2nd Assessment En

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UNEP

PNUE

WM O

OMM

INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE

IPCC S e c o n d As s e s s m e n tCl im a t e Ch a n g e 1 9 9 5

A REPORT OF THE



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UNEP

PNUE

WM O

OMM


IPCC S e c o n d As s e s s m e n t

Cl im a t e Ch a n g e 1 9 9 5

A REPORT OF THE



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CONTENTS

Page

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

IPCC SECOND ASSESSMENT SYNTHESIS OF SCIENTIFIC-TECHNICAL INFORMATION RELEVANT TO

INTERPRETING ARTICLE 2 OF THE UN FRAMEWORK CONVENTION ON CLIMATE CHANGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1. Addressing the UNFCCC Article 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Anth ropogenic in terference with th e cl imate system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3. Sensit ivi ty and adaptat ion of systems to cl imate change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4. Analyt ical approach to s tabi lizat ion of atmospheric concentrat ions of greenhouse gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5. Technology and policy options for mit igat ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6. Equity and social considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7. Economic development to proceed in a sustainable mann er . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

8. The road forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

SUMMARY FOR POLICYMAKERS: THE SCIENCE OF CLIMATE CHANGE IPCC WORKING GROUP I . . . . . . . . . . . . . . . . . . . . 19

1. Greenhou se gas concentrat ions have continued to increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2. Anth ropogenic aerosols tend to produce negative radiat ive forcings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3. Climate has changed over the past century . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4. The balance of evidence suggests a d iscernible human influence on global cl imate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5. Climate is expected to continue to change in th e future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6. There are still man y uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

SUMMARY FOR PO LICYMAKERS: SCIENTIFIC-TECH NIC AL ANALYSES OF IMPACTS, ADAPTATIONS

AND MITIGATION OF CLIMATE CHANGE IPCC WORKING GROUP II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1. Scope of the assessmen t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2. Nature of the issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3. Vulnerability to climate chan ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283.1 Terrestrial and aq uatic ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.2 Hydrology and water resources management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.3 Food an d fibre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.4 Hum an infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.5 Hum an h ealth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4. Options to reduce emissions and enhan ce sinks of greenh ouse gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.1 Energy, industrial process and h uman set t lement em issions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.1.1 Energy deman d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.1.2 Mitigat ing industrial process and hum an set t lemen t emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.1.3 Energy supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.1.4 Integrat ion of energy system m it igat ion options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.2 Agriculture, rangelands and forestry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.3 Cross-sectoral issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.4 Policy instrum ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

SUMMARY FOR PO LICYMAKERS: THE ECONO MIC AND SOC IAL DIMENSION S OF CLIMATE CHANGE

IPCC W ORKING G ROUP III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2. Scope of the assessmen t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3. Decision-making frameworks for addressing climate chan ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4. Equity and social considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5. Intertemporal equity and discounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6. Applicability of cost and benefit assessment s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

7. The social costs of anthropogenic climate change: Damages of increased greenh ouse gas emissions . . . . . . . . . . . . . . . . . . . . 50

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8. Generic assessment of response strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

9. Costs of respon se option s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

10. Integrated assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

11. An econom ic assessmen t of policy instruments to combat cl imate change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

APPENDIX: HEAD AUTHORS, AUTHORS AND CONTRIBUTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

LIST OF IPCC OUTPUTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

CLIMATE CHANGE 1 995 : IPCC SECO ND ASSESSMENT REPORT

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The Intergovernm ental Panel on Climate Ch ange (IPCC) was jointlyestablished by th e World Meteorological Organization an d th e United

Nations Environm ent Programm e in 1988, in order to: (i) assess avail-

able scientific information on climate change, (ii) assess the

environmental and socio-economic impacts of climate change, and

(iii) formulate response strategies. The IPCC First Assessment Report

was completed in August 1990 an d served as the basis for n egotiating

the UN Framework Convention on Climate Change. The IPCC also

completed its 1992 Supplement and Climate Change 1994: Radiative

Forcing of Climate Change and An Evaluation of the IPCC IS92 Emission

Scenarios to assist the Con vention process further.

In 1992, the Panel reorganized its Working Groups II and III to

assess, respectively, the impacts and response options, and the

social and econom ic aspects of climate ch ange. It comm itted itself

to com pleting its Second Assessment in 1995, not only upd ating th e

information on th e same range of topics as in the First Assessment ,

but also includin g the n ew subject area of techn ical issues related to

th e socio-econom ic aspects of climate chan ge. We applaud t he IPCC

for prod ucin g its Secon d Assessmen t Report (SAR) as scheduled. We

are convinced that the SAR, as the earlier IPCC reports, would

become a standard work of reference, widely used by policymakers,

scientists and oth er experts.

As usual in th e IPCC, success in p roducing th is report h as depended

upon the enthusiasm and cooperation of numerous busy scientistsand other experts worldwide. We are exceedingly pleased to note

here the very special efforts made by the IPCC in ensuring the

participation of scientists and other experts from the developing

and transitional econom y coun tries in its activities, in particular in

th e writing, reviewing and revising of its reports. Th e scient ists an d

experts from the developed, developing and transitional economy

countries have given of their time very generously, and govern-

ments have supported them, in the enormous intellectual and

ph ysical effort requ ired, often going substantially beyond reason-

able demand s of duty. Without such conscientious and professional

involvement, th e IPCC would be greatly im poverished. We express

to all these scientists and experts, and the governments whosupported them, our sincere appreciation for their commitment.

We take th is opportunity to express our gratitude to th e following

individuals for nurtu ring anoth er IPCC report th rough to a success-

ful com pletion:

Prof. Bolin, th e Chairman of the IPCC, for his able leadership andskilful guidan ce of th e IPCC;

th e Vice-Chairmen of th e IPCC, Prof. Yu. A. Izrael (Russian

Federation ) an d Dr A. Al-Gain (Saudi Arabia);

th e Co-Chairmen of Working Group I, Dr L.G. Meira Filho (Brazil)

and Sir John Houghton (UK); the Vice-Chairmen of the W orking

Group, Dr Ding Yihui (China), Dr H. Grassl and later Prof.

D. Ehh alt (German y) and Dr A.B. Diop (Senegal);

the Co-Chairmen of Working Group II, Dr R. T. Watson (USA) and

Dr M.C. Zinyowera (Zimbabwe); the Vice-Chairmen of the

Working Group, Dr O. Canziani (Argentina), Dr M. Petit (France),

Dr S. K. Sha rma (India), Mr H. Tsukam oto (Japan ), Prof. P. Vellinga

(the Netherlands), Dr M. Beniston (Switzerland) Dr A. Hentati and

later Dr J. Friaa (Tunisia) and Ing. (Mrs) M. Perdom o (Venezuela);

the Co-Chairmen of Working Group III, Dr J.P. Bruce (Canada) and

Dr Hoesung Lee (Republic of Korea); the Vice-Chairmen of the

Working Group, Prof. R. Odingo (Kenya) and Dr T. Hanisch and

later Dr L. Loren tsen (Norw ay);

th e Regional Representatives in th e IPCC Bureau, Dr A. Adejokun

(Nigeria for Africa), Dr H. Nasrallah (Kuwait for Asia), Dr F. Fajardo

Moros (Cuba for North and Central America and the Caribbean),

Dr N. Sabogal and later Dr K. Robertson (Colombia for South

Am erica), Dr J. Zillman (Australia for Sout h west Pacific) an d Dr

M. Bautista Perez (Spain for Europ e); Dr B. Callander, the Head of the Technical Support Unit of

Working Group I and his staff, Ms K. Maskell, Mrs J.A. Lakeman

and Mrs F. Mills, and those who provided additional assistance,

namely, Dr N. Harris (European Ozone Research Co-ordinating

Unit, Cambridge, UK) and Dr A. Kattenberg (Royal Netherlands

Meteorological Institute);

Dr R. H. Moss, the Head of the Technical Support Unit of Working

Group II and his staff, interns or volunteers, namely, Mr

S. Agarwala, Mr D.J. Dokken, Mr S. Greco, Ms D. Hagag, Ms

S. MacCracken, Ms F. Ormo nd , Ms M. Taylor, Ms A. Tenney an d

Ms L. Van Wie;

Dr E. Haites, the Head of the Technical Support Unit of Working

Group III and h is staff Ms L. Lawson an d Ms V. Dreja;

and Dr N. Sundararaman, the Secretary of the IPCC and his staff in

the IPCC Secretariat, the late Mr S. Tewungwa, Mrs R. Bourgeois,

Ms C. Ettori an d Ms C. Tanikie.

