September 30, 2016

Analysis and assessment of 1.5℃ target

Systems Analysis Group
Research Institute of Innovative Technology for the Earth (RITE)
Contact to : Fuminori Sano, Keigo Akimoto
TEL: +81-774-75-2304、E-mail: sysinfo@rite.or.jp

Contents
１．Evaluation examples of the 1.5℃ target in previous
studies including IPCC AR5
２．Uncertainties for the temperature targets and theassumed temperature trajectories for the 1.5 C target
３．Emission pathways for the 1.5℃ target
４．Emission reduction costs and measures forthe 1.5 C target
５．Conclusions

2

Long-term target decided at the Paris Agreement (COP21)3

 To hold the increase in the global average temperature to well below 2℃

above pre-industrial levels and to pursue efforts to limit the temperature
increase to 1.5℃ . (Article 2, Para. 1 (a)) (=> At the COP21, COP invited IPCC
to provide a special report in 2018 on the impacts of global warming of 1.5℃
and related global greenhouse gas emissions pathways. IPCC decided toprovide a special report at the plenary session in Apr. 2016)
 In order to achieve the long-term temperature goal set out in Article 2,Parties aim to reach global peaking of greenhouse gas emissions as soon
as possible, and to undertake rapid reductions thereafter so as to achieve abalance between anthropogenic emissions by sources and removals bysinks of greenhouse gases in the second half of this century. (Article 4, Para.
1)
 All Parties should strive to formulate and communicate long-term low

greenhouse gas emission development strategies (Article 4, Para. 19)(COP21 decision clearly indicates its time period as 2020)
 COP shall periodically take stock of the implementation of this Agreement toassess the collective progress towards achieving the purpose of thisAgreement and its long-term goals every five years (“global stocktake”, tobe started from 2023)

1. Evaluation on 1.5℃ target by
IPCC AR5

Long-term scenarios for the global emissions
reduction in IPCC AR5

5

<430

CO2eq
2100
Probability of exceeding theemissionstemperature target temperatures
Subcategories
RCP
in 2050(C, relative
relative toto 18501.5C
2.0C
3.0C
2010
1900)
Only a limited number of analyses reported (no registration to AR5 scenario D/B)

450 (430-480)

―

CO2eq
concentrationin 2100 (ppm
CO2eq)

500 (480-530)

550 (530-580)(580-650)

RCP2.6 -72 to -41%

No exceedance of
530 ppm CO2eq
Once exceed 530
ppm CO2eq by
2100
No exceedance of
580 ppm CO2eq
Once exceed 580
ppm CO2eq by
2100-57 to -42%―

1.5 - 1.7C(1.0 - 2.8)
1.7 - 1.9C(1.2 - 2.9)

49-86%

12-37%

1-3%

80-87%

32-40%

3-4%-55 to -25%

1.8 - 2.0C(1.2 - 3.3)

88-96%

39-61%

4-10%-47 to -19%

2.0 - 2.2C(1.4 - 3.6)

93-95%

54-70%

8-13%-16 to +7%

2.1 - 2.3C(1.4 - .6)

95-99%

66-84%

8-19%

2.3 - 2.6C(1.5 - 4.2)
2.6 - 2.9C(1.8 - 4.5)
3.1 - 3.7C(2.1 - 5.8)
4.1 - 4.8C(2.8 - 7.8)96100%
99100%
100100%100100%74-93%

14-35%

88-95%

26-43%-38 to +24%
RCP4.5(650-720)―-11 to +17%

(720-1000)―

RCP6.0 +18 to +54%

>1000

―

RCP8.5 +52 to +95%

97100%
100100%55-83%
92-98%

The 1.5℃ target and the Allowable cumulativeemissions expected (IPCC AR5)

6

Estimates of climate
sensitivity based on CMIP5 :2 ~ 4.5℃ (mean: 3.2℃)

IPCC Synthesis report, Table 2.2

Estimates of climate
sensitivity by MAGICC : likely
2.0 ~ 4.5℃ (mode: 3.0℃)
Note: The ranges in the table are
generated by differences in non-CO2
GHG emission scenarios.

2. Uncertainties regarding thetemperature targets and theassumed temperature
trajectories for the 1.5℃ target

Political and Scientific Uncertainties
8 When should the temperature goal be achieved below +1.5 ℃

under the Paris Agreement?
 How high probability should be assigned to achieve the

1.5 ℃ target under the Paris Agreement? (How shall “wellbelow” be scientifically interpreted?) The climate sensitivity and its probability density function isstill uncertain scientifically.

