The Science of the Total Environment, 113 (1992) 229-250 Elsevier Science Publishers B.V., Amsterdam

229

Strengthening the Montreal Protocol: does it cool down the greenhouse? M . G . J . d e n Elzen, R . J . S w a r t a n d J. R o t m a n s National Institute for Public Health and Environmental Protection, P.O. Box 1, 3720 BA Bilthoven, The Netherlands

(Received August 3rd, 1990; accepted November 24th, 1990)

ABSTRACT Strengthening of the Montreal Protocol is recently being negotiated in London in 1990 in order to achieve further reductions of the regulated CFCs and to include possibly more substances. In this article the implications of different policies with respect to control of ozone depleting substances for climate change are analysed, including the proposed substitution by HCFCs and HFCs, carbon tetrachloride and methylchloroform. A special halocarbon module was developed within the framework of RIVM's Integrated Model to Assess the Greenhouse Effect (IMAGE). IMAGE is a parameterized science based policy model and has been developed to give policy agencies a concise overview of the quantitative aspects of the greenhouse problem, to evaluate various policy options concerning climate change and to serve as a means of communication. It is concluded, from simulations with the halocarbon module, that it is of primary importance to achieve a further reduction of the regulated CFCs compared to the Montreal Protocol with compliance by as many countries as possible. From the perspective of the greenhouse effect the inclusion of longer lived halocarbons, such as carbon tetrachloride and HCFC-22 in the protocol comes second. The application of methylchloroform, halons and HCFCs and HFCs with lower global warming potentials (GWPs) than HCFC-22 contributes only marginally to the greenhouse effect in comparison with the much more important greenhouse gases carbon dioxide, methane, ozone and nitrous oxide. Especially if further growth of the total production of HCFCs after complete replacement of the present CFCs can be avoided by using these alternatives with a lower GWP, these substances could therefore be tolerated in a transition period, from the perspective of global warming. Key words: chlorofluorocarbons; alternative; global warming; Integrated Model to Assess the Greenhouse Effect

INTRODUCTION B e c a u s e o f t h e g l o b a l c o n c e r n a b o u t the d e p l e t i o n o f the s t r a t o s p h e r i c o z o n e layer, t r i g g e r e d b y t h e a p p e a r a n c e o f the A n t a r c t i c o z o n e hole, in 1988 an international agreement controlled the production and emission of ozone 0048-9697/92/$05.00

© 1992 Elsevier Scientific Publishers B.V. All rights reserved

230

M.G.J. DEN ELZEN ET AL.

depleting substances: the Montreal Protocol (UNEP, 1987 and UNEP, 1989a). This protocol regulates the consumption of the most important chlorofluorocarbons and halons that have been identified as ozone depleting substances. According to this protocol the production of C F C - 11, C F C - 12, CFC-113, C F C - 1 1 4 and C F C - 1 1 5 should initially be frozen and finally reduced by 50% by the year 2000. The production of halons should be frozen since 1992. After the establishment of the protocol new scientific evidence and an increasing consensus on the contribution of the anthropogenic halocarbon emissions to the ozone depletion continued the discussions concerning the possible strengthening of the protocol (UNEP and WMO, 1989, UNEP, 1989 and Fisher et al., 1990). This strengthening, which is presently being negotiated, in London in 1990, resulting in the London Amendments, which include further reductions in the emissions of the regulated substances, and the addition of a number of other ozone depleting substances. These additional reductions, or a complete phase-out of the CFCs, are at least partly dependent on the availability of substitutes (UNEP, 1989a). Prather and Watson (1989) provide an overview of the ozone implications of different policy options with respect to a strengthening of the protocol. Since most ozone depleting substances also have radiative properties, and contribute to the greenhouse effect (Fisher et al., 1990), we want to assess the implications of various policies for the problem of the climate change. The analysis was undertaken within the framework of RIVM's Integrated Model to Assess the Greenhouse Effect (IMAGE). METHODOLOGY

