1039
19
Emergent Risks
and Key Vulnerabilities
Coordinating Lead Authors:
Michael Oppenheimer (USA), Maximiliano Campos (Costa Rica), Rachel Warren (UK)
Lead Authors:
Joern Birkmann (Germany), George Luber (USA), Brian O’Neill (USA), Kiyoshi Takahashi
(Japan)
Contributing Authors:
Franz Berkhout (Netherlands), Pauline Dube (Botswana), Wendy Foden (South Africa),
Stefan Greiving (Germany), Solomon Hsiang (USA), Matt Johnston (USA), Klaus Keller (USA),
Joan Kleypas (USA), Robert Kopp (USA), Rachel Licker (USA), Carlos Peres (UK), Jeff Price
(UK), Alan Robock (USA), Wolfram Schlenker (USA), John Richard Stepp (USA), Richard Tol
(UK), Detlef van Vuuren (Netherlands)
Review Editors:
Mike Brklacich (Canada), Sergey Semenov (Russian Federation)
Volunteer Chapter Scientists:
Rachel Licker (USA), Solomon Hsiang (USA)
This chapter should be cited as:
Oppenheimer
, M., M. Campos, R. Warren, J. Birkmann, G. Luber, B. O’Neill, and K. Takahashi, 2014: Emergent risks
and key vulnerabilities. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and
Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir,
M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken,
P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and
New York, NY, USA, pp. 1039-1099.
19
1040
Executive Summary ......................................................................................................................................................... 1042
19.1. Purpose, Scope, and Structure of this Chapter ..................................................................................................... 1046
19.1.1. Historical Development of this Chapter .......................................................................................................................................... 1046
19.1.2. The Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation .................. 1047
Box 19-1. Article 2 of the United Nations Framework Convention on Climate Change ........................................................... 1047
Box 19-2. Definitions ................................................................................................................................................................. 1048
19.1.3. New Developments in this Chapter ................................................................................................................................................ 1049
19.2. Framework for Identifying Key Vulnerabilities, Key Risks, and Emergent Risks ................................................... 1050
19.2.1. Risk and Vulnerability ..................................................................................................................................................................... 1050
19.2.2. Criteria for Identifying Key Vulnerabilities and Key Risks ................................................................................................................ 1050
19.2.2.1. Criteria for Identifying Key Vulnerabilities ....................................................................................................................... 1051
19.2.2.2. Criteria for Identifying Key Risks ...................................................................................................................................... 1051
19.2.3. Criteria for Identifying Emergent Risks ........................................................................................................................................... 1052
19.2.4. Identifying Key and Emergent Risks under Alternative Development Pathways .............................................................................. 1052
19.2.5. Assessing Key Vulnerabilities and Emergent Risks .......................................................................................................................... 1052
19.3. Emergent Risk: Multiple Interacting Systems and Stresses .................................................................................. 1053
19.3.1. Limitations of Previous Approaches Imply Key Risks Overlooked .................................................................................................... 1053
19.3.2. Examples of Emergent Risks ........................................................................................................................................................... 1053
19.3.2.1. Emergent Risks Arising from the Effects of Degradation of Ecosystem Services by Climate Change ............................... 1053
19.3.2.2. Emergent Risk Involving Non-Climate Stressors: The Management of Water, Land, and Energy ...................................... 1054
19.3.2.3. Emergent Risks Involving Health Effects ......................................................................................................................... 1056
19.3.2.4. Spatial Convergence of Multiple Impacts: Areas of Compound Risk ................................................................................ 1057
19.4. Emergent Risk: Indirect, Trans-boundary, and Long-Distance Impacts ................................................................. 1059
19.4.1. Crop Production, Prices, and Risk of Increased Food Insecurity ...................................................................................................... 1059
19.4.2. Indirect, Trans-boundary, and Long-Distance Impacts of Adaptation .............................................................................................. 1060
19.4.2.1. Risks Associated with Human Migration and Displacement ............................................................................................ 1060
19.4.2.2. Risk of Conflict and Insecurity ......................................................................................................................................... 1060
19.4.2.3. Risks Associated with Species Range Shifts ..................................................................................................................... 1061
19.4.3. Indirect, Trans-boundary, and Long-Distance Impacts of Mitigation Measures ............................................................................... 1061
19.5. Newly Assessed Risks ........................................................................................................................................... 1062