History of climate sensitivity judgment by IPCC and the sensitivity
employed in the scenario assessments of the IPCC WG3 AR5Equilibrium climate sensitivity
Likely range (“best estimate” or“median”)

Before IPCC WG1 AR4

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 estimates in the 2.0-4.5C（3.0C）
IPCC WG3 scenarios (employing MAGICC) [Based on the AR4]
[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 assessedlines of evidence and studies.

 The equilibrium climate sensitivity, which corresponds to global mean temperature increase inequilibrium when GHG concentration doubles, is still greatly uncertain.
 AR5 WG1 modified the likely range of climate sensitivity to be smaller than that in AR4 (1.54.5 C),
based on the synthetic judgement on various analyses including climate sensitivity assessment ofobservational data.
 However, AR5 WG3 adopted the climate sensitivity of AR4, which has the likely range of 2.04.5 Cwith the best estimate of 3.0 C, for temperature rise estimates of long-term emission scenarios.

9Climate sensitivity of MAGICC model which was employed forthe temperature change estimates in the long term scenarios of
IPCC WG3 AR5
WG3 AR5 employed a simple climate change model
MAGICC for the temperature estimates for the longterm scenarios

10

Estimates by
WG1 AR5

GCM estimates計
CMIP3→AR4
CMIP5→AR5

600 model runs were conducted in
MAGICC assuming the probability
density function of equilibrium climate
sensitivity to be consistent with theAR4Source：J. Rogelj et al., 2012
出典：IPCC WG1 AR5, 2013

 WG3 AR5 employed the climate sensitivity of AR4 (likely range: 2.0ｰ4.5 C, best estimate: 3.0 C) for estimating thetemperature of long-term scenarios. This is almost consistent with the CMIP5 results but is inconsistent with the new
synthetic judgment of WG1 AR5 considering other studies (shown in a gray zone in the right figure).
 Therefore, when compared with the latest judgment by WG1 AR5, the temperature rise estimates can be greater.

The assumed scenarios for the 1.5 C target andthe temperature trajectories

11

Equilibrium climate sensitivitya) 3.4 Cb) 3.0 Cc) 2.5 CI) 1.5 C stabilization (below 1.5 C over time)

I-a

I-b

I-c

II) Below 1.5 C by 2100 (temperature overshoot;peak temperature: around 1.75 C)

II-a

II-b

II-c

III) Below 1.5 C by 2300 (temperature overshoot;peak temperature: around 2.0 C)

III-a

III-b

III-c

Temperature trajectories

The assumed trajectories of temperature rise
2.2I-a) 1.5 °C stabilization (C.S.=3.4 °C)
2Global mean tempearture change
relative to 1850-1899 [K]I-b) 1.5 °C stabilization (C.S.=3.0 °C)

1.8I-c) 1.5 °C stabilization (C.S.=2.5 °C)
1.6II-a) Below 1.5 °C by 2100 (C.S.=3.4 °C)

1.4II-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)II-c) Below 1.5 °C by 2100 (C.S.=2.5 °C)

1.2

III-a) Below 1.5 °C by 2300 (C.S.=3.4 °C)
1III-b) Below 1.5 °C by 2300 (C.S.=3.0 °C)
0.8
III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)
0.6
1990

2040

2090
2100

2140

2190

2240

2290
2300

3. Emission pathways forthe 1.5 C target

Atmospheric GHG concentration pathways
for the 1.5 C target scenario

13

600

Atmospheric GHG concentration [ppm]I-a) 1.5 °C stabilization (C.S.=3.4 °C)
550I-b) 1.5 °C stabilization (C.S.=3.0 °C)I-c) 1.5 °C stabilization (C.S.=2.5 °C)

500II-a) Below 1.5 °C by 2100 (C.S.=3.4 °C)
450II-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)II-c) Below 1.5 °C by 2100 (C.S.=2.5 °C)

400
III-a) Below 1.5 °C by 2300 (C.S.=3.4 °C)
III-b) Below 1.5 °C by 2300 (C.S.=3.0 °C)

350

III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)
300
1990

2040

2100

2090

2140

2190

2240

2290

Source: estimated by RITE using MAGICC

The atmospheric GHG concentration peaks at each level and thereafter declines for all of
the assumed scenarios. The concentration levels in 2300 for the 1.5 C stabilization
scenarios are 400-450 ppm CO2eq. (The range depends on climate sensitivity.) The
temperatures of the scenarios below 1.5 C in 2100 decrease and the concentration levels
reach about 370-400 ppm CO2eq.