A halocarbon module was developed as part of IMAGE in order to address different policy questions regarding the implications of a phase-out of the regulated CFCs for climate change, their replacement by partly halogenated chlorofluorocarbons (HCFCs) or fluorocarbons (HFCs) and the continued use of other ozone depleting substances such as carbon tetrachloride and methylchloroform (Elzen et al., 1990). Following current scientific opinion (UNEP, 1989a and 1989c) the role of halons in climate change is rather limited, therefore the halons are not modelled in this study. IMAGE is a decision support model covering a number of cause-effect relationships of climate change (Rotmans et al., 1990; Rotmans, 1990 and den Elzen and Rotmans, 1992). It has been used at a national (Langeweg, 1988) and at international level (IPCC, 1990). Figure 1 shows the structure of the model. Besides the halocarbons, the model also includes carbon dioxide, methane, carbon monoxide and nitrous oxide. Different global scenarios serve as the input for the model. Both global average equilibrium and transient temperature rise and sea level rise are the main outputs of the model.

STRENGTHENTHE INGMONTREPARLOTOCOL

NATURAL SOURCES V

23 i

ENERGY

INDUSTRY

I

I

t

V

i

I

j

J

AGRICULTURE I

t

t

CO-EMISSIONS

I

i,t I HCFC/HFC/ other emissions

DECAYBY ~ ATMOSPHERIC -I~ CHEMISTRY

JATMOSPHERIC CONCENTRATIONI~ OFTRACEGASESI~ ~

J

I CH4-CO-OH

I

OCEAN

J TERRESTRIAL BIOSPHERE

,,

V

I ALPINEG~CIERS I I ANTARCT'CICE CAP I

EXPANSION

IGREEN~NOICECAPI

~;T'OALI t ICOSTSOF I COASTA,OEFENCEI I RISK ANALYSISI

I

Fig. 1. Structure of the Integrated Model for the Assessment of the Greenhouse Effect (IMAGE).

232

M.G.J. D E N E L Z E N ET A L

Sources refrigeration [

herm~cally sealed refrigeration=

aerosols/ ] open ce/Ifoam,=J

solvents

¢lo4wdcell foams l

=

CFC-production

Other chemicalproduction/ emission

I

=

~

=

I

Substitution-mechanism

recycflng recovecy use°f HCFCs

[

u'of HFCs

I

i HCFC/HFC-production

CFCIHCFCmFCI] erlr~lK~On

[

=

I

CFCmCFCIHFCI] dJsye¢l Won

I atmospheric concentration of trace gases radiative

absorption Fig. 2. S t r u c t u r e o f the h a l o c a r b o n model.

233

STRENGTHENING THE MONTREAL PROTOCOL

In addition, for the Netherlands a number of specific effect modules have been developed, including the impact of climate change on coastal protection and water management (den Elzen and Rotmans, 1992). In Fig. 2 the structure of the halocarbon module is shown. Basically the module consists of the following elements.

(a) End-use categories: five different applications for the halocarbons are distinguished, determining the different delay time between production and emission according to Gamlen et al. (1986): aerosols, open cell foams and solvents (less than one year), closed cell foams and not hermetically sealed refrigeration (four years) and hermetically sealed refrigeration (twelve years). (b) Substitution scheme: for the regulated CFCs by alternative substances, such as non-halocarbons, HCFCs and HFCs (Du Pont, 1989a and 1989b) (c) Conservation and recycling: including recovery and better operating practices for the now regulated CFCs and substitution by non fluorocarbons (UNEP, 1989a and 1989b) (d) (Delayed) emissions: modelled by a delayed-release box according to Wigley (1988) for all regulated CFCs (CFC-11, CFC-12, CFC-113, C F C 114 and CFC-115) and alternative substances HCFCs (HCFC-22, H C F C 123, HCFC-124, HCFC-141b, HCFC-142b) and HFCs (HFC-134a and HFC-152a) and other chemicals (methylchloroform and carbon tetrachloride) (e) Concentrations: translation of emissions and delayed emissions into concentrations assuming constant atmospheric lifetimes (f) Temperature response: radiative absorption and temperature response are modelled according to Wigley (1987), Tricot and Berger (1987) and Ramanathan et al. (1985). We suppose a global increase of 3°C for doubling of the CO2-concentration. The tropospheric concentration of the halocarbons is determined by the initial concentration, the emissions and the removal. CFCs are assumed to be removed from the atmosphere due to stratospheric loss only and in proportion to their concentration. The global tropospheric concentration used in the model is as follows: l

