Chapter 5

A Focus on Information and 

Options for Policymakers

Coordinating Lead Authors:

J.S. Daniel

G.J.M. Velders

Lead Authors:

O. Morgenstern

D.W. Toohey

T.J. Wallington

D.J. Wuebbles

Coauthors:

H. Akiyoshi

A.F. Bais

E.L. Fleming

C.H. Jackman

L.J.M. Kuijpers

M. McFarland

S.A. Montzka

M.N. Ross

S. Tilmes

M.B. Tully

Contributors:

S.O. Andersen

U. Langematz

P.M. Midgley

SCIENTIFIC SUMMARY .............................................................................................................................................1

5.1 SUMMARY OF PREVIOUS ASSESSMENT AND KEY ISSUES 

TO BE ADDRESSED IN THE CURRENT ASSESSMENT.................................................................................5

5.2 METRICS USED TO QUANTIFY OZONE AND CLIMATE IMPACTS ...........................................................5

5.2.1 Background ...............................................................................................................................................5

5.2.2 Ozone Impacts: ODPs and EESC..............................................................................................................7

5.2.2.1 Fractional Release Values and Global Lifetimes........................................................................7

5.2.2.2 Ozone Depletion Potentials.........................................................................................................9

5.2.2.3 Equivalent Effective Stratospheric Chlorine ..............................................................................9

5.2.3 Climate Impacts: GWPs and Radiative Forcing......................................................................................10

5.2.3.1 Lifetime Updates.......................................................................................................................11

5.2.3.2 Radiative Efficiency Updates ...................................................................................................11

5.2.3.3 Updates to Indirect GWPs from Ozone Destruction.................................................................12

5.3 FUTURE BASELINE SCENARIOS ....................................................................................................................14

5.3.1 Chlorine- and Bromine-Containing Ozone-Depleting Substances .........................................................14

5.3.2 CO2, CH4, and N2O .................................................................................................................................16

5.3.3 ODP- and GWP-Weighted Emissions, EESC, and Radiative Forcing ...................................................16

5.4 IMPACTS OF HUMAN ACTIVITIES RELEVANT TO OZONE POLICY ......................................................19

5.4.1 Background .............................................................................................................................................19

5.4.2 Ozone Impacts.........................................................................................................................................20

5.4.2.1 Chlorine- and Bromine-Containing ODSs................................................................................20

5.4.2.2 CO2, CH4, and N2O...................................................................................................................22

5.4.2.3 N2O from Automotive Biofuels................................................................................................22

5.4.2.4 Geoengineering: Enhancing Earth’s Albedo by Stratospheric Injection of Sulfur...................23

5.4.2.5 Emissions from Aviation and Rockets......................................................................................24

5.4.2.6 Summary...................................................................................................................................25

5.4.3 Climate Impacts.......................................................................................................................................25

5.4.3.1 Major HFCs Used as Replacements for ODSs.........................................................................25

5.4.3.2 Other Replacements for ODSs..................................................................................................30

5.4.4 Other Environmental Impacts .................................................................................................................31

5.4.5 Impact of 2007 Accelerated HCFC Phase-Out .......................................................................................32

5.5 THE WORLD AVOIDED BY OZONE POLICY ................................................................................................33

5.5.1 ODS Production ......................................................................................................................................33

5.5.2 Radiative Forcing ....................................................................................................................................34

5.5.3 Climate and Ozone Impacts Avoided by the Montreal Protocol.............................................................35

5.5.4 UV Impacts of the Avoided Ozone Depletion ........................................................................................37

5.5.5 Summary .................................................................................................................................................37

REFERENCES .............................................................................................................................................................38

Appendix 5A

Table 5A-1. Direct Global Warming Potentials for selected gases....................................................................47

Chapter 5

A Focus on Information and Options for Policymakers

Contents
Table 5A-2. Assumptions made in obtaining production and emission estimates for

the baseline (A1) scenario..............................................................................................................50

Table 5A-3. Mixing ratios (ppt) of the ODSs considered in the baseline (A1) scenario ...................................54

Table 5A-4. Halocarbon indirect GWPs from ozone depletion using the EESC-based 

method described in Daniel et al. (1995).......................................................................................56
5.1

A Focus on Information for Policymakers

SCIENTIFIC SUMMARY

Ozone Depletion Potentials (ODPs) and Global Warming Potentials (GWPs) are metrics frequently used to quantify the relative impacts of substances on ozone depletion and climate forcing. In Chapter 5, both ODPs and GWPs have 

been updated. The direct GWPs for some compounds presented here have not appeared previously in WMO/UNEP or 

Intergovernmental Panel on Climate Change (IPCC) assessments. Indirect GWPs have also been re-evaluated.

INFORMATION FOR POLICYMAKERS

•	 The Montreal Protocol is working. It has protected the stratospheric ozone layer from much higher levels of

depletion by phasing out production and consumption of ozone-depleting substances (ODSs). Simulations show 

that unchecked growth in the emissions of ODSs would have led to ozone depletion globally in the coming decades 

much larger than has been observed. Solar ultraviolet-B (UV-B) radiation at the surface would also have increased 

substantially.

•	 The Montreal Protocol and its Amendments and Adjustments have made large contributions toward reducing global greenhouse gas emissions. Because many ODSs are potent greenhouse gases, the Montreal Protocol 

has successfully avoided larger climate forcing. In 2010, the decrease of annual ODS emissions under the Montreal 

Protocol is estimated to be about 10 gigatonnes (Gt) of carbon dioxide–equivalent (GtCO2-eq) per year, which is 

about five times larger than the annual emissions reduction target for the first commitment period (2008–2012) of 

the Kyoto Protocol.

•	 The accelerated hydrochlorofluorocarbon (HCFC) phase-out agreed to by the Parties to the Montreal Protocol

in 2007 is projected to reduce cumulative HCFC emissions by 0.6–0.8 million ODP-tonnes between 2011 and

2050 and bring forward the year equivalent effective stratospheric chlorine (EESC) returns to 1980 levels by

4–5 years. In terms relevant to climate, the accelerated HCFC phase-out is projected to reduce emissions by

0.4–0.6 GtCO2-eq per year averaged over 2011 through 2050. The actual climate benefit will be determined, 

in part, by the climate impact of the compounds used to replace the HCFCs. In comparison, global anthropogenic 

emissions of CO2 were greater than 30 Gt per year in 2008.

•	 EESC at midlatitudes is projected to return to 1980 levels in 2046 for the baseline (A1) scenario, 2–3 years

earlier than projected in the previous Assessment. This revision is primarily due to an improved understanding of 

lower stratospheric chlorine and bromine release from ODSs, along with contributions from smaller projected HCFC 

emissions, and despite larger projected emissions of carbon tetrachloride (CCl4) and a smaller 1980 mixing ratio of 

methyl bromide (CH3Br).

•	 EESC in the Antarctic vortex is projected to return to 1980 levels around 2073 for the baseline (A1) scenario,

7–8 years later than projected in the previous Assessment. This is primarily due to an improved understanding of lower stratospheric chlorine and bromine release from ODSs, with smaller contributions from changes in the 

emissions of CCl4 and HCFCs and a smaller 1980 mixing ratio of CH3Br. The return to 1980 levels in the Antarctic 

vortex is about 26 years later than the return of midlatitude EESC to 1980 levels.

•	 Due to the ongoing success of the Montreal Protocol and its Amendments and Adjustments in reducing the

production, emissions, and abundances of controlled ODSs, other compounds and activities not controlled by

the Montreal Protocol are becoming relatively more important to stratospheric ozone levels.

•	 Increasing abundances of radiatively important gases that are not controlled by the Montreal Protocol, especially CO2, methane (CH4), and nitrous oxide (N2O), are expected to significantly affect future stratospheric

ozone levels (see also Chapter 3). Under many IPCC future scenarios, it is projected that these gases will cause globally averaged ozone changes larger than those resulting from any of the ODS reduction cases explored in this chapter.
5.2

Chapter 5

•	 A nitrous oxide (N2O) ODP of 0.017 has been calculated. The anthropogenic ODP-weighted emission of N2O

is larger than that of any current halogenated ODS emission. The ODP of N2O is more uncertain than it is for 

halogenated substances, but it has been known since 1970 that N2O depletes stratospheric ozone. Reductions in N2O 

emissions would also reduce climate forcing.

•	 Since the previous Assessment, new fluorocarbons have been suggested as possible replacements for potent

HCFC and hydrofluorocarbon (HFC) greenhouse gases. For example, HFC-1234yf (CF3CF=CH2) (ODP = 0; 

100-year GWP = 4) is proposed to replace HFC-134a (CH2FCF3) (ODP = 0; 100-year GWP = 1370) in motor vehicle 

(mobile) air conditioning. Each new fluorocarbon proposed as a replacement will require an evaluation for ODP, 

GWP, atmospheric fate, safety, and toxicity for a thorough understanding of its potential environmental impact. 

Preliminary analyses of the atmospheric fate of HFC-1234yf indicate that global replacement of HFC-134a with 

HFC-1234yf at today’s level of use is not expected to contribute significantly to tropospheric ozone formation or 

harmful levels of the degradation product TFA (trifluoroacetic acid). It is well established that TFA is a ubiquitous 

natural component of the hydrosphere, but uncertainties remain regarding its natural and anthropogenic sources, longterm fate, and abundances.

OPTIONS FOR POLICYMAKERS

A new baseline scenario for ODSs is presented in Chapter 5 that reflects our current understanding of atmospheric mixing ratios, production levels, and bank sizes. Elimination of future emissions, production, and banks of various ODSs are applied to this scenario to evaluate the maximum impacts of various hypothetical phase-outs (see Table 

S5-1). The year EESC returns to 1980 levels, and integrated EESC changes, are two metrics used in the evaluation. The 

calculations of the years when EESC returns to the 1980 level in these hypothetical cases do not consider other effects 

such as changing atmospheric transport and lifetimes. An elimination of anthropogenic N2O emissions is also considered 

and compared to some ODS cases using globally averaged total ozone. In addition to the hypothetical cases discussed 

below, the impacts on stratospheric ozone of other activities, such as the use of automotive biofuels, commercial subsonic 

aircraft, and rocket launches, are considered in Chapter 5. These other activities are not expected to substantially affect 

stratospheric ozone now or in the near future.

•	 Projections suggest that unmitigated HFC growth could result in GWP-weighted emissions up to 8.8 GtCO2-eq

per year by 2050, comparable to the GWP-weighted emissions of chlorofluorocarbons (CFCs) at their peak in

1988. The highest of these projections assumes that developing countries use HFCs with GWPs comparable to those 

currently used in the same applications in developed countries. The projected radiative forcing in 2050 from these 

compounds (up to 0.4 W/m2) can be reduced by using compounds with lower GWPs.

•	 Options available for limiting future halocarbon emissions will have less impact on future ozone levels than

what has already been accomplished by the Montreal Protocol.

•	 Leakage of CFCs and leakage of halons from the banks are the largest sources of current ODP-weighted

emissions of ODSs. A delay of four years, from 2011 to 2015, in the capture and destruction of the estimated CFC 

banks is currently thought to reduce the potential ozone and climate benefits from these actions by about 30%. The 

percentage impact of a four-year delay in the capture and destruction of the halon banks is similar.

•	 Elimination of future CCl4 emissions is now projected to have a larger impact on integrated EESC than was

projected in the previous Assessment. Recent observed CCl4 mixing ratios have declined more slowly than previously projected. Extrapolation of this trend leads to larger future projected emissions in the baseline scenario and thus 

to the increased projected impact of the elimination of emissions. 

•	 The estimated impact on integrated EESC resulting from elimination of future HCFC production is slightly

smaller than in the previous Assessment. The recent growth in reported HCFC production in developing countries 

was larger than projected in the previous Assessment. This alone would have resulted in a larger projected HCFC
5.3

A Focus on Information for Policymakers

Table S5-1. Summary of hypothetical cases for accelerating the recovery of the ozone layer and reducing carbon-equivalent emissions. The table below shows the reductions in integrated EESC and integrated 

CO2-eq emissions relative to the baseline (A1) scenario that can be achieved in several hypothetical cases. 

The EESC excess above 1980 levels is integrated from 2011 until the time EESC returns to the 1980 level 

(before 2050). Any potential contribution from very short-lived substances is neglected.

Substance or Group of

Substances

Reductions (%) in

Integrated EESC

(equivalent effective

stratospheric chlorine)

Reduction in Cumulative

GWP-Weighted Emissions

from 2011 to 2050

(Gt of CO2-equivalent)

Bank capture and 

destruction in 2011 and 2015:

2011 2015 2011 2015

CFCs 11 7.0 7.9 5.5

Halons 14 9.1 0.4 0.3

HCFCs 4.8 5.3 1 4.9 5.5 1

Production elimination after 2010:

HCFCs 8.8 13.2

CH3Br for quarantine and pre-shipment 6.7 0.002

Total emissions elimination after 2010:

CCl4

 2 7.6 0.9

CH3CCl3 0.1 0.004

HFCs 0.0 Up to 170 3

1 The impact of a 2015 HCFC bank recovery is larger than a 2011 bank recovery because this calculation assumes destruction of the bank in only a 

single year, and because the bank in 2015 is larger than the bank in 2011 owing to continued annual production that is larger than the annual bank 

release. 2 Banks are assumed to be zero. Emissions include uncertain sources such as possible fugitive emissions and unintended by-product emissions. 3 Strongly dependent on future projections and does not consider HFC-23 emissions. HFCs are not controlled by the Montreal Protocol, but are included 

in the basket of gases of the Kyoto Protocol.

production in the new baseline scenario compared to the previous Assessment, but is projected to be more than compensated for by the accelerated HCFC phase-out agreed to by the Parties to the Montreal Protocol in 2007. Projections 

suggest that total emissions of HCFCs will begin to decline in the coming decade due to measures already agreed to 

under the Montreal Protocol. 

•	 The elimination of all emissions of chlorine- and bromine-containing ODSs after 2010 would shift the year

EESC reaches the 1980 level by about 13 years, from 2046 to 2033. In terms relevant to climate, this would reduce 

emissions of these substances by about 0.7 GtCO2-eq per year averaged over 2011 through 2050. Future production 

of HCFCs and the sum of the current banks of CFCs plus HCFCs contribute about equally to this number. In comparison, global anthropogenic emissions of CO2 were greater than 30 Gt per year in 2008.

•	 A phase-out of methyl bromide emissions from quarantine and pre-shipment (QPS) applications beginning in

2011 would shift the year EESC reaches the 1980 level earlier by 1.5 years compared to continued use at current levels. Continuing critical-use exemptions (CUEs) indefinitely at the approved 2011 level would delay the return 

of EESC to 1980 levels by 0.2 years.

•	 Elimination of anthropogenic emissions of very short-lived substances (VSLS) could shift the year EESC reaches the 1980 level earlier by almost 3 years, if anthropogenic VSLS contribute 40 parts per trillion of EESC to the 

stratosphere. It remains unclear, however, how VSLS emissions reductions at different surface locations would affect 

their contribution to stratospheric chlorine. VSLS are not controlled by the Montreal Protocol.

5.5

A Focus on Information for Policymakers

5.1 SUMMARY OF PREVIOUS ASSESSMENT

AND KEY ISSUES TO BE ADDRESSED IN

THE CURRENT ASSESSMENT

The benefits of the Montreal Protocol and its 

Amendments and Adjustments to both stratospheric ozone 

and climate have been well documented. Controls on the 

production and consumption of ozone-depleting substances have been so successful, in fact, that remaining options 

for further reducing future emissions of ozone-depleting 

substances (ODSs) are not expected to be as effective in 

reducing future ozone depletion and climate forcing as 

what has already been accomplished. As the ability to 

make further ODS reductions becomes more limited and 

ODS emissions continue to decline, other processes and 

anthropogenic activities are expected to become relatively 

more important in affecting future ozone evolution.

The majority of this chapter is devoted to assessing the impacts of various ozone-relevant processes and 

activities on ozone depletion and climate forcing. It serves 

primarily as an update to Chapter 8 of the previous Assessment (Daniel and Velders et al., 2007). In that chapter, 

future equivalent effective stratospheric chlorine (EESC) 

projections were updated with the goal of providing a more 

accurate estimate of the time when the impact of ODSs on 

stratospheric ozone depletion would return to its 1980 level. The most significant updates resulted from improved 

bank estimates of chlorofluorocarbon-11 (CFC-11) and 

CFC-12. For the first time, bank estimates were available 

from a bottom-up method, leading to more reliable future 

projections. Before the previous Assessment, banks were 

estimated from the cumulative difference between production and emissions, a technique thought to be characterized by large uncertainties. The value for the relative effectiveness of bromine compared with chlorine was also 

increased to be consistent with the latest literature, making 

methyl bromide (CH3Br) emissions and halon banks more 

important relative to the chorine-containing ODSs than 

they would have been otherwise. Using the updated EESC 

projections, the impacts of eliminating future production, 

bank release, and emissions of several compound groups 

were quantified. It was found that the elimination of future hydrochlorofluorocarbon (HCFC) emissions could reduce future EESC more than the elimination of emissions 

of any other compound group. In 2007, the Parties to the 

Montreal Protocol decided to accelerate the production 

and consumption phase-out of the HCFCs. The previous 

Assessment was also the first assessment that presented 

dates for the return of EESC to 1980 levels relevant to 

both the midlatitude and Antarctic stratosphere.

In the current chapter, Ozone Depletion Potentials 

(ODPs) and Global Warming Potentials (GWPs) for ODSs 

and their replacements are updated. New scenarios are 

generated to explore the potential impacts of some current 

hypothetical ODS and nitrous oxide (N2O) emissions reductions on future ozone depletion and climate forcing. 

These new scenarios incorporate updated bottom-up bank 

estimates and the latest ODS mixing ratio observations. 

The impact of the 2007 HCFC accelerated phase-out is 

also quantified. This chapter assesses some additional 

processes and activities that are expected to affect future 

ozone levels through mechanisms that do not necessarily 

involve the emission of chlorine- and bromine-containing 

source gases. Some of these processes could affect future ozone levels more than future emissions of controlled 

ODSs. We also discuss the impact of the Montreal Protocol on climate forcing where appropriate. For example, 

in addition to the climate forcing of ODSs, we assess the 

impact of future hydrofluorocarbon (HFC) abundances 

on climate because these chemicals are commonly used 

as replacement compounds for ODSs. Finally, since the 

previous Assessment, additional work has been published 

that investigates the impact of the Montreal Protocol on 

both ozone and climate. These studies support our understanding that the Montreal Protocol and its Amendments 

and Adjustments have averted many profound changes to 

Earth and its atmosphere.

Uncertainties remain in our ability to evaluate the 

effects of human activities on future ozone levels. Where 

appropriate, we identify gaps in our understanding that 

inhibit a precise quantification of ozone impacts.

5.2 METRICS USED TO QUANTIFY OZONE

AND CLIMATE IMPACTS

5.2.1 Background

Halocarbons and other long-lived gases released 

from Earth’s surface become mixed in the lower atmosphere and are transported into the stratosphere by atmospheric dynamical processes. They are removed from 

the atmosphere by photolysis, reaction with excited-state 

oxygen atoms (O(1D)) and hydroxyl radicals (OH) (the 

latter typically only for unsaturated compounds or those 

containing C-H bonds), and for some compounds, uptake 

by the oceans and/or land (see Chapter 1). Halocarbons 

that are transported intact to the stratosphere can react or 

undergo photolysis and release their degradation products 

there directly. Some fraction of the degradation products 

from halocarbons that react before leaving the troposphere 

can also be transported to the stratosphere. The final degradation products are inorganic halogen species containing 

fluorine, chlorine, bromine, and iodine atoms. The fraction of the inorganic halogen present in the stratosphere as 

X atoms (X = Cl, Br, or I) and XO largely determines the 

efficiency of ozone destruction there. Fluorine atoms, for 
5.6

Chapter 5

example, exist as F and FO in very small relative quantities because fluorine species are rapidly converted into hydrogen fluoride (HF), a stable reservoir species that does 

not react with ozone. This prevents fluorine from contributing to ozone destruction to any significant degree (Ravishankara et al., 1994; Wallington et al., 1995). Iodine atoms participate in catalytic ozone destruction cycles, but 

rapid tropospheric loss of iodine-containing compounds 

reduces the amount of iodine reaching the stratosphere 

from surface emissions (see Chapter 1). Thus, it is primarily chlorine- and bromine-containing compounds that lead 

to ozone depletion. Halocarbons also absorb terrestrial radiation (long-wavelength infrared radiation emitted from 

Earth’s surface and by the atmosphere) and contribute to 

the radiative forcing of climate.

Simple metrics have been widely used to quantify 

the contribution of individual compounds to stratospheric 

ozone depletion and climate change. ODPs and GWPs are 

the most established metrics and have been used in past 

climate and ozone assessments (IPCC, 1990, 1995, 1996, 

2001, 2007; IPCC/TEAP, 2005; WMO, 1989, 1991, 1995, 

1999, 2003, 2007). They have qualities that are particularly useful in policy discussions. Specifically, they are 

simple and transparent concepts that are straightforward 

to estimate and communicate. They approximate the integrated impact of the emission of a given gas relative to that 

for the emission of the same mass of a reference compound 

(generally CFC-11 for ODPs and carbon dioxide (CO2) 

for GWPs). Some uncertainties in translating emissions 

into absolute environmental impacts tend to cancel, and 

the relative benefits of controlling emissions of different 

gases are highlighted when using such indices. ODPs and 

GWPs have found widespread use in international agreements such as the Montreal Protocol and Kyoto Protocol 

and in national regulatory discussions.

Both steady-state and time-dependent ODPs can 

provide valuable information about the potential for ozone 

destruction by a compound. Steady-state ODPs are defined as the change in global ozone for a sustained unit 

mass emission of a specific compound relative to the 

change in global ozone for the sustained unit mass emission of CFC-11 (CFCl3) (Fisher et al., 1990; Solomon et 

al., 1992; Wuebbles, 1983). For compounds that are removed by linear processes, this is equivalent to assuming 

an emission pulse and integrating over the entire decay of 

the compound (Prather, 1996; 2002). CFC-11 was a widely used industrial compound in the 1970s and 1980s and 

so has been chosen as a convenient reference gas (Fisher 

et al., 1990; Wuebbles, 1981; Wuebbles, 1983). Steadystate ODPs have no time dependence and are frequently 

calculated using chemical transport models. The accuracy 

of the calculation depends on the model’s ability to simulate the distribution of the considered compound and the 

associated ozone loss. However, because the ODPs are 

defined relative to the ozone loss caused by CFC-11, it 

is generally expected that for chlorocarbon compounds 

ODPs demonstrate less sensitivity to photochemical 

modeling errors than do absolute ozone loss calculations. 

Steady-state ODPs are normally derived relative to a fixed 

atmosphere; there would be differences in some ODPs if 

calculations were made for a future atmosphere with different background composition. ODPs with some time 

horizon, referred to as time-dependent ODPs (Solomon 

and Albritton, 1992), are more analogous to GWPs and 

provide information regarding the different timescales 

over which the compound and reference gas (CFC-11) 

liberate chlorine and bromine into the stratosphere. Compounds that have shorter (longer) atmospheric lifetimes 

than CFC-11 have ODPs that decrease (increase) with increasing integration time. Semi-empirical ODPs have also 

been developed (Solomon et al., 1992) so steady-state and 

time-dependent ODPs could have an observational basis. 

Some semi-empirical steady-state values have been revised in this chapter to reflect updates to fractional release 

values and to some lifetimes. In previous assessments, 

the semi-empirical approach and model calculations have 

been shown to yield similar values for most gases.