CO2 emissions pathways until 2300 for the 1.5 C target
1450I-a) 1.5 °C stabilization (C.S.=3.4 °C)

40

CO2 emission [GtCO2eq/yr]I-b) 1.5 °C stabilization (C.S.=3.0 °C)

30I-c) 1.5 °C stabilization (C.S.=2.5 °C)20II-a) Below 1.5 °C by 2100 (C.S.=3.4 °C)

10II-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)

0II-c) Below 1.5 °C by 2100 (C.S.=2.5 °C)

III-a) Below 1.5 °C by 2300 (C.S.=3.4 °C)-10III-b) Below 1.5 °C by 2300 (C.S.=3.0 °C)-20
III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)

-30
2010

2050
2060

2100
2110

2160

2210

2260

2300

Source: estimated by RITE using MAGICC- All of the scenarios require global net negative emissions. Especially, every scenario of
temperature overshoot (case II and III) requires large amounts of net negative emissions(around 20 GtCO2/yr) in 2100.
- All of the scenarios require negative emissions for long terms to stabilize temperature.

GHG emissions pathways until 2100 for the 1.5 C target
1570I-a) 1.5 °C stabilization (C.S.=3.4 °C)60

GHG emission [GtCO2eq/yr]I-b) 1.5 °C stabilization (C.S.=3.0 °C)50I-c) 1.5 °C stabilization (C.S.=2.5 °C)II-a) Below 1.5 °C by 2100 (C.S.=3.4 °C)

40

▲10%

II-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)30II-c) Below 1.5 °C by 2100 (C.S.=2.5 °C)▲22%III-a) Below 1.5 °C by 2300 (C.S.=3.4 °C)

20

▲52%

III-b) Below 1.5 °C by 2300 (C.S.=3.0 °C)

10III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)

0Historical

▲85%
-10

Baseline (current policy) outlook

relative to 2010

NDCs outlook

-20
1990

2010

2030

2050

2070

2090 2100

Source: estimated by RITE using MAGICC- The GHG emission pathways for stabilizing below 1.5 C with over 66% probabilities (equivalent to
C.S. of 3.4 C) requires 85% reduction compared with 2010 by 2030. Even for over 50% probabilities,
52% reduction is required. (in the case of best estimates for C.S. is 3 C and likely range is 2.0 to 4.5 C)- For the achievement of below 1.5 C with over 66% in 2100 while allowing temperature overshoot, 22%
reduction compared with 2010 by 2030 is required. For over 50%, 10% reduction by 2030 is required.
(NDC outlook: +21%)

GHG Emissions Pathways －2 C vs 1.5 C targets－
16
70

Temperature stabilization scenarios(climate sensitivity: 3.0 C)

Historical
Baseline (current policy) outlook
NDCs outlookI-b) 1.5 °C stabilization (C.S.=3.0 °C)

50

Ref.1) 2.0 °C stabilization (C.S.=3.0 °C)
40

▲43%
30

▲10%

20

10

0
1990

Source: estimated by RITE
▲52%

Temperature overshoot scenarios
2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 (climate sensitivity: 3.0 C and 2.5 C)
▲81%

70

- The emission pathway for below 1.5
C by 2300 under climate sensitivityof 2.5 C is similar by around 2070 tothat for below 2 C by 2300, and bothof them are consistent withaggregated NDCs.
- However, the scenario for below 1.5
C by 2300 requires deep emission
reductions after about 2070, andnegative emissions of about
10GtCO2eq/yr in 2100.

Historical
Baseline (current policy) outlook
NDCs outlookII-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)
Ref.2) Below 2.0 °C by 2100 (C.S.=3.0 °C)
III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)
Ref.3) Below 2.0 °C by 2100 (C.S.=2.5 °C)60

GHG emissions [GtCO2eq./yr]

GHG emissions [GtCO2eq./yr]

60

50
40
30
20
10
0
1990
-10
-20

2000

2010

2020

2030

2040

2050

2060

2070

2080

2090

2100

Required emission reductions and cumulative emissions
for the 1.5 C targets

17

Global mean
temperature relative
to 1850-1900

Required GHG
emission
reductions in
2030(GtCO2eq./yr)

RequiredGHG
emissionscomparedwith 2010 (%)

Cumulative
net CO2emissions(GtCO2)

Peak
temp.

