Emissions Scenarios

7/28/2019 Emissions Scenarios

1/607


2/607


3/607

S p e c i a l R e p o r t o nE m i s s i o n s S c e n a r i o s

Nebojsa Nakicenovic, Joseph Alcamo, Gerald Davis, Bert de Vries, Joergen Fenhann,Stuart Gaffin, Kermeth Gregory, A m u l f Griibler, Tae Yong Jung, Tom Kram,E m i l i o Lebre La Rovere, Laurie Michaelis, Shunsuke M o r i , Tsuneyuki Morita,W i l l i a m Pepper, Hugh Pitcher, Lynn Price, Keywan Riahi, Alexander Roehrl,Hans-Holger Rogner, A l e x e i Sankovski, Michael Schlesinger, Priyadarshi Shukla,Steven Smith, Robert Swart, Sascha van Rooijen, Nadejda Victor, Zhou Dadi

A Special Report of Working Group III of tiie Intergovernmental Panelon Climate Change

P u b l i s h e d f o r t h e I n t e r g o v e r n m e n t a l P a n e l o n C l i m a t e C h a n g e


4/607

P U B L I SH E D B Y T H E P R E S S S Y N D I C A T E OF T H E U N I V E R S I T Y OF C A M B R I D G EThe Pitt B u i l d i n g , Trampington Street, Cambridge, United KingdomC A M B R I D G E U N I V E R S IT Y P R E S SThe Edinburgh B u i l d i n g , Cambridge CB2 2 R U , U K http://www.cup.cam.ac.uk40 West 20th Street, New Y o r k , N Y 10011-4211, U S A http://www.cup.org10 Stamford Road, Oakleigh, Melbourne 3166, AustraliaR u i z de Alarcn 13, 28014 M a d r i d , SpainIntergovenmiental Panel on Climate Change 2000This book is in copyright. Subject to statutory exceptionand to the provisions of relevant collective licensing agreements,no reproduction of any part may take place withoutthe written permission of Cambridge University Press.First published 2000Printed in the United States of AmericaA c a t a l o g r e c o r d f o r t h i s b o o k i s a v a i l a b l e f r o m t h e B r i t i s h L i b r a r yL i b r a r y of C o n g r e s s C a t a l o g i n g - i n - P u b l i c a t i o n D a t a a v a i l a b l eI S B N 0 521 80081 1 hardbackI S B N 0 521 80493 0 paperback
http://www.cup.cam.ac.uk/http://www.cup.org/http://www.cup.org/http://www.cup.cam.ac.uk/


5/607

Special Report on Emissions ScenariosCoordinating Lead Author: Nebojsa Nakicenovic (Austria)Lead Authors: Joseph Alcamo (Germany), Gerald Davis (United Kingdom), Bert de Vries (The Netherlands),^ Joergen Fenhann(Denmark), Stuart Gaff in (United States), Kenneth Gregory (United Kingdom), A m u l f Griibler ( I I A S A ) , Tae Y o n g Jung(Republic of Korea), Tom Kram (The Netherlands), E m i l i o Lebre La Rovere (Brazil), Laurie Michaelis (United Kingdom),Shunsuke M o r i (Japan),' Tsuneyuki Morita (Japan), W i l l i a m Pepper (United States),' Hugh Pitcher (United States),' L y n n Price(United States), Keywan R i a h i ( I I A S A ) , ' Alexander Roehrl ( I I A S A ) , ' Hans-Holger Rogner ( I A E A ) , A l e x e i Sankovski (UnitedStates),' Michael Schlesinger (United States), Priyadarshi Shukla (India), Steven Smith (United States), Robert Swart (TheNetherlands), Sascha van Rooijen (The Netherlands), Nadejda V i c t o r (United States), Zhou Dadi (China)Contributing Authors: Dennis Anderson (United Kingdom), Johannes B o l l e n (The Netherlands),' Lex Bouwman (TheNetherlands), Ogunlade Davidson ( I P C C ) , Jae Edmonds (United States), Christopher Elvidge (United States), M i c h e l den Elzen(The Netherlands),' Heiuyk Gaj (Poland), E r i k Haites (Canada), W i l l i a m Hare (The Netherlands), Marco Janssen (TheNetherlands),' Kejun Jiang (China),' Anne Johnson (United States), E r i c Kreileman (The Netherlands),' Mathew Luhanga(United Republic of Tanzania), Nicolette Manson (United States), Toshihiko Masui (Japan),' A l a n McDonald ( I I A S A ) , DouglasM c K a y (United Kingdom), Bert Metz ( I P C C ) , Leena Srivastava (India), Cees Volkers (The Netherlands), Robert Watson ( I P C C ) ,John Weyant (United States), Ernst Worrell (United States), Xiaoshi X i n g (United States)Review Editors: Eduardo Calvo (Peru), Michael Chadwick (United Kingdom), Y u k i o Ishiumi (Japan), Jyoti Parikh (India)Report Editors: Nebojsa Nakicenovic (Austria) and Robert Swart (The Netherlands)Acknowledgements: Thomas Bttner (United Nations), Renate Christ ( I P C C ) , Ewa Delpos ( I I A S A ) , Angela Dowds ( I I A S A ) ,Gnther Fischer ( I I A S A ) , Anne Goujon ( I I A S A ) , Andrei Gritsevskii ( I I A S A ) , Niklas Hohne ( U N F C C C ) , Fortunat Joos(University of Bern), Frank Kasper (University of Kassel), Kathy Kienleitner ( I I A S A ) , Ger Klaassen ( I I A S A ) , Katalin Kuszko( I I A S A ) , Matt L l o y d (Cambridge University Press), Yuzuru Matsuoka (Kyoto University), Mack McFarland (DuPont), A n i t aMeier (IPCC-WGIII Technical Support U n i t / R I V M ) , Martin Middelburg (Report Layout, R I V M ) , Roberta M i l l e r (CIESIN),Janina Onigkeit (University of Kassel), John Ormiston (Copy Editor), Jiahua Pan ( I P C C - W G I I I Technical Support U n i t / R I V M ) ,Joyce Penner (University of Michigan), Michael Prather (University of California), Paul Reuter (University of Kassel) , SusanR i l e y ( I I A S A ) , Cynthia Rosenzweig (Goddard Institute for Space Studies), Stephen Schneider (Stanford University), LeoSchrattenholzer ( I I A S A ) , Dennis Tirpak ( U N F C C C ) , David V i c t o r (US Council on Foreign Relations), Patricia Wagner ( I I A S A )

' Members of the ModelingTeamsAffiliations indicate country of residency or an intemational organization and not necessarily citizenship.


6/607

ContentsF o r e w o r d

P r e f a c e

S u m m a r y for P o l i c y m a k e r s 1T e c h n i c a l S um m a r y 21

1. Background and Overview 592 . An Overview of the Scenario Literature 773 . Scenario Dr i v i ng Forces 4. An Overview of Scenarios 1675. Emission Scenarios 2396. Summary Discussions and Recommendations 293

AppendicesI: S R E S Terms of Reference 323I I: S R E S Writing Team and S R E S reviewers 325III: Definition of S R E S W o r ld Regions 331I V : Six Modeling Approaches 335V : Database Description 347V I : Open Process 353V I I : Statistical Tables 379VIII : Acronyms and Abbreviations -581I X : Chemical Symbols 585X : Units 587X I : Glossary of Terms 589X I I : L is t of Major I P C C Reports 597


7/607

ForewordTh e Intergovernmental Panel on CHmate Change ( I P C C ) wasjointly established by the W o r l d Meteorological Organization( W M O ) and the United Nations Environment Programme( U N E P ) to assess the scientific, technical and socio-economicinformation relevant for the understanding of the risk ofhuman-induced climate change. Since its inception the I P C Chas produced a series of comprehensive Assessment Reports onthe state of understanding of causes of climate change, itspotential impacts and options for response strategies. Itprepared also Special Reports, Technical Papers,methodologies and guidelines. These I P C C publications havebecome standard works of reference, widely used bypolicymakers, scientists and other experts.In 1992 the I P C C released emission scenarios to be used fordriving global circulation models to develop climate changescenarios. The so-called IS92 scenarios were pathbreaking.They were the first global scenarios to provide estimates for thefu l l suite of greenhouse gases. M u c h has changed since then inour understanding of possible future greenhouse gas emissionsand climate change. Therefore the I P C C decided in 1996 todevelop a new set of emissions .scenarios which w i l l provideinput to the I P C C third assessment report but can be of broaderuse than the IS92 scenarios. The new scenarios provide alsoinput for evaluating climatic and environmental consequencesof future greenhouse gas emissions and for assessingalternative mitigation and adaptation strategies. They includeimproved emission baselines and latest information oneconomic restructuring throughout the world, examinedifferent rates and trends in technological change and expandthe range of different economic-development pathways,including narrowing of the income gap between developed anddeveloping countries. To achieve this a new approach wasadopted to take into account a wide range of scientificperspectives, and interactions between regions and sectors.Thiough the so-called "open process" input and feedback from

G . O . P . ObasiSecretary-GeneralW o r l d Meteorological Organization

a community of experts much broader than the writing teamwere solicited. The results of this work show that differentsocial, economic and technological developments have a strongimpact on emission trends, without assuming explicit climatepolicy interventions. The new scenarios provide also importantinsights about the interlinkages between environmental qualityand development choices and w i l l certainly be a useful tool forexperts and decision makers.A s usual in the I P C C , success in producing this report hasdepended first and foremost on the co-operation of scientistsand other experts worldwide. In the case of this report theactive contribution of a broad expert community to the openprocess was an important element of the success. Theseindividuals have devoted enormous time and effort toproducing this report and we are extremely grateful for theircommitment to the I P C C process. We would l i k e to highlightin particular the enthusiasm and tireless efforts of the coordinating lead author for this report Nebojsa Nakicenovic andhis team at the International Institute for A p p l i e d SystemsAnalysis ( I I A S A ) in Laxenburg/Austria who ensured the highquality of this report.Further we would l ike to express our sincere thanks to:

Robert T. Watson, the Chairman of the I P C C , The Co-chairs of Working Group III Bert Metz andOgunlade Davidson,T he members of the writing team.Th e staff of the Working Group III Technical SupportU n i t , including Rob Swart, Jiahua Pan, Tom K r a m , andA n i t a Meier,N . Sundararaman, the Secretary of the I P C C , RenateChrist Deputy Secretary of the I P C C and the staff of theI P C C Secretariat Rudie Bourgeois, Chantai Ettori andAnnie Courtin.

