Impacts, Adaptations, and Mitigation of Climate Change

857 Pages·2015·14.87 MB·English

by  David Dokken

Climate Change 1995:
The IPCC Second Assessment Report
Scientific-Technical Analyses of Impacts,
Adaptations, and Mitigation of Climate Change
Editors:
Robert T. Watson, M.C. Zinyowera, and Richard H. Moss
Project Administrator:
David Jon Dokken
Contribution of Working Group II of the Intergovernmental Panel on Climate Change,
forming part of the IPCC Second Assessment Report
Published for the Intergovernmental Panel on Climate Change
place Cambridge University Press logo here
drop holding line
Over the past 2 years, the following individuals have committed
a portion of their time and talents to the Working Group II Technical Support Unit:
Richard H. Moss, Head
Shardul Agrawala, Intern
David Jon Dokken, Project Administrator
Steve Greco, Staff Scientist
Dottie Hagag, Secretary
Sandy MacCracken, Administrative Assistant
Flo Ormond, Technical Specialist
Melissa Taylor, Intern
Anne Tenney, Intern
Laura Van Wie, Intern
Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Summary for Policymakers: Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change. . . . . 1
Technical Summary: Impacts, Adaptations, and Mitigation Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Part I—Introductory Materials
A. Ecophysiological, Ecological, and Soil Processes in Terrestrial Ecosystems:
A Primer on General Concepts and Relationships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
B. Energy Primer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Part II—Assessment of Impacts and Adaptation Options
1. Climate Change Impacts on Forests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
2. Rangelands in a Changing Climate: Impacts, Adaptations, and Mitigation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
3. Deserts in a Changing Climate: Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
4. Land Degradation and Desertification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5. Impacts of Climate Change on Mountain Regions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
6. Non-Tidal Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
7. The Cryosphere: Changes and Their Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
8. Oceans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
9. Coastal Zones and Small Islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
10. Hydrology and Freshwater Ecology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
11. Industry, Energy, and Transportation: Impacts and Adaptation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
12. Human Settlements in a Changing Climate: Impacts and Adaptation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
13. Agriculture in a Changing Climate: Impacts and Adaptation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
14. Water Resources Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
15. Wood Production under Changing Climate and Land Use. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
16. Fisheries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
17. Financial Services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539
18. Human Population Health. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
Part III—Assessment of Mitigation Options
19. Energy Supply Mitigation Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587
20. Industry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
21. Mitigation Options in the Transportation Sector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679
22. Mitigation Options for Human Settlements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
23. Agricultural Options for Mitigation of Greenhouse Gas Emissions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
24. Management of Forests for Mitigation of Greenhouse Gas Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
25. Mitigation: Cross-Sectoral and Other Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799
Part IV—Technical Appendices
26. Technical Guidelines for Assessing Climate Change Impacts and Adaptations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823
27. Methods for Assessment of Mitigation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
28. Inventory of Technologies, Methods, and Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845
Appendix A. Expert Reviewers of the IPCC Working Group II Volume. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
Appendix B. Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863
Appendix C. Acronyms and Chemical Symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
Appendix D. Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
Appendix E. List of Major IPCC Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879
Foreword
The Intergovernmental Panel on Climate Change (IPCC) was by the IPCC in ensuring the participation of experts from the
jointly established by the World Meteorological Organization developing and transitional economy countries in its activities,
and the United Nations Environment Programme in 1988, in in particular in the writing, reviewing, and revising of its
order to (i) assess available scientific information on climate reports. The experts have given of their time very generously,
change, (ii) assess the environmental and socioeconomic and governments have supported them in the enormous intel-
impacts of climate change, and (iii) formulate response strate- lectual and physical effort required, often going substantially
gies. The IPCC First Assessment Report was completed in beyond reasonable demands of duty. Without such conscien-
August 1990, and served as the basis for negotiating the UN tious and professional involvement, the IPCC would be great-
Framework Convention on Climate Change. The IPCC also ly impoverished. We express to all these experts, and the gov-
completed its 1992 Supplement and “Climate Change 1994: ernments who supported them, our grateful and sincere appre-
Radiative Forcing of Climate Change and an Evaluation of the ciation for their commitment.