PREFACE

G.O.P. Obasi

Secretary-General

World Meterological Organization

Ms E. Dowdeswell

Executive D irector

United Nations Environment Programme


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The IPCC completed its Second Assessment Report (SAR) inDecemb er 1995. Th e SAR consists of four part s:

th e IPCC Second Assessment Synthesis of Scientific-Techn ical

Information Relevant to Interpreting Article 2 of the UN

Framework Convention on Climate Change;

the Report of Working Group I of the IPCC, the Science of Climate

Change, with a Summary for Policymakers (SPM);

th e Report of Working Group II of th e IPCC, Scient ific-Techn ical

Analyses of Impacts, Adaptations and Mitigation of Climate

Change, with SPM;

the Report of Working Group III of the IPCC, the Economic and

Social Dimensions of Climate Change, with SPM.

The IPCC Second Assessment Synthesis and the Summaries for

Policymakers of the th ree Working Groups constitute th e Report of

th e IPCC (1995). They are published in t h is volum e and available in

the six UN languages, namely, Arabic, Chinese, English, French,

Russian an d Span ish. Th e Reports of the W orking Group s, with th eir

respective SPMs, are available in English on ly and each is separately

published com mercially.

We take this opportunity, because of much misinformation and

misunderstanding on the subject , to inform the reader on h ow the

IPCC conducts its assessments.

1 . Th e Pa nel a t t h e o ut set d ecid es t h e co n ten t , b ro ken d ow n

into chapters, of the report of each of its Working Group s. A writing

team of th ree to six experts (on som e rare occasions, m ore) is con sti-

tuted for the in itial drafting and subsequent revisions of a ch apter.

Governm ents and intergovernm ental and non -governm ental orga-

nizations are requested to nominate individuals with appropriate

expertise for consideration for inclusion in the writing teams. The

publication record of the nom inees and ot her relevant in formation

are also requested. Lists of such individuals are compiled from

which the writing team is selected by the Bureau of the Working

Group con cerned (i.e., the Co-Chairmen an d th e Vice-Chairmen of

th e Working Group). The IPCC requires that at least one m ember ofeach writing team be from the d eveloping world.

2. Th e rep ort s are req uired to h ave a Su m m ary fo r

Policymakers (SPM). The SPM should reflect the state-of-the-art

understanding of the subject matter and be wri t ten in a manner

that is readily comprehensible to the non-specialist. Differing but

scientifically or technically well-founded views should be so

exposed in the reports and th e SPMs, if they cann ot be reconciled in

th e course of the assessmen t.

3 . Th e w rit in g t ea m s d ra ft t h e ch a pt er s a n d t h e m a te ria l fo r

inclusion in the SPMs. The drafts are based on literature published

in peer-reviewed journals and reports of professional organizationssuch as th e Internat ional Coun cil of Scient ific Unions, the World

Meteorological Organization, the United Nations Environment

Programm e, the World Health O rganization an d th e United Nations

Food an d Agriculture Organization. Som etimes, the IPCC holds

workshop s to collect in formation that is otherwise n ot readily avail-

able; th is is particularly done t o en courage information-gathering

on an d in th e developing count ries.

4 . Ea ch d r aft ch a pt er is se n t t o te n s o f e xp ert s w or ld wid e fo r

expert review. The reviewers are also chosen from nominations

made by governments and organizations. The mandated time for

this review is six weeks. The draft, revised in the light of the

comments received, is sent to governments and organizations for

th eir techn ical review. The man dated tim e for this (second) review

is also six weeks. In som e cases, the exp ert an d govern m ent reviews

are conducted simultaneously when the time factor would not

permit sequential reviews.

5 . Th e dr aft is r ev ise d a se co n d tim e in t h e ligh t o f t h e r ev ie ws

received from governments and organizations. It is then sent to

governments (and organizations) one month in advance of the

session of the Working Group wh ich would con sider it. The Wo rking

Group approves the SPM line by line and accepts the underlying

chapters; the two together constitute the Report of the Working

Group. It is not practical for th e Working Group to app rove its Reportwhich usually runs to two h un dred pages or more. The meanin g of

the term acceptance in th is context is that t he un derlying chapters

and the SPM are consistent with each other.

6 . W h en t h e W orkin g G ro up ap pro ves t h e SPM , select ed

mem bers of the writing teams from the d eveloping as well as the

developed wo rlds are present an d th e text of th e SPM is revised at

th e session with t heir con currence. Thu s, in reality, the Reports of

the Working Groups are written and revised by experts and

reviewed by other experts.

7 . Th e Rep ort of t h e W orkin g G ro up (w it h th e ap pro vedSPM) is sent to governments and organizations one month before

th e session of the IPCC which would con sider it for acceptan ce.

8 . Th e r ea der m a y n o t e t h at th e IPC C is a fu lly in t er go ve rn -

m en tal, scient ific-techn ical body. All States th at are Memb ers of th e

United Nation s and of th e World Meteorological Organization are

Members of the IPCC and its Working Groups. As such, govern-

men ts approve the SPMs and accept th e un derlying chap ters, which

are, as stated earlier, written and revised by experts.

The IPCC Second Assessment Synthesis was drafted by a Drafting

Team con st itu ted un der the chairmanship of the Ch airman of the

FOREWORD


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IPCC. It un derwent expert and governm ent reviews simultan eously.

It was approved line by line by the IPCC at its Eleventh Session

(Rom e, 11-15 December 1995).

May we reiterate that the reports of the IPCC and of its Working

Groups contain the factual basis of the issue of climate change,

gleaned from available expert literature and further carefullyreviewed by experts and governm ents. In tot al more than two th ou-

sand experts worldwide participate in drafting an d reviewing th em.

Governm ents of th e world approve/accept them for their scientific-

techn ical conten t. The final product is written by experts selected

worldwide an d accepted by governm ents sitting in plenary sessions.

We also take this opportunity to record the sad loss of a valued

m em ber of the IPCC Secretariat. Mr Sam uel Tewungwa, wh o passed

away in January 1996, was seconded by the United NationsEnvironment Programme to the Secretariat. His good cheer and

good hum our and d edication to du ty are, and will be, much missed.


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N. Sun dararaman

Secretary of th e IPCC

B. Bolin

Chairman of the IPCC


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IPCC SECOND ASSESSMENT SYNTHESIS OF

SCIENTIFIC-TECHNICAL INFORMATION

RELEVANT TO INTERPRETING ARTICLE 2

OF THE UN FRAMEWORK CONVENTION

ON CLIMATE CHANGE


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1 .1 Fo ll ow in g a r eso lu t io n o f t h e Ex ec ut iv e C ou n c il o f t h e

World Meteorological Organization (July 1992), the IPCC decided

to in clude an exam ination of approaches to Article 2, th e Objective

of the UN Framework Convent ion on Climate Chan ge (UNFCCC),

in its work programme. It organized a workshop on th e subject in

October 1994 in Fortaleza, Brazi l , at the invi tat ion of the

Governm ent of Brazil. Thereafter, th e IPCC Chairman assembled a

team of lead authors (listed at the end of this report in the

Appen dix) under h is chairman ship to draft th e Synth esis. The team

produced th e draft which was subm itted for expert and governm ent

review and com m ent . The final draft Synt hesis was approved lin e by

line by the IPCC at its eleventh session (Rome, 11-15 December

1995), where representatives of 116 governments were present as

well as 13 intergovernmental and 25 non-governmental organiza-

tions. It may be no ted for information that all Member States of the

World Meteorological Organization and of the Un ited Nations are

Members of the IPCC and can attend its sessions and those of its

Working Groups. The Synth esis presents informat ion on th e scien-

tific and technical issues related to interpreting Article 2 of the

UNFCCC, drawing on the underlying IPCC Second Assessment

Report. Since the Synthesis is not simply a summary of the IPCC

Second Assessment Report, the Summaries for Policymakers of the

three IPCC Working Groups should also be consulted for a

summ ary of th e Second Assessmen t Report.