The advantages and disadvantages of the ODP metric have been discussed in previous WMO/UNEP reports 

(WMO, 1989, 1991, 1995, 1999, 2003, 2007). The projected importance of non-halocarbon emissions to future 

ozone levels presents new challenges to the ODP concept 

and raises questions about their continued comprehensiveness. Emissions occurring in the stratosphere or upper troposphere from aviation and rockets present special challenges to the ODP concept, but may be able to be treated 

in a manner similar to how very-short-lived species are 

treated (as a function of where and when emissions occur). 

ODPs are discussed in more detail in Section 5.2.2 below.

Calculation of the GWP of a compound requires 

knowledge of its radiative efficiency and global lifetime. 

The change in net radiation at the tropopause caused by 

a given change in greenhouse gas concentration or mass 

is referred to as radiative efficiency. Radiative efficiency 

has units of Watts per square meter per part per billion (W 

m−2 ppb−1) or Watts per square meter per kilogram (W m−2

kg−1); it is calculated using radiative transfer models of 

the atmosphere and depends upon the strength and spectral 

position of a compound’s absorption bands as well as atmospheric structure, surface temperature, and clouds. The 

Absolute Global Warming Potential (AGWP) for time horizon t' is defined as

 AGWPx(t') = ∫

0

Fx·x(t)dt (5-1)

where Fx is the radiative efficiency of species x, x(t) describes the decay with time of a unit pulse of compound x, 

and t' is the time horizon considered. Fx is given in terms 

t'
5.7

A Focus on Information for Policymakers

of W m−2 kg−1 or in W m−2 ppb−1. The AGWP usually has 

units of W m−2 kg−1 yr and quantifies the future integrated 

radiative forcing over the time horizon of a unit mass pulse 

emission of a greenhouse gas. To compare the relative 

integrated effect of various compounds on climate, the 

GWP metric was developed. The GWP for time horizon t'

(IPCC, 1990; 2001; 2007) can be defined as

(5-2)

where FCO2 is the radiative efficiency of CO2, R(t) is the 

response function that describes the decay of an instantaneous pulse of CO2, and the decay of the pulse of compound x has been rewritten assuming it obeys a simple exponential decay curve with a response time of τx. The pulse 

response terms lead to a dependence of GWPs on the integration time horizon; compounds that decay more quickly 

(slowly) than the reference (CO2) have GWPs that decrease 

(increase) with increasing time horizon. As shown in equations (5-1) and (5-2), the most common definition of GWPs 

applies to pulsed emissions. However, GWPs have also 

been developed to evaluate the effect of sustained emissions (Berntsen et al., 2005; Johnson and Derwent, 1996).

We note that GWP is not the only metric available to compare the climatic impacts of different gases. 

The science of alternative metrics was considered by an 

Intergovernmental Panel on Climate Change (IPCC) expert panel recently (IPCC, 2009), which noted that metric 

design depends critically on the policy goal, and that “the 

GWP was not designed with a particular policy goal in 

mind.” Furthermore, the choice of time horizon used in 

calculating GWPs is not determined purely by climate science considerations. Rather, the choice often depends on 

what information is useful to decision makers, based in 

part on the time horizon of the impacts and on the values 

they consider most important. In an effort to account for 

the impact of the choice of time horizon, typically three 

time horizons have been considered (20, 100, and 500 

years) when reporting GWPs.

The GWP index has three major advantages over 

most other indices used to measure the contribution of 

greenhouse gases to global warming: transparency, simplicity, and widespread acceptance. However, it also has 

several disadvantages (see, e.g., IPCC, 2009 and references therein). There is growing recognition of the limitations of the GWP metric especially when the impacts 

of short- and long-lived pollutants need to be considered 

together (Johansson et al., 2008; Tanaka et al., 2009; 

Fuglestvedt et al., 2010) and it has been argued that it is 

time to consider whether other metrics might be more useful (Shine, 2009). For example, there has been interest 

in including the economics of emissions mitigation into a 

climate metric by applying cost-benefit and cost-effective 

approaches (e.g., Manne and Richels, 2001). Various 

alternatives have been presented to overcome some of the 

GWP limitations, but none has been widely accepted as a 

suitable replacement to date.

ODP and GWP metrics are often used to evaluate 

the relative integrated impacts arising from emissions, 

banks, production, etc., on ozone destruction and climate 

forcing. If time series of these potential impacts are desired, EESC and radiative forcing are used. These metrics 

are discussed in Sections 5.2.2 and 5.2.3.

5.2.2 Ozone Impacts: ODPs and EESC

5.2.2.1 Fractional Release Values and

Global Lifetimes

Fractional release values for various halocarbons 

are used both in the calculation of semi-empirical ODPs 

and in deriving EESC. The fractional release value at 

some location in the stratosphere quantifies the fraction 

of the source gas that has become photochemically degraded and has released its halogen atoms since it entered 

the stratosphere. The previous Assessment (Daniel and 

Velders et al., 2007) used fractional release values from 

earlier assessments, only updating CFC-114 to the value 

suggested by Schauffler et al. (2003). For this Assessment, we adopt most of the Newman et al. (2007) updated release values; these values are based on National 

Aeronautics and Space Administration (NASA) ER-2 

field campaign observations using an approach similar to 

Schauffler et al. (2003). Douglass et al. (2008) showed 

that the lower stratospheric relationships between the 

fractional release of chlorine from CFC-11 and CFC-12 

and the age of air (as discussed in Chapter 1) produced 

by simulations with realistic age-of-air values are in good 

agreement with relationships derived from aircraft observations (Schauffler et al., 2003). Another advantage of 

using the Newman et al. (2007) results is that they provide observationally based relationships between fractional release values and age-of-air values. This allows 

for more appropriate estimates of EESC that are relevant 

to various stratospheric locations, and in particular, polar 

regions. In the derivation of semi-empirical ODPs and of 

EESC presented in this chapter (see Table 5-1), we use 

the values of Newman et al. (2007) for all compounds 

in that study except for HCFC-141b and HCFC-142b. 

These two compounds were present in small abundances and had large temporal trends when the atmospheric 

measurements upon which these fractional release values are based were made, leading to large uncertainties. 

For this reason, we have retained the fractional release 

GWPx(t') = = AGWPx(t')

AGWPCO2

(t')

∫

∫

Fx exp

FCO2

 R(t)dt

dt

t'

t'

0

0

( ) −t

τx
5.8

Chapter 5

Table 5-1. Lifetimes, fractional release values, and Ozone Depletion Potentials (ODPs) for long-lived 

halocarbons. ODPs recommended in this Assessment and ODPs adopted in the Montreal Protocol are 

included a.

Halocarbon Lifetime

(years)

Fractional Release Value Semi-Empirical ODP ODP in

Montreal

WMO Protocol

(2007) b

This

Assessment c

WMO

(2007)

This

Assessment d

Annex A-I

CFC-11 45 0.47 0.47 1.0 1.0 1.0

CFC-12 100 0.28 0.23 1.0 0.82 1.0

CFC-113 85 0.35 0.29 1.0 0.85 0.8

CFC-114 190 0.13 0.12 1.0 0.58 1.0

CFC-115 1020 0.04 0.44 e 0.57 0.6

Annex A-II

Halon-1301 65 0.29 0.28 16 15.9 10.0

Halon-1211 16 0.55 0.62 7.1 7.9 3.0

Halon-2402 20 0.57 0.65 11.5 13.0 6.0

Annex B-II

CCl4 26 0.50 0.56 0.73 0.82 1.1

Annex B-III

CH3CCl3 5.0 0.51 0.67 0.12 0.16 0.1

Annex C-I

HCFC-22 11.9 0.16 0.13 0.05 0.04 0.055

HCFC-123 1.3 0.02 0.01 f 0.02

HCFC-124 5.9 0.02 0.022

HCFC-141b 9.2 0.34 0.34 g 0.12 0.12 0.11

HCFC-142b 17.2 0.17 0.17 g 0.07 0.06 0.065

HCFC-225ca 1.9 0.02 0.025

HCFC-225cb 5.9 0.03 0.033

Annex E

CH3Br 0.8 0.53 0.60 0.51 0.66 0.6

Others

Halon-1202 2.9 0.62 1.7

CH3Cl 1.0 0.38 0.44 0.02 0.02

a Ravishankara et al. (2009) have calculated an ODP for N2O of 0.017. b In the previous Assessment, fractional release values relative to CFC-11 were used, with CFC-11 assumed to be 0.84. For this table, WMO (2007) 

values are scaled to a CFC-11 value of 0.47 to allow easy comparison with the current values. c From Newman et al. (2007), values for 3-year-old age of air. d Semi-empirical ODP values are not updated in this Assessment for halocarbons whose fractional release values were not estimated in Newman et 

al. (2007). e Model-derived value, WMO (2003). f From Wuebbles and Patten (2009) MOZART 3-D model calculation. g Values relative to CFC-11 are retained from WMO (2007) because of large uncertainties associated with the Newman et al. (2007) estimates for 

these compounds.
5.9

A Focus on Information for Policymakers

values relative to CFC-11 assumed in WMO (2007) for 

these two HCFCs, and we scale them to the appropriate 

CFC-11 fractional release value depending on the age of 

air considered. Additional information regarding the use 

of fractional release values can be found in Chapter 1. In 

calculating the 2010 ODP-weighted anthropogenic emissions for the A1 baseline scenario (Section 5.3.1), the 

most significant fractional release changes are for, in order of decreasing importance, CFC-12, HCFC-22, carbon 

tetrachloride (CCl4), and halon-1211. A description of 

the sensitivity of EESC to fractional release and to other 

parameters can be found in Newman et al. (2007). We 

also use absolute fractional release values in this chapter, 

rather than normalizing all of the values as was done in 

previous assessments. We do this so the portion of EESC 

estimates attributable to chlorine and bromine source gases are representative of the actual amount of total inorganic chlorine (Cly) and total inorganic bromine (Bry), respectively, in the regions of the stratosphere considered.

Global lifetimes are also used in the calculation of 

ODPs and EESC. As discussed in Chapter 1, lifetimes 

of CFC-114 and CFC-115 have been substantially revised since the previous Assessment. There have also 

been smaller revisions to several of the HCFCs that are 

included in Table 5-1. Douglass et al. (2008) also find, 

based on results from two-dimensional (2-D) and threedimensional (3-D) models, that the range of atmospheric 

lifetime estimates for CFC-11 from models that best reproduce the observed relationship between age of air and 

fractional release is 56–64 years. The lifetime calculated 

for CFC-12 in this study was consistent with the value 

from the previous Assessment (100 years). Wuebbles et 

al. (2009) find consistent lifetimes for CFC-11, 54 years in 

the Model of Ozone and Related Tracers (MOZART) 3-D 

model (version 3.1) and 57 years in the current version of 

the University of Illinois Urbana-Champaign (UIUC) 2-D 

model, which includes an improved calculation of stratospheric age of air (Youn et al., 2010). In the previous three 

assessments (WMO, 1999, 2003, 2007), ODP derivations 

assumed an atmospheric lifetime for CFC-11 of 45 years 

based on analyses of observations (Cunnold et al., 1997; 

Volk et al., 1997) and older model results (Prinn and Zander, 1999). Because of the dearth of studies estimating 

ODS lifetimes with models that accurately calculate age 

of air, and because the Douglass et al. (2008) study only 

evaluated the lifetimes of CFC-11 and CFC-12, we continue to use a lifetime of 45 years for CFC-11; however, 

it should be recognized that in the future this lifetime may 

be assessed to be too small. The lack of comprehensive 

studies examining halocarbon lifetimes with models that 

accurately calculate age of air can be considered a gap in 

our current understanding. A full discussion of lifetime 

revisions can be found in Chapter 1.

5.2.2.2 Ozone Depletion Potentials

An updated list of ODPs is provided in Table 5-1 for 

a number of long-lived halocarbons. The primary change 

from the previous Assessment (Daniel and Velders et al., 

2007) is to update the semi-empirical ODPs by incorporating revised fractional release values and global lifetimes 

for some compounds. For ODP estimates in this chapter, 

fractional release values representative of air that has been 

in the stratosphere for 3 years are used. In the absence 

of new evidence, we continue to use a value of 60 for the 

relative effectiveness of bromine compared to chlorine for 

destroying ozone (α) at midlatitudes. For Antarctic calculations we continue to use a value of 65 (WMO, 2007). 

The semi-empirical ODP of CCl4 is 10% higher than in the 

previous Assessment owing to a larger fractional release 

value (see Table 5-1 and Section 5.2.2.1). Although there 

are still significant gaps in our understanding of the CCl4

budget, the recommended lifetime remains 26 years (see 

Chapter 1).

The ODP for HCFC-123 has been updated based 

on results from a three-dimensional model (Wuebbles and 

Patten, 2009). The calculated value of 0.0098 is similar 

to but smaller than the previous model-derived value of 

0.014 based on 2-D model results (WMO, 2003). The 

ODPs for several short-lived compounds have also been 

discussed in Chapter 1.

Looking beyond the analyses of ODPs for halocarbons, Ravishankara et al. (2009) have calculated an ODP 

for nitrous oxide (N2O) of 0.017 using a 2-D model. Although N2O has a relatively small ODP, future changes in 

emissions and atmospheric concentrations of N2O could 

have a significant effect on ozone compared with emissions of controlled ODSs because of the larger magnitude 

of N2O’s anthropogenic emissions. The impact of N2O 

emissions will be quantified in Section 5.4. The magnitude of past and future N2O ODP-weighted emissions 

leads to concerns that include influences on the timing of 

the recovery of ozone, the “background” ozone level, the 

distribution of stratospheric ozone depletion, and the possibility of future decreases in ozone due to increasing N2O 

(Ravishankara et al., 2009; Wuebbles, 2009).

5.2.2.3 Equivalent Effective Stratospheric

Chlorine

EESC has historically been used to relate measured 

surface mixing ratios of chlorine- and bromine-containing 

source gases to the stratospheric inorganic chlorine and 

bromine arising from these gases in key regions of the 

stratosphere and thus to the amount of ozone they will 

destroy (Daniel et al., 1995; WMO, 1995, 1999, 2003, 

2007). It accounts for the fact that bromine is more 
5.10

Chapter 5

efficient than chlorine (on a per-atom basis) at destroying stratospheric ozone and that different source gases 

release their chlorine and bromine at different rates and 

locations. Both integrated EESC changes and the date 

when EESC returns to 1980 levels have been used in previous assessments to quantify the relative impacts of various hypothetical ODS emission cases. This approach has 

worked well because all the major anthropogenic sources 

of stratospheric chlorine and bromine are thought to be 

known, and they all have reasonably well-understood 

global lifetimes and stratospheric dissociation rates. 

Recently, EESC was reformulated so that it accounts for 

the age-of-air spectrum and the age-of-air dependent fractional release values (Newman et al., 2007). This reformulation allows EESC to represent the total Cly and Bry

in various regions of the stratosphere.

The concept of EESC does have limitations because of uncertainties in the transport time, uncertainties 

in the spatial and temporal dependencies of the bromine 

efficiency for ozone destruction versus chlorine (α) (generally considered a constant), the efficiency of stratospheric halogen release from the source gas, and possible temporal changes in transport times and source gas lifetimes 

(some effects described in Newman et al., 2006, 2007). It 

should be noted that the EESC concept also does not explicitly account for changing atmospheric emissions and 

concentration of other relevant constituents that can also 

affect ozone, such as CO2 and methane (CH4). Daniel et 

al. (2010) have recently provided a method to incorporate 

N2O abundances into EESC. We will not adopt this method for the calculation of EESC in this Assessment because 

its publication was so recent, but we do show the impact 

of a hypothetical N2O emission phase-out on globally averaged total column ozone that can be compared with the 

impact of other ODS phase-outs on ozone. By comparing 

2-D model results with EESC, Daniel et al. (2010) showed 

that integrated EESC, despite its limitations, is proportional to the calculated integrated total ozone depletion 

reductions arising from various hypothetical ODS policy 

actions to within 30%.

The year 1980 is often taken as roughly representative of the time before the major stratospheric ozone 

losses occurred due to halocarbons. As a result, analyses 

are often based on the return of EESC to 1980 levels. If 

stratospheric ozone levels were affected by only halocarbons, the ozone layer would be expected to recover from 

human activities as anthropogenic ODSs are removed 

from the atmosphere. However, the actual picture of future levels of stratospheric ozone and the recovery from 

the past emissions of halocarbons is more complicated, 

making the use of a single date as a metric for total ozone 

recovery less meaningful. There are a number of activities and processes that are likely to substantially affect the 

future distribution and integrated amounts of ozone (see 

Section 5.4 and Chapter 3). Some of these potential activities and processes include rocket launches, aviation, 

climate-related geoengineering actions, and emissions of 

CO2, CH4, and N2O. So while the evolution of EESC in 

this chapter provides important information regarding the 

impact of certain human activities on stratospheric ozone, 

ozone is expected to recover at a different rate than this 

simple metric might imply.

The relative importance of the various future chlorine- and bromine-containing emissions, production, 

and banks are compared as in previous assessments using EESC in Section 5.4. New in this Assessment is that 

the impacts of some of these ODS cases are compared in 

terms of ozone depletion using the results of the Daniel 

et al. (2010) study (see Section 5.4.2). The intent of this 

approach is to provide information that can be used for 

determining which options are available and what their 

potential effects are on the future ozone layer. It will 

also allow us to compare the expected impacts of several 

potential ODS policy options with ozone changes from 

a broader range of activities, including expected future 

changes in greenhouse gases such as CO2, N2O, and CH4.

5.2.3 Climate Impacts: GWPs and 

Radiative Forcing

Direct GWPs are tabulated in this chapter’s Appendix 5A. The list of compounds evaluated in Appendix 

Table 5A-1 is intended to include potential replacements 

for the Montreal Protocol ODSs, but this list is not exhaustive. CO2 and N2O are also included in the table. 

Most source gases with atmospheric lifetimes of less than 

6 months are not believed to contribute significantly to 

radiative forcing and are not included in Appendix Table 

5A-1 (note that, in contrast to short-lived source gases, 

short-lived aerosols and tropospheric ozone are thought 

to contribute significantly to radiative forcing (IPCC, 

2007)). Indirect GWPs are discussed later in this section and are also tabulated in Appendix 5A (Appendix 

Table 5A-4). The uncertainty associated with the direct 

GWPs listed in Appendix Table 5A-1 is estimated to be 

±35% with 90% confidence (IPCC, 2007) reflecting uncertainties in the radiative efficiencies, lifetimes of the 

halocarbons, and uncertainties in our understanding of the 

carbon cycle (IPCC, 2001). It should be noted that because uncertainties in the carbon cycle make an important 

contribution to the total GWP uncertainty (IPCC, 2007), 

the relative climatic effects of different halocarbons (e.g., 

expressed as ratios of their GWPs) are likely accurate to 

much better than 35%.

We limit further discussion of GWPs to updates 

since the last Ozone Assessment. There are two reasons that updates have been made: (1) updates to the 
5.11

A Focus on Information for Policymakers

atmospheric lifetimes and (2) new radiative efficiency 

recommendations. Although the atmospheric concentration of CO2 continues to increase, its AGWPs were chosen to be the same as the IPCC (2007) Assessment so as 

to reduce confusion when comparing to values from that 

Assessment. The revisions to the lifetimes and radiative 

efficiencies discussed below affect GWP calculations and 

radiative forcing projections.

5.2.3.1 Lifetime Updates

The lifetimes of several HCFCs and of most 

HFCs, including hydrofluoroethers (HFEs), have been 

updated from the previous Assessment. The lifetime for 

CH3CH2OCF2CHF2 (HFE-374pc2) of 5 years given in 

the previous Assessment was erroneous; the lifetime for 

this compound is actually rather short (approximately 2 

months, see Chapter 1). Accordingly, this compound is 

now classified as a short-lived species. The lifetimes of 

CFC-114, CFC-115, and nitrogen trifluoride (NF3) were 

also updated in response to work by Prather and Hsu 

(2008). A discussion of these lifetime updates and others, 

and the distinction between short- and long-lived species, 

can be found in Chapter 1.

5.2.3.2 Radiative Efficiency Updates

The radiative efficiency values used in the previous Assessment, the currently recommended values, and 

the values presented in the relevant references for the 

new and revised compounds are presented in Table 5-2. 

Since the last Assessment (WMO, 2007), additional radiative efficiency data have become available for HFE43-10pccc124, HFC-365mfc, HFC-263fb, HFC-245eb, 

HFC-245ea, and HFC-329p (all calculated assuming 

constant vertical profiles). Rajakumar et al. (2006) have 

provided the first measurements of the lifetimes and the 

radiative efficiencies for HFC-263fb, HFC-245eb, and 

HFC-245ea. These radiative efficiencies (Table 5-2) 

have been adopted in the calculation of the GWPs in the 

appendix (Appendix Table 5A-1). Inoue et al. (2008) report a radiative efficiency of 0.23 W m−2 ppb−1 for HFC365mfc. This value is 10% larger than the value of 0.209 

W m−2 ppb−1 reported by Barry et al. (1997) that was used 

in the previous Assessment (WMO, 2007). Inoue et al. 

(2008) concluded that the approximately 10% difference 

in the intensity of the infrared (IR) absorption spectrum 

was the origin of the different radiative efficiencies in 

the two studies. There being no obvious reason to prefer 

either study, an average of the results from Barry et al. 

(1997) and Inoue et al. (2008) was adopted in the current 

Assessment.

Sulfuryl fluoride (SO2F2) is being used increasingly as a replacement for methyl bromide (see Chapter 1, Section 1.5.2.2). It has an atmospheric lifetime of 

about 36 years and a substantial GWP. Papadimitriou et 

al. (2008a) and Sulbaek Andersen et al. (2009) measured 

the IR spectrum of SO2F2 and reported radiative efficiencies of 0.222 and 0.196 W m−2 ppb−1, respectively, for 

this molecule. The integrated absorption cross sections 

reported by Papadimitriou et al. (2008a) and Sulbaek 

Andersen et al. (2009) over the range 800–1540 cm−1 are 

in excellent agreement (within approximately 1%) and 

both differ by only about 5% from that reported by Dillon 

et al. (2008). The approximately 10% difference in radiative efficiencies reported by Papadimitriou et al. (2008a) 

and Sulbaek Andersen et al. (2009) is probably due to the 

fact that Sulbaek Andersen et al. (2009) did not consider 

Table 5-2. Radiative efficiency estimates (W m−2 ppb−1) for seven compounds whose recommended 

values have either changed since, or were not included in, the previous Assessment.

Chemical Formula

Common or

Industrial

Name

WMO

(2007)

Recent

Published

Estimates

This

Assessment

CHF2OCF2OC2F4OCHF2 HFE-43-10pccc124 a 1.37 1.02 (Wallington et al., 2009) 1.02

CH3CF2CH2CF3 HFC-365mfc 0.21 0.23 (Inoue et al., 2008) 0.22

CHF2CF2CF2CF3 HFC-329p 0.45 0.31 (Young et al., 2009) 0.31

CH3CH2CF3 HFC-263fb 0.13 (Rajakumar et al., 2006) 0.13

CH2FCHFCF3 HFC-245eb 0.23 (Rajakumar et al., 2006) 0.23

CHF2CHFCHF2 HFC-245ea 0.18 (Rajakumar et al., 2006) 0.18

SO2F2 sulfuryl fluoride 0.222 (Papadimitriou et al., 2008a) 0.22

0.196 (Sulbaek Andersen et al., 2009)

a Also referred to as H-Galden 1040x.
5.12

Chapter 5

stratospheric adjustment (allowing the stratospheric temperatures to equilibrate to the greenhouse gas perturbation) in their radiative efficiency calculations. Sulbaek 

Andersen et al. (2009) used the estimation method described by Pinnock et al. (1995), which agrees to within 

±0.3% with the global annual and annual cloudy-sky instantaneous radiative forcing calculations using the Reading narrowband model (Shine, 1991). Papadimitriou et 

al. (2008a) applied a line-by-line radiative transfer code, 

developed at the National Oceanic and Atmospheric 

Administration (NOAA), to a global-average cloudy-sky 

profile taking into account stratospheric adjustment. The 

effect of including stratospheric adjustment for a given gas 

depends on the position and intensity of its IR absorption 

features. Forster et al. (2005) have shown that inclusion 

of stratospheric adjustment increases the instantaneous 

radiative forcing of HFC-134a by approximately 10%. 