K . TopferExecutive DirectorUnited Nations Environment ProgrammeandDirector-GeneralUnited Nations Office in Nairobi


8/607

PrefaceThe Intergovernmental Panel on Climate Change ( I P C C ) wasestablished jointly by the W o r l d Meteorological Organisation( W M O ) and the United Nations Environment Programme( U N E P ) to assess periodically the science, impacts, and socioeconomics of climate change and of adaptation and mitigationoptions. The I P C C provides, on request, scientific andtechnical advice to the Conference of the Parties to the UnitedNations Framework Convention on Climate Change( U N F C C C ) and its bodies. In response to a 1994 evaluation ofthe earlier I P C C IS92 emissions scenarios, the 1996 Plenaiy ofthe I P C C requested this Special Report on Emissions Scenarios( S R E S ) (see Appendix I for the Teims of Reference). Thisreport was accepted by the Working Group III (WGIII) plenarysession in March 2000. The long-term nature and imcertaintyof climate change and its driving forces require scenarios thatextend to the end of the 21st century. This report describes thenew scenarios and how they were developed.The S R E S scenarios cover a wide range of the main drivingforces of future emissions, from demographic to technologicaland economic developments. As required by the Terms ofReference, none of the scenarios in the set includes any futurepolicies that explicitly address climate change, although allscenarios necessarily encompass various policies of othertypes. The set of S R E S emissions scenarios is based on anextensive assessment of the literature, six alternative modellingapproaches, and an "open process" that solicited wideparticipation and feedback from many groups and individuals.The S R E S scenarios include the range of emissions of allrelevant species of greenhouse gases ( G H G s ) and sulfur andtheir driving forces.The S R E S writing team included more than 50 members from18 countries who represent a broad range of scientificdisciplines, regional backgrounds, and non-governmentalorganizations (see Appendix II). The team, led by NebojsaNakicenovic of the International Institute for A p p l i e d SystemsAnalysis ( I I A S A ) in Austria, included representatives of sixscenario modeling groups and lead authors from all threeearUer I P C C scenario activities - the 1990 and 1992 scenariosand the 1994 scenario evaluation. The S R E S preparationincluded six major steps;

analysis of existing scenarios in the literature; analysis of major scenario characteristics, drivingforces, and their relationships; fonnulation of four narrative scenario "storylines" todescribe alternative futures; quantification of each storyline using a variety ofmodelling approaches; an "open" review process of the resultant emissionscenarios and their assumptions; and three revisions of the scenarios and the reportsubsequent to the open review process, i.e., the formalI P C C Expert Review and the final combined I P C CExpert and Government Review.

A s required by the Terms of Reference, the S R E S preparationprocess was open with no single "of f ic ia l " model and noexclusive "expert teams." To this end, in 1997 the I P C Cadvertised in relevant scientific journals and other publicationsto solicit wide participation in the process. A web sitedocumenting the S R E S process and intermediate results wascreated to facilitate outside input. Members of the writing teamalso published much of their background research in the peer-reviewed literature and on web sites.In June 1998, the I P C C Bureau agreed to make theunapproved, preliminary scenarios available to climatemodelers, who could use the scenarios as a basis for theassessment of climatic changes in time for consideration in theI P C C ' s T h i r d Assessment Report. We recommend that the newscenarios be used not only in the I P C C ' s future assessments ofclimate change, its impacts, and adaptation and mitigationoptions, but also as the basis for analyses by the wider researchand policy community of climate change and otherenvironmental problems.

Ogunlade Davidson and Bert MetzCo-chairs of I P C C WGIII


9/607


10/607

C O N T E N T S

W h y n ew I n t e r g o v e r n m e n t a l P a n e l o n C l i m a t e C h an ge s ce na ri os ? 3W h a t a r e s c e n a ri o s a n d w h a t i s t h e ir p u r p o s e? 3W h a t a r e t h e m a i n c h a r a c te r is t ic s o f t h e n e w s ce n a r io s ? 3W h a t a r e th e m a i n d r i v i n g f o r ce s o f t h e G H G e m i s si o n s i n t h e s c e n a ri o s ? 5W h a t i s t h e r a ng e o f G H G e m i ss io n s i n t h e S R E S s cen ar ios an d h ow do th ey r e la te to d r i v i n g f or ces ? 9H o w can th e S R E S s cen ar ios be u s ed? 11W h a t f u t u r e wor k on em is s ion s s cen ar ios wou ld be u s e f u l? 11


11/607

S u m m a r y f o r P o l i c y m a k e r s 3

W h y new I n t e r g o v e r n m e n t a l P a n e l on C l i m a t e C h an gescena r io s?T h e I n t e r g o v e r m n e n t a l P a n e l o n C l i m a t e C h a n g e ( I P C C )d e v e l o p e d l o n g - t e r m e m i s s i o n s c e n a r i o s i n 1 9 9 0 a n d 1 9 9 2 .These scenaiios have been widely used in the analysis ofpossible climate change, its impacts, and options to mitigateclimate change. In 1995, the I P C C 1992 scenarios wereevaluated. The evaluation recommended that significantchanges (since 1992) in the understanding of driving forces ofemissions and methodologies should be addressed. Thesechanges in understanding relate to, e.g., the carbon intensity ofenergy supply, the income gap between developed anddeveloping countries, and to sulfur emissions. This led to adecision by the I P C C Plenary in 1996 to develop a new set ofscenarios. The new set of scenarios is presented in this report.

W h a t a r e s cen ar ios and w h a t is t h e i r p urp o se?F u t u r e g r e e n h o u s e gas ( G H G ) e m is s i o n s a r e t l i e p r o d u c t ofv e r y c o m p l e x d y n a m i c s y s tems , d e t e r m i n e d by d r i v i n g f o r c e ss u c h as d e m o g r a p h i c d e v e l o p m en t , s o c i o - e c o n o m i cd ev e l o pm e n t, a n d t e c h n o l o g i c a l c h a n g e . Their future evolutionis highly uncertain. Scenarios are alternative images of how thefuture might unfold and are an appropriate tool with which toanalyze how driving forces may influence future emissionoutcomes and to assess the associated uncertainties. They assisti n climate change analysis, including climate modeling and theassessment of impacts, adaptation, and mitigation. Thepossibility that any single emissions path w i l l occur asdescribed in scenarios is highly uncertain.

W h a t a r e the m a i n c h a r a c t e r i s t i c s of the new scena r io s?A set of s c e n a r i o s was d e v e l o p e d t o r e p r e s e n t t h e r a n g e ofd r i v i n g f o r c e s a n d e m is s i o ns i n t h e s c e n a r i o l i t e r a t u r e so as t or e f l e c t c u r r e n t u n d e r s t a n d i n g a n d k n o w l e d g e a b o u t u n d e r l y i n gu n c e r t a i n t i e s . They exclude only outlying "surprise" or"disaster" scenarios in the literature. Any scenario necessarilyincludes subjective elements and is open to various . Preferences for the scenaiios presented herevary among users. No judgment is offered in this report as tothe preference for any of the scenarios and they are notassigned probabilities of occurrence, neither must they beinteipreted as policy recommendations.T h e s c e n a r i o s a r e b a s ed o n a n e x t e n s iv e assessment o f d r i v i n g

f o r c e s a n d e m is si o n s i n t h e s c e n a r i o l i t e r a t u r e , a l t e r n a t i v em o d e l i n g a p p r o a c h e s , a n d a n " o pe n p ro ce s s " ' t h a t s o l i c i t e d' The open process defined in the Special Report on EmissionsScenarios (SRES) Terms of Reference calls for the use of multiplemodels, seeking inputs from a wide community as well as makingscenario results widely available for comments and review. Theseobjectives were fulfilled by the SRES multi-model approach and theopen SRES website.

w i d e p a r t i c i p a t i o n a n d f e e d b a c k . These are all-importantelements of the Terms of Reference (see Appendix I).F o u r d i f f e r e n t n a r r a t i v e s t o r y l i n e s w e r e d e v e l o p e d t o d e s c r i b ec o n s i s t e n t l y t h e r e l a t i o n s h i p s b e tw e e n e m i s s i o n d r i v i n g f o r c e sa n d t h e i r e v o l u t i o n a n d a d d c o n t e x t f o r t h e s c e n a r i oq u a n t i f i c a t i o n . Each storyline represents differentdemographic, social, economic, technological, andenvironmental developments, which may be viewed positivelyb y some people and negatively by others.T h e s c e n a r i o s c o v e r a w i d e r a n g e of t h e m a i n d e m o g r a p h i c ,e c o n o m i c , a n d t e c h n o l o g i c a l d r i v i n g f o r c e s o f G H G a n d su lf ure m i s s i o n s ^ a n d a r e r e p r e s e n t a t i v e of t he l i t e r a t u r e . Eachscenario represents a specific quantitative interpretation of oneo f four storylines. A l l the scenarios based on the same storylineconstitute a scenario "family".A s r e q u i r e d by t h e T e r m s of R e f e re n c e , t h e s c e n a r i o s i n t h i sr e p o r t do n o t i n c l u d e a d d i t i o n a l c l i m a t e i n i t i a t i v e s , w h i c hm e a n s t h a t no s c e n a r i o s a r e i n c l u d e d t h a t e x p l i c i t l y a s s u m ei m p l e m e n t a t i o n of t h e U n i t e d N a t i o n s F r a m e w o r k C o n v e n t i o n

f o r C l i m a t e C h a n g e ( U N F C C C ) o r t h e e m is s i o n s t a r g e t s of t h eK y o t o P r o t o c o l . However, G H G emissions are directly affectedb y non-climate change policies designed for a wide range ofother purposes. Fuzthermore government policies can, tovarying degrees, influence the G H G emission drivers such asdemographic change, social and economic development,technological change, resource use, and pol lutionmanagement. This influence is broadly reflected in thestorylines and resultant scenarios.F o r e a c h s t o r y l i n e s e v e r a l d if f e r e n t s c e n a r i o s w e r e d e v e l o p e du s i n g d if f e r e n t m o d e l i n g a p p r o a c h e s t o e x a m i n e t h e r a n g e ofo u t c o m es a r i s i n g f r o m a r a n g e of m o d e l s t h a t use s i m i l a ra s s um p ti o n s a b o u t d r i v i n g f o r c e s . Six models were used whichare representative of integrated assessment frameworks in theliterature. One advantage of a multi-model approach is that theresultant 40 S R E S scenarios together encompass the cuiTentrange of uncertainties of future GHG emissions arising fromdifferent characteristics of these models, in addition to thecurrent knowledge of and uncertainties that arise from scenariodriving forces such as demographic, social and economic, andbroad technological developments that drive the models, asdescribed in the storylines. Thirteen of these 40 scenariosexplore variations in energy technology assumptions.

