ALPS International Symposium
Toranomon Hills Forum
February 7, 2017

Evaluations on Emission Reduction
Efforts of Nationally Determined
Contributions under the Paris Agreement
Keigo AkimotoGroup Leader, Systems Analysis Group
Research Institute of Innovative Technology for the Earth (RITE)

Contents
1. Background and objectives
2. Understanding on current global greenhousegas emissions
3. Evaluations on the NDCs (emission
reductions) for the Paris Agreement
4. Detailed evaluations on emission reduction
costs of Japan’s NDC
5. Toward a better management of climatechange risks
6. Conclusions2

1. Background and objectives

Background and objectives of ALPS projectand its major topics

4

Climate change is a very complex issue. Effectiveness of response measures in the realworld is important. The aim of the ALPS project is to support the developments ofinternational frameworks to achieve green growth and effective response measuresthrough better understandings of technologies, economics, policies etc. and quantitative
analyses and evaluations.
【major topics】♦ Risk management strategy for climate change responses- Estimates of climate change damages, adaptations, and mitigation costs and theiruncertainties- Long-term target and the corresponding emission pathways- Risk management strategy for climate change responses under uncertainties etc.
♦ Better and deeper understandings of economics for real green growth- Consideration of the possibilities and limitations of removing energy saving barriers,
relationship between climate change and air pollution mitigation, etc., and evaluation basedon model analyses- Estimations of international energy productivity gaps (comparisons between the U.S. and Japan)- Analyses for international financial constraint to coal power installationetc.
♦ Climate change mitigation measures, particularly the integrated measures.
- hydrogen systems (total systems including supply, transport, consumption)- opportunities of integrated measures of building, and transportationsetc.
♦ Analyses regarding international frameworks, discussions and policy interests- Evaluations of emission reduction targets of NDCs
- Contributions to international model comparison projectsetc.

2. Understanding on current
global greenhouse gas emissions

Trajectory of Global GHG Emission by Source
6

Source) IPCC AR5, 2014

The global emissions after 2000 increased more rapidly. The Kyoto Protocol was not able
to exert large effects on emission reductions.

Trajectory of Global CO2 Emission by Region
7

Consumption-based
CO2 emissions haveHigh income not decreased even incountries
HIC.
($12,616 and more)

Upper middle income countries($4,086 to $12,615)(China, Brazil, Iran, Malaysia, South
Africa etc.)
Rapid increase in CO2 emissions

Lower middle income countries($1,036 to $4,085)(India, Indonesia, Philippine, Egypt etc.)
Tackling poverty; lower priority
to CO2 emission mitigation

Low income countries($1,035 and less)

Source) IPCC AR5, 2014

A paper by President Obama “The irreversible
momentum of clean energy”, Science, January 9, 2017
♦
♦

♦

♦
♦

♦

8

CO2 emissions from the energy sector fell by 9.5% from 2008 to 2015, while the economy
grew by more than 10%.
This “decoupling” of energy sector emissions and economic growth should put to rest theargument that combatting climate change requires accepting lower growth or a lower
standard of living.
The American electric-power sector—the largest source of GHG emissions in our
economy—is being transformed, in large part, because of market dynamics. In 2008, natural
gas made up ~21% of U.S. electricity generation. Today, it makes up ~33%, an increase due
almost entirely to the shift from higher-emitting coal to lower-emitting natural gas.
Renewable electricity costs also fell dramatically between 2008 and 2015: the cost ofelectricity fell 41% for wind, 54% for rooftop PV installations, and 64% for utility-scale PV.
Public policy—ranging from Recovery
Act investments to recent tax credit
extensions—has played a crucial role,
but technology advances and market
forces will continue to drive renewabledeployment.
The latest science and economics
provide a helpful guide for what the
future may bring, in many cases
independent of near-term policy
choices, when it comes to combatting
climate change and transitioning to aclean-energy economy.
Source: United States Mid-Century Strategy for Deep Decarbonization, Nov. 2016

Consumption-based CO2 emissions of the U.S.
Production-based CO2

7,000

9

2000

Consumption-based CO2
1800

+24%

Large effects of shale gas?

6,500

1600

Difference in the CO2 emissions (MtCO2)

Differences [Right vertical axis]

CO2 emissions (MtCO2)

Large effects of Lehman shock?
1400

6,000

1200

+9%

5,500

1000
800

+3%

5,000

600
400

4,500

+220%
200

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

0

1995

4,000

Source) OECD (2015)- The difference between the consumption-based CO2 and the production-based CO2 hadgreatly increased by 2005 in the U.S. The consumption-based CO2 in 2005 was +24%
compared to that in 1995.
- On the other hand, the difference became small from the 2006 in which shale gas expanded.
However, the consumption-based CO2 in 2011 was +9% compared to that in 1995. (Theproduction-based CO2 was +3%.)

