IPCC WG3 Symposium, Tokyo
January 26, 2017

Evaluations of climate change response
measures considering several constraints
and multi objectives in the real world

Keigo Akimoto,Systems Analysis Group
Research Institute of Innovative Technology for the Earth (RITE)

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 to achieve
the 2 °C or 1.5 °C target under the Paris Agreement?

The climate sensitivity and its probability density
function is still uncertain scientifically.

2

History of climate sensitivity judgment by IPCC and thesensitivity employed in the scenario assessments of theIPCC WG3 AR5

3Equilibrium 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 butalso 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

450

CO2 emissions [GtCO2/yr]

40[3] Below +2.0℃ in 2100
under climate sensitivity of2.5℃

30[2] +2.0℃ stabilization
under climate sensitivity of3.0℃

20[1] 450ppm CO2eq.
Stabilization
10[0] +1.5℃ stabilization
under climate sensitivity of3.0℃02010
-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 after 2050 are required for the 1.5 °C scenario.

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

570

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

4030[0] +1.5℃ stabilization underclimate sensitivity of 3.0℃-42%

Historical

20-74%
INDC submitted by Octover 1,2015 (119 nations) (estimated byRITE)

10-81%
01990

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 andthe 2 °C target.

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%

6

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 reduced byadaptation 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
7

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 theleast 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

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%-4%w.o. adaptation-6%

w. adaptation

RCP2.6

-8%
2030

2050

Mitigation

0%

2.5%

5.2%

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

2100

There are large uncertainties in estimates on climate change damages and adaptation costs; however, if adaptation
measures can reduce such large damages due to climate change, and the mitigation costs are large, the long-termtargets, such as the 2 °C target like RCP2.), should be considered more flexibly.

Climate Change Mitigation & Food Access (1/2)

8

Food access index (Amounts of food consumption／GDP)
686

400

Food Access Index[amounts of food consumptions/GDP](US.Y2000=100)

Bioenergy and forestation
effects

651 715754
1315 655 745

801916w.o. Bioenergy andforestation effects

350
300

Vulnerable

250
200
15010050

2000

2050

2100
China

2000

2050

2100
India

2000

2050

2100

2000

Other Asia

2050

2100

Sub-saharan Africa

A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0
A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0

A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0
A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0

A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0
A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0
A-baseline
A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0
A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0

A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.0
A-baseline
A-CP6.0
A-CP4.5
A-CP3.7
A-CP3.00

20002050
L. AmericaSource) K. Akimoto et al., Natural Resources Forum, 36(4), 231-244, 2012

- Vulnerabilities of food access will decrease in most countries and regions in thelong-term under any emission scenarios, because future incomes are expected toincrease in the future.
- Global warming counter-measures of large scale of forestation and bioenergy use
slightly increase vulnerabilities of food access.

2100

Climate Change Mitigation & Food Access (2/2)

9

Food access index (amounts of food consumption/GDP) in 2050 by factor
30%－△(GDP)/GDP : due to climate damage

Change rates of food access(%, relative to the baseline)

25%
20%

－△(GDP)/GDP : due to climate mitigation

15%
10%

△(Food consumptions)/(Food consumptions):
due to land-use changes for "bioenergy
production and afforestation"

5%△(Food consumptions)/(Food consumptions):
due to land-use changes for "food production"

0%△(Food consumptions/GDP)/(Foodconsumptions/GDP)-5%

CP4.5 CP3.7 CP3.0 CP4.5 CP3.7 CP3.0 CP4.5 CP3.7 CP3.0 CP4.5 CP3.7 CP3.0 CP4.5 CP3.7 CP3.0
China

India

Midde-East &N.Africa

Subsahara Africa

Latin America- The impacts of increase in vulnerability on food access due to climate change(synergy effects) can be seen but are not large.
- Food access can be significantly more vulnerable to large deployments of forestation
and bioenergy use and large mitigation costs in the case that the emission reductions
are large (adverse side effects).