19.5.1. Risks from Large Global Temperature Rise >4°C above Preindustrial Levels .................................................................................. 1062
19.5.2. Risks from Ocean Acidification ....................................................................................................................................................... 1064
19.5.3. Risks from Carbon Dioxide Health Effects ....................................................................................................................................... 1064
19.5.4. Risks from Geoengineering (Solar Radiation Management) ........................................................................................................... 1065
Table of Contents
1041
Emergent Risks and Key Vulnerabilities Chapter 19
19
19.6. Key Vulnerabilities, Key Risks, and Reasons for Concern ...................................................................................... 1066
19.6.1. Key Vulnerabilities .......................................................................................................................................................................... 1066
19.6.1.1. Dynamics of Exposure and Vulnerability .......................................................................................................................... 1066
19.6.1.2. Differential Vulnerability and Exposure ........................................................................................................................... 1066
19.6.1.3. Trends in Exposure and Vulnerability ............................................................................................................................... 1067
19.6.1.4. Risk Perception ................................................................................................................................................................ 1068
19.6.2. Key Risks ......................................................................................................................................................................................... 1069
19.6.2.1. Assessing Key Risks ......................................................................................................................................................... 1069
19.6.2.2. The Role of Adaptation and Alternative Development Pathways ..................................................................................... 1072
19.6.3. Updating Reasons for Concern ....................................................................................................................................................... 1073
19.6.3.1. Variations in Reasons for Concern across Socioeconomic Pathways ............................................................................... 1074
19.6.3.2. Unique and Threatened Systems ...................................................................................................................................... 1075
19.6.3.3. Extreme Weather Events .................................................................................................................................................. 1076
19.6.3.4. Distribution of Impacts .................................................................................................................................................... 1077
19.6.3.5. Global Aggregate Impacts ............................................................................................................................................... 1078
19.6.3.6. Large-Scale Singular Events: Physical, Ecological, and Social System Thresholds and Irreversible Change ....................... 1079
19.7. Assessment of Response Strategies to Manage Risks .......................................................................................... 1080
19.7.1. Relationship between Adaptation Efforts, Mitigation Efforts, and Residual Impacts ....................................................................... 1080
19.7.2. Limits to Mitigation ........................................................................................................................................................................ 1083
19.7.3. Avoiding Thresholds, Irreversible Change, and Large-Scale Singularities in the Earth System ......................................................... 1084
19.7.4. Avoiding Tipping Points in Social/Ecological Systems ..................................................................................................................... 1085
19.7.5. Limits to Adaptation ....................................................................................................................................................................... 1085
References ....................................................................................................................................................................... 1085
Frequently Asked Questions
19.1: Does science provide an answer to the question of how much warming is unacceptable? ............................................................ 1047
19.2: How does climate change interact with and amplify preexisting risks? .......................................................................................... 1057
19.3: How can climate change impacts on one region cause impacts on other distant areas? ............................................................... 1062
1042
Chapter 19 Emergent Risks and Key Vulnerabilities
19
Executive Summary
This chapter assesses climate-related risks in the context of Article 2 of the United Nations Framework Convention on Climate
Change (UNFCCC). {Box 19.1} Such risks arise from the interaction of the evolving exposure and vulnerability of human, socioeconomic,
and biological systems with changing physical characteristics of the climate system. {19.2} Alternative development paths influence risk by
changing the likelihood of climatic events and trends (through their effects on greenhouse gases (GHGs) and other emissions) and by altering
vulnerability and exposure. {19.2.4, Figure 19-1, Box 19-2}
Interactions of climate change impacts on one sector with changes in exposure and vulnerability, as well as adaptation and
mitigation actions affecting the same or a different sector are generally not included or well integrated into projections of risk.