^ Included are anthropogenic emissions of carbon dioxide (COj),methane (CH^), nitrous oxide (NjO), hydrofluorocarbons (HFCs),perfluorocarbons (PFCs), sulfur hexafluoride (SF ), hydrochloro-fluorocaibons(HCFCs), chlorofluorocarbons (CFCs), the aerosolprecursor and the chemically active gases sulfur dioxide (SO ),carbon monoxide (CO), niogen oxides (N0,,), and non-methanevolatile organic compounds ( N M V O C s ) . Emissions are providedaggregated into four world i-egions and global totals. In the newscenarios no feedback effect of future climate change on emissionsfrom biosphere and energy has been assumed.


12/607

4 S u m m a r y f o r P o l i c y m a k

B o x SPM-1: The Main Characteristics of the Four S R E S Storylines and Scenario Families.

A lStoryline

i Illustrativ~|Scenario IllustrativeScenario

S c e n a r i o G r o u p s

IllustrativeMarkerScenarioIllustrativeMarkerScenario

IllustratKeMarkerScenarioIllustrativeMarkerScenario

IOS I I HS I I OS I IHS I I OS I I HS I I OS I IHS I I OS I I HS I I OS I I HS I1 5 1 2 2 6 4 2 2 7 4 4

N u m b e r of S c e n a r i o sFigure SPM-1: Schematic illustration of SRES scenarios. Four qualitative storylines yield four sets of scenarios called"families": Al , A2, Bl , and B2. Altogether 40 SRES scenarios have been developed by six modeling teams. Al l are equallyvalid with no assigned probabilities of occurrence. The set of scenarios consists of six scenario groups drawn from the fourfamilies: one group each in A2, Bl , B2, and three groups within the Al family, characterizing alternative developments ofenergy technologies: Al FI (fossil fuel intensive), Al B (balanced), and AIT (predomnantly non-fossil fuel). Within eachfamy and group of scenarios, some share "harmonized" assumptions on global population, gross world product, and finalenergy. These are marked as "HS" for harmonized scenarios. "OS" denotes scenarios that explore uncertainties in drivingforces beyond those of the harmonized scenarios. The number of scenarios developed within each category is shown. Foreachof the six scenario groups an illustrative scenario (which is always harmonized) is provided. Four illustrative markerscenarios, one for each scenario family, were used in draft form in the 1998 SRES open process and are included in revisedform in this report. Two additional illustrative scenarios for the groups Al FI and AI T are also provided and complete a setof six that illustrate all scenario groups. Al l are equally sound.

By 2100 the world will have changed in ways that aredifficult to imagine - asdifficult as it would have been at the end of t19th century to imagine the changes of the 100 years since. Each storyline assumes a distinctly different direction for futudevelopments, suchthat the four storylines differ in increasingly irreversible ways. Together they describe divergent futures thencompass a significant portion of the underlying uncertainties in the main driving forces. They cover a wde range of k"future" characteristics such as demographic change, economic development, and technological change. For this reason, thplausibility or feasibility should not be considered solely on the basis of an extrapolation of c u r r e n t economic, technologicand social trends.

The Al storyline and scenario family describes a future world of very rapid economic growth, global population thpeaks in md-century and declines thereafter, and the rapid introduction of newand more efficient technologies. Majunderlying themes are convergence among regions, capacity building, and increased cultural and social interactions, wa substantial reduction in regional differences in per capita income. The Al scenario family develops into three grouthat describe alternative directions of technological change in the energy system. The three Al groups are distinguishby their technological emphasis: fossil intensive (AlFI), non-fossil energy sources (AIT), or a balance across all sourc(A1B)3.

^ Balanced is defined as not relying too heavily on one particular energy source, on the assumptionthat simlar improvement rates applyto all energy supply and end use technologies.


13/607

S u m m ar y f o r P o l i c y m a k e r s 5

The A2 storylme and scenario family describes a very heterogeneous world. The underlying theme is self-reliance andpreservation of l oc a l identities. Fertility patterns across regions converge very slowly, which results in continuouslyincreasing global population. Economic development is primarily regionally oriented and per capita economic growthand technological change are more fragmented and slower than in other storylines.

The B l storyline and scenario family describes a convergent world with the same global population that peaks in mid-century and declines thereafter, as in the A l storyline, but with rapid changes in economic structures toward a serviceand information economy, with reductions in material intensity, and the mtroduction of clean and resource-efficienttechnologies. The emphasis is on global solutions to economic, social, and envh-onmental sustainability, includmgimproved equity, but without additional clknate initiatives.

The B2 storyline and scenario family describes a world in which the emphasis is on loca l solutions to economic, social,and environmental sustainability. It is a world with continuously increasing global population at a rate lower than A 2 ,intermediate levels of economic development, and less rapid and more diverse technological change than in the 1 andA l storylines. While the scenario is also oriented toward environmental protection and social equity, it focuses on loca land regional levels.

W i t h i n e a c h s c e n a r i o f a m i l y t w o m a i n t y p e s of s c e n a r i o s w e r ed e v e l o p e d - t h o se w i t h h a r m o n i z e d a s s u m p t i o ns a b o u t g l o b a lp o p u l a t i o n , e c o n o m i c g r o w t h , a n d f i n a l e n e r g y use a n d th o s ew i t h a l t e r n a t i v e q u a n t i f i c a t i o n of t h e s t o r y l i n e . Together, 26scenarios were harmonized by adopting common assumptionso n global population and gross domestic product (GDP)development. Thus, the harmonized scenarios in each familyare not independent of each other. The remaining 14 scenariosadopted alternative interpretations of the four scenariostorylines to explore additional scenario uncertainties beyonddifferences in mthodologie approaches. They are also relatedto each other within each family, even though they do not sharecommon assumptions about some of the driving forces.T h e r e a r e six s c e n a r i o g r o u p s t h a t s h o u l d be c o n s i d e r e de q u a l l y s o u n d t h a t s p an a w i d e r a n g e of u n c e r t a i n t y , asr e q u i r e d by the T e r m s of R e f e r e n c e . These encompass fourcombinations of demographic change, social and economicdevelopment, and broad technological developments,corresponding to the four families ( A l , A 2 , B l , B2) , each withan illustrative "marker" scenario. Two of the scenario groups ofthe A l family ( A l F I , AIT) explicitly explore alternativeenergy technology developments, holding the other drivingforces constant, each with an illustrative scenario. Rapidgrowth leads to high capital turnover rates, which means thatearly small differences among scenarios can lead to a largedivergence by 2100. Therefore the A l family, which has thehighest rates of technological change and economicdevelopment, was selected to show this effect.

I n a c c o r d a n c e w i t h a d e c i s i o n of t h e I P C C B u r e a u i n 1 9 9 8 t or e l e a s e d ra ft s c e n a r i o s t o c l i m a t e m o d e l e r s f o r t h e i r i n p u t i nt h e T h i r d Assessment R e p o r t , a n d su b s e q u e n tl y t o s o l i c i tc o m m e n t s d u r i n g t h e o p e n p ro c e ss , one m a r k e r s c e n a r i o wasc h o s e n f r o m e a c h o f f o u r of t h e s c e n a r i o g r o u p s b as e d o n t h es t o r y l i n e s . The choice of the markers was based on which ofthe in i t ia l quantifications best reflected the storyline, andfeatures of specific models. Marker scenarios are no more orless l i k e l y than any other scenarios, but are considered by theS R E S writing team as illustrative of a particular storyline.These scenarios have received the closest scrutiny of the entirewriting team and via the S R E S open process. Scenarios have

also been selected to illustrate the other two scenario groups.Hence, this report has an illustrative scenario for each of the sixscenario groups.

W h a t a r e the m a i n d r i v i n g f or ces of the G H G e m i s s i o n s i nth e s cen ar ios ?T h i s R e p o r t r e i n f o r c e s o u r u n d e r s t a n d i n g t h a t t h e m a i nd r i v i n g f o r c e s of f u t u r e g r e e n h o u se gas t r a j e c t o r i e s w i l lc o n t i n u e t o be d e m o g r a p h i c c h a n g e , s o c i a l a n d e c o n o m i cd e v e l o p m e n t , a n d t h e r a t e a n d d i r e c t i o n of t e c h n o l o g i c a lc h a n g e . This finding is consistent with the I P C C 1990, 1992and 1995 scenario reports. Table S P M - 1 (see later) summarizesthe demographic, social, and economic driving forces acrossthe scenarios in 2020, 2050, and 2100". The intermediateenergy result (shown in table S P M 2, see later) and land useresults^ reflect the influences of driving forces.R e c e n t g l o b a l p o p u l a t i o n p r o j e c t i o n s a r e g e n e r a l l y l o w e r t h a nt h o s e i n t h e I S 9 2 s c e n a r i o s . Three different populationtrajectories that coixespond to socio-economic developments inthe storylines were chosen from recently published projections.The A l and B l scenario families are based on the lowIntemational Institute for A p p l i e d Systems Analysis ( I I A S A )1996 projection. They share the lowest trajectory, increasing to8.7 b i l l i o n by 2050 and declining toward 7 b i l l i o n by 2100,which combines low fertility with low mortality. The B2scenario family is based on the long-term U N Medium 1998population projection of 10.4 b i l l i o n by 2100. The A 2 scenariofamily is based on a high population growth scenario of 15b i l l i o n by 2100 that assumes a significant decline in fertility formost regions and stabilization at above replacement levels. Itfalls below the long-term 1998 UN H i g h projection of 18b i l l i o n .