1 .2 D ur in g th e pa st fe w d eca de s, tw o im p o rt an t fa ct or s

regarding th e relationship between h um ans and the Earths climate

have become apparent. First, human activities, including the

burn ing of fossil fuels, lan d-use chan ge and agriculture, are increas-

ing the atmospheric concentrations of greenhouse gases (which

tend to warm the atmosphere) and, in some regions, aerosols

(microscopic airborne particles, which tend to cool the atmos-

phere). These changes in greenhouse gases and aerosols, taken

together, are projected to change regional and global climate and

climat e-related parameters such as tem perature, precipitation, soil

moisture and sea level. Second, some human communities have

become more vulnerable1

to hazards such as storms, floods anddroughts as a result of increasing population density in sensitive

areas such as river basins and coastal plains. Potentially serious

chan ges have been identified, including an increase in som e regions

in the incidence of extreme high-temperature events, floods and

drought s, with resultant consequences for fires, pest ou tbreaks, and

ecosystem composit ion, s t ructure and funct ioning, including

primary p roductivity.

1 .3 Scie n t ific an d t e ch n i ca l a sse ssm e n t s o f c lim a t e c h an g e a n d

its imp acts have been conducted by th e Intergovernmen tal Panel on

Climate Change (IPCC). The First Assessment, published in 1990,

provided a scientific and technical base for the UN Framework

Convention on Climate Change (UNFCCC) which was open for

signat ure at th e Earth Sum mit in Rio in 1992.

1 .4 Th e u lt im a t e o b je ct iv e o f t h e UN FC CC , a s e xp re sse d i n

Article 2 is:

. . . stabilization o f greenh ouse gas concen trations in th e atmo sphere at

a level that wou ld prevent dan gerous ant hrop ogenic interference with

the climate system. Such a level should be achieved within a time-

frame sufficient to allow ecosystems to adapt naturally to climate

change, to ensure that food production is not threatened and to enable

econom ic developmen t to proceed in a sustainable man ner.

1 .5 Th e c h all en g es p re se n t ed to th e p o lic ym a ke r b y Ar tic le 2

are the determination of what concentrations of greenhouse gases

might be regarded as dangerous anthropogenic interference with

the climate system and the charting of a future which allows for

economic development which is sustainable. The purpose of this

synthesis report is to provide scientific, technical and socio-

economic information that can be used, inter alia, in addressing

these challenges. It is based on the 1994 and 1995 reports of the

IPCC Working Groups.

1 .6 Th e re po rt fo llo ws th r ou gh t h e va rio us m at ter s w h ich a r e

addressed in Article 2. It first briefly summarizes the degree ofclimat e change th e int erference with th e climate system

which is projected to occur as a result of hum an activities. It th en

goes on to highlight what we know about the vulnerabilities of

ecosystems and human communities to likely climate changes,

especially in regard to agriculture and food production and to oth er

factors such as water availability, health and the impact of sea-level

rise which are important considerations for sustainable develop-

m ent . The task of the IPCC is to pro vide a sound scien tific basis th at

would enable policymakers to better interpret dangerous anthro-

pogenic interference with th e climat e system.

1 .7 G iv en cu r re n t t re n d s o f i n cr ea si n g e m issio n s o f m o stgreenhouse gases, atmospheric concentrations of these gases will

increase through th e next century and beyond. With th e growth in

atm ospheric concentration s of greenh ouse gases, int erference with

the climate system will grow in magnitude and the likelihood of

adverse impacts from climate chan ge that could be judged danger-

ous will become greater. Therefore, possible pathways of future net

emissions were considered which might lead to stabilization at

different levels and the general constraints these imply. This

3

1 Vulnerability defines the extent to which climate change may damage orharm a system. It depends not only on a systems sensitivity but also on itsability to adapt to new climatic conditions.

ADDRESSING THE UNFCCC ARTICLE 2 1


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consideration forms the n ext part of the report an d is followed by a

summ ary of the techn ical and policy options for reducing emissions

and enh ancing sinks of greenho use gases.

1 .8 Th e re po rt th e n ad d re sse s i ssu e s r ela t ed t o e q ui ty a n d to

ensuring that economic development proceeds in a sustainable

manner. This involves addressing, for instance, estimates of thelikely dam age of climate chan ge impacts, and th e impacts, includ-

ing costs and benefits, of adaptation and mitigation. Finally, a

nu mb er of insights from available studies point to ways of taking

initial actions (see the section on Road Forward) even if, at present,

it is difficult to decide upon a target for atm osph eric concen tration s,

includin g consideration s of time-frames, that would prevent danger-

ous anth ropogenic interference with th e climat e system.

1 .9 C lim a te ch a n ge p resen t s t h e de cisio n m a ke r w it h a set o f

formidable complications: considerable remaining uncertainties

inherent in the complexity of the problem, the potential for

irreversible damages or costs, a very long planning horizon, long

tim e lags between em ission s and effects, wide regional variation s in

causes and effects, an irreducibly global problem, and a multiple of

greenhouse gases and aerosols to consider. Yet another compli-

cation is that effective protection of the climate system requires

international cooperation in the context of wide variations in

income levels, flexibility and expectations of the future; this raises

issues of efficiency and intra-national, international and inter-

generational equity. Equity is an importan t elemen t for legitimizing

decisions and prom oting cooperation.

1 .10 Decis ions with respect to Art icle 2 of the UNFCCC involve

three distinct but interrelated choices: stabilization level, net

emissions pathway and mitigation technologies and policies. The

report presents available scientific and techn ical information on th ese

th ree choices. It also n otes where un certainties rem ain regarding such

informat ion. Article 3 of th e UNFCCC ident ifies a range of prin ciples

that shall guide, inter alia, decision-making with respect to t he u ltimate

objective of the Con vent ion, as foun d in Article 2. Article 3.32 provides

guidance, inter alia, on decision-makin g where th ere is a lack of full

scientific certainty, n amely th at th e Parties shou ld:

take precautionary measures to anticipate, prevent or minimize the

causes of climate ch ange an d m itigate its adverse effects. Where th ere

are threats of serious or irreversible damage, lack of full scientific

certainty sh ould n ot be used as a reason for postpon ing such m easures,

taking into account that policies and measures to deal with climate

chan ge should b e cost effective so as to en sure global benefits at th e

lowest possible cost. To achieve this, such po licies and m easures sho uld

take into account different socio-economic contexts, be comprehen-

sive, cover all relevant sou rces, sinks an d reservoirs of greenho use gases

and adaptation and comp rise all econ om ic sectors. Efforts to address

climat e chan ge may be carried o ut cooperatively by in terested Parties.

The Second Assessment Report of the IPCC also provides informa-

tion in th is regard.

1 .11 The long t ime-sca les involved in the c limate system (e .g .,

the lon g residence time of greenhou se gases in th e atmo sphere) and

in th e time for replacement of infrastructure, and th e lag by man y

decades to centuries between stabilization of concentrations and

stabilization of temperature and mean sea level, indicate the

importan ce for timely decision-making.


4

ANTHROPOGENIC INTERFERENCE WITH

THE CLIMATE SYSTEM 2

Interference to the present day

2 .1 In o r der t o u n d er st an d w h at co n st it u te s co n cen t ra tio n s o f greenh ouse gases that would prevent dangerous interference with

the climate system, it is first necessary to u nd erstand current atm os-

pheric concentrations and trends of greenhouse gases, and their

consequences (both present an d projected) to the climate system.

2 .2 Th e at m o sp h er ic co n ce n tr at io n s o f t h e gr ee n h ou se ga ses,

and am ong them , carbon dioxide (CO2), methane (CH4) and nitrous

oxide (N2O), have grown significantly sin ce pre-ind ustrial times (about

1750 A.D.): CO2 from about 280 to almost 360 ppmv3, CH4 from 700

to 1720 ppbv and N2O from about 275 to abou t 310 ppbv. These trends

can be attribut ed largely to h um an activities, m ostly fossil-fuel use,

land-use change and agriculture. Concentrations of other anthro-

pogenic greenh ouse gases have also increased. An increase of green-

house gas concentrations leads on average to an additional warming

of the atmosphere and the Earths surface. Many greenhouse gasesremain in th e atmosph ere and affect climate for a long tim e.

2 .3 Trop o sp h e ric ae ro so ls re su lt in g from c o m b u st io n o f fo ssi l

fuels, biomass burning and other sources have led to a negative

direct forcing and possibly also to a negative indirect forcing of a

similar m agnitude. Wh ile the n egative forcing is focused in partic-

ular regions and subcontinental areas, it can have continental to

hemispheric scale effects on climate patterns. Locally, the aerosol

forcing can be large enough to m ore than offset th e positive forcing

3 ppmv stands for parts per million by volume; ppbv stands for parts perbillion (th ousan d million) by volume. Values quoted are for 1992.