However, their consideration leads to the identification of a variety of emergent risks {Box 19-2} that were not previously
assessed or recognized (high confidence). {19.3}
This chapter identifies several such complex system interactions that increase vulnerability
and risk synergistically. For example:
The risk of climate change to human systems (e.g., agriculture and water supply) is increased by the loss of ecosystem services
that are supported by biodiversity (e.g., water purification, protection from extreme weather events, preservation of soils, recycling of
nutrients, and pollination of crops) (high confidence). Studies since the Fourth Assessment Report (AR4) broadly confirm that a large
proportion of species are at increased risk of extinction at all but the lowest levels of warming. {19.3.2.1, 19.5.1, 19.6.3.5}
Risks result from the management of water, land, and energy in the context of climate change. For example, in some water
stressed regions, as groundwater stores that have historically acted as buffers against impacts of climate variations and change are
depleted, adverse consequences arise for human systems and ecosystems simultaneously undergoing alteration of regional groundwater
resources due to climate change. The production of bioenergy crops to mitigate climate change leads to land conversion (e.g., from food
crops and unmanaged ecosystems to energy crops; high confidence) and in some scenarios, reduced food security as well as additional
GHG emissions over the course of decades or centuries. {19.3.2.2}
Climate change has the potential to adversely affect human health by increasing exposure and vulnerability to a variety of
stresses. For example, the interaction of climate change with food security can exacerbate malnutrition, increasing vulnerability of
individuals to a range of diseases (high confidence). {19.3.2.3}
The risk of severe harm and loss due to climate change-related hazards and various vulnerabilities is particularly high in large
urban and rural areas in low-lying coastal zones (high confidence). These areas, many characterized by increasing populations, are
exposed to multiple hazards and potential failures of critical infrastructure, generating new systemic risks. Cities in Asian megadeltas,
where populations are subject to sea level rise, storm surge, coastal erosion, saline intrusion, and flooding, provide an example. {19.2.3,
19.3.2.4, 19.4.2.1, 19.6.1.3.1, 19.6.2.1, 19.7.5, Table 19-4}
Spatial convergence of impacts in different sectors creates compound risk in many areas (medium confidence). Examples
include the Arctic (where thawing and sea ice loss disrupt land transportation, buildings, other infrastructure, and are projected to disrupt
indigenous culture); and the environs of Micronesia, Mariana Island, and Papua New Guinea (where coral reefs are highly threatened due
to exposure to concomitant sea surface temperature rise and ocean acidification). {19.3.2.4}
Emergent risks also arise from indirect, trans-boundary, and long-distance impacts of climate change. Adaptive responses and
mitigation measures sometimes increase such risks (high confidence). {19.4}
Human or ecological responses to local impacts of climate
change can generate harm at distant places.
Increasing prices of food commodities on the global market due to local climate impacts, in conjunction with other stressors, decrease food
security and exacerbate food insecurity at distant locations. {19.4.1}
Climate change will bear significant consequences for human migration flows at particular times and places, creating risks as well as
benefits for migrants and for sending and receiving regions and states (high confidence). {19.4.2.1}
The effect of climate change on conflict and insecurity is an emergent risk because factors such as poverty and economic shocks that are
associated with a higher risk of violent conflict are themselves sensitive to climate change. In numerous statistical studies, the influence of
climate variability on violent conflict is large in magnitude (medium confidence). {19.4.2.2}
Many species shift their ranges in response to climate change, adversely affecting ecosystem function and services while presenting new
challenges to conservation efforts (medium confidence). {19.4.2.3}
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Emergent Risks and Key Vulnerabilities Chapter 19
19
Mitigation measures taken in one location can have long-distance or indirect impacts on biodiversity and/or human systems. For example,
the development of biofuels as energy sources can increase food prices (high confidence) and affect distant land use practices. {19.4.1,
19.4.3}
Additional risks related to particular biophysical impacts of climate change have arisen recently in the literature in sufficient
detail to permit assessment (high confidence). {19.5}
Risks associated with global temperature rise in excess of 4°C relative to preindustrial levels
1
arise from severe and widespread
impacts on unique and threatened systems, substantial species extinction, extensive loss of ecosystem functioning, large risks to global and
regional food security, and the combination of high temperature and humidity compromising normal human activities, including growing
food or working outdoors in some areas for parts of the year (high confidence) and the potential for traversing thresholds that lead to
disproportionately large Earth systems responses (medium confidence). {19.5.1}
Ocean acidification poses risks to marine ecosystems and the societies that depend on them. For example, ocean acidification is
very likely to lead to changes in coral calcification rates. Reduced coral calcification is projected to have impacts of medium to high
magnitude on some ecosystem services, including tourism and the provisioning of fishing. {19.5.2}
There is increasing evidence in the literature that high ambient carbon dioxide (CO
2
) concentrations in the atmosphere will
affect human health by increasing the production and allergenicity of pollen and allergenic compounds and by decreasing
nutritional quality of important food crops. {19.5.3}
In addition to providing potential climate change abatement benefits, geoengineering poses widespread risks to society and
ecosystems. For example, in some model experiments the implementation of Solar Radiation Management (SRM) for the purpose of limiting
global warming leads to ozone depletion and reduces precipitation. In addition, the failure or abrupt halting of SRM risks rapid climate
change. {19.5.4}
Global, regional, and local socioeconomic, environmental, and governance trends indicate that vulnerability and exposure of
communities or social-ecological systems to climatic hazards related to extreme events are dynamic and thus vary across temporal
and spatial scales (high confidence).
