IPCCシンポジウム「IPCC第6次評価報告書統合報告書から気候変動の最新知見を学ぶ」 2023年5月22日IPCC統合報告書:科学的正確性とわかりやすさとの間で(公財)地球環境産業技術研究機構(RITE)システム研究グループグループリーダー秋元主吾
Mitigation options Wind energy Carbon capture and storage (CCS Bioelectricity with CCS Reduce CH, emission from coal mining Reduce CH  emission from oil and gas Carbon sequestration in agriculture Reduce CH, and N,0 emission in agriculture Reduced conversion of f orests and other ecosystems Ecosystem restoration, afforestation, reforestation Improved sustainable forest management Reduce food loss and food waste Shift to balanced, sustainable healthy diets Avoid demand for energy services Efficient lighting, appliances and equipment New buildings with high energy performance Onsite renewable production and use Improvement of existing building stock Enhanced use of wood products Fuel efficient light duty vehicles Electric light duty vehicles Shift to public transportation Shift to bikes and e-bike Fuel efficient heavy duty vehicles Electric heavy duty vehicles, incl. buses Shipping – efficiency and optimization Aviation – energy efficiency Biotuels Energy elficiency Material efficiency Enhanced recycling Fuel switching (electr, nat. gas, bio-energy, H :) Feedstock decarbonisation, process change Carbon capture with utilisation (CCU) and CCS Cementitious material substitution Reduction of non-CDs en Reduce emission of fluorinated i Reduce CH, emissions from wastewater WG3, Fig. SPM.7 SPM C12.1 (部門別、技術別の積み上げ評価から） 100 $/tCO2eq以下のコストの緩和オプションで、世界全体GHG排出量を2030年までに少なくとも2019年レベルの半分に削減しうるだろう（確信度中位）。その削滅ポテンシャルの半分以上は、 20 $/tCO2eq以下✓後述のように、統合評価モデル(IAM)ののコスト推計とは大きな差異があり、IAMと比べ率事的／負の費用の意味は？IAMでは、原則、負の費用はベースライン推計に含まれる。 ✓隠れたコストの扱い。割引率の問題variability or lack of data Uncertainty range applies to the total potential contribution to emission reduction. The individual cost ranges are also associated with uncertainty GtCO:1-eq yr
Costs shown are net lifetime costs of avoided greenhouse gas emissions. Costs are calculated relative to a reference technology. The assessments per sector were carried out using a common methodology, including definition of potentials, target year, reference scenarios, and cost definitions. The mitigation potential (shown in the horizontal axis) is the quantity of net greenhouse gas emission reductions that can be achieved by a given mitigation option relative to a specified emission baseline. Net greenhouse gas emission reductions are the sum of reduced emissions and/or enhanced sinks. The baseline used consists of current policy (~ 2019) reference scenarios from the AR6 scenarios database (25/75 percentile values). The assessment relies on approximately 175 underlying sources, that together give a fair representation of emission reduction potentials across all regions. The mitigation potentials are assessed independently for each option and are not necessarily additive. {12.2.1, 12.2.2} The length of the solid bars represents the mitigation potential of an option. The error bars display the full ranges of the estimates for the total mitigation potentials. Sources of uncertainty for the cost estimates include assumptions on the rate of technological advancement, regional differences, and economies of scale, among others. Those uncertainties are not displayed in the figure. Potentials are broken down into cost categories, indicated by different colours (see legend). Only discounted lifetime monetary costs are considered. Where a gradual colour transition is shown, the breakdown of the potential into cost categories is not well known or depends heavily on factors such as geographical location, resource availability, and regional circumstances, and the colours indicate the range of estimates. Costs were taken directly from the underlying studies (mostly in the period 2015-2020) or recent datasets. No correction