溫室氣體排放情景：背景、問題和政策相關(guān)性

1、Contents HYPERLINK l _bookmark0 Introduction 1 HYPERLINK l _bookmark1 Economic, Energy, and Climate Modeling: Use of Integrated Assessment Models (IAMs) 2 HYPERLINK l _bookmark2 Overview 2 HYPERLINK l _bookmark4 IAMs and the IPCC Assessment Process 5 HYPERLINK l _bookmark5 Scenarios of Global Warmin

2、g and Socioeconomic Storylines 5 HYPERLINK l _bookmark8 Results from Emissions Scenarios Consistent with 1.5C and 2C Warming 8 HYPERLINK l _bookmark9 Methodology for Scenario Selection 10 HYPERLINK l _bookmark10 Primary Energy Use 11 HYPERLINK l _bookmark12 Electrification 14 HYPERLINK l _bookmark14

3、 Peak and Net-Zero CO2 Emissions 15 HYPERLINK l _bookmark17 Negative Emissions Technologies 17 HYPERLINK l _bookmark22 Strengths and Criticisms of IAMs 22 HYPERLINK l _bookmark23 Concluding Observations 24 HYPERLINK l _bookmark24 The Role of IAMs in Climate Legislation 25 HYPERLINK l _bookmark25 Tec

4、hnologies to Reduce GHG Emissions 25Figures HYPERLINK l _bookmark3 Figure 1. Illustrative Example of IAM Inputs, Building Blocks, and Outputs 4 HYPERLINK l _bookmark7 Figure 2. SSPs and Population and GDP Assumptions 8 HYPERLINK l _bookmark11 Figure 3. Global Primary Energy Mix in 2050, by IAM 13 HY

5、PERLINK l _bookmark13 Figure 4. Global Electrification in 2050, by IAM 14 HYPERLINK l _bookmark15 Figure 5. Global CO2 Emissions over Time Across 2C-Consistent Scenarios 16 HYPERLINK l _bookmark16 Figure 6. Global CO2 Emissions over Time Across 1.5C-Consistent Scenarios 17 HYPERLINK l _bookmark18 Fi

6、gure 7. Total Annual Global Carbon Capture from BECCS in 2050, by IAM 18 HYPERLINK l _bookmark19 Figure 8. Bioenergy Crop Production in 2050, by IAM 20 HYPERLINK l _bookmark20 Figure 9. Global Net Land Use Emissions in 2050, by IAM 21 HYPERLINK l _bookmark21 Figure 10. CO2 Emissions in 2050, by IAM

7、22Tables HYPERLINK l _bookmark6 Table 1. Overview of the RCPs 6 HYPERLINK l _bookmark27 Table A-1. Comparison of IAMs Referenced in this Report 26 HYPERLINK l _bookmark29 Table B-1. Assumptions Regarding Economy, Lifestyle, Policies, and Institutions for the HYPERLINK l _bookmark29 Five SSPs of the

8、Intergovernmental Panel on Climate Change 27Appendixes HYPERLINK l _bookmark26 Appendix A. Details of the IAMs 26 HYPERLINK l _bookmark28 Appendix B. Summary of SSPs 27ContactsAuthor Information 30IntroductionThe use of scenario analysis began with military planning and gaming and moved into the bus

9、iness world by the early 1960s as a way to analyze in a systematic way the long-term consequences of strategic decisions.1 The goal of scenario analysis is neither to predict nor forecast, but rather explore possible futures in order to understand uncertainties and key variables and aid in decisionm

10、aking.Greenhouse gas (GHG) emissions scenarios are fundamental to understanding the long-term implications of both future anthropogenic climate change2 and policy options to mitigate it. GHG emissions scenarios are plausible emissions futures based on socioeconomic, environmental, and technological

11、trends and drivers.3 They are used as inputs in climate models to explore how changes in GHG concentrations alter the earths radiative balance4 and thus affect the global climate.5As Congress considers whether and how to address climate change, and particularly legislation drafted with a policy obje

12、ctive to mitigate GHG emissions, Members may have emissions scenarios as evaluations of their options. Moreover, President Biden has announced a number of climate change targets in the Nationally Determined Contribution (NDC) submitted on April 21, 2021, to the United Nations Framework Convention on

13、 Climate Change (UNFCCC) as part of the Paris Agreement.6 The NDC includes a 50% reduction in GHG emissions by 2030 (compared to 2005) and net-zero emissions by 2050.7 Congress may find it useful to better understand the models that the Administration may use to evaluate and present its strategies.