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

End-of-pipe measures (CCS)

10Co-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 (%)

807060adversesideeffects

Larger co-benefit ofPM2.5 reductions on
CO2 reductions

50403020100-10-20020406080100
CO2 emission reduction relative to Reference (%)

PM2.5 reduction relative to Reference (%)

PM2.5 concentration reduction cases

Fuel switching
80706050

Energy saving

CO2 emission reduction cases
Larger co-benefit ofCO2 reductions onPM2.5 reductions

403020100-10

adverse side-effects-2002040
6080100
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); butfor 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)

7060

2500

CO2 ($/tCO2)

1050

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

11

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.

CO2 marginal abatement costs of the NDCs
12

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

EU28210

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

Turkey0India

0Ukraine

0China0050

100

150200250300350

CO2 marginal abatement cost ($/tCO2)

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

Emission reduction costs are an important indicator for measuring emission reduction efforts. The
marginal abatement cost of Japan’s NDC is estimated to be high across countries. However, theestimated marginal costs of NDCs are largely different among countries, and such large difference will
induce carbon leakages, and the leakages will reduce the effectiveness of global emission reductions.

400Issues of IPCC

13♦ The IPCC assessment reports are written basically basedon the scientifically reviewed articles.
♦ In addition, the principle of IPCC is “not policy

prescriptive but policy relevant”.
♦ Under the conditions, the IPCC reports have the dilemmathat it is valuable in practice but not easily accepted to
the realistic solutions considering economic, social andpolitical constraints in the real world.

Appendix

The Assumed Scenarios for Obtaining the Emission
Pathways Meeting the 2 °C and 1.5 °C targets
C.S. likely: 2.0-4.5°C,
most likely:3.0°Cby IPCC AR4 (=WG3 AR5)
Category byconcentration in2100 (ppmCO2eq)

Global GHGemissions

Sub-category(relative to2010)[0] <430[1] 450 (430-480)

in 2050

Temperaturein 2100 (°C,relative to1850-1900)

Only a limited number of studies exist.
(There are no scenarios in the AR5 DB.)―-72～-41%

1.5～1.7℃(1.0～2.8)[2a] No exceedanceof 530 ppm CO2eq-57～-42%1.7～1.9℃(1.2～2.9)[2] 500 (480-530)

C.S. likely: 1.5-4.5°C,
Most likely: 2.5°C
by IPCC WG1 AR5+ TARProbability of notexceeding the temp.
rise over 21st century(relative to 1850-1900)*

Probability of notexceeding the temp.
rise over 21st century(relative to 1850-1900)*

1.5℃

1.5℃

2.0℃

50%以上*-55～-25%

1.8～2.0℃(1.2～3.3)[2a] No exceedanceof 580 ppm CO2eq-47～-19%2.0～2.2℃(1.4～3.6)[3] 550 (530-580)

2.0℃

66%以上
66%以上50%以上[2b] Exceedance of530 ppm CO2eq

1550%以上

66%以上50%以上[2b] Exceedance of580 ppm CO2eq

Source) IPCC AR5; * simply estimated by RITE-16～+7%

2.1～2.3℃(1.4～3.6)

Climate Change Mitigation & Energy Security
16()(c gascoil22⋅+⋅
ESI =rSrS∑ i i, oil TPES ∑i i i, gas
TPES i
Share of imported oil in TPES

Political risks of region i)

Dependence on region i

ESI : energy security index, TPES: total primary energy supply
Note: index based on IEA, 2007
10,000Vulnerable

Energy security index

2000
7,500

2050 A-Baseline
2050 A-CP4.5

5,000

2050 A-CP3.0

2,5000US

W. EuropeJapan

China

India and S. AsiaSource) K. Akimoto et al., Natural Resources Forum, 36(4), 231-244, 2012

While the energy security index of Japan decreases (less vulnerable) for CP3.0 (synergyeffects), that of China, India increases (more vulnerable) for deeper emission reductions
due to increase in imported gas shares (adverse side effects).