IPCC IS92 Emission Scenarios” to assist the Convention
process further. We take this opportunity to express our gratitude for nurturing
another IPCC report through to a successful completion to:
In 1992, the Panel reorganized its Working Groups II and III
and committed itself to complete a Second Assessment in • Professor Bolin, Chairman of the IPCC, for his able
1995, not only updating the information on the same range of leadership and skillful guidance of the IPCC
topics as in the First Assessment, but also including the new • The Co-Chairs of Working Group II, Dr. R.T. Watson
subject area of technical issues related to the economic aspects (USA) and Dr. M.C. Zinyowera (Zimbabwe)
of climate change. We applaud the IPCC for producing its • The Vice-Chairs of the Working Group, Dr. M.
Second Assessment Report (SAR) as scheduled. We are con- Beniston (Switzerland), Dr. O. Canziani (Argentina),
vinced that the SAR, as the earlier IPCC reports, would Dr. J. Friaa (Tunisia), Ing. (Mrs.) M. Perdomo
become a standard work of reference, widely used by policy- (Venezuela), Dr. M. Petit (France), Dr. S.K. Sharma
makers, scientists, and other experts. (India), Mr. H. Tsukamoto (Japan), and Professor P.
Vellinga (The Netherlands)
This volume, which forms part of the SAR, has been produced • Dr. R.H. Moss, the Head of the Technical Support
by Working Group II of the IPCC, and focuses on potential Unit of the Working Group, and his staff including
impacts of climate change, adaptive responses, and measures Mr. David Jon Dokken, Ms. Flo Ormond, Ms. Sandy
that could mitigate future emissions. It consists of 25 chapters MacCracken, and Ms. Laura VanWie, as well as Mr.
covering a wide range of ecological systems and socioeconomic Shardul Agrawala, Ms. Melissa Taylor, and Ms. Anne
sectors and activities. It also includes brief descriptions of three Tenney, who served as interns for various periods
appendices—two sets of guidelines or methodologies for with the Technical Support Unit
assessing the potential efficacy of adaptation and mitigation • Dr. N. Sundararaman, Secretary of the IPCC, and his
strategies, and an inventory of technology databases and infor- staff including Mr. S. Tewungwa, Mrs. R. Bourgeois,
mation. The appendices themselves have been or are being Ms. C. Ettori, and Ms. C. Tanikie.
published in full as separate stand-alone volumes.
As usual in the IPCC, success in producing this report has
depended upon the enthusiasm and cooperation of numerous
busy scientists and other experts world-wide. We are exceed-
ingly pleased to note here the very special efforts implemented
G.O.P. Obasi Ms. E. Dowdeswell
Secretary-General Executive Director
World Meteorological Organization United Nations Environment Programme
Preface
In June 1993, Working Group II of the Intergovernmental identified response functions and/or potential thresholds, on
Panel on Climate Change (IPCC) was asked to review the evaluating the plausibleimpactsthat would result from a par-
state of knowledge concerning the impacts of climate change ticular regional climate scenario. In essence, the approach first
on physical and ecological systems, human health, and socio- sought to clarify what was known and unknown about three
economic sectors. Working Group II also was charged with distinct issues before applying regional climate scenarios to
reviewing available information on the technical and econom- estimate potential impacts. These issues were:
ic feasibility of a range of potential adaptation and mitigation
strategies. • How sensitive is a particular system to climate
change—that is, in simplified terms, how will a sys-
This volume responds to this charge and represents a tremen- tem respond to given changes in climate? Given the
dous achievement—the coordinated contributions of well over wide range of systems reviewed in this assessment,
a thousand individuals from over 50 developed and developing these relationships are described in a variety of forms,
countries and a dozen international organizations. It includes ranging from specification of quantitative functional
introductory “primers” on ecological systems and energy pro- relationships for some systems (e.g., climate-yield
duction and use; 25 chapters, covering both vulnerability to models for agriculture, rainfall-runoff models for
climate change and options for reducing emissions or enhanc- hydrological systems, models of energy demand for
ing sinks; and three appendices that inventory mitigation tech- heating or cooling driven by temperature change) to
nologies and delineate methodologies for assessing impacts/ more qualitative relationships for other systems.
