1. 1
Abatement opportunities for non-CO2
climate forcers
Black carbon, methane, nitrous oxide and f-gas emissions
reductions to complement CO2 reductions and enable
national environmental and social objectives
Briefing paper, May 2011

2. 2
Major Findings
While there is still much uncertainty around the emissions and abatement
opportunities for black carbon, methane, nitrous oxide and f-gases,
enough is now known to inform action.
These non-CO2 climate forcers collectively cause at least one quarter of
global warming and accelerate the rate of temperature change.
In addition, black carbon and methane contribute significantly to air
pollution, which causes millions of premature deaths and even higher rates
of disease.
Emissions from the four non-CO2 climate forcers can be reduced by over
20 percent by 2030 using available methods: fugitive emissions capture,
efficient agricultural practices, combustion optimization, diesel particulate
controls, and alternative cooling technologies.
Reducing non-CO2 emissions is essential to limit global warming during
this century, slow the rate of temperature increase, and reduce the risk of
adverse climate feedbacks.
On top of the positive climate effects, 80 percent of the measures also
improve public health and half come at a net savings to society.
While a large share of the measures is relatively straightforward to
implement, capturing the remainder will be challenging, as millions of
people would need to take action, some of whom are the world’s poorest.
In developed countries, the principal abatement opportunities lie in waste
management, air conditioning and refrigeration, and diesel engines.
Opportunity areas for developing countries are diesel engines, natural gas
production, waste management, and traditional combustion technologies.
None of the measures in this report can substitute for the immediate and
massive carbon dioxide reductions needed for long-term climate
stabilization. Non-CO2 mitigation measures are complementary to CO2
controls.

3. 3
Table of Contents
Preface 4
Executive Summary 6
Study approach 16
Global perspective on non-CO2 climate forcers 20
Non-CO2 climate forcer perspectives
Black Carbon 43
Methane 56
Nitrous oxide 62
F-Gases 66
References 74
Appendix A: Key contacts and contributors 82
Appendix B: Glossary 84
Appendix C: Abatement potential in 2020 87
Appendix D: Black and organic carbon in tonnes 92
Appendix E: Areas of further research 93
Appendix F: Alternative metrics considerations 93
Appendix G: List of major assumptions 94

4. 4
Preface
Greenhouse gas (GHG) emissions have risen significantly over the past 15 years, from 36
gigatonnes of carbon dioxide equivalent (GtCO2e) in 1990 to over 45 GtCO2e in 2005. The
net effect of black carbon1 accounts for an additional 6 GtCO2e of global warming emissions
in 2005. Black carbon is a climate forcing aerosol that is not part of the Kyoto protocol, and
thus has not yet received as much attention as the GHGs. Without collective attempts to curb
emissions, GHGs and net black carbon combined are likely to grow to about 75 GtCO2e by
2030. However, many scientific estimates suggest that emissions would instead need to fall
dramatically by that point in order to maintain a chance of keeping global warming to within
2 degrees Celsius—the level above which dangerous climate changes occur.2
To date, most attention has been focused on carbon dioxide (CO2), as it accounts for the
largest share of human-induced global warming emissions. Also, most scientists agree that
CO2 emissions will determine the climate outcome a century from today and beyond, since it
is the most abundant long-lived gas. But nearer term effects are also important. Methane,
nitrous oxide, the fluorinated gases (f-gases), and black carbon are expected to account for
over 25 percent of the total global warming impact in 2030. These four main non-CO2
emissions3 exert a powerful influence on the climate. Their radiative forcing is between 20
and 20,000 times greater on a unit basis than CO2. They accelerate the rate of temperature
change, which in turn affects the ability of ecosystems to adapt. Black carbon also reduces
the reflectivity of snow and ice, causing those surfaces to melt faster than they otherwise
would, threatening the Arctic and the world's glacier systems. Methane is a precursor to
ozone, which damages plant tissues thereby reducing their ability to sequester CO2.
Furthermore, black carbon and methane are contributors to air pollution, adding to unhealthy
levels of fine particulate matter and ground level ozone throughout the world.
Taking action to reduce these non-CO2 emissions therefore delivers a triple benefit. First, it
complements national and international efforts to reduce CO2, increasing the chances of
climate stabilization in the medium to longer term4. Second, reducing emissions of methane
and black carbon increases the resilience of the planet’s ecosystem, preserving natural
1 The warming effect of black carbon, net of the cooling effect of co-emitted organic carbon.
2 den Elzen and Meinshausen (2006); den Elzen et al. (2007); den Elzen and van Vuuren (2007); Meinshausen (2006); and
Ramanathan and Xu (2010).
3 Not included here are several other non-CO2 climate forcers, such as sulfur dioxide (which has a cooling effect) and other warming
emissions, such as volatile organic compounds and carbon monoxide, that are smaller in size.
4 “Failing to reduce carbonaceous aerosol emissions requires a greater reduction in CO2 emissions to meet the same Radiative
Forcing equivalent or temperature target.” Kopp and Mauzerall (2010).

5. 5
carbon sinks, glaciers, and Arctic ice. Third, controlling methane and black carbon emissions
reduces air pollution, improving public health.5
Actions that improve public health produce an economic benefit to society through greater
productivity. In addition, some of the black carbon abatement measures can more directly
work to alleviate poverty. For example, improving access to clean fuels for residential
cooking and heating would substantially reduce the labor required to collect dirtier biomass
fuels. The time savings could then be applied to productive economic activity that increases
personal wealth.
This report is intended to provide a fact base for policymakers, companies, and NGOs on
these four important non-CO2 climate forcers. Specifically, it seeks to:
■ Describe their impact, highlighting the role of black carbon
■ Quantify expected emissions development in the absence of any major policy changes
■ Assess and quantify abatement opportunities in terms of mass, cost, and investment
requirements
■ Assess the main additional benefits of reducing emissions, particularly the impact on
public health
The results of this analysis, especially the relative magnitude of the emissions, may be new
to many readers. Previous reports on greenhouse gas abatement have included some analysis
of methane, nitrous oxide, and f-gas emissions,6 but not at the level of detail in this report.
Black carbon was not included at all. For all of the climate forcers we have used the most
updated emissions inventories and projections available. That said, research is ongoing and
refined data is expected from several institutions in the near future.
The principal metric used in this report is 100-year Global Warming Potential (GWP 100)
carbon dioxide equivalent (CO2e). This is the standard metric used by the
Intergovernmental Panel on Climate Change (IPCC) to compare different climate forcers
with one another. However, readers should understand that short-lived climate forcers are
distinctly different from CO2 in time and space. Methane and black carbon have much more
immediate climate impacts than carbon dioxide, but then disappear from the atmosphere
unless replenished with new emissions. For black carbon, the majority of those impacts may
be further restricted to discrete regional areas. Conversely, CO2 and other long-lived gases
(including nitrous oxide and some f-gases) are globally mixed into relatively uniform
concentrations and remain for in the atmosphere for centuries.
5 Details on health impacts and benefits can be found in the "Study Approach" and respective "Climate Forcer Perspectives" chapters.
6 Based on McKinsey & Company, 2009.

6. 6
By using 100-year CO2e GWP values, it is not our intent to imply that all climate forcers are
equal or interchangeable. There are several good scientific reasons to handle short and long
term climate forcers differently.7 Rather, our goal is to convey that non-CO2 pollutants are a
significant part of the climate change problem and to put that contribution into perspective.
There are a number of remaining uncertainties concerning both the level of emissions from
non-CO2 climate forcers and the abatement potential. Nevertheless, the analysis at hand
provides a strong indication that large-scale efforts should be made to reduce non-CO2
emissions, in order to tackle climate change and air pollution.
We have produced this report in cooperation with a global network of leading academics,
government bodies, think tanks, NGOs, and companies in order to incorporate the most up-
to-date and detailed understanding of climate science and emission abatement. McKinsey &
Company provided analytical support for this report based on its global and national
greenhouse gas abatement studies. We would like to thank all of these individuals and
organizations for their contributions. The full list of contributors is included in Appendix A.
7 “We need to separate the policy frameworks and interventions for attending to short-lived versus long-lived climate forcing
agents… The physical properties, sources and policy levers of short-lived forcing agents – black soot, aerosols, methane and
tropospheric ozone – are quite different from those of long-lived forcing agents – carbon dioxide, halocarbons, nitrous oxide.” Molina
et al., 2009.
“One potential alternative to the single greenhouse gas basket approach is to have several baskets with trading only within each
particular one. While still imperfect, if the baskets contain gases of comparable lifetimes, the confounding tradeoffs of short- vs. long-
lived gases will be reduced in importance.” Daniel et al., 2009.

7. 7
Executive Summary
This report is intended to provide a fact base for policymakers, companies, and NGOs to
better understand methane, nitrous oxide, f-gases, and black carbon. It identifies the
climate, health, and environmental impacts of these non-CO2 climate forcers and assesses
abatement opportunities.
While there is still much uncertainty around the emissions and abatement
opportunities for black carbon, methane, nitrous oxide, and f-gases,
enough is now known to inform action.
The state of knowledge for these four climate forcers is less advanced than for carbon
dioxide for two reasons. First, emissions estimates are less precise for non-CO2 climate
forcers since some source categories are more difficult to measure and there have been
fewer analyses conducted. For example, some methane comes from leaks that are difficult to
identify and from biological sources that are subject to varying conditions. Second, there is
some uncertainty about the magnitude of the effect that each climate forcer has on
temperature increase. The current state of science regarding radiative forcing values for
black carbon includes an uncertainty range of almost ±50 percent and there is considerable
uncertainty about aerosol and cloud interactions.
There is a policy dimension as well, since the international climate community has not come
to consensus yet on the best way to compare short-lived and long-lived climate forcers. The
100-year and 20-year CO2 equivalent values discussed in this report are just a rough
approximation of what is actually happening in the atmosphere. In reality, long lived forcers
can persist for thousands of years and certain short lived forcers leave the atmosphere within
days. The geographical location of climate impacts also varies depending on whether the
pollutant is uniformly mixed in the global atmosphere or regionally constrained.
Fortunately, there is a rapidly growing body of research that has helped to narrow these
uncertainties. Methane, nitrous oxide, and f-gases are included in the Kyoto Protocol and
therefore have been a part of national submissions to the UNFCCC, and of several other
inventory and future projection analyses. Black carbon, while not included in these
submissions, is being actively studied by several leading researchers8 with a number of
publications upcoming in 2011. Additionally, there is an international scientific debate on
climate metrics underway which is expected to be reflected in the next major Assessment
Report of the IPCC, currently scheduled for 2014.
Some have argued that there are too many uncertainties surrounding those non-CO2 climate
forcers for policymakers to take any decisive action. However, the conclusion of this
8 See, for example, Bond 2007; IIASA’s GAINS model; and Fuglestvedt 2009.

