Climatic Change
DOI 10.1007/s10584-015-1333-2
Allocation of global temperature change to consumers
Jonas Karstensen & Glen P. Peters & Robbie M. Andrew
Received: 13 August 2014 / Accepted: 13 January 2015
# Springer Science+Business Media Dordrecht 2015
Abstract Climate policy is generally concerned with the mitigation of well-mixed greenhouse
gases, allocated to the country where the emissions occur, and with different emissions
weighted together with the Global Warming Potential (GWP) using a 100 year time horizon.
This perspective is not unique. Recent research has considered the inclusion of Short-Lived
Climate Forcers (SCLFs), allocated emissions to the consumption of goods and services, and
used alternative emissions metrics. Here, for the first time, we combine these alternative
perspectives to explore the potential policy implications of three alternative framings: 1) using
the Global Temperature change Potential (GTP) to directly link current emissions to temperature change, 2) including SLCFs that have both warming and cooling effects on climate, and
3) allocating emissions to consuming sectors and regions. Collectively, we use these three
aspects to allocate the future temperature response to the consumption of goods and services in
a given year. We show, in order of importance, that the method of allocating emissions to
economic sectors is the most important, followed by the emission metric (including timehorizon), and then the mix of short-lived and well-mixed climate forcers. The consumption
perspective reallocates emissions from electricity and manufacturing to service sectors, which
suggests different policy options for demand and supply. The net effect of multiple pollutants
and GTP significantly change the importance of the sectors compared to when only considering CO2 or when using the GWP. We argue that a focus on only one accounting system and
framing in climate policy can potentially limit consideration of mitigation options to a reduced
set of activities, and thereby missing significant opportunities for mitigation in other aspects.
1 Introduction
Global climate change mitigation policies are usually framed around the Kyoto Protocol’s core
concepts of territorial emissions accounting, mitigation of well-mixed greenhouse gases
(WMGHGs), and integrated radiative forcing (via the Global Warming Potential, GWP).
However, these three choices are far from unique. First, regional emissions can be accounted
on an extraction, territorial, or consumption basis (Andrew et al. 2013; Davis et al. 2011),
meaning that they are allocated to where the mining occurred, where the combustion
Electronic supplementary material The online version of this article (doi:10.1007/s10584-015-1333-2)
contains supplementary material, which is available to authorized users.
J. Karstensen (*) : G. P. Peters : R. M. Andrew
Center for International Climate and Environmental Research Oslo (CICERO), P.O. Box. 1129 Blindern,
N-0318 Oslo, Norway
e-mail: jonas.karstensen@cicero.oslo.no
Climatic Change
happened, or where the products where finally bought, respectively. These accounting schemes
can additionally be integrated over time (cumulative) or normalized (e.g., per capita, per unit
economic activity). Second, Short-Lived Climate Forcers (SLCFs) also cause both global
warming and cooling, and have an important effect on the net temperature change (Stocker
et al. 2013). Although recent focus on these gases has gained political momentum, such as in
UNEP’s Climate and Clean Air Coalition to Reduce Short-Lived Climate Pollutants, they are
often excluded from mitigation studies (e.g., in Life Cycle Assessment; (Peters et al. 2011b))
and are not part of the Kyoto protocol (except for CH4, which we treat as a WMGHGs). Third,
there are a number of alternative emissions metrics (Aamaas et al. 2013b; Tanaka et al. 2010),
some of which relate more directly to temperature (Shine et al. 2005) and are therefore
potentially more consistent with current global negotiations, which have as their main goal
keeping the global average temperature increase below 2 °C above pre-industrial levels (Major
Economies Forum on Energy and Climate 2009; UNFCCC 2011a, b). We now give a brief
background of each of these different framings.
Accounting systems are human constructs (Davis and Caldeira 2010), and policy goals will
determine which systems are appropriate. Climate policies have traditionally had a territorial
accounting focus, built on existing processes to collect energy-consumption statistics and
allocating CO2 emissions at the point in space where and time when it enters the atmosphere.