Pinnock et al. (1995) studied 19 halogenated alkanes and 

found that inclusion of stratospheric adjustment typically 

increased the instantaneous radiative efficiency by 5–10% 

(although in the case of HFC-41 there was actually a 7% 

decrease, see Table 4 in Pinnock et al. (1995)). Radiative 

forcing as defined by IPCC is based on the globally and 

annually averaged net downward irradiance change at the 

tropopause after allowing for stratospheric temperatures 

to adjust to radiative equilibrium. Hence, we adopt a value of 0.22 W m−2 ppb−1 from Papadimitriou et al. (2008a), 

which is consistent with the value reported by Sulbaek 

Andersen et al. (2009).

Wallington et al. (2009) revisited the IR spectrum 

of HFE-43-10pccc124, previously also referred to as HGalden 1040x, and argued that the IR spectrum reported 

by Cavalli et al. (1998) used in previous WMO and IPCC 

reports is approximately 30% too strong. It was noted 

that use of the reference spectrum of Cavalli et al. (1998) 

would lead to carbon balances substantially greater than 

100% in laboratory experiments of HFE-43-10pccc124 

oxidation. The IR spectrum reported by Wallington et al. 

(2009) is in good agreement with that measured using the 

same experimental set-up 12 years earlier by Christidis et 

al. (1997). As discussed by Young et al. (2008), the radiative efficiency of HFE-43-10pccc124 in WMO (2007) is 

inconsistent with the expected trends based upon the database for other HFEs. The radiative efficiency reported by 

Wallington et al. (2009) is adopted here.

Young et al. (2009) reported the first measurements 

of the lifetime and radiative efficiency for CHF2CF2CF2CF3

(HFC-329p); these are used here.

As in all previous assessments, the atmospheric 

lifetime and radiative efficiency values used in the present Assessment can be traced to experimentally measured rate coefficients and IR spectra. Ab-initio quantum mechanical computational methods are available to 

calculate rate coefficients and IR spectra. Results from 

ab-initio calculations have provided valuable fundamental insight into reaction mechanisms and the underling 

processes giving rise to the IR spectra. However, such 

computational results have generally not been used directly to calculate GWPs. With advances in computational techniques, recent studies (e.g., Blowers and 

Hollingshead, 2009) suggest that atmospheric lifetimes 

and radiative efficiencies can now be calculated from 

first principles with accuracies comparable to those from 

experimental studies. This suggestion has yet to be fully 

investigated by the scientific community, and in the present Assessment we do not consider atmospheric lifetimes 

and radiative efficiencies that have been evaluated only 

by ab-initio methods.

5.2.3.3 Updates to Indirect GWPs from

Ozone Destruction

In addition to being greenhouse gases themselves, 

the ODSs play a significant role in the destruction of 

stratospheric ozone, another radiatively important gas. 

The distribution of ozone has important implications for 

Earth’s climate system, not only because ozone absorbs 

solar radiation but also because it is a greenhouse gas 

that absorbs some of the infrared radiation emitted from 

Earth’s surface and atmosphere. The change in ozone 

radiative forcing due to the addition of some ODS can 

be attributed to that ODS as an indirect radiative forcing. Stratospheric ozone losses are generally thought to 

cause a negative radiative forcing, canceling part of the 

increased radiative forcing arising from the direct influence of the halocarbons. The magnitude of the indirect 

effect is strongly dependent on the altitude profile of the 

halogen-induced ozone loss and will vary depending on 

the source gas considered. The latest estimate of radiative forcing from changes in stratospheric ozone since 

preindustrial times is −0.05 ± 0.10 W/m2

 (IPCC, 2007). 

However, there have not been recent studies that clearly 

estimate the amount of the ozone forcing attributable to 

halocarbon changes only.

In spite of the uncertainty associated with the radiative forcing from ozone loss caused by halocarbons, the 

indirect GWPs for various halocarbons have been included 

in previous Ozone Assessments using an approach similar 

to that described in Daniel et al. (1995) (e.g., see WMO, 

2003, 2007). This approach is also used here to update 

indirect GWPs for selected halocarbons (Appendix Table 

5A-4) and is based on the assumption of an approximate 

linear relationship between the change in EESC arising 

from a particular source gas and radiative forcing arising 

from stratospheric ozone loss. A complication that is ignored by this approach is that some of the observed ozone 

depletion, and its associated radiative forcing, is due to 

processes not related to ODSs. The previously published 
5.13

A Focus on Information for Policymakers

indirect GWPs have primarily changed over time as a response to updates in the EESC scenarios, changes in the 

estimated efficiency of bromine relative to chlorine for destroying ozone, and changes in the estimates of the overall 

stratospheric ozone radiative forcing owing to halocarbon 

changes. These factors continue to represent important 

uncertainties in estimating the indirect GWPs using the 

EESC approach. This approach also cannot capture the 

source gas-dependent variations in the ozone loss profile 

and its resulting impact on radiative forcing. In past estimates of these indirect GWPs, the 1980 level of EESC 

has been assumed to represent a value below which no additional ozone loss occurs. This implied that the presence 

of an ODS after EESC fell below this level would lead to 

no additional ozone loss or negative radiative forcing due 

to that loss. No such threshold is adopted here, leading 

to slightly more negative indirect GWPs for the longerlived ODSs in the absence of other changes. However, 

the change in stratospheric ozone from 1979 to 1998 is 

now estimated to be responsible for −0.05 W/m2

 forcing 

(IPCC, 2007). The adoption of this lower revised IPCC 

radiative forcing due to stratospheric ozone, compared 

with −0.15 ± 0.10 W/m2 in WMO (2007), dominates the 

changes compared to the previous Assessment and makes 

the indirect effects less negative. The current calculations 

also incorporate the updated fractional release values for 

midlatitudes and polar regions (Newman et al., 2007). 

We continue to assume that radiative forcing due to polar 

ozone loss is responsible for 40% of the −0.05 W/m2 and 

that the polar depletion saturates at 1990 EESC levels 

(Daniel et al., 1995).

As a step toward obtaining indirect GWPs through 

a more fundamental approach, Youn et al. (2009) have 

explicitly evaluated the indirect radiative forcing for two 

of the halons, halon-1211 and halon-1301, using 2-D 

and 3-D atmospheric models. In Table 5-3, these values 

are compared with the direct and indirect GWPs found 

in WMO, 2007 (Daniel and Velders et al., 2007) and 

those updated for this Assessment using the approach 

discussed in the previous paragraph. The indirect GWP 

for halon-1211 derived by Youn et al. (2009) is much 

smaller (about 60%) than the WMO (2007) value, but 

does fall within a single standard deviation of it. The 

Youn et al. (2009) indirect GWP is larger in magnitude 

by about a factor of ten compared to its direct effect. 

The indirect effect of halon-1301 is about 25% smaller 

than previously reported but also agrees with the WMO 

(2007) value to within a single standard deviation. The 

updated indirect GWPs reported here for halon-1211 calculated using the EESC scaling approach is in much better agreement with the Youn et al. (2009) values than the 

WMO (2007) central estimate was. While the Youn et 

al. (2009) work represents a single study, these analyses 

suggest that more comprehensive atmospheric models 

have the potential to reduce our uncertainties in the halocarbon indirect GWPs.

Table 5-3. Direct and indirect Global Warming Potentials (mass basis) of halons. Youn et al. (2009) lifetimes are e-folding times based on an exponential curve fitted to the simulated atmospheric decay.

Lifetimes (years)

Global Warming Potentials

for 100-years Time Horizon

Direct GWP Indirect GWP Net GWPa

Halon1211Halon1301Halon1211Halon1301Halon1211Halon1301Halon1211Halon1301

This

Assessment

16 65 1890

± 660

7140

± 2500

−11,720

± 23,430

−27,060

± 54,130

WMO (2007) 16 65 1890

± 660

7140

± 2500

−40,280

± 27,120

−49,090

± 34,280

Youn et al. (2009)

2-D Model

14.4 72.4 1796 7122 −16,294 −36,247 −14,498 −29,127

Youn et al. (2009)

3-D Model

10.9 70.1 1699 6903 −17,050 −37,252 −15,351 −30,349

a Concerns remain about the quantitative accuracy of adding the indirect forcing due to ozone changes to the direct forcing for the well-mixed halons. 

This addition was not performed in WMO (2007) or in this chapter, except for the results taken from Youn et al. (2009).
5.14

Chapter 5

5.3 FUTURE BASELINE SCENARIOS

5.3.1 Chlorine- and Bromine-Containing 

Ozone-Depleting Substances

A new baseline scenario for the period 1950–2100 is 

developed for all ODSs along the same lines as in the previous Assessment (WMO, 2007), with future projections 

consistent with current controls imposed by the Montreal 

Protocol. Observed global average mixing ratios through 

the beginning of 2009 are used as a starting point for the 

projections, together with the production of ODSs through 

2008 reported by the countries to the United Nations Environment Programme (UNEP, 2009), estimates of the bank 

sizes of ODSs for 2008 from the Technology and Economic Assessment Panel (TEAP, 2009), approved essential use exemptions for CFCs, critical-use exemptions for 

methyl bromide for 2008–2010, and production estimates 

of methyl bromide for quarantine and pre-shipment (QPS) 

use. Details of the baseline scenario are given in Appendix Table 5A-2. Calculated mixing ratios are tabulated in 

Appendix Table 5A-3 for each of the considered halocarbons from 1955 through 2100 (See also Figure 5-1). The 

years when observations are used are indicated in the table 

by the shaded regions. For those years, scenario mixing 

ratios are equal to the observations.

The mixing ratios in the new baseline scenario 

are similar to those in the previous Assessment (WMO, 

2007) for most species. The larger future mixing ratios (2010–2050) for CFC-11 (+5 to 9 parts per trillion 

(ppt)) and CFC-12 (up to +9 ppt) are the result of slightly 

larger fractions of the bank emitted annually, based on 

1999–2008 averages. The new baseline scenario has significantly larger future mixing ratios for CCl4 (up to +12 

ppt) than in WMO (2007) because of a different assumption regarding the decrease in future emissions (see Section 5.4.2.1). Emissions of each of the three considered 

HCFCs begin to decline at some time in the next decade 

in the baseline scenario due to existing Montreal Protocol 

controls. The projected future mixing ratios of HCFC-22 

after about 2025 are lower than projected in the previous 

Assessment as a direct result of the accelerated HCFC 

phase-out (Montreal Protocol Adjustment of 2007, see 

Section 5.4.5). The initially larger mixing ratios in the 

period 2010–2020 are the result of an increase in reported 

production and a larger fraction of the bank emitted annually. The mixing ratios of HCFC-141b and HCFC-142b 

are larger than in the previous Assessment, by up to 8 ppt 

and 20 ppt, respectively, because of an increase in reported production and a different assumption regarding the 

future distribution of the total HCFC consumption over 

the three main HCFCs (see Appendix Table 5A-2). The 

mixing ratios of halon-1301 in the new baseline scenario 

are somewhat different from those in the previous Assessment’s baseline scenario. The older ones were based on a 

bank release calculation after 1995 because of large differences in observational records that existed at that time for 

the 1995–2005 period. Revised calibrations and measurements with new instruments using mass spectrometry (at 

NOAA) have led to an improved consistency between the 

labs (NOAA and Advanced Global Atmospheric Gases 

Experiment (AGAGE)) for the global mean mixing ratios 

and the rates of change in recent years (see Figure 1-1 of 

Chapter 1). Therefore, the mixing ratios here are taken as 

an average of the observations from those two networks 

in recent years and are derived using a consistent scaling to the NOAA data in years before AGAGE measured 

halon-1301 (before 2004).

The EESC corresponding to the baseline scenario is 

shown in Figure 5-2. The absolute values of EESC (righthand axis) are substantially lower than presented in the 

previous Assessment because different fractional release 

values have been adopted and they are no longer scaled so 

the fractional release value of CFC-11 is 0.84. As stated 

in Section 5.2.2.1, this approach is taken because it allows 

the values now to provide meaningful estimates of Cly and 

Bry abundances for 3-year-old air, a benefit that would be 

lost if the former scaling method were applied. Furthermore, since EESC is used in this chapter only as a relative 

measure, the absolute values are not important. If current 

EESC values are scaled so the peak value is the same as 

in the previous Assessment, the figure shows that the time 

series are quite similar. Differences appear because of the 

revised relative fractional release values and because of 

slightly revised emissions. In previous assessments, the 

year 1980 was taken as a benchmark year, representing a 

time before the major stratospheric ozone losses occurred 

due to halocarbons. Some ozone losses caused by human 

activities likely had already occurred due to, for example, 

halocarbon and N2O emissions (see Chapter 3). Nevertheless, the year EESC returns to 1980 levels has been used 

as a measure for some degree of ozone layer recovery and 

to compare scenarios. Although we continue to recognize 

the limitations of this metric (see Section 5.2.2) it is used 

here to compare the new baseline scenario with the one 

in the previous Assessment and to compare the effects of 

hypothetical ODS emission reductions of chlorine- and 

bromine-containing ODSs (Table 5-4). In the new baseline scenario, including only Montreal Protocol-controlled 

ODSs, EESC returns to its 1980 levels in 2046 for midlatitude conditions. This is 2–3 years earlier than in the 

previous Assessment (WMO, 2007) and is the result of 

two partially offsetting changes. First, future emissions of 

ODSs give a delay of 2–3 years, mainly as the net result of 

larger future emissions of CCl4, smaller future emissions 

of HCFCs owing to the accelerated HCFC phase-out (2007 

Adjustment of the Montreal Protocol, see Section 5.4.5), 
5.15

A Focus on Information for Policymakers

CFC-11

1980 2000 2020 2040

Year

140

160

180

200

220

240

260

280

ppt

CFC-12

1980 2000 2020 2040

Year

300

350

400

450

500

550

ppt

CFC-113

1980 2000 2020 2040

Year

20

40

60

80

100

ppt

CFC-114

1980 2000 2020 2040

Year

10

12

14

16

18

ppt

CCl4

1980 2000 2020 2040

Year

20

40

60

80

100

120

ppt

CH3CCl3

1980 2000 2020 2040

Year

0

50

100

150

ppt

HCFC-22

1980 2000 2020 2040

Year

0

50

100

150

200

250

300

350

ppt

HCFC-141b

1980 2000 2020 2040

Year

0

10

20

30

40

ppt

HCFC-142b

1980 2000 2020 2040

Year

0

10

20

30

40

ppt

halon-1211

1980 2000 2020 2040

Year

0

1

2

3

4

5

ppt

halon-1301

1980 2000 2020 2040

Year

0

1

2

3

4

ppt

CH3Br

1980 2000 2020 2040

Year

6.5

7.0

7.5

8.0

8.5

9.0

9.5

ppt

Figure 5-1. Historical and projected mixing ratios (in parts per trillion, ppt) of selected ODSs for the new baseline (A1) scenario (black) compared with the baseline scenarios of the previous Assessment (WMO, 2007) 

(solid red) and for WMO (2003) (dashed red). Shaded regions indicate years when mixing ratios are taken 

directly from observations (see Chapter 1).
5.16

Chapter 5

and a smaller 1980 mixing ratio of CH3Br (see Chapter 1, 

Section 1.2.1.6). Second, the use of revised fractional release values based on recent measurements brings forward 

the return to 1980 levels by 5–6 years. For Antarctic conditions EESC returns to its 1980 levels in the baseline in 

2073. This is 7–8 years later than in the previous Assessment (WMO, 2007), mainly due to the use of fractional 

release values representative for Antarctic conditions (age 

of air = 5.5 years) and of a smaller 1980 mixing ratio of 

CH3Br (Chapter 1, Section 1.2.1.6), with smaller contributions from the revisions in CCl4 and HCFCs emissions.

5.3.2 CO2, CH4, and N2O

The importance of non-ODS greenhouse gases to 

future ozone levels has been quantified in several published articles and is discussed in Chapter 3. In this chapter, IPCC Special Report on Emissions Scenarios (SRES) 

(IPCC, 2000) scenario A1B is used to prescribe the future 

evolution of these three gases in the two 2-D model runs 

described in Daniel et al. (2010). The results of that study 

are used here to evaluate the impact of hypothetical future 

controls involving N2O and the ODSs on globally averaged total column ozone against a backdrop of CO2 and 

CH4 changes and their associated impacts on ozone.

5.3.3 ODP- and GWP-Weighted Emissions, 

EESC, and Radiative Forcing

The contributions of ODSs to metrics relevant 

to ozone depletion and to climate change are shown in 

Figures 5-3 and 5-6. The panels of Figure 5-3 show the 

ODP-weighted emissions, GWP-weighted (100-year) 

emissions, EESC, and radiative forcing (RF) for the A1 

baseline scenario from 1980–2100. In terms of EESC 

Figure 5-2. Midlatitude EESC projections (in parts per trillion, ppt) calculated for the current baseline (A1) 

scenario (solid black) and three test 

cases: zero future production (dotted), full recovery and destruction of 

the 2010 bank (dashed), and zero 

future emission (dot-dashed) (all 

right-hand axis). EESC values for 

the baseline scenario of the previous 

Assessment are also shown (red, lefthand axis). For ease of comparison, 

the two ordinate axes are relatively 

scaled so the EESC peak of the current baseline scenario falls on top of 

the previous baseline scenario peak. 

Absolute EESC values are different in 

the two Assessments because in the 

previous Assessment, different relative halogen fractional release values 

were used, and the values were scaled so the CFC-11 absolute fractional release value was 0.84. No scaling 

was performed here so that EESC is more directly representative of Cly and Bry.

Table 5-4 (at right). Comparison of scenarios and cases a: the year when EESC drops below the 1980 

value for both midlatitude and Antarctic vortex cases, and integrated EESC differences (midlatitude 

case) relative to the baseline (A1) scenario b. Also shown are changes in integrated ODP- and GWPweighted emissions and, for selected cases, changes in integrated ozone depletion from 2011−2050. Future 

projected changes in CH4 and CO2 are also expected to significantly alter ozone levels, perhaps by amounts 

larger than any of the cases considered in this table. However, their effects are not included here because 

changes in CH4 and CO2 that would decrease globally averaged ozone depletion would increase climate forcing. Values cited in chapter text calculated as differences between table entries may appear slightly inconsistent with table entries because of rounding.

Midlatitude EESC

1980 2000 2020 2040 2060 2080 2100

Year

0

1000

2000

3000

4000

EESC in Previous Assessment (ppt)

0

500

1000

1500

2000

EESC in Current Assessment (ppt)

Baseline, this Assessment

No Production

Bank Recovery

No Emission

Baseline, previous Assessment
5.17

A Focus on Information for Policymakers

Scenario and Cases a

Percent Difference in

Integrated EESC

Relative to Baseline

Scenario for the

Midlatitude Case

Year (x) When EESC is

Expected to Drop Below

1980 Value b

Change in

ODPWeighted d

Emission:

2011−2050

Change

in GWPWeighted e

Emission:

2011−2050

Percent

Difference in

Integrated O3

Depletion f:

2011−2050

Midlatitude c Antarctic

Vortex c

x

∫ EESC dt

x

∫ EESC dt (Million tons 

CFC-11-eq)

(Billion tons

CO2-eq)

Scenarios

A1: Baseline scenario - - 2046.5 2072.7 - - -

Cases of zero production from 2011 onward of:

P0: All ODSs −5.4 −15.0 2043.0 2069.7 −0.70 −13.2

CFCs 0.0 0.0 2043.0 2069.7 0 0

Halons 0.0 0.0 2043.0 2069.7 0 0

HCFCs −3.2 −8.8 2044.5 2071.8 −0.45 −13.2 −0.15

CH3Br for QPS −2.4 −6.7 2044.9 2070.8 −0.26 −0.002

Cases of zero emissions from 2011 onward of:

E0: All ODSs (does not 

include N2O)

−16.0 −43.0 2033.5 2059.4 −3.82 −27.2 −0.67

CFCs −3.9 −11.0 2043.3 2068.5 −1.27 −7.9

Halons −5.0 −14.0 2043.3 2069.4 −1.09 −0.4

HCFCs −4.9 −13.0 2043.8 2071.4 −0.66 −18.1

CCl4

g −2.8 −7.6 2044.6 2071.6 −0.54 −0.9

CH3CCl3 0.0 −0.1 2046.5 2072.7 −0.004 −0.004

CH3Br for QPS −2.4 −6.7 2044.9 2070.8 −0.26 −0.002 −0.09

Anthropogenic N2O h −6.0 −103 −0.35

Cases of full recovery of the 2011 banks of:

B0: All ODSs −10.0 −27.0 2039.3 2064.6 −2.57 −13.1

CFCs −3.9 −11.0 2043.3 2068.5 −1.27 −7.9 −0.13

Halons −5.0 −14.0 2043.3 2069.4 −1.09 −0.4 −0.15

HCFCs −1.8 −4.8 2045.8 2072.4 −0.22 −4.9 −0.07

Cases of full recovery of the 2015 banks of:

B0: All ODSs −7.1 20.0 2040.3 2065.7 −2.03 −11.3

CFCs −2.6 −7.0 2044.0 2069.4 −0.95 −5.5

Halons −3.3 −9.1 2043.8 2069.8 −0.83 −0.3

HCFCs −1.9 −5.3 2045.5 2072.2 −0.26 −5.5

CH3Br sensitivity:

Same as A1, but 

critical-use exemptions 

continue at 2011 levels

+0.3 +0.8 2046.6 2073.0 +0.03 +0.0003

a Significance of ozone-depleting substances for future EESC were calculated in the hypothetical “cases” by setting production or emission to zero in 

2011 and subsequent years or the bank of the ODSs to zero in the year 2011 or 2015. b When comparing to WMO (2007), revised fractional halogen release values have contributed to an earlier EESC recovery year for midlatitudes and a 

later one for the Antarctic vortex. c For midlatitude conditions, an age-of-air value of 3 years, corresponding fractional release values, and a value for α of 60 are used. For Antarctic 

vortex conditions, an age-of-air value of 5.5 years with corresponding fractional release values and a value for α of 65 are used. d Using semi-empirical ODPs from Table 5-1. e Using direct GWPs with 100-year time horizon (see Appendix Table 5A-1). f Integrated globally averaged total column ozone changes are taken from Daniel et al. (2010). g Banks are assumed to be zero. Emissions include uncertain sources such as possible fugitive emissions and unintended by-product emissions. h The integrated ODP- and GWP-weighted emissions correspond to the elimination of all anthropogenic N2O emissions from 2011 onward in the A1B 

SRES scenario.