8. 8
research is that the uncertainties involved do not detract from the main findings. Whatever
climate metric is applied, non-CO2 climate forcers clearly cause a substantial portion of
global warming. In addition, black carbon and methane emissions increase air pollution and
consequential disease and premature mortality. A range of abatement measures exists that
can be quantified to capture both climate and associated public health benefits.
These non-CO2 climate forcers collectively cause at least one quarter of
global warming9 and accelerate the rate of temperature change
CO2 is the most prevalent of the greenhouse gases (GHGs) and among the longest lasting in
the atmosphere. As such, it is the single biggest cause of long-term climate change and the
focus of most discussions and efforts to reduce emissions. Yet there are a number of other,
significant non-CO2 “climate forcers” that have received less focus. These are methane,
nitrous oxide, fluorinated gases (f-gases), and black carbon.
These four climate forcers are emitted from a variety of sources (Exhibit 1). Methane and
nitrous oxide arise from biological processes in agriculture and waste decomposition, and
from certain industrial processes. F-gases are used as coolants in refrigeration and air
conditioning and are emitted to a lesser extent from industrial processes. Black carbon, an
aerosol and component of soot, results from incomplete combustion—that is, when a
carbonaceous fuel fails to get fully converted into CO2. Major sources of human-induced
black carbon are diesel engines, traditional brick kilns and coke ovens, and domestic
cookstoves.
These non-CO2 climate forcers will account for over 25 percent of the global warming
impact from emissions in 2030 from a 100-year perspective. They have an even greater
impact over shorter time scales. Hence, reducing these emissions in parallel to CO2
abatement would therefore play an important role in stabilizing the climate by slowing the
rate of temperature change.10 (These concepts are discussed in more detail in the “Study
Approach - Climate Metrics” chapter.)
9 Using 100-year GWP carbon dioxide equivalent metric.
10 See, for example, Molina et al., 2009; Kopp and Mauzerall, 2010; and Ramanathan and Xu, 2010.

9. 9
EXHIBIT 1
Non-CO2 climate forcers – emission sources
▪ GHG, emitted from industries
and anaerobic digestion
▪ Precursor to tropospheric
ozone which causes disease
and inhibits growth of
vegetation
Description and impact
Methane
(CH4)
SOURCE: Non-CO2 Climate Forcers Report (2010); IPCC Second Assessment Report (SAR) (1995); IPCC Fourth Assessment Report (AR4) (2007); Rypdal
et al. (2009)
Nitrous
oxide
(N2O)
Fluorinated
gases
(F-gases)
Black
carbon
12 years
Lifetime
72
20-year
21
100-year
114 years289310
Varies by
f-gas
(HFC-134a:
14 years)
Main sources
▪ Livestock
▪ Petroleum and
gas production
▪ Rice farming
▪ Waste
decomposition
▪ GHG, primarily formed through
chemical processes in
agricultural soils
▪ Fertilizers
▪ Manure
management
▪ Acid production
▪ GHG, used as coolants
(refrigeration, air-conditioning),
accelerants and insulators
▪ Refrigeration
▪ Air conditioning
▪ Electric power
transmission
▪ HCFC-22
production
▪ Carbonaceous aerosol, emitted
as product of incomplete
combustion
▪ Co-emitted with other
particulates that combined have
strong negative health effects
▪ Increases the rate of Arctic and
glacial melting
▪ Diesel engines
▪ Brick kilns and
coke ovens
▪ Biomass and
coal cookstoves
1-2 weeks3,230917
Varies by
f-gas
(HFC-134a:
1,300)
Varies by
f-gas
(HFC-134a:
3,830)
NOTE: 100-year GWP expressed in SAR values; 20-year GWP expressed in AR4 values
Global Warming
Potential (GWP)
In addition, black carbon and methane contribute significantly to air
pollution, which causes millions of premature deaths and even higher
incidence of disease
Emissions from non-CO2 climate forcers affect not only climate change, but also public
health. Although significant strides have been made toward a cleaner, healthier atmosphere,
globally millions of people are still exposed to dangerous levels of air pollution – especially
in the developing world. Every year, more than 3 million people11 worldwide die from
respiratory problems, cardiovascular problems, and lung cancer caused by indoor and
outdoor air pollution. Premature mortality, illness, and lost productivity reduce quality of
life and undercut national GDP growth in several developing nations.
Black carbon and methane contribute to this public health burden by adding to fine
particulate matter12 and tropospheric ozone concentrations,13 respectively, both of which are
11 Approximately 1.2 million deaths attributable to urban outdoor air pollution and 2.0 million deaths attributable to indoor smoke
from solid fuels (WHO, 2009).
12 “Fine particulate matter” refers to particles that are 2.5 microns in diameter or smaller. Black carbon particles are below 1 micron
in diameter, in the 1-100 nanometer range. (A nanometer is about 1/50,000 the diameter of a human hair.)

10. 10
important components of air pollution. Fine particulate matter is the most damaging air
pollutant worldwide, with the highest morbidity and premature mortality impacts of any air
pollutant. Tropospheric ozone exposures also lead to increased disease and, in some cases,
death, but the incidence rates are significantly lower.
Emissions from the four non-CO2 climate forcers can be reduced by over
20 percent by 2030 using available methods: fugitive emissions capture,
efficient agricultural practices, combustion optimization, diesel particulate
controls, and alternative cooling technologies
Emissions from the non-CO2 climate forcers are forecast to grow by nearly 30 percent
between 2005 and 2030 in the business-as-usual case (from 15.8 GtCO2e to 20.1 GtCO2e
GWP100). There is potential to reduce emissions from non-CO2 climate forcers in 2030 by
over 20 percent, or 4.5 GtCO2e from the business-as-usual (BAU) levels, through technical
abatement measures.14Capturing this total abatement potential would eliminate growth in
non-CO2 emissions. Behavioral changes would provide additional abatement potential, with
the biggest opportunity being up to 1.8 GtCO2e from reduced meat and dairy consumption.
There are five major opportunities for abatement of non-CO2 forcers (Exhibit 2):
■ Capturing fugitive emissions from gas handling, coal mining, and waste management
■ Improved agricultural practices to curb methane and nitrous oxide emissions
■ Improved combustion technologies to reduce black carbon emissions
■ Improving cooling technologies to reduce emissions of f-gases
■ Reduced transport particulate emissions, particularly from diesel engines
More than 50 percent of the abatement potential comes at a net profit to society, meaning
that subsequent economic benefits outweigh the initial investment and incremental operating
costs. For example, the cost of capturing methane gas generated from landfill sites can be
recouped through the value of electricity generated with the methane. Another 30 percent of
the abatement potential can be captured at a cost of $20/tCO2e or less. Nearly all of the
remaining abatement, though more expensive, would deliver important health and other
non-climate-related environmental benefits.
13 Pew Center, 2009; and Smith, K., 2009. Tropospheric ozone is also referred to as "ground level ozone." Methane is one of several
precursors to ground level ozone and contributes mostly to background ozone levels (as opposed to peak concentrations) because
of its relatively low reactivity.
14 Uncertainty analysis shows that at minimum the abatement potential is 3.5 GtCO2e, but it is likely to be over 5 GtCO2e.

11. 11
EXHIBIT 2
SOURCE: Non-CO2 Climate Forcers Report (2010)
Key opportunities
Improved
combustion
technologies
0.5
15.6
1.0
Abatement
Case
2030
Improved
cooling
technologies
0.7
Capturing
fugitive
emissions
20.1
BAU
growth
15.8
4.3
BAU
Emissions
2005
1.8
Improved
agricultural
practices
0.6
Reduced
transportation
particulate
emissions
BAU
Emissions
2030
-22%
▪ Water and nutrient
management in
rice cultivation
▪ Anti-methanogen
vaccines and feed
supplements for
livestock
▪ Improved
cookstoves and
LPG cookstoves
▪ Replacing
traditional kilns with
vertical shaft and
tunnel kilns
▪ Emission controls
for on-road and off-
road vehicles,
particularly heavy-
duty diesel trucks
▪ Landfill gas
capture
▪ Oxidation of coal
mine ventilation
air and mine
degasification
▪ Electrostatic
precipitators for
coke ovens
▪ Low GWP coolants
for motor vehicle
air conditioning
▪ Lower leakage in
retail food
refrigeration using
secondary loops or
distributed systems
Abatement divided into categories for action
GtCO2e (GWP 100) per year
~40% ~20% ~20% ~10% ~10%
X% Share of total
abatement potential
Reducing non-CO2 emissions is essential to limit global warming during
this century, slow the rate of temperature increase, and reduce the risk of
adverse climate feedbacks
There are three angles from which to assess the need for urgency to reduce the non-CO2
climate forcers in parallel to carbon dioxide: limiting the total amount of global warming;
reducing the rate of temperature increase; and reducing the risk of adverse climate feedbacks
on both a global and regional scale.
Ultimately, long-term temperature increases and temperature stabilization levels after
mitigation will be determined by the level and pathway of carbon dioxide emissions, the
most prevalent GHG. Still, abating non-CO2 climate forcers in parallel to CO2 is essential to
achieving temperature stabilization at all. Even assuming no growth in non-CO2 emissions
after 2030, there would be about 20 GtCO2e of emissions without abatement. This amount
represents nearly all of, if not more than, the total emissions per year that could be
perpetually emitted without further increasing the temperature, i.e., to enable temperature
stabilization. No abatement of the non-CO2 forcers would essentially mean that CO2
emissions would need to be cut close to zero in order to achieve stabilization.
In the short-term, non-CO2 abatement has an even greater impact on slowing the rate of
temperature increase, due to the high short-term warming effect of those climate forcers.