PCFC(t) = PCFC(t-1) +

I

[CVFCFC × EMCFC(r) -

t-I

PCFC(r)/LFTCFC + CVFCFC x CFCBET × DLEMCFC(r)] d(r)

(1)

234

M.G.J. D E N E L Z E N ET AL.

where, PCFC(t) is tropospheric concentration of CFCs at time t (in ppt); PCFC(0), initial tropospheric concentration of CFCs is 0; CVFCFC, conversion factor of CFCs, according to Prather and Watson (1989) (in ppt/Mkg) (Table 1); EMCFC(t), emission of CFCs at time t (in Mkg/year); LFTCFC, atmospheric lifetime of CFCs, assumed to be constant (Table 1); DLEMCFC(t), delayed emission of CFCs (in Mkg/year) and CFCBET is annual fraction that leaks from the delayed release box into the atmospheric box; calibrated on historical data. The tropospheric concentration for the alternatives is similarly modelled. The same holds for carbon tetrachloride and methylchloroform, except while these gases are mainly used for solvents or aerosols, the delayed emissions are zero. For different applications several substitutes are available or are under development. For the purpose of this article we followed the method of Prather and Watson (1989) and use two imaginary substitute substances,

TABLE 1

Halocarbon data for IMAGE Halocarbon

C F C - 11 (CFCL3) CFC-12 (CF2C12) CFC-113 (C2F3C13)

Lifetime (years) [range]

60 [50-107] 120 [65-400] 90

Flux (kt/yr) in 1 9 8 5

Growth factor

Concentration

(19861990) (%/yr)

(1985)

Factor (kt/ppt)

dT s (°C/

ppb)

(ppt)

350.4

4

220

23.2

0.19

450

4

375

20.4

0.21

165

7.6

30

31.6

0.19

[90-1101 CFC-114 (C2F4C12)

200

15

4

5

28.9

0.21

10

4

4

26.1

0.19

80

4

100

25.9

0.08

600

24.0

130

22.4

0.02

140

5.6

89

14.6

0.04

89 0

19.3 19.3

0.04 0.09

[ 180- 300] CFC-115 (C2F5C1)

400

[380-800] Carbon (CC14) tetrachloride Methylchloroform HCFC-22 (CHF2CI)

Compound X (CxC1) Compound Y (CxC1)

50 [50-70] 6.3 [6.2-7.4] 15.3 [15-221 15 7.8

235

STRENGTHENING THE MONTREAL PROTOCOL

called compound X and compound Y. Each compound represents a group of possible alternatives, in the sense that they have the average properties of these groups with respect to ODP and in this case, more particularly GWP. These two groups cover most of the present possible alternatives for substituting the CFC market. The chemical properties of these compounds are listed in Table 1. C o m p o u n d X is comparable to the chemicals H C F C 22, H C F C - 1 4 2 b and HFC-134a. The alternative H C F C - 2 2 is already in production. Compound Y is comparable to HCFC-141b, HCFC-123, H C F C - 1 2 4 and HFC-152a. For each application the different options for the alternatives from the two groups are described in Table 2. Compound Y is the optimistic alternative with a short atmospheric lifetime and a smaller radiative forcing. Such an alternative is not presently commercially available, but it is reasonable to assume that it soon will be. The alternative H C F C - 2 2 , which belongs to the group of alternatives represented by compound X is already in production; present emission is more than 140 kt. The production of compound X is divided into two parts; the production for the present H C F C - 2 2 market, and the additional production due to the substitution of the CFC market. The first part, production of the present H C F C - 2 2 market is assumed to be subject to continuous growth. In the model calculations we made assumptions about this future growth. The second part of the produc-

TABLE 2 The implemented options divided over the five major application categories for compound X and Y within the model Application

CFCs

Compound X

Compound Y

Closed cell foams Aerosols and open cell foams Hermetically sealed refrigerations Non-herm. sealed refrigerations Solvents

CFC-11/CFC-12

H C F C - 2 2 / H C F C - 142b

CFC-I1/CFC-12

H C F C - 142b/HFC- 134a

HCFCHCFCHCFCHCFC-

C F C - 12

H F C - 134a/HCFC-22

H C F C - 123/HCFC- 124

C F C - 11/CFC- 12

H F C - 134a/HCFC-22

H C F C - 123/HCFC- 124

C F C - 113

123/HFC- 152a 141b/HCFC- 124 141b / H C F C - 123 124

CH3CCI 3

236

M.G.J. DEN ELZEN ET AL.

tion, caused by substitution is determined by different displacementfractions of the CFC market, which are described in the scenarios. For compound Y the new total production is assumed to be only dependent on the substitution of the CFC market.