2 Kuwait registered its objection to q uotin g on ly subparagraph 3 of Article 3

and n ot th e Article in its entirety.


15/73

due to greenhouse gases. In contrast to the long-lived greenhouse

gases, anth ropogen ic aerosols are very short-lived in t he atm osph ere

and hence their radiative forcing adjusts rapidly to increases or

decreases in em issions.

2 .4 G lo ba l m e an s ur fa ce te m p erat u re h as in c re ase d b y b et we en

about 0.3 and 0.6C since the late 19th century, a change that isunlikely to be entirely natural in origin. The balance of evidence,

from changes in global mean surface air temperature and from

changes in geographical, seasonal and vertical patterns of atmos-

ph eric tem perature, suggests a discernible hum an in fluence on global

climate. There are uncertainties in key factors, including the magni-

tude and patterns of long-term natural variability. Global sea level

has risen by between 10 an d 25 cm o ver the past 100 years and mu ch

of the rise may be related to th e increase in global mean temperature.

2 .5 Th e re ar e in a deq u at e d at a t o de ter m in e wh e th e r co n sist -

ent global chan ges in climate variability or weather extrem es have

occurred over the 20th century. On regional scales there is clear

evidence of chan ges in some extremes an d climate variability indi-

cators. Some of these changes have been toward greater variability,

some have been toward lower variability. However, to date it has

not been possible to firmly establish a clear connection between

th ese region al changes and h um an activities.

Possible consequences of future interference

2 .6 In the absence o f mi t igat ion pol ic ies o r sign ifican t techno-

logical advances that reduce emissions and/or enhance sinks,

concen trations of greenho use gases and aerosols are expected to grow

throughout the next century. The IPCC has developed a range of

scenarios, IS92a-f, of future green ho use gas and a erosol precursor em is-sions based on assumptions concerning population and economic

growth, land-use, techn ological chan ges, energy availability and fuel

m ix during the period 1990 to 21004. By th e year 2100, carbon d iox-

ide emissions un der th ese scenarios are projected to be in th e range of

about 6 GtC5 per year, roughly equal to current em ission s, to as much

as 36 GtC per year, with th e lower end of th e IPCC range assum ing low

population and economic growth to 2100. Methane emissions are

projected to be in th e range 540 to 1170 Tg6 CH 4 per year (1990 emis-

sions were about 500 Tg CH4); nitrous oxide emissions are projected

to be in th e range 14 to 19 Tg N per year (1990 em ission s were about

13 Tg N). In all cases, the atm ospheric concent rations of greenhou se

gases and total radiative forcing con tinu e to increase throu ghout th esimulation p eriod of 1990 to 2100.

2 .7 Fo r th e m i d-r an g e IPC C em i ssio n sc en a rio , IS9 2a , a ssu m -

ing the best estimate value of climate sensitivity7 and including

the effects of future increases in aerosol concentrations, models

project an increase in global m ean surface temp erature relative to

1990 of about 2C by 2100. This estimate is approximately one-

th ird lower than the best estimate in 1990. This is due primarily

to lower emission scenarios (particularly for CO 2 and CFCs), the

inclusion of th e cooling effect of sulphate aerosols, and improve-

ments in the treatment of the carbon cycle. Combining the lowest

IPCC emission scenario (IS92c) with a low value of climate

sensitivity and including the effects of future changes in aerosol

concent rations leads to a projected increase of about 1C by 2100.

The corresponding projection for the highest IPCC scenario (IS92e)

com bined with a high value of climat e sensitivity gives a warmin g

of about 3 .5C. In all cases the average rate of warmin g would pro b-

ably be greater than any seen in the last 10,000 years, but the actu al

ann ual to decadal chan ges would include con siderable natural vari-ability. Regional temperature changes could differ substantially

from the global mean value. Because of the thermal inertia of the

oceans, only 50-90% of the eventual equilibrium temperature

change would have been realized by 2100 and temperature would

contin ue to in crease beyond 2100, even if concentrations of green-

house gases were stabilized by that time.

2 .8 Av erag e se a l ev el is e xp e ct e d t o ri se as a re su l t o f t h e rm a l

expansion of th e oceans an d m elting of glaciers and ice-sheets. For

th e IS92a scenario, assum ing th e best estimate values of climat e

sensitivity and of ice melt sensitivity to warming, and including

the effects of future changes in aerosol concentrations, models

project an in crease in sea level of about 50 cm from th e present to

2100. This estimate is approximately 25% lower than the best

est imate in 1990 due to the lower temperature project ion, but

also reflect ing im provements in the cl imate and ice melt mod els.

Combining the lowest emission scenario (IS92c) with the low

climate and ice melt sensitivities and including aerosol effects

gives a projected sea-level rise of about 15 cm from t he p resent to

2100. The corresponding projection for the highest emission

scenario (IS92e) combined with high climate and ice-melt

sensitivities gives a sea-level rise of about 95 cm from th e present

to 2100. Sea level would con tinu e to rise at a similar rate in future

centu ries beyond 2100, even if concentration s of greenh ouse gases

were s tabi l ized by that t ime, and would continue to do so evenbeyond the t ime of s tabi l izat ion of g lobal mean temperature.

Regional sea-level chan ges may differ from th e global mean value

owing to land m ovement an d ocean current ch anges.

2 .9 Conf idence i s h igher in the hemispheric -to -con t inen tal sca le

projections of coupled atmo sphere-ocean climate mo dels th an in th e

regional projections, where confidence remains low. There is more

confidence in temp erature projections th an h ydrological chan ges.

2 .10 Al l model simula t ions , whether they were fo rced with

increased concentrations of greenhouse gases and aerosols or with

increased concent rations of greenho use gases alon e, show th e follow-ing features: greater surface warming of the land than of the sea in

winter; a maximum surface warming in high northern

IPCC SECOND ASSESSMENT SYNTHESIS OF SCIENTIFIC-TECHNICAL INFORMATION RELEVANT

TO INTERPRETING ARTICLE 2 OF THE UN FRAMEWORK CONVENTION ON CLIMATE CHANGE

5

4 See Table 1 in t he Sum mary for Policymakers of IPCC Working Group II.

5 To convert GtC (gigatonnes of carbon or thousand mill ion tonnes ofcarbon) to m ass of carbon dioxide, multiply GtC by 3.67.

6 Tg: teragram is 1012 grams.

7 In IPCC reports, climate sensitivity usually refers to long-term (equilib-rium) change in global mean surface temperature following a doubling ofatmospheric equivalent CO2 concentration. More generally, it refers to theequilibrium change in surface air temperature following a unit change inradiative forcing (C/Wm -2).


16/73

latitudes in wint er, little surface warmin g over the Arctic in sum m er;

an enhanced global mean hydrological cycle, and increased precipi-

tation an d soil moisture in h igh latitudes in win ter. All these changes

are associated with iden tifiable physical m echan isms.

2 .1 1 W a rm e r te m p er at u re s w ill le ad t o a m o re vigo ro u s

hydrological cycle; this translates into prospects for more severedroughts and/or floods in some places and less severe droughts

an d/o r floods in ot h er places. Several mod els ind icate an in crease in

precipitation intensity, suggesting a possibility for more extreme

rainfall events. Knowledge is currently insufficient to say whether

there will be any changes in the occurrence or geographical

distribution of severe storm s, e.g., tropical cyclones.

2 .1 2 Th e re a re m a n y u n ce rt a in t i es a n d m a n y fa ct o rs c u rr en t l y

l imit our abi l i ty to project and detect fu ture cl imate change.

Future unexpected, large and rapid cl imate system changes

(as have occurred in the past) are, by their nature, difficult to

predict. This im plies th at future climat e chan ges m ay also involve

surprises. In particular, these arise from the non-linear nature

of the climate system. When rapidly forced, non-linear systemsare especially subject to unexpected behaviour. Progress can

be made by invest igat ing non-l inear processes and sub-

compon ents of th e cl imatic system. Examples of such non -linear

behaviour include rapid circulat ion changes in the North

Atlantic and feedbacks associated with terrestrial ecosystem

changes.


