http://unu.edu/

世界の「水」と「気候変動」の未来シナリオ
Future Scenario on waterand climate in the world

沖 大幹
国連大学 上級副学長、国際連合事務次長補

Apollo 17,Dec. 1973

(東京大学 総長特別参与、未来ビジョン研究センター 教授)

Taikan Oki
Senior Vice-Rector, United Nations University
Special Advisor to President, Professor, IFI, The University of Tokyo
UNEPフォーラム2019、2019年5月21日(火)、国連大学ウ・タント国際会議場、東京、日本
UNEP Forum 2019, May 21, 2019, U Thant Hall, UNU, Tokyo, Japan1

http://unu.edu/

気候変動影響・対策の効果推計に必要な社会シナリオ
social scenario to estimate impacts and effectiveness容易 ← 緩和策 → 困難easy ← mitigation → difficult

人口や社会経済的発展度合い、技術の進歩と普及次第で気候変動影響や対策の効果は大きく異なる
Impacts of climate change and effectiveness of adaptation depend on social scenario

SSP5
在来型発展
conventional
development

SSP3
分断
divided

SSP2
過去の延長
BAU

SSP1
持続可能
sustainable

SSP2
SSP1

SSP4
格差
gap

容易 ← 適応策 → 困難easy ← adaptation → difficult
https://tntcat.iiasa.ac.at/SspDb/dsd?Action=htmlpage&page=30

2

仮(temporary)3

Impacts and Adaptation
 Around 2080 under RCP8.5-SSP3…
 Global mean Temp: approx. +3.7 ℃
 Additional economic damage: 3.58 % GDP energy demand, labor, famine, food, hydro only.

 Flood damage ≒ +3.28% GDP ≒ +416 tril. Y
 Adaptation cost ≒ +16 tril. Yen/y Yield decline of maize ≒ 16.8 tril. Yen/y Adaptation cost ≒ 19.5 tril. Yen/year Food shortage ≒ 1.68 bill. ≒ 18％ global population
 price↑, harvest and irrigated areas↑, diet change, …

 Potential coastal inundation ≒ 0.7 tril. Yen/y Adaptation cost ≒ 0.3 tril. Yen/y4

Temperature rise and economic damage
0-3-6-9

RCP2.6

RCP8.5

mitigation
adaptation

Change in GDP（％）

3

SSP1

SSP2SSP3

From “S-14” project:• Energy demand, laborefficiency, famine, foodproduction, hydro power
are considered.
• Impacts for fluvial andcoastal floods andecosystems will beconsidered.
Before AR4-12

After AR4
Additional temperature rise（℃）



RCP8.5 should better be avoided but the difference between
2℃ and 1.5℃ targets was unclear.
Socioeconomic pathway also matters a lot for climate change
impacts on GDP.

http://www.ipcc.ch/report/sr15/

5SR1.5

From Special report on “1.5degree warming” (SR15)

Human activities are estimated to have caused approximately 1.0°C of
global warming above pre-industrial levels, with a likely range of 0.8°C to
1.2°C. Global warming is likely to reach 1.5°C between 2030 and 2052 if
it continues to increase at the current rate. (high confidence)SR1.5

http://unu.edu/

Major messages from SR15
 An additional 0.5°C of warming compared to present isassociated with further detectable changes including warmingof extreme temperatures in many regions, increases infrequency, intensity, and/or amount of heavy precipitation inseveral regions, and an increase in intensity or frequency ofdroughts in some regions.
 At 1.5°C compared to 2°C: global mean sea level rise is projected to be around 0.1 m
 Lower risks of ocean acidification, decreases in ocean oxygen
levels, health, livelihoods, food security, water supply, humansecurity, and economic growth Most adaptation needs will be lower The avoided climate change impacts on sustainable development,
eradication of poverty and reducing inequalities would be greater There are limits to adaptation and adaptive capacity for somehuman and natural systems at global warming of 1.5°C
 Under the Paris Agreement: global GHG emissions in 2030
 52–58 Gt CO2eq yr-1  ΔT > 1.5°C global CO2 emissions start to decline well before 2030

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仮7(Tang et al., submitted)

Approx. 1.15 bill. tCO2 in 2015 from Japan

Social cost of 1 billion t of CO2
 1.3～2.0 mill.人・Y DALY ≒ 0.34～0.52 bill.Yen
 1DALY ≒ 2.60 mill. Yen 1～3 EINES ≒ 1.3～4 trill. Yen 1 EINES ≒ 1.3 trill. Yen  ～ 5～9 trill. Yen of global damage
単位CO2DF Human Health

DALY/ton

1.3 – 2.2 ×10-3

DF Biodiversity

EINES/ton

9.3×10-10 – 3.0×10-9

WF2 Human Health (global mean) (LIME3)