Characteristics of the halocarbons Within the framework of the deliberations on the Montreal Protocol considerable information has become available on the characteristics of the halocarbons. The main features are listed in Table 1. The emission data for all the different halocarbons are derived from GEMS (1989), CMA (1987), CMA (1988) and Prather and Watson (1989). Other data concerning the other elements of the framework are taken from UNEP (1989a, 1989b, 1989c, 1989d, 1989e and 1989f), Ramanathan et al. (1985), Prather et al. (1988), Fisher et al. (1990), U N E P and WMO (1989) and Tricot and Berger (1987). In Fig. 3 the main applications are shown. The usage of controlled CFCs over the different applications is based on UNEP (1989a and 1989b). In Fig. 4 the best alternatives for substituting the CFCs for every application are given (Du Pont, 1989a). According to Du Pont's analysis non-fluorocarbons will displace about 30% of the CFC market, conservation and recycling also about 30% and alternative substances, HCFCs and HFCs, about 30% and 10% of the CFC market, respectively. Methylchloroform is important from the perspective of ozone. It does not have a particularly high ozone depletion potential (0.1-0.15 relative to CFC-12), but it is produced in large quantities. The main application of this chemical is as a cleaning solvent (80%). The remaining use of methylchloro-

Foame

25.0%

rs 7.0%

Aerosc

Fig. 3. World usage of controlled CFCs over the different categories of end-use (UNEP, 1989b).

237

STRENGTHENING THE MONTREALPROTOCOL

CH3CCI3 2b, HFC-134a, lb, HCFC-123, 4 HCF-134a, IHCFC-124, I nd :OarTIS

re

~u13S

HCFC-22, HCFC-123 HCFC-124, HCFC-141b, HCFC-142b, HCFC-152a Fig. 4. T h e p o t e n t i a l alternatives C F C m a r k e t .

form is in aerosols. According to UNEP (1989b) and ECSA (1989) the adhesive solvents applications of methylchloroform can be substituted by waterbased adhesives, and aerosols applications can be substituted by petroleum distillates. In many countries the use of carbon tetrachloride has been reduced, because of its toxicity, however increasing concentrations indicate that CC14 must still be used in some countries of the world for non-feedstock applications. The main use of CC14 is still as a feedstock in the production of CFC-11 and C F C - 1 2 . Since 1960 the use of CC14 in the USA and other countries was prohibited, and acceptable substitutes were developed for most uses. It is however presently not possible because of lack of information to define technical control options for reducing the use of CC14 (UNEP, 1989b). Scenarios

A number of important assumptions have to be made with respect to future developments of the production of halocarbons. It is assumed that a further reduction of the regulated CFC will be made possible by three mechanisms: conservation and recycling, substitution by non-halocarbons and substitution by alternative halocarbon products. Figure 5 shows the relative market potential of these options according to Dupont (1989b).

238

M.G.J. D E N E L Z E N ET AL.

-

/atlon 29.o%

H C F C 3o.(r

HF

,.v,,-,

,.,~,..arbon

32.0%

Fig. 5. The best options for meeting the CFC-demand in 2000 according to DuPonts analysis (DuPont, 1989b).

For usage, in conjunction with the other greenhouse gases within the general framework of the larger IMAGE-model, four standard scenarios were developed. In Table 3 the main assumptions have been listed. We assume optimistically that future emissions are determined by different international policies rather than by economic development. We also assume, optimistically, in all standard cases that after completion of the substitution, as necessary for implementing a strengthened Montreal Protocol, no further expansion of the emissions of halocarbons will take place, but that by the beginning of the next century basically zero ODP and zero GWP substances will be available and that recovery and recycling will increase. The production of methylchloroform and carbon tetrachloride in the non complying countries in all standard scenarios is assumed to continue growing by 2% annually until 2050. For the autonomous production of compound X due to the increasing present H C F C - 2 2 market we assume an annual growth of 4% to 2000, after which a stabilization is assumed to follow. For the production of compounds X and Y due to substitution of the CFC market, we assume in every scenario different displacement-fractions (Table 3). The part not substituted by halocarbons will be substituted by non-halocarbons, conservation and recycling. In summary, scenario A (unrestricted trends) assumes the implementation of the original Montreal Protocol with eventually 50% reduction of CFCproduction and consumption and 85% participation. No new substances are added. The CFC market will be partly (40%) displaced by the alternative compound X with a higher Global Warming Potential (GWP) compared to compound Y, which substitutes 10% of the market. Scenario B (reduced trends) assumes an upgraded version of the Protocol, including a 95% phase out for the regulated CFCs with 85% compliance in the developed countries and a 50% reduction of the production of CC14 in 2010. In this case, for the