12. 12
The rate of change in local climate has implications for the ability of those ecosystems to
adapt– the faster the change, the lower the ability to adapt, the higher the risk of irreversible
changes. Berntsen et al. demonstrated that drastically reducing non-CO2 climate forcers in
the short term prolongs the time needed to reach maximum temperatures by several decades
– slowing the rate of change, thus improving the ability of humans and ecosystems to
adapt.15 Van Vuuren et al. confirm this finding and conclude that multi-gas abatement
scenarios are also the most cost-effective way to contain warming.16
Moreover, reducing black carbon would help alleviate non-temperature related climate
changes, such as the melting of glaciers and arctic ice. Abating methane, which as a
precursor of tropospheric ozone damages vegetation, would improve the ability of plants to
sequester carbon.17 These are both areas where abatement would substantially reduce
adverse climate feedbacks.
On top of the positive climate effects, 80 percent of the measures also
improve public health and half come at a net savings to society
Reducing methane and black carbon emissions will deliver near-term health benefits. Nearly
80 percent of the abatement measures result in air pollution reduction, thereby improving
public health (Exhibit 3). The remaining 20 percent of abatement can be divided into those
measures that result in a net societal profit (such as refrigerant leak prevention) and those
that are pure global climate change mitigation measures (such as industrial nitrous oxide
controls). Overall, half of the measures come at societal profit, independent of whether the
motivation to pursue them is improved public health or purely climate change.
The health and quality of life benefits from reducing air pollution are substantial. Using
IIASA's health models, life expectancies in China and India were found to be reduced by an
average of 3 years per person due to air pollution of particulate matter under business-as-
usual conditions.18 This is an average over the entire population, but only a subset of the
population actually dies of air pollution influenced causes. For the individuals affected,
years of life lost are substantially higher. Using the same models, it was found that if the full
abatement potential of black carbon were captured in China and India, life expectancies in
2030 in these countries could be increased by an average of 2-4 months per person. There
15 Berntsen et al., CICERO, 2010. Temperature increase target set at 1.5°C warming. In the case of the same abatement for all
climate forcers, maximum temperature is reached after 50 years (1.5% p.a. rate of temperature increase); whereas in the case of
drastic non-CO2 reduction it takes 80 years (1.0% p.a.).
16 Van Vuuren et al., 2006. Including non-CO2 gases is crucial in the formulation of a cost-effective abatement response, and can
reduce costs by 30-40 percent compared to a CO2 only reduction strategy for the same radiative forcing target.
17 Royal Society, 2008.
18 Amann et al, 2008a, and additional GAINS model runs for this study.

13. 13
EXHIBIT 3
Abatement divided into impact and abatement cost
SOURCE: Non-CO2 Climate Forcers Report (2010)
51%
at
profit
49%
at net
cost
78% impact
public health and climate
22% impact
only climate
▪ Improved cook stoves that reduce fuel consumption
compared to traditional residential stoves
▪ Reducing methane emissions from the petroleum and
gas sector by upgrading equipment or improving
maintenance
▪ Improved emissions controls in the transport sector for
both on-road and off-road diesel vehicles
▪ Improved treatment of industrial wastewater that
reduces methane emissions
▪ Reducing leakage
of refrigeration
systems which
saves expensive
refrigerant
▪ Improved nutrient
management in
agriculture
▪ Changing
refrigerant for
motor vehicle air
conditioning
▪ Capturing and
decomposing
nitrous oxide from
acid production
Updated 100706
are many uncertainties surrounding the calculation of health impacts, but these figures
provide a clear indication that there would be large benefits to quality of life. Additionally,
the calculations are for outdoor air pollution only; if indoor air pollution effects were
included the impact would be substantially larger given the higher concentration levels of
black carbon.
Scientists concur that reducing methane will reduce the air pollutant tropospheric ozone,
which consequentially reduces morbidity around the globe. Some health studies have also
identified a link of methane to ozone mortality, but the strength of the connection is under
scientific debate.19
Other, non-climate-related environmental benefits include safeguarding water resources,
protecting forests, increasing crop yields, and reducing the use of fossil fuels, which
improves energy security.
19 The link between methane and mortality assumes that 1) methane contributes to all ozone concentrations and not just background
levels and 2) the dose-response relationship for mortality effects is linear and that there is no threshold below which premature
death does not occur; see also Jerrett, 2009.

14. 14
While a large share of the measures is relatively straightforward to
implement, capturing the remainder will be challenging, as millions of
people would need to take action, some of whom are the world’s poorest
Reducing emissions of non-CO2 forcers is comparatively straightforward on some
dimensions. In many cases, there is little infrastructure “lock in” since emissions sources
such as refrigerators and diesel engines are replaced every 10 to 15 years. In cases of capital
intensive assets, such as coal mines or landfills, there are “end of pipe” technologies
available that do not require stock replacement. Moreover, the technologies are largely
already available today, well understood, and relatively simple.
However, half of the abatement potential for non-CO2 climate forcers comes at a net cost
to society. And even those measures that come at a net profit, such as more efficient brick
kilns, may prove difficult to finance as the initial investments are needed from some of the
world’s poorest. Individual families, rural farmers, and small businesses will have
significant difficulty in gathering the necessary capital for new appliances, diesel retrofits,
or alternative fertilizers. The very poor will have no ability to switch cookstoves without
direct financial assistance. Governments wanting to pursue these abatement measures will
have to devise both regulatory and fiscal policies to address these challenges.
Additionally, many of the sources of non-CO2 emissions are relatively small and diffuse,
such as agricultural emissions. The majority of the abatement opportunity is in the
developing world where many countries are not as well equipped with institutions or
resources to reach and change the conduct of thousands – or sometimes millions – of
individuals. These countries will need to develop regulatory expertise to set standards, and
enforce as well as monitor progress towards goals, such as those set for industrial
mandates. For other measures, such as in agriculture, the expertise and capacity to educate
people on emissions abatement measures will need to be built up.
In developed countries, the principal abatement opportunities lie in waste
management, air conditioning and refrigeration, and diesel engines
The developed world has taken significant strides to reduce air pollution, and climate change
legislation has either been enacted, as in the European Union, or is under consideration.
However, there are a number of further steps that can be taken to reduce emissions from the
non-CO2 forcers that will complement efforts to reduce CO2 emissions.
The three areas with the largest abatement potential are: the reduction of emissions from
landfills, either through methane capture or composting; the reduction of f-gas emissions by
using new coolants in motor vehicle air conditioning and new systems for retail food
refrigeration; and, in the near term, retrofitting of existing vehicles with diesel engine
particulate controls.

15. 15
Opportunity areas for developing countries are diesel engines, natural gas
production, waste management and traditional combustion technologies
In the developing world, different social, economic, environmental, and health objectives
vie for resources. Nonetheless, significant efforts have been made to reduce air pollution and
to increase energy efficiency in order to improve public health and limit climate warming.
Further potential exists to reduce the non-CO2 forcers, which will complement these efforts.
The developing world will account for over 80 percent of non-CO2 emissions in 2030. Thus,
in line with CO2, it is the developing world that has the largest abatement potential, and it is
there that most investments will be required to capture that potential.
Four emissions sources could each provide around 15 percent of the total abatement
potential: diesel engines, natural gas production, waste management, and traditional
combustion technologies. Diesel engine particulate controls for new on-road and off-road
vehicles would reduce health-damaging black carbon emissions. Methane emissions that are
vented during natural gas production and from solid waste landfills can be captured and
utilized. Improving traditional combustion technologies—such as cook stoves and brick
kilns—would both increase energy efficiency and reduce black carbon. At about 10 percent
each of the total abatement opportunity, changed rice growing and livestock practices can
reduce emissions, though these are challenging to implement.
None of the measures in this report can substitute for the immediate and
massive carbon dioxide reductions needed for long-term climate stabilization.
Non-CO2 mitigation measures are complementary to CO2 controls.
Carbon dioxide accounts for more than half of global warming. Its atmospheric
concentration has risen 35 percent since 1750 and is now at about 390 ppmv, the highest
level in 800,000 years. Annual CO2 emissions must be reduced more than 80 percent to
stabilize carbon dioxide concentrations in the atmosphere. If global CO2 emissions peak in
the next decade and fall to 50-85 percent of 2000 levels by 2050, global mean temperature
increases could be limited to 2.0-2.4°C above pre-industrial levels.20
The need for CO2 reductions is urgent. Even a few years' delay in the peak can mean the
world is committed to a significantly higher temperature rise than would otherwise be the
case - for every ten years the peak is postponed, another half degree of temperature increase
becomes unavoidable.21
Non-CO2 mitigation measures will not eliminate the need for massive CO2 reductions but
can ease the pathway to long-term climate stabilization. Non-CO2 measures will slow the
20 Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia, 2011, National Research
Council.
21 Dr. Vicky Pope, Hadley Centre, Director of Climate Change, 2008.

16. 16
rate of temperature change over the next several decades. The near- and mid-term benefits
of non-CO2 abatement will also reduce the risk of triggering irreversible tipping points in the
earth’s climate system, as well as capturing public health benefits. Combining CO2 and non-
CO2 strategies, therefore, offers the greatest chance of achieving the limitation to 2 degrees
Celsius of warming adopted in the Copenhagen Accord.

17. 17
Study approach
There are three parts to the analysis of non-CO2 climate forcer abatement. The first is the
choice of climate metrics to quantify the global warming impact of the four non-CO2
forcers. The second is to determine the business-as-usual (BAU) emissions baseline, as well
as the abatement potential and cost, forming the abatement cost curve. The third examines
the non-climate related benefits of abatement, with a focus on public health.
Climate metrics
This section covers the metrics chosen to quantify climate “forcing” – the impact that
GHGs and aerosols have on the energy balance of the earth. The potency of a climate
forcer is characterized by its radiative forcing and its global warming potential. The
concepts of radiative forcing (RF) and global warming potential (GWP) were introduced
in the late 1980s. Now enshrined in the Kyoto Protocol, RF and GWP are the prevailing
climate metrics in the international climate community.
Radiative Forcing is the rate of energy change from a pulse of emissions, per square meter,
at the top of the atmosphere. RF may be positive (warming) or negative (cooling). RF
values come from satellite data, climate models, and direct observations in laboratory or
field experiments. RF can be direct (from the emissions themselves) or indirect (from the
interaction of those emissions with other physical factors, such as clouds or rain).
Global Warming Potential is defined as cumulative radiative forcing, over a specified
time period, from one unit of a given climate forcer’s emissions, relative to the same
mass of carbon dioxide which is by definition valued at one (1.0). Since the mass of the
two pollutants being compared is the same, GWP values can then used to calculate
metric tonnes of CO2 equivalent (tCO2e). Carbon dioxide is the basis of comparison for
all GWP values because it is the primary cause of anthropogenic climate change. GWP
values come from multiple data sets and analyses, the most comprehensive of which are
set forth in the IPCC AR4 from 2007.
Different climate forcers endure in the atmosphere for different periods of time. For
example, CO2 persists almost infinitely while black carbon falls to the surface within days.
Climate forcers with shorter lifetimes trap more heat initially but diminish in potency over
time. Long-lived climate forcers, by contrast, are dominant over extended periods of time.
To capture these differences, GWP values are calculated over a specific time interval to
reflect the total relative warming effect of the forcers over that interval.