Effective risk reduction and adaptation strategies consider these dynamics and the inter-linkages between
socioeconomic development pathways and the vulnerability and exposure of people. Changes in poverty or socioeconomic status, ethnic
composition, age structure, and governance had a significant influence on the outcome of past crises associated with climatic hazards. {19.6.1}
Challenges for vulnerability reduction and adaptation actions are particularly high in regions that have shown severe difficulties
in governance. Studies confirm that countries that are classified as failed states and afflicted by violence are often not able to reduce
vulnerability effectively. Unless governance improves in countries with severe governance failure, risk will increase as a result of climate
changes interacting with increased human vulnerability (high confidence). {19.6.1.3.3}
Key risks inform evaluation of “dangerous anthropogenic interference with the climate system, in the terminology of UNFCCC
Article 2. These are potentially severe adverse consequences for humans and social-ecological systems resulting from the
interaction of hazards linked to climate change and the vulnerability of exposed societies and systems. Key risks were identified
in this assessment based on expert judgments made by authors of the various chapters of this report in light of criteria described
here {19.2.2.2} and consolidated into the following representative list (high confidence).
{19.2.2.2, 19.6.2.1, Table 19-4, Boxes 19-2
and CC-KR} (Roman numerals indicate corresponding entries in Table 19-4; notation at end of each entry indicates corresponding Reasons for
Concern (RFCs), discussed below.)
1
Levels of global mean temperature change are variously presented in the literature with respect to “preindustrial” temperatures in a specified year or period, e.g., 1850–1900.
Alternatively, the average temperature within a recent period, e.g., 1986–2005, is used as a baseline. In this chapter, we use both, depending on the literature being assessed.
The increase above preindustrial (1850–1900) levels for the period 1986–2005 is estimated at 0.61°C (WGI AR5 Section 11.3.6.3). For example, using these baselines, a 2°C
increase above preindustrial levels corresponds to a 1.39°C increase above 1986–2005 levels. We use other baselines on occasion depending on the literature cited and explicitly
indicate where this is the case. Climate impact studies often report outcomes as a function of regional temperature change, which can differ significantly from changes in global
mean temperature. In most land areas, regional warming is larger than global warming (WGI AR5 Section 10.3.1.1.2). However, given the many conventions in the literature
for baseline periods, readers are advised to check carefully and to adjust baseline levels for consistency when comparing outcomes.
1044
Chapter 19 Emergent Risks and Key Vulnerabilities
19
i) Risk of death, injury, ill-health, or disrupted livelihoods in low-lying coastal zones and small island developing states and other small islands,
due to storm surges, coastal flooding, and sea level rise. [RFC 1-5]
ii) Risk of severe ill-health and disrupted livelihoods for large urban populations due to inland flooding in some regions. [RFC 2 and 3]
iii) Systemic risks due to extreme weather events leading to breakdown of infrastructure networks and critical services such as electricity,
water supply, and health and emergency services. [RFC 2-4]
iv) Risk of mortality and morbidity during periods of extreme heat, particularly for vulnerable urban populations and those working outdoors
in urban or rural areas. [RFC 2 and 3]
v) Risk of food insecurity and the breakdown of food systems linked to warming, drought, flooding, and precipitation variability and extremes,
particularly for poorer populations in urban and rural settings. [RFC 2-4]
vi) Risk of loss of rural livelihoods and income due to insufficient access to drinking and irrigation water and reduced agricultural productivity,
particularly for farmers and pastoralists with minimal capital in semi-arid regions. [RFC 2 and 3]
vii) Risk of loss of marine and coastal ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for coastal
livelihoods, especially for fishing communities in the tropics and the Arctic. [RFC 1, 2, and 4]
viii) Risk of loss of terrestrial and inland water ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for
livelihoods. [RFC 1, 3, and 4]
Climate change risks vary substantially across plausible alternative development pathways and the relative importance of
development and climate change varies by sector, region, and time period; both are important to understanding possible
outcomes (high confidence).