US$/DALY

2.3E+4WF2 Biodiversity (global mean) (LIME3)

US$/EINES

1.1E+10

US$/ton40 - 84

IF2 Global Mean

Social cost of 1t CO2 ≒ 5K～10K Yen

8SCC in US under Obama Presidency
12$(5% discount)

42$(3% discount)62$(2.5% discount)

Technical Support Document– Technical Update of theSocial Cost of Carbon forRegulatory Impact Analysis –Under Executive Order 12866
合衆国政府、大統領経済諮問委員会、環境基準諮問委員会、農務省、商務省、エネルギー省、内務省、運輸省、財務省、環境保護庁、国家経済会議、行政予算管理局、科学技術政策室

 Based on 3 models (DICE, FUND, PAGE) 3 sets of discount rate with Monte Carlo method

9

SCC in US under Trump Presidency (2017)1$(7% discount)

7$(3% discount)

USEPA (2017) Regulatory
Impact Analysis for theReview of the Clean Power
Plan: Proposal

 Impacts within US only Higher discount rate (3～7%)

USD2010 tCO2-eq –1

Cost of mitigation

http://unu.edu/

10

LED: low energy
demand (no CCS)
S1: a sustainability
oriented scenario
S2: a middle-of-the-roadscenario
S5: a fossil-fuel intensive
and high energy
demand scenario

SR1.5
Fig.2.26(b) Global price of carbon emissions consistent with mitigation pathways.
Average price of carbon (2030-2100) discounted at a 5% discount rate.
AC: Annually compounded. NPV: Net present value. Median values in floating
black line. The number of pathways included in boxplots is indicated in thelegend. Number of pathways outside the figure range is noted at the top.

Figure 4
Ricke et al. (2018, Nature Climate Change)

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Shares of CO2 emission and global SCC
Impact＞Emission(looser)

Impacts＜ Emision(winner)

National SCC are with 2% discount rate with SSP2-RCP6.0. Colors
are SSC/person, sizes reflect the logGDP. The box in the left panel
indicates the bounds of the detail shown in the right panel.

12
Mitigation options
deployed in each sector
can be associated withpotential positive effects(synergies) or negativeeffects (trade-offs) withthe SDGs. The degree towhich this potential isrealized will depend on theselected portfolio ofmitigation options,mitigation policy design,and local circumstancesand context.
Particularly in the energydemand sector, thepotential for synergies islarger than for trade-offs.
The bars group individuallyassessed options by levelof confidence and take into
account the relative
strength of the assessed
mitigation-SDG
connections.

SR1.5

http://www.ipcc.ch/report/sr15/

SR1.5

http://unu.edu/

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Climate change and SDGs
 Mitigation options consistent with 1.5°C pathways
are associated with multiple synergies and trade-offs
across the SDGs.
 Adaptation options specific to national contexts will
have benefits for SD and poverty reduction withwarming of 1.5°C, although trade-offs are possible.
 Limiting the risks from global warming of 1.5°C
implies system transitions that can be enabled by anincrease of adaptation and mitigation investments,
policy instruments, the acceleration of technologicalinnovation and behaviour changes
 Education, information, and community approaches,
including those that are informed by indigenous knowledge
and local knowledge, can accelerate the wide scale
behaviour changes consistent with adapting to and limiting
global warming to 1.5°C

Figure 2
Fujimori et al. (2019, Nature Sustainability)

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14

Potential negative trade-offs between
food security and climate mitigation
飢餓の危険性がある世界人口(百万人)。ベースライン、各国が定めた貢献(NDC)、2℃目標、1.5℃
目標達成の緩和策を実現する社会経済シナリオに対応。
↓Population at risk ofhunger in 2050 under thevarious scenarios.
↑The population at risk of hunger
under the baseline and mitigation
scenarios. The solid line indicatesmedian value across the models
and the shaded area represents
upper and lower ranges of themodel estimates for each scenario.

Figure 2
Fukuda, Noda, and Oki (2019, Nature Sustainability)

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GDP and Water Access2015 figure
1990 figure
an arrow = a country

15Remarks16

 Transformative change is necessary toachieve SDGs and the 1.5°C target.
 Side effect of radical change? 急激な変化の副作用は?
 “change must proceed slowly” (Wealth of Nations,Adam Smith; 国富論、アダム・スミス)

 “man of humanity and benevolence” who uses reasonand persuasion and “the man of system” who imposes
his own “ideal plan of government” on others by force: The man of system is apt to be very wise in his own conceit; and isoften so enamoured with the supposed beauty of his own idealplan of government, that he cannot suffer the smallest deviationfrom any part of it.

 No one will be left behind (誰一人取り残さない)  the greatest happiness of the greatest number(最大多数の最大幸福) What is the ultimate goal? (究極の目標は?)
 Well-being? Of what? (幸福度? 何の?)