adaptations and mitigation options. • How adaptable is a particular system to climate
change—that is, to what degree are adjustments pos-
The chapters provide an overview of developments in our sci- sible in practices, processes, or structures of systems
entific understanding since the first IPCC assessments of in response to projected or actual changes of climate?
impacts and response options in 1990, and the supplemental This issue is important for both ecological and social
IPCC assessments of 1992. Uncertainties are described, with systems because it is critical to recognize that both
an eye for identifying both policy significance and research types of systems have capacities that will enable them
opportunities. In presenting this information, each team of to resist adverse consequences of new conditions or to
authors has sought to communicate its findings in way that is capitalize on new opportunities. Adaptation can be
useful to decisionmakers, research managers, and peers within spontaneous or planned, and can be carried out in
their field of research; we hope that these audiences, in addi- response to or in anticipation of changes.
tion to educators and the general public, will find this volume • Finally, how vulnerable is a system to climate
useful. change—that is, how susceptible is it to damage or
harm? Vulnerability defines the extent to which cli-
mate change may damage or harm a system. It
Approach of the Assessment depends not only on a system’s sensitivity but also on
its ability to adapt to new climate conditions. Both the
From the earliest stages of the process, participants in the magnitude and rate of climate change are important in
assessment understood the need to confront the fact that confi- determining the sensitivity, adaptability, and vulnera-
dence in regional projections of temperature, precipitation, soil bility of a system.
moisture, and other climate parameters important to impacts
models remains low, that uncertainty increases as scale Building on this sensitivity/vulnerability approach, the chap-
decreases, that patterns of climate change are interwoven with ters of the assessment distinguish, to the extent possible, uncer-
climate variability, and that regional patterns are likely to be tainties relating to remaining questions about the sensitivity,
affected by both greenhouse gases and anthropogenic aerosols, adaptability, or vulnerability of systems to climate change from
the latter of which are only now beginning to be incorporated uncertainties related to the particular regional climate scenar-
into transient GCM simulations. To provide useful information ios used in their estimation of potential impacts.
to decisionmakers, Working Group II needed to find a way to
distinguish between uncertainties arising from remaining ques-
tions about the responses of systems to a given level or rate of Levels of Confidence
climate change and uncertainties related to the regional-scale cli-
mate projections themselves. Consequently, Working Group II In the course of the assessment, Working Group II also devel-
decided to focus on assessing the sensitivity and vulnerability of oped a common approach to describe the levels of confidence
systems to a range of climate changes, and only then, having that author teams were asked to assign to the major findings in
viii Technical Preface
the executive summaries of their chapters. Several approaches because they demand different standards of proof. Moreover,
were considered, and the lead authors finally selected a there are multiple sources of uncertainty, some of which are
straight-forward, three-tiered structure: difficult to identify with precision, leading different individu-
als to make different judgments. Finally, the amount of evi-
• High Confidence—This category denotes wide agree- dence that an individual will require to view a finding as “well-
ment, based on multiple findings through multiple established” has been shown to be higher for findings that have
lines of investigation. In other words, there was a high high consequence than for findings of lesser consequence or
degree of consensus among the authors based on the for which less is at stake.
existence of substantial evidence in support of the
conclusion.