The U.S. Primary Energy Supply
10

Renewable increase is not so large (4.8% in 2000⇒6.7% in 2014）
Coal and coal products

100%

Peat and peat products

90%

nuclear Oil shale and oil sands
80%

Crude, NGL and feedstocks

Primary enegy supply

70%

gas

Oil products
Natural gas

60%

Nuclear

50%

Hydro
40%

oil

Geothermal

30%

Solar/wind/other

20%

Biofuels and waste

10%

coal

Heat production from non-specified
combustible fuelsElectricity

0%

-10%

Heat
Oil
products (export)

Source) IEA

Coal supply has decreased and gas share has increased since 2005 due to increases in shale gas
productions, and this contributes to CO2 emission reductions. Gas increase induced exports of oil
products, which does not contribute to global CO2 emission reductions. We should note that the shale
gas expansions were not induced by climate policies.

The relationship between global GDP growthand global CO2 emission between 1971 and 2015

11

Energy-related CO2 emissions (GtCO2/yr)

35

CO2 elasticity of
GDP
30

25

1971-2013

0.68

2000-2013

0.98

2009-2013

1.13

2013

2015

2010

Linear regression(1971-2010)
y = 0.3957x + 8.0843
R² = 0.9872

20

15
1971年

10
15

25

Source) IEA statistics, 2016

35

45

55

65

GDP (Trillion US$/yr)

The strong positive relationship between global GDP and CO2 emissions was observed. On theother hand, global CO2 emissions from 2013 to 2015 were almost constant; however, comparedto the long-term trend, the emission increase from 2009 to 2013 was too rapid, and the trend from2013 to 2015 can be explained just as a return to the historical regression trend.

The relationship between global GDP growthand global CO2 emission between 2000 and 2015
Energy-related CO2 emissions (GtCO2/yr)

34

12

2015

1.09 GtCO2
32

30

2010

Linear regression (2000-2015)
y = 0.5211x + 2.2712
R² = 0.9793

28

26

24
2000

22
40
Source) IEA statistics, 2016

45

50

55

60

65

GDP (Trillion US$/yr)

While the emission in 2013-15 is regarded just as a return to the long-term trend(1971-2015), the gap between the emission expected from the linear regression
for a shorter term trend (2000-2015) and the actual emission in 2015 wasestimated to be about 1090 MtCO2/yr in 2015.

Global GDP growth v.s. primary energy and electricity
13
15000
2014

World primary energy supply

2015

2010

13000

2009

12000

Linear regression (1971-2014)

11000

y = 189.55x + 2682.6
R² = 0.994

10000
9000
8000

World electricity supply

7000
25000

6000

y = 435.06x - 1809.2
R² = 0.9971

5000
15

25

35

45

GDP (Trillion US$/yr)

1971～2014
Source) IEA, 2016

20000 65

55

Electricity (TWh/yr)

Primary energy supply (Mtoe/yr)

14000

15000

10000

5000

0
15

25

35

45

55

GDP (Trillion US$/yr)

The relationship between the global GDP and the primary energy supply or electricity
consumption shows a stronger linearity than that between the GDP and CO2 emissions.
With respect to primary energy and electricity supply, no decoupling with GDP is observed.

65

The relationship between global GDP growth andglobal iron and steel productions
1500

Note: Production data in 2016 is based on preliminary
figures released by worldsteel.

2014: 1.67 Gt

1400

1250
2013: 1.21 Gt

2015

1000

1200

750
500

Crude steel

250
0
1990

Pig iron

1995

2000

2005

2010

2015

Pig iron (Million tons/yr)

World production (Million tons/yr)

1750

14

2010

1000

0.1 Gt pig iron(corresponds to0.25 GtCO2)

Linear regression(2000-2015)
y = 36.6x - 916
R² = 0.98

800

600
2000

400
40

45

50

55

60

GDP (Trillion US$/yr)

Global productions of pig iron in 2013 was about 1.2 Gton and decreased toward 2015 due
to decrease in demands of China. From the trend of global GDP and pig iron productions
between 2000 and 2015, the production decreased by about 0.1 Gton in 2015, and thiscorresponds to CO2 emission reductions of about 0.25 GtCO2.

Rough estimations of global emission reduction effects in 201515

Emission reduction factors

Emission reduction
effects in 2015

Specific factors

Reductions in global ironproduction

about 250 MtCO2/yr

Decrease in global iron production of about
100 ton (particularly in China)

Reductions in global cement
production

about 50 MtCO2/yr

Decrease in global cement production of about
170 ton (particularly in China)

Emission reductions due toabout 220 MtCO2/yr
increase in shale gas in the U.S.

Shifts from coal to gas (shale gas)
economically in the U.S.

Expansion of renewableenergies

about 160 MtCO2/yr

Higher expansions by 1.2%/yr point comparedwith the average annual expansion rate
between 2000 and 2015

Reduction in CO2 emissions ofJapanabout 40 MtCO2/yr

Due to Fukushima-daiichi nuclear power
accident, the emission in Japan increased byabout 110 MtCO2 from 2011 to 2013, but by
about 70 MtCO2 from 2011 to 2015

sub-total

about 720 MtCO2/yr

Total emission reductions

about 1090 MtCO2/yr- The emission reduction effects due to reductions in iron and cement productions were observed as
only temporary effects because of the decrease in China, and global productions of iron and cement will
increase to meet growing demands in India etc.
- For renewables, the expansions are considered as the effects of political support such as FiT. This is
not necessarily regarded as an example of “decoupling”.