Two key alternatives are consumption-based accounting, which allocates emissions to the
point where goods and services are finally consumed (Davis and Caldeira 2010), and
extraction-based accounting, which allocates emissions to the point where fossil fuels are
extracted (Andrew et al. 2013). These three accounting systems are connected via trade, and
several studies have demonstrated the increased linkages between global producers and
consumers as international trade continues to grow rapidly (Andrew et al. 2013; Karstensen
et al. 2013; Moran et al. 2013; Peters et al. 2011d; Wiebe et al. 2012). Under any accounting
system, carbon leakage (emission increases in an unregulated region due to activities in a
regulated region; (Peters 2010)) is a possibility when only a limited number of countries accept
emission caps or an effective carbon price (Felder and Rutherford 1993; Peters and Hertwich
2008). Most research on extraction- or consumption-based accounting has focused on regional
differences (comparisons of countries), with fewer studies focusing on sector differences
(Hertwich and Peters 2009). Since mitigation practically occurs at a much deeper level
(sectors, activities, etc.), it is important to elaborate on the differences in accounting at a more
detailed level. With a focus on the climate forcing from sectoral emissions (Unger et al. 2010),
the significant redistributions of sectoral impacts under a consumption perspective (Peters and
Hertwich 2006) become increasingly relevant.
Climate policies have almost exclusively focused on WMGHGs such as CO2, CH4, N2O,
and synthetic gases as specified in the Kyoto Protocol. While CO2 remains the most important
species to mitigate due to its strong radiative forcing, long-lived nature and large emissions
(Solomon et al. 2010), complementary mitigation of SLCFs could help reduce near-term
warming (Shindell et al. 2012) or delay the peak in temperature increases (Myhre et al.
2011). Some SLCFs have a cooling effect (e.g., SO2) and so their mitigation could lead to a
warming (Berntsen and Fuglestvedt 2008; Unger et al. 2010). Recently, there has been
increased focus on the climate and health benefits of reductions in pollutants (Chen et al.
2013), particularly for CH4 and black carbon (BC) (Shindell et al. 2012). Careful holistic
analysis is required to ensure solving one problem does not exacerbate problems elsewhere.
Most proposals for multi-pollutant climate policy require the effects of different climate
forcers to be made comparable. This is generally implemented using an emission metric
(Aamaas et al. 2013b; Fuglestvedt et al. 2003). The Kyoto Protocol uses the GWP with a
100-year time horizon, the choice of which has recently been labeled ‘inadvertent’ (Shine
Climatic Change
2009). Yet, since 2010’s UNFCCC Conference of the Parties in Cancun, the overarching goal
of climate negotiations has been framed explicitly in terms of temperature increase (UNFCCC
2011b), and thus a metric based on temperature, such as the Global Temperature change
Potential (Shine et al. 2007), may be more suited to the cost-effectiveness framing of climate
policy (Tol et al. 2012). In addition, the GWP places more weight on SLCFs (Shine et al.
2007) in the long run as it ‘remembers’ short-lived effects via integration, in contrast to
temperature-based metrics, in which the contribution of short-lived pollutants decays over
time (Peters et al. 2011a; Solomon et al. 2010). As a consequence, the use of the GTP may lead
to alternative mitigation priorities.
Here, we combine these three alternative framings of climate policy—consumption-based
accounting, including SLCFs along with WMGHGs, and a temperature-based metric—to give
consumption-based emission inventories measured in terms of temperature. We quantify how
much the results change depending on the different perspectives. We use the framework to
illustrate how alternative choices can change mitigation priorities, and to facilitate this we
focus on both the region and sector level. We argue that a focus on only one accounting system
and framing in global policy (e.g., those presently used under the UNFCCC and the Kyoto
Protocol) can potentially limit consideration of mitigation options to a reduced set of activities
(e.g., power generation), missing significant opportunities for mitigation in other aspects (e.g.,
manufactured products, services).
2 Materials and methods
We use country- and sector-specific emissions data from the EDGAR database (Emissions
Database for Global Atmospheric Research) (Andrew and Peters 2013; European Commission
2011) as the basis of our analysis, with the exception of organic carbon and black carbon
(Shindell et al. 2012). The dataset includes CO2, CH4, NOX, SO2, NF3, CO, N2O, NMVOC,
NH3, SF6, 8 PFCs and 11 HFCs for the year 2007, aggregated according to UNEP (2012) (see
Table S1). We base our analysis on 2007 as that is the most recent year of our economic dataset
(discussed below). Organic carbon (OC) and black carbon (BC) data are from the years 2005
and 2010. BC and OC emissions from biomass burning are not included. We estimate 2007
BC and OC emissions by using a weighted average of 2005 and 2010 emissions. We take into
account agricultural waste and savanna burning, but we do not include the emissions from
deforestation. We exclude deforestation emissions since detailed analysis is required to
determine the country-specific sectors that are allocated deforestation (European Commission
2013), and this work is beyond the scope of this current paper.