14、These models can inform deliberations on the feasibility of achieving various emissions reduction trajectories and help to identify policies and tradeoffs, such as competition for land, in meeting those emissions constraints.This report provides background on emissions scenarios, some of the main ec

15、onomic-energy models that have been used to construct emissions scenarios as part of the Intergovernmental Panel on Climate Change (IPCC) and national policy processes (including those of the United States), and some of the key findings of the scenarios consistent with keeping mean global warming to

16、 1.5C or 2C. The report then concludes with observations for Congress.1 Richard H. Moss et al., “The Next Generation of Scenarios for Climate Change Research and Assessment,” Nature, vol. 463, no. 7282 (February 11, 2010), pp. 747-756; Eric V. Larson, Force Planning Scenarios, 19452016: Their Origin

17、s and Use in Defense Strategic Planning, Santa Monica, CA: RAND Corporation, 2019.2 For a discussion of the scientific understanding and confidence regarding the drivers of recent global climate change, see CRS Report R45086, Evolving Assessments of Human and Natural Contributions to Climate Change,

18、 by Jane A. Leggett.3 Hereinafter referred to simply as emissions scenarios. Richard H. Moss et al., “The Next Generation of Scenarios for Climate Change Research and Assessment,” Nature 463, no. 7282 (February 11, 2010), pp. 747-756, / 10.1038/nature08823; Aurore Colin, Charlotte Vailles, and Romai

19、n Hubert, “Understanding Transition Scenarios: Eight Steps for Reading and Interpreting These Scenarios,” I4CE: Institute for Climate Economics, November 2019.4 The radiative balance is the difference between solar irradiance (suns energy entering the atmosphere) and energy radiated back to space.5

20、For more discussion of the drivers of climate change, see U.S. Environmental Protection Agency, “Climate Change Science,” May 12, 2017, at /epa/climate-change-science/causes-climate-change.html; R. K. Pachauri et al., Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and II

21、I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, eds. R. K. Pachauri and L. Meyer (Geneva, Switzerland: IPCC, 2014).6 U.S. Government, “Nationally Determined Contribution. Reducing Greenhouse Gases in the United States: A 2030 Emissions Target,” April 21, 2021, at /

22、sites/ndcstaging/PublishedDocuments/ United%20States%20of%20America%20First/United%20States%20NDC%20April%2021%202021%20Final.pdf.7 For a discussion of net-zero emissions, see CRS In Focus IF11821, Net-Zero Emissions Pledges: Background and Recent Developments, by Michael I. Westphal.Economic, Energ

23、y, and Climate Modeling:Use of Integrated Assessment Models (IAMs)OverviewThe construction of GHG emissions scenarios is generally done with quantitative models, which are abstractions, or simplified representations of reality. Models capture the essence of the relationships in a system, but are red

24、uced in their complexity to allow one to gain insights not possible simply from available information.8 Models are often mathematical in nature, but not necessarily so. Best practices for modeling include clearly stated assumptions and transparent relationships among model variables.9Integrated asse

25、ssment models (IAMs) are a prominent type of economic-energy model that combine elements of the human system (e.g., population, economy, and energy use) and the biophysicalearth system into one modeling framework.10 There are two basic types of IAMs: (1) relatively simple IAMs11 that incorporate eco

26、nomic damages from climate change but have fairly limited representations of the economy and are highly spatially aggregated,12 and (2) detailed, higher- spatial-resolution, process-based IAMs that represent the drivers and processes of change in global energy and sometimes land use systems linked t

27、o the broader economy, but typically lack a comprehensive representation of climate impacts (e.g., changes in gross domestic product GDP from physical climate impacts).13 The focus of this report is on the latter process-based type of IAMs, which are discussed below in detail.While one could use var

28、ious models to generate emissions scenarios,14 analyses from these more detailed, process-based IAMs have been a key component of the mitigation working group (Working Group III) of the IPCC, the main international scientific body for assessing global climate change.15 They have also been used in a

29、number of countries scenarios for decarbonizationfor8 Katy Borner et al., “An Introduction to Modeling Science: Basic Model Types, Key Definitions, and a General Framework for the Comparison of Process Models,” in Understanding Complex Systems, 2012.9 Katy Borner et al., “An Introduction to Modeling