3. Evaluations on the NDCs (emission
reductions) for the Paris Agreement

The Paris Agreement; significance and concern♦ Almost all nations participated in the Paris Agreement and are

expected to tackle emission reductions continuously, and the Paris
Agreement is welcomed as a first step to achieve the green growth.
♦ However, appropriate reviews of NDCs are crucially important,measuring emission reduction efforts.
♦ If marginal abatement costs of emission reduction targets varylargely across nations, leakages of industries and carbon andconsequent ineffectiveness in emission reductions will be a great
concern.

17

How to measure the comparability of efforts
The submitted NDCs are expressed using various kinds of targets;the targets of emissions reduction from different base years, CO2
intensity, and CO2 emission reductions from baseline (w/w.o. clear
definition of baseline). We need to interpret them throughcomparable metrics to measure the efforts:
Simple metrics (easily measurable and replicable)- Emissions reduction from the same base yearetc.

Advanced metrics (more comprehensive, but require forecasts)- Emission reduction ratios from baseline emissions- Emissions per unit of GDP
etc.

More advanced metrics (most comprehensive, but require
modeling)- Energy price impacts- Marginal abatement cost (per ton of CO2)
- Abatement costs as a share of GDP
etc.

18

International comparison of emission reduction ratios
in 2030 (in 2025 for the U.S.) from the base year of 2005
Switzerland
NorwayEU28
CanadaNew ZealandUnitedUnitedStatesStates(2025)
Australia
Japan
Korea
Russia-EU
countries)
East Europe(Non-EU
countries)
Belarus
Kazakhstan
ThailandUkraineMexicoSouth Af rica
China
Turkey
India
300

-51.6
-44.5
-34.8
-30.0
-30.0
-27.0
-26.0
-25.4

19

larger

-5.3
14.2
15.6
19.0
19.7
30.1
32.2
32.8
38.2
116.9

smaller

180.9
235.4

250

200

150

100

50

0

-50

-100

GHG emission compared to base year (2005) (%)* The average values are shown for the countries submitted the NDC with the upper and lower ranges.

It is not easy to measure ‘emission reduction efforts’ by using the emission reduction ratios from acertain base year due to large differences across countries in future economic growth and historicalachievements of energy saving and emission reductions, for example.

International comparison of CO2 marginal abatement
costs in 2030 (in 2025 for the U.S.) (RITE DNE21+ model)
Switzerland
Japan
EU28
CanadaKorea
New ZealandUnitedUnitedStatesStates(2025)
NorwayEastastEurope(Non-EU
countries)…
Europe(Non-EU
Thailand33
Australia
27
Mexico14
Kazakhstan
12
Belarus4
Russia1South Af rica0
Turkey0India
0Ukraine
0
China
0

50

20

380
378

bigger

210
166
144
95
85
70
58
54

smaller
100

150

200

250

300

350

400

CO2 marginal abatement cost ($/tCO2)* The average values are shown for the countries submitted the NDC with the upper and lower ranges.

Large differences in marginal abatement costs are estimated across countries. The large differences raise
concern about inducing the carbon leakage and the ineffectiveness of global emission reductions.

International comparison of emission reduction
costs per GDP in 2030 (in 2025 for the U.S.) (RITE DNE21+ model)

21

Australia
UkraineThailand
New Zealand
East
Europe(Non-EU
countries)
East
Europe(Non-EU…
Switzerland
Korea
EU28
Japan
CanadaUnitedUnitedStatesStates(2025)South Af rica
MexicoBelarus
0.0
Russia0.0
Turkey
0.0
India
0.0
Kazakhstan
0.0
China
0.0
Norway0

2.4
1.8

bigger

1.4
1.1
1.0
1.0
0.8
0.8
0.6
0.5
0.4
0.3
0.3
0.2

smaller
0.5

11.5
Emission reduction cost per GDP (%)

2* The average values are shown for the countries submitted the NDC with the upper and lower ranges.
Note: The emission reduction costs include the net cost changes due to changes of energy import and export.

This indicator is a metric in terms of the economy’s capability of emission reductions.

2.5

Marginal abatement costs estimations across models(RITE DNE21+, FEEM WITCH and NIES AIM)
Only energy-related CO2
emission reductions in 2030

250
200
The average between 2025 and 2030 for GHG emission recutions
150
100

USG Social Cost of
Carbon (SCC):
53$/tCO2 for 2025-30

50

U.S.

EU

China

India

WITCH

DNE21+WITCH

DNE21+WITCH

DNE21+WITCH

DNE21+

DNE21+

AIM/Enduse
Japan

WITCH

0

DNE21+

CO2 marginal abatement cost (US$2005/tCO2)

300

22

Marginal abatement
costs if theaggregated NDCs areachieved most costefficiently:
16$/tCO2 by WITCH,
6$/tCO2 by DNE21+

Korea/S.Africa/Australia

Source: B. Pizer, J. Aldy, R. Kopp, K. Akimoto, F. Sano, M. Tavoni, COP21 side-event; MILES project report for Japan- The marginal abatement costs vary across models for some countries, but can be comparable for many
countries/regions.
- The CO2 marginal abatement costs of the NDCs of OECD countries are much higher than the uniform
marginal cost for achieving the aggregated NDCs most cost-efficiently (globally uniform marginal
abatement cost).