Technological change is not quantified in table S P M - 1 .5 Because of the impossibilityof including the complex way land useis changing between the various land use types, this information is notin the table.


14/607

6 S u m m a r y f o r P o l i c y m a k e

-3.5 i i I ! ! I > ! I I I 1 L^-l f ^ ^ i I I I1900 1950 2000 2025 2050 2100Figure S P M - 2 : G l o b a l C O j emissions related to energy and industry (Figure SFM-2a) and land-use changes (Figure SPM-2bfrom 1900 to 1990, and for the 40 S R E S scenarios from 1990 to 2100, shown as an index (1990 = 1). The dashed time-pathsdepict individual S R E S scenarios and the area shaded in blue the range of scenarios from the literature as documented in theS R E S database. The scenarios are classified into six scenario groups drawn from the four scenario families. Six illustrativescenarios are highlighted. The colored vertical bars indicate the range of emissions in 2100. The four black bars on the right oFigure S P M - l a indicate the emission ranges in 2100 for the IS92 scenarios and three ranges of scenarios from the literature,documented in the S R E S database. These three ranges indicate those scenarios that include some additional climate initiative(designated as "intervention" scenarios), those that do not ("non-intervention"), and those that cannot be assigned to eithercategory ("non-classified"). This classification is based on a subjective evaluation of the scenarios in the database and waspossible only for energy and industry emissions. S A R , Second Assessment Report.


15/607

S u m m a r y f o r P o l i c y m a k e r s 7

0' ' 1 ' ' 1 1 f 1 1 1 Ql 1 I ^ I I I I I I1990 2010 2030 2050 2070 2090 1990 2010 2030 2050 2070 2090Figure S P M - 3 : Total global annual CO^ emissions from al l sources (energy, industry, and land-use change) from 1990 to 2100(in gigatonnes of carbon (GtC/yr) for the families and six scenario groups. The 40 S R E S scenarios are presented by the fourfamilies ( A l , A 2 , B l , and B2) and six scenario groups: the fossil-intensive A l F I (comprising the high-coal and high-oil-and-gasscenarios), the predominantly non-fossil fuel A I T , the balanced A l B in Figure S P M - 3 a ; A2 in Figure S P M - 3 b ; B l in FigureS P M - 3 c , and B2 in Figure S P M - 3 d . Each colored emission band shows the range of harmonized and non-haiTnonized scenarioswithin each group. For each of the six scenario groups an illustrative scenario is provided, including the four illustrative markerscenarios ( A l , A 2 , 1 , B2, solid lines) and two illustrative scenarios for A l F I and AI T (dashed lines).

A l l s c e n a r i o s d e s c r i b e f u t u r e s t h a t a r e g e n e r a l l y m o r e a f f l u e n tt h a n t o d a y . The scenarios span a wide range of future levels ofeconomic activity, with gross world product rising to 10 timestoday's values by 2100 in the lowest to 26-fold in the highestscenarios.

A n a r r o w i n g of i n c o m e d i ff er e n ce s a t? io n g w o r l d r e g i o n s i sa s s u m e d i n m a n y of t h e SRES s c e n a r i o s . Two of the scenariofamilies, A l and B l , explicitly explore alternative pathwaysthat gradually close existing income gaps in relative terms.T e c h n o l o g y is at l e a s t as i m p o r t a n t a d r i v i n g f o r c e asd e m o g r a p h i c c h a n g e a n d e c o n o m i c d e ve lo p m e n t . Thesedriving forces are related. With in the A l scenario family,scenarios with common demographic and socio-economicdriving forces but different assumptions about technology andresource dynamics illustrate the possibility of very divergentpaths for developments in the energy system and land-usepatterns.T h e S R E S s c e n a r i o s c o v e r a w i d e r r a n g e of e ne rg y s t r u c t u r e st h a n t h e 1S92 s c e n a r i o s . This reflects uncertainties about futurefossi l resources and technological change. The scenarios covervirtually all the possible directions of change, from high sharesof fossil fuels, o il and gas or coal, to high shares of non-fossils.

I n m o s t s c e n a r i o s , g l o b a l f o r e s t a r e a c o n t i n u e s t o d e c r e a s e f o rs o m e d e c a d e s , p r i m a r i l y b e c a u s e of i n c r e a s i n g p o p u l a t i o n a n di n c o m e g r o w t h . T h i s c u r r e n t t r e n d i s e v e n t u a l l y r e v e r s e d i n m o s ts c e n a r i o s w i t h t h e g r e a t e s t e v e n t u a l i n c r e a s e i n f o r e s t a r e a by2 1 0 0 i n t h e B l a n d B2 s c e n a r i o f a m i l i e s , as c o m p a r e d t o 1 9 9 0 .Associated changes in agricultural land use are driven principallyby changing food demands caused by demographic and dietaryshifts. Numerous other social, economic, institutional, andtechnological factors also affect the relative shares of agriculturallands, forests, and other types of land use. Different analyticmethods lead to very different results, indicating that future landuse change in the scenarios is very model specific.A l l t h e a b o v e d r i v i n g f o r c e s n o t o n l y i n f l u e n c e CO2 e m i s s i o n s ,b u t a l s o t h e e m i s s i o n s of o t h e r G H G s . The relationshipsbetween the driving forces and non-CO^ GHG emissions aregenerally more complex and less studied, and the models usedfor the scenarios less sophisticated. Hence, the uncertainties inthe S R E S emissions for non-CO^ greenhouse gases aregenerally greater than those for energy CO^^.

* Therefore, the ranges of non-CO^ G H G emissions provided in theReport may not fully reflect the level of uncertainty compared to CO^ ,for example only a single model provided the sole value forhalocarbon emissions.


16/607

8 S u m m a r y f o r P o U c y m a k e .

b Scenarios grouped bycumulative emissions Low Medium-Low Medium-High High

Cumulative Emission 1990-2100, GtCFigure S P M - 4 : Total global cumulative COj emissions (GtC) from 1990 to 2100 (SP]V[-4a) and histogram of their distributionb y scenario groups (SPM-4b). No probability of occurrence should be inferred from the distribution of S R E S scenarios or thosei n the literature. Both figures show the ranges of cumulative emissions for the 40 S R E S scenarios. Scenarios are also groupedinto four cumulative emissions categories; low, medium-low, medium-high, and high emissions. Each category contains oneillustrative marker scenario plus alternatives that lead to comparable cumulative emissions, although often through differentdriving forces. This categorization can guide comparisons using either scenarios with different driving forces yet similaremissions, or scenarios with similar driving forces but different emissions. The cumulative emissions of the IS92 scenarios arealso shown.


17/607

S u m m a r y f o r P o l i c y m a k e r s 9W h a t is the r a n g e of G H G e m i s s i o n s i n the S R E S s cen ar iosa n d how do th ey r e l a t e to d r i v i n g f or ces ?T h e S R E S s c e n a r i o s c o v e r m o s t of t h e r a n g e o f c a r b o n d i o x i d e( C O ^ ; see F i g u r e s S P M - 2 a a n d S P M - 2 b ) , o t h e r G H G s , a n ds u l f u r e m i s si o n s f o u n d i n t h e r e c e n t l i t e r a t u r e a n d SR E Ss c e n a r i o d a t a b a s e . Their spread is similar to that of the IS92scenarios for C O ^ emissions from energy and industry as w e l las total emissions but represents a much wider range for land-use change. The six scenario groups cover wide andoverlapping emission ranges. The range of G H G emissions inthe scenarios widens over time to capture the long-termuncertainties reflected in the literature for many of the drivingforces, and after 2050 widens significantly as a result ofdifferent socio-economic developments. Table S P M - 2 bsummarizes the emissions across the scenarios in 2020, 2050,and 2100. Figure S P M - 3 shows in greater detail the ranges oftotal emissions for the six scenario groups of scenariosthat constitute the four families (the three scenario families A 2 ,B l , and B 2 , plus three groups within the A l family A l F I , A I T ,and A l B ) .Some SR E S s c e n a r i o s sh o w t r e n d r e v e r s a l s , t u r n i n g p o i n t s ( i . e . ,i n i t i a l e m i s s i o n i n c r e a s e s f o l l o w e d by d e c r e a s e s ) , a n dc r o s s o v e r s ( i . e . , i n i t i a l l y e m is s i o n s a r e h i g h e r i n one s c e n a r i o ,b u t l a t e r e m i s s i o n s a r e h i g h e r i n a n o t h e r s c e n a r i o ) . Emissiontrend reversals (see Figures SPvl-2 and S P M - 3 ) depart fromhistorical emission increases. In most of these cases, theupward emissions trend due to income growth is more thancompensated by productivity improvements combined with aslowly growing or declining population.I n m a n y SR E S s c e n a r i o s CO2 e m i ss io n s f r o m l os s of f o r e s tc o v e r p e a k a ft e r s e v e r a l d e c a d e s a n d t h e n g r a d u a l l y d e c l i n e ' '( F i g u r e S P M - l b ) . This pattern is consistent with scenarios inthe literature and can be associated with slowing populationgrowth, followed by a decline in some scenarios, increasingagricultural productivity, and increasing scarcity of forest land.These factors allow for a reversal of the current trend of loss offorest cover in many cases. Emissions decline fastest in the 1family. O n ly in the A2 family do net anthropogenic C Ojemissions from land use change^ remain positive through 2100.A s was the case for energy-related emissions, C O 2 emissionsrelated to land-use change in the A l family cover the widestrange. The diversity across these scenarios is amplified throughthe high economic growth, increasing the range of alternatives,and through the different modeling approaches and theirtreatment of technology.T o t a l c u m u l a t i v e SRES c a r b o n e m is si o n s f r o m a l l s o u r ce st h r o u g h 2 1 0 0 r a n g e f r o m a p p r o x i m a t e l y 7 7 0 G t C t oa p p r o x i m a t e l y 2 5 4 0 G t C . According to the I P C C SecondAssessment Report ( S A R ) , "any eventual stabilisedconcentration is governed more by the accumulated

' In the new scenarios no feedback effect of future climate change onemissions from the biosphere has been assumed.

anthropogenic C O j emissions from now until the time ofstabilisation than by the way emissions change over theperiod." Therefore, the scenarios are also grouped in the reportaccording to their cumulative emissions.^ (see Figure S P M - 4 ) .T h e S R E S scenarios extend the IS92 range toward higheremissions ( S R E S maximum of 2538 GtC compared to 2140G t C for IS92), but not toward lower emissions. The lowerbound for both scenario sets is approximately 770 G t C .