18. 18
EXHIBIT 4
Metrics options
SOURCE:Non-CO2 Climate Forcers Report (2010); IPCC SAR, IPCC AR4; Fuglestvedt, 2009
Global Warming Potential –
20 Year (GWP20)
Instantaneous
Radiative Forcing (RF)
Global Warming Potential –
100 Year (GWP100)
Communication units
▪ W/m2 ▪ CO2e (GWP20) ▪ CO2e (GWP100)
Description
▪ Additional energy captured
in the Earth-atmosphere
system by a climate forcer,
as a reference to the base
concentration in the
atmosphere
▪ Time integral of radiative
forcing over 20 yrs for a “pulse
of emissions” (e.g. 1 kg)
▪ Expressed in terms of
equivalent radiative forcing
over the period that would
result from a “pulse” of CO2
▪ Time integral of radiative
forcing over 100 yrs for a “pulse
of emissions” (e.g. 1 kg)
▪ Expressed in terms of
equivalent radiative forcing over
the period that would result
from a “pulse” of CO2
Advantages
▪ Pure physical discussion
▪ Captures climate effect of
each climate forcer
▪ Accounts for fact that climate
change occurs over long time
scales and forcers have different
atmospheric lifetimes
▪ Comparability across climate
forcers
▪ Most commonly used metric,
familiar to policy makers
▪ Accounts for fact that climate
change occurs over long time
scales and gases have different
atmospheric lifetimes
▪ Comparability across climate
forcers
Drawbacks
▪ RF value is an instantaneous
value upon emission, does not
include lifetime effect
▪ Assumes all radiative forcing
acts equally on climate, but in
models shown to depend on
location, season, etc.
▪ Not familiar to policy makers
▪ Timescale-dependent, with value
placed on near-term effects
▪ Assumes all radiative forcing acts
equally on climate, but actually
varies on location, season, etc.
▪ Partly familiar to policy makers
though not highly used in the
literature
▪ Timescale-dependent, with
value placed on long-term
effects
▪ Assumes all radiative forcing
acts equally on climate, but in
models shown to depend on
location, season, etc.
Mass of climate forcer
▪ Metric tonne
▪ Mass of climate forcer
emitted over a period
of time
▪ Pure physical discussion
▪ Warming potentials could
be applied later as
needed
▪ Would not give a clear
indication of relative
importance of different
forcers to allow
comparison
Methane Example
▪ 1.82 x 10-13 W/m2/kg ▪ 72 (AR4) ▪ 21 (SAR)▪ 1 metric tonne (t)
Updated
100630 –
latest in
report
In this study, we use 100-year GWP to describe the long-term effects of climate forcing and
to calculate CO2 equivalents. The values for 100-year GWP are taken from the IPCC’s 2004
Second Assessment Report to conform this report to previous cost curves for GHGs and to
US EPA's baseline values. This is the most common climate metric in the world and is used
widely in policy discussions and by international climate organizations like the UNFCCC.
It is also the basis for international emission trading regimes, meaning that policy concerns
can arise whenever the metric is employed in new ways (see below). Climate scientists
view 100-year GWP as the best available compromise for comparing short and long lived
species, though it has severe limitations at both temporal extremes (very short and very long
time spans).
By using 100-year GWP values, it is not our intent to imply that all climate forcers are equal
or interchangeable. For example, we are not advocating that black carbon be added to
international emission trading schemes simply because it can be expressed in CO2e units.
Trading rules and other international climate agreements are beyond the scope of this report.
Rather, we used 100-year GWP values to convey the relative weight of non-CO2 measures
to each other and to compare their aggregate impact to prior work on GHG abatement cost
curves. We believe that tonnage-based calculations are a useful orientation to mitigation
options even if they do not perfectly capture how the climate responds to various
interventions.

19. 19
To describe the impact that the non-CO2 forcers have on the rate of temperature change, a
shorter-term perspective, we applied 20-year GWP values in this study. Methane, with a
lifetime of 12 years, has a GWP of 21 over the 100-year interval but a much stronger GWP
of 72 over the 20-year interval. For 20-year GWP calculations, the values from the IPCC’s
2007 Fourth Assessment Report are used, reflecting the latest scientific assessment. Global
average GWP values for black and organic carbon are derived from Rypdal et al. (2009) and
fall in the mid-range of recent estimates.22 (Exhibit 4.)
There is no “correct” or “perfect” GWP value. Focusing on near term effects generates
higher values for short-lived forcers. Conversely, long-lived climate forcers show the
highest warming potential over a century or more (Exhibit 5). Both metrics are only rough
approximations of what is actually happening in the atmosphere. Moreover, neither 100-
year nor 20-year GWP values convey the full range of climate effects or regional
differences. Detailed atmospheric modelling with high scale geographical resolution is
needed for the latter. The IPCC has recognized that new metrics are needed and
commissioned a special committee on this topic. A more detailed discussion of these issues
is provided in Appendix F.
22 See e.g., Bond, 2007; Boucher and Reddy, 2008; and Rypdal et al., 2009.

20. 20
EXHIBIT 5
Source: IPCC AR4 WG3, Figure 2.22, 2007.

21. 21
Business as usual emissions and abatement cost curve
The analysis starts with an understanding of the business-as-usual emissions trajectory from
2005 to 2030. The inventory of emissions in 2005 is used as the base year, as this is the last
year in which reliable data can be gathered from across sectors and climate forcers. The
2005 inventory is then extrapolated into the future using several methods, including basing
future growth off historical growth patterns or in projecting activity data, such as with the
number of vehicles in the transportation sector, and then estimating future emissions based
on emissions factors, i.e., the amount of climate forcer emitted per unit of activity. For
methane, nitrous oxide, and f-gases, the analyses rely mainly on assessments by the US
Environmental Protection Agency’s (US EPA) 2006 Global Anthropogenic Emissions
Report, as well as other complementing sources. The effect of CDM projects on BAU
emissions is accounted for to the extent that the US EPA included it in their analyses. For
black carbon, emissions factors are largely drawn from Bond (2007) and the GAINS model
from the International Institute for Applied Systems Analysis (IIASA, 2010), and were
compared against estimates by Tsinghua University in Beijing. Energy-use data have been
derived from the International Energy Agency (IEA), GAINS, and other sources. The BAU
assumptions are described in more detail in Appendix F.
The methodology used to calculate the abatement potential and cost is based on that used in
McKinsey's Pathways to a Low-carbon Economy (2009), which is similar to that used by
other researchers in the field. The combined axes of an abatement cost curve depict the
available technical measures, their relative impact (volume reduction potential), and cost in
a specific year. Potential and cost are incremental to the BAU case (Exhibit 6).
The width of each bar on the cost curve represents the technical potential (not a forecast) to
reduce emissions by that measure, assuming that implementation starts in 2010. This
technical potential assumes concerted action to capture the opportunity. The height of each
bar represents the average cost of avoiding one metric tonne of carbon dioxide equivalent
(tCO2e). Abatement costs are defined as the incremental cost of a low-emission technology
compared with the BAU case measured as USD/tCO2e of abated emissions. Abatement
costs include annualized incremental capital expenditure and changes in operating
expenditure. The cost therefore represents the “project cost” of installing and operating the
low-emission technology, and excludes transaction costs such as capacity building,
education, and enforcement monitoring. Transaction costs will depend on the policies
chosen to incentivize implementation.

22. 22
EXHIBIT 6
Abatement cost curve methodology
SOURCE: McKinsey
Abatement cost
USD/tCO2e
Abatement potential
tCO2e per year
Width quantifies emission reduction
potential relative to BAU
Height quantifies incremental cost relative
to BAU (incremental annualized capital costs
plus change in net operating costs)
Abatement cost
[Full cost of CO2e efficient alternative] [Full cost of reference solution]–
[CO2e emissions from alternative][CO2e emissions from reference solution] –
=
pdated
00630 –
test in text
The cost curve takes a societal perspective instead of that of a specific decision-maker, such
as a company or a consumer, illustrating the costs required of the society. The societal
perspective uses a real long-term government bond rate of 4 percent for repayments, based
on historical global averages for long-term bond rates. Furthermore, subsidies, taxes, and
CO2 prices are excluded. From an investor/decision-maker perspective, there could be
higher costs, such as an increased cost of capital or tax implications.
The societal perspective enables the usage of the abatement cost curve as a fact base for
global and country discussions about what levers exist to reduce emissions, how to compare
reduction opportunities and costs between countries and sectors, and how to discuss what
incentives (e.g., subsidies, taxes, and CO2 pricing) to put in place. While we realize that the
choice of which emission reduction measures to implement involves many non-economic
considerations, this societal project economics perspective can be a useful starting point for
discussions on how to reduce emissions and prioritize abatement action.
It has been necessary to make many assumptions in order to estimate the impact and cost of
the abatement opportunities. We believe all figures are reasonable estimates given the
information available, but they inevitably contain uncertainty. Each step of the analysis
contains a degree of uncertainty—the emissions inventory, the emissions growth trajectory,
the scientific assessment of the climate impact of each climate forcer, the abatement
potential, and the abatement cost. The largest areas of uncertainty for the purposes of this

23. 23
report are the emissions inventory, GWP values, and the abatement implementation shares.
Given these uncertainties, a Monte Carlo analysis was used to describe the range of
abatement potentials that might be expected. (For further discussion of the uncertainties, see
the Global Perspective chapter of this report.)
Health benefits
It is very difficult to calculate the health benefits of non-CO2 interventions for three reasons.
The first obstacle is data availability. Measurements of existing air pollution exposures and
mortality rates are limited, and some countries have no ambient particulate measurements at
all (a necessary prerequisite to evaluating black carbon changes). The second obstacle is
methodological. Large-scale air quality models are substantially less reliable than higher
resolution urban air shed models, adding a higher degree of uncertainty. The third and final
problem is imprecision about the effect of each technological intervention. For all of these
reasons, the health analyses below should be viewed as indicative rather than determinative.
To analyze the impact of the abatement of black carbon on health, IIASA performed
calculations with their scientific air pollution model, described in their GAINS model
documentations.23 For methane, this analysis is based on scientific studies by West et al.24
and Fiore et al.25 More information about the air pollution and health effects of black
carbon, methane, and tropospheric ozone can be found, for example, in documents from the
Pew Center26 and Smith.27
Black Carbon: IIASA's GAINS model determines the effect of particulate matter PM2.5
emissions, which are directly associated with black carbon, on a decrease in statistical life
expectancy. When assessing the benefit of black carbon abatement, the difference between
two cases is calculated: the business-as-usual case and the abatement case. This will show
the improvement of statistical average life expectancy due to abatement.
In detail, IIASA describes the approach as follows:
"For Asia (i.e., China, India, Pakistan), the GAINS analysis uses
 annual mean PM2.5 concentrations of primary particulate matter (black carbon, organic
carbon, other organic matter, mineral dust, etc.) and secondary inorganic aerosols
emitted from anthropogenic sources as calculated with the GAINS model (based on
23 Amann et al., 2008a; Amann et al., 2008b.
24 West et al., 2006.
25 Fiore et al., 2008.
26 Pew Center, 2009.
27 Smith, K., 2009.