CO2 marginal abatement costs of the NDCs
23

Average of 2025-2030
2030 (2025 for the U.S.)【World GDP loss due to mitigation】
NDCs:0.38%; the global least cost：0.06%
The least cost (equal marginal abatement costs)：6$/tCO2
Switzerland

380

Japan

378

EU28

210

Canada

166

Korea

144

New Zealand95

United States

85

NorwaySource: J. Aldy et al., Nature Climate Change, 201670

East Europe (Non-EU member)

58

Thailand54

Australia

33

Mexico27

Kazakhstan

14

Belarus12

Russia4South Africa

1

Turkey

0

India

0

Ukraine

0

China

0

0

50

100

150

200

250

300

350

CO2 marginal abatement cost ($/tCO2)

Source: K. Akimoto et al., Evol. Inst. Econ. Rev., 2016

- The marginal abatement costs for NDCs are greatly different across nations.
- The global costs are estimated to be about 6.5 times as large as the least cost for the sameamount of global reductions.
- The mitigation costs in the real world will be much higher than those of the ideal case.

400

4. Detailed evaluations onemission reduction costs ofJapan’s NDC

Consideration of country's political and social
situations in evaluation of the cost metrics
Cost metrics are comprehensive and good indicators formeasuring emission reduction efforts, but …
♦ How should we treat the considerations of social constraints

for implementing climate policies? ⇒ public acceptance of
nuclear power, CCS etc.; considerations of energy security♦ How should we treat the considerations of politicalconstraints for implementing climate policies? ⇒ For
example, in the U.S. it is not easy to establish a new climate
policy act due to the political systems.
♦ When the governments make/implement inefficient policies,

how should we treat them for measuring the costs for theemission reduction efforts? ⇒ FIT policies can be inefficient,and how should we treat them for the mitigation costs?

25

2030 Emission Target of Japan’s NDC andthe Energy Mix (Electricity)262030; Compared to 2013（compared to 2005）
Energy-related CO2-21.9% （-20.9%）

Other GHGs

-1.5% （-1.8%）

Reduction by absorption-2.6% （-2.6%）

Total GHGs

-26.0% （-25.4%）

The Japanese government, July 2015

The analysis cases for Japan’s NDC
GHG
emis.
target[A0] GHG target + Level-26%
2 energy mix[A](The same as the case assumed for theinternational comparison in previous slides)

Energyrelated CO2
emissiontargetElectricity share
Fossil fuelNuclearpower

Renewables

Cost min.

Coal: 26%
LNG: 27%
Oil: 3%20%-21.9%

Coal: 26%
LNG: 27%
Oil: 3%27

w./w.o.
CCS
optionElectricity
saving24%(cost min. withinrenewable sources)

Cost
min.

Cost min.

20%

24%(cost min. withinrenewable sources)

Cost
min.

Cost min.

[B0] CO2 target + Level 2energy mix-[B1] CO2 target + Level 0energy mix--21.9%

Coal: 26%
LNG: 27%
Oil: 3%20%

24%(PV: 7%, wind:
1.7% etc.)

w.o.
CCS

Total elec.
supply:1065
TWh/yr[B2] CO2 target + Level 1energy mix--21.9%

Coal: 26%
LNG: 27%
Oil: 3%20%

24%(cost min. withinrenewable sources)

w.o.
CCS

Cost min.

[B3] CO2 target + Level 3energy mix (coal 26% +nuclear 20%)-

-21.9%

Coal: 26%
LNG: cost min.
Oil: cost min.

20%

Cost min.

Cost
min.

Cost min.

[B4] CO2 target + Level 4energy mix (nuclear20%)--21.9%

Cost min.

20%

Cost min.

Cost
min.

Cost min.

[B5] CO2 target + costmin. energy mix (Level5)--21.9%

Cost min.

Cost
min.

Cost min.

Cost
min.

Cost min.

[B](The highest consistency
with the specific measureslisted in the Japan’s NDC)

Note: Higher level of energy mix provides more flexibility.