From
From
baseline NDCs

2030

20162100

58.1

52.4

-85%

-85%

230

-210

-615

41.6

35.9

-52%

-81%

469

154

-414

18.2

12.5

-4%

-67%

873

756

-148

27.0

21.3

-22%

-90%

394

-360

-1069

21.5

15.8

-10%

-63%

577

-221

-1065

II-c

15.3

9.6

+2%

-19%

919

121

-1024

III-a

17.8

12.1

-3%

-56%

711

-3

-950

12.3

6.6

+8%

-31%

926

261

-862

5.2

-0.5 +23%

+13%

1427

777

-738

2100

2300

I-a
1.5 C 1.5 C

I-b
I-c
II-a

1.5 C

1.1
1.75
1.2 C C

II-b

III-b
III-c

1.8
1.9 C1.5 C 2.0 C

2050

Cumulative
net negative
CO2
emissions(GtCO2)*

20162016-2300
2300* * Only annual net negative CO2 emissions are summed up

Required emission reductions in II-c, III-b and III-c from NDCs are relatively small compared withother scenarios. However, these cases require cumulative net negative emissions only bysumming up annual net negative emissions.

4. Emission reduction costs
and measures forthe 1.5 C target

CO2 marginal abatement costs for the 1.5 C target
5880 $/tCO2 in 2050

CO2 marginal abatement cost [$/tCO2]

500

19

1290 $/tCO2 in 2050 710 $/tCO2 in 2050

I-b) 1.5 °C stabilization(C.S.=3.0 °C)

400I-c) 1.5 °C stabilization(C.S.=2.5 °C)II-b) Below 1.5 °C by 2100
(C.S.=3.0 °C)

300II-c) Below 1.5 °C by 2100
(C.S.=2.5 °C)

200

III-a) Below 1.5 °C by 2100
(C.S.=3.4 °C)
III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)

100

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

0
2015

2020

2025

2030

2035

2040

2045

2050

Source: estimated by RITE DNE21+- There were no feasible solutions by DNE21+ in Cases I-a and II-a(C.S = 3.4 C for both).
- While there are feasible solutions for emission trajectories for 1.5 C target with C.S. of
3.0 C (cases I-b and II-b) at least by 2050, marginal abatement cost in 2050 would be
710$tCO2 for the 1.5 C convergence in 2100 (overshoot) case, and 5900$/tCO2 for the
1.5 C stabilization case (cost minimization for both cases).

Amounts of CCS and CO2 fixation byreforestation/afforestation for the 1.5 C target

20

18

Amounts of CO2 storage by CCSI-c) 1.5 °C stabilization (C.S.=2.5 °C)
III-b) Below 1.5 °C by 2300 (C.S.=3.0 °C)

14III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)II-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)

12II-c) Below 1.5 °C by 2100 (C.S.=2.5 °C)
10
8

Source: estimated by RITE DNE21+

64

CO2 fixation byreforestation/afforestation

2
0
2015

2020

2025

2030

2035

2040

- According to the model calculation,
more than 20GtCO2 fixation byreforestation/afforestation is
forecasted in 2050.
- To achieve global net negativeemissions of 20GtCO2 around 2100
indicates requiring both 20GtCO2
fixation of positive emissions and
20GtCO2 negative emissions.

2045

18
2050

CO2 fixation by afforestation/reforestation(GtCO2/yr)

CO2 geological storage (GtCO2/yr)I-b) 1.5 °C stabilization (C.S.=3.0 °C)
16I-b) 1.5 °C stabilization (C.S.=3.0 °C)

16I-c) 1.5 °C stabilization (C.S.=2.5 °C)
III-b) Below 1.5 °C by 2300 (C.S.=3.0 °C)

14III-c) Below 1.5 °C by 2300 (C.S.=2.5 °C)II-b) Below 1.5 °C by 2100 (C.S.=3.0 °C)

12II-c) Below 1.5 °C by 2100 (C.S.=2.5 °C)
10
8
6
4
2
0
2015

2020

2025

2030

2035

2040

2045

2050

Global Primary Energy Supply for the 1.5 C Target
21

20000
Primary energy supply [Mtoe/yr]

Solar PV

Only Cases I-b, I-c,
III-b, III-c are shown

Wind power
15000
NuclearHydro and Geothermal
10000
Biomass w/ CCS
Biomass w/o CCS
5000
Gas w/ CCS
Gas w/o CCS