We first converted emissions data to radiative forcing and then to global temperature
change potential (GTP) using impulse response functions (IRFs), based on equations from
Fuglestvedt et al. (2010) and Aamaas et al. (2013b), and pollutant parameters from Fuglestvedt
et al. (2010) and IPCC (2007). GWP calculations use the same pollutant parameters. The
temperature IRF includes the heat capacity of the ocean (two layers), and has an equilibrium
climate sensitivity (λ) of 0.75 K/Wm−2, based on the latest CMIP5 data (Olivié and Peters
2013). The IRF of CO2 is modelled with parameters from Joos et al. (2013), as explained by
Olivié and Peters (2013). We use single global estimates for the SLCFs, which is an
approximation as the response to emissions of SLCFs often depends on location (Berntsen
et al. 2006).
We use the absolute GTP (AGTP; in units of global mean temperature change, K) for the
temporal change of sectors and the relative metric (GTP; in units of CO2 emissions that will
induce equivalent temperature change, CO2-eq) for the remainder of the analysis. Assuming
Climatic Change
that global emissions will follow high emission scenarios, it is likely that a 2 °C global mean
temperature increase will occur before or around 2060 (Joshi et al. 2011; Peters et al. 2013).
Because our study is set in the backdrop of international policy aimed at preventing this level
being breached, and to be consistent with other recent studies (Aamaas et al. 2013a; Peters
et al. 2011b), we use GTP with a 50-year time horizon (GTP50) to illustrate the effects of the
emissions (compare with Myhre et al. (2013) who present a range of time-horizons). The most
commonly chosen time horizon used with GWP is 100 years, but it has been suggested that
this is not based on scientific arguments, and that it may have initially been chosen because it
was the middle of the three options first presented (Shine 2009). The appropriate choice of
time horizon is determined primarily by the policy context (Myhre et al. 2013). Our intention
here is not to advocate 50 years as the optimal time horizon, but we feel it is a choice that we
can support based on the literature. We also do not wish to focus on the importance of the time
horizon in this article, but use 50 years as a point of departure to analyze the consequences of
choices in emission accounting, SLCF, and alternative metrics. Although uncertainties are
larger for instantaneous (e.g., GTP) compared to integrated (e.g., GWP) metrics and for SLCFs
(Olivié and Peters 2013; Reisinger et al. 2010), we choose to incorporate these aspects to
indicate how the results depend on choices for parameters and metric. We do not perform an
uncertainty analysis in this article, but refer to ongoing work (Karstensen et al. 2014).
The sectoral emissions data were allocated through the global supply chain to consuming
regions and economic sectors by using a Multi-Regional Input–Output (MRIO) model based
on data from the Global Trade Analysis Project (GTAP), with 129 regions and 57 sectors for
the year 2007 (Andrew and Peters 2013; Peters et al. 2011c). While our analysis is performed
for all regions and sectors, we allocate the results to nine sectors (see Table S2). The supply
chain model is fully explained elsewhere (Andrew and Peters 2013), and references therein
point to numerous applications.
Territorial accounting of emissions always allocates emissions to the sector where the
emitting activity takes place, but when presenting consumption-based emissions there are
alternative ways to allocate the consuming region’s consumption emissions to sectors (Peters
and Hertwich 2006). First, it is possible to account consumption-based emissions according to
the sector in which the emissions occurred, revealing, for the goods and services consumed by
a given country, in which sector the emissions occurred (e.g., US consumption might induce
emissions in electricity production in China). An alternative is to account the consumptionbased emissions according to the final sector in the supply chain, showing the emissions
required to produce the goods and services consumed (e.g., the majority of emissions from
agriculture are allocated to food sectors as this is where the purchases are made). Because
direct emissions by households do not occur in the production process (they are at the very end
of the supply chain), they are not redistributed under a change of accounting system, and are
therefore identical under both the territorial and consumption perspective.