T o t a l a n t h r o p o g e n i c m e t h a n e (CH^) a n d n i t r o u s o x i d e (N^O)e m i s s i o n s s p a n a w i d e r a n g e by t h e e n d o f t h e 2 P ' c e n t u r y (seeF i g u r e s S P M - 5 a n d S P M - 6 d e r i v e d f r o m F i g u r e s 5.5 a n d 5 . 7 ) .Emissions of these gases in a number of scenarios begin todecline by 2050. The range of emissions is wider than in theIS92 scenarios due to the multimodel approach, which leads toa better treatment of uncertainties and to a wide range ofdriving forces. These totals include emissions from land use,energy systems, industry, and waste management.M e t h a n e a n d n i t r o u s o x i d e e m i s s i o ns f r o m l a n d use a r e l i m i t e di n A l a n d B l f a m i l i e s by s l o w e r p o p u l a t i o n g r o w t h f o l l o w e d bya d e c l i n e , a n d i n c r e a s e d a g r i c u l t u r a l p r o d u c t i v i t y . After theini t ia l increases, emissions related to land use peak anddecline. In the B2 family, emissions continue to grow, albeitvery slowly. In the A 2 family, both high population growth andless rapid increases in agricultural productivity result in acontinuous rapid growth in those emissions related to land use.T he r a n g e of e m i s s i o n s of H F C s i n the S R E S s c e n a r i o isg e n e r a l l y l o w e r t h a n i n e a r l i e r I P C C s c e n a r i o s . Because of newinsights about the availability of alternatives to H F C s asreplacements for substances controlled by the Montreal Protocol,initially HFC emissions are generally lower than in previousI P C C scenarios. In the A2 and B2 scenario families HFCemissions increase rapidly in the second half of the this century,while in the A 2 and B2 scenario families the growth of emissionsis significantly slowed down or reversed in that period.S u l fu r e m i s s io n s i n t h e S R E S s c e n a r i o s a r e g e n e r a l l y b e l o w t h eI S9 2 r a n g e , b e c au se o f s t r u c t u r a l c h a ng e s i n t h e e n e r gy sys tema s w e l l as c o n c e r n s a b o u t l o c a l a n d r e g i o n a l a i r p o l l u t i o n .These reflect sulfur control legislation in Europe, NorthAmerica, Japan, and (more receny) other parts of A s i a andother developing regions. The timing and impact of thesechanges and controls vary across scenarios and regions^. After

^ In this Report, cumulative emissions are calculated by addingannual net anthropogenic emissions in the scenarios over their timehorizon. When relating these cumulative emissions to atmosphericconcentrations, a l l natural processes that affect carbon concentrationsin the atmosphere have to be taken into account.' Although global emissions of S O ^ for the SRES scenarios are lowerthan the IS92 scenarios, uncertainty about SOj emissions and theireffect on sulfate aerosols has increased compared to the IS92scenarios because of very diverse regional pattems of S O 2 emissionsin the scenarios.


18/607

l u S u m m a r y f o r P o l i c y m a k e r s

0 I I I I I I 1 1 I \ I I1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Figure S P M - 5 : Standardized (to common 1990 and 2000 values) global annual methane emissions for the S R E S scenarios (inM t C H 4 / y r ) . The range of emissions by 2100 for the six scenario groups is indicated to the right. Illustrative (including marker)scenarios are highlighted.

25

Figure S P M - 6 : Standardized (to common 1990 and 2000 values) global annual nitrous oxides emissions for the S R E Sscenarios (in M t N / y r ) . The range of emissions by 2100 for the six scenario groups is indicated to the right. Illustrative (marker)scenarios are highlighted.


19/607

S u m m ar y f o r P o l i c y m a k e r s 1 1init ial increases over the next two to three decades, globalsulfur emissions in the S R E S scenarios decrease (see TableS P M - l b ) , consistent with the findings of the 1995 I P C Cscenario evaluation and recent peer-reviewed literature.S i m i l a r f u t u r e G H G e m is s i o n s c a n r e s u l t f r o m v e r y d if f e re n ts o c i o - e c o n o m i c d e v el o p m e n t s , a n d s i m i l a r d ev e l o p m e n t s ofd r i v i n g f o r c e s c a n r e s u l t i n d i ff e re n t f u t u r e e m i s si o ns .Uncertainties in the future developments of key emissiondriving forces create large uncertainties in future emissions,even within the same socio-economic development paths.Therefore, emissions from each scenario family overlapsubstantially with emissions from other scenario families. Theoverlap implies that a given level of future emissions can arisefrom very different combinations of driving forces. FiguresS P M - 1 , S P M - 2 , and S P M - 3 show this for C O , .C o n v e r g e n c e o f r e g i o n a l per c a p i t a i n co m es c a n l e a d t o e i t h e rh i g h o r l o w G H G e m is s i o n s . Tables S P M - l a and S P M - l bindicate that there ai'e scenarios with high per capita incomesin all regions that lead to high C O j emissions (e.g., in the high-growth, fossil fuel intensive scenario group A l F I ) . They alsoindicate that there are scenarios with high per capita incomesthat lead to low emissions (e.g., the A I T scenario group or theB l scenario family). This suggests that in some cases otherdriving forces may have a greater inuence on G H G emissionsthan income growth.

H o w can the S R E S s cen ar ios be u s e d ?I t is r e c o m m e n d e d t h a t a r a n g e of S RES s c e n a r i o s w i t h av a r i e t y o f a ss u m p t i o n s r e g a r d i n g d r i v i n g f o r c e s be u s e d i n anya n a l y s i s . Thus more than one family should be used in mostanalyses. The six scenario groups - the three scenario familiesA 2 , B l , and B 2, plus three groups within the A l scenariofamily, A l B , A l F I , and A I T - and four cumulative emissionscategories were developed as the smallest subsets of S R E Sscenarios that capture the range of uncertainties associatedwith driving forces and emissions.T h e i m p o r t a n t u n c e r t a i n t i e s r a n g i n g f r o m d r i v i n g f o r c e s t oe m i s s i o n s may be d i f f e r e n t i n d if f e re nt a p p l i c a t i o n s - f o re x a m p l e c l i m a t e m o d e l i n g ; assessment of i m p a c t s ,v u l n e r a b i l i t y , m i t i g a t i o n , a n d a d a p t a t i o n o p t i o n s ; a n d p o l i c ya n a l y s i s . CHmate modelers may want to cover the rangereflected by the cumulative emissions categories. To assess therobustness of options in terms of impacts, vulnerability, andadaptation may require scenarios with similar emissions butdifferent socio-economic characteristics, as reflected by the sixscenario groups. For mitigation analysis, variation in bothemissions and socio-economic characteristics may benecessary. For analysis at the national or regional scale, themost appropriate scenarios may be those that best reflectspecific circumstances and perspectives.T h e r e is no s i n g l e m o s t l i k e l y , " c e n t r a l " , o r " b e s t - g u e s s "s c e n a r i o , e i t h e r w i t h re s p e c t t o S RES s c e n a r i o s o r to t he

u n d e r l y i n g s c e n a r i o l i t e r a t u r e . Probabilities or likelihood arenot assigned to individual S R E S scenarios. None of the S R E Sscenarios represents an estimate of a central tendency for alldriving forces or emissions, such as the mean or median, andnone should be interpreted as such. The distribution of thescenarios provides a useful context for understanding therelative position of a scenario but does not represent thelikelihood of its occurrence.T h e d r i v i n g f o r c e s a n d em i s s i o n s o f e a c h S RES s c e n a r i o s h o u l db e u s e d t o g e t h e r . To avoid internal inconsistencies,components of S R E S scenarios should not be mixed. Forexample, the G H G emissions from one scenario and the S O 2emissions from another scenario, or the population from oneand economic development path from another, should not becombined.W h i l e r e c o g n i z i n g t h e i n h e r e n t u n c e r t a i n t i e s i n l o n g - t e r m

p r o j e c t i o n s ^ ' ^ , t h e S RES s c e n a r i o s may p r o v i d e p o l i c y m a k e r sw i t h a l o n g - t e r m c o n t e x t f o r n e a r - t e r m a n a l y s i s . The modelingtools that have been used to develop these scenarios that focuso n the century time scale are less suitable for analysis of nearterm (a decade or less) developments. When analyzingmitigation and adaptation options, the user should be awarethat although no additional climate initiatives are included inthe S R E S scenarios, various changes have been assumed tooccur that would require other interventions, such as thoseleading to reductions in sulfur emissions and significantpenetration of new energy technologies.

W h a t f u t u r e w o r k on em is s ion s s cen ar ios w o u l d be u s e f u l ? Establishment of a program for on-going evaluationsand comparisons of long-term emission scenarios,including a regularly updated scenario database; Capacity building, particularly in developing countries,

i n the area of modeling tools and emissions scenarios; M u l t i p l e storyline, multi-model approaches in futurescenario analyses; New research activities to assess future developments

i n key GH G driving forces in greater regional,subregional, and sectoral detail which allow for aclearer l i n k between emissions scenarios and mitigationoptions; Improved specification and data for, and integration ofthe -2 G H G and non-energy sectors, such as land

use, land-use change and forestry, in models, as w e l l asmodel inter-comparison to improve scenarios andanalyses;

Integration into models emissions of particulate,hydrogen, or nitrate aerosol precursors, and processes,

Confidence in the quantification of any scenario decreasessubstantially as the time horizon increases because the basis forthe assumptions becomes increasingly speculative. This is why aset of scenarios was developed.