1980 2011
5.18

Chapter 5

Figure 5-4 (at right). Banks of CFCs, HCFCs, and halons in 1995, 2008, and 2020 in megatonnes (Mt) and 

weighted by their ODPs and 100-year GWPs (direct term only). The 2008 bank is from TEAP (2009) for almost 

all compounds. The 1995 bank is derived by a backwards calculation using the historic emissions, UNEP production data, and the 2008 bank. The 2020 bank is calculated in the baseline scenario from estimates of future 

production and bank release rates. The pie slices show the sizes relative to those of the maximum values (1995 

for the ODP- and GWP-weighted banks and 2008 for the bank in Mt) and therefore don’t fill a full circle. The 

total bank size is given below each pie chart. For comparison, the HFC bank size has been estimated to have 

been 1.1 GtCO2-eq in 2002 and 2.4 GtCO2-eq in 2008, and has been projected to be 4.6 GtCO2-eq in 2015 in 

a business-as-usual scenario (Velders et al., 2009).

1980 2000 2020 2040 2060 2080 2100

Year

0. 0

0. 5

1. 0

1. 5

2. 0

ODP-Weighted Emissions

Natural CH3Br and CH3Cl

CFCs

Halons

CCl4 + CH3CCl3

HCFCs

Anthropogenic

CH3Br

1980 2000 2020 2040 2060 2080 2100

Year

0. 0

0. 5

1. 0

1. 5

2. 0

2. 5

EESC (ppb)

EESC

Natural CH3Br and CH3Cl

CFCs

Halons

CCl4

CH3CCl3

HCFCs

Anthropogenic

CH3Br

1980 2000 2020 2040 2060 2080 2100

Year

0

2

4

6

8

10

GWP-Weighted Emissions

(100-yr)

CFCs HCFCs

Other ODSs

1980 2000 2020 2040 2060 2080 2100

Year

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Radiative Forcing

CFCs

HCFCs

Other ODSs

RF (W

m−2)

Emissions (GtC

O2-eq yr−1) Emissions (MtCFC-11-eq yr−1)

Figure 5-3. ODP- and GWP-weighted emissions, EESC, and radiative forcing of the chlorine- and brominecontaining ODSs of the baseline (A1) scenario. Only the direct GWP-weighted emissions and radiative forcing 

are considered here. Semi-empirical steady-state ODPs (Table 5-1) and 100-year GWPs (Appendix Table 

5A-1) are used to weight emissions. The emissions and radiative forcing of the HFCs are not included in these 

graphs because of the large range in HFC scenarios. They are shown in Figure 5-5.
5.19

A Focus on Information for Policymakers

contribution, the largest contribution in the past and future comes from the CFCs and natural CH3Cl and CH3Br 

emissions. In terms of radiative forcing the CFCs are also 

the most important ODSs, but the HCFCs are projected to 

contribute more than 0.05 W/m2 at their peak.

CFC, HCFC, and halon bank size estimates for 

1995 and 2008 and projections for 2020 are shown in Figure 5-4. The contributions of the ODSs to the bank are 

compared by mass and when weighted by their ODPs and 

GWPs (100-year). The total size of the bank by mass remains more or less constant over time, but decreases significantly when considering their potential effect on depletion of the ozone layer (ODP-weighted) and on climate 

forcing (GWP-weighted). The decreasing contribution 

of the CFCs and increasing contribution of the HCFCs is 

particularly apparent when examining the banks by mass 

and when weighted by GWPs. The relative contributions 

of both the CFCs and halons remain the largest when considering the ODP-weighted banks.

5.4 IMPACTS OF HUMAN ACTIVITIES

RELEVANT TO OZONE POLICY

5.4.1 Background

In this section, we assess the importance of various 

human activities that are relevant to ozone policy formulation. The focus is primarily on the extent to which future ozone depletion may be affected. We also discuss the 

potential effect of HFCs on climate forcing because the 

widespread use of HFCs has occurred directly as a result 

of ODS controls of the Montreal Protocol. We discuss 

geoengineering using atmospheric sulfur injections, and 

CO2 and CH4 emissions not because they necessarily have 

relevance for ozone policy decisions, but to assess their 

potential for inadvertent ozone impacts as a result of climate change policies or the absence of such policies.

1995

Bank in Mt

CFCs

(79%)

Halons

(5%)

HCFCs

(16%)

4.5 Mt

2008

CFCs

(39%)

Halons

(3%)

HCFCs

(59%)

4.8 Mt

2020

CFCs

(18%)

Halons

(1%)

HCFCs

(81%)

4.7 Mt

Bank ODP-weighted

CFCs

(58%)

Halons (41%)

HCFCs (1%)

5.6 MtCFC-11-eq

CFCs

(52%)

HCFCs Halons (43%) (6%)

3.4 MtCFC-11-eq

CFCs

(44%)

Halons

(40%)

HCFCs

(16%)

1.9 MtCFC-11-eq

Bank GWP-weighted

CFCs (93%)

Halons (3%) HCFCs (4%)

26 GtCO2-eq

CFCs

(71%)

HCFCs (26% Halons (3%) )

16 GtCO2-eq

CFCs

(44%)

Halons

(3%)

HCFCs

(53%)

 9 GtCO2-eq
5.20

Chapter 5

5.4.2 Ozone Impacts

The Montreal Protocol and its Amendments and 

Adjustments have effectively controlled the emission 

of the most important ozone-depletion gases containing chlorine and bromine. It is a testament to the success of the Montreal Protocol that current potential policy 

options and activities that do not involve chlorine- or 

bromine-containing compounds are expected to have 

some of the greatest effects on future ozone levels. However, to maintain consistency with past reports and to 

address the relative importance of continued emissions of 

halogenated source gases, we provide in Section 5.4.2.1 

an analysis of various hypothetical test cases using EESC 

as the comparison metric.

Chapter 8 of the previous Assessment (Daniel and 

Velders et al., 2007) focused strictly on the EESC index to 

quantify the potential effects of additional ODS controls 

on stratospheric ozone depletion. Here, results from 2-D 

model calculations in Daniel et al. (2010) are presented to 

augment the historical reliance on EESC and as a way to 

assess the ozone impact of several different assumptions of 

future emissions of halocarbons (e.g., CFCs, HCFCs, halons, CH3Br) and N2O (Section 5.4.2.2 and Chapter 3) (see 

Table 5-4). The phase-out and baseline scenarios assumed 

in Daniel et al. (2010) were similar to those in this chapter. However, that paper should be consulted for a consistent comparison of ozone changes with EESC changes. 

Estimates of ozone impacts from ODSs and N2O future 

emission changes also allow for comparison with other 

activities and emissions, such as CO2 and CH4. The computational efficiency of 2-D models makes it possible now 

to perform multiple long-term simulations in a reasonable 

amount of time to examine the effects of various scenarios. 

The residual circulation framework used in 2-D models has 

been shown to provide realistic simulations of atmospheric 

transport on long timescales (>30 days). Recent studies 

have demonstrated good overall model agreement with a 

variety of observations in reproducing transport-sensitive 

features in the meridional plane (e.g., Fleming et al., 2007). 

These capabilities make these models useful tools for 

studying long-term ozone changes.

5.4.2.1 Chlorine- and Bromine-Containing ODSs

Alternative test cases, based on the baseline scenario of ODSs (Section 5.3.1), are constructed and used 

to examine the relative effects of reducing future emissions of groups of halocarbons on EESC and stratospheric 

ozone levels. These alternative cases fall into four categories: (1) “No future emission” cases; (2) “No future 

production” cases; (3) cases assuming the full capture and 

destruction of the 2011 bank; and (4) cases assuming full 

capture and destruction of the 2015 bank. For the bank 

cases, the entire bank is considered, not just the portion 

that is estimated to be “accessible.” The 2015 bank recovery cases are run to quantify the impact of the implementation date of hypothetical bank emission controls; it 

should be recognized, however, that we do not have an 

estimate of the uncertainty in the future bank projections, 

on which these calculations are based. Full elimination 

of emissions, production, and banks are considered rather 

than some smaller fractional reduction because the intent 

is to provide policy-neutral cases that can be used to determine the impacts of other specific policy options. The 

impact of any option that involves a smaller reduction can 

be determined by simply scaling the results of Table 5-4. 

For example, if the “accessible” bank is estimated to be 

30% of the total bank, the results in the table for that compound can be simply multiplied by 0.3 to determine the 

impact of capture and destruction of the accessible bank. 

The elimination of all future emissions represents the 

greatest possible reduction in future abundances that can 

be imparted by direct controls. The elimination of future 

production allows the ODSs currently residing in banks to 

continue to be released to the atmosphere as they would 

in the baseline scenario. The projections that consider 

the full capture and destruction of the 2011 bank complement the “No Production” scenarios in that the full 2011 

bank is destroyed in a manner that releases no ODSs to 

the atmosphere; future production and the resulting future 

buildup of banks is allowed to continue, however. The 

expected future production is virtually zero for the CFCs 

and halons, but still significant for the HCFCs and possibly for CCl4. The “No production” and “Full capture and 

destruction of the 2011 bank” cases are complementary 

in the sense that they may be combined to approximately 

estimate the “No emission” cases.

The effects of the alternative test cases are presented in Table 5-4 using metrics similar to those of previous assessments, i.e., the year EESC returns to its 1980 

level for midlatitude and Antarctic vortex conditions, and 

the change in integrated EESC relative to the baseline 

scenario. These integrated values are dependent on the 

choice of the 1980 level. If a lower level were chosen, 

for example the 1975 level, the tendency is for the CFC 

options to gain in importance relative to the other ODS 

policy options. This results from the longer atmospheric 

lifetimes of the CFCs. Also in this table is the change in 

cumulative ODP- and GWP-weighted (direct contribution 

only) emissions. The latter gives an indication of the potential effects of the cases for climate forcing. In general, 

the various cases presented here lead to smaller integrated 

EESC differences (when integrated from 1980) and return 

year differences from the baseline scenario than the same 

test cases from WMO (2007). This is expected, as banks 

of most ODSs are smaller due to continued emission for 

4 more years, and there are now fewer years to continue 
5.21

A Focus on Information for Policymakers

to produce the various ODSs before the mandated phaseout. CCl4 represents an exception to this. The increasing 

apparent importance of a CCl4 production or consumption phase-out arises from projected CCl4 emissions being larger in the current baseline scenario than in WMO 

(2007). The increased future emissions are based on an 

extrapolation of declining global emissions over the last 

5 years (6%/year). This decline in CCl4 emissions has 

not mirrored the strong decrease in reported production 

of CFC-11 and CFC-12 as it did in the 1980s and 1990s. 

This revised projection is thus not based on an improved 

understanding of the budget of CCl4, which still cannot be 

balanced nor can the interannual variability be explained 

with our current knowledge of CCl4 sources and sinks (see 

Chapter 1). The incomplete understanding of the CCl4

budget represents a significant gap.

Emissions of CFCs and halons from the banks are 

the largest sources of current ODP-weighted emissions 

of ODSs. An immediate phase-out of halon bank emission sources reduces future integrated EESC more than 

the elimination of emissions of any other compound or 

compound group, with slightly more of an impact than the 

elimination of future HCFC emissions. A delay of four 

years, from 2011 to 2015, in the capture and destruction 

of the estimated banks of CFCs and halons is currently 

thought to reduce the potential ozone and climate benefits 

by about 30% since ODSs continue to be emitted from 

these banks and production is thought to have essentially 

ceased.

A phase-out of methyl bromide emissions from 

quarantine and pre-shipment (QPS) applications beginning 

in 2011 would shift the year midlatitude EESC reaches 

the 1980 level earlier by 1.5 years compared to continued 

use at current levels. Continuing critical-use exemptions 

(CUE) at the approved 2011 level would delay the return 

of EESC to 1980 levels by 0.2 years.

The elimination of all emissions of chlorine- and 

bromine-containing ODSs after 2010 would shift the year 

midlatitude EESC reaches the 1980 level by about 13 

years, from 2046 to 2033. In terms relevant to climate, 

this would reduce emissions of these compounds by about 

0.7 gigatonnes (Gt) of CO2-equivalent (GtCO2-eq) per 

year averaged over 2011 through 2050. Future production of HCFCs and the sum of the current banks of CFCs 

plus HCFCs contribute about equally to this number. In 

comparison, global anthropogenic emissions of CO2 were 

greater than 30 Gt per year in 2008.

In past assessments, the potential impact of 

chlorine-containing VSLS has been neglected in the evaluation of hypothetical ODS emissions phase-outs. However, it is likely that their contribution is not negligible. 

As discussed in Chapter 1, anthropogenic VSLS are currently expected to contribute about 39 ppt chlorine to the 

stratosphere with fairly large uncertainty. Because these 

likely release their chlorine quickly, this amount could 

contribute directly to EESC with a unit fractional release 

value. If included in EESC in this way, at midlatitudes, 

a phase-out of these compounds is expected to advance 

the return of EESC to 1980 levels by almost 3 years. The 

magnitude of this effect is significant compared to the 

long-lived ODS cases presented in Table 5-4. This impact 

depends strongly on the region of the stratosphere considered, with greater impacts in regions where less chlorine 

has been liberated from long-lived source gases, but where 

chemical ozone loss is still important. It is also unclear 

how VSLS emission reductions in specific locations and 

during different times of the year would quantitatively affect the abundance of stratospheric chlorine.

The uncertainties of the effects of the test cases presented in Table 5-4 have been estimated by varying several model parameters for each class of compounds (CFC, 

HCFCs, etc.) in the calculation: the size of the banks in 

2008, the annual emission rate from the banks, the fractional release values, and the lifetimes of the compounds 

(Douglass et al., 2008; Martinerie et al., 2009). The lifetimes and annual emission rate from the banks are only 

varied for 2009–2100, since the data through 2008 is constrained by observations. A variation of 20% in the size of 

the 2008 banks of CFCs, HCFCs, and halons results in a 

variation of about 20% in the change in integrated EESC, 

for each class of compounds, in the case of a full recovery 

of the banks. The year EESC returns to the 1980 level varies by less than a year. Doubling the annual emission rate 

from the banks increases the change in integrated EESC 

by up to 15%, while reducing the annual emission rate by 

50% decreases the changes in integrated EESC by up to 

30%. Again, for most cases, the year EESC returns to the 

1980 level varies by less than a year. Variations of 20% in 

the fractional release values per class of compound gives 

similar variations. Variations of up to ±3 years occur in 

the year EESC returns to the 1980 level when varying the 

lifetimes of the CFCs by ±20%. The effects of such a 

variation on the change in integrated EESC is less than 

±20% for each compound group. These uncertainties have 

been applied to entire groups of compounds. These uncertainties are likely independent across compound groups 

for the size of the banks and annual emission rates from 

the banks, but perhaps not for the fractional release values 

and lifetimes.

The benefits of the Montreal Protocol that are calculated to have already been achieved are highlighted in 

Section 5.5. The cases considered here show that the options for limiting future halogenated ODS emissions are 

expected to have a much smaller impact on future ozone 

depletion and climate than what has already been accomplished by the Montreal Protocol.
5.22

Chapter 5

5.4.2.2 CO2, CH4, and N2O

The increasing concentration of carbon dioxide 

(CO2) in Earth’s atmosphere warms the troposphere but 

cools the stratosphere. This cooling leads to slower gasphase ozone loss reactions (Haigh and Pyle, 1979; Rosenfield et al., 2002), and thus to an increase in stratospheric 

ozone. Cooling of the polar lower stratosphere can also 

lead to enhanced polar stratospheric cloud (PSC) formation and more ozone destruction via more efficient heterogeneous chemistry (Chapter 3, Section 3.2.3). Increasing concentrations of methane and its effects on hydrogen 

oxides can enhance the destruction of ozone in the upper 

stratosphere. Increases in methane (CH4) can also reduce 

the ozone loss in the stratosphere by converting chlorine 

from active species to the reservoir HCl, and can lead to 

NOx-induced ozone production in the troposphere and 

lower stratosphere via the CH4 oxidation cycle. Increases 

in methane and the subsequent oxidation to water vapor 

will also lead to weak stratospheric cooling. Future levels 

of CO2 and CH4 may be higher for some period of time 

compared with today. If they are, they would be expected 

to lead to higher levels of column ozone at midlatitudes 

(e.g., Li et al., 2009; Waugh et al., 2009; Hsu and Prather, 

2010). Thus, there is the possibility of a “super-recovery,” 

where the total amount of atmospheric ozone exceeds 1960 

levels. Both 2-D (Rosenfield et al., 2002; Chipperfield 

and Feng, 2003; Portmann and Solomon, 2007; Daniel et 

al., 2010), and 3-D model (SPARC CCMVal, 2010) calculations suggest that increases in CO2 and CH4 will lead 

to total column ozone increases that are larger than what 

can be caused by decreases in future ODS or nitrous oxide 

(N2O) emissions. Because increasing levels of CO2 and 

CH4 are expected to continue to lead to increased total 

ozone, but also increased climate forcing, we present this 

information as relevant for inadvertent ozone impacts due 

to climate policy choices. Further complicating the matter 

is that, for ozone, changes in circulation due to greenhouse 

gases are expected to be the dominant factor in the tropics, and this will lead to lower column ozone levels there. 

Additional discussion of the impacts of CO2 and CH4 on 

ozone can be found in Chapter 3.

N2O emissions reductions, in contrast, would reduce climate forcing, and the resulting decrease in stratospheric nitrogen oxides would lead to higher ozone levels. 

Ravishankara et al. (2009) have shown that when ODS 

emissions are weighted by their steady-state ODPs, N2O 

emissions represent the single most important anthropogenic emissions today for ozone depletion. Unmitigated, 

these emissions are also expected to remain the most significant throughout the 21st century. In the current atmosphere, CFCs lead to much more ozone depletion than 

does N2O because of the large historic emissions and long 

lifetimes of the CFCs. The 2-D models used in Daniel et 

al. (2010) suggest that N2O causes an ozone depletion in 

the current atmosphere of about 3 Dobson units (DU) 

compared with the ODSs depleting about 18 DU. However, when the impact of phase-outs of future emissions 

are considered, an immediate phase-out of all anthropogenic N2O emissions leads to a greater reduction in ozone 

depletion integrated through 2100 than the integrated 

ozone depletion reduction arising from an elimination of 

all future ODS emissions (Daniel et al., 2010). The climate forcing and ozone impacts of a hypothetical emissions phase-out beginning in 2011 of several ODSs and 

anthropogenic N2O are compared in the final three columns of Table 5-4. These comparisons show the relative 

significance of these policy options using cumulative 

ODP- and GWP-weighted emissions and ozone integrated 

from 2011–2050. The significance of N2O compared to 

the ODSs is not surprising given the higher current ODPweighted emissions compared to the controlled ODSs. 

We emphasize that all the phase-outs considered are purely hypothetical with no consideration given to the economic or technological feasibility of implementing them.

5.4.2.3 N2O from Automotive Biofuels

Anthropogenic emissions of N2O total approximately 6.7 TgN yr−1 (IPCC, 2007). Agriculture is responsible for 2.8 TgN yr−1 and related emissions from rivers, 

estuaries and coastal zones add a further 1.7 TgN yr−1. 

Emissions associated with fossil fuel combustion and 

industrial activities, biomass burning, atmospheric deposition, and human excreta combined account for the remaining 2.2 TgN yr−1. The Greenhouse Gases, Regulated 

Emissions, and Energy Use in Transportation (GREET) 

model provides a life cycle assessment of biofuel production and uses, and includes allocation and differentiation 

of biofuels based on different agricultural practices (Wang, 

2010). The GREET model provides N2O emission factors 

for corn ethanol, sugarcane ethanol, and soy biodiesel in 

the United States of America (USA) of approximately 45, 

25, and 17 g/MMBtu of fuel produced (MMBtu = million 

British thermal units, 1 MMBtu = 1.055 gigajoules (GJ)). 

The USA is the largest biofuel producer, and corn ethanol 

is the dominant biofuel produced in the USA and has the 

highest N2O emissions per megajoule (MJ) of fuel produced. Combining 40 g N2O/MMBtu with a production 

of 17.5 million tonnes of oil equivalent in 2008 (British 

Petroleum, 2009; 1 tonne of oil equivalent = 42 GJ) we 

estimate an emission of 0.018 TgN yr−1 associated with 

production of corn ethanol in the USA. This is approximately 0.2% of the total anthropogenic emission of 6.7 

TgN yr−1 (IPCC, 2007). Crutzen et al. (2008) have argued 

that depending on N fertilizer uptake efficiency by plants, 

the formation of N2O during the production of commonly 

used automotive biofuels, such as biodiesel from rapeseed 
5.23

A Focus on Information for Policymakers

and bioethanol from corn (maize), can negate the CO2

mitigation from fossil fuel savings. However, the analysis 

by Crutzen et al. (2008) does not consider allocation of 

emissions to the coproducts in the process (e.g., animal 

feed produced during corn ethanol production).

The contribution of automotive biofuels to global 

N2O emissions is currently significantly below 1% and 

expected to remain so in the future. While global agricultural activities emit substantial amounts of N2O, biofuel 

production itself is currently not a major contributor to 

N2O emissions. Although current biofuel production represents a small fraction of total crude oil production, and 

increases in biofuel production appear likely, second generation biofuels (e.g., lignocellulosic ethanol) are anticipated to have substantially lower environmental impacts. 

Historical changes in the atmospheric concentrations 

of N2O and emissions sources are discussed in Section 

1.5.1.2 of Chapter 1.

5.4.2.4 Geoengineering: Enhancing Earth’s

Albedo by Stratospheric Injection

of Sulfur

There is increasing concern that efforts to reduce 

global greenhouse gas emissions will not be sufficient to 

prevent Earth’s climate from warming to levels that have 

never been experienced by modern societies. This has 

intensified the discussion about deliberate atmospheric 

modification schemes (“geoengineering”) to counteract 

enhanced greenhouse warming due to industrial emissions 

(for example, see the review panel report on geoengineering (Royal Society, 2009)). Although fraught with uncertainties and side effects that have yet to be studied in detail 

(Keith et al., 2010), the notion of enhancing Earth’s albedo by increasing particulate scattering of visible light in 

the stratosphere dates back many decades (e.g., Budyko, 

1977; Dyson and Marland, 1979). It has been estimated 

that injection of particles designed for optimum scattering of shortwave radiation (e.g., sulfate or aluminum oxide) might be economically viable and would likely be the 

most cost-effective method of a class of geoengineering 

options called “solar radiation management” (Teller et al., 

1997; Lenton et al., 2009; Royal Society, 2009). These 

studies also point out that the proposed solar radiation 

management techniques likely have the largest side effects of the geoengineering options considered. For example, changes in shortwave radiation would likely result 

in local temperature and precipitation changes, including 

increased prevalence of droughts (Hegerl and Solomon, 

2009). Various possible side effects of geoengineering 

(e.g., Robock, 2008) besides the impact on ozone are 

not further discussed in this Assessment. Other methods 

that have been suggested for managing solar radiation 

or taking up carbon dioxide (e.g., launching mirrors into 

space to harvest or block radiation; fertilizing the ocean to 

promote uptake of CO2 by phytoplankton) could also impact stratospheric ozone, but are not considered here due 

to a lack of scientific investigations that would allow for 

an assessment of the impacts of these approaches.

Part of the reason injection of sulfate into the stratosphere has received considerable attention in recent years 

from the scientific community as an option for solar radiation management (Crutzen, 2006) is due to observations 

of modest cooling of the globe following major volcanic 

eruptions, which may be viewed a natural analog to this 

particular approach to manage Earth’s radiation budget. 