• Medium Confidence—This category indicates that Acknowledgments
there is a consensus, but not a strong one, in support
of the conclusion. This ranking could be applied to a We wish to acknowledge the tireless, voluntary efforts of
situation in which an hypothesis or conclusion is sup- authors, contributors, and reviewers (from universities, private
ported by a fair amount of information, but not a suf- and government laboratories, and industry and environmental
ficient amount to convince all participating authors, organizations). We wish to thank the following talented and
or where other less plausible hypotheses cannot yet be dedicated individuals who served as staff, interns, or volunteers
completely ruled out. at the Working Group II Technical Support Unit during portions
• Low Confidence—This category is reserved for cases of this assessment: Mr. Shardul Agrawala, Mr. David Jon
when lead authors were highly uncertain about a par- Dokken, Mr. Steve Greco, Ms. Dottie Hagag, Ms. Sandy
ticular conclusion. This uncertainty could be a reflec- MacCracken, Ms. Flo Ormond, Ms. Melissa Taylor, Ms. Anne
tion of a lack of consensus or the existence of serious Tenney, and Ms. Laura Van Wie. Without the willingness of all
competing hypotheses, each with adherents and evi- these individuals to give unstintingly of their professional
dence to support their positions. Alternatively, this expertise and free time, this assessment would not have been
ranking could result from the existence of extremely possible. We acknowledge the critical role of many program
limited information to support an initial plausible idea managers in national and international research programs who
or hypothesis. supported the work of the authors through grants and release
time from other responsibilities. We also note that the volume
Readers of the assessment need to keep in mind that while the benefitted greatly from the close working relationship estab-
confidence levels used in the report are an attempt to commu- lished with the authors and Technical Support Units of Working
nicate to decisionmakers a rough sense of the collective judg- Groups I and III. Last, but certainly not least, we wish to
ment by the authors of the degree of certainty or uncertainty acknowledge the leadership of the IPCC Chairman, Professor
that should be associated with a particular finding, they are an Bert Bolin, and the IPCC Secretary, Dr. N. Sundararaman.
imperfect tool. In particular, it should be noted that assigning
levels of confidence to research findings is a subjective Robert T. Watson
process; different individuals will assign different levels of M.C. Zinyowera
confidence to the same findings and the same base of evidence Richard H. Moss
Summary for Policymakers:
Scientific-Technical Analyses of Impacts,
Adaptations, and Mitigation of Climate Change
A Report of Working Group II
of the Intergovernmental Panel on Climate Change
CONTENTS
1. Scope of the Assessment 3
2. Nature of the Issue 3
3. Vulnerability to Climate Change 4
3.1. Terrestrial and Aquatic Ecosystems 5
3.2. Hydrology and Water Resources Management 8
3.3. Food and Fiber 9
3.4. Human Infrastructure 9
3.5. Human Health 11
4. Options to Reduce Emissions and Enhance Sinks of Greenhouse Gases 12
4.1. Energy, Industrial Process, and Human Settlement Emissions 12
4.1.1. Energy Demand 13
4.1.2. Mitigating Industrial Process and Human Settlement Emissions 14
4.1.3. Energy Supply 14
4.1.4. Integration of Energy System Mitigation Options 15
4.2. Agriculture, Rangelands, and Forestry 16
4.3. Cross-Sectoral Issues 17
4.4. Policy Instruments 18
Authors/Contributors 18
Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change 3
1. Scope of the Assessment
Box 1. Ultimate Objective of the UNFCCC (Article 2)
The charge to Working Group II of the Intergovernmental
Panel on Climate Change (IPCC) was to review the state of “...stabilization of greenhouse gas concentrations in the
knowledge concerning the impacts of climate change on phys- atmosphere at a level that would prevent dangerous
ical and ecological systems, human health, and socioeconomic anthropogenic interference with the climate system.