0[B5] CO2 target + cost min. energy[B5] Cost min. energy mix
mix (Level 5)[B4] CO2 target + Level 4 energy[B4] Level 4 energy mix (nuclear 20%)
mix (nuclear 20%)

[B3] CO2 target+ Levelenergymix[B3]
Level 33 energy(coal 26% +20%)
nuclear 20%)
mix (coal 26%+nuclear

The same as the case assumed for theinternational comparison in previous slides[B0] Energy-related CO2 target (-21.9%)[B0] CO2 target + Level 2 energy mix+ Level 2 energy mix

1400[B2] Energy-related CO2 target (-21.9%)[B2] CO2 target + Level 1 energy mix+ Level 1 energy mix

The highest consistency with the specificmeasures listed in the Japan’s NDC[B1] Energy-related CO2 target (-21.9%)[B1] CO2 target
0 mix
energy mix+ Level+0Level
energyElectricity generation [TWh/yr]

Evaluations of Japan’s NDC in Electricity in 2030
Energy-related CO2 target: -21.9%

1200

1000

800

600
Biomass (w/o CCS)

400
Gas power (w/ CCS)

200
28

Solar PV

Wind power

Nuclear power

Hydro and Geothermal

Biomass (w/ CCS)

Gas power (w/o CCS)

Oil power (w/ CCS)

Oil power (w/o CCS)

Coal power (w/ CCS)

Coal power (w/o CCS)

Estimated by RITE DNE21+ modelEvaluations of Japan’s NDC in Mitigation Cost in 2030
29

Marginal
abatement
cost of CO2($2000/tCO2)

Mitigation
cost
increase(billion$2000/yr)

Mitigation
cost
increase perreference
GDP (%)[A0] GHG target (-26%) + Level378
2 energy mix The same as the case assumed for the

99

1.41

[B0] CO2 target (-21.9%) + Level
2 energy mix

227

28

0.40

[B1] CO2 target (-21.9%) + Level242
0 energy mix The highest consistency with the listed

38

0.55

[B2] CO2 target (-21.9%) + Level
1 energy mix

272

32

0.46

[B3] CO2 target (-21.9%) + Level
3 energy mix (coal 26% +nuclear 20%)

277

24

0.34

[B4] CO2 target (-21.9%) + Level
4 energy mix (nuclear 20%)

165

20

0.28

[B5] CO2 target (-21.9%) + costmin. energy mix (Level 5)

50

10

0.15

international comparison in previous slides

specific measures in the Japan’s NDC

Estimated by RITEDNE21+ model

4.1% GHG reductions by nonenergy CO2 is much more
expensive than 21.9% GHG
reductions by energy related CO2
Energy-related
CO2 target (-21.9%)
Electricity saving target , CCS
constraint

Renewable energy target etc.

Considering energy security issue

Considering social constraintof nuclear power

Note: it should be noted that the orders of between marginal cost and mitigation cost are different. The constraints for specific measures
could reduce the CO2 marginal abatement cost while total mitigation cost increases.

Which constraints should we consider as appropriate or inevitable?

Other sensitivity analyses ーThe cases ofunachievement of the GDP growth rate and nuclear power target 30♦ The future government targets are also uncertain in terms ofachievement, and some sensitivity studies were conducted as follows;a) GDP growth rate assumed in the NDC and energy mix: 1.7%/yr ⇒ 0.9%/yrb) Nuclear power share assumed in the NDC and energy mix: 20-22% ⇒ 15%
Marginal
abatement costof CO2($2000/tCO2)

Mitigation cost
increase (billion$2000/yr)

Mitigation cost
increase perreference GDP(%)[B0] CO2 target (-21.9%) + Level 2energy mix(GDP：1.7%/yr, nuclear power: 20%)

227

28

0.40

[B0-a] Low GDP growth (0.9%/yr)

151

18

0.31

[B0-b] Nuclear power share: 15%

228

36

0.51

[B0-c] Low GDP growth (0.9%/yr)+ Nuclear power share: 15%

142

24

0.40
Estimated by RITE DNE21+ model5. Toward a better managementof climate change risksTemperature targets under the Paris Agreement
and their Political and Scientific Uncertainties♦ Regarding the long term targets, the Paris Agreement

contains: “To hold the increase in the global averagetemperature to well below 2 °C above pre-industrial
levels and to pursue efforts to limit the temperature
increase to 1.5 °C above pre-industrial levels.”When should the temperature goal be achieved below+2 °C or +1.5 °C under the Paris Agreement?

How high probability should be assigned for theachievement of the 2 °C or 1.5 °C target under theParis Agreement?



The climate sensitivity and its probability density
function are still greatly uncertain scientifically.

32

History of climate sensitivity judgment by IPCC and thesensitivity employed in the scenario assessments of the
IPCC WG3 AR533

Equilibrium climate sensitivity
Likely range (“best estimate” or “mostlikely value”)

Before IPCC WG1 AR4Same “likely” range
1.5−4.5°C (2.5°C)

IPCC WG1 AR4

2.0−4.5°C (3.0°C)

IPCC WG1 AR5

1.5−4.5°C (no consensus)

Global mean temperature estimations for the long-term
scenarios in the IPCC WG3 AR5 (employing MAGICC)

2.0ｰ4.5°C（3.0°C）[Based on the AR4][The related descriptions of the SPM of WG1 AR5]

Likely in the range 1.5 °C to 4.5 °C (high confidence)
Extremely unlikely less than 1 °C (high confidence)
Very unlikely greater than 6 °C (medium confidence)
No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines ofevidence and studies.