The 1991 eruption of Mt. Pinatubo, for example, resulted in a decrease of global mean temperatures by 0.5°C 

for a few years (Soden et al., 2002). Observations from 

recent volcanic eruptions have shown that stratospheric 

ozone in middle and high latitudes is strongly influenced 

by the enhanced burden of liquid sulfate aerosols (e.g., 

Tabazadeh et al., 2002; Solomon et al.,1996; Portmann et 

al.,1996; Tilmes et al., 2008a). Recent model calculations 

have estimated a global temperature decrease of about one 

degree at Earth’s surface could be achieved within about 

five years after the start of a hypothetical sulfate aerosol 

injection experiment (Robock et al., 2008; Tilmes et al., 

2009). However, Heckendorn et al. (2009) have shown 

that the size distribution of aerosol particles is not fixed 

as assumed in earlier studies but strongly depends on 

different injection assumptions. The ability to achieve 

some amount of cooling that might be required to offset 

enhanced greenhouse-gas warming may be limited due 

to the coagulating and settling of aerosols. This process 

would also warm the tropical tropopause, perhaps resulting in enhanced abundances of stratospheric water vapor, 

which could accelerate ozone loss especially in the tropics 

and midlatitudes (Heckendorn et al., 2009). However, a 

significant increase of stratospheric water vapor was not 

observed after large volcanic eruptions.

Tilmes et al. (2008b, 2009) estimated the impact 

of an enhanced burden of stratospheric sulfur on the 

ozone layer during the period of time when stratospheric halogen loading is projected to slowly decline (Newman et al., 2007). Assuming an injection into the tropical stratosphere of a mass of volcanic-sized (submicron) 

sulfate aerosols large enough to counteract a doubling 

of CO2 with respect to preindustrial values (Rasch et al., 

2008a), ozone depletion in the Arctic polar vortex might 

be expected to double or triple (Tilmes et al., 2009). In 

addition, the expected recovery of the Antarctic ozone 

hole from the reduction in atmospheric halogen loading 

brought about by the Montreal Protocol might be delayed 

by between 30 and 70 years, depending on the assumed 

particle sizes (Tilmes et al., 2008b) (see Chapter 3). The 
5.24

Chapter 5

estimated impact on stratospheric ozone at low latitudes 

is expected to be smaller (about ±3%) for 2050 chlorine 

conditions (Tilmes et al., 2009).

Studies to quantify the impact of geoengineering 

on ozone have so far assumed basic scenarios and idealized conditions, and they have focused entirely on sulfate 

aerosols. Particle size distributions are usually described 

in simple terms, with large uncertainties in the evolution 

of those distributions (Rasch et al., 2008b). More comprehensive microphysical models, such as the one described 

in Heckendorn et al. (2009), are necessary to describe the 

complete size-distributions for geoengineering experiments. Dynamical and chemical changes in the stratosphere as a result of geoengineering are still uncertain 

given our current modeling capabilities (Chapter 3).

Uncertainties also exist in the amount of sulfur 

necessary to counteract global warming, which in turn depends on the amount of aerosol deposition (e.g., Heckendorn et al., 2009) and on the strength of the stratospheric 

circulation in the models, whether assumed for presentday conditions, or for a future accelerated stratospheric 

circulation (Rasch et al., 2008a). To date there have been 

no investigations of the impact on ozone caused by a gradual ramp-up of the amount of SO2 injected, with the purpose of keeping global average temperature nearly constant (Wigley, 2006). The amount of ozone that might be 

destroyed by deliberately increasing the aerosol loading of 

the stratosphere might also differ following a large volcanic eruption that further increases the amount of sulfur in 

the stratosphere (Tilmes et al., 2008b). Finally, there has 

been little study of an engineered stratospheric reflecting 

layer that uses materials other than sulfate (e.g., particles 

manufactured for maximum scattering of shortwave radiation and extended stratospheric lifetimes, as proposed by 

Teller et al., 1997).

These and other remaining gaps in our understanding of the full impacts of geoengineering on stratospheric 

ozone (and other aspects of the environment) are significant. The potential for significant risks to the ozone layer 

and the climate system, both known and unknown, from 

solar radiation management, as well as the fact that these 

approaches do not address other problems like ocean acidification as a result of increasing CO2 levels, have been 

acknowledged (Royal Society, 2009).

5.4.2.5 Emissions from Aviation and Rockets

Aviation

The importance of current aircraft emissions for 

ozone is well recognized (IPCC, 1999; WMO, 2003; 

Wuebbles et al., 2006; Maurice and Lee, 2009; Lee et 

al., 2009). Aircraft emissions, overall, are thought to 

increase globally averaged ozone columns by less than 

0.5%, primarily due to photochemical production of ozone 

catalyzed by nitrogen oxides (NOx), odd hydrogen (HOx) 

(from H2O), and hydrocarbon (HC) emissions. The production of ozone by emissions of NOx and HCs is offset 

by the destruction of ozone that occurs when emissions of 

aerosols and water vapor enhance abundances of ozonedestroying active halogens. As a consequence, little or no 

impact on stratospheric ozone column abundances is expected from aircraft emissions transported into the lower 

stratosphere from the troposphere (WMO, 2003; Brasseur, 

2008; Lee et al., 2009). New studies reinforce that there 

is a dual nature of aircraft emissions directly within the 

stratosphere or near the tropopause, with ozone production in some regions, and losses in others, and a strong dependence of the sign of net ozone changes on the latitude 

and altitude of those assumed emissions (Meilinger et al., 

2005; Søvde et al., 2007; Pitari et al., 2008; Köhler et al., 

2008; Cariolle et al., 2009).

Aviation-perturbed ozone can also affect the tropospheric oxidizing capacity, and thus levels of methane, 

a species that influences ozone chemistry in both the troposphere and stratosphere. Köhler et al. (2008) estimate 

that the increase in the oxidizing capacity of the troposphere due to aircraft emissions has reduced the lifetime 

of methane by 3.0%. Given that increases in methane 

are expected to increase stratospheric ozone (e.g., Section 5.4.2.2), this indirect change due to aircraft would 

be expected to have an offsetting effect on the increase 

in ozone columns.

Given that a large shift of worldwide aviation from 

subsonic to supersonic travel is unlikely in the foreseeable future, this Assessment assumes that aircraft emissions will be predominantly tropospheric. In this case, the 

net impact of those emissions will be ozone production, 

with some regional variation such as larger enhancements 

in heavily traveled flight corridors (e.g., Northern Hemisphere middle latitudes in summer). Ozone changes are 

expected to be smaller in the Southern Hemisphere, where 

there are fewer flights and emissions.

Rockets

A summary of the important processes that can 

contribute to ozone loss from rocket launches is found 

in Chapter 1. In the context of scientific and regulatory 

frameworks for protecting stratospheric ozone, the treatment of combustion emissions from rockets is somewhat 

complicated because ODP calculations involve some 

poorly understood processes, may be only regionally appropriate (not globally), and depend on many factors (e.g., 

propellant type, trajectory, latitude of launch site, etc.). 

In addition, the atmospheric lifetimes of rocket emissions (except for CO2) are less than a few years, which are 

short compared to the lifetimes of most halocarbon source 
5.25

A Focus on Information for Policymakers

gases. As is the case for aircraft, the impacts from rockets 

are due to primary and secondary products of combustion 

(e.g., H2O, NOx, hydrogen chloride (HCl), alumina, soot, 

and sulfate), and not to the fuels themselves. As with other processes presented in this chapter, the impact of rocket 

emissions on ozone may attract more attention in the coming decades if the space launch market grows (Ross et al., 

2009).

Several new classes of rocket propellant are of particular concern even though they do not contain chlorine, 

because they could still have significant effects on ozone. 

The first, composed of aluminum and H2O, has been proposed recently as an “environmentally friendly” solid 

rocket motor replacement. Because the emission from an 

Al/H2O rocket is mainly composed of alumina particles 

(compared to 30% for conventional solid rocket motors), 

ozone losses from such a rocket could exceed those from 

conventional solid rocket motors for equal emission rates 

if there is an ample reservoir of chlorine in the stratosphere, which will be the case for at least a few decades. 

The second, a “hybrid” that uses N2O and solid hydrocarbon as propellants, is being developed for widespread 

commercial spaceflight and could account for about onethird of all rocket emissions by 2020 (Seedhouse, 2008). 

Very little is known about the nature and magnitude of 

the emissions from this new hybrid rocket engine, though 

initial concerns for stratospheric ozone will focus on uncombusted N2O and soot.

Given these uncertainties and the long lead times in 

space launch hardware engineering and development, the 

lack of metrics for addressing the global impacts of rocket 

emissions can be particularly problematic (Ross et al., 

2009). Improved understanding of the processes involved 

in ozone depletion and development of suitable metrics 

can provide an important framework for launch industries 

to identify the factors responsible for the environmental 

impacts of rockets. This could allow, for example, for 

choice of propellant that best minimizes the environmental impacts.

5.4.2.6 Summary

The ozone impacts of the processes discussed in 

Section 5.4.2 are qualitatively compared in Table 5-5. Our 

understanding of the ozone impact of activities directly 

relating to production and emissions of halocarbons and 

CO2, CH4, and N2O is fairly advanced, while important 

gaps remain in our understanding of the impacts of other 

activities like aviation, space transport, and geoengineering. Chlorine- and bromine-containing ODSs play the 

largest role in current ozone depletion while the enhancement of CO2 and CH4 above background levels has likely 

led to higher globally averaged ozone levels than otherwise 

would have occurred. However, because of the controls 

already imposed by the Montreal Protocol on production 

and consumption of ODSs and the long atmospheric lifetimes of these compounds, the ability to further reduce 

future atmospheric ODS concentrations and thus ozone 

depletion through additional controls is more limited than 

before. Future ozone evolution is expected to be largely 

affected by activities and emissions not currently regulated 

by the Montreal Protocol, particularly by changes in CO2, 

CH4, and N2O. Some of these activities and emissions will 

likely increase ozone and some will decrease it. Our ability to project future stratospheric ozone is becoming more 

complicated, in that activities controlled by the Montreal 

Protocol are likely no longer the most important ones for 

the future evolution of stratospheric ozone.

5.4.3 Climate Impacts

5.4.3.1 Major HFCs Used as Replacements

for ODSs

Global production and use of CFCs and halons 

have decreased significantly because of the phase-outs under the Montreal Protocol and its subsequent Amendments 

and Adjustments. As a direct result, the use of HCFCs and 

HFCs as replacements has increased in Article 5 and nonArticle 5 countries (see Chapter 1). The HCFC increases 

occurred earlier and have been confirmed by long-term 

growth in observed atmospheric mixing ratios (Montzka et 

al., 2009; Stohl et al., 2009) (Chapter 1). Recent changes 

in northern-latitude mixing ratio observations are consistent with reduced use of HCFCs in non-Article 5 countries 

and increased use in Article 5 countries (Montzka et al., 

2009). HCFCs have been used as low-ODP substitutes 

in many applications for high-ODP substances and were 

classified under the Protocol as “transitional substitutes” 

to be used during the time it took to commercialize new 

ozone-safe alternatives and replacements. In 2007 the 

Parties to the Montreal Protocol decided to accelerate the 

HCFC phase-out, in part to protect future climate. HCFC 

production and consumption in Article 5 countries will 

be frozen in 2013 and stepwise reduced, with a virtually 

complete phase-out in 2030. Non-Article 5 countries have 

agreed to a virtually complete phase-out in 2020. In adopting the accelerated HCFC phase-out, the Parties agreed to 

promote the use of HCFC alternatives that minimize the 

impact on climate.

With the global phase-out of HCFCs, much of the 

future application demand for refrigeration and air conditioning and heating is likely to met by HFCs, while the 

demand for thermal-insulating foam production is likely 

to be met by HFCs as well as hydrocarbons and not-inkind thermal insulation such as fiberglass and mineral 

wool (IPCC/TEAP, 2005; Velders et al., 2009). HFCs 
5.26

Chapter 5

Table 5-5. Qualitative summary of anthropogenic processes affecting stratospheric ozone.

Activity Mechanism

Effect on Ozone Layer

Ozone

Column

Increase or

Decrease a

Understanding b

Approximate

Maximum

Impact c

Destruction of CFC banks Ozone destruction by

chlorine chemistry

+ High Medium

Destruction of HCFC banks Ozone destruction by

chlorine chemistry

+ High Small

Destruction of halon banks Ozone destruction

by chlorine and

bromine chemistry

+ High Medium

Eliminate HCFC production Ozone destruction by

chlorine chemistry

+ High Medium

Eliminate CH3Br production Ozone destruction by

bromine chemistry

+ Medium Medium

Eliminate CCl4 production Ozone destruction by

chlorine chemistry

+ Medium-Low Medium

Reduction in N2O emissions d Ozone destruction by NOx + High Medium

Mitigation of ozone destruction

by chlorine/bromine chemistry

− Medium Small

Reduction in CH4 emissions d Ozone production − Medium Large

Ozone destruction by HOx + Medium Small

Mitigation of ozone destruction 

by chlorine chemistry

− Medium Small

Reduction in CO2 emissions d Middle- and upperstratospheric temperature 

changes

− High Large

Formation of PSCs + Medium Large

Circulation changes e + & − Low Large

Increased aviation emissions Aerosols: heterogeneous ozone 

destruction by halogens

− Medium Depends on # of 

flights, altitudes,

and locations

Production of ozone by 

HC/HOx/NOx chemistry

+ Medium

Contrail frequency ? Low

Activation of halogens − Low

Increased rocket / 

space-transport 

emissions

SRM f

 – ozone destruction by 

chlorine chemistry

− High Small at present 

launch rate

SRM f

 – aerosols: 

Heterogeneous ozone 

destruction by halogens

− Medium

Water vapor − Low

Soot ? Low

Ozone destruction by NOx − Low

Geoengineering by 

sulfur injection

Heterogeneous ozone 

destruction by halogens

− Medium-Low Potentially large

"

"

"

"

"

"

"
5.27

A Focus on Information for Policymakers

do not deplete the ozone layer but, along with CFCs and 

HCFCs, are greenhouse gases, which contribute to the radiative forcing of climate (IPCC/TEAP, 2005; Velders et 

al., 2009). Thus, the current transition away from CFCs 

in Article 5 countries and HCFCs in Article 5 and nonArticle 5 countries has implications not only for the ozone 

layer, but also for future climate. HFCs are not controlled 

by the Montreal Protocol, but they are included in the basket of gases of the Kyoto Protocol.

The HFC emissions scenarios discussed here can be 

divided in two classes:

• One class consists of non-intervention scenarios 

based on growth rates in gross domestic product and 

population (IPCC, 2000) for the period up to the middle or end of the 21st century. In these scenarios, 

historical and current technological developments 

are extrapolated without intervention from political 

processes. Such scenarios were first developed for 

the IPCC–Special Report on Emissions Scenarios 

(SRES) (IPCC, 2000) during the time when HFCs 

had still very limited usage and when the transition 

from CFCs and HCFCs had just begun. New nonintervention HFC scenarios have been formulated 

by Velders et al. (2009) and by the German Federal 

Environment Agency (UBA, 2009). The scenarios in 

Velders et al. (2009) are based on assumptions similar 

to those of IPCC-SRES with respect to growth rates 

in gross domestic product and population, but have 

incorporated new current information on (1) reported 

recent increases in consumption of HCFCs in Article 

5 countries of about 20% yr−1 (through 2007), (2) replacement patterns of HCFCs by HFCs as reported 

in non-Article 5 countries, and (3) accelerated phaseout schedules of HCFCs in Article 5 and non-Article 

5 countries (2007 Adjustment of the Montreal Protocol). The scenarios of UBA (2009) are based on 

more fundamental sector-specific growth rates and 

emissions factors for all relevant sectors in Article 5 

and non-Article 5 countries and take into account the 

accelerated HCFC phase-out schedules.

• The other class of scenarios is based on projections of 

technological developments affected by policy incentives and can therefore be seen as intervention scenarios. The discussions by the Parties of the Montreal 

Protocol to promote the use of HCFC alternatives that 

minimize the impact on climate can also be considered an intervention. An intervention scenario was 

developed for IPCC/TEAP (2005) and recently updated (TEAP, 2009), covering short time periods up to 

2015 and 2020, respectively. Others (Rao and Riahi, 

2006; Ottinger Schaefer et al., 2006; van Vuuren et al., 

2006) have reported HFC scenarios similar to those of 

SRES. Many of these latter scenarios have performed 

a relatively simple analysis to project future HFC 

emissions. Ottinger Schaefer et al. (2006) estimated 

HFC emissions through 2020 using a detailed sector 

analysis, but their analysis was performed before the 

2007 accelerated HCFC phase-out was adopted, and 

their 2008 HFC emissions do not agree with the emissions derived from observations.

The new scenarios constructed for IPCC, the Representative Concentration Pathways (RCPs), also contain 

HFC emissions, but use relatively simple or older analyses for the HFCs (Riahi and Nakicenovic, 2007; Clarke et 

al., 2007; Smith and Wigley, 2006; Wise et al., 2009; van 

Vuuren et al., 2006, 2007).

In Figure 5-5 global HFC emissions and radiative forcing are shown for six of the scenarios described 

above. The scenarios do not contain emissions from 

HFC-23, which is a by-product from the production of 

HCFC-22 and is not significantly used as a replacement 

for ODSs. HFC-23 emissions are estimated to be 0.20 ± 

0.03 GtCO2-eq yr−1 for 2006–2008 (Montzka et al., 2010), 

but are likely to decrease in the coming decade as a result 

of mitigation efforts for climate protection and because of 

projected decreases in HCFC-22 production. However, if 

mitigation is not successful, and unregulated production 

of HCFC-22 for use as a feedstock increases substantially, it is possible for HFC-23 emissions to increase in the 

future. The GWP-weighted HFC emissions are similar 

Table 5-5, continued (notes).

Notes:

a The “+” sign indicates more column ozone (i.e., less depletion) for the indicated policy option or activity; the “−” sign indicates less column ozone. b Understanding: “Low” indicates an inability to accurately quantify due to unknown or unquantifiable processes or emissions; “Medium” indicates 

remaining gaps in our understanding; “High” indicates that processes and values are believed to be well modeled and understood. c Approximate maximum impact: a relative scale that relates the various activities. This column is somewhat subjective and some of the entries depend 

strongly on the amount of future activity. Rocket emissions and aviation emissions have the potential to be important, given our current understanding, but specific information regarding flight altitude, number of flights, type of fuel, aerosol emissions, etc., needs to be specified before they can be 

usefully compared to the other ozone impacts. d The impacts of a reduction in N2O, CH4, and/or CO2 emissions will depend on the sizes of the reductions. Therefore, the “Approximate maximum 

impact” is somewhat more subjective than for the ODS phase-outs. e Circulation changes are expected to decrease (increase) total column ozone in the tropics (extratropics). See discussion in Chapter 3. f SRM stands for solid rocket motor.
5.28

Chapter 5

through about 2015 for all six scenarios. However, while 

the emissions of TEAP (2009) increase linearly through 

2020, the emissions of Velders et al. (2009) and UBA 

(2009) increase faster as a consequence of the growth 

rates in gross domestic product and the limits on consumption of HCFCs in Article 5 countries. By 2050, the 

total GWP-weighted HFC emissions are 5.5–8.8 GtCO2-

eq yr−1 in Velders et al. (2009) and 3.5 GtCO2-eq yr−1 in 

UBA (2009); both are significantly larger than those of 

SRES (1.3–2.3 GtCO2-eq yr−1) (IPCC, 2000). The HFC 

emissions in Velders et al. (2009) are about four times 

larger than those of SRES in 2050 for two principal reasons. First, the starting points (2008) for consumption of 

HFCs by Velders et al. (2009) are substantially higher than 

assumed in SRES, based on higher reported consumption 

of HCFCs from 2000 to 2007 (UNEP, 2009) than was 

assumed in SRES. Second, in the Velders et al. (2009) 

study, the HFCs assumed to meet future demand (HFC125 and HFC-143a) have larger GWPs than the HFCs 

assumed in SRES (mostly HFC-134a). This follows from 

assuming that the future use of HFCs in applications in 

developing countries will follow the same trends already 

observed in developed countries. The current consumption values for HFC-125 and HFC-143a are supported by 

their emissions as estimated from observed atmospheric 

mixing ratios and account for approximately 80% of the 

CO2-eq emission of HFCs in the year 2050. The lower 

emissions in the UBA (2009) scenarios compared with 

Velders et al. (2009) are the result of lower growth rates 

during 2020−2050 for the major HFC-consuming sectors 

and different replacement patterns for ODSs by HFCs and 

not-in-kind alternatives.

The current and expected future increased use of 

HFCs is largely the result of the phase-out of CFCs and 

HCFCs by the provisions of the Montreal Protocol, in 

combination with economic growth and an increase in 

living standards. As shown in Figure 5-6, total direct 

GWP-weighted emissions of ODSs peaked in 1988 at 

HFC Emissions

2000 2010 2020 2030 2040 2050

Year

0

2

4

6

8

10

Emissions (GtC

O2-eq yr

GWP-weighted (100-yr)

(excl. HFC-23)

Velders et al. (2009)

SRES (2000)

RCP (2009)

UBA (2009)

IPCC/TEAP(2005)

TEAP(2009)

HFC Radiative Forcing

2000 2010 2020 2030 2040 2050

Year

0.0

0.1

0.2

0.3

0.4

Radiative forcing (W 

m

Velders et al. (2009)

SRES (2000)

RCP (2009)

IPCC/TEAP(2005)

−1)

−2)

Figure 5-5. Global HFC emissions (left) and radiative forcing (right) in four long-term and two short-term scenarios. The long-term scenarios for the period 2000–2050 include the RCP scenarios and the non-intervention 

scenarios from Velders et al. (2009), UBA (2009), and SRES (IPCC, 2001). The short-term scenarios for the 

period 2000–2015/2020 include the IPCC-TEAP (2005) and TEAP (2009) scenarios. The RCP scenarios and 

the short-term scenarios assume intervention to mitigate climate forcing. Emissions of HFC-23, which is a 

by-product from the production of HCFC-22, are not included. HFC-23 emissions are estimated to be 0.20 ± 

0.03 GtCO2-eq yr−1 for 2006–2008 (Montzka et al., 2010). The emission values are multiplied by their GWPs 

(100-year time horizon) to obtain annual equivalent GtCO2 emissions. A GtCO2-eq equals 1000 million metric 

tons carbon dioxide equivalent (MMTCO2e). The color-shaded regions bound the upper and lower limits of the 

respective scenarios. Adapted from Velders et al. (2009).
5.29

A Focus on Information for Policymakers

9.4 GtCO2-eq yr−1 and decreased after that, whereas HFC 

emissions are projected to monotonically increase, primarily in Article 5 countries, exceeding those of ODSs 

after about 2020 in both Velders et al. (2009) and UBA 

(2009). In a business-as-usual scenario, starting in 1987, 

without Montreal Protocol regulations the GWP-weighted 

emissions of ODSs reach 15–18 GtCO2-eq yr−1 by 2010 

(Velders et al., 2007). So, growth in HFC use and emissions would offset at least part of the climate benefits calculated to have been achieved by the Montreal Protocol.

The HFC scenario results are further put into context by comparing to projected global CO2 emissions. 

Global annual HFC emissions in 2050 as projected by 

UBA (2009) and Velders et al. (2009) are equivalent 

(CO2-eq basis) to 6–8% and 9–19%, respectively, of projected global CO2 emissions in IPCC/SRES business-asusual scenarios (A1B, A2, B1, and B2) (Figure 5-6).