30、 Science: Basic Model Types, Key Definitions, and a General Framework for the Comparison of Process Models,” in Understanding Complex Systems, 2012.10 James A. Edmonds et al., “Integrated Assessment Modeling (IAM),” in Encyclopedia of Sustainability Science and Technology, ed. Robert A. Meyers (New

31、York, NY: Springer New York, 2012), pp. 5398-5428.11 These include the DICE, PAGE, and FUND models. William Nordhaus, “Evolution of Modeling of the Economics of Global Warming: Changes in the DICE Model, 1992-2017,” Climatic Change, vol. 148, no. 4 (June 2018), pp. 623-640, at /10.1007/s10584-018-22

32、18-y; David Anthoff and Richard S. J. Tol, The Climate Framework for Uncertainty, Negotiation, and Distribution (FUND), Technical Description, Version 3.9, 2014; C. W. Hope, The PAGE09 Integrated Assessment Model: A Technical Description, Judge Business School, University of Cambridge, 2011.12 They

33、are spatially aggregated in that they typically operate at no smaller than the country-scale. They have been used to calculate the social cost of carbon, a monetary estimate of the discounted climate change impacts to society over time from an additional ton of carbon dioxide. See Delavane Diaz and

34、Frances Moore, “Quantifying the Economic Risks of Climate Change,” Nature Climate Change, vol. 7, no. 11 (November 2017), pp. 774-782 ; CRS In Focus IF10625, Social Costs of Carbon/Greenhouse Gases: Issues for Congress, by Jane A. Leggett.13 These are called process-based because they offer a detail

35、ed representation of the energy system, including energy demand, future extraction, transformation, distribution, and use of energy and explore linkages with other sectors in the economy, such as agriculture and land use. They have a higher spatial resolution in that they incorporate features at fin

36、er spatial scales than the country-scale (for example, agro-ecological zones or hydrologic basins).14 For an example of a web-based emissions scenario tool, see Energy Policy Simulator: Energy Innovation, “Energy Policy Solutions,” at https:/ HYPERLINK http:/www.energypolicy.solutions/ www.energypol

37、icy.solutions/.15 For a review of some of the main conclusions from the IPCC assessment reports over time, see CRS Report R45086,example, the U.S. midterm strategy for deep decarbonization developed during the Obama Administration.16These detailed, process-based IAMs17 are numerical, computer models

38、. They vary considerably in their sectoral (e.g., transportation, power generation, industry), technological, or macroeconomic detail; geographic representation; availability of technologies and mitigation options; economic structure; and solution approach ( HYPERLINK l _bookmark26 Appendix A).18 Ho

39、wever, they are typically structured to include several principal building blocks, or modules ( HYPERLINK l _bookmark3 Figure 1):19Macroeconomy System. This module uses outside (“exogenous” to the model) macroeconomic inputs (e.g., population, labor productivity, sometimes GDP) to estimate energy de

40、mands for each sector and world region. The most common sectors include transport, buildings, industry, and agriculture.Energy System. This module typically includes a representation of the sources of primary energy20 supply, modes of energy transformation (e.g., combustion of fossil fuels into heat

41、 and electricity), and energy service demands (e.g., passenger and freight transport, industry energy use, residential and commercial heating and electricity). This building block allows the model to choose a wide range of fuels and technologies to meet the energy demands and represents the costs an

42、d performance (efficiency, lifetime) of the energy technologies.21 It would include energy supply technologies (e.g., fossil fuels, nuclear, solar photovoltaics, wind), as well as energy demand technologies (e.g., gas stoves and boilers, electric heat pumps, internal combustion and electric vehicles

43、, blast furnaces). This module could also include energy demand from agriculture and water systems. The fuels used to meet energy demand in each time period have associated emissions factors that relate fuel combustion to greenhouse gas emissions. Many IAMs also represent the nonenergy sectors, such

44、 as land use and agriculture, and include noncombustion CO2, and non-CO2 GHGs, such as methane and nitrous dioxide. The ways in which IAMs “choose” technologies and fuels vary with model structure and the criteria or “objective functions” that the modelers specify, and these can explain many differe

45、nces across model results.Climate System. This module relates emissions over any time period to changes in atmospheric concentrations of GHGs and the resulting changes in earths meanEvolving Assessments of Human and Natural Contributions to Climate Change, by Jane A. Leggett16 The White House, “Unit

46、ed States Mid-Century Strategy for Deep Decarbonization,” November 2016, at /files/focus/long-term_strategies/application/pdf/mid_century_strategy_report-final_red.pdf.17 Henceforth, these detailed, process-based IAMs will simply be referred to as IAMs.18 Integrated Assessment Modelling Consortium,

47、“IAMC Wiki,” 2020, at https:/ HYPERLINK http:/www.iamcdocumentation.eu/index.php/ www.iamcdocumentation.eu/index.php/ IAMC_wiki.19 Ajay Gambhir et al., “A Review of Criticisms of Integrated Assessment Models and Proposed Approaches to Address These, Through the Lens of BECCS,” Energies, vol. 12, no.

