosol ban (23); 6% growth (19701993) in global HCFC-22 production (23); 20% growth (1981-1993) in global HCFC-142b production (23); 16% growth (1968-1975) in Soviet Union CFC-12 production (24); and 7.4% growth (1986-1992) in CFC production in the developing world (25). The degree of adherence to the accord was also critical to our analysis. Future scenarios explore the effects of long-term halocarbon demand in the small percentage of noncompliance nations and halocarbon demand from noncompliance behavior by compliance nations. The issue of noncompliance behavior is not confined to the developing world; a black market for CFCs has developed in the United States that is possibly as large as 10-33% of the legal market (26). Other possible noncompliance behaviors include not reporting data as required by the Proto-
FIGURE 1
The integrated assessment model The structure of the integrated assessment model includes automated links (arrows) and energy-economic parameters (dashed lines) that are manually entered into the halocarbon production-emissions component.
col (25) and increased CFC production in developing nations that do not voluntarily report to the Alternative Fluorocarbons Environmental Acceptability Study (23). Given CFCs' economic advantages (27), it is important to examine long-term expansion of noncompliance demand. Our integrated assessment model is limited by its inability to represent the effects of emissions in a general equilibrium sense with full representation of the relationships between the modeling components. Another limitation is the model's inability to disaggregate impacts below the global scale; this analysis assumes that the environmental impacts of future emissions scenarios can be usefully represented by aggregate descriptions of critical processes and feedbacks. VOL. 30, NO. 8, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 3 4 9 A
TABLE 1
Halocarbon production characteristics Base-year production estimates are from UIMEP (5) or, for carbon tetrachloride and methyl chloroform, estimated from Hammitt et al. {6) and Hammitt et al. (7). Global 1986 Base production 3 year (xlO metric tons)
Substance
Uses
CCI3F (CFC-11)
1986
400.1
Aerosols, open-cell foams, closed-cell foams, nonhermetically sealed refrigeration
CCI2F2 (CFC-12)
1986
482.1
Aerosols, closed-cell foams, nonhermetically sealed refrigeration, hermetically sealed refrigeration
CFCI2CF2CI (CFC-113)
1986
225.9
Solvent
CCI4 (carbon tetrachloride)
1989
1138
Solvent, feedstock
CF2CIBr (Halon 1211)
1986
13.4
Fire extinguishing
CF3Br (Halon 1301)
1986
11.8
Fire extinguishing
CH3CCI3 (methyl chloroform)
1989
613.2
Solvent
CHCIF2 (HCFC-22)
none
180.5
Aerosols, open-cell foams, nonhermetically sealed refrigeration, hermetically sealed refrigeration, feedstock, replacement
CF3CH2F (HFC-134a)
none
0.00
Replacement
CH3CI (methyl chloride)
none
3300.0
Naturally occurring
CH3Br (methyl bromide)
none
169.0
Naturally occurring, fumigant
The model's advantages include its flexibility to incorporate new requirements or trends in halocarbon production and multiple theories on halocarbon interactions in the environment. Moreover, it allows representation of processes that give rise to halocarbon production and consumption to be coupled to the processes that transform these emissions in the environment within a unified framework. Finally, it incorporates additional contributing factors such as the influences of halocarboninduced ozone depletion on radiative forcing of stratospheric ozone; halocarbon destruction indirectly related to other emissions such as carbon dioxide, methane, nitrous oxide, and carbon monoxide; energy management policies; and the influences of demographic trends on halocarbon demand. Production and emissions module Halocarbons have four end uses: for prompt emitters (including aerosols, solvents, and open-cell foams), hermetically sealed refrigeration (home refrigerators and freezers), nonhermetically sealed refrigeration (building chillers, automotive air condi3 5 0 A • VOL. 30, NO. 8, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
tioners, retail refrigeration), and closed-cell foams. Each end use has characteristic manufacturing losses, immediate emissions, and delayed emissions. The fraction of the total production allocated to any use remains constant over time, an appropriate assumption for substances with well-established and often specialized uses such as in solvents or fire extinguishers. However, we recognize that development of new applications means the fraction allocated to any use may change over time. There also are three compliance categories for halocarbons: high-use, low-use, and noncompliance countries. The Montreal Protocol and subsequent London and Copenhagen amendments constrain the production and consumption of halocarbons in high-use compliance countries {2830). High-use compliance countries are those in which the protocol has entered into force, and the annual per capita halocarbon use is >0.3 kg; this category represents about 90% of all compliance production (5). Future production levels for controlled halocarbons in high-use compliance countries are mandated to be a ratio of base-year production. Table 1 shows base-year and estimated global production for 1986. Demand for goods and services using controlled halocarbons continues to grow beyond the year in which these halocarbons are eliminated; this is modeled as a long-term annual average growth rate linked to global GNP in most scenarios presented here. Satisfying this demand are HCFCs, HFCs, conservation, and nonhalocarbon replacements. Replacement substances shown in Table 1, HCFC-22 and HFC-134a, represent general HCFC and HFC substitution. These two substances will satisfy most substitution demands {14); however, other HCFCs (HCFC-123, HCFC-141b, HCFC-142b) and HFCs (HFC-125, HFC-152a) will still be required for some uses. The model also simulates the eventual replacement of HCFCs by HFCs. Under Article 5 of the Montreal Protocol, countries with annual per capita use of