24. 24
TM5 calculations), distinguishing in each grid cell urban background and rural
concentrations. The health impact calculation does not quantify impacts from emissions
from natural sources and of secondary organic aerosols
 population maps with a 1*1 degree resolution distinguishing urban and rural population
in each grid cell
 population projections by cohort up to 2030 from IIASA’s World Population
programme by country
 epidemiological evidence on premature mortality as reported by Pope et al., 2002 for
the United States and the relative risk numbers given in this paper
 life tables that quantify current mortality rates for different cohorts for China, India,
Pakistan, as well as the life table of Japan, from the UN population database
The current GAINS calculation assumes a linear exposure-response curves up to the
concentrations calculated for future years (i.e., up to 200 µg/m3) based on the findings of the
PAPA study (2004)."
IIASA also takes into account uncertainties around applicable rate of health risk and
baseline mortality rates. The results represent the mean of the uncertainty analysis.
For this report, the black carbon analysis was undertaken for China and India only and
separately, as these are the countries where the abatement potential for particulate matter is
greatest. It should be noted that the model only calculates the effect on health of lowering
outdoor air pollution levels. Lowering indoor air pollution levels from cookstoves would
have greater impact given the very direct exposure of people, particularly women and
children, to pollutants from that source category.
Methane: Health is affected via tropospheric ozone, to which methane is a precursor.
Tropospheric ozone is also referred to as ground level ozone. Ozone is a secondary pollutant
that is formed through complex photochemical reactions involving nitrogen oxides and
volatile organic compounds in the presence of ultraviolet sunlight. Tropospheric ozone
concentrations have doubled worldwide since preindustrial times.
Studies identified a significant association between long-term ozone exposure and
cardiovascular, cardiopulmonary, and respiratory health issues. Ozone has also been
associated with morbidity, including asthma exacerbation and hospital admissions for
respiratory causes. Some studies (West, Fiore, Jerrett) also indicate a link between ozone
exposure and premature mortality, and suggest a linear dose-response relationship.
However, the strength of the mortality finding at low ozone concentrations is scientifically
debated and there is not yet consensus. 28
28 Smith, K., 2009.

25. 25
Methane abatement first reduces emissions of methane, then, with a time lag, atmospheric
concentrations of methane, which subsequently lowers the levels of tropospheric ozone,
improving health. We relied in our health benefits calculation on two main studies: West et
al.29 calculated the impact on premature deaths from a constant 20 percent reduction in
methane emissions starting in 2010 and sustained into 2030. A constant reduction of 65 Mt
of methane per year would result in approximately 30,000 reduced premature all-cause
mortalities in 2030.
In detail, West et al. state: "We first estimate the global decrease in surface O3 concentration
due to CH4 mitigation, using the MOZART-2 global three-dimensional tropospheric
chemistry transport model. This spatial distribution of O3 is then overlaid on projections of
population, and avoided premature mortalities are estimated by using daily O3-mortality
relationships from epidemiologic studies from Bell and others."
The study from Fiore et al.30 demonstrated how scenarios like this can be used to calculate
the health impact for different abatement pathways. Based on these studies, premature, all-
cause mortality in 2030 is derived from the abatement potential identified in this study.31
Those calculations are founded on two key assumptions for the link between methane and
mortality: 1) methane contributes to all ozone concentrations and not just background levels
and 2) the dose-response relationship for mortality effects is linear and there is no threshold
below which premature death does not occur.
Knowledge about the connections between methane and health effects is still nascent, e.g.,
in models to analyze global levels of tropospheric ozone or the contribution of methane to
background vs. peak level ozone. Jerrett et al.32 released a study in which the researchers
"were unable to detect a significant effect of exposure to ozone on the risk of death from
cardiovascular causes when particulates were taken into account, but... did demonstrate a
significant effect of exposure to ozone on the risk of death from respiratory causes."
Scientific work is ongoing to better understand these linkages.
29 West et al., 2006.
30 Fiore et al., 2008.
31 The 2030 number gives a conservative picture of the health benefits. In 2030, only 51 percent of the full positive health effect of
abatement is reached due to time lag between cause and action. In 2050, 90 percent of the full effect could be observed based on
modelling, if abatement is kept at a constant level.
32 Jerrett et al., 2009.

26. 26
Global perspective on non-CO2 climate
forcers
Black carbon, methane, nitrous oxide, and f-gases collectively cause at least one
quarter of global warming and accelerate the rate of temperature change. In
addition, black carbon and methane contribute significantly to air pollution,
which causes millions of premature deaths and even higher incidence of disease
Emissions sources for non-CO2 climate forcers
CO2 is the most common of the greenhouse gases (GHGs) and one of the longest lived in the
atmosphere. It is therefore the largest contributor to long-term temperature increase, both in
terms of the impact of historical emissions since the industrial revolution and of that of
today’s emissions.33 Most studies that assess abatement opportunities have therefore
focused on CO2, highlighting actions to transition to an economy that burns dramatically
less fossil fuel and avoids deforestation.
There are a number of other “climate forcers,”34 however, that contribute towards climate
change. Those with the greatest emissions volume are methane, nitrous oxide, the
fluorinated gases (f-gases), and black carbon. These are the focus of this report due to their
relatively strong warming impact and the quantity of emissions.
Black carbon, methane, nitrous oxide, and f-gases are emitted from a variety of sources
(Exhibit 7). Methane and nitrous oxide arise from biological processes in agriculture and
waste decomposition, and from certain industrial processes. F-gases are used as coolants in
refrigeration and air conditioning and are emitted to a lesser extent from industrial
processes. Black carbon, an aerosol, results from incomplete combustion—that is, when a
carbonaceous fuel fails to be fully converted into CO2. The main sources of human-induced
black carbon emissions are diesel engines, industrial and domestic kilns and stoves,
agricultural burning, and planned forest fires. In this report, the global warming potential
(GWP) of black carbon is net of the cooling effect of organic carbon, which is co-emitted in
the combustion process.35 (See sidebar, “Climate effects of black carbon.”)
33 IPCC Fourth Assessment Report, 2007.
34 We use the term “climate forcers” as a summary term for the greenhouse gases and aerosols that have an impact on the energy
balance of the Earth. See the GWP Sidebar.
35 Combustion processes also emit other pollutants such as CO and SO2. Their climate effects have not been included in the net
effect of black carbon as shown in this report.

27. 27
EXHIBIT 7
Non-CO2 climate forcers – emission sources
▪ GHG, emitted from industries
and anaerobic digestion
▪ Precursor to tropospheric
ozone which causes disease
and inhibits growth of
vegetation
Description and impact
Methane
(CH4)
SOURCE: Non-CO2 Climate Forcers Report (2010); IPCC Second Assessment Report (SAR) (1995); IPCC Fourth Assessment Report (AR4) (2007); Rypdal
et al. (2009)
Nitrous
oxide
(N2O)
Fluorinated
gases
(F-gases)
Black
carbon
12 years
Lifetime
72
20-year
21
100-year
114 years289310
Varies by
f-gas
(HFC-134a:
14 years)
Main sources
▪ Livestock
▪ Petroleum and
gas production
▪ Rice farming
▪ Waste
decomposition
▪ GHG, primarily formed through
chemical processes in
agricultural soils
▪ Fertilizers
▪ Manure
management
▪ Acid production
▪ GHG, used as coolants
(refrigeration, air-conditioning),
accelerants and insulators
▪ Refrigeration
▪ Air conditioning
▪ Electric power
transmission
▪ HCFC-22
production
▪ Carbonaceous aerosol, emitted
as product of incomplete
combustion
▪ Co-emitted with other
particulates that combined have
strong negative health effects
▪ Increases the rate of Arctic and
glacial melting
▪ Diesel engines
▪ Brick kilns and
coke ovens
▪ Biomass and
coal cookstoves
1-2 weeks3,230917
Varies by
f-gas
(HFC-134a:
1,300)
Varies by
f-gas
(HFC-134a:
3,830)
NOTE: 100-year GWP expressed in SAR values; 20-year GWP expressed in AR4 values
Global Warming
Potential (GWP)
While all four of the non-CO2 climate forcers increase global warming, methane and black
carbon also have additional climate effects. Black carbon influences the hydrological cycle
and snow and ice coverage. Methane, as a precursor to tropospheric ozone, impairs crop
growth. These climate-related effects are explained in more detail in later chapters.
Methane and black carbon also damage health.36 Although significant strides have been
made towards reducing air pollution around the globe, millions of people are still exposed to
dangerous levels—especially in the developing world. Every year, more than 3 million
people37 die from respiratory problems, cardiovascular problems, and lung cancer caused by
indoor and outdoor air pollution. Illness and premature death are the result, which undercuts
productivity and GDP growth in several developing nations.
Business-as-usual growth
In 2005, emissions from the four non-CO2 climate forcers were 15.8 GtCO2e, accounting
for 30 percent of total global warming emissions. This is in addition to the 35.6 Gt of
36 See the chapter "Study Approach" for details.
37 Approximately 1.2 million deaths annually are attributable to urban outdoor air pollution and 2.0 million deaths attributable to
indoor smoke from solid fuels (WHO, 2009).

28. 28
carbon dioxide emissions in 2005. As previous reports38 did not include net black carbon,
the total emissions in 2005 are larger than previously communicated, totalling 51.4
GtCO2e. By 2030, emissions of the four non-CO2 climate forcers are expected to grow to
20.1 GtCO2e, and their share of total emissions will fall slightly to 27 percent. This is due
to the faster annual growth of CO2 emissions (1.7 percent per year) compared with the non-
CO2 forcers (1.0 percent per year) (Exhibit 8).
Because most non-CO2 climate forcers are short-lived compared with CO2, and because they
have a higher GWP, they have a greater short-term impact on the climate and the rate of
temperature change. Using a 20-year GWP, the non-CO2 forcers account for 50 percent of
global warming (Exhibit 9). This higher short-term effect of the non-CO2 forcers provides a
ready opportunity to slow the rate of temperature increase.
EXHIBIT 8
Business as usual emissions of the four non-CO2 forcers and CO2
1 Net of co-emitted Organic Carbon
6
8
9
5
4
3
5
5
6
Carbon
Dioxide (CO2)
Methane
Nitrous Oxide
F-gases
Net Black
Carbon1
2030
75
55
2
2020
66
48
1
2005
51
36
1
Long-term perspective (100 years)
GtCO2e (GWP 100) per year
Covered in
previous
Climate
Works
reports
Covered
in this
report
27%
contribution
SOURCE: Non-CO2 Climate Forcers Report (2010); Pathways to a low-carbon economy (2009); IEA WEO2009; IPCC SAR (1995); IPCC AR4
(2007); US EPA Global Anthropogenic Emissions Report (2006)
38 McKinsey & Company, 2009.