48、 9 (May 1, 2019), pp. 1-21; Joint Global Change Research Institute, “GCAM v4.3 Documentation,” at https:/jgcri.github.io/gcam-doc/.20 Primary energy is energy found in nature and not subject to any human conversion process. Primary energy includes fossil fuels (petroleum, natural gas, and coal), nuc

49、lear energy, and renewable sources of energy, such as wind and solar. Secondary energy refers to resources that have been converted (for example, crude oil that is refined into fuels, coal that is used in a coal-fired plant to generate electricity, or wind that is harnessed by a turbine to generate

50、electricity).21 Models very greatly in the amount of technological detail they contain. This can greatly affect the options available in the model for responding to policy constraints, and ultimately the results from the model.surface temperature. Some IAMs include reduced-form global climate carbon

51、-cycle models that include feedbacks among the atmosphere, soil, and oceans.22One key distinction among IAMs is how they structure the economy. Equilibrium in economic theory is reached when prices are found to match supply and demand in a market. Generalequilibrium models represent the entire econo

52、my (though the sectoral detail could vary significantly) and find a set of prices that have the effect of “clearing” all markets simultaneously. Partial equilibrium models do so for just one or a couple of markets/sectors (e.g., energy, agriculture), assuming prices in other markets remain constant.

53、23All IAMs generally are designed to meet some emissions limit or climate threshold in a cost- effective manner.24 They vary in how they represent costs and whether they simulate futureemissions and technology paths, or whether they optimize them over time (i.e., least-cost pathway), assuming perfec

54、t foresight.25 IAMs are often used to compare a baseline scenario26an emissions trajectory under current conditions/policieswith a policy scenario, where climate policies, targets, constraints, or changes in the technology availability, cost, and mix are explored.Figure 1. Illustrative Example of IA

55、M Inputs, Building Blocks, and OutputsSource: Adapted from CarbonBrief, “Q&A: How Integrated Assessment Models Are Used to Study Climate Change,” February 10, 2018, at https: HYPERLINK /qa-how-integrated-assessment-models-are-used-to- /www.carbo HYPERLINK /qa-how-integrated-assessment-models-are-use

56、d-to- /qa-how-integrated-assessment-models-are-used-to- study-climate-change.Note: IAMs vary in how they incorporate socioeconomics (for example, population and labor productivity may be used to generate GDP estimates) and their sectoral representation.22 GCAM, for example, has a global climate carb

57、on-cycle model, Hector, that models carbon flux in the atmosphere, three “pools” on land, and four “pools” in the ocean. Joint Global Change Research Institute, “GCAM v5.3 Documentation: Earth System Module Hector v2.0,” at HYPERLINK http:/jgcri.github.io/gcam-doc/gcam-usa.html http:/jgcri.github.io

58、/gcam-doc/gcam-usa.html.23 Elizabeth A. Stanton, Frank Ackerman, and Sivan Kartha, “Inside the Integrated Assessment Models: Four Issues in Climate Economics,” Climate and Development, vol. 1, no. 2 (2009), pp. 166-184.24 Ajay Gambhir et al., “A Review of Criticisms of Integrated Assessment Models a

59、nd Proposed Approaches to Address These, through the Lens of BECCS,” Energies, vol. 12, no. 9 (May 1, 2019), pp. 1-21.25 Elizabeth A. Stanton, Frank Ackerman, and Sivan Kartha, “Inside the Integrated Assessment Models: Four Issues in Climate Economics,” Climate and Development, vol. 1, no. 2 (2009),

60、 pp. 166-184.26 Aurore Colin, Charlotte Vailles, and Romain Hubert, “Understanding Transition Scenarios: Eight Steps for Reading and Interpreting These Scenarios,” I4CE: Institute for Climate Economics, November 2019.IAMs and the IPCC Assessment ProcessThe IPCC has used emissions scenarios since its