In these HFC scenarios, only the direct contribution to climate forcing due to ODS and HFC emissions 

is considered. Indirect climate forcings associated with 

0

1

2

3

4

Megatonnes per year

Mass-Weighted Emissions

Without Montreal Protocol

HFCs

ODSs

HCFCs

CFCs-only

Without accelerated

HCFC phaseout

high

low

0.0

0.5

1.0

1.5

2.0

Megatonnes CFC-11-eq per year

ODP-Weighted

Emissions

Without Montreal

Protocol

ODSs

HCFCs

CFCs, 

halons,

others

10

20

30

Gigatonnes CO2-eq per year

HFCs

ODSs

HCFCs

CFCs, halons, others

GWP-Weighted Emissions

Without Montreal Protocol

IPCC-SRES CO2 range

Magnitude of

Kyoto Protocol

reduction target

 2.0

high

low

1950 1970 1990 2010 2030 2050

Year

0

Figure 5-6. Emissions of ODSs (CFCs, halons, 

HCFCs, and others) and their non-ozone-depleting 

substitutes (HFCs) from 1950 to 2050 (adapted from 

Velders et al., 2007, 2009). Emissions are the total from developing and developed countries. The 

legends identify the specific compound classes included in each panel. The high and low HFC labels 

identify the upper and lower limits, respectively, in 

global baseline scenarios from Velders et al. (2009). 

The blue hatched regions indicate the emissions that 

would have occurred, in the absence of the Montreal 

Protocol, with 2–3% annual production increases 

in ODSs. Top panel: Global mass-weighted emissions expressed in megatonnes per year. The yellow 

dashed line shows HCFC emissions calculated without the provisions of the accelerated HCFC phaseout under the 2007 Adjustment of the Montreal Protocol. Middle panel: Global ODP-weighted emissions 

expressed in megatonnes of CFC-11-equivalent per 

year. The emissions of individual gases are multiplied 

by their respective ODPs (CFC-11 = 1) to obtain aggregate, equivalent CFC-11 emissions. The dashed 

line marks 1987, the year of the Montreal Protocol 

signing. Bottom panel: Global GWP-weighted emissions expressed in gigatonnes of CO2-equivalent per 

year. The emissions of individual gases are multiplied by their respective GWPs (direct, 100-year time 

horizon; CO2 = 1) to obtain aggregate, equivalent 

CO2 emissions. Shown for reference are emissions 

for the range of IPCC-SRES CO2 scenarios (IPCC, 

2000). The CO2 emissions for 1950–2007 are from 

global fossil fuel and cement production. Beyond 

2007, the shaded region for CO2 reflects the range 

bracketed by the A1B and B2 SRES scenarios. The 

dashed line denotes 2010, the middle year of the 

first commitment period of the Kyoto Protocol. Also 

shown 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 reduction target for participating countries.
5.30

Chapter 5

halocarbon usage arise from the energy used or saved during the application or product lifetime and energy required 

to manufacture the product, including the halocarbon used. 

For example, thermal insulating products in buildings and 

appliances reduce energy consumption, and refrigeration 

and AC systems consume energy over their lifetimes. A 

full evaluation of the total climate forcing resulting from 

the global transition away from CFCs and HCFCs toward 

HFCs requires consideration of both direct and indirect 

impacts over all associated halocarbon, non-halocarbon, 

and not-in-kind application lifecycles.

Three primary options are available to reduce the 

future climate impact of HFCs as demand continues to 

increase for products currently using HCFCs and HFCs: 

first is an increasing implementation of not-in-kind technologies (non-fluorocarbon based); second, use of HFCs 

that result in less energy used, because many products 

have significantly higher indirect climate impacts due 

to the energy used over the lifetime of the product than 

they do from emissions of the chemicals contained in the 

product; and third, lower-GWP HFC or other replacement chemicals could be used to satisfy demand. Figure 

5-7 shows steady-state radiative forcing resulting from a 

given annual emission rate for seven representative GWP 

limits on replacements. If the total 2050 HFC production projected in Velders et al. (2009) were to be met, for 

example, by HFCs with an average GWP less than 10 or 

100, and emissions are assumed to equal production, the 

steady-state globally averaged radiative forcing would be 

less than 0.003 or 0.03 W/m2

, respectively. These values 

are substantially smaller than the 0.25–0.4 W/m2 range estimated in the unmitigated case in Velders et al. (2009). 

This analysis assumes that even very short-lived HFCs 

can be considered to be well mixed. In reality, the globalmean lifetimes and radiative efficiencies of substances 

that are not well mixed will depend on the location of 

emission. There is currently not sufficient discussion of 

impacts of such short-lived substances on radiative forcing 

and climate in the literature to assess the significance of 

their inhomogeneous abundances on this type of analysis.

5.4.3.2 Other Replacements for ODSs

Unsaturated HFCs (also known as hydrofluoroolefins, HFOs), hydrofluoroketones and perfluoroketones, 

hydrofluoroethers (HFEs), perfluoropolyethers, ammonia, 

hydrocarbons and CO2 are either under consideration or 

in use as replacements for ODSs. The potential for these 

compounds to contribute to radiative forcing of climate 

is considered in this section (other potential environmental impacts are discussed in Section 5.4.4). Most of these 

compounds are short-lived, which limits their radiative 

forcing. See Chapter 1 for additional discussion of these 

compounds, and Tables 1-10 and 1-11 for a list of alternatives for ozone-depleting substances.

The reaction of hydroxyl radicals (OH) with unsaturated HFCs proceeds rapidly, and as a consequence, 

these unsaturated HFCs have atmospheric lifetimes that 

are in the range of 1–20 days. With such short lifetimes 

the contribution of unsaturated HFCs to radiative forcing 

will be small. For example, HFC-1234yf (CF3CF=CH2) 

has a GWP of approximately 4 (Nielsen et al., 2007; 

Papadimitriou et al., 2008b). HFC emissions are projected to be dominated by HFC-125 and HFC-143a and 

reach 3.5–8.8 GtCO2-eq yr−1 in 2050 (see Section 5.4.3.1). 

While substitution by unsaturated HFCs would reduce the 

Steady-State Radiative Forcing

100 1000 10000

Annual Emission (106 kg/yr)

10-5

10-4

10-3

10-2

10-1

Radiative Forcing (W/m2

)

Range of 2050 HFC Radiative Forcing from Velders et al. [2009] Peak CFC Production (1988)

Annual Unmitigated HFC Production Projected in 2050 from Velders et al.

GWP=1000

300

100

30

10

3

1

Figure 5-7. Relationship between annual emission rates and 

steady-state radiative forcing for 

compounds having seven different GWPs. Relationships are valid 

for compounds having lifetimes 

less than 20 years or so. For example, if 1 Tg/yr (109

 kg/yr) were 

emitted of a gas with a GWP of 1, 

the steady-state radiative forcing 

would be slightly less than 10−4 W/

m2. For comparison, the 2008 estimated radiative forcing from CO2, 

CH4, and N2O was 1.74, 0.5, and 

0.17 W/m2, respectively (http://

www.esrl.noaa.gov/gmd/aggi/).
5.31

A Focus on Information for Policymakers

contribution of HFCs to radiative forcing, a full life cycle 

analysis (including emissions associated with the energy 

usage by appliances using the different compounds and 

including an analysis of the production of trifluoroacetic 

acid (TFA) and tropospheric ozone) would be needed to 

assess the total systemic environmental impact.

The atmospheric removal mechanism for HFEs is 

reaction with OH radicals. These rate coefficients decrease with increasing degree of fluorination of the ether. 

As seen from Appendix Table 5A-1, highly fluorinated 

HFEs (e.g., CHF2OCF3) can have substantial atmospheric 

lifetimes and large GWPs. Also, as evident from Appendix Table 5A-1 and discussed in Chapter 1, HFEs bearing several hydrogen atoms (e.g., C2H5OC4F9) have short 

atmospheric lifetimes and small GWPs. The GWPs for 

HFEs thus span a large range, and it is not possible to 

make any general statement regarding the benefit of the 

substitution of HFCs by HFEs. The benefits need to be 

assessed on a case-by-case basis. Perfluoropolyethers are 

not reactive toward OH radicals, or any other oxidant species in the atmosphere, have atmospheric lifetimes probably in excess of 800 years (Young et al., 2006), and will 

have large GWPs. The volatility and magnitude of possible emissions need to be considered when assessing the 

potential environmental impact of perfluoropolyethers. 

Finally, we note that the atmospheric oxidation products 

of unsaturated HFCs (HFOs), HFEs, hydrofluoroketones, 

perfluoroketones, and perfluoropolyethers are COF2, 

HC(O)F, HF, and fluorinated carboxylic acids (Calvert et 

al., 2008; D’Anna et al., 2005; Good and Francisco, 2003; 

Taniguchi et al., 2003; Wallington et al., 1994). These 

products have short atmospheric lifetimes and are not expected to contribute to radiative forcing.

As for the HFCs (Section 5.4.3.1), a full evaluation of the total environmental effects resulting from the 

global transition away from CFCs and HCFCs toward the 

compounds discussed in this section or other compounds 

requires consideration of both direct and indirect environmental impacts over all associated halocarbon, nonhalocarbon, and not-in-kind application lifecycles.

5.4.4 Other Environmental Impacts

The potential exists for certain HCFCs, HFCs, 

HFEs, and unsaturated HFCs (HFOs) to contribute to tropospheric ozone formation, and degrade to give toxic compounds. The atmospheric degradation of HCFCs, HFCs, 

HFEs, and unsaturated HFCs is initiated by reaction with 

OH radicals leading to the formation of halogenated carbonyl compounds, which undergo further oxidation to HF, 

HCl, CO2, and, in some cases, trifluoroacetic acid (TFA) 

(see for example, IPCC/TEAP 2005; Calvert et al., 2008; 

Hurley et al., 2008; Nielsen et al., 2007; Papadimitriou et 

al., 2008b).

Hayman and Derwent (1997) assessed the potential contribution of HCFCs and HFCs to the formation of 

tropospheric ozone and concluded that these compounds 

do not have a large potential to contribute to ground-level 

ozone formation. As indicated from the lifetimes of the 

compounds listed in Appendix Table 5A-1, the reactivity of HFEs toward OH radicals is comparable to those of 

analogous HCFCs and HFCs. As with HCFCs and HFCs, 

HFEs are not expected to make a significant contribution 

to ground-level ozone formation. OH radicals react rapidly with >C=C< double bonds, and unsaturated HFCs 

are typically much more reactive than HCFCs, saturated 

HFCs, and HFEs. The photochemical ozone creation potential (POCP) concept is a well-established method of 

ranking compounds by their ability to form ozone in the 

troposphere. POCP values are determined along an idealized straight-line trajectory using a photochemical trajectory model. Using the approach outlined by Derwent et al. 

(1998) and Jenkin (1998), Wallington et al. (2010) have 

estimated POCPs for representative unsaturated HFCs. 

The results are presented in Table 5-6 together with values 

for selected alkanes, alkenes, and HFCs. As seen from this 

table, the POCPs for unsaturated HFCs (HFOs) are much 

larger than those for longer-lived HFCs, much smaller than 

those for the parent alkenes, and for many compounds (including the commercially significant HFC-1234yf) lie between those of methane and ethane. Methane and ethane 

are oxidized sufficiently slowly that they do not contribute 

to any appreciable degree to local air quality issues and are 

generally exempt from air quality regulations. Luecken 

et al. (2010) conducted an atmospheric modeling study 

of the impact of replacing all HFC-134a currently used in 

vehicle air conditioning systems in the USA with HFC1234yf. They concluded that such large-scale use of HFC1234yf would result in a less than 0.01% increase in total 

ozone formed. Thus, this study provides further support 

for the expectation that unsaturated HFCs from mobile air 

conditioning will not make a significant contribution to 

tropospheric ozone formation in the near future.

The formation of hydrogen fluoride (HF) and hydrogen chloride (HCl) from the degradation of these 

source gases also should be addressed. Assuming that the 

combined global emissions of HCFCs, HFCs, HFEs, and 

unsaturated HFCs (HFOs) are of the order of 100 kilotonnes (Kt) per year, that they are uniformly distributed in 

the atmosphere, and an annual global precipitation of 4.9 

× 1017 liters (Erchel, 1975), the concentrations of HF and 

HCl in precipitation from degradation of HCFCs, HFCs, 

HFEs, and HFOs will be of the order of 3 × 10−9 molar. 

Although HF and HCl are strong acids, the concentration of fluoride and chloride and the additional acidity 

in precipitation resulting from the atmospheric oxidation 

of HCFCs, HFCs (saturated and unsaturated), and HFEs 

would be minor.
5.32

Chapter 5

TFA is a persistent, potentially toxic degradation 

product of some HCFCs (e.g., HCFC-123, -124), HFCs 

(e.g., HFC-134a, -227ea), and unsaturated HFCs (e.g., 

-1234yf, -1225ye (CF3CF=CHF)). Its sources (natural 

and anthropogenic), sinks, and potential environmental effects have been reviewed by Tang et al. (1998), Solomon 

et al. (2003), and IPCC/TEAP (2005). In WMO (2007) it 

was concluded that “TFA from the degradation of HCFCs 

and HFCs will not result in environmental concentrations 

capable of significant ecosystem damage.” The available 

data suggest that the same conclusion is applicable to unsaturated HFCs and HFEs. It has been shown that TFA is 

ubiquitous in precipitation and ocean water even in remote 

areas (Berg et al., 2000; Frank et al., 2002; Scott et al., 

2005; Scott et al., 2006; Von Sydow et al., 2000). Frank 

et al. (2002) estimated that the oceans contain 268 million 

tonnes of TFA. At a global level, the natural environmental loading of TFA greatly exceeds that expected from the 

atmospheric degradation of HCFCs, HFCs, and unsaturated HFCs (Kotamarthi et al., 1998). While Tromp et al. 

(1995) have argued that TFA will accumulate to high levels in seasonal wetlands, Boutonnet et al. (1999) showed 

that the assumptions made by Tromp et al. were highly improbable. Benesch et al. (2002) showed that TFA does not 

adversely affect the development of soil microbial communities and pool plant species in vernal ponds. Luecken 

et al. (2010) assessed the TFA concentrations following 

replacement of all HFC-134a currently used in vehicle air 

conditioning systems in the USA with HFC-1234yf. Their 

model predicted peak concentrations in rainfall of 1264 

nanograms per liter. This level is similar to peak concentrations currently observed (Scott et al., 2006) and is approximately two orders of magnitude lower than the level 

considered safe for the most sensitive aquatic organisms 

(Luecken et al., 2010). See also Section 1.3.6.3 of Chapter 

1 for a discussion on HFC-1234yf. Chapter 1 also discusses our current understanding of the sources of TFA. A 

current gap in our understanding is the lack of information 

concerning the natural sources and loss processes of TFA. 

This gap limits our ability to provide a precise assessment 

of the role of human activities in affecting local or regional 

abundances of TFA.

In summary, HCFCs, HFCs, HFEs, and HFOs are 

not expected to contribute significantly to the formation of 

tropospheric ozone. In the concentrations expected in the 

environment in the near future, the degradation products 

of HCFCs, HFCs (saturated and unsaturated), and HFEs 

are not expected to be toxic. However, for thorough understanding of the environmental impacts of replacements 

for CFCs, HCFCs, and long-lived HFCs, an evaluation of 

the ODPs, GWPs, atmospheric fate, safety, and toxicity is 

required for each replacement.

5.4.5 Impact of 2007 Accelerated 

HCFC Phase-Out

In 2007 the Parties to the Montreal Protocol adjusted the Protocol by accelerating the HCFC phase-out 

to protect the ozone layer and, in part, to further protect 

future climate. HCFC consumption in Article 5 countries 

will be frozen in 2013 and stepwise reduced, with a virtually complete phase-out in 2030. Before the 2007 Adjustment, a freeze in consumption was in place for Article 5 

countries starting in 2016 with a complete phase-out in 

2040. Non-Article 5 countries have agreed to a virtually 

Table 5-6. Photochemical ozone creation potentials (POCPs) for selected hydrofluoro-olefins 

and related alkanes, alkenes, and hydrofluorocarbons.

Compound Industrial or

Common Name POCP

CH2=CH2 ethylene; ethene 100 a

CH2=CF2 1,1 difluoroethylene;

HFO-1132a

18.0 b

CF2=CF2 Perfluoroethylene; 

HFO-1114

12.5 b

CH3CH=CH2 propylene; propene 117 c

CH2=CHCF3 HFO-1243zf 10.7 b

CH2=CFCF3 HFO-1234yf 7.0 b

(Z)-CHF=CFCF3 HFO-1225ye(Z) 5.6 b

CF2=CFCF3 Perfluoropropylene; 

HFO-1216

5.4 b

CH3CH2CH=CH2 1-butene 104 c

CH2=CHCF2CF3 HFO-1345czf 6.6 b

CH4 methane 0.6 d

CH2F2 HFC-32 0.2 e

C2H6 ethane 8 c

CH3CHF2 HFC-152a 1.0 e

CH3CF3 HFC-143a 0.0 e

CH2FCF3 HFC-134a 0.1 e

C3H8 propane 14 c

CH2FCHFCF3 HFC-245eb 0.2 b

CHF2CHFCF3 HFC-236ea 0.0 b

CF3CHFCF3 HFC-227ea 0.0 e

n-C4H10 butane 31 c

a By definition. b Wallington et al. (2010). c Derwent et al. (2007). d Derwent et al. (1998). e Hayman and Derwent (1997).
5.33

A Focus on Information for Policymakers

complete phase-out in 2020. The Adjustment also slightly 

changed the phase-out schedule for non-Article 5 countries, increasing the interim reduction during 2010 through 

2014 from 65% to 75% below the baseline level.

The accelerated HCFC phase-out has beneficial implications for the ozone layer and does have the potential 

to reduce climate forcing. It is expected to cause a reduction in cumulative HCFC emissions, relative to the current 

baseline scenario of this chapter, of 11−14 megatonnes 

(Mt) for the period 2011−2050, or an ODP-weighted 

equivalence of 0.6−0.8 MtCFC-11-eq (Figure 5-6). Following the same methods of calculating mixing ratios and 

EESC as described in Section 5.2, this emission reduction 

accelerates the projected return of EESC to 1980 levels by 

4−5 years. The resulting percentage reduction in EESC, 

integrated from 2011 until the 1980 level is reattained, is 

10−12%, which is larger than any of the hypothetical zeroproduction cases discussed in Section 5.4.3.1.

In adopting the accelerated HCFC phase-out, the 

Parties agreed to promote the use of HCFC alternatives 

that minimize the impact on climate and other environmental effects. The evaluation of the impact of a replacement of HCFCs with HFCs and other compounds requires 

consideration of both direct and indirect impacts, such 

as due to changes in energy usage associated with a particular replacement, over all associated halocarbon and 

not-in-kind application lifecycles. However, estimating 

all indirect impacts is extremely difficult. If only direct 

contributions are considered, the HCFC cumulative emissions reduction attributable to the accelerated phase-out 

is, in terms of climate forcing and relative to the current 

baseline, estimated to be 0.4−0.6 GtCO2-eq yr−1 averaged 

over 2011 through 2050. In comparison, global anthropogenic emissions of CO2 were greater than 30 Gt per year in 

2008. Not-in-kind alternative technologies (such as Stirling cycles, mineral wool, thermoacoustic refrigeration) 

are expected to only play a minor replacement role for the 

HCFCs. Therefore, to realize most of this forcing reduction, the avoided HCFC consumption and emissions must 

be replaced by alternative compounds with small GWPs 

(e.g., ammonia, hydrocarbons, CO2, low-GWP HFCs).

In addition to these potential benefits of the accelerated HCFC phase-out, there is also a climate benefit from 

the reduction in HFC-23 by-product emissions resulting 

from reduced HCFC-22 production. 

5.5 THE WORLD AVOIDED BY OZONE POLICY

The success of the Montreal Protocol and its subsequent Amendments and Adjustments (Andersen and 

Sarma, 2002; UNEP, 2009) is evident from the large 

decreases in the production of ODSs since their peak at the 

end of the 1980s, from the large decreases in emissions, and 

from decreases in midlatitude EESC since the middle of 

the 1990s that are expected to continue throughout the 21st

century. The success becomes even more striking when 

comparing current projections of production, emissions, 

and mixing ratios of ODSs and of the ozone layer with 

what might have happened without the Montreal Protocol. 

Scenarios generated to explore what might have occurred 

in the absence of ozone mitigation policies have been 

sometimes referred to as the “road not taken” or “world 

avoided” scenarios. The studies discussed in Section 5.5.3, 

made possible by the recent progress in chemistry-climate 

modeling (CCM), demonstrate the considerable damage 

mankind could have inflicted upon the Earth System in the 

space of just a few decades, and the benefit of the Montreal 

Protocol for both the ozone layer and climate.

ODSs affect the climate system both as greenhouse 

gases and indirectly through their effect on ozone. Both 

mechanisms are discussed below, starting with a discussion of ODS emission scenarios in a “World Avoided” by 

the Montreal Protocol.

5.5.1 ODS Production

An assessment of how ODS mitigation policies 

have affected climate and the ozone layer first requires 

establishing alternative scenarios of ODS production and 

emission. These scenarios are based on various reasonable assumptions about what might have happened in the 

absence of a policy response to scientific advances regarding the environmental impact of halocarbons, and about 

rates of emissions growth in such non-intervention scenarios. For example, two of the different scenarios that 

have been considered follow from the assumptions that (1) 

early warnings of dangers posed by CFCs to the ozone 

layer (Molina and Rowland, 1974) would have been ignored or would not have existed (referred to here as the 

MR74 scenario), and (2) that the Montreal Protocol was 

not implemented (NMP87 scenario) (Velders et al., 2007). 

Although negotiations about limiting the emissions of 

ODSs had started prior to the discovery of the ozone hole 

(Farman et al., 1985; Chubachi and Kajiwara, 1986), a 

failure to detect polar ozone depletion or to link it to CFCs 

would likely have led to the adoption of weaker controls, 

particularly in subsequent negotiations that tightened the 

initial measures following dissemination of the results 

attributing the Antarctic losses to halocarbons (Parson, 

2003). Prather et al. (1996) developed a scenario similar to MR74 assuming business-as-usual market-driven 

growth of CFC production after 1974. Under that scenario, although the ozone hole would have been detected, ozone science would have been delayed by around a 

decade. The mechanism of ozone depletion would have 

been established later, and emissions would have kept 

rising at 6% per year, with new uses for CFCs being introduced, until with a delay of 10 years ODS mitigation 
5.34

Chapter 5

policies would have been introduced. In this scenario, the 

tropospheric abundance of total chlorine would rise to 9 

parts per billion (ppb) by 2002 before mitigation policies 

took effect to reduce atmospheric abundances of chlorine. The Velders et al. (2007) MR74 scenario does not 

include mitigation. The second scenario from Velders et 

al. (2007), NMP87, is more conservative than MR74 and 

assumes CFC production would grow in proportion to the 

economy after 1987 (a characteristic of mature markets), 

with growth rates of 2−3%/year. Figure 5-8 summarizes the various World Avoided scenarios. Before 1987, 

NMP87 follows the observed chlorine abundance. Figure 

5-6 shows the global emissions of ODSs and HFCs from 

1950 to 2050 weighted by mass, ODPs, and GWPs for the 

baseline scenario and for the NMP87 scenario (Velders 

et al., 2007, 2009). Each of these scenarios results in a 

greatly enhanced stratospheric halogen loading compared 

to what has actually occurred.