3 Results
Using GTP50 as the metric, global emissions in 2007 were 35.2 Gt CO2-eq., and of these 24 %
were embodied in international trade (Fig. 1). For the purpose of the discussion, we define
globally traded emissions as the emissions that, under a consumption perspective, are allocated
to a different region than the one in which they occurred as a consequence of a production
activity. The traded share varies by pollutant, ranging from 8 % globally for OC (mainly
associated with domestic economic activities, such as households) to 69 % globally for NF3
(mainly associated with manufacturing of electronic equipment). International trade is
Climatic Change
a. Global
GTP50 (Gt CO −eq.)
40
2
30
20
10
0
Territorial
Exports
Imports
Consumption
b. United States of America
6
2
GTP50 (Gt CO −eq.)
8
4
2
0
Territorial
Exports
Imports
Consumption
Imports
Consumption
Imports
Consumption
c. China
6
2
GTP50 (Gt CO −eq.)
8
4
2
0
Territorial
Exports
d. EU27
5
2
GTP50 (Gt CO −eq.)
6
4
3
2
1
0
Territorial
EU27
USA
China
Exports
India
Brazil
South Africa
Russian Federation
Rest of AnnexB
Rest of Non−AnnexB
Climatic Change
ƒFig. 1
Regional breakdown of emissions for the year 2007 from territorial and consumption perspectives
globally, for USA, China and EU27, using GTP50. First bar shows emissions occurring within the regions’
borders, while the second and third bar shows emissions connected to exports from and imports to the regions.
Last bar shows emissions from consumption, which subtracts exports from and adds imports to territorial
emissions. The “Export” bars are colored according to where emissions embodied in products are exported
and finally consumed, while colors in the “Imports” and “Consumption” bars indicate where emissions originally
occurred. EU27 imports and export include intra-EU trade
dominated by China on the export side (24 % of globally exported emissions), and the US and
EU27 on the import side (17 and 33 %, respectively, where the latter includes trade within the
EU27). There are larger relative disparities between territorial and consumption emissions
for small countries (Davis and Caldeira 2010), but we focus on the world total and the three
world regions with the largest absolute disparities (Fig. 1). The US and EU27 are net
importers of emissions, with the largest imports coming from China (nearly 500 Mt CO2eq. to the US and about the same amount to the EU27). China, as with many other nonAnnex B countries, is a net exporter of emissions. The inclusion of SLCFs as well as
multiple WMGHGs only marginally changes the allocated emissions for the three regions,
compared to when only accounting for CO2 (7 % increase of emissions for the US, 4 % for
China and 4 % for EU27 in territorial perspective). The differences are, however, more
significant on a sectoral basis (Fig. 3), with different time horizons, and with different
metrics.
Recent studies have highlighted the value in considering emissions, and their climate
impacts, from a sectoral perspective (Aamaas et al. 2013b; Shindell et al. 2012; Unger et al.
2010). Figure 2 shows the same regions with emissions allocated to emitting territories on a
source basis, consumption by source sector, and consumption by final sector (see Methods).
The difference between territorial and consumption is the emissions embodied in exports and
imports at the sector level, as in Fig. 1 for regions. While consumption by source shows where
the emissions originally occur for a given final consumption of products, consumption by final
sector allocates the same emissions to the sectors that sell products to final consumption
(household demand, government demand, or capital investments).
Figure 2 shows that the same source sectors dominate in the territorial and consumption
perspectives: electricity generation, energy-intensive manufacturing, and transport sectors (see
SI for sector definitions). The similarity between the source sector figures reflects that
electricity and energy-intensive industries are at the core of many production processes,
regardless of whether final consumers purchase services or manufactured products. As most
final products are processed, the emissions by final sector are reallocated from primary and
secondary sectors, to secondary and tertiary sectors.
Figure 2a shows the large redistribution of emissions between sectors at the global level.