20/607

S u m m a r y f o r P o l i c y m a k e r ssuch as feedback o f climate change on emissions, thatmay significantly influence scenario results andanalyses;Development of additional gridded emissions forscenarios which would facilitate improved regionalassessment;Assessment of strategies that would address multiplenational, regional, or global priorities;Development of methods for scientifically soundaggregation of emissions data;More detailed information on assumptions, inputs, andthe results of the 40 S R E S scenarios should be madeavailable at a web site and on a C D - R O M . Regularmaintenance of the S R E S web site is needed;

Extension of the S R E S web site and production of aC D - R O M to provide, if appropriate, time-dependentgeographic distributions of driving forces andemissions, and concentrations of G H G s and sulfateaerosols. Development of a classification scheme for classifyingscenarios as intervention or non-intervention scenarios.


21/607

S u m m a r y f o r P o l i c y m a k e r s 1 3

- S i

s - s- s - s"s i

3 s

I I1 11 ^s ' i

C5-S

i li - c io \

00 u. s ;

I ^

C l ^

C l.' s: Si5

5^ - 5 ;la

tu

V5I

ItaI

3

I

-1

S4

o~ ' 0 0 f


22/607

1 4 S u m m ar y f o r P o l i c y m a k

fe 5

? ^ . S

tu

- i

1.O5>

- i

S - I

^ -1=

I

I

i

S ^

IsUI-sIs-s;

CQ

i-HCQ

< n pq

CNr O C ^ lCNl 0 0 4 - > n -r r ^ON Mr - (

n

tN 4 Di n -OO C N I 4 ^ P O " - V )

-s

, ^ , , , ,

- O N O S ( N i n - O N Ti >n - (N r o oo

1O N 1 1 0 0 i n ^ ^ ^ O N O N ^ ' N -. T t 00

m(N

O N

N OT f

tN - m -

. T fO N 0 0

3 5

- -7 0 0 T l -

^ 0 0 *T t

in O N inO N VTl - ^ T l -u ~ "ON

CN CNCO CO0 \0 0

O NCO O Nd

>< 3g

< N i n


27/607

S u m m a r y f o r P o l i c y m a k e r s 1 9

r ln pa

r H pa

T O N O > i > s o

r < 0 0 O S ! 2 * i< ^ C O fs |

t - - ; O Ni H r i T CO T t T t C ^lC O s o

^ C N , Ô N , H C S C O l >

O N C ^ J T t r i 0 0V ) O S

C O s or ~ ~ C O c e n ^

- O S

C O l > C OC O i N O ^ 0 0 I H

0 0 s ot - ^ O S T T t O N

> e T tC O s oC O V ) s ot ~ - C O

C^ * 0 0 i r iT t 0 0 ^0 0t O N -

O S so

rN |2

^ ^2

^ ^rN |2

C N 2 O S rN |2 (N C O o orN |2 C O C O

11 1 c ^ 1

^ 1 O N - O N C OT 0 0 o o r T 1O S T f ' 4 ^ ^ '0 0I 1 t -

T t O N s o c ; -

i n 1^ C OsoC O

^ ^ s ii n

0 0 25 i n ^ ^ ;5 f:;^- H j ; :^ O S ^ i q

( NCO

C N4 COr a so

s 5$^ ^ g ^^ ^ < ^C O O S

N Osor -co0 0O Sr ar a

os O NC O ^ ) I \S O 0 0i n" - ^ r - -S O 0 0

r a C NO S i nr a C io s l ot - ~ T H

o ^ o oO N ^ C N^ r a ^0 0 so T f00 o ^C U' C i C - - H 0 0o s 4- 1 I n r H

r ar a

e s

' r )o i n i nI IO N t - -i n C Or a r - ^ ^

r a r aC N N O

i nw C i - < sO S r ^ C O

C O i n ^T f m soI 1 10 0 T fC O T f C OC O V ) ^ V ) s o

O Ni no oC O

C N i nC OO N S OO S O SC O

i n Ip -

^

so O S'

O S ^ T f N Oso O S o os s c ts o T H 0 0

s o r i

sosoN O

1

0 0 T f'

T t

N OT f

i n Ô N i nO N ' 7^ O S

C NN O C O C O

O S00

O SC O O SdCO

o ,i

Ii

o osr

3

i n " - 1

'

s ^ i n _ N 8

IDS ^ m _- C N C N r ali(

oos s C NC N

mr az ;

r a i n - Hr ^ i r a )

Z2

Z<

2

> N V s

6

3

00

s

3

. H J

^ "t c i 0 3i s

. a s

(U

>

1N 2

- 3

- gSi

H

i n3E 2

1 .

| |

l i l0 i n

^ a

1 S 3 ^

s ^ i

s I^ * Û ^ .S Z

(3

X I 3

t - r a

< u

1

I1

00

I ^ 3 - ,

2 3

g 8

_ X "

3 1^

1 ^

Si l

2

i l

2 ^

I

C L ,

.SiI tl

it +H

^_ )


29/607

T E C H N I C A L S U M M A R Y


30/607

CONTENTS1. Introduction and Background 23 9.1.1. Carbon Dioxide Emissions and TheirD r i v i n g Forces 362. Emissions Scenarios and Their Purposes 23 9.1.2. Carbon Dioxide Emissions fromEnergy, Industry, and Land Use 363. Review of Past IPCC Emissions Scenarios 24 9.1.3. Scenario Groups and Four Categoriesof Cumulative Emissions 394. SRES Writing Team, Approach, and Process 24 9.2. Other Greenhouse Gases 419.2.1. Methane Emissions 425. Scenario Literature Review and Analysis 25 9.2.2. Nitrous Oxide Emissions 429.2.3. Halocarbons and Halogenated6. Narrative Scenarios and Storylines 27 Compounds 429.3. Sulfur Dioxide Emissions 437. Quantitative Scenarios and 9.4. Other Chemically A c t i v e Gases 44Modeling Approaches 29 9.4.1. Nitrogen Oxides Emissions 44

9.4.2. Volatile Organic Compounds,8. Main Scenario Driving Forces Based Excluding Methane 45on Literature 31 9.4.3. Carbon Monoxide Emissions 458.1. Population Projections 31 9.5. Emissions Overview 458.2. Economic Development 328.3. Structural and Technological Change 33 10. Summary, Conclusions, and Recommendations 459. Greenhouse Gases and Sulfur Emissions 36 References 569.1. Carbon Dioxide Emissions 36


31/607

T e c h n i c a l S u m m a r y 2 31. Introduction and BackgroundThe Intergovernmental Panel on Climate Change ( I P C C )decided at its September 1996 plenary session in M e x i c o C i t yto develop a new set of emissions scenarios (see Appendix I forthe Terms of Reference). This Special Report on EmissionScenarios ( S R E S ) describes the new scenarios and how theywere developed.The S R E S writing team formulated a set of emissionsscenarios. These scenarios cover a wide range of the maindriving forces of future emissions, from demographic totechnological and economic developments. The scenariosencompass different future developments that might influencegreenhouse gas (GHG) sources and sinks, such as alternativestructures of energy systems and land-use changes. As requiredb y the Terms of Reference however, n o n e of the scenarios inthe set includes any future policies that explicitly addressadditional climate change initia tives' , although GH Gemissions are directly affected by non-climate change policiesdesigned for a wide range of other purpose.The set of S R E S emissions scenarios is based on an extensiveassessment of the literature, six alternative modelingapproaches, and an "open process" that solicited wideparticipation and feedback from many groups and individuals.The set of scenarios includes anthropogenic emissions of allrelevant G H G species, sulfur dioxide (SOj), carbon monoxide( C O ) , nitrogen oxides (NO^,), and non-methane volatile organiccompounds ( N M V O C s ) , see Table 1-1 in Chapter 1. It coversmost of the range of G H G emissions compared with thepublished scenario literature. For example, emissions of carbondioxide (COj) in 2100 range from more than 40 to less than 6giga (or b i l l i o n ) tons^ of elemental carbon ( G t C ) , that is, fromalmost a sevenfold increase to roughly the same emissionslevel as in 1990.Future emissions and the evolution of their underlying drivingforces are highly uncertain, as reflected in the very wide rangeo f future emissions paths in the literature that is also capturedb y the S R E S scenarios. The use of scenarios in this reportaddresses the uncertainties related to k n o w n factors.Uncertainties related to u n k n o w n factors can of course never bepersuasively captured by any approach. As the prediction offuture anthropogenic G H G emissions is impossible, alternativeG H G emissions scenarios become a major tool for analyzingpotential long-range developments of the socio-economicsystem and corresponding emission sources.Emissions scenarios are a central component of any assessmento f climate change. G H G and S O 2 emissions are the basic input' For example, no scenarios are included that explicitly assumeimplementation of the emission targets in the U N F C C C and the Kyotoprotocol.^ Metric tons are used throughout this report. Unless otherwisespecified, monetary units are 1990 US dollars (see Chapter 4).

f o r determining future climate patterns with simple climatemodels, as w e l l as with complex general circulation models( G C M s ) . Possible climate change, together with the majordriving forces of future emissions, such as demographicpattems, economic development and environmental conditions,provide the basis for the assessment of vulnerability, possibleadverse impacts and adaptation strategies and policies toclimate change. The major driving forces of future emissionsalso provide the basis for the assessment of possible mitigationstrategies and policies designed to avoid climate change. Thenew set of emissions scenarios is intended for use in futureI P C C assessments and by wider scientific and policymakingcommunities for analyzing the effects of future GH Gemissions and for developing mitigation and adaptationmeasures and policies.