♦ The equilibrium climate sensitivity, which corresponds to global mean temperature increase inequilibrium when GHG concentration doubles, is still greatly uncertain.
♦ AR5 WG1 judged the likely range of climate sensitivity to be 1.5−4.5 °C, in which the bottom range
was changed to a smaller number than that in the AR4, based not only on CMIP5 (AOGCM) results but
also other study results.
♦ AR5 WG3 adopted the climate sensitivity of AR4, which has the likely range of 2.0−4.5 °C with the best
estimate of 3.0 °C, for temperature rise estimates of long-term emission scenarios.

Global CO2 emission profiles toward 2300
for the 2 °C and 1.5 °C targets

34

50

CO2 emissions [GtCO2/yr]

40[3] Below +2.0℃ in 2100
under climate sensitivity of
2.5℃

30

[2] +2.0℃ stabilization
under climate sensitivity of
3.0℃

20

[1] 450ppm CO2eq.
Stabilization
10[0] +1.5℃ stabilization
under climate sensitivity of
3.0℃

0
2010
-10

2060

2050

2110

2160

2100

2210

2260

2300

Estimated by RITE using MAGICC and DNE21+- The CO2 emissions should be nearly zero for long future in any pathways for thetemperature stabilization.
- Large amounts of negative CO2 emissions are required after 2050 for the 1.5 °C scenario.

Global GHG emission profiles toward 2100
for the 2 °C and 1.5 °C targets

35

70

GHG emissions [GtCO2eq/yr]

60[3] Below +2.0℃ in 2100 underclimate sensitivity of 2.5℃

+13%[2] +2.0℃ stabilization underclimate sensitivity of 3.0℃

50[1] 450ppm CO2eq. Stabilization

40
30[0] +1.5℃ stabilization underclimate sensitivity of 3.0℃

-42%

Historical

20

-74%
INDC submitted by Octover 1,
2015 (119 nations) (estimated by
RITE)

10

-81%
0
1990

2010

2030

2050

2070

2090 2100

Estimated by RITE using MAGICC, DNE21+ and non-CO2 GHG models- The corresponding GHG emission trajectories for the 2 °C target vary widely
particularly before 2050.
- There are large gaps between the expected emissions under the submitted NDCs andmost of the pathways for the 2 °C target.

CO2 Marginal Abatement Costs
for Achieving the Emission Pathways

36

CO2 marginal abatement cost [$/tCO2]

5000
4500

[3] Below +2.0℃ in 2100 underclimate sensitivity of 2.5℃

4000
3500
3000
2500

[2] +2.0℃ stabilization underclimate sensitivity of 3.0℃

2600 $/tCO2

2000[1] 450ppm CO2eq.
Stabilization

1500
1000
294 $/tCO2

500
0
2010

2030

Estimated by RITE using DNE21+ model

46 $/tCO2

2050

2070

2090 2100

There are no feasible solutions for the
scenario of [0] +1.5℃ stabilization underclimate sensitivity of 3.0℃

- The marginal abatement cost for the case of [1] 450 ppm stabilization is extremely higheven in 2030, and it will be difficult to achieve it in reality.
- The costs for the [2] and [3] scenarios in 2100 are around 1000 $/tCO2 or larger, andinnovations, especially technological ones, are necessary even for these scenarios.

Climate Change Damages and Adaptation (GDP impacts)－Comparison of the estimates by three models－
RITE Adaptation model
7.0%

GDP Loss

6.0%
5.0%
4.0%
3.0%

5.0%

6.6%

w.o. adaptation
w. adaptation
Global mean
temperature change: Adaptation
effects
about +4.2 °C in
2100 (RCP8.7)
3.2%

37

Global mean temperature change:
about +3.0 °C in 2100

Adaptation
effects

2.0%

2.0%
1.0%
0.0%
2030

2040

2050

2060

2070

2080

2090

2100

Note 1) RITE adaptation model does not cover broad
adaptation measures but consider only coastal dike incoastal sector as adaptation measures
Note 2) The estimates of all the models are highly
uncertain in the damage and adaptation costs.

In all of the model analyses, the GDP
losses due to climate change
damages can be significantly reduced
by adaptation measures.
(Reductions in GDP loss due toadaptation measures: 2.1 to 3.4%
points in 2100)

Global mean temperature change:
about +3.7 °C in 2100

3.9%

Adaptation
effects

1.8%

Source: Agrawala et al.2010, Fig13

Climate Change Damages, Adaptation and Mitigation Costs
38

World GDP damages w.o./w. adaptation

GDP loss due to mitigation (IPCC AR5)(compared to the case without consideration of climate change)0%

GDP change (%)

RCP8.5-2%-3.15%-4%-6%

w.o. adaptation
w. adaptation

GDP change (%)

0%-2%

RCP4.52100

baseline=RCP8.5-1.25%Note) The costs are
estimated under the
least global costmeasures.

-2.30%-4%

w.o. adaptation-6%

w. adaptation-8%0%

GDP change (%)

2050-0.40%-0.82%-0.50%-1.14%

2030

RCP2.6-6.58%-8%2030

RCP4.5

RCP2.6-0.46%-1.08%-0.56%-1.58%-2%2050-0.36%-0.60%-0.46%-0.83%% of GDP

2100

RCP8.5-0.99%

RCP4.5-4%

w.o. adaptation-6%

w. adaptation

RCP2.6

-8%
2030

2050

2100

Damage &adaptation

w.o. adapt.