6

SENSITIVITY AND ADAPTATION OF

SYSTEMS TO CLIMATE CHANGE 33 .1 Th i s se ct io n p rov id es sc ie n t ific an d t e ch n i ca l in form a tio n

that can be used, inter alia, in evaluating whether the projected

range of plausible impacts constitutes dangerous anthropogenic

interference with th e clim ate system , as referred to in Article 2, an d

in evaluating adaptat ion op tions. However, it is not yet possible to

link particular imp acts with specific atmosph eric concen trations of

greenhouse gases.

3 .2 H u m an h e a lt h , t er re st ri al a n d aq u at ic ec olo gi ca l sy st em s ,

an d socio-econom ic system s (e.g., agriculture, forestry, fisheries an dwater resources) are all vital to hu m an d evelopm ent and well-being

and are all sensitive to both t he m agnitude and th e rate of climate

chan ge. Whereas man y region s are likely to experience th e adverse

effects of climate change some of which are potentially

irreversible some effects of climate change are likely to be

beneficial. Hence, different segments of society can expect to

confront a variety of chan ges and th e need to adapt to th em.

3 .3 H um a n -in d uced c lim a te ch a n ge rep resen t s a n im p o rt an t

additional stress, particularly to the many ecological and socio-

econo mic systems already affected by po llution, in creasing resource

demands, and non-sustainable management pract ices . Thevulnerability of h um an health and socio-econom ic systems and,

to a lesser extent, ecological systems depends upon economic

circumstances and institutional infrastructure. This implies that

system s typically are more vulnerable in developin g count ries wh ere

economic and institutional circumstances are less favourable.

3 .4 Alt h o u gh o u r k n ow le dge h as in c re ase d sign i fica n t ly

during th e last decade and qualitative estim ates can be developed,

quantitative projections of the impacts of climate change on any

particular system at any particular location are difficult because

regional-scale climate chan ge projections are un certain; o ur curren t

understanding of many critical processes is limited; systems are

subject to mu ltiple climatic and non -climatic stresses, th e interac-

tion s of wh ich are no t always linear or add itive; and very few studies

have con sidered dyn amic responses to steadily increasing con cen-

trations of greenhouse gases or the consequences of increases

beyond a dou bling of equivalent atmo spheric CO2 concentrations.

3 .5 U n am b igu ou s d et ect io n o f clim a te -in d u ce d ch a n ge s in

m ost ecological and social system s will prove extrem ely difficult in

the coming decades. This is because of the complexity of these

systems, their m any n on-linear feedbacks, and their sensitivity to alarge nu mb er of clim atic and non -climat ic factors, all of which are

expected to continue to change simultaneously. As future climate

extends beyond the boundaries of empirical knowledge (i.e., the

documented impacts of climate variation in the past), it becomes

more likely that actual outcomes will include surprises and

un anticipated rapid chan ges.

Sensitivity of systems

Terrestrial and aquatic ecosystems

3 .6 Ecosystems con ta in the Earth s en t ire reservoi r o f gene t icand species diversity an d provide m any good s and services including:

(i) providing food, fibre, medicines and energy; (ii) processing and

storing carbon an d ot her n utrient s; (iii) assimilating wastes, purifying

water, regulating water run off, and con trolling floods, soil degrada-

tion and beach erosion; and (iv) providing opportunities for

recreation and tourism. The comp osition and geographic distribu-

tion of man y ecosystem s (e.g., forests, rangelands, deserts, moun tain

system s, lakes, wetlands an d o ceans) will shift as in dividual species

respond to changes in climate; there will likely be reductions in

biological diversity and in the goods and services that ecosystems

provide society. Som e ecological systems m ay no t reach a n ew equi-

librium for several cent uries after th e climate ach ieves a n ew balance.


17/73

This section illustrates the impact of climate chan ge on a nu mber of

selected ecological systems.

3.7 Forests: Models project that as a consequence of possible

chan ges in tem perature and water availability under doubled equiv-

alent8 CO 2 equilibrium condition s, a substantial fraction (a global

average of one-third, varying by region from one-seventh to two-th irds) of the existing forested area of the wo rld will un dergo major

changes in broad vegetation types with the greatest changes

occurring in high latitudes and the least in the tropics. Climate

chan ge is expected to occur at a rapid rate relative to the speed at

which forest species grow, reproduce and re-establish themselves.

Therefore, the species composition of forests is likely to change;

en tire forest types may disappear, wh ile new assemblages of species

and hence new ecosystems may be established. Large amounts of

carbon could be released into the atmosphere during transitions

from one forest type to another because the rate at which carbon

can be lost during tim es of high forest mortality is greater than th e

rate at which it can be gained th rough growth to m aturity.

3. 8 Deserts and desertification : Deserts are likely to becom e

m ore extreme in th at, with few exceptions, they are projected to

become h otter but not significantly wetter. Temperature increases

could be a threat to organisms that exist near their heat tolerance

limits. Desertification lan d degradation in arid, semi-arid and dry

sub-humid areas resulting from various factors, including climatic

variations and human activities is more likely to become irre-

versible if the environment becomes drier and the soil becomes

further degraded through erosion and compaction.

3.9 Mountain ecosystems: The altitudinal distribution of

vegetation is projected to shift to h igher elevation ; some species withclimatic ranges limited to mountain tops could become extinct

because of disappearance of habitat or reduced migration potential.

3.10 Aquatic and coastal ecosystems: In lakes and streams,

warm ing would h ave the greatest biological effects at h igh latitudes,

where biological productivity would increase, and at the low-

latitude boundaries of cold- and cool-water species ranges, where

extinctions would be greatest. The geographical distribution of

wetlands is likely to shift with chan ges in temp erature and precipi-

tation . Coastal system s are econo m ically and ecologically import an t

and are expected to vary widely in their response to changes in

climate and sea level. Some coastal ecosystems are particularly atrisk, including saltwater marshes, mangrove ecosystems, coastal

wetlands, sandy beaches, coral reefs, coral atolls and river deltas.

Chan ges in these ecosystems would h ave major n egative effects on

tourism, freshwater supplies, fisheries and biodiversity.

Hydrology and water resources management

3 .1 1 M od els p ro je ct t h at b et w ee n o n e-t h ird a n d on e -h a lf o f

existing mountain glacier mass could disappear over the next

hundred years. The reduced extent of glaciers and depth of snow

cover also would affect the seasonal distribution of river flow and

water supply for hydroelectric generat ion and agricul ture.

Ant icipated h ydrological chan ges and reductions in th e areal extent

and depth of permafrost could lead to large-scale damage to in fra-

structure, an add itional flux of carbon dioxide into th e atmosph ere,

and changes in processes that contribute to the flux of methane

into the atm osphere.

3 .1 2 C lim a t e c h an g e w il l le ad t o an i n t en s ific at io n o f t h eglobal hydrological cycle and can have m ajor impacts on regional

water resources. Changes in the total amount of precipitation and

in its frequency and intensity directly affect the magnitude and

timin g of run off and the in tensity of floods and drough ts; however,

at present, specific regional effects are uncertain. Relatively small

changes in temperature and precipitation, together with the non-

linear effects on evapotranspiration and soil m oisture, can result in

relatively large changes in runoff, especially in arid and semi-arid

regions. The quantity and quality of water supplies already are

serious problems today in man y regions, including som e low-lying

coastal areas, deltas and small islands, making countries in these

regions particularly vulnerable to any additional reduction in

indigenous water supplies.

Agriculture and forestry

3 .13 Crop y ie lds and changes in p roduct iv ity due to c limate

change will vary considerably across regions and among localities,

th us chan ging the pattern s of produ ction. Productivity is projected to

increase in some areas an d decrease in oth ers, especially the tro pics

an d subtropics. Existin g stud ies show th at on th e who le, global agri-

cultural production could be maintained relative to baseline

production in the face of climate chan ge projected under do ubled

equivalent CO2 equilibrium conditions. This conclusion takes into

accoun t th e beneficial effects of CO2 fertilization but d oes not allowfor chan ges in agricultural pests and th e possible effects of changin g

climatic variability. However, focusing o n global agricultural prod uc-

tion does not address the potentially serious consequences of large

differences at local and regional scales, even at m id-latitud es. There

may be in creased risk of hun ger and famine in some locations; man y

of th e worlds poorest people particularly those living in subt rop-

ical and tropical areas and depen den t on isolated agricultural system s

in sem i-arid and arid region s are mo st at risk of increased hu n ger.

Global wood supplies during the next cent ury m ay become increas-

ingly inadequate to meet projected consumption due to both

climatic and non-climatic factors.