In some cases, there is substantial potential for adaptation to reduce risks, with development pathways playing
a key role in determining challenges to adaptation, including through their effects on ecosystems and ecosystem services. {19.6.2.2}
Assessment of the RFC framework pertinent to Article 2 of the UNFCCC has led to evaluations of risk being updated in light of
the advances since the AR4. {19.6.3}
(All temperature changes are relative to 1986–2005, i.e., “recent.” Numbers are indicative of RFC
designation in key risk enumeration, above.)
1.
Unique and threatened systems: Some unique and threatened systems, including ecosystems and cultures, are already at risk from climate
change (high confidence). The number of such systems at risk of severe consequences is higher with additional warming of around 1°C.
Many species and systems with limited adaptive capacity are subject to very high risks with additional warming of 2°C, particularly Arctic-
sea-ice and coral-reef systems. {19.6.3.2}
2.
Extreme weather events: Climate-change-related risks from extreme events, such as heat waves, extreme precipitation, and coastal
flooding, are already moderate (high confidence) and high with 1°C additional warming (medium confidence). Risks associated with some
types of extreme events (e.g., extreme heat) increase further at higher temperatures (high confidence). {19.6.3.3}
3.
Distribution of impacts: Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries
at all levels of development. Risks are already moderate because of regionally differentiated climate-change impacts on crop production in
particular (medium to high confidence). Based on projected decreases in regional crop yields and water availability, risks of unevenly
distributed impacts are high for additional warming above 2°C (medium confidence). {19.6.3.4}
4.
Global aggregate impacts: Risks of global aggregate impacts are moderate for additional warming between 1-2°C, reflecting impacts to
both Earth’s biodiversity and the overall global economy (medium confidence). Extensive biodiversity loss with associated loss of ecosystem
goods and services results in high risks around 3°C additional warming (high confidence). Aggregate economic damages accelerate with
increasing temperature (limited evidence, high agreement), but few quantitative estimates have been completed for additional warming
around 3°C or above. {19.3.2.1, 19.5.1, 19.6.3.5}
5.
Large-scale singular events: With increasing warming, some physical systems or ecosystems may be at risk of abrupt and irreversible
changes. Risks associated with such tipping points become moderate between 0-1°C additional warming, due to early warning signs that
both warm-water coral reef and Arctic ecosystems are already experiencing irreversible regime shifts (medium confidence). Risks increase
disproportionately as temperature increases between 1-2°C additional warming and become high above 3°C, due to the potential for a
large and irreversible sea level rise from ice sheet loss. For sustained warming greater than some threshold, near-complete loss of the
Greenland ice sheet would occur over a millennium or more, contributing up to 7 m of global mean sea level rise. {19.6.3.6}
1045
Emergent Risks and Key Vulnerabilities Chapter 19
19
Impacts of climate change avoided under a range of scenarios for mitigation of GHG emissions are potentially large and increasing
over the 21st century (high confidence). {19.7.1}
Among the impacts assessed here, benefits from mitigation are most immediate for surface
ocean acidification and least immediate for impacts related to sea level rise. Because mitigation reduces the rate as well as the magnitude of
warming, it also increases the time available for adaptation to a particular level of climate change, potentially by several decades.
Only mitigation scenarios in the most stringent category (i.e., with 2100 CO
2
-eq concentrations of 430 to 480 ppm) maintain
moderately healthy coral reefs (medium confidence). With respect to the RFCs, only the most stringent of scenarios in this category
constrain overall risks to unique and threatened systems, and those associated with extreme weather events to a moderate level,
while the other scenarios in this category create risk in the high range for these two RFCs. The most stringent among these
scenarios constrain the level of risk associated with all other RFCs to the moderate level (high confidence). {19.6.3.2-3, 19.7.1}
The higher part of the range of GHG emission scenarios in the literature, that is, those with 2100 CO
2
-eq concentrations above
720 ppm create risks associated with extreme weather events and large-scale singular events that are in the high range, and
very high range (reflecting inability to adapt) for unique and threatened systems. Risks associated with the distribution of impacts
increase toward the very high range (high confidence). Risks of global aggregate impacts transition from moderate to high as
CO
2
-eq concentrations increase from 720 ppm. {19.6.3.2, 19.6.3.4, 19.7.1}
Under any plausible scenario for mitigation and adaptation, some degree of risk from residual damages is unavoidable (very high
confidence).