239

STRENGTHENINGTHEMONTREALPROTOCOL TABLE 3 Standard production scenarios for all halocarbons A

B

C

D

CFC-11, CFC-12, CFC-113 CFC-114 and CFC-115 Reduction pathway, 1993, 20% developed countries 1998, 50% (complying/strengthening (C/S))

1995, 85% 2000, 95%

1995, 85% 2000, 95% 2010, 100%

1995, 85% 2000, 100%

Developed countries (C/S)

85%

85%

100%

Reduction pathway, 2003, 20% developing countries (C/S) 2008, 50%

2003, 20% 2008, 50%

1995, 85% 2000, 95% 2010, 100%

1995, 85% 2000, 100%

Developing countries (C/S) Reduction pathway, developed countries (not C/S)

50% Continued growth (4%) to 1998

5O% Continued growth (4%) to 1998

85% 1993, 20% 1998, 50%

100% 1993, 20% 1998, 50%

Reduction pathway, developing countries (not C/S)

Continued growth (4%) to 2003

Continued growth (4%) to 2003

1993, 20% 1998, 50%

1993, 20% 1998, 50%

Substitution path of compound X

1985, 0% 1993, 40% 2100, 40%

1985, 0% 1993, 40% 2050, 30% 2100, 30%

1985, 0% 1993, 30% 2050, 30% 2100, 30%

1985, 2100,

0% 0%

Substitution path of compound Y

1985, 0% 1993, 10% 2100, 10%

1985, 0% 1993, 0% 2050, 10% 2100, 10%

1985, 0% 1993, 10% 2000, 10% 2100, 10%

1985, 2100,

0% 0%

Methyl chloroform Reduction pathway, developed countries (C/S)

Continued growth (2%)

Continued growth

Freeze in 2000

1995, 85% 2000, 95% 2010, 100%

Developed countries (C/S)

--

85%

85%

100%

Reduction pathway developing countries (C/S)

Continued growth (2%) to 2050

Continued growth (1%) to 2050

Freeze in 2000

1995, 85% 2000, 90% 2010, 100%

Developing countries (C/S)

--

50%

85%

100%

85%

240

M.G.J. D E N E L Z E N ET AL.

TABLE 3 (continued) A

B

C

D

Reduction pathway, developed Carbon tetrachloride Reduction pathway, developed countries (C/S)

Continued

Continued

Continued

Continued

Continued growth (1%) to 2050

2000, 0% 2010, 50%

1995, 85% 2000, 95% 2010, 100%

1995, 85% 2000, 95% 2010, 100%

Developed countries (C/S)

--

85%

85%

100%

Reduction pathway (C/S)

Continued growth (1%) to 2050

Freeze in 2000

2000, 0% 2010, 50%

1995, 85% 2000, 90% 2010, 100%

Developing countries (C/S)