for inflation was applied, given the wide cost ranges used. The cost of the reference technologies were also taken from the underlying studies and recent datasets. Cost reductions through technological learning are taken into account (FOOTNOTE 70). When interpreting this figure, the following should be taken into account: – - ' The mitigation potential is uncertain, as it will depend on the reference technology (and emissions) being displaced, the rate of new technology adoption, and several other factors. Cost and mitigation potential estimates were extrapolated from available sectoral studies. Actual costs and potentials would vary by place, context and time. Beyond 2030, the relative importance of the assessed mitigation options is expected to change, in particular while pursuing long-term mitigation goals, recognising also that the emphasis for particular options will vary across regions (for specific mitigation options see sections C4.1, C5.2, C7.3, C8.3 and C9.1). Different options have different feasibilities beyond the cost aspects, which are not reflected in the figure (cf. section E.1). The potentials in the cost range 100 to 200 USD tCO 2 -eq 11 may be underestimated for some options. Costs for accommodating the integration of variable renewable energy sources in electricity systems are expected to be modest until 2030, and are not included because of complexities in attributing such costs to individual technology options. Cost range categories are ordered from low to high. This order does not imply any sequence of implementation. Externalities are not taken into account. {12.2, Table 12.3, 6.4, Table 7.3, Supplementary Material Table 9.2, Supplementary Material Table 9.3, 10.6. 11.4, Fig 11.13, Supplementary Material 12.A.2.3} FOOTNOTE 70: For nuclear energy, modelled costs for long-term storage of radio-active waste are included. WG3, Fig. SPM.7
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Global CO¸ emissions in 2030 (GtCO¸ yr-¹)部門、技術積み上げのコスト評価のFig. SPM7では、2030年の100 $/tCO2eq以下のポテンシャルは、2019年排出量の少なくとも半分と評価（2019年排出量を59 GtCO2eq/yrとすると、29.5 GtCO2eg/yr)。20 $/tCO2egで少なくともその半分のポテンシャルとしており44.3 GtCO2eg/yr。上記のグラフは、CO2なので、GHGとの2019年時点での差分14 GtCO2eq/yr程度を単純に追加すると、100 $/tCO2で、36～47 GtCO2eq/yr程度。20 $/tCO2程度では、49～59 GtCO2eq/yr程度であり、統合評価モデルIAMの分析と、部門、技術積み上げのコスト評価のFig. SPM7では、かなり大きな評価のギャップが見られる。 (Fig. SPM7はかなり楽観的にコスト・ポテンシャルを推計) WG3, Fig. 3.33 Category limit warming to 1.5°C 0%) with no or limited overshoot C2: return warming to 1.5°C (>50%) after a high overshoot 3: limit warming to 2°C 44: limit warming to 2°C limit warming to 2.5°C limit warming to 3°C
WG3, Fig. 3.34 2.5°C程度の目標であれば、GDPにプラスとなる推計も少しは見られるが（多数ではない）、2℃ (>67%)や1.5℃目標では、GDPにには負の影響との推計のみ。 「環境と経済の好循環」は、少なくとも世界全体としては、また、影響被害緩和の便益をもなければ、実現しがたい世界である。 Cumultative CO, emissions (Gt) from 2020 to year of net zero emissions IAMのシナリオ分析では、費用最小化(＝限界削減費用世界均等化)を仮定することが多いが、このとき、低所得国のGDPロスは大きくなりやすい。逆にGDPロスを均等化しようとすれば、先進国は、より大きな限界削減費用の負担が必要になり、それは、産業や炭素のリーケージを生じやすい。⇒理想的なモデル分析の世界とは別に、現実世界の負担、対策の難しさが存在していたEU NAM PAC CHN MEA LAM IND AFR REF C1: limit warming to 1.5°C (>50%) with no or limited overshoot C2: return warming to 1.5°C (>50%) after a high overshoot C3: limit warming to 2°C (>67%) nted consumption loss (%
6 Climate responses and adaptation options otential up to 1.5 easibility with