sectors. Working Group II also was charged with reviewing Such a level should be achieved within a time frame
available information on the technical and economic feasibili- sufficient to allow ecosystems to adapt naturally to cli-
ty of a range of potential adaptation and mitigation strategies. mate change, to ensure that food production is not
This assessment provides scientific, technical, and economic threatened, and to enable economic development to
information that can be used, inter alia, in evaluating whether proceed in a sustainable manner.”
the projected range of plausible impacts constitutes “dangerous
anthropogenic interference with the climate system,” as
referred to in Article 2 of the United Nations Framework precipitation, soil moisture, and sea level. Based on the range
Convention on Climate Change (UNFCCC), and in evaluat- of sensitivities of climate to increases in greenhouse gas con-
ing adaptation and mitigation options that could be used in centrations reported by IPCC Working Group I and plausible
progressing towards the ultimate objective of the UNFCCC ranges of emissions (IPCC IS92; see Table 1), climate models,
(see Box 1). taking into account greenhouse gases and aerosols, project an
increase in global mean surface temperature of about 1–3.5°C
by 2100, and an associated increase in sea level of about 15–95
2. Nature of the Issue cm. The reliability of regional-scale predictions is still low, and
the degree to which climate variability may change is uncer-
Human activities are increasing the atmospheric concentrations tain. However, potentially serious changes have been identi-
of greenhouse gases—which tend to warm the atmosphere— fied, including anincrease in some regions in the incidence of
and, in some regions, aerosols—which tend to cool the atmos- extreme high-temperature events, floods, and droughts, with
phere. These changes in greenhouse gases and aerosols, taken resultant consequences for fires, pest outbreaks, and ecosystem
together, are projected to lead to regional and global changes in composition, structure, and functioning, including primary
climate and climate-related parameters such as temperature, productivity.
Table 1: Summary of assumptions in the six IPCC 1992 alternative scenarios.
Scenario Population Economic Growth Energy Supplies
IS92a,b World Bank 1991 1990–2025: 2.9% 12,000 EJ conventional oil
11.3 billion by 2100 1990–2100: 2.3% 13,000 EJ natural gas
Solar costs fall to $0.075/kWh
191 EJ of biofuels available at $70/barrela
IS92c UN Medium-Low Case 1990–2025: 2.0% 8,000 EJ conventional oil
6.4 billion by 2100 1990–2100: 1.2% 7,300 EJ natural gas
Nuclear costs decline by 0.4% annually
IS92d UN Medium-Low Case 1990–2025: 2.7% Oil and gas same as IS92c
6.4 billion by 2100 1990–2100: 2.0% Solar costs fall to $0.065/kWh
272 EJ of biofuels available at $50/barrel
IS92e World Bank 1991 1990–2025: 3.5% 18,400 EJ conventional oil
11.3 billion by 2100 1990–2100: 3.0% Gas same as IS92a,b
Phase out nuclear by 2075
IS92f UN Medium-High Case 1990–2025: 2.9% Oil and gas same as IS92e
17.6 billion by 2100 1990–2100: 2.3% Solar costs fall to $0.083/kWh
Nuclear costs increase to $0.09/kWh
aApproximate conversion factor: 1 barrel = 6 GJ.
Source: IPCC, 1992: Emissions scenarios for IPCC: an update. In: Climate Change 1992: The Supplementary Report to the
IPCC Scientific Assessment[J.T. Houghton, B.A. Callander, and S.K. Varney (eds.)]. Section A3, prepared by J. Leggett,
W.J. Pepper, and R.J. Swart, and WMO/UNEP. Cambridge University Press, Cambridge, UK, 200 pp.
4 Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change
Human health, terrestrial and aquatic ecological systems, and Options for adapting to change or mitigating change that can
socioeconomic systems (e.g., agriculture, forestry, fisheries, be justified for other reasons today (e.g., abatement of air
and water resources) are all vital to human development and and water pollution) and make society more flexible or
well-being and are all sensitive to changes in climate. Whereas resilient to anticipated adverse effects of climate change
many regions are likely to experience the adverse effects of cli- appear particularly desirable.
mate 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 3. Vulnerability to Climate Change
variety of changes and the need to adaptto them.