29. 29
EXHIBIT 9
Comparison of near-term and long-term global warming impact
27%
50%
73%
50%
Non-CO2
climate
forcers
CO2
Near-term (20yr GWP)Long-term (100yr GWP)
SOURCE: Non-CO2 Climate Forcers Report (2010); Pathways to a low-carbon economy (2009); IEA WEO2009; IPCC SAR (1995); IPCC AR4
(2007); US EPA Global Anthropogenic Emissions Report (2006)
Percent of total GtCO2e – 2030
Contribution to global warming
In 2030, methane will account for the largest share of non-CO2 emissions (43 percent),
followed by net black carbon (26 percent),39 nitrous oxide (23 percent), and the f-gases (8
percent). Increases in methane and nitrous oxide over the time period are strongly tied to
population growth, which drives more waste creation and more intensive farming methods.
The f-gases are the fastest growing of all the climate forcers, growing at an annual rate of
around 5 percent. A switch to f-gases to replace the ozone-depleting substances (ODS) that
were previously used as coolants and accelerants, as well as an increase in demand for
refrigeration and air conditioning in the developing world, explains this rapid growth.
Black carbon emissions, on the other hand, will fall slowly. Many sources of black carbon,
such as inefficient wood cook stoves and the brick kilns and coke ovens used in industry,
are associated with lower levels of economic development. As wealth grows, black carbon
emissions from these sources should fall, although the gains are somewhat offset by overall
growth in fuel usage (Exhibit 10).
Agriculture accounts for the largest proportion of non-CO2 climate forcers (approximately
50 percent). Emissions from the sector show steady annual growth of 1 percent between
2005 and 2030. Emissions from petroleum and gas, part of the industry sector, and the
residential and commercial sectors will grow slightly faster as a result of higher GDP growth
and higher consumption. Emissions from the transportation sector and other sub-sectors of
39 Net black carbon is the warming impact of black carbon net of the cooling effect of co-emitted organic carbon.

30. 30
the industry sector will grow more slowly thanks to increased energy efficiency, stricter
regulations, and industry initiatives to reduce f-gas emissions.
It should be noted that figures both for current and future emissions are difficult to measure
accurately. This is explained in detail later in this chapter.
EXHIBIT 10
Business as usual emissions of non-CO2 climate forcers
1 Net of co-emitted organic carbon
2 For regional consistency, Mexico is in Latin America and not Other OECD
SOURCE: Non-CO2 Climate Forcers Report (2010)
5.6
5.1
1.6
Methane
Nitrous
oxide
F-gases
Net
black
carbon1
2030
20.1
8.7
4.7
2005
15.8
6.5
3.3
0.5
1.2
4.7
1.5
-0.3
1.0Total
3.1
4.0
1.9
1.9
Agriculture/
forestry
Waste
Residential/
commercial
Industry
Transport
2030
20.1
9.8
1.8
2.6
2005
15.8
7.7
1.4
1.8
Total
0.9
1.0
1.6
1.1
0.1
1.0
By climate forcer
Other
non-OECD
Africa
Latin
America2
India
China
Other
OECD2
EU 27
US
2030
20.1
4.6
3.7
3.1
1.6
3.3
1.2
1.2
1.5
2005
15.9
3.6
2.7
2.2
1.1
2.7
1.0
1.3
1.3
Total
0.9
1.0
1.0
-0.5
0.4
1.0
1.5
1.4
1.3
Annual growth, 2005–2030
Percent
By sector By region
GtCO2e (GWP 100) per year
Emissions from the four non-CO2 climate forcers can be reduced by over 20
percent by 2030 using available methods: fugitive emissions capture, efficient
agricultural practices, combustion optimization, diesel particulate controls, and
alternative cooling technologies
Abatement potential
Using the technical abatement measures identified in this report, there is potential to reduce
emissions from the non-CO2 climate forcers by over 20 percent, or 4.5 GtCO2e, from BAU
levels in 2030. Implementing the measures would also cut CO2 emissions by 0.8 Gt,
bringing the total to 5.3 GtCO2e and effectively eliminating growth in non-CO2 emissions
by 2030. Behavioral change, which was not analyzed in detail in this report, would provide
additional abatement potential, the biggest opportunity being up to 1.8 GtCO2e from reduced
consumption of meat and dairy products.
The 50 abatement measures with the largest potential were assessed and quantified for this
report. There are remaining measures, including those that would reduce PFC emissions

31. 31
(an f-gas), which were not quantified in the costs curves. These are estimated to have a
total global additional reduction potential of about 0.5 GtCO2e.
There are five major groups of opportunities for abatement of non-CO2 forcers (Exhibits 11
and 12):
Capturing fugitive emissions (1.8 GtCO2e of abatement potential in 2030): Climate
forcers emitted from industrial and waste processes can be captured and often re-used. For
example, methane can be used to generate electricity, while f-gases can be recycled or
destroyed. Examples of the way emissions can be captured include the installation of gas
capturing systems at landfill sites; the replacement of equipment used in natural gas
production that would otherwise vent methane, such as pneumatic pumps; and the recovery
and recycling of SF6 (an f-gas), emitted from high voltage switchgears and circuit breakers
for electric power transmission. The technology already exists to do all of this. To illustrate
the potential of this set of abatement measures, around 70 percent (640 MtCO2e) of the
methane produced in landfills by 2030 could be captured using these technologies.
Improving agricultural practices (1.0 GtCO2e): Methane is produced in the rice paddies
of Southeast Asia and India and in the digestive systems of cattle and other ruminants
(enteric fermentation). When the rice fields are flooded, microbes in the soil digest
anaerobically, rather than aerobically, producing methane. Abating these emissions requires
rice farmers to use different farming methods—for example, shallow flooding or mid-season
drainage. These methods are already being used in China. Spreading them worldwide
would reduce emissions by 240 MtCO2e by 2030, or by 30 percent from BAU levels. To
reduce methane emissions from cattle, feed supplements are available and vaccines are
being developed. Nitrous oxide emissions largely stem from the use of fertilizers, when
crops fail to absorb all the nutrients. Abatement entails a variety of management practices
that reduce the application of nitrogen—for example, better crop rotation, using fertilizer
less frequently, or slow-release fertilizers.
Improving combustion technologies (0.7 GtCO2e): Some combustion technologies in the
developing world tend to use dirtier fuels and are less efficient as they do not fully utilize
the fuel. As a result, they emit black carbon. Emissions can be reduced by switching to more
efficient systems, such as by using energy-efficient brick kilns and by fitting coke ovens
with modern emission controls. Additionally, residential cook stoves can be replaced with
more fuel-efficient ones, or by using different fuels, such as liquid petroleum gas (LPG).
Replacing traditional residential cookstoves with more efficient stoves could reduce
emissions by 370 GtCO2e in 2030.
Improving cooling technologies (0.6 GtCO2e): F-gases are used as coolants in
refrigeration and air-conditioning systems. F-gas emissions can be reduced by replacing
them with other gases, by preventing leaks, or both. The high-GWP f-gases used in air-
conditioning systems in motor vehicles can be replaced with gases such as HFO-1234yf,

32. 32
HFC-152, or CO2. This would capture abatement potential of 200 GtCO2e, reducing f-gas
emissions by 75 percent from BAU levels. It is the largest abatement opportunity for f-
gases. In the retail sector, distributed systems and secondary loops using a smaller charge of
coolants can be deployed. In air-conditioning systems installed in buildings, it is often
harder to introduce more climate-friendly coolants due to security and energy efficiency
concerns. Here, the abatement option is to recover the gas.
Reducing transportation particulate emissions (0.5 GtCO2e): Emissions from the
combustion of transport fuels, particularly diesel, in passenger vehicles, trucks, and off-road
machinery can be controlled through available technologies, such as particulate filters.
Introducing particulate filters for new trucks in China, for example, to reach Euro 6
equivalent emission standards, would reduce black carbon emissions per vehicle by more
than 90 percent compared with the Euro 5 standards, due to be introduced in 2012.
EXHIBIT 11
Categories for abatement action
Improving
agricultural
practices
Improving
cooling
technologies
Capturing
fugitive
emissions
Reduced
transportation
particulate
emissions
Improving
combustion
technologies
Main climate
forcers abated Main abatement opportunities
▪ Methane
▪ Nitrous oxide
▪ Replace equipment and improve maintenance in natural
gas production
▪ Capture landfill methane
▪ Capture coal mine methane
▪ Decompose nitrous oxide from acid production
▪ Methane
▪ Nitrous oxide
▪ Improve fertilizer practices
▪ Change flooding techniques to lower water use in rice
cultivation
▪ Black carbon ▪ Use improved cookstoves instead of traditional ones
▪ Replace indigenous with modern brick kilns
▪ Introduce modern emission controls for coke ovens and
improve operations
▪ F-gases ▪ Use lower-GWP refrigerants in existing technologies
▪ Choose cooling designs that use smaller refrigerant charge
sizes and less piping
▪ Repair leaks and recover gas when new technologies are
not available
▪ Black carbon ▪ Equip new on- and off-road vehicles and machinery with
improved emissions control devices (e.g., catalytic
converters, particulate filters)
▪ Retrofit existing diesel fleet with particulate filters
SOURCE: Non-CO2 Climate Forcers Report (2010)

33. 33
EXHIBIT 12
SOURCE: Non-CO2 Climate Forcers Report (2010)
Key opportunities
Improved
combustion
technologies
0.5
15.6
1.0
Abatement
Case
2030
Improved
cooling
technologies
0.7
Capturing
fugitive
emissions
20.1
BAU
growth
15.8
4.3
BAU
Emissions
2005
1.8
Improved
agricultural
practices
0.6
Reduced
transportation
particulate
emissions
BAU
Emissions
2030
-22%
▪ Water and nutrient
management in
rice cultivation
▪ Anti-methanogen
vaccines and feed
supplements for
livestock
▪ Improved
cookstoves and
LPG cookstoves
▪ Replacing
traditional kilns with
vertical shaft and
tunnel kilns
▪ Emission controls
for on-road and off-
road vehicles,
particularly heavy-
duty diesel trucks
▪ Landfill gas
capture
▪ Oxidation of coal
mine ventilation
air and mine
degasification
▪ Electrostatic
precipitators for
coke ovens
▪ Low GWP coolants
for motor vehicle
air conditioning
▪ Lower leakage in
retail food
refrigeration using
secondary loops or
distributed systems
Abatement divided into categories for action
GtCO2e (GWP 100) per year
~40% ~20% ~20% ~10% ~10%
X% Share of total
abatement potential
Methane, the f-gases, and black carbon have the greatest relative abatement potential. In
2030, emissions could be cut by 26 percent, 40 percent, and 24 percent respectively from
BAU levels. Nitrous oxide emissions are harder to tackle, with only 8 percent abatement
potential identified. Emissions would drop if fertilizers were no longer used, but that could
jeopardize productivity and the ability to meet food requirements. Therefore, only
relatively small changes in the amount of fertilizer used are envisaged in this report.
The waste sector is the sector with the greatest relative abatement potential as emissions
can be captured relatively easily for solid waste, which is quite concentrated. The same is
true for the industrial sector, which includes petroleum and gas that emits much methane
from fairly concentrated sources. The agricultural sector is the sector with the highest
emissions, but these are also the most difficult to abate as there are so many small emission
sources. This sector thus has the smallest relative abatement potential—just 10 percent of
2030 BAU levels (Exhibit 13). Across regions relative abatement potential is fairly similar,
with a higher BAU share of f-gases and black carbon in a region increasing the relative
abatement potential (Exhibit 14).