6.6%

w. adapt.

3.2%

w.o. adapt.

2.3%

w. adapt.

1.3%

w.o. adapt.

1.0%

w. adapt.

0%

Mitigation

0%

2.5%

5.2%

There are large uncertainties in estimates on climate change damages and adaptation costs; however, if
adaptation measures can reduce climate damages significantly, and the mitigation costs are large, thenstringent long-term targets, such as the 2 °C like RCP2.), will be debatable.

Total
6.6%
3.2%
4.8%
3.8%
6.2%
5.2%

Climate risk management strategy for the case of high climate sensitivity−Framework on evaluating the option value of SRM−
39

Solar radiation management (SRM) is proposed as a geoengineering method. The option valueof SRM under a temperature target with uncertainty in climate sensitivity was evaluated.
DNE21 model which is simplified from DNE21+ evaluated the option value by employing adecision tree having simplified three scenarios regarding climate sensitivity.
Y. Arino, K. Akimoto et al., PNAS, 113(21), 2016

【Assumptions】(1) Climate sensitivity is uncertain before 2050,(2) Climate sensitivity uncertainty would be resolved in 2050, and(3) SRM would be implemented (a) to a limited extent of cooling (-0.5°C), (b) only after 2050,
and (c) only when true climate sensitivity would turn out to be high.

Scenarios after the learning of uncertain climate sensitivity 40


CO2 emission pathways were estimated with the expected least-cost for acertain level of temperature increase target.



The probability of climate sensitivity was assumed based on the Rogelji et al. (2012)
which is consistent with the IPCC AR4 (2.0-4.5 °C: likely; 3.0 °C: mean).

[Scenarios]
Climate sensitivity（T2x）

Occurrence
probability

SRM implementation

Scenario 1

2.0℃

10%

No SRM

Scenario 2

3.0℃

71%

No SRM

Scenario 3

4.0℃

19%

Y. Arino, K. Akimoto et al., PNAS, 113(21), 2016

SRM implementation(cooling capacity limited to -0.5 °C)

The CO2 emission pathways for the 2.5 °C target
with and without SRM option
Baseline
Uncertain T2x=2℃ w/o SRM
Uncertain T2x=3℃ w/o SRM
Uncertain T2x=4℃ w/o SRM
Uncertain T2x=2℃ with SRM (option)
Uncertain T2x=3℃ with SRM (option)
Uncertain T2x=4℃ with SRM

80

Energy-related CO2 emission (GtCO2/year)

41

60

Without SRM option

40

30.1GtWith SRM option
24.5Gt20

SRM option value
T2x = 3℃

0
2000

2010

2020

2030

2040

2050

2060

2070

2080

2090

2100

SRM’s direct effects on
the emission pathway-20

Y. Arino, K. Akimoto et al., PNAS, 113(21), 2016

Holding SRM options during the uncertain periods (2000-2040) alleviates the stringency ofemission reduction in the short to medium term even though SRM is not truly deployed.

Relationship between temperature targets
and SRM option values

42

Y. Arino, K. Akimoto et al., PNAS, 113(21), 2016

Discount rate: 5%/yearMore stringent target in temperature

7.0

Option value A [1990-2049][SRM≦0.5℃]
Option value B [1990-2100][SRM≦0.5℃]

5.9

Option values (Trillion US2010$)

6.0

5.0

(for the medium scenario T2x = 3℃)

4.0

There are no feasible
solutions.

3.3
3.1

3.0

1990-2049
2.0
1.6

1.0

0.5

1990-2100

0.2

0.0
2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

3.1

Temperature change targets relative to preindustrial levels in 2100 (°C)

The SRM option values increase with the stringency of temperature change targets, and thevalues of US$ 3.1 and US$ 5.9 trillion for the 2.5 and 2.4 °C targets when accumulated
during 1990-2049.

Climate Change Mitigation &Air Pollution (PM2.5) Reduction Measures
Kaya identity

End-of-pipe measures (CCS)43

Co-benefit measures

Net CO2 = (Net CO2／Gross CO2) × (Gross CO2／PE) × (PE／GDP) × (GDP)PM2.5 = (PM2.5／Gross PM2.5) × (Gross PM2.5／PE) × (PE／GDP) × (GDP)End-of-pipe measures(de-Sulfer, de-NOx etc.)
PM2.5 reduction relative to Reference (%)

80
70
60

adversesideeffects

Larger co-benefit of
PM2.5 reductions on
CO2 reductions

50
40
30
20
10
0
-10

-20
0
20
40
60
80
100
CO2 emission reduction relative to Reference (%)

PM2.5 reduction relative to Reference (%)

PM2.5 concentration reduction cases

Fuel switching
80
70
60
50

Energy saving

CO2 emission reduction cases
Larger co-benefit of
CO2 reductions on
PM2.5 reductions

40
30
20
10
0
-10

adverse side-effects

-20
0
20
40
60
80
100
CO2 emission reduction relative to Reference (%)

Estimated by RITE DNE21+ model (up to 2050)- The co-benefit of CO2 emission reductions on PM2.5 reductions are larger than that of PM2.5
reductions on CO2 emission reductions. Large co-benefits are not necessarily observed for all
countries but are observed particularly in India, South Africa, and the U.S.
- For PM2.5 reductions, relatively cheap end-of-pipe type measures exist (e.g., de-Sulfer, de-NOx); but
for CO2 reductions, the end-of-pipe type measures (e.g., CCS) are relatively expensive.