5.5.2 Radiative Forcing

The radiative forcing (RF) potential of CFCs is well 

established, as was highlighted in WMO (1986). Velders 

et al. (2007) calculated the radiative forcing for the MR74 

and NMP87 scenarios introduced above, and for the actual 

and projected emissions of all ODSs (Table 5-7). For 

present-day abundances, the RF associated with halocarbons is around 0.3 W/m2

 or approximately 18% of that of 

CO2 (IPCC, 2007). Under the MR74 scenario, by 2010 the 

radiative forcing due to all ODS would contribute 44% to 

89% as much to global warming as CO2. Under NMP87, 

in 2010 the RF associated with ODSs would amount to 

about one-third of that of CO2. Even under this more conservative scenario, the RF increase due to ODSs between 

1988 and 2010 would be at least 0.34 W/m2, which is substantial compared to the increase in RF due to CO2 of 0.55 

W/m2 that has been experienced over that period.

The ODS forcing results should be adjusted for (a) 

the likely negative radiative forcings associated with ozone 

depletion caused by the ODS emissions (IPCC, 2007), and 

(b) the reduced emissions of replacement products that 

would not be needed without the mandated ODS reductions. 

HFCs are examples of replacement compounds; their usage 

is projected to grow sharply as a side effect of the Montreal 

Protocol (Figure 5-6), with potentially large increases in 

associated RF of up to 0.4 W/m2

 in non-intervention scenarios by 2050 (Velders et al., 2009). Although the ODS 

emissions under a no-Montreal Protocol scenario (NMP87) 

would have a considerably larger radiative forcing, continuing unmitigated emissions of high-GWP HFCs could 

1960 1970 1980 1990 2000 2010 2020

Year

0.0

0.2

0.4

0.6

0.8

1.0

Mixing ratio (ppb)

Mixing ratio

CFC-11

CFC-12

MR74

NMP87

Baseline

1960 1980 2000 2020 2040 2060 2080 2100

Year

0

2

4

6

8

Tropospheric Chlorine (ppb)

Tropospheric Cl

MR74

NMP87

Baseline

Road-not-taken

Figure 5-8. Left panel: Total chlorine from the baseline scenario (black) compared with three “World Avoided” 

scenarios. The “Road-not-taken” scenario is from Prather et al. (1996) and includes only the portion of the “Free 

Market” curve (described in that study) before controls were implemented. The MR74 and NMP87 scenarios are 

derived from Velders et al. (2007). Right panel: Tropospheric mixing ratios of the most significant CFCs under 

the MR74 (green) (no identification of the link between CFCs and ozone in 1974 by Molina and Rowland (1974)) 

and the NMP87 (blue) (no Montreal Protocol restrictions) scenarios; and as observed and assuming compliance 

with the fully amended and adjusted Montreal Protocol (black). (From Velders et al., 2007).
5.35

A Focus on Information for Policymakers

nonetheless substantially offset the effects of other greenhouse gas mitigation efforts. See Section 5.4.2.1 for more 

details regarding future HFC emissions. The combined 

effects of ozone depletion and enhanced HFC emissions 

are estimated to offset about 30% of the radiative forcing 

avoided by the ODSs phased out under the Montreal Protocol by 2010 (Velders et al., 2007).

In comparing the benefits of the Montreal and Kyoto Protocols for climate, one also needs to assume that if 

the Montreal Protocol did not exist, the ODSs would almost certainly have been included in the Kyoto Protocol 

because of the ODSs’ considerable GWPs. However, this 

would have likely resulted in a delay in implementing controls similar to the one described by Prather et al. (1996), 

and could have led to unmitigated growth of CFCs lasting 

longer than what actually occurred.

Even allowing for these offsetting effects, Velders 

et al. (2007) note that actions taken under the Montreal 

Protocol have been of considerably greater benefit to climate than the reduction target of the first commitment 

period (2008−2012) of the Kyoto Protocol (Figure 5-6). 

The annual ODS emission reduction resulting from the 

Montreal Protocol is estimated to be 10 to 12 GtCO2-eq 

yr−1 by 2010, or 5 to 6 times the Kyoto Protocol reduction target. In making this comparison, it is acknowledged 

that the Kyoto Protocol does not include anthropogenic 

halocarbons because these substances had previously been 

regulated by the Montreal Protocol. Also unlike the Kyoto 

Protocol, the Montreal Protocol has gone through a series 

of Amendments and Adjustments that have led to further 

emission reductions. The Kyoto Protocol has not yet gone 

through this process. The first commitment period aims 

for an overall reduction, relative to 1990 levels, of 5.2% 

of CO2-equivalent greenhouse gas emissions in Annex 1 

countries. A proposed target for 2050 aims for 80% emission reductions, relative to 1990. Even compared to this 

much more ambitious target, the climate benefit of the 

Montreal Protocol calculated to date is significant.

5.5.3 Climate and Ozone Impacts Avoided 

by the Montreal Protocol

Prather et al. (1996) also estimated the consequences to ozone of unmitigated halocarbon emissions 

growth. Using a 2-D model, they calculated a 10% loss of 

extrapolar, annual-mean ozone by 1998, relative to 1980. 

More recently, Morgenstern et al. (2008) and Newman et 

al. (2009) assessed the impact of a continuing increase of 

chlorine in the atmosphere on both ozone depletion and 

climate. By using comprehensive CCMs, these are the 

first studies to examine the atmospheric structural and dynamical response to highly elevated chlorine. Both studies demonstrate the substantial changes that would likely 

have occurred if it were not for the Montreal Protocol.

Morgenstern et al. (2008) compare climate under a 

9 ppb total chlorine loading—the peak chlorine abundance 

projected in the Prather et al. (1996) scenario in about 

2002—to the actual peak chlorine loading of around 3.5 

ppb, which occurred in the late 1990s. In designing their 

calculations, they deliberately exclude the direct radiative 

effect of the CFC increases (the main topic of Velders et 

al., 2007) to focus exclusively on ozone changes and their 

climate impacts. The additional chlorine leads to a reduction of total ozone everywhere in their model (Morgenstern 

et al., 2009), with losses ranging from about 5% in the 

tropics to 20−30% in Arctic and over 50% in Antarctic 

spring; the average ozone loss between 60°S and 60°N in 

their model amounts to 8.3%. This is slightly less than 

estimated by Prather et al. (1996) for a somewhat lower 

chlorine abundance. The losses peak in three regions, 

namely in the chlorine layer around 40 km associated with 

gas-phase catalytic ozone destruction (Molina and Rowland, 1974), and at both high-latitude regions around 20 

km, associated with heterogeneous polar processes. The 

ozone loss has a considerable impact on stratospheric temperatures, with the upper stratosphere cooling by up to 6 K, 

and a few degrees cooling in the lower stratosphere with 

warming above it associated with a change in upwelling 

of 9.6 μm radiation due to the ozone loss. Morgenstern et 

al. (2008) also find substantial extratropical near-surface 

regional climate change. At southern high latitudes, they 

find a surface warming of up to 3 K in spring in the lee of 

the Antarctic Peninsula, and cooling in parts of Western 

and Eastern Antarctica (Figure 5-9); these calculations are 

qualitatively consistent with observations in recent decades 

(leading for example to the collapse of the Larsen B ice 

shelf; MacAyeal et al., 2003). Morgenstern et al. (2008) 

associate the climate change found in their model simulations with a further strengthening of the Southern Annular 

Table 5-7. Direct radiative forcing (W/m2

) of controlled ODSs and CO2 (Velders et al., 2007; IPCC, 

2001; IPCC, 2007). For comparison: in 2008, CH4

and N2O were responsible for a direct radiative forcing of 0.50, and 0.17 W/m2

, respectively (www.esrl.

noaa.gov/gmd/aggi/).

Scenario 1975 1988 2010

ODS Baseline 0.12 0.26 0.32

ODS MR74 a 0.12 0.30–0.34 0.8–1.6

ODS NMP87 b 0.12 0.26 0.60–0.65

CO2 0.94 1.25 1.78–1.82

a Scenario in which the early warnings of dangers posed by CFCs to 

the ozone layer (Molina and Rowland, 1974) were ignored or did not 

exist.

b Scenario in which the Montreal Protocol was not implemented (“no 

Montreal Protocol”).
5.36

Chapter 5

Mode (SAM), the leading mode of variability of the southern extratropics, as has been observed during the period of 

historic ozone depletion (Thompson and Solomon, 2002; 

Fogt et al., 2009). For the Northern Hemisphere, their 

model produces substantial cooling in winter over Northern Asia and Western Europe, and warming over Northern 

North America and Greenland. Morgenstern et al. (2008) 

calculate a radiative forcing associated with the ozone depletion of –0.05 W/m2

, which, in absolute terms, is at least 

an order of magnitude less than the direct radiative forcing 

associated with the increased ODSs (Velders et al., 2007). 

However, they note that regional climate change due to 

the additional ozone depletion, over Antarctica and the 

northern continents, is large compared to recent observed 

climate changes.

In assessing these regional climate impacts, one 

needs to consider that the skill of climate models in representing regional climate trends on decadal timescales is 

often low, particularly in the Northern Hemisphere (e.g., 

Figure TS.24 of IPCC, 2007). In the Northern Hemisphere, 

atmosphere-ocean global circulation models (AOGCMs) 

typically disagree on basic patterns of climate change, both 

among each other and compared with observations (e.g., 

Gillett, 2005). At southern high latitudes, climate models 

are somewhat more successful in representing patterns of 

climate change (e.g., Gillett and Thompson, 2003). The 

projection by Morgenstern et al. (2008) appears plausible 

when comparing the patterns of the results to past climate 

changes in the Antarctic region. For the Northern Hemisphere, it is likely that ozone depletion would have led to 

substantial regional climate change, but the geographical 

pattern of change remains poorly understood.

Newman et al. (2009) perform and evaluate a 

transient simulation using the Goddard Earth Observing 

System Chemistry Climate Model (GEOSCCM) model 

(Pawson et al., 2008) in which EESC follows the MR74 

scenario of Velders et al. (2007) with an assumed growth 

rate of 3% per year, leading to 9 ppb in 2019. They terminate their simulation in 2065 when EESC reaches 45 ppb. 

Other greenhouse gases follow the IPCC (2000) A1B scenario. In their simulation, such drastic increases of ODSs 

completely alter the structure of the stratosphere. Total 

global ozone drops by two-thirds during the course of the 

simulation; the loss is approximately linear in EESC. The 

ozone loss produced by Newman et al. (2009) is similar to 

that of Prather et al. (1996) for similar chlorine loading, 

although a strict comparison is complicated by Newman et 

al. (2009) displaying ozone loss as a function of equivalent 

effective chlorine and Prather et al. (1996) using actual 

chlorine. The changes found by Newman et al. (2009) 

are initially largely driven by high-latitude ozone loss 

(Figure 5-10). In around 2020 in the simulation, Arctic 

ozone in April drops below 220 Dobson units (DU) and 

would thus satisfy a common definition of an Arctic ozone 

hole. By 2060, Arctic ozone in the simulation drops below 

100 DU in spring. There is a progressive deepening and 

lengthening of the lifetime of the Antarctic polar vortex in 

the simulation, eventually leading to a year-round ozone 

hole with westerlies in the southern mid- and high-latitude 

stratosphere. Newman et al. (2009) refer to this as the 

“perpetual winter.” At the end of the simulation, minimum 

ozone columns reach about 50 DU over Antarctica. After 

about 2045 in the simulation, enhanced upwelling cools 

the tropical lower stratosphere and triggers heterogeneous 

chemical processes similar to those currently observed in 

the Antarctic ozone hole. In the simulation, this leads to 

precipitous ozone depletion and nearly complete ozone 

loss in the tropical lower stratosphere by 2058. Newman 

et al. (2009) compare their results to complementary simulations assuming ODS abundances fixed at 1960 levels or 

following the A1 scenario (WMO, 2007) to demonstrate 

the effect of mitigating ODS emissions when the reference 

scenario has such dramatic chlorine increases.

Both Morgenstern et al. (2008) and Newman et al. 

(2009) exclude certain feedbacks that would have otherwise affected their results. In both studies, climate change 

due to ozone loss is not allowed to affect ocean conditions, 

which can have impacts that extend into the middle atmosphere (Kodama et al., 2007). In Newman et al. (2009), the 

direct RF due to the increasing ODSs (Velders et al., 2007) 

−3 −2 −1.5 −1 −0.5 0 0.5 1 1.5 2 3

SON

Temperature (°C)

Figure 5-9. Difference between the 9 and 3.5 ppb 

total chlorine cases in Antarctic spring (September–

November) temperature (°C) 20 m above the surface. (From Morgenstern et al., 2008).
5.37

A Focus on Information for Policymakers

is also not reflected in the ocean conditions; Morgenstern 

et al. (2008) exclude this effect by keeping the ODSs 

the same for radiation as in their reference simulation. 

Newman et al. (2009) prescribe tropospheric ozone and 

thus suppress feedback effects on tropospheric chemistry 

(e.g., tropospheric ozone production or loss caused by the 

increasing ultraviolet (UV) radiation). Morgenstern et al. 

(2008) use photolysis rates in the troposphere that do not 

reflect changes to the ozone column, thus also not allowing for such feedbacks. However, substantial decreases of 

tropospheric ozone do occur in Morgenstern et al. (2008) 

due to a decreased influx of stratospheric ozone. Further 

feedbacks not correctly treated in the simulations relate to a 

shortening of lifetimes of ODSs and long-lived greenhouse 

gases in the World Avoided simulations. Such shortening could occur from increased actinic fluxes and an acceleration of the Brewer-Dobson circulation, and would 

cause increasing emissions of ODSs to lead to less-thanproportional increases in their atmospheric abundances.

5.5.4 UV Impacts of the Avoided 

Ozone Depletion

The decreases in ozone abundances in the World 

Avoided simulations (Prather et al., 1996; Morgenstern 

et al., 2008; Newman et al., 2009) would have led to an 

increase in solar ultraviolet radiation at Earth’s surface. 

The magnitude of these increases varies with wavelength, 

depending on the absorption cross section of ozone, and 

with latitude, according to the latitudinal distribution 

of ozone depletion. Newman et al. (2009) calculate the 

spectral changes in UV occurring in their simulation. At 

the shortest UV-B wavelengths, in relative terms, the 

calculated changes are extremely large; however, in absolute terms the surface irradiance at these wavelengths 

is weak. Regarding biologically relevant radiation, they 

show that decreases in stratospheric ozone due to increasing CFCs would have led to marked increases in erythemally weighted irradiance (which is proportional to the 

UV Index; Chapter 2), up to three times more in the summer of northern midlatitudes by 2065 (Figure 5-11), and 

with UV Index values in excess of 30 at midlatitudes of 

both hemispheres. The excess radiation would have had 

large impacts on the biosphere and on human health; for 

example, Northern Hemisphere midlatitude ozone losses 

would have led to a reduction of the sunburn time, at local 

noon for clear-sky midsummer conditions, from 15 to 5 

minutes, and would increase DNA-damaging UV by approximately 550% between 1980 and 2065 (Newman et 

al., 2009).

5.5.5 Summary

“Road not taken” or “World Avoided” studies indicate that the Montreal Protocol has had considerable 

benefits for both the ozone layer and climate change. 

Total chlorine would have increased much beyond the 

observed peak of around 3.5 ppb. Consequences of uncontrolled growth in ODSs would have resulted both directly from the radiative forcing of the halocarbons, and 

indirectly from the ensuing ozone depletion. In 2010, the 

-90 -60 -30 0 30 60 90

Latitude

0

100

200

300

400

500

Total Ozone (DU)

2065

2040

2020

2000

fixed Cl (1970)

baseline (1970)

baseline (2000)

2052

WORLD AVOIDED

Figure 5-10. Zonal-mean 

total ozone in the World 

Avoided simulation (black), 

in 1970 for chlorine fixed at 

1960 levels (green), and for 

a baseline scenario simulation in 1970 (blue) and 2000 

(red). (Adapted from Newman et al., 2009).
5.38

Chapter 5

RF associated with unmitigated emissions of halocarbons 

could have reached 2 to 5 times what has actually occurred. 

The chemical consequences could have included a thinned 

ozone layer everywhere on the globe, the occurrence of an 

Arctic ozone hole, regional climate change in middle and 

high latitudes of both hemispheres, increased UV with associated biological and medical consequences, and changes in stratospheric circulation including, in an extreme 

case, year-round westerlies in the Southern-Hemisphere 

stratosphere (the “perpetual winter”). While many details 

associated with these calculated World Avoided impacts 

may have large uncertainties associated with them, there 

is no doubt that the Montreal Protocol and its Amendments and Adjustments have avoided additional profound 

changes to stratospheric ozone and climate.

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5.47

A Focus on Information for Policymakers

Table 5A-1. Direct Global Warming Potentials for selected gases.

Industrial

Designation or

Common Name

Chemical Formula Radiative

Efficiency a

(W m−2 ppb−1)

Lifetime b

(years)

Global Warming Potential for

Given Time Horizon

20 years 100 years 500 years

Carbon dioxide CO2 1.38×10−5 c 1 1 1

Nitrous oxide N2O 3.03×10−3 114 289 298 153

Chlorofluorocarbons

CFC-11 CCl3F 0.25 45 6,730 4,750 1,620

CFC-12 CCl2F2 0.32 100 11,000 10,900 5,200

CFC-13 CClF3 0.25 640 10,800 14,400 16,400

CFC-113 CCl2FCClF2 0.30 85 6,540 6,130 2,690

CFC-114 CClF2CClF2 0.31 190 7,890 9,180 6,330

CFC-115 CClF2CF3 0.18 1,020 5,290 7,230 9,120

Hydrochlorofluorocarbons

HCFC-21 CHCl2F 0.14 1.7 530 151 46

HCFC-22 CHClF2 0.20 11.9 5,130 1,790 545

HCFC-123 CHCl2CF3 0.14 1.3 273 77 24

HCFC-124 CHClFCF3 0.22 5.9 2,110 619 188

HCFC-141b CH3CCl2F 0.14 9.2 2,240 717 218

HCFC-142b CH3CClF2 0.20 17.2 5,390 2,220 678

HCFC-225ca CHCl2CF2CF3 0.20 1.9 429 122 37

HCFC-225cb CHClFCF2CClF2 0.32 5.9 2,060 606 184

Hydrofluorocarbons

HFC-23 CHF3 0.19 222.0 11,900 14,200 10,700

HFC-32 CH2F2 0.11 5.2 2,470 716 218

HFC-41 CH3F 0.02 2.8 377 107 33

HFC-125 CHF2CF3 0.23 28.2 6,290 3,420 1,070

HFC-134 CHF2CHF2 0.18 9.7 3,420 1,110 339

HFC-134a CH2FCF3 0.16 13.4 3,730 1,370 416

HFC-143 CH2FCHF2 0.13 3.5 1,240 352 107

HFC-143a CH3CF3 0.13 47.1 5,780 4,180 1,440

HFC-152a CH3CHF2 0.09 1.5 468 133 40

HFC-227ea CF3CHFCF3 0.26 38.9 5,480 3,580 1,180

HFC-236cb CH2FCF2CF3 0.23 13.1 3,560 1,290 392

Appendix 5A

TABLES
5.48

Chapter 5

Industrial

Designation or

Common Name

Chemical Formula Radiative

Efficiency a

(W m−2 ppb−1)

Lifetime b

(years)

Global Warming Potential for

Given Time Horizon

20 years 100 years 500 years

HFC-236ea CHF2CHFCF3 0.30 11.0 4,170 1,410 430

HFC-236fa CF3CH2CF3 0.28 242.0 8,100 9,820 7,710

HFC-245ca CH2FCF2CHF2 0.23 6.5 2,440 726 221

HFC-245ea CHF2CHFCHF2 0.18 d 3.2 983 280 85

HFC-245eb CH2FCHFCF3 0.23 d 3.1 1,220 346 105

HFC-245fa CHF2CH2CF3 0.28 7.7 3,410 1,050 318

HFC-263fb CH3CH2CF3 0.13 d 1.2 365 104 31

HFC-329p CHF2CF2CF2CF3 0.31 d 28.4 4,640 2,530 792

HFC-365mfc CH3CF2CH2CF3 0.22 d 8.7 2,670 842 256

HFC-43-10mee CF3CHFCHFCF2CF3 0.40 16.1 4,170 1,660 506

Chlorocarbons

Methyl chloroform CH3CCl3 0.06 5.0 506 146 45

Carbon tetrachloride CCl4 0.13 26.0 2,700 1,400 435

Methyl chloride CH3Cl 0.01 1.0 45 13 4

Bromocarbons and Halons

Methyl bromide CH3Br 0.01 0.8 19 5 2

Bromodifluoromethane CHBrF2 0.14 5.2 1,250 362 110

Halon-1211 CBrClF2 0.30 16.0 4,750 1,890 575

Halon-1301 CBrF3 0.32 65.0 8,480 7,140 2,760

Halon-2402 CBrF2CBrF2 0.33 20.0 3,680 1,640 503

Fully Fluorinated Species

Nitrogen trifluoride NF3 0.21 500 13,300 17,500 18,500

Sulfur hexafluoride SF6 0.52 3,200 16,300 22,800 32,600

TrifluoromethylsulfurpentafluorideSF5CF3 0.57 800 e 13,200 17,800 21,400

Perfluoromethane CF4 0.10 50,000 5,210 7,390 11,200

Perfluoroethane C2F6 0.26 10,000 8,630 12,200 18,200

Perfluoropropane C3F8 0.26 2,600 6,310 8,830 12,500

Perfluorocyclopropane c-C3F6 0.42 ~3,000 12,800 17,900 25,500

Perfluorobutane C4F10 0.33 2,600 6,330 8,850 12,500

Perfluorocyclobutane c-C4F8 0.32 3,200 7,310 10,300 14,700

Perfluoropentane C5F12 0.41 4,100 6,510 9,150 13,300

Perfluorohexane C6F14 0.49 3,100 6,620 9,290 13,300

Perfluorodecalin C10F18 0.56 ~2,000 5,530 7,700 10,600

Table 5A-1, continued.
5.49

A Focus on Information for Policymakers

Table 5A-1, continued.

Industrial

Designation or

Common Name

Chemical Formula Radiative

Efficiency a

(W m−2 ppb−1)

Lifetime b

(years)

Global Warming Potential for

Given Time Horizon

20 years 100 years 500 years

Halogenated Alcohols and Ethers

HFE-125 CHF2OCF3 0.44 119.0 13,700 14,200 7,510

HFE-134 CHF2OCHF2 0.45 24.4 11,930 5,960 1,840

HFE-143a CH3OCF3 0.27 4.8 2,920 840 256

HFE-227ea CF3OCHFCF3 0.40 51.6 8,170 6,180 2,200

HFCE-235da2 

(isoflurane) CHF2OCHClCF3 0.38 3.5 1,650 470 143

HFE-236ea2

(desflurane)

CHF2OCHFCF3 0.44 10.8 5,460 1,840 560

HFE-236fa CF3OCH2CF3 0.34 7.5 3,240 988 300

HFE-245cb2 CH3OCF2CF3 0.32 4.9 2,350 680 207

HFE-245fa1 CF3OCH2CHF2 0.30 6.6 2,880 859 261

HFE-245fa2 CHF2OCH2CF3 0.31 5.5 2,540 740 225

HFE-254cb2 CH3OCF2CHF2 0.28 2.5 1,210 345 105

HFE-329mcc2 CF3CF2OCF2CHF2 0.49 22.5 6,300 3,000 925

HFE-338mcf2 CF3CF2OCH2CF3 0.43 7.5 3,150 963 293

HFE-347mcc3 CF3CF2CF2OCH3 0.34 5.0 1,910 553 168

HFE-347mcf2 CF3CF2OCH2CHF2 0.41 6.6 2,950 881 268

HFE-356mec3 CF3CHFCF2OCH3 0.30 3.8 1,430 408 124

HFE-356pcf2 CHF2CF2OCH2CHF2 0.37 5.7 2,580 754 229

HFE-356pcf3 CHF2CF2CH2OCHF2 0.39 3.5 1,710 488 148

HFE-356pcc3 CHF2CF2CF2OCH3 0.33 3.8 1,570 448 136

(CF3)2CHOCHF2 0.41 21.2 5,580 2,570 789

(CF3)2CFOCH3 0.31 3.7 1,310 373 114

HFE-43-10pccc124 CHF2OCF2OC2F4OCHF2 1.02 d 13.5 8,130 2,990 909

HFE-7100 (HFE-449 blend) C4F9OCH3 0.31 4.7 1,320 379 115

HFE-7200 (HFE-569 blend) C4F9OC2H5 0.30 0.8 208 59 18

HFE-236ca12 CHF2OCF2OCHF2 0.66 25.0 11,320 5,730 1,770

HFE-338pcc13 CHF2OCF2CF2OCHF2 0.87 12.9 8,660 3,120 949

(CF3)2CHOH 0.28 1.9 726 206 63

Miscellaneous

Sulfuryl fluoride SO2F2 0.22 d 36 7,580 4,740 1,540

a Taken from WMO (2007), unless stated otherwise. b Taken from Chapter 1, unless stated otherwise. c Assumes CO2 mixing ratio is 378 parts per million (ppm). d See Table 5-2. e Midpoint of range given in Chapter 1.
5.50

Chapter 5

Table 5A-2. Assumptions made in obtaining production and emission estimates for the baseline (A1) 

scenario.