Human infrastructure

3 .14 Climate change clearly wil l increase the vu lnerab il ity o f

some coastal populations to flooding and erosional land loss.

Estimat es put abou t 46 million people p er year currently at risk of

flooding due to storm surges. In the absence of adaptation

measures, and not taking into account anticipated population

growth , 50-cm sea-level rise would increase this num ber to abou t 92

m illion ; a 1-m eter sea-level rise would raise it to about 118 m illion .



7

8 See paragraph 4.17 for a description o f equivalent CO 2.


18/73

Studies using a 1-meter projection show a particular risk for small

islan ds and deltas. This increase is at th e top ran ge of IPCC Working

Group I estimates for 2100; it should be noted, however, that sea

level is actually projected to continue to rise in future centuries

beyond 2100. Estimat ed land losses range from 0.05% in Uruguay,

1.0% for Egypt, 6% for the Netherlands and 17.5% for Bangladesh

to about 80% for the Majuro Atoll in th e Marshall Islands, given th epresent state of protection systems. Some small island nation s and

other countries will confront greater vulnerability because their

existing sea and coastal defense systems are less well established.

Coun tries with h igher population den sities would be m ore vulner-

able. Storm surges and flooding could threaten entire cultures. For

these countries, sea-level rise could force internal or international

migration of populations.

Human health

3 .15 Climate change is like ly to have wide-rang ing and mos tly

adverse im pacts on hu man health , with significant loss of life. Direct

health effects include increases in (predomin ant ly cardio-respiratory)

mortality and illness due to an anticipated increase in the in tensity and

durat ion of heat wa ves. Temperat ure increases in colder regions sh ould

result in fewer cold-related d eaths. Ind irect effects of climate chan ge,

which are expected to predom inate, include increases in th e potent ial

tran smission of vector-borne in fectious diseases (e.g., malaria, dengu e,

yellow fever and some viral enceph alitis) resulting from exten sion s of

th e geographical range and season for vector organ ism s. Models (that

entail necessary simplifying assumptions) project that temperature

increases of 3-5C (compared to the IPCC projection of 1-3.5C by

2100) could lead to potential increases in malaria incidence (of the

order of 5080 m illion ad ditional an nu al cases, relative to an assum ed

global background total of 500 million cases), primarily in tropical,subtropical and less well-protected temperate-zone populations.

Some increases in non-vector-borne infectious diseases such as

salmonellosis, cholera and giardiasis also could occur as a result of

elevated temperatures and increased flooding. Limitations on fresh-

water supplies and on nu tritious food, as well as the aggravation of air

pollution, will also have human health consequences.

3 .16 Quan t ifying the p ro jected impacts i s d i ff icu lt because the

extent of climate-induced health disorders depends on numerous

coexistent an d interacting factors that characterize the vulnerability

of the particular population, including environmental and socio-

economic c i rcumstances , nu t r i t iona l and immune s ta tus ,

popu lation den sity an d access to quality health care services. Hen ce,

populations with different levels of natural, technical and social

resources would differ in their vulnerability to climate-induced

health impacts.

Technology and policy options for adaptation

3 .17 Techno logica l advances genera lly have increased adap ta-

tion op tion s for man aged systems. Adapta tion op tion s for freshwater

resources include more efficient management of existing supplies

and infrastructure; institutional arrangements to limit future

deman ds/promote con servation; improved m onitoring and forecast-

ing systems for floods/droughts; rehabilitation of watersheds,

especially in t h e tropics; and constru ction of n ew reservoir capacity.

Adaptation options for agriculture such as changes in types and

varieties of crops, improved water-management and irrigation

systems, and changes in planting schedules and tillage practices

will be impo rtan t in limitin g negative effects and taking advan tage of

beneficial changes in climate. Effective coastal-zone management

and land-use plann ing can h elp direct po pulation shifts away from

vulnerable locations such as flood plains, steep hillsides and low-

lying coastlines. Adaptive options to reduce health impacts include

protective technology (e.g., housing, air conditioning, water purifi-

cation and vaccination), disaster preparedness and appropriate

health care.

3 .1 8 H ow ev er , m a n y re gio n s o f t h e wo rld cu r re n tl y h a ve

l imited access to these techn ologies and app ropriate information.

For some is land nat ions, the high cost of providing adequateprotection would make it essentially infeasible, especially given

th e limited availability of capital for investm ent . The efficacy an d

cost-effective use of adaptation strategies will depend upon the

availabi l i ty of f inancial resources , technology transfer, and

cultural , educat ional , managerial , ins t i tu t ional , legal and

regulatory pract ices , both domestic and internat ional in scope.

Incorporating climate-change concerns into resource-use and

development decis ions and plans for regularly scheduled

investments in infrastructure will facilitate adaptation.


8

ANALYTICAL APPROACH TO STABILIZATION OF

ATMOSPHERIC CONCENTRATIONS OF GREENHOUSE GASES 44 .1 Ar ticle 2 o f t h e U N Fr am e wo rk Co n ve n tio n o n Clim a te

Change refers explicitly to stabilization of greenhouse gas concen-

trat ions. This sect ion provides information on the relat ive

importance of various greenhouse gases to climate forcing and

discusses how greenhouse gas emissions might be varied to achieve

stabilization at selected atm ospheric concen tration levels.

4 .2 C arbo n dio xid e, m e th a n e a n d n it ro u s o xid e h a ve n a tu ra l a s

well as anth ropogen ic origin s. The anth ropogen ic em issions of th ese

gases have contributed about 80% of the additional climate forcing

due to greenhouse gases since pre-industrial times (i.e., since about

1750 A.D.). The contribution of CO 2 is about 60% of this forcing,

about four times that from CH4.


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4 .3 O t h er gr ee n h o use ga se s in c lu d e t ro p osp h e ric ozo n e (w h o se

chemical precursors include n itrogen oxides, non -methan e h ydro-

carbons and carbon m onoxide), halocarbons9 (including HCFCs and

HFCs) and SF6. Tropospheric aerosols and tropospheric ozone are

inhomogeneously distributed in time and space and their atmos-

pheric lifetimes are short (days to weeks). Sulphate aerosols are

amen able to abatement m easures and such m easures are presum ed inth e IPCC scenarios.

4 .4 M ost em i ssio n sc en a rio s in d i ca te t h a t, in t h e a bse n ce o f

mitigation policies, greenhouse gas emissions will continue to rise

during th e next century and lead to greenh ouse gas concentration s

that by the year 2100 are projected to change climate more than

th at projected for twice the pre-industrial concen trations of carbon

dioxide.

Stabilization of greenhouse gases

4 .5 Al l r ele va n t gr ee n h o u se ga se s n e ed t o b e c on si de re d in

addressing stabilization of greenhouse gas concentrations. First,

carbon d ioxide is considered which, because of its imp ortance an d

complicated behaviour, needs more detailed consideration t han th e

oth er greenh ouse gases.

Carbon dioxide

4 .6 C arb on d io xid e is r em o ve d fro m t h e a tm o sp h er e b y a

n um ber of processes that op erate on d ifferent t ime-scales. It has a

relatively lon g residence tim e in t he climate system of th e order

of a cent ury or more. If net global an th ropogenic em issions10 (i.e.,

anthropogenic sources minus anthropogenic s inks) were

main tained at current levels (about 7 GtC/ yr including emissionsfrom fossi l -fuel combustion, cement production and land-use

change), they would lead to a nearly constant rate of increase in

atmospheric concentrat ions for at least two centuries , reaching

about 500 ppmv (approaching twice the pre-industrial

concentrat ion of 280 ppmv) by the end of the 21st century.

Carbon cycle models show that immediate s tabi l izat ion of the

concentration of carbon dioxide at its present level could only be

achieved th rough an imm ediate reduction in i ts emissions of 50-

70% and further reductions thereafter .

4 .7 C arbo n cy cle m o d els h a ve b ee n use d t o e st im a t e p rofil es

of carbon dioxide emissions for stabilization at various carbondioxide concentration levels. Such profiles have been generated for

an illustrative set of levels: 450, 550, 650, 750 and 1000 ppmv.

Amon g the m any p ossible pathways to reach stabilization, two are

illustrated in Figure 1 for each o f the stab ilization levels of 450, 550,

650 and 750 ppmv, and one for 1000 ppmv. The steeper the

increase in th e emissions (hen ce concentration ) in th ese scenarios,

th e more qu ickly is the climate projected to chan ge.