34. 34
EXHIBIT 13
Abatement opportunities 2030 – by sector
Transport 1.9
Waste 1.8
Residential/Commercial 2.6
Agriculture and forestry 9.8
Industry1
4.0
Total
2030 Abatement Potential
GtCO2e per year, (GWP100)
2030 BAU Emissions
GtCO2e per year, (GWP100)
Note: BC emissions shown as net of co-emitted organic carbon
1 Industry includes petroleum & gas and f-gas emissions from power sector
44%
37%
Relative abatement
2030, percent
4.5
2.3 0.4 0.6 1.2
22%20.1
8.7 4.7 1.6 5.1
33%
27%
10%
F-gases
Black Carbon
Methane
Nitrous Oxide
0.7
0.8
0.7
1.0
1.3
SOURCE: Non-CO2 Climate Forcers Report (2010)
EXHIBIT 14
1.6
China 3.3
Other OECD1
1.2
EU 27 1.2
US 1.5
Other non-OECD 4.6
Africa 3.7
Latin America1
3.1
India
Total
Relative abatement
2030, percent
2030 Abatement Potential
GtCO2e per year, (GWP100)
2030 BAU Emissions
GtCO2e per year, (GWP100)
1.3
0.7
0.5
0.5
0.7
0.3
0.2
0.4
21%
15%
25%
20%
30%
18%
18%
F-gases
Black Carbon
Methane
Nitrous Oxide
Abatement opportunities 2030 – by region
22%20.1
8.7 4.7 1.6 5.1
29%
Note: BC emissions shown as net of co-emitted organic carbon
SOURCE: Non-CO2 Climate Forcers Report (2010)
4.5
2.3 0.4 0.6 1.2
1 For regional consistency, Mexico is in Latin America and not Other OECD

35. 35
Abatement cost
Half of the abatement potential identified in this report comes at a societal profit,40
meaning that initial investments would be outweighed by the subsequent economic
benefits. Examples include abatement measures to capture methane gas that is then used to
generate electricity, and the recovery and re-use of f-gases. Another 30 percent of the
abatement potential can be captured in 2030 at up to $20/tCO2e (Exhibit 15). In general,
the methane abatement measures are the least expensive and the black carbon measures the
most expensive. However, the latter also deliver important health and other non-climate-
related environmental benefits.
In our analysis, we did not include a monetary value for the additional benefits of
abatement, such as the value of lives saved or of prevented crop losses. The cost curves
show the pure project costs. Many organizations do assign a value to the prevention of
premature deaths in order to calculate the cost benefit of safety and public health measures.
These should be looked at on a country-by-country basis when prioritizing abatement
measures.
In addition, it should be noted that the cost curve takes a societal perspective, thus taxes and
subsidies are excluded and a societal interest rate is used; an individual decision-maker
would face slightly different costs. Furthermore, transaction costs such as those for capacity
building, education, or enforcement monitoring are excluded, as these will depend on the
policies chosen to incentivize implementation.
40 See the “Study Approach” chapter for a more detailed explanation.

36. 36
EXHIBIT 15
Abatement cost curve of non-CO2 climate forcers in 2030
80
200
3.0 4.0
Abatement cost, societal perspective
USD/tCO2e
-40
60
0
20
40
2.0
Abatement potential
GtCO2e per year
-60
1.00
-20
F-gases
Nitrous oxide
Methane
Black carbon
2.3 GtCO2e at societal profit 1.4 GtCO2e at 0-20
USD/tCO2e
0.8 GtCO2e at >20
USD/tCO2e
SOURCE: Non-CO2 Climate Forcers Report (2010)
Landfill gas - direct use
VSBK replacing BTK & IDK
P&G upstream - equipment upgrades
Rice cultivation - changed nutrient management
Rice cultivation - water management
Improved cook stoves
Composting of new solid waste
Landfill gas - electricity generation
Motor vehicle air conditioning systems – low-GWP refrigerants
Livestock - antimethanogen vaccine
HDV diesel US 04/Euro 5 controls
2-/3-wheeler TWC
Livestock - feed supplements
Agricultural machinery, stage 2 controls
Industrial wastewater - improved treatment
HDV particulate filters, new (Euro 6)
Project cost only, value
of public health and
environmental benefits
not included
100-year
GWP
The capital investments needed to implement all the measures would be approximately $77
billion per year in 2030 (Exhibit 16). Most of this investment is required in the developing
world, as this is where most abatement potential lies. The issue of how the investment will
be financed is outside the scope of this report, which focuses on the technical abatement
measures.
The two sectors with the greatest investment needs are transportation and waste
management. In transportation, black carbon is reduced through the addition of filters and
other capture technologies, and f-gas emissions are reduced by using new air conditioning
systems, both of which require upfront investments, but are relatively modest compared to
the cost of the car. For a light duty vehicle with a production cost of $15,000, the cost
increase of moving to a low GWP air conditioning system would only be about $75 of
incremental investment, or 0.5 percent of the total production cost. The waste sector capital
expenditures are a result of the need to install gas capturing piping and in many cases
electricity generators at landfills and onsite wastewater management systems at industrial
sources.
The capital requirements may look daunting, but are less so if the net cost of the abatement
measures is taken into account. For the abatement that would occur in 2030, less than 15
percent of the total capital investment is needed for those measures that will return a net
profit to society – which represents 50 percent of the total abatement.

37. 37
EXHIBIT 16
By sector
77Total
Incremental investment requirements in 2030
USD billions per year, 2030; in addition to current projected / business-as-usual investments
Abatement volume
incl. CO2 co-effects
(GtCO2e)
0.8
Agriculture &
Forestry
5
11
2
233
1
Waste 35
Residential/
Commercial
Industry
Transport 2810 7 6
5.3
SOURCE: Non-CO2 Climate Forcers Report (2010)
0.8
0.8
1.5
1.4
Solid wasteWastewater
Air
conditioning
LDV/MDV
motorcyclesHDVs Off-road
Updated 100701
Uncertainty
The state of knowledge regarding these four climate forcers is less advanced than that for
carbon dioxide because it is more difficult to quantify their impact and abatement potential.
Emissions estimates are less precise as sources are more difficult to measure and there have
been fewer analyses conducted. For example, methane comes from leaks that are difficult to
identify and biological sources that are subject to varying conditions. Additionally, there is
some uncertainty about the magnitude of the effect that these climate forcers have on
temperature. Black carbon is the most uncertain with a range of almost ±50 percent on its
radiative forcing impact plus additional uncertainty related to aerosol cloud interactions.
Despite this uncertainty there is strong evidence that it has in summary a net warming effect
and accelerates the melting of ice and snow.
There is a rapidly growing body of research that has helped to narrow these uncertainties.
Methane, nitrous oxide, and f-gases are included in the Kyoto Protocol and therefore have
been a part of national submissions to the UNFCCC, and of several other inventory and
future projection analyses. Black carbon, while not included in these submissions, is being

38. 38
actively studied by several leading researchers41 with a number of publications in 2011 and
2012.
Some have argued that there are too many uncertainties surrounding those non-CO2 climate
forcers for policymakers to take any decisive action. However, the conclusion of this
research is that the uncertainties involved do not detract from the main findings. Non-CO2
climate forcers cause a substantial portion of global warming (at least 25 percent, but likely
closer to 30 percent) and black carbon and methane increase air pollution and consequential
disease and premature mortality. Furthermore a range of abatement measures exists that can
be quantified (at least 3.5 GtCO2e of abatement potential, but likely over 5 GtCO2e) to
capture both climate and associated public health benefits.
That said, it is important to understand how the uncertainties might impact the more
detailed analysis. To account for those, a Monte Carlo analysis was performed to assess the
expected value and variation for the baseline emissions (expressed in CO2e) and the
abatement potential in 2030.
The major areas of uncertainty are:
Emissions inventory: The difficulty in measuring emissions arises from both a lack of
global data and the nature of the emissions. Human-induced CO2 largely results from
burning fossil fuels, which directly correlates with CO2 emissions, and for which fuel
consumption is measured. Non-CO2 forcers, however, often leak into the atmosphere or
result from incomplete combustion processes, making it more difficult to measure
emissions or even identify all the sources. In this analysis, the uncertainty bands from the
US EPA 2010 United States Inventory of Emissions42 are used for methane, nitrous oxide,
and f-gases. For example, the inventory range for nitrous oxide is from about 10 percent
lower to nearly 50 percent higher emissions. This EPA source likely underestimates the
range of uncertainty as global emissions measurements are more difficult to obtain
compared to those for the United States. The uncertainty bands for the black carbon
inventory are those used by Bond et al.43 Please see Appendix E for areas of suggested
further scientific research that would reduce inventory uncertainty.
Global warming impact: Sophisticated climate models exist to understand the impact that
human-induced emissions have on the climate. Scientists use these models to derive the
GWP values that allow them to compare the global warming impact of the different
climate forcers (see also the chapter “Study Approach – Climate Metrics”), but there is still
uncertainty around these numbers. This report uses the uncertainty bands for methane,
nitrous oxide, and the f-gases from the IPCC’s Fourth Assessment Report at ±35 percent of
41 See for example, Bond (2007); IIASA GAINS model; and Fuglestvedt (2009).
42 US EPA (2010).
43 Bond et al. (2007).