--

50%

85%

100%

Reduction pathway developed

Continued

Continued

Continued

Continued

developing countries, regulations according to the original Protocol are assumed. In this scenario the displacement-fractions for both compounds X and Y are respectively 30% and 10% for most of the period. Scenario C (changed trends) assumes the enforcement of stricter environmental controls: a full phase out of all C F C s and CC14 (85% compliance) globally, and a stabilization of the emissions of methylchloroform at 2000 level. F o r the alternatives the same assumptions concerning displacement are used as in scenario B. FinaIly scenario D (forced trends) assesses the possibilities of maximum feasible efforts towards control of halocarbon emissions: a phase out o f all CFCs, methylchloroform and CC14 in 2000, stabilization o f c o m p o u n d X (equiv. H C F C - 2 2 ) production at 2000 level and 40% substitution of the C F C market by c o m p o u n d Y by 2000. The remaining 60% substitution is by non-halocarbons or conservation. Figure 6 shows the outcome of the calculation for the concentration of C F C - 11. Only by a full phase out of all C F C - 11 with at least 85% participation in 2010 (scenario C, changed trends), the concentrations reach a lower level than those at present. Generally this holds for all CFCs. With full participation by all countries some remaining emissions could be tolerated and still enable stabilization of the concentrations. C F C - 1 1 5 which has the longest atmospheric lifetime, requires the strictest control to stabilize or decrease concentrations.

STRENGTHENING

THE

MONTREAL

241

PROTOCOL

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••

i ii i iiii¸iiiiiiiiiii

8oo -[i] ~en'~'gc ~!i!i!i~:i:i~ii!i!iiiiiiiiiiiii~iiiiiiii!i!iiiiiiii!i:iii!iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii:U• [•] ~;~'o'D ~i~i•i~i~ii~i•i•i~i~i~iiiiiiiiiiiiiii!!i!ii~i:i:i:i:i:i~i~i~i:i:i:i:i:i:i:i:i:i:i:i:i:i: •• |i~~iii!!iii!iiiiiiiii:i:i:!:i:i:i~i:i:i:i:!:i:!!iiiiiii!iiiii!iiiii!!!i!ii!!!!i!iii:~ LL

60O

"6 cO

400

0 c-

8

200

1900

1950

r

t

2000 time In years

2050

i

210

Fig. 6. Concentration of CFC-11.

For all CFCs and CC14 a reduction by 50% of the present emissions in the industrialized countries would be sufficient to maintain 1986 concentration levels. The model simulations generally show that only by a full phase out of all the CFCs with at least 85% participation in 2010 (scenario C, changed trends), the concentrations of the chlorofluorocarbons reach a lower level than the present level. Because of the shorter atmospheric lifetime for carbon tetrachloride a reduction by 50% of the present emissions in the industrialized countries, combined with a stabilization in the developing countries would be sufficient to maintain or reduce the 1986 concentration levels. However, for methylchloroform a stabilization of the emissions at the 2000 level is practically enough to stabilise the concentrations. The controls suggested in scenario C lead to a stabilization of the concentration at approximately the 1986 level, implying a gradual reduction by 50% in the industrialized countries and a stabilization of the global emission after 2050. A fully 'implemented phase out leads to a decrease of the concentrations to the zero level within some decades. In addition the equilibrium temperature for all IMAGE-trace gases is calculated and is shown in Fig. 7. In Rotmans et al. (1990) a detailed description of the assumptions for the other greenhouse gases: CO2, CH4 and N 20 , is presented. In all calculations we used for the climate sensitivity, or equivalently, the global equilibrium temperature rise for a doubling of the CO2-equivalent concentration, a value of 3°C. This value remains a crucial source of uncertainty. This picture shows that the contribution of the halocarbons to the greenhouse effect after implementation of the Montreal

242

M.G.J. D E N E L Z E N ET AL.

10 ~T~ CO2 []CH 4 []N20 ]

CFC'I1

[ ] CFC'12 ]

ot~erCFCs

B alternatives Bother

1900

!

I

I

1950

2OO0

2050

2100

tlmeIn years Fig. 7. Relative contribution to the greenhouse effect for scenario A.

Protocol is small, but not negligible (lower than 10%). Figure 8 gives the total equilibrium temperature rise, as caused by the halocarbons for the four standard scenarios. This rise varies from 0.13°C for scenario D to 0.78°C for scenario A. For scenario A the temperature effect is mainly caused by C F C - 1 1 and C F C - 1 2 and for scenario D by the alternatives.

STRENGTHENING

THE MONTREAL

243

PROTOCOL

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n

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. . . . . . . . . . . . . . . . . . . . . .

:2"i':'1"2'1"2"~'2''2'2'1'1"2"2'2"2"2'52"2-2--"'

......

' " " ' i ~ : ~

......