Significant redistributions from territorial to consumption perspective at the global level
include: 47 % of emissions associated with energy-intensive manufacturing (EIM) are reallocated to services and 18 % of EIM to non-energy intensive manufacturing (NEIM), 40 %
of agriculture to food, 40 % of electricity to services and 18 % of electricity to NEIM, 37 % of
transport to services and 11 % of transport to NEIM, 28 % of NEIM to services, 18 % of
mining to EIM and 16 % of mining to NEIM, and 16 % of food to services. The service sector
is the largest final sector, with 36 % of global emissions, which also includes construction
which represents 35 % of final service emissions. The shares of EIM and NEIM change
between the two perspectives. EIM is more important in the territorial emissions, while NEIM
is more important in consumption by final sectors. All manufacturing combined is allocated 25
and 21 % of the global emissions in territorial and consumption by final sector perspectives,
respectively, while it contributes 39 % of traded emission globally.
Climatic Change
a. Global
GTP50 (Gt CO −eq.)
40
2
30
20
10
0
Territorial
Exports
Imports
Consumption Consumption
source sector final sector
b. United States of America
6
2
GTP50 (Gt CO −eq.)
8
4
2
0
Territorial
Exports
Imports
Consumption Consumption
source sector final sector
c. China
6
2
GTP50 (Gt CO −eq.)
8
4
2
0
Territorial
Exports
Imports
Consumption Consumption
source sector final sector
d. EU27
5
2
GTP50 (Gt CO −eq.)
6
4
3
2
1
0
Territorial
Exports
Agriculture
Mining
Food
Imports
Consumption Consumption
source sector final sector
E−intensive manu.
NE−intensive manu.
Transport
Services
Electricity
Households
Climatic Change
ƒFig. 2
Sectoral breakdown of emissions for the year 2007 from territorial and consumption perspectives,
including imports and exports globally, for USA, China, and EU27, using GTP50. The territorial emissions
occur within regions’ borders, while consumption by source and final sector include imports and exclude exports.
Consumption by source sector allocates emissions to the sectors that originally emitted the emissions, while the
final sectors represent the sectors consumers purchase from. Bars are colored according to sector attributions
The transport sector is allocated 12 % of global territorial emissions, and as a significant
part of the transport sector involves delivery of products, only 66 % of the territorial emissions
remain allocated to transport in the consumption view. The rest (34 %) is embodied in the
transported products in the consumption by final sector perspective. The proportion of
emissions accounted to agriculture varies significantly by region, due to factors such as
geography, climate and production methods, but it is allocated 13 % of global territorial
emissions, which reduces by about half when allocated to final sectors, with the other half
allocated to other sectors such as food. The food sector has low production emissions, but is
allocated 9 % of global emissions from consumption by final sector due to supply-chain
contributions from agriculture and transport. Emissions from households include activities
causing direct emissions (personal transport, usage of gas, etc.). This sector is equal in all
perspectives, by definition (see Materials and Methods), with 13 % of global emissions.
In the US (Fig. 2b), the electricity sector dominates with 34 % of territorial emissions. The
majority of electricity generation is used by other productive sectors of the economy, and only
37 % of direct emissions are retained by electricity when using the final-sector perspective.
Manufacturing accounts for 18 % of territorial emissions, which grow to 23 % at consumption
by final sector. Transport is also an important emitter in the US, with 19 % of emissions, but
this drops to 6 % in the final sector view.
Table 1 Changes in CO2-eq. emissions when changing perspectives for selected regions and sectors. As the
Global row shows, the first two perspectives change the global emissions, while the third column only allocates
the same emissions differently. Colored bars are normalised to ±50 %. Small global emitting sectors (such as
Food sectors) that are allocated large emissions in a consumption perspective lead to large changes
a
using production emissions and all pollutants
b
using production emissions and GTP50
c
using all pollutants and GTP50
d
from production GWP100 emissions to consumption-based GTP50 emissions using all pollutants
Climatic Change
CO
14
2
SO
2
N O
10
CO
BC
NO
2
Territorial
Consumption
X
HFCs
NH3
8
OC
NMVOC
SF6
2
GTP50 (Gt CO −eq.)