Article 2 of the UNFCCC explicitly acknowledges the impor-
Policymakers are faced with responding to the risks posed by tance of natural ecosystems, food production, and sustainable
anthropogenic emissions of greenhouse gases in the face of economic development. This report addresses the potential
significant scientific uncertainties. It is appropriate to con- sensitivity, adaptability, and vulnerability of ecological and
sider these uncertainties in the context of information indi- socioeconomic systems—including hydrology and water
cating that climate-induced environmental changes cannot resources management, human infrastructure, and human
be reversed quickly, if at all, due to the long time scales asso- health—to changes in climate (see Box 3).
ciated with the climate system (see Box 2). Decisions taken
during the next few years may limit the range of possible Human-induced climate change adds an important new
policy options in the future because high near-term emis- stress. Human-induced climate change represents an important
sions would require deeper reductions in the future to meet additional stress, particularly to the many ecological and
any given target concentration. Delaying action might reduce socioeconomic systems already affected by pollution, increas-
the overall costs of mitigation because of potential techno- ing resource demands, and nonsustainable management prac-
logical advances but could increase both the rate and the tices. The most vulnerable systems are those with the greatest
eventual magnitude of climate change, hence the adaptation sensitivity to climate changes and the least adaptability.
and damage costs.
Most systems are sensitive to climate change. Natural eco-
Policymakers will have to decide to what degree they want logical systems, socioeconomic systems, and human health are
to take precautionary measures by mitigating greenhouse gas all sensitive to both the magnitude and the rate of climate
emissions and enhancing the resilience of vulnerable sys- change.
tems by means of adaptation. Uncertainty does not mean that
a nation or the world community cannot position itself better Impacts are difficult to quantify, and existing studies are
to cope with the broad range of possible climate changes or limited in scope. Although our knowledge has increased sig-
protect against potentially costly future outcomes. Delaying nificantly during the last decade, and qualitative estimates can
such measures may leave a nation or the world poorly pre- be developed, quantitative projections of the impacts of cli-
pared to deal with adverse changes and may increase the mate change on any particular system at any particular location
possibility of irreversible or very costly consequences. are difficult because regional-scale climate change predictions
are uncertain; our current understanding of many critical
processes is limited; and systems are subject to multiple cli-
Box 2. Time Scales of Processes matic and non-climatic stresses, the interactions of which are
Influencing the Climate System not always linear or additive. Most impact studies have
assessed how systems would respond to climate change result-
• Turnover of the capital stock responsible for emis- ing from an arbitrary doubling of equivalent atmospheric car-
sions of greenhouse gases: Years to decades bon dioxide (CO ) concentrations. Furthermore, very few
2
(without premature retirement) studies have considered dynamic responses to steadily increas-
• Stabilization of atmospheric concentrations of long- ing concentrations of greenhouse gases; fewer still have exam-
lived greenhouse gases given a stable level of ined the consequences of increases beyond a doubling of
greenhouse gas emissions: Decades to millennia equivalent atmospheric CO concentrations or assessed the
2
• Equilibration of the climate system given a stable implications of multiple stress factors.
level of greenhouse gas concentrations:
Decades to centuries Successful adaptation depends upon technological advances,
• Equilibration of sea level given a stable climate: institutional arrangements, availability of financing, and
Centuries information exchange. Technological advances generally have
• Restoration/rehabilitation of damaged or disturbed increased adaptation options for managed systems such as agri-
ecological systems: Decades to centuries culture and water supply. However, many regions of the world
(some changes, such as species extinction, are irre- currently have limited access to these technologies and appro-
versible, and it may be impossible to reconstruct priate information. The efficacy and cost-effective use of adap-
and reestablish some disturbed ecosystems) tation strategies will depend upon the availability of finan-
cial resources, technology transfer, and cultural, educational,