2010

2030

2050

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)I-c) 1.5 °C stabilization(C.S.=2.5 °C)I-b) 1.5 °C stabilization(C.S.=3.0 °C)

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)I-c) 1.5 °C stabilization(C.S.=2.5 °C)I-b) 1.5 °C stabilization(C.S.=3.0 °C)

0Oil w/ CCS
Oil w/o CCS
Coal w/ CCS

Coal w/o CCS

Source: estimated by RITE DNE21+- In Case I-b, global coal supply should be small and BECCS will be required in 2030.
- On the other hand, in Cases I-c、III-b、III-c, no big changes in primary energy supply by2030 are observed. In Case III-c, no big changes are observed even in 2050 (in this case,drastic reduction is required after 2050).

Global Electricity Supply for the 1.5 C Target

Only Cases I-b, I-c,
III-b, III-c are shown

70000

Electricity generation [TWh/yr]

22

Hydrogen

60000

Solar PV
50000
Wind power
40000

Nuclear

30000

Hydro and Geothermal

20000

Biomass w/ CCS
Biomass w/o CCS

10000

Gas w/ CCS

2010

2030

2050

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)I-c) 1.5 °C stabilization(C.S.=2.5 °C)I-b) 1.5 °C stabilization(C.S.=3.0 °C)

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)I-c) 1.5 °C stabilization(C.S.=2.5 °C)I-b) 1.5 °C stabilization(C.S.=3.0 °C)

0Gas w/o CCS
Oil w/ CCS
Oil w/o CCS
Coal w/ CCS

Coal w/o CCS

Source: estimated by RITE DNE21+- In contrast to primary energy supply or final energy demand, amounts of electricity
generation are observed to be larger for deeper emission reduction pathways while thetotal amounts of primary energy decrease.
- Composition rate of renewable energy (w/o hydrogen) in 2050 for Case I-b is approx. 51%

Global Final Energy Consumption for the 1.5 C Target
23

Only Cases I-b, I-c,
III-b, III-c are shown

12000

Electricity

10000

Gaseous fuel: hydrogen

8000

Gaseous fuel: natural gas

6000

Liquid fuel: biomass

4000

Liquid fuel: oil

2000

Solid fuel: biomass
Solid fuel: coal

2010

2030

2050

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)I-c) 1.5 °C stabilization(C.S.=2.5 °C)I-b) 1.5 °C stabilization(C.S.=3.0 °C)

III-c) Below 1.5 °C by 2300
(C.S.=2.5 °C)

III-b) Below 1.5 °C by 2300
(C.S.=3.0 °C)I-c) 1.5 °C stabilization(C.S.=2.5 °C)0I-b) 1.5 °C stabilization(C.S.=3.0 °C)

Final energy consumption [Mtoe/yr]

14000

Source: estimated by RITE DNE21+- In accordance with a stringent target, final energy demand is significantly suppressed.
- More than half of gaseous fuel demand in 2050 is supplied with hydrogen in cases I-b and I-c- Composition rate of electricity in Case III-c requiring comparatively moderate emission reduction
is 26%; on the other hand, approx. 40% in Case I-b requiring stringent reduction.

5. Conclusions

Conclusions
25

 The Paris Agreement mentioned 2 C and 1.5 C as a temperature target. As

there have been less evaluation examples for 1.5 C target, IPCC has been
invited to provide a special report on the impacts of 1.5 C.

 However, emission pathways and intensities for the 1.5 C target vary widely

when considering political uncertainties in interpreting a description of thetemperature target in the Paris Agreement, as well as scientific uncertainties
in temperature estimates themselves.
 This analysis shows significant gap between most of the 1.5 C target

scenarios assumed here and NDCs in 2030.
 Meanwhile, in the case of climate sensitivity is 2.5 C, a scenario withtemperature peaking at 2 C, then converging on +1.8 C in 2100 and +1.5 Cby 2300 is consistent with NDCs in 2030.

 However, this scenario requires net negative emissions continuously fromthe late 21th century to 2300 (infeasible with afforestation due to therestriction of land area; geoengineering measures like large-scale BECCS or
DAC (direct air capture) are required). Therefore, there seems to be very little
possibilities for achieving the target. There also shall be a discuss whether
achieving + 1.5 C in a quite long term like 2300 shall be consistent with “topursue efforts to limit the temperature increase to 1.5℃”.