Climate Change Mitigation &Air Pollution (PM2.5) Reduction Measures − Costs

CO2, PM2.5 price assumptions (in 2030)

Total costs of 2010-50 (discount rate: 5%/yr)
PM2.5 cost

CO₂ cost

Abatement cost

(C:▲29/P:▲11)

70
60

2500

CO2 ($/tCO2)

10

50

PM (H) + CO2 (H) ＞＞ IM (H&H)
57 (9.3)
46 (8.9)

21.2

26.2

C:10/P:7
5.7
6.8
1.7

IM (PM(L)&CO₂(L))

C:10/P:0

20.9

1.7

5.8
0.4

7.6

6.9
1.2

9.3

8.0

6.7
3.0

IM (PM(H)&CO₂(L))

C:0/P:7

21.4

IM (PM(L)&CO₂(H))

0

26.2

500

5.6

IM (PM(H)&CO₂(H))

10(C:−/P:▲11)

CO₂ (L)20

C:0/P:37

CO₂ (H)30

C:10/P:37

PM (L)

40

PM2.5 (M$/(µg/m3))(Parenthesis: total mitigation costs)(C:▲29/P:▲2)
25.9(C:▲3/P:▲11)(C:▲29/P:−)High (H)

Total cost [Trillion US$]

C:50/P:7

C:50/P:0

Low (L)The price increase of +10%/yr is assumed between 2010 and 2050.
The CO2 price scenarios of “Low” and “High” correspond to RCP4.5
and RCP2.6, respectively.

PM (H)

Total abatement costs (Trillion US$)80

50

REF cost (CO₂ + PM2.5)

C:50/P:37

90

44

The REF cost is simply estimated by theassumed prices x reference emissions.

Estimated by RITE DNE21+

PM (L) + CO2 (H)35 (7.9)≈＜ IM (L&H)
35 (8.0)

PM (H) + CO2 (L) ＞≈ IM (H&L)
34 (3.0)33 (3.0)
PM (L) + CO2 (L) ＞≈ IM (L&L)
14 (1.6)
13 (1.6)- Relatively large co-benefits are estimated in the case that both CO2 and PM2.5 reduction levels arelarge (both CO2 and PM2.5 emission damages are large). ⇒ In this case, large scales of energy
saving and fuel switching are cost-effective.
- On the other hand, large co-benefits are not observed in other cases. ⇒ In the case that the humanhealth impacts of PM2.5 are large and the resources for the mitigation measures are limited, the endof-pipe type measures for PM2.5 reductions are cost effective in early stages.

6. Conclusions

Climate Change Risk Management to be Considered
46

IPCC bureau sometimes simply explains that the remaining
carbon budget is only1000 GtCO2 for the 2 °C target; however
there are large uncertainties in the budget.
(This IPCC figure shows the uncertainties, but it is drawn only by GCM results; wider
ranges exist if climate sensitivity ranges 1.5-4.5 °(likely value of IPCC AR5))- Scientific uncertainties: risk management
recognizing various uncertainties is prerequisite.
- CO2 zero emissions are required in the long-term⇒ technology innovation is essential.
- The potentials of adaptation to reduce climatechange damages significantly- Potential increase in mitigation costs: politicalfactors (large differences in MAC across nations,
Trump Administration etc.), social constraints oftechnology deployment, inefficient policies etc.
- Potential decrease in mitigation costs (future
unknown innovations)- High climate sensitivity case: increase in costs if it
is tackled only by mitigation measures ⇒ potential
response by SRM as an option- Pursuing co-benefits in line with several objectivesof sustainable development including PM2.5
reductions. But some are trade-offs. Our resources
are limited and total risk management is required.

Conclusions

47♦ The Paris Agreement is an international framework where all nations

tackle climate change, and is welcomed.
♦ It is a key to appropriately compare and review NDCs, measuring
emission reduction efforts for the effective achievement of deeper
reductions.
♦ The marginal abatement costs of NDCs vary widely across nations,and the global costs are estimated to be over six times as large as theleast cost for the same amount of global reductions. This big
difference will hinder effective global emission reductions.
♦ Even within a nation, there are lots of other policies, social constraints
etc. to be considered and they will increase the emission reduction
costs greatly compared to the ideally least cost.
♦ The Paris Agreement aims the 2 °C target (also pursuing the 1.5 °C
target), but the nominal temperature target has a wide range of global
emission pathways.
♦ We should recognize such various uncertainties, and manage not only
climate change risks but also total risks of society in order to achievea better sustainable development in a better way.