2. Emissions Scenarios and Their PurposesScenarios are images of the future, or alternative futures. Theyare neither predictions nor forecasts. Rather, each scenario isone alternative image of how the future might unfold (seeChapters 1 and 4 for more detail). As such they enhance ourunderstanding of how systems behave, evolve and interact.They are useful tools for scientific assessments, learning aboutcomplex systems behavior and for policymaking and assist inclimate change analysis, including climate modeling and theassessment of impacts, adaptation and mitigation.Future levels of global G H G emissions are a product of verycomplex, ill-understood dynamic systems, driven by forcessuch as population growth, socio-economic development, andtechnological progress among others, thus making long-termpredictions about emissions virtually impossible. However,near-term policies may have profound long-term climateimpacts. Consequently, policy makers need a summary of whati s understood about possible future G H G emissions, and giventhe uncertainties in both emissions models and ourunderstanding of key driving forces, scenarios are anappropriate tool for summarizing both current understandingand current uncertainties.G H G emissions scenarios are usually based on an internallyconsistent and reproducible set of assumptions about the keyrelationships and driving forces of change, which are derivedfrom our understanding of both history and the currentsituation. Often these scenarios are formulated with the help offormal models. Sometimes G H G emissions scenarios are lessquantitative and more descriptive, and in a few cases they donot involve any formal analysis and are expressed in qualitativeterms. The S R E S scenarios involve both qualitative andquantitative components; they have a narrative part called"storylines" and a number of corresponding quantitativescenarios for each storyline. S R E S scenarios can be viewed asa l i n k i n g tool that integrates qualitative narratives or storiesabout the future and quantitative formulations based ondifferent formal modeling approaches. Although no scenariosare value free, the S R E S scenarios are descriptive and are not


32/607

2 4 T e c h n i c a l S u m m a i -intended to be desirable or undesirable in their own right. Theyhave been built as descriptions of plausible alternative futures,rather than preferred developments.However, developing scenarios for a period of one hundredyears is a relatively new field. This is not only because of largescientific uncertainties and data inadequacies. For example,within the 2P'century technological discontinuities should beexpected, and possibly major shifts in societal values and i n thebalance of geopolitical power. The study of past trends oversuch long periods is hampered by the fact that most databasesare incomplete if we go back much further than 50 years. G i v e nthese gaps in our data, methods, and understanding, scenariosare the best way to integrate demographic, economic, societal,and technological knowledge with our understanding ofecological systems to evaluate sources and sinks of GH Gemissions. Scenarios as an integration tool in the assessment ofclimate change allow a role for intuition, analysis, andsynthesis, and thus we turn to scenarios in this report to takeadvantage of those features to aid the assessment of futureclimate change, impacts, vulnerabilities, adaptation, andmitigation. Since the scenarios focus on the century time scale,tools have been used that have been developed for this puipose.These tools are less suitable for analysis of near-termdevelopments and this report does not intend to providereliable projections for the near term.

3. Review of Past IPCC Emissions ScenariosThe I P C C developed sets of emissions scenarios in 1990 and1992. The six IS92 scenarios developed in 1992 (Leggett et a i ,1992; Pepper et a l . , 1992), have been used very widely inclimate change assessments. In 1995 the I P C C formallyevaluated the 1992 scenarios and found that they wereinnovative at the time of their publication, path-breaking intheir coverage of the f u l l range of G H G emissions and usefulfor the puipose of driving atmospheric and climate models(Alcamo et a i , 1995). Specifically, their global carbonemissions spanned most of the range of other scenariosidentified in the literature at that time.The review also identified a number of weaknesses. Theseincluded the limited range of carbon intensities of energy(carbon emissions per unit energy) and the absence of anyscenario with significant closure in the income gap betweendeveloped and developing countries, even after a fu l l century(Parikh, 1992). Furthermore, rapid growth of sulfur emissionsi n the IS92 scenarios had been questioned on the basis that theydid not reflect recent legislation in Japan, Europe, and NorthAmerica and that in general regional and l o c a l air qualityconcerns might prompt limits on future sulfur emissions.A n important recommendation of the 1995 I P C C review wasthat, given the degree of uncertainty about future climatechange, analysts should use the fu l l range of IS92 emissions asinput to climate models rather than a single scenario. This is instark contrast to the actual use of one scenario from the set, the

IS92a scenario, as the reference scenario in numerous studiesThe review concluded that the mere fact of the IS92a being anintermediate, or central, CO 2 emissions scenario at the globalevel at that time does not equate it with being the most l ike lscenario. Indeed, the conclusion was that there was nobjective basis on which to assign likelihood to any of thscenai'ios. Furthermore, the IS92a scenario was shown to b"central" for only a few of its salient characteristics such aglobal population growth, global economic development anglobal C O 2 emissions. In other ways, IS92a was found not tbe central with respect to the published literature, particularlyi n some of its regional assumptions and emissions. The same ithe case with the new set of S R E S scenarios, as is shownbelow.The new set of S R E S scenarios presented here is designed trespond to the IS92 weaknesses identified in the 1995 I P C Cscenario evaluation and to incorporate advances in the state othe art since 1992. As in the case of the IS92 scenario seriesalso in this new set of S R E S scenarios there is no single centracase with respect to all characteristics that are relevant fodifferent uses of emissions scenarios and there is no objectivway to assign likelihood to any of the scenarios. Hence there ino "best guess" or "business-as-usual" scenario.

4. SRE S Writing Team, Approach, and ProcessI P C C Working Group III (WGIII) appointed the S R E S writingteam in January 1997. After some adjustments, it eventuallycame to include more than 50 members from 18 countriesTogether they represent a broad range of scientific disciplineregional backgrounds, and non-governmental organizations. Inparticular, the team includes representatives of six scenariomodeling groups and a number of lead authors from all threeearlier I P C C scenario activities: the 1990 and 1992 scenai'iosand the 1995 scenario evaluation. Their expertise andfamiliarity with earlier I P C C emissions scenario work assuredcontinuity and allowed the S R E S effort to b u i l d efficiendyupon prior work. The S R E S team worked in closecollaboration with colleagues on the I P C C Task Group onClimate Scenarios for Impact Assessment ( T G C I A ) and withcolleagues from all three I P C C Working Groups (WGs) of theT h i r d Assessment Report ( T A R ) . Appendix II lists themembers of the writing team and their affiliations and Chapter1 gives a more detailed description of the S R E S approach andprocess.Taking the above audiences and purposes into account, thefollowing more precise specifications for the new S R E Sscenarios were developed. The new scenarios should:

cover the fu l l range of radiatively important gaseswhich include direct and indirect G H G s and SOj, have sufficient spatial resolution to allow regionaassessments of climate change in the global context; cover a wide spectrum of alternative futures to reflecrelevant uncertainties and knowledge gaps;


33/607

T e c h n i c a l S u m m a r y 2 5 use a variety of models to reflect methodologicalpluralism and uncertainty; incorporate input from a wide range of scientificdisciplines and expertise from non-academic sourcesthrough an open process; exclude additional initiatives and policies specificallydesigned to reduce climate change; cover and describe to the extent possible a range ofpolicies that could affect climate change although theyare targeted at other issues, for example, reductions inS O , emissions to l i m i t acid rain; cover as much as possible of the range of majorunderlying driving forces of emission scenariosidentified in the open literature; be transparent with input assumptions, modelingapproaches, and results open to external review; be reproducible - document data and methodologyadequately enough to allow other researchers toreproduce the scenarios; and be internally consistent - the various input assumptions

and data of the scenarios are internally consistent to theextent possible.T h e writing team agreed that the scenario formulation processwould consist of five major components:

review of existing scenarios in the literature; analysis of their main characteristics and drivingforces; formulation of narrative "storylines" to describealternative futures; quantification of storylines with different modelingapproaches; and "open" review process of emissions scenarios and theirassumptions

A s is evident from the components of the work program, therewas agreement that the process be an open one with no single"off ic ia l" model and no exclusive "expert teams." In 1997 theI P C C advertised in a number of relevant scientific journals andother publications to solicit wide participation in the process.T o facilitate participation and improve the usefulness of thenew scenarios, the S R E S web site (www.sres.ciesin) wascreated. In addition, members of the writing team publishedmuch of the background work used for formulating S R E Sscenarios in the peer-reviewed literature^ and on web sites (seeAppendix IV). F i n a l l y , the revised set of scenarios, the websites, and the draft of this report have been evaluated throughthe I P C C expert and government review processes. This

^ Alcamo and Nakicenovic, 1998; Alcamo and Swart, 1998; Anderson,1 9 9 8 ; Gaff in , 1998; Gregory, 1998; Gregory and Rogner, 1998;Grbler, 1998; Michaelis, 1998; Monta and L e e , 1998; Nakicenovic eta l, 1998; Price et al, 1998; de Vries et al., 2000; Fenhann, 2000; Jiange t al, 2000, Jung et al, 2000; K r a m et al., 2000; M o r i , 2000;Nakicenovic, 2000; R i a h i and Roehrl, 2000; Roehrl and R i a h i , 2000;Sankovski et al., 2000.

process resulted in numerous changes and revisions of thereport. In particular, during the approval process of IheSummary for Policymakers (SPM) in March 2000 at the 5"'Session of the W G III in Katmandu changes in this S P M wereagreed that necessitated some changes in the underlyingdocument, including this Technical Summary. These changeshave been implemented in agreement with the Lead Authors.

5. Scenario Literature Review and AnalysisT h e first step in the formulation of the S R E S scenarios was thereview and the analysis of the published literature and thedevelopment of the database with more than 400 emissionsscenarios that is accessible through the web site (www-cger.nies.go.jp/cger-e/db/ipcc.html); 190 of these extend to2100 and are considered in the comparison with the S R E Sscenarios in the subsequent Figures. Chapters 2 and 3 give amore detailed description of the Hterature review and analysis.Figure TS-1 shows the global energy-related and industrialC O j emission paths from the database as "spaghetti" curves forthe period to 2100 against the background of the historicalemissions from 1900 to 1990. These curves are plotted againstan index on the vertical axis rather than as absolute valuesbecause of the large differences and discrepancies for thevalues assumed for the base year 1990. These sometimes arisefrom genuine differences among the scenarios (e.g., differentdata sources, definitions) and sometimes from different baseyears assumed in the analysis or from alternative calibrations.'*T h e differences among the scenarios in the specification of thebase year illustrate the large genuine scientific and datauncertainty that surrounds emissions and their main drivingforces captured in the scenarios. The literature includesscenarios with additional climate polices, which are sometimesreferred to as mitigation or intervention scenarios.There are many ambiguities associated with the classificationo f emissions scenarios into those that include additionalclimate initiatives and those that do not. Many cannot beclassified in this way on the basis of the information availablefrom the database. Figure TS-1 indicates the ranges ofemissions in 2100 from scenarios that apparently includeadditional climate initiatives (designated as "intervention"emissions range), those that do not ("non-intervention") andthose that caimot be assigned to either of these two categories("non-classified"). This classification is based on thesubjective evaluation of the scenarios in the database by themembers of the writing team and is explained in Chapter 2.T h e range of the whole sample of scenarios has significant