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2+2"2"2"2

:~.~:~.~.~.~:`~.~.:~`~.].].~.~.5].:~[~]~:~.~:.~[~.~[.~.~:~]~

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i

I

i

i

i

1950

2000 time in years

2050

2100

Fig. 8. Total temperature rise due to the halocarbons for the four standard scenarios.

In this scenario A the contribution by the C F C s to the temperature rise is about 14% in 2000 and 10% in 2100. In the other cases the relative contribution is about the same, in 2000 more than 10% and in 2100 less than 10%.

Specific policy questions In addition to these standard cases we have addressed a number of specific policy questions. F o r these cases we compare the temperature effects of the halocarbon emissions with a reference case. This reference case assumes a complete phase out of all CFCs, CC14, CH3CC13 and alternatives, including H C F C - 2 2 in the year 2000 with no substitution by radiatively active gases. This reference case is similar to scenario D except for the fact that also the compounds X and Y are now also phased out in 2000 to show the implications of the various policies as compared to a maximum phase-out of all halocarbon. The reference case is therefore a theoretical case and certainly neither practically feasible nor necessarily desirable.

What wouM a delayed CFC-phase-out mean for climate change? In order to answer this question the emissions of all halocarbons have been assumed to be eliminated in different years: C F C s at the end of the year 2000 (reference case, A), 2010 (scenario B), 2020 (scenario C) and 2030 (scenario D), respectively and for CC14,CH3CC13 and the compounds X and Y, 20 years later. In all the different cases a reduction of 85% in 1995 for all halocarbons is assumed. F o r this case the range of the final temperature rise

244

M.G,J. DEN ELZEN ET AL.

in 2100 is calculated to be 0.10°C to 0.13°C, assuming 3°C climate sensitivity (Fig. 9). The value of the peak equilibrium temperature rise in the reference case is nearly 0.23°C. It appears that each 10 years delay in the total phase out of these chemicals results in a rise of the peak equilibrium temperature by about 0.015°C, hence in case of a phase out in 2030 the peak equilibrium temperature would be 0.28°C. At the end of the simulation the differences between each 10 years delay in total phase out remain nearly 0.015°C. What are the implications o f a limited level o f participation in strengthening the Montreal Protocol? In this case we examined the impact of a partial phase out of all halocarbons as a group without substitution by any new alternative. We assume 100%, 85%, 50% and 0% participation, respectively in a full phase out to be reached in 2000 for the CFCs presently regulated and in 2010 for the other halocarbons, including the alternative substances. This case is shown in Fig. 10. This picture stresses the fact that if the level of participation in a phase out exceeds 50%, the temperature rise would be limited to 0.45°C in 2100, assuming 3°C climate sensitivity. For 85% participation the equilibrium temperature will stay at the levels of the warming commitment by the cumulative halocarbons to date and would prevent further temperature increase due to the halocarbons. The first two cases show that the timing of a phase out is less important than the control and participation levels.

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What is the greenhouse impact of the level of substitution by HCFCs and HFCs? This case is examined by substituting the use of CFCs by different levels of compound Y and compound X, respectively. The substitution starts after 1990, and the substituted fraction will be 0% (reference case), 40%, 75% and 100%. The remainder of the market is assumed to be captured by nonradiatively active gases, recycling or conservation measures. For substitution by compound Y the range of final temperature increase is calculated to be 0.11-0.13°C for compound Y, for compound X (Fig. 11) 0.11-0.2°C (3°C climate sensitivity). We assumed in these two cases, the production of the alternatives will not increase after 2000, but be frozen. This is analogous to the four standard scenarios. The conclusion is that substitution by compound Y is preferable to substitution by compound X, because of a shorter atmospheric lifetime and smaller radiative forcing. However, if compound Y is not fully available in time for all applications and it would be necessary to use compound X instead, a greater temperature rise would result. What are the climate consequences of a delay in the phase-out of methylchloroform and carbon tetrachloride? In both cases all halocarbons, except CH3CC13 and CC14 respectively are assumed to be eliminated. At the end of 2000 all the CFCs are phased out, and in 2010 the other fluorocarbons. For CH3CC13 and CC14 the reduction pathway selected implies a phase out in 2000 (reference case A), 2025

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Strengthening the Montreal protocol: does it cool down the greenhouse?

Strengthening of the Montreal Protocol is recently being negotiated in London in 1990 in order to achieve further reductions of the regulated CFCs and...
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