CH4
12
6
PFCs
NF3
4
2
0
−2
Agr
Mining
Food
EIM
NEIM
Trans
Services
EL
Households
Fig. 3 Global emissions for the year 2007 by species and sector using GTP50, where the first bar in each sector
is territorial emissions and the second bar shows emissions reallocated to final sectors. The black circles represent
the net effect of each sector
In China (Fig. 2c), the domestic manufacturing sector is the largest emitter (39 % of
territorial emissions), of which 33 % is exported, while the electricity sector is close behind
with 32 % of territorial emissions. By final sector, however, the shares only amount to 20 % and
7 %, respectively. As China exports more emissions than it imports, the emissions allocated to
Chinese consumption are less than its territorial emissions. The transport sector in China has a
relatively small overall contribution to territorial emissions, due both to relatively low emissions, and similar contributions from warming species such as CO2 and cooling species such as
NOX and SO2, resulting in a net effect closer to zero than the other regions. The service sector
increases from 7 % under the territorial perspective to 51 % under the final-sector perspective,
due mainly to that sector’s consumption of the output of electricity, EIM, NEIM and transport.
In EU27 (Fig. 2d), the largest sector by territorial emissions was electricity (27 % of
emissions), while only 7 % is allocated in the final sector consumption perspective.
Manufacturing is allocated 23 % of territorial emissions, and, at 25 %, is about the same at
consumption by final sector. As with the US, transport has substantial emissions, accounting
for 19 and 12 % of the emissions in the two perspectives. With respect to trade, 42 % of US
imports are from manufacturing, while the same sector is allocated 39 % of EU27’s imports.
Chinese emissions exports are dominated by electricity (35 %) and manufacturing (48 %), and
of the total Chinese export, 25 % goes to the US and 25 % to EU27.
Figures 1 and 2 show a Bsnapshot^ of the temperature response after 50 years, and therefore
do not capture the different temporal effects of the pollutants, such as the trade-off between
WMGHGs and SLCFs. As the pollutants’ lifetimes and effects in the atmosphere differ, the
ordering of the largest sectors may change depending on the chosen time horizon. Fig. S1
shows the distribution of sectors for the three regions over time. Uniquely, we show the results
from a consumption by final sector perspective, which is significantly different to a territorial
Climatic Change
by source distribution (Andrew et al. 2013; Davis and Caldeira 2010). All regions show
emissions starting with a net-negative effect, and peaks in net effect occur within 3 decades of
the pulse emission. The figure illustrates the consequence of choosing different time horizons
for the metric, with the effect on temperature changing significantly over 100 years.
Three examples serve to demonstrate how the allocation of emissions to sectors, using
AGTP and a territorial basis, can change markedly depending on the time horizon chosen:
when shifting between the often-chosen time horizons of 20 and 100 years, net warming from
emissions of the electricity sector in China increases from 22 to 36 % of China’s contribution
to global warming, US agriculture declines from 8 to 3 %, and EU27’s transport increases from
13 to 21 % of EU27’s contribution to global warming. Comparisons between global emissions
of GWP100 and GTP50 reveal that the latter has higher magnitude since it places less weight
on SLCFs with cooling effects (mainly SO2, OC, and NH3). In a sectoral view, the differences
between allocation methods are usually much larger than the differences between metric values
(Fig. S3), although some sectors show substantial differences in metric values: agriculture is
25 % lower using GTP50 than with GWP100 (due mainly to CH4), while the electricity sector
is 56 % higher (due mainly to SO2).
A change in perspective will have very different sectoral and regional impacts (Table 1).
Globally, the net GTP50 values are 9 % higher than GWP100 when including all pollutants, but
while China has a 22 % increase in emissions when using GTP50, Brazil’s emissions decrease by
12 %. At the global sector level, agriculture, mining, services and household sectors have
decreased emissions when using GTP50, while the other sectors have an increase. The inclusion
of all pollutants, instead of including only the Kyoto Protocol gases, decreases the global net
emissions by 11 % and a similar result follows in most countries. Allocating emissions to
consumption instead of production often changes the emissions substantially, especially in sectors
as e.g. secondary and tertiary sectors (such as food and service sectors) with small production
emissions may be allocated relatively large emissions in a consumption perspective (Table 1).