39. 39
the 100-year GWP value for these greenhouse gases.44 For black carbon, whose climatic
effects are less well understood, recent 100-year GWP estimates range from 200 to 1500.45
The GWP value used in this report, of 917, falls in the mid-range of these estimates, where
recent studies, including the ongoing assessment “Bounding the Role of Black Carbon in
Climate,”46 seem to converge. The 95 percent confidence interval for black and organic
carbon is still under scientific discussion, but for this analysis we have used an uncertainty
band for the GWP for black carbon of 490 to 1350, where the most common values lie.
Implementation share: The extent to which emissions can be reduced depends on
technical feasibility and costs, which in turn determine the percentage of an activity that
can be changed through implementation of the abatement measure. It also depends on the
skill and ambitions of the program and individuals. The abatement potential in this report
is based on technical implementation shares used in previous assessments made by the US
EPA, by IIASA, by the Technology and Economic Assessment Panel of the Montreal
Protocol (TEAP), by McKinsey & Company; and by expert panels formed for this report.
Together, these three major areas of uncertainty can have a significant impact on the total
abatement potential. The first two suggest that this report likely underestimates BAU
emission levels. This is for two reasons. First, because of the nature of the emissions,
many are likely to be overlooked. Second, this report uses the IPCC’s Second Assessment
report 100-year GWP values for methane, nitrous oxide, and f-gases, as these are still
widely used. However, these GWP values are lower than those in the IPCC’s more recent
Fourth Assessment report – which means that on average the impact of these emissions on
the global climate are underestimated. Adjusting for these two factors would raise BAU
emission levels by 22 percent (Exhibit 17). The full range is from about 25 percent lower
to nearly 95 percent greater than the value of 20.1 GtCO2e identified in the main text.
Additionally, the analysis indicates that there is a less than 15 percent probability that
emissions in 2030 would be less than 20 GtCO2e under business-as-usual. This implies that
non-CO2 forcers contribute at least 25 percent, but more likely 30 percent to global
warming in 2030.
44 In the main analysis, we use the GWP values from the Second Assessment Report in order to make our report comparable with
other reports, which though still within the bands of uncertainty are not the expected values.
45 Bond et al., 2005; Bond, 2007; Boucher and Reddy, 2008; and Rypdal et al., 2009.
46 A study is currently underway which will further narrow the uncertainty around the global warming potential of black carbon.

40. 40
EXHIBIT 17
Uncertainty around the business-as-usual emissions - 2030
SOURCE: Non-CO2 Climate Forcers Report (2010)
0
5
10
15
20
Total BAU emissions
GtCO2e / year - 2030
% Probability
Expected value (after
uncertainty analysis)
24.5 GtCO2e
Base case
20.1 GtCO2e
+22%
GtCO2e (GWP 100) per year
16 18 20 3422 24 26 28 30 32 36 38
Updated 100701
Abhishek
An increase in abatement potential of approximately 22 percent would follow from the
previous analysis, as it raises the business-as-usual emissions. However, adding in the
uncertainty around the implementation shares reduces this expected increase in abatement
potential. The reason is that the distribution of implementation shares is expected to be
skewed towards lower rather than higher values, because the factors discussed above are
likely to make reductions harder rather than easier to capture. This would bring the
expected abatement potential to 5.3 GtCO2e for the non-CO2 forcers, 16 percent higher
than the 4.5 GtCO2e discussed in the main text (Exhibit 18). The full range of potential
values is from about 30 percent lower to nearly 90 percent greater abatement – making it
an essential contributor to solving the climate challenge.

41. 41
EXHIBIT 18
Uncertainty around the abatement potential for non-CO2 forcers– 2030
SOURCE: Non-CO2 Climate Forcers Report (2010)
0
5
10
15
20
Abatement potential
GtCO2e / year
% Probability Expected value (after
uncertainty analysis)
5.3 GtCO2e
Base case
4.5 GtCO2e
+16%
GtCO2e (GWP 100) per year
3 4 5 6 7 8
NEEDS UPDATING –
Abhishek please use this
format
Updated 100701
Abhishek
The cost of abatement, which is driven by factors such as capital costs, is also uncertain.
In general, almost all cost assumptions are specific to individual abatement measures and
any changes in input costs do not have a large impact on the overall results. The major
exceptions to this are energy prices and societal interest rates, to which the analysis is quite
sensitive. Many abatement levers either save fuel, such as natural gas equipment
replacements, or use more fuel, such as some off-road vehicle particulate control measures.
A 50 percent increase in energy prices results in a 30 percent reduction in the average cost
of abatement from baseline levels going from about $11/tCO2e down to $8/tCO2e. Higher
energy prices lead to a lower cost of abatement because of the sales value of methane and
fuel savings in some black carbon and f-gas abatement.
Changes to the interest rate likewise have a strong impact on the cost of abatement. If
interest rates go up to 10 percent from 4 percent, closer to investor interest rates, emissions
reduction measures with large capital costs become more expensive. The average cost of
abatement rises about 75 percent with such an increase, to nearly $20/tCO2e.
The major implications of this uncertainty analysis are, first, that it is likely that we have
underestimated the size of the overall emissions, which would increase their importance in
global temperature stabilization discussions. Second, it is likely that a lower percentage,
but a higher absolute value, of emissions will technically be able to be reduced. Costs will
change significantly if key externalities such as energy prices change; however, changes in
individual lever costs only marginally impact overall findings. Consequently, the

42. 42
uncertainties are not such that they would change the basic findings of the report – there is
enough known now to support action.
Reducing non-CO2 emissions is essential to limit global warming during this
century, slow the rate of temperature increase, and reduce the risk of adverse
climate feedbacks
There are three angles from which to assess the need for urgency to reduce the non-CO2
climate forcers in parallel to carbon dioxide. The first is the need to limit global warming,
given that many governments and scientists have agreed on 2 degrees Celsius as the
maximum acceptable increase.47 The second is the need to reduce the rate of temperature
increase as this rate influences the ability of ecosystems to adapt.48 The third is the need to
reduce the risk of adverse climate feedbacks on both a global and regional scale. One
example of an adverse climate feedback is accelerated Arctic melting, which would further
speed up temperature increases.
Ultimately, long-term temperature increases and temperature stabilization levels after
mitigation will be determined by the level and pathway of carbon dioxide emissions, the
most prevalent GHG. Still, abating non-CO2 climate forcers in parallel to CO2 is essential to
achieving temperature stabilization at all. Even assuming no growth in non-CO2 emissions
after 2030, there would be about 20 GtCO2e of emissions without abatement. This amount
represents nearly all of, if not more than, the total emissions per year that could be
perpetually emitted without further increasing the temperature, i.e., the level that would
enable temperature stabilization. No abatement of the non-CO2 forcers would essentially
mean that CO2 emissions would need to be cut close to zero in order to achieve stabilization.
In the short term, non-CO2 abatement has an even greater impact on slowing the rate of
temperature increase, due to the high short-term warming effect of those climate forcers.
The IPCC has concluded with high confidence that temperature increases are already
occurring and having an effect on ecosystems.49 Evidence includes glacial melting rates,
earlier “greening” of vegetation, shifts in plant and animal ranges towards the poles and to
high altitudes, and changes in aquatic life associated with warmer ocean temperatures. The
rate of change in local climate has implications for the ability of those ecosystems to adapt:
the faster the change, the lower the ability to adapt, and the higher the risk of irreversible
changes. Berntsen et al. demonstrated that drastically reducing non-CO2 climate forcers in
the short term prolongs the time to reach maximum temperatures by several decades –
47 See e.g., Copenhagen Accord, 2009.
48 Root et al., 2003.
49 IPCC AR4, 2007.

43. 43
slowing the rate of change, thus improving the ability to adapt.50 Van Vuuren et al. confirm
this finding and conclude that multi-gas abatement scenarios are also the most cost-effective
way to contain warming.51
Moreover, reducing black carbon would help alleviate non-temperature-related climate
changes, such as the melting of glaciers and arctic ice through changes in surface
reflectivity. This melting would otherwise accelerate the rate of temperature change by
exposing darker surfaces underneath and also contributes to potential sea level increases.
Abating methane, which as a precursor of tropospheric ozone damages vegetation, would
improve the ability of plants to sequester carbon.52 These are both areas where abatement
would substantially reduce adverse climate feedbacks.53
On top of the positive climate effects, 80 percent of the measures also improve
public health and half come at a net savings to society
Reducing methane and black carbon emissions will deliver near-term health benefits. Nearly
80 percent of the abatement measures result in air pollution reduction, thereby improving
public health (Exhibit 19). The remaining 20 percent of the abatement measures can be
divided into those that result in a net societal savings (such as refrigerant leak prevention)
and those that are purely climate change mitigation measures (such as industrial nitrous
oxide controls). Overall, half of the measures come at societal profit, independent of
whether the motivation to pursue them is improved public health or purely climate change.
50 Berntsen et al., CICERO, 2010. Temperature increase target set at 1.5°C warming. In the case of the same abatement for all
climate forcers maximum temperature is reached after 50 years (1.5% p.a. rate of temperature increase); whereas in the case of
drastic non-CO2 reduction it takes 80 years (1.0% p.a.).
51 Van Vuuren et al., 2006. Including non-CO2 gases is crucial to the formulation of a cost-effective abatement response, and can
reduce costs by 30-40 percent compared to a CO2 only reduction strategy for the same radiative forcing target.
52 Royal Society, 2008.
53 Lenton, 2008.

44. 44
EXHIBIT 19
Abatement divided into impact and abatement cost
SOURCE: Non-CO2 Climate Forcers Report (2010)
51%
at
profit
49%
at net
cost
78% impact
public health and climate
22% impact
only climate
▪ Improved cook stoves that reduce fuel consumption
compared to traditional residential stoves
▪ Reducing methane emissions from the petroleum and
gas sector by upgrading equipment or improving
maintenance
▪ Improved emissions controls in the transport sector for
both on-road and off-road diesel vehicles
▪ Improved treatment of industrial wastewater that
reduces methane emissions
▪ Reducing leakage
of refrigeration
systems which
saves expensive
refrigerant
▪ Improved nutrient
management in
agriculture
▪ Changing
refrigerant for
motor vehicle air
conditioning
▪ Capturing and
decomposing
nitrous oxide from
acid production
Updated 100706
Black carbon is a fine particulate, and methane a precursor of tropospheric ozone, both of
which are air pollutants that damage the human respiratory and cardiovascular systems,
resulting in disease, reduced birth weight, and premature death. Due to its relatively longer
lifetime of 12 years, methane spreads more evenly than black carbon in the atmosphere,
meaning its effects are felt globally.54 Particulate matter (PM) remains more local in
health impact.
In the case of black carbon, abatement measures will also reduce other particulates that are
released simultaneously as a result of incomplete combustion, such as organic carbon and
sulfur dioxide. All contribute to the loading of PM in the atmosphere. In certain highly
populated regions of Asia, annual PM2.5 concentrations exceed World Health Organization
(WHO) guidelines by factors of 2 to 4.55 It is estimated that black carbon and its co-
pollutants are the third-largest cause of disease in South Asia and the fifth-largest cause of
mortality in Asia as a whole.56
In China and India, IIASA health models show that life expectancies are currently reduced
by an average of 3 years due to particulate matter air pollution.57 If the full abatement
54 West et al., 2006; Fiore et al., 2008.
55 Carmichael et al., 2009.
56 Ezzati et al., 2006.
57 Amann et al., 2008a, and additional GAINS model runs for this study.