T h e 1990 emissions from energy production and use are estimatedb y Marland e t a l . (1994) at 5.9 G t C excluding cement production. The1990 base year values in the scenarios reviewed range from 4.8( C E T A / E M F 1 4 , Scenario M A G I C O CO^) to 6.4 GtC( I C A M 2 / E M F 1 4 ) , see Dowlatabadi et al, 1995; Peck and Teisberg,1 9 9 5 .
http://www.sres.ciesin/http://www.sres.ciesin/


34/607

2 6 T e c h n i c a l S u m m a

1900 1950 2000 2050 2100Figure TS-1: G l o b a l energy-related and industrial emissions - historical development and future scenarios, shown as anindex (1990 = 1). The median (50*), the 5*, and 95" percentiles of the frequency distribution are also shown. The statisticsassociated with scenarios from the literature do not imply probability of occurrence (e.g., the frequency distribution of thescenarios may be influenced by the use of IS92a as a reference for many subsequent studies). The emissions paths indicate awide range of future emissions. The range is also large in the base year 1990 and is indicated by an "error" bar. To separate thvariation due to base-year specification from different future paths, emissions are indexed for the year 1990, when actual globenergy-related and industrial C O , emissions were about 6 G t C . The coverage of C O j emissions sources may vary across the256 different scenarios from the database included in the figure. The scenario samples used vary across the time steps (for 199256 scenarios, for 2020 and 2030 247, for 2050 211, and for 2100 190 scenarios). A l s o shown, as vertical bars on the right ofthe figure, are the ranges of emissions in 2100 of IS92 scenarios and for scenarios from the literature that apparently includeadditional climate initiatives (designated as "intervention" scenarios emissions range), those that do not ("non-intervention"),and those that cannot be assigned to either of these two categories ("non-classified"). This classification is based on thesubjective evaluation of the scenarios in the database by the members of the writing team and is explained in Chapter 2. Datasources: M o r i t a and Lee, 1998a, 1998b; Nakicenovic et a l . , 1998.

overlap with the range of those that cannot be classified andthey share virtually the same median (15.7 and 15.2 GtC in2100, respectively), but the non-classified scenarios do notcover the high part of the range. A l s o , the range of thescenarios that apparenfly do not include climate polices (nonintervention) has considerable overlap with the other tworanges (the lower bound of non-intervention scenarios ishigher than the lower bounds of the intei-venfion and nonclassified scenarios), but with a significantly higher median(of 21.3 GtC in 2100).Historically, gross anthropogenic CO j emissions haveincreased at an average rate of about 1.7% per year since 1900(Nakicenovic et a l . , 1996); if that historical trend continuesglobal emissions would double during the next three to fourdecades and increase more than s ixfold by 2100. Manyscenarios in the database describe such a development.However, the range is very large around this historical trend sothat the highest scenarios envisage about a tenfold increase of

global emissions by 2100 as compared with 1990, while thlowest have emissions lower than today. The median and thaverage of the scenaiios lead to about a threefold emissionincrease over the same time period or to about 16 G tC by 210This is lower than the median of the IS92 set and is lower thathe IS92a scenario, often considered as the "central" scenarwith respect to some of its tendencies. However, thdistribution of emissions is asymmetric. The thin emission" t a i l " that extends above the 95"' percenfile (i.e., between ths ix- and tenfold increase of emissions by 2100 compared 1990) includes only a few scenarios. The range of othemissions and the main scenario driving forces (such population growth, economic development and energproduction, conversion and end use) for the scenariodocumented in the database is also laige and comparable to thvariation of C O 2 emissions. Statistics associated with scenarifrom the literature do not imply probability of occurrence likelihood of the scenarios. The frequency distribution of thdatabase may be influenced by the use of IS92a as a referenc


35/607

T e c h n i c a l S u m m a r y 2 7for scenario studies and by the fact that many scenarios in thedatabase share common assumptions prescribed for thepurpose of model comparisons with similar scenario drivingforces.O ne of the recommendations of the writing team is that I P C Cor a similar international institution should maintain such adatabase thereby ensuring continuity of knowledge andscientific progress in any future assessments of GHGscenarios. An equivalent database for documenting naiTativeand other qualitative scenarios is considered to be also veryuseful for future climate-change assessments. One difficultyencountered in the analysis of the emissions scenarios is thatthe disnction between climate policies and non-climate policyscenarios and other scenarios appeared to be to a degreearbitrary and often impossible to make. Therefore, the wrhingteam recommends that an effort should be made in the futureto develop an appropriate emissions scenario classificationscheme.

6. Narrative Scenarios and StorylinesG i v e n these large ranges of future emissions and their drivingforces, there is an infinite number of possible alternativefutures to explore. The S R E S scenarios cover a finite, albeit avery wide range, of future emissions. The approach involvedthe development of a set of four alternative scenario "families"comprising 40 S R E S scenarios subdivided into seven scenariogroups. During the approval process of the S P M in March 2000at the 5* Session of WGIII in Katmandu, it was decided tocombine two of these groups into one, resulting in six groups.To facilitate the process of identifying and describingalternafive future developments, each scenario family includesa coherent narrative part called a "storyline," and a number ofalternative interetatons and quantifications of each storylinedeveloped by six different modeling approaches. A l l theinterpretations and quantifications of one storyline together arecalled a scenario family (see also Box 1-1 in Chapter 1 onterminology). Each storyline describes a demographic, social,economic, technological, environmental, and policy future forone of these scenario families. Storylines were formulated bythe writing team in a process which identified driving forces,key uncertainties, possible scenario families, and their l o g i c .W i t h i n each family different scenarios explore variations ofglobal and regional developments and their implications forG H G and sulfur emissions. Each of these scenarios isconsistent with the broad framework of that scenario family asspecified by the storyline. Consequently, each scenario familyand scenario group is equally sound. Chapters 4 and 5 give amore detailed description of the storylines, theirquantifications, and the resultant 40 emissions scenarios.Th e main reasons for foimulating storylines are:

to help the writing team to think more coherentiy aboutthe complex interplay among scenario driving forceswithin each and across alternative scenarios;

to make it easier to explain the scenarios to the varioususer communities by providing a narrative descriptionof alternative futures that goes beyond quantitativescenario features; to make the scenaiios more useful, in particular toanalysts who contribute to I P C C W G I I and W G I I I ; thesocial, p o l i t i c a l , and technological context described inthe scenario storylines is all-important in analyzing theeffects of policies either to adapt to climate change orto reduce G H G emissions; and to provide a guide for additional assumptions to bemade in detailed climate impact and mitigationanalyses, because at present no single model orscenario can possibly respond to the wide variety ofinfonnational and data needs of the different usercommunities of long-term emissions scenarios.

T he S R E S writing team reached broad agreement that therecould be no "best guess" scenarios; that the future is inherentiyunpredictable and that views w i l l differ on which of thestorylines could be more l ike ly . The writing team decided onfour storylines: an even number helps to avoid the impressionthat there is a "central" or "most l i k e l y " case. The team wantedmore than two in order to help illustrate that the future dependson many different underlying dynamics; the team did not wantmore than four, as they wanted to avoid complicating theprocess by too many alternatives. There is no "business-as-usual" scenario. Nor should the scenarios be taken as policyrecommendations. The storylines represent the playing out ofcertain social, economic, technological, and environmentalparadigms, which w i l l be viewed positively by some peopleand negatively by others. The scenarios cover a wide range, butnot all possible futures. In particular, it was decided thatpossible "surprises" would not be considered and that therewould be no "disaster" scenarios that are difficult to quantifywith the aid of formal models.Th e titles of the storyhnes have been kept simple: A l , A 2 , B l ,and B 2 . There is no particular order among the storylines; BoxTS-1 lists them in alphabetic order. Figure TS-2 schematicallyillustrates the four storylines and scenario families. Each isbased on a common specification of the main driving forces.They are shown, very simplistically, as branches of a two-dimensional tree. The two dimensions shown indicate theglobal-regional and the development-environmentalorientation, respectively. In reality, the four scenario familiesshare a space of a much higher dimensionality given thenumerous driving forces and other assumptions needed todefine any given scenario in a particular modeling approach.T he team decided to carry out sensitivity tests within some ofthe storylines by considering alternative scenarios withdifferent fossil-fuel reserves, rates of economic growth, or ratesof technical change within a given scenario family. Forexample, four scenario "groups" within the A l scenario familywere explored. As mentioned, two of these four groups thatexplore fossil-intensive developments in the energy systemwere merged in the S PM . Together with the other threescenario families this results in seven groups of scenarios -


36/607

2 8 T e c h n i c a l S u m m

Figure T S - 2 : S che ma t i c il l u s t r a t ion o f S R E S scena r i os . T hfou r scena r i o " f a m i l i e s " a re show n , ve r y s imp l i s t i ca l l y , asbranches of a two -d im ens iona l tree . In rea l i t y , the fou rscenar io fam i l ies share a space o f a mu ch h ighe rd imen s iona l i t y g i ven t he numer ous assump t i ons needed t ode f i ne any g i ven scena r i o i n a pa r t i cu la r mo de l i n g app r oacT h e schemat ic d iagram i l lus t ra tes that the scenar ios bu i ld ot he m a i n d r i v i n g f o r c e s o f G H G e m i s s i o n s . E a c h scena r i of am i l y i s b ased on a com mo n spec i f i ca t i on o f some o f t hema in d r i v i n g f o r ces . T he A l s t o r y l i ne b r anches ou t into f ogroups o f scen ar ios to i l lus t ra te that a l t e rna t ive deve lopmenpaths are poss ib le within one scenar io fam i ly . Tw o o f thesegroups were merged in the S P M .

B o x T S - 1 : T h e Main Characteristics o f t h e F o u r S R E S Storylines a n d Scenario FamiliesB y 2100 t he w o r l d wi l l have changed i n w ays that are hard to im agin e - as hard as i t wo u l

Date post:	14-Apr-2018
Category:	Documents
Upload:	patricia-dillon
View:	214 times
Download:	0 times

Emissions Scenarios

Documents