One further breakdown is instructive: contrasting the differences between sectors by the
species of pollutant, from territorial and consumption perspectives using GTP50. Figure 3
shows that CO2, CH4, and N2O are the largest contributors to temperature increase, while SO2
and NOX are the largest cooling components, though these change strongly with different time
horizons (Fig. S2). Globally, the temperature-weighted magnitude of cooling species relative
to warming species decline from 20 % at 20 years to only 8 % at 100 years. Mitigation by
sectors with high emissions of cooling pollutants (e.g. SO2 and NOX) may lead to increased
global warming in the short term (Matthews and Zickfeld 2012). At 100 years, all sectors’
emissions profiles are dominated by CO2, except agriculture, where N2O still has the largest
effect. Shifting from territorial emissions to consumption also shifts the relative importance of
pollutants within sectors. Figure 3 shows that a change of perspective reallocates more than
half of the emissions to other sectors.
4 Discussion and conclusion
Our analysis gives an alternative perspective on climate policy in three key areas. First, there is
significant added value in considering mitigation from a temperature perspective. The climate
policy community is working to keep the global average temperature increase below 2 °C relative
to pre-industrial levels, and analyses of the largest drivers of temperature change are needed. The
widely used GWP does not relate directly to temperature (Shine et al. 2005). A temperature-based
metric, like the GTP, leads to different weighting of emissions at the sector level, particularly for
sectors with a large share of SLCFs like BC and SO2. While the global manufacturing sector is the
Climatic Change
largest emitter using the GWP, the GTP suggests the electricity sector is largest. Thus the use of
the GWP may lead to different mitigation priorities compared to using a GTP (c.f. Fig. S3).
Second, including SLCFs in addition to WMGHGs reveals the overall net climate effect of
economic activities (Unger et al. 2010). By adding the non-Kyoto SLCFs and WMGHGs to
the Kyoto basket of pollutants (in a territorial view), the global emissions allocated to each
sector can change substantially, from -11 % for transport, -14 % for NEIM and -19 % for
electricity (due to cooling effects of NOX and SO2) to +3 % for household emissions (due to
warming effects of BC and CO).
Third, and as argued by others (Barrett et al. 2013; Wiedmann 2009), a consumption
perspective can be complementary to the established territorial perspective to emission allocation.
More than 75 % of global emissions in 2007 occurred in electricity generation, energy-intensive
manufacturing, transport and agriculture, and only 10 % of the global emissions are allocated to
services (including construction), non energy-intensive manufacturing and food in the territorial
perspective. Using the consumption perspective, however, nearly 60 % are allocated to services,
NEIM and food, while electricity generation, EIM, transport and agriculture only accounts for
29 %. This change of allocation is due to a large redistribution of emissions from the producing
sectors to the sectors consuming goods and services, and may lead to different mitigation priorities
(Barrett et al. 2013; Hertwich and Peters 2009). At the global sector level, a change in emissions
accounting proposes significant changes, often larger than the inclusion of additional gases
outside of the Kyoto Protocol and changes in metrics (Table 1).
An important remaining question regards the uncertainty in our analysis. While previous
work has investigated the uncertainty of individual components of the analysis we have
performed (Aamaas et al. 2013b; Lenzen et al. 2010; Olivié and Peters 2013; Peters et al.
2012; Reisinger et al. 2010; UNEP 2012; Wilting 2012), the quantification of overall uncertainty of this chained system remains an open research question. In parallel work we are using
Monte Carlo techniques to address this research gap (Karstensen et al. 2014). The parametric
uncertainty in consumption-based temperature allocations to global sectors is in the range from
±9 to ±27 % using GTP50, although structural uncertainties might increase these values. As in
other work, higher uncertainties are found at the regional and sectoral levels.
Our analysis clearly demonstrates the dependency of results on allocation methods, metric,
time horizon of metric, and whether the territorial or consumption perspective is used.
Emission mitigation strategies should consider these alternative approaches carefully, as
priorities can change depending on the choices that are made. Allocating emissions to
consumption by final sector suggests the secondary and tertiary sectors are the largest drivers
of emissions and temperature change. Recognizing these underlying drivers from multiple
perspectives can help in developing alternative mitigation strategies, where a significant
reduction in emissions from one sector can have significant impacts throughout the supply
chain, which in turn can help keep global warming below 2 °C.
Acknowledgments The authors acknowledge funding from the Norwegian Research Council project
BQuantifying the global socio-economic and policy drivers for Brazil’s contribution to global warming^ (Project
Number: 196090).
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