4 .8 An y ev en t u al st ab ilize d c on c en t r at io n is go ve rn e d m or e

by the accumulated anthropogenic carbon dioxide emissions from

now unti l the t ime of s tabi l izat ion, than by the way those

emissions change over the period. This means that, for a given

stabilized concentration value, higher emissions in early decades

require lower emissions later on . Cum ulative emissions from 1991

to 2100 corresponding to these stabilization levels are shown in

Table 1, together with t he cum ulative emissions of carbon dioxide

for all of th e IPCC IS92 em ission scenar ios (see Figure 2 below a n d

Table 1 in th e Sum m ary for Policymakers of IPCC Working Grou p

II for details of these scenarios).

4 .9 Fig ure 1 an d Ta ble 1 a re pr ese n t ed t o c la rify so m e of t h e

constraints that wo uld be imposed on future carbon dioxide emis-

sions, if stabilization at the concentration levels illustrated were to

be achieved. These examples do n ot represent an y form of recom-

men dation about how such stabilization levels might be ach ieved or

th e level of stabilization wh ich m ight be ch osen.

4 .10 Given cumula t ive emissions , and IPCC IS92a popu la t ion

and economic scenarios for 1990-2100, global annual average

carbon d ioxide emission s can be derived for the stabilization scen ar-

ios on a per capita or per unit of economic activity basis. If the

atmo spheric concentration is to remain below 550 ppm v, the future

global annual average emissions cannot, during the next century,

exceed th e current global average and would h ave to be mu ch lower

before and beyond the end of the next century. Global annual

average emissions could be higher for stabilization levels of 750 to

1000 ppmv. Nevertheless, even to achieve these latter stabilization

levels, the global annual average emissions would need to be less

th an 50% above current levels on a per capita basis or less th an h alf

of current levels per un it of econom ic activity11 .

4.1112 The global average annual per capita emissions of carbon

dioxide due to the combu stion of fossil fuels is at present abou t 1.1

ton nes (as carbon). In add ition, a net of about 0.2 ton nes per capitaare emitted from deforestation and land-use change. The average

ann ual fossil fuel per capita emission in developed an d tran sitional

economy countries is about 2.8 tonnes and ranges from 1.5 to 5.5

tonnes. The figure for the developing countries is 0.5 tonnes

ranging from 0.1 ton nes to, in some few cases, above 2.0 tonn es (all

figures are for 1990).

4.1213 Using World Bank estimates of GDP (gross domestic

product) at market exchange rates, the current global annual

average emission of energy-related carbon dioxide is about 0.3

ton nes per th ousand 1990 US dollars output. In add ition, global net

emissions from land-use changes are about 0.05 tonnes perth ousand US dollars of output. The current average ann ual energy-



9

9 Most halocarbons, but neither HFCs nor PFCs, are controlled by theMontreal Protocol and i ts Adjustments an d Amendm ents.

10 For th e remaind er of Section 4, n et global anth ropogenic em issions (i.e.,anthropogenic sources minus anthropogenic sinks) will be abbreviated toemissions.

11 Chin a registered its disagreemen t on t he use of carbon dioxide emissionsderived on th e basis of a per unit econ om ic activity.

12 The Panel agreed that th is paragraph shall not p rejudge the current n ego-tiations under the UNFCCC.

13 The Panel agreed that th is paragraph shall not p rejudge the current n ego-tiations under the UNFCCC.


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10


CO2concentration(ppmv)

S 450

S 550

S 650

S 750

S 10001000

950

900

850

800

750

700

650

600

550

500

450

400

350

Year2000 2050 2100 2150 2200 2250 2300 2350

10

5

0

15

20

Anthropog

enicCO2emissions(GtC/yr)

Current anthropogenic

CO2 emissions

Year2000 2050 2100 2150 2200 2250 2300 2350

S1000S750S650S550S450

IS92a

Figure 1 (a ) . Carbon dioxide concentration profiles leading to

stabilization at 450, 550, 650 and 750 ppm v following the p athways

defined in IPCC (1994) (solid curves) and for pathways that allow

emissions to follow IS92a until at least the year 2000 (dashed

curves). A single profile that stabilizes at a carbon dioxide concen-

tration o f 1000 ppm v an d follows IS92a emissions u ntil at least th eyear 2000 has also been defined. Stabilization at concen trations of

450, 650 and 1000 ppmv would lead to equilibrium temperature

increases relative to 199014 due to carbon dioxide alone (i.e., not

includ ing effects of oth er greenh ouse gases (GHGs) and aero sols) of

about 1C (range: 0.5 to 1.5C), 2C (range: 1.5 to 4C) and 3.5C

(range: 2 to 7C), respectively. A doubling of the pre-industrial

carbon dioxide concen tration of 280 ppmv would lead to a concen-

tration of 560 ppmv and doubling of the current concentration of

358 ppmv would lead to a concentration of about 720 ppm v.

Figu re 1 (b) . Carbon dioxide emissions leading to stabilization at

concentration s of 450, 550, 650, 750 and 1000 ppm v following the

profiles shown in (a) from a mid-range carbon cycle model. Results

from oth er mod els could differ from th ose presented h ere by up to

approximately 15%. For comparison, the carbon dioxide em is-

sions for IS92a and current emissions (fine solid line) are also

shown.

40

30

20

10

02000 2020 2040 2060 2080 2100

AnthropogenicCO2emission

s(GtC/yr)

Year

IS92e

IS92f

IS92aIS92b

IS92d

IS92c

Figu re 2 . Ann ual anth ropogenic carbon dioxide emissions under

the IS92 emission scenarios (see Table 1 in the Summary for

Policym akers of IPCC Workin g Group II for furth er details).

14 These nu mbers do n ot take into account the in crease in temperature (0.1to 0.7C) which would occur after 1990 because of CO 2 emissions prior to1990.


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11

related em issions p er th ousand 1990 US dollars output, evaluated at

market exchange rates, is about 0.27 tonnes in developed and

t rans i t iona l economy coun t r ies and abou t 0 .41 tonnes in

developing countries. Using World Bank estimates of GDP at

purchasing power parity exchange rates, the average ann ual energy-

related emissions per thou sand 1990 US dollars outpu t is about 0.26

ton nes in developed and tran sitional econom y coun tries and abou t

0.16 tonn es in d eveloping coun tries.15

Methane

4 .1 3 At m o sp h e ric m e th a n e co n ce n t ra ti on s ad ju st t o ch a n ge s in

anthropogenic emissions over a period of 9 to 15 years. If the

annual methane emissions were immediately reduced by about 30

Tg CH4 (about 8% of current anthropogenic emissions), methane

concentrations would remain at todays levels. If methane emis-

sions were to remain constant at their current levels, methane

concent rations (1720 ppbv in 1994) would rise to about 1820 ppbv

over the n ext 40 years.

Nitrous oxide

4 .1 4 N it ro u s o xid e h as a lo n g life ti m e (a bo u t 12 0 y ea rs). In

order for th e concent ration t o be stabilized near current levels (312

ppbv in 1994), anthropogenic sources would need to be reduced

imm ediately by more th an 50%. If emissions of nitrous oxide were

held con stant at current levels, its concentration would rise to about

400 ppbv over several hundred years, which would increase its

incremental radiative forcing by a factor of four over its current

level.

Further points on stabilization

4 .15 Stab il izat ion o f the concen t ra t ions o f very long-l ived

gases, such as SF6 or perfluorocarbons, can only be achieved effec-

tively by stopping emissions.

4 .1 6 Th e im p o rt an c e o f t h e co n tr ib ut io n of C O2 to climate

forcing, relative to that of the other greenhouse gases, increases

with tim e in all of th e IS92 em ission scen arios (a to f). For exam ple,

in the IS92a scenario, the CO 2 contribution increases from thepresent 60% to about 75% by the year 2100. During the same

period, methane and nitrous oxide forcings increase in absolute

terms by a factor that ran ges between two an d th ree.

4 .17 The combined e ffec t o f a ll g reenhouse gases in p roducing

radiative forcing is often expressed in terms of the equivalent

concentration of carbon dioxide which would produce the same

forcing. Because of the effects of the other greenhouse gases, stabi-

lization at some level of equivalent carbon d ioxide con centration

implies maintainin g carbon dioxide con centration at a lower level.