General Approach for All Species

Production: For the years when production is reported to UNEP, reported values (or best estimates of production 

values for cases in which reporting is incomplete) are used. Before this, WMO (2007) production values are 

generally used. In the future, annual figures are determined from the lesser of the Protocol limitations and the 

most recent annual estimates.

Emission: For the years when mixing ratio observations are available, emissions are calculated using the box model 

described in Daniel and Velders et al. (2007) with the lifetimes of Appendix Table 5A-1. Emissions before this 

are usually consistent with WMO (2007) but are also forced to yield mixing ratios that meld smoothly into the 

measurement record. Future emissions are determined using a fixed annual bank release fraction, calculated as 

the average ratio over the past 10 years between the annual emissions and estimated bank plus production.

Bank: The bank assumed to be in place at the start of the measurement record is set at such a value that the IPCC 

(2009) bank for 2008 is attained. The bank at the end of each year is equal to the bank at the beginning of the 

year plus production during that year minus emissions during that year.

Approach for Specific Species

Species Description

CFC-11 Production:

1950–1985: WMO (2007)

1986, 1989–2008: UNEP (2009) a, 1987–1988 interpolated from 1986 and 1989 values

2009–2010: Approved critical-use exemptions for non-Article 5(1) countries

2010: Approved critical-use exemptions for Article 5(1) countries, 2009 value interpolated from 

 2008 and 2010 values. All critical-use exemptions for CFCs are assumed to be CFC-11

After 2010: No production

Emission:

1979–2008: Emissions calculated from observed global abundance trends

2009–2100: Annual emissions are a constant fraction of 0.05 of the bank, extrapolated from the 

 previous years

Bank:

1979 bank set to 1,705 Kt to attain a 2008 bank of 1,420 Kt (TEAP, 2009). The bank projected 

 for 2008 in the previous Assessment was 1,380 Kt.

CFC-12 Same as CFC-11, except:

Annual emissions from 2009–2100 are a constant fraction of 0.15 of the bank

Bank:

1979 bank set to 941 Kt to attain a 2008 bank of 394 Kt (TEAP, 2009). The bank projected for 

 2008 in the previous Assessment was 499 Kt.

CFC-113 Same formalism as for CFC-11, except:

Annual emissions from 2009–2100 are a constant fraction of 0.5 of the estimated bank. (Although 

 our scenario has a non-zero bank in 2010, according to TEAP (2009) the bank has been zero 

since 2002.)

CFC-114 Same formalism as for CFC-11 except:

Bank calculated based on historic production and emission data

Annual emission from 2009–2100 is a constant fraction of 0.1 of the estimated bank

CFC-115 Same as CFC-11, except:

Emissions from 2009–2100 are a constant fraction of 0.02 of the bank

Bank:

2008 bank of 16 Kt (TEAP, 2009)
5.51

A Focus on Information for Policymakers

Approach for Specific Species

CCl4 Production and bank not considered due to gaps in our understanding of the origin of much of the 

global emission

Emission:

1951–1979: WMO (2003)

1980–2008: Emissions calculated from observed global abundance trends

2009–2050: Emissions decrease by 6% per year (average derived from observations and a 26-year 

 lifetime during 2004 to 2008)

2051–2100: No emission

CH3CCl3 Production not explicitly considered

Emission:

1950–1978: WMO (2003)

1979–2008: Emissions calculated from observed global abundance trends

2009–2014: Emission equal to the 2004–2008 average

2015–2100: No emission

HCFC-22 Production:

1950–1988: WMO (2003)

1989, 1992–2008: UNEP (2009)a

, 1990–1991 interpolated from 1989 and 1992 values

Non-Article 5(1) countries: 2009 production is 2004–2008 average; 2010–2013 Montreal Protocol 

 phase-out schedule applied

The base level HCFC consumption in non-Article 5(1) countries is calculated as the consumption 

 in 1989 + 2.8% of the 1989 CFC consumption (ODP-weighted). In WMO (2007), the 

 2.8% of the CFC consumption was assigned completely to HCFC-22. In this Assessment it is 

 distributed over the three main HCFCs based on their historic production. This results in 

 larger future emissions of HCFC-141b and HCFC-142b.

Article 5(1) countries: 2009–2012 is linearly extrapolated from 2004–2008; 2013–2040 Montreal 

 Protocol phase-out schedule applied

Emission:

1950–1992: Emissions calculated to yield mixing ratios consistent with WMO (2007)

1993–2008: Emissions calculated from observed global abundance trends

2009–2100: Assume an annual bank release fraction of 0.18 (average of 2002–2008)

Bank:

1993 bank set to 302 Kt to attain a 2008 bank of 1,618 Kt (TEAP, 2009). The bank projected for 

 2008 in the previous Assessment was 2,083 Kt.

HCFC-141b Production as in HCFC-22

Emission:

1990–2008: Emissions calculated from observed global abundance trends

2009–2100: Annual emissions calculated assuming a bank release fraction of 0.05 (average of 

 2003–2008)

Bank:

1994 bank set to 115 Kt to attain a 2008 bank of 941 Kt (TEAP, 2009). The bank projected for 

 2008 in the previous Assessment was 961 Kt.

HCFC-142b Production as in HCFC-22

Emission:

1979–2008: Emissions calculated from observed global abundance trends

2009–2100: Annual emissions calculated assuming a bank release fraction of 0.11 (average of 

 1999–2008)

Bank:

1993 bank set to 95 Kt to attain a 2008 bank of 273 Kt (TEAP, 2009). The bank projected for 

 2008 in the previous Assessment was 211 Kt.

Table 5A-2, continued.
5.52

Chapter 5

Approach for Specific Species

Halon-1211 Production:

1986, 1989–2008: UNEP (2009), 1987–1988 interpolated from 1986 and 1989 values

non-Article 5(1) countries: zero production from 2009–2100

Article 5(1) countries: 2009 production is 2006–2008 average; zero from 2010–2100

Emission:

1950–1992: WMO (2007)

1993–2008: Emissions calculated from observed global abundance trends

2009–2100: Annual emissions calculated assuming a bank release fraction of 0.075 (average of 

 1999–2008)

Bank:

1993 bank is set to 128 Kt to attain a 2008 bank of 74 Kt (TEAP, 2009). The bank projected for 

 2008 in the previous Assessment was 86 Kt. 

Halon-1301 Production as in halon-1211

Emission:

1950–1992: WMO (2007)

1992–2008: Emissions calculated from observed global abundance trends

2009–2100: Annual emissions calculated assuming a bank release fraction of 0.04 (average of 

 1999–2008)

Bank:

1992 bank is set to 74 Kt to attain a 2008 bank of 47 Kt (TEAP, 2009). The bank projected for 

 2008 in the previous Assessment was 31 Kt.

Halon-1202 Same as WMO (2007)

Halon-2402 Production as in halon-1211

Emission:

1970–2003: based on WMO (2007), but adjusted to meld smoothly into the measurement record 

2004–2008: Emissions calculated from observed global abundance trends

2009–2100: Annual emissions calculated assume a bank release fraction of 0.08 (average of 

 2004–2008)

Bank:

1995 bank is set to 20 Kt to allow the emissions meld smoothly into the emissions derived from 

 observations. The corresponding 2008 bank of 9.1 Kt is much larger than from TEAP (2009) 

 of 1.3 Kt. A bank of 1.3 Kt would result in emissions a factor of 8 smaller than derived from 

 observations for 2004–2008. The bank projected for 2008 in the previous Assessment was 

 1.8 Kt.

CH3Br Production/emissions from Yvon-Lewis et al. (2009): natural production/emission (102 Kt), gasoline 

(5.7 Kt), biomass (11.3 Kt), biofuel (6.1 Kt), non QPS-fumigation. Parenthetical values for 

anthropogenic sources are emission estimates for 1996 and 2007 (Yvon-Lewis et al., 2009 and 

references therein) and are held constant into the future.

QPS production from 1995–2008 from UNEP (2009), held constant at 11.2 Kt (2004–2008 

 average) for 2009–2100

Approved critical-use exemptions (CUE) for 2009–2011 (no CUE after 2011)

Emissions:

1950–2008: Emissions calculated from surface observations and derived from South Pole firn 

 measurements (using a global lifetime of 0.75 years to be consistent with Yvon-Lewis et al., 

 2009)

2009–2100: Fumigation emissions equal 0.6 times production for fumigation. The combination 

 of anthropogenic and natural emissions, constrained by the total emissions derived from 

 observations of concentrations, leads to an anthropogenic fraction of total emissions of 0.30 

Table 5A-2, continued.
5.53

A Focus on Information for Policymakers

Approach for Specific Species

(CH3Br,

continued)

 in 1992, in agreement with Montzka et al. (2003) (see also Chapter 1).

Bank:

No bank considered

CH3Cl Emission:

1950–1995: Global emissions derived from firn measurements at the South Pole

1996–2100: Emissions held constant at 1995 levels, as in WMO (2003) and WMO (2007)

a Estimated in cases in which reporting is not complete or reporting is made in compound classes rather than individually. The production data for each 

species in each year is obtained from UNEP (2009) and is consistent with the totals for each group of species as usually reported by UNEP.

Table 5A-2, continued.
5.54

Chapter 5Table 5A-3. Mixing ratios (ppt) of the ODSs considered in the baseline (A1) scenario 1. Values are for the beginning of the corresponding 

year. Potentially important short-lived gases that may currently contribute 3–8 ppt of stratospheric bromine and 40–130 ppt of stratospheric chlorine (see Chapter 1) are not shown in the table.

CFC-11 CFC-113 CFC-115 CH CCl 3 3 HCFC-141b Halon-1211 Halon-1301 CH Br 3

CFC-12 CFC-114 CCl4 HCFC-22 HCFC-142b Halon-1202 Halon-2402 CH Cl 3

1955 3.3 14.3 1.2 2.6 0.0 42.3 0.1 1.0 0.0 0.0 0.00 0.00 0.00 0.00 6.3 491.3

1960 9.5 29.5 1.9 3.8 0.0 52.1 1.5 2.1 0.0 0.0 0.00 0.00 0.00 0.00 6.5 510.3

1965 23.5 58.8 3.1 5.0 0.0 64.4 4.7 4.9 0.0 0.0 0.00 0.00 0.00 0.00 6.7 528.1

1970 52.8 114.3 5.5 6.5 0.2 75.9 16.2 12.1 0.0 0.0 0.02 0.00 0.00 0.02 7.0 539.9

1975 106.1 203.1 10.4 8.3 0.6 85.5 40.0 23.8 0.0 0.2 0.12 0.01 0.04 0.06 7.4 545.8

1980 161.9 297.4 19.0 10.7 1.3 93.3 81.6 42.5 0.0 0.4 0.42 0.01 0.24 0.15 7.7 548.3

1981 170.3 313.9 21.5 11.1 1.5 94.8 88.3 46.6 0.0 0.5 0.52 0.01 0.31 0.17 7.8 548.6

1982 179.2 329.9 25.3 11.6 1.8 95.8 93.0 50.7 0.0 0.5 0.63 0.02 0.39 0.19 7.9 548.9

1983 187.4 346.7 29.2 12.0 2.1 97.1 97.2 54.8 0.0 0.6 0.75 0.02 0.49 0.21 8.0 549.1

1984 196.0 363.9 32.5 12.4 2.4 98.2 101.7 58.8 0.0 0.7 0.88 0.02 0.61 0.24 8.1 549.3

1985 205.4 381.2 37.3 12.9 2.8 99.6 106.1 62.7 0.0 0.7 1.04 0.02 0.74 0.26 8.2 549.4

1986 215.8 399.3 42.0 13.4 3.1 100.8 110.0 66.9 0.0 0.8 1.22 0.02 0.89 0.29 8.2 549.5

1987 227.0 419.2 47.4 14.0 3.5 102.5 112.3 71.5 0.0 0.8 1.44 0.02 1.06 0.32 8.3 549.6

1988 238.0 438.4 54.4 14.5 3.9 103.6 118.0 76.7 0.0 0.9 1.69 0.03 1.25 0.35 8.4 549.7

1989 247.7 459.6 61.3 15.0 4.3 104.9 122.5 82.5 0.0 1.0 1.98 0.03 1.46 0.38 8.5 549.8

1990 256.2 477.5 67.6 15.4 4.7 106.5 127.2 88.2 0.0 1.2 2.27 0.03 1.66 0.41 8.6 549.8

1991 262.2 491.0 73.8 15.7 5.1 106.3 130.0 93.7 0.0 1.8 2.54 0.03 1.84 0.44 8.7 549.9

1992 265.2 500.7 78.7 15.8 5.6 105.3 131.4 99.1 0.1 2.8 2.79 0.03 1.97 0.46 8.9 549.9

1993 267.8 510.1 81.6 15.9 6.0 104.7 130.1 103.9 0.3 3.9 3.02 0.04 2.20 0.49 9.0 549.9

1994 267.8 517.1 83.0 16.0 6.4 104.0 121.5 109.2 1.2 5.1 3.20 0.04 2.48 0.51 9.1 549.9

1995 267.4 523.8 83.6 16.1 6.8 103.2 110.3 113.6 2.7 6.3 3.34 0.04 2.63 0.52 9.2 550.0

1996 266.8 528.9 83.7 16.2 7.1 102.5 97.8 119.4 4.5 7.3 3.50 0.05 2.60 0.51 9.1 550.0

1997 266.0 533.5 83.6 16.3 7.4 101.3 83.4 124.2 6.4 8.4 3.66 0.05 2.67 0.51 9.1 550.0

1998 264.5 536.4 83.3 16.4 7.6 100.5 70.6 128.7 8.2 9.3 3.80 0.05 2.70 0.51 9.2 550.0

1999 263.3 539.0 82.9 16.4 7.7 99.8 59.3 134.7 10.1 10.3 3.92 0.05 2.73 0.51 9.3 550.0

2000 261.7 541.0 82.3 16.5 7.9 98.6 49.7 139.5 11.8 11.4 4.02 0.04 2.84 0.50 8.9 550.0

2001 260.1 542.8 81.8 16.5 8.0 97.7 41.6 144.7 13.5 12.4 4.11 0.04 2.85 0.50 8.5 550.0

2002 258.3 543.4 81.1 16.5 8.0 96.6 34.6 150.9 14.8 13.2 4.17 0.03 2.87 0.50 8.2 550.0

2003 255.9 543.5 80.3 16.5 8.1 95.6 28.9 155.4 16.1 13.9 4.22 0.03 2.88 0.49 8.2 550.0

2004 253.9 543.4 79.6 16.5 8.2 94.7 24.1 160.3 17.0 14.5 4.25 0.02 2.95 0.49 8.0 550.0
5.55

A Focus on Information for Policymakers

CFC-11 CFC-113 CFC-115 CH CCl 3 3 HCFC-141b Halon-1211 Halon-1301 CH Br 3

CFC-12 CFC-114 CCl4 HCFC-22 HCFC-142b Halon-1202 Halon-2402 CH Cl 3

2005 251.6 542.7 78.8 16.6 8.3 93.7 20.1 165.5 17.5 15.1 4.26 0.02 3.03 0.48 7.9 550.0

2006 249.4 541.8 78.2 16.5 8.3 92.7 16.7 172.2 17.8 15.8 4.27 0.01 3.06 0.48 7.7 550.0

2007 247.2 539.8 77.6 16.5 8.4 91.6 14.1 179.3 18.6 16.9 4.24 0.01 3.12 0.48 7.6 550.0

2008 245.1 537.7 76.8 16.5 8.4 90.4 11.7 187.3 19.0 18.2 4.19 0.01 3.15 0.47 7.5 550.0

2009 243.3 535.3 76.2 16.4 8.4 89.0 9.8 195.2 19.6 19.3 4.14 0.00 3.18 0.47 7.2 550.0

2010 240.9 532.5 75.6 16.4 8.4 87.6 8.3 206.8 20.3 20.5 4.07 0.00 3.20 0.46 7.2 550.0

2011 238.4 529.4 74.8 16.3 8.4 86.0 7.1 218.6 21.1 21.7 3.99 0.00 3.22 0.46 7.2 550.0

2012 235.8 525.9 74.0 16.3 8.4 84.5 6.1 230.9 22.1 22.9 3.91 0.00 3.24 0.45 7.2 550.0

2013 233.1 522.3 73.2 16.2 8.4 82.8 5.3 243.6 23.2 24.2 3.82 0.00 3.26 0.44 7.1 550.0

2014 230.4 518.4 72.3 16.2 8.4 81.2 4.6 255.7 24.4 25.4 3.72 0.00 3.27 0.44 7.1 550.0

2015 227.6 514.4 71.5 16.1 8.4 79.5 4.1 267.1 25.6 26.6 3.62 0.00 3.28 0.43 7.1 550.0

2020 213.0 492.8 67.4 15.8 8.4 70.9 1.5 301.8 30.9 30.9 3.08 0.00 3.29 0.38 7.1 550.0

2025 197.8 470.3 63.6 15.5 8.4 62.4 0.5 299.8 34.1 32.4 2.55 0.00 3.26 0.32 7.1 550.0

2030 182.6 448.0 59.9 15.1 8.4 54.4 0.2 265.4 34.4 31.2 2.06 0.00 3.19 0.27 7.1 550.0

2035 167.7 426.5 56.5 14.7 8.4 47.0 0.1 208.0 31.9 27.8 1.65 0.00 3.09 0.22 7.1 550.0

2040 153.5 405.8 53.3 14.4 8.4 40.3 0.0 151.0 27.9 23.3 1.30 0.00 2.97 0.18 7.1 550.0

2045 139.9 386.1 50.2 14.0 8.4 34.4 0.0 105.0 23.5 18.9 1.01 0.00 2.85 0.15 7.1 550.0

2050 127.2 367.3 47.4 13.6 8.4 29.2 0.0 71.1 19.3 14.9 0.78 0.00 2.71 0.12 7.1 550.0

2055 115.4 349.4 44.7 13.3 8.4 24.2 0.0 47.5 15.6 11.6 0.60 0.00 2.57 0.09 7.1 550.0

2060 104.4 332.4 42.1 12.9 8.3 20.0 0.0 31.5 12.4 9.0 0.46 0.00 2.43 0.07 7.1 550.0

2065 94.4 316.2 39.7 12.6 8.3 16.5 0.0 20.8 9.8 6.8 0.35 0.00 2.29 0.06 7.1 550.0

2070 85.2 300.7 37.4 12.3 8.3 13.6 0.0 13.7 7.7 5.2 0.26 0.00 2.16 0.05 7.1 550.0

2075 76.8 286.1 35.3 12.0 8.3 11.2 0.0 9.0 6.1 3.9 0.20 0.00 2.02 0.04 7.1 550.0

2080 69.1 272.1 33.3 11.6 8.2 9.3 0.0 5.9 4.7 3.0 0.15 0.00 1.90 0.03 7.1 550.0

2085 62.2 258.8 31.4 11.3 8.2 7.6 0.0 3.9 3.7 2.2 0.11 0.00 1.77 0.02 7.1 550.0

2090 55.9 246.2 29.6 11.1 8.2 6.3 0.0 2.6 2.9 1.7 0.08 0.00 1.66 0.02 7.1 550.0

2095 50.2 234.2 27.9 10.8 8.2 5.2 0.0 1.7 2.2 1.3 0.06 0.00 1.55 0.01 7.1 550.0

2100 45.1 222.8 26.3 10.5 8.1 4.3 0.0 1.1 1.7 0.9 0.05 0.00 1.44 0.01 7.1 550.0

1Note: Areas are shaded for compounds in years when mixing ratio values are forced to equal global estimates inferred from observations. The pre-1995 global mixing ratio trend for CH Br was derived 3

from SH firn data by including a time-varying hemispheric ratio that increased linearly from 1.0 in 1940 to 1.3 in 1995 (see Section 1.2.1.6 of Chapter 1). This is based on the concurrent decline in the measured hemispheric difference and industrially averaged emissions since 1998, and suggests a mean hemispheric mixing ratio difference close to 0 ppt for CH Br in preindustrial times. Previously, 3

a constant hemispheric ratio had been used. CH Cl mixing ratios before 1995 were also derived from South Pole firn data (Butler et al., 1999). From 1995 onward, global means of CH 3 Br are based 3

on surface observations, while global means of CH Cl are held constant (Chapter 1). All other shaded areas are from atmospheric observations from one or more measurement networks (Chapter 1). 3
5.56

Chapter 5

Table 5A-4. Halocarbon indirect GWPs from ozone depletion using the EESC-based method described in Daniel et al. (1995). Values have been updated for the new scenarios and fractional release 

values. Indirect forcing from ozone depletion is also now assumed to continue even after EESC drops below 

the 1980 level, consistent with our understanding that this level does not represent a threshold value for 

ozone depletion. Uncertainties in direct GWPs represent 35% of the direct value; uncertainties in the indirect GWPs reflect the uncertainty in stratospheric ozone radiative forcing quoted in IPCC (−0.05 ± 0.10 W/

m2) even though that forcing is not attributed to only halocarbons.

Gas Direct GWP Indirect GWP

CFC-11 4,750 ± 1,660 −1,630 ± 3,250

CFC-12 10,900 ± 3,810 −1,270 ± 2,540

CFC-113 6,130 ± 2,150 −1,310 ± 2,630

CFC-114 9,180 ± 3,210 −562 ± 1,120

CFC-115 7,230 ± 2,530 −137 ± 275

HCFC-22 1,790 ± 630 −58 ± 116

HCFC-123 77 ± 27 −25 ± 50

HCFC-124 619 ± 217 −30 ± 60

HCFC-141b 717 ± 252 −158 ± 316

HCFC-142b 2,220 ± 780 −97 ± 193

HCFC-225ca 122 ± 42 −27 ± 54

HCFC-225cb 606 ± 214 −39 ± 78

CH3CCl3 146 ± 53 −212 ± 424

CCl4 1,400 ± 490 −1,300 ± 2,600

CH3Br 5 ± 2 −851 ± 1,700

Halon-1211 1,890 ± 660 −11,720 ± 23,430

Halon-1301 7,140 ± 2,500 −27,060 ± 54,130

Halon-2402 1,640 ± 570 −19,780 ± 39,570