mitigation Synergies Mitigation options 0 Solar Wind統合報告書, Fig. SPM.7 options costing 100 USD tC0₂-eq or less could redŭce global emissions at least half of the 2019 level by 2030 Potential contribution to net emission reduction, 2030 ❏ GtC0²-eq/yr Energy reliability (e.g. diversification, access, stability) Resilient power systems Improve water use efficiency Reduce methane from coal, oil and gas Bioelectricity (includes BECCS) Geothermal and hydropower Nuclear- Fossil Carbon Capture and Storage (CCS) Efficient livestock systems 8 9 9 Improved cropland management Water use efficiency and water resource management Biodiversity management and ecosystem connectivity Agroforestry Sustainable aquaculture and fisheries Forest-based adaptation Integrated coastal zone management Coastal defence and hardening e e e not assessed Confidence level in potential feasibility and in synergies with mitigation Net lifetime cost of options: Costs are lower than the reference 0–20 (USD per tCO₂-eq) 20–50 (USD per tCO₂-eq) 50–100 (USD per tCO 2-eq) 100–200 (USD per tCO 2 -eq) Cost not allocated due to high variability or lack of data ● ● Reduce conversion of natural ecosystems Carbon sequestration in agriculture Ecosystem restoration, afforestation, reforestation Shift to sustainable healthy diets Improved sustainable forest management Reduce methane and N,0 in agriculture Reduce food loss and food waste Feasibility level and synergies with mitigation High Medium Low Insufficient evidence e e   High ●● Medium • Low ERGY SUP D, WATER, FO(
7 Climate responses and adaptation options easibility up to 1.5 Synergies
with mitigation Sustainable urban water management Sustainable land use and urban planning Green infrastructure and ecosystem services ihanced health services (e.g. WASH, nutrition and diets) e e ● ● Human migration Planned relocation and resettlement Livelihood diversification �� Feasibility level and synergies with mitigation High Medium Low ��� High ●● Medium • Low Insufficient evidence TLEMENTS
FRASTRUCT HEALTE ETY, LIVELIHOOD Risk spreading and sharing Social safety nets Climate services, including Early Warning Systems Disaster risk management Efficient buildings Fuel efficient vehicles Electric vehicles Efficient lighting, appliances and equipment Public transport and bicycling Biofuels for transport Efficient shipping and aviation Avoid demand for energy services Onsite renewables Fuel switching Reduce emission of fluorinated gas Energy efficiency Material efficiency Reduce methane from waste/wastewater Construction materials substitution Enhanced recycling Carbon capture with utilisation (CCU) and CCS Net lifetime cost of options: Costs are lower than the reference 0–20 (USD per tCO₂-eq) 20–50 (USD per tCO 2-eq)統合報告書, Fig. SPM.7 options costing 100 USD tC0₂-eg or less could redŭce global emissions by at least half of the 2019 level by 2030 Potential contribution to net emission reduction, 2030 ❏ GtC0₂-eq/yr 4 Confidence level in potential feasibility and in synergies with mitigation 50–100 (USD per tCO₂-eq) 100–200 (USD per tCO 2-eq) Cost not allocated due to high variability or lack of data Mitigation options 0
収集されたシナリオ数GHG排出削減率(2019年比) 500 450 400 WG3, Fig.3.3部のみ掲載) WG3, Table 3.2 (一部のみ掲載) 2030 2040 2050 limit warming to 1.5°C C1 [97] (>50%) with 43 69 84 no or limited overshoot [34–60] [58–90]  [73–98] return warming to C2 [133] 1.5°C (≥50%) after a high overshoot limit warming C3 [311] to 2°C (≥67%)統合報告書, Table SPM.XX ?
✓実際の排出は、過去のベースライン出量の上限程度を推移。意欲的な標と、実績との間のギャップが広まいる。 IAMsの分析は、技術積み上げ評価に比べると保守的な推計であるが、現実の世界排出量はIAMs推計よりも、策がうまくいっていない。 AR4, Fig. 3.11 AR5, Fig. 6.7 2019年CO2排出↑ IPCC報告書は最新の科学的知見を集約しており、多くの有用な情報の集積となっている。 ↑一方、報告書本文（承諾）⇒WG報告書政策決定者向け要約（SPM）【一文一文の政府承認】⇒統合報告書SPM【一文一文の政府承認】となるに従って、字数制約や、政府、メディア等へのわかりやすさへの配慮によって、「伝言ゲーム」のように、本来、理解を促すための重要な記述が落ちていき、誤った理解を誘発するリスクの懸念あり◆ 排出削減費用と削減ポテンシャル推計には、留意が必要。現実世界では、間接的な費用を含め、様々な「隠れた費用」が存在。それも理解した上で、対応策を考えることが重要。現状では、排出削減費用は安価ではない。安価ではないから、世界は大幅な排出削減に成功していない。WG3のSPMには一定の注記がなされているが、統合報告書では注記はない。統合報告書公表後、メディア等は、IPCCは、1.5℃以内に抑制するには「温暖化ガス排出量を2035年に19年比で60％」減らす必要があると提示したと伝えている。誤ってはいないが、「伝言ゲーム」で一部の切り取られた情報となっていることが感念される。 ◆気候変動問題、対策は、エネルギー対策・政策と表裏一体。エネルギー対策・政策◆は、エネルギー安全保障・安定供給への配慮が必要であるが、統合評価モデルIAMの分析を含めて、IPCC報告書はどうしても環境効果（排出削減効果）が強調されやすい。IPCC報告書が、現実の政策との大きなギャップを生まないようにするため、より多様な視点での評価が求められる。