4 .18 The stabi li za t ion o f g reenhouse gas concen t ra tions doesnot imply that there will be no further climate change. After

stabilization is achieved, global mean surface temperature would

cont inu e to rise for som e centuries and sea level for man y centu ries.



Accumulated carbon dioxide emissions1991 to 2100 (GtC)

IS92 scenariosc 770d 980b 1430

a 1500f 1830e 2190

Stabilizat ion case For profiles A* For p rofiles B

450 ppm v 630 650550 ppm v 870 990650 ppm v 1030 1190750 ppm v 1200 13001000 ppm v 1410

Table 1 . Total anthropogenic carbon dioxide emis-

sions accum ulated from 1991 to 2100 in clusive (GtC)

for the IS92 scenarios (see Table 1 in the Summary for

Policym akers of IPCC Workin g Group II) and for stabi-

l izat ion at various levels of carbon dioxide

concentration following the two sets of pathways

shown in Figure 1 (a). The accumulated emissions

leading to stabilization of carbon dioxide concentra-

tion were calculated using a mid-range carbon cycle

model. Results from other models could be up to

approx imate ly 15% h igher o r lower than those

presented h ere.

For compar ison , emissions dur ing the per iod 1860 to 1994 amounted to about360 GtC, of which abo ut 240 GtC w ere due to fossil-fuel use and 120 GtC du eto d eforestation an d land-use chan ge.

* As in IPCC (1994) see Figure 1 (a) (solid curves).

Profiles th at allow emissions to follow IS92a until at least th e year 2000 see figure 1 (a) (dashed curves).

Con centration s will no t stabilize by 2100.

15 These calculations of emissions per unit of economic activity do notinclude em issions from land -use chan ges or adjustm ents to reflect th e infor-mal economy.


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5 .1 The IPCC Second Assessmen t Report (1995) examines a wide

range of approaches to reduce em ission s and en han ce sinks of green-

ho use gases. This section provides techn ical informat ion on option s

that could be used to reduce anth ropogenic emissions and en han ce

sinks of th e principal greenh ouse gases with a view to stabilizing t heir

atm ospheric concentration s; ho wever, th is analysis does not attem pt

to quan tify poten tial macroecon om ic consequen ces th at may be asso-

ciated with m itigation.

5 .2 Sign i fic an t r ed u ct io n s in n e t gr ee n h o u se ga s e m issio n s a re

technically possible and can be economically feasible. These reduc-

tion s can be ach ieved by utilizing an exten sive array of tech no logies

and policy measures that accelerate techn ology developmen t, diffu-

sion and transfer in all sectors, including the energy, industry,

transportation, residential/commercial and agricultural/forestry

sectors.

5 .3 Th e de gree t o w h ic h te ch n i ca l p o t en t ia l a n d co st -e ffe c-

tiveness are realized is dependen t on initiatives to coun ter lack of

information and overcome cultural, institutional, legal, financial

and econom ic barriers which can h inder diffusion of techn ology or

behavioural chan ges.

5 .4 By t h e y ea r 2 10 0, t h e w or ld s co m m e rc ia l e n ergy sy st em i n

effect will be replaced at least twice, offering opportunities tochange the energy system without premature retirement of capital

stock; significant amounts of capital stock in the industrial,

com m ercial, residential an d agricultural/forestry sectors will also be

replaced. These cycles of capital replacement provide opportunities

to u tilize new, better p erformin g techn ologies.

Energy demand

5 .5 Th e IPC C p ro je ct s (IPC C 1 99 2; IPC C 1 99 4) th a t wit h o ut

policy intervention, there could be significant growth in emissions

from th e ind ustrial, tran sportation an d comm ercial/residen tial build-ings sectors. Numerous studies have indicated that 10-30% energy

efficiency gains above p resent levels are feasible at negative16 to zero

cost in each of the sectors in m any parts of the world th rough tech-

nical conservation measures and improved management practices

over the n ext two t o th ree decades. Using techn ologies that presently

yield the highest output of energy services for a given input of

energy, efficiency gains of 5060% wou ld be t echn ically feasible in

man y count ries over the same time period. Achieving th ese poten -

tials will depend on future cost reductions, the rate of development

and im plementation of new technologies, finan cing and techn ology

transfer, as well as measures to overcome a variety of non-technical

barriers. Because energy use is growing worldwide, even replacing

current tech no logy with m ore-efficient tech no logy could still lead to

an absolute increase in greenhouse gas emissions in the future.

Technologies and measures to reduce greenhouse gas emissions in

energy end -use sectors include:

Industry: improvin g efficiency; recycling m aterials and switchin g tothose with lower greenhouse gas emissions; and developing

processes that use less energy and materials.

Transportation: the use of very efficient vehicle drive-trains, light-weight construction and low-air-resistance design; th e use of smaller

vehicles; altered land-use patterns, transport systems, mobility

patterns and lifestyles; and shifting to less energy-intensive trans-

port modes; and the use of alternative fuels and electricity from

renewable and other fuel sources which do not enhance atmos-

pheric greenhouse gas concentration s.

Commercial/residential: reduced heat transfers through buildingstructures and m ore-efficient space-cond itioning an d water supply

systems, light ing an d appliances.

Energy supply

5 .6 It i s t echn ically possib le to realize deep emissions reduct ions

in the energy supply sector within 50 to 100 years using alternative

strategies, in step with the normal timing of investments to replace

infrastructure and equipment as it wears out or becomes obsolete.Promising app roaches, not ordered according to priority, include:

(a) Greenhouse gas reductions in th e use of fossil fuels

More-efficient con version of fossil fuels (e.g., combin ed h eatand power production and more-efficient generation of

electricity);

Switching to low-carbon fossil fuels and suppressing emis-sions (switchin g from coal to oil or n atural gas, and from oil

to n atural gas);

Decarbonization of flue gases and fuels and carbon dioxidestorage (e.g., rem oval an d storage of CO2 from t h e use of fossil

fuel feedstocks to make hydrogen-rich fuels); Reducing fugitive emissions, especially of methane, in fuelextraction an d distribution .

(b) Switching to non-fossil fuel sources of energy

Switching to nuclear energy (if generally acceptableresponses can be found to concerns such as about reactor

safety, radioactive-waste transport and disposal, and nuclear

proliferation);

Switching to renewable sources of energy (e.g., solar,biomass, wind, h ydro and geoth ermal).


12

16 Negative cost means an economic benefit.

TECH NO LOGY AND POLICY OPTIONS FOR MITIGATION 5


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Integration of energy system mitigation options

5 .7 Th e po t en t ia l fo r gr ee n h o use ga s e m issio n re du ct io n s

exceeds the potential for energy use efficiency because of the

possibility of switching fuels and en ergy sources, and redu cing th e

demand for energy services. Even greater energy efficiency, and

hence reduced greenhouse gas emissions, could be attained withcom preh ensive energy source-to-service chains.

5 .8 To asse ss t h e p o te n t ia l i m p ac t o f c om b in a t io n s o f i n di vi d-

ual measures at the energy systems level, thought experiments

exploring varian ts of a low-CO2 em itting energy supply system were

described. These variants illustrate the technical possibility of d eep

reductions in CO 2 emissions from t he en ergy supply system within

50 to 1 00 years using altern ative strategies. These exercises indicate

th e technical possibility of reducing annual global emissions from 6

GtC in 1990 to about 4 GtC in 2050 and to about 2 GtC by 2100.

Cumulative CO2 emissions from 1990 to 2100 would range from

about 450 GtC to about 470 GtC in these constructions, thus

keeping atm ospheric concen trations below 500 ppm v.

5 .9 C o st s fo r in t e grat ed e n ergy se rv ic es re la t iv e t o co st s fo r

convention al energy depend on relative future en ergy prices, which

are uncertain within a wide range, and on the performance and

cost characteristics assum ed for alternative t echn ologies. However,

within the wide range of future energy prices, one or more of the

variants would plausibly be capable of providing the demanded

energy services at estimated costs th at are approxim ately the same

as estimat ed future costs for current conven tional en ergy. It is not

possible to iden tify a least-cost futu re energy system for th e longer

term, as th e relative costs of options depen d on resource constraints

and technological opportunities that are imperfectly known, andon actions by governments and the private sector. Improving

energy efficiency, a strong and sustained investment in research,

and development and demonstrat ion to encourage transfer and

diffusion o f alternative en ergy supply techn ologies are critical to

deep reductions in greenhouse gas emissions. Many of the

technologies being developed would need initial support to enter

th e market

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