For example, very few integrated assessment model-based scenarios in the literature demonstrate the feasibility of limiting
warming to a maximum of 1.5°C with at least 50% likelihood. {19.7.1-2}
The risk of crossing tipping points (critical thresholds) in the Earth system or socio-ecological systems is projected to decrease
with reduced GHG emissions {19.7.3}, and the risk of crossing tipping points in socio-ecological systems can also be reduced by
reducing human vulnerability or by preserving ecosystem services, or both (medium confidence). {19.7.4}
The risk of crossing tipping
points is reduced by limiting the level of climate change and/or removing concomitant stresses such as overgrazing, overfishing, and pollution,
but there is low confidence in the level of climate change associated with such tipping points and measures to avoid them.
1046
Chapter 19 Emergent Risks and Key Vulnerabilities
19
19.1. Purpose, Scope, and Structure
of this Chapter
The objective of this chapter is to assess new literature published
since the Fourth Assessment Report (AR4) on emergent risks and key
vulnerabilities to climate change from the perspective of the distribution
of risk over geographic location, economic sector, time period, and
socioeconomic characteristics of individuals and societies. Frameworks
used in previous IPCC reports to assess risk in the context of Article 2
of the United Nations Framework Convention on Climate Change
(UNFCCC) are updated and extended in light of new literature, and
additional frameworks arising in recent literature are examined. A
focal point of this chapter is the interaction of the changing physical
characteristics of the climate system with evolving characteristics of
socioeconomic and biological systems (exposure and vulnerability) to
produce risk (see Figure 19-1). Given the centrality of Article 2 to this
chapter, the greater emphasis is on harmful outcomes of climate change
rather than potential benefits.
19.1.1. Historical Development of this Chapter
The Third and Fourth Assessment Reports (TAR and AR4, respectively)
each devoted chapters to evaluating the state of knowledge relevant
t
o Article 2 of the UNFCCC (Smith et al., 2001; Schneider et al., 2007;
see Box 19-1). The TAR sorted and aggregated impacts discussed in
the literature according to a framework called Reasons for Concern
(RFCs), and assessed the level of risk associated with individual impacts
of climate change as well as each category or reason” as a whole,
generally as a function of global mean warming. This assessment took
account of the distribution of vulnerability across particular regions,
countries, and sectors.
AR4 furthered the discussion relevant to Article 2 by assessing new
literature and developing criteria potentially useful for policy makers in
the determination of key impacts and vulnerabilities, that is, those
meriting particular attention in respect to Article 2. See Box 19-2 for
definitions of Reasons for Concern, Key Vulnerabilities (KVs), and related
terms. Some definitions go beyond those in the Glossary to provide
details especially pertinent to this chapter.
AR4 emphasized the differences in vulnerability between developed
and developing countries but also assessed new literature describing
vulnerability pertaining to various aggregations of people (such as by
ethnic, cultural, age, gender, or income status) and response strategies
for avoiding key impacts. The RFCs were updated and the Synthesis
Report (IPCC, 2007a) noted that they “remain a viable framework to
consider key vulnerabilities” (IPCC, 2007a, Section 5.2). However, their
EMISSIONS
and Land-use Change
Vulnerability
Exposure
RISK
Hazards
Anthropogenic
Climate Change
Socioeconomic
Pathways
Adaptation and
Mitigation
Actions
Governance
IMPACTS
Natural
Variability
SOCIOECONOMIC
PROCESSES
CLIMATE
Key
Emergent
Figure 19-1 | Schematic of the interaction among the physical climate system, exposure, and vulnerability producing risk. The figure visualizes the different terms and concepts
discussed in this chapter. Risk of climate-related impacts results from the interaction of climate-related hazards (including hazardous events and trends) with the vulnerability and
exposure of human and natural systems. The definition and use of “key” and “emergent” are indicated in Box 19-2 and the Glossary. Vulnerability and exposure are, as the figure
shows, largely the result of socioeconomic pathways and societal conditions (although changing hazard patterns also play a role; see Section 19.6.1.1). Changes in both the
climate system (left side) and socioeconomic processes (right side) are central drivers of the different core components (vulnerability, exposure, and hazards) that constitute risk
(modified version of SREX Figure SPM.1 (IPCC, 2012a)).
R
1047
Emergent Risks and Key Vulnerabilities Chapter 19
19
u
tility was limited by several factors: the lack of a time dimension (i.e.,
representation of impacts arising from timing and rates of climate
change and climate forcing); the focus on risk only as a function of
global mean temperature; lack of a clear distinction between impacts
and vulnerability; and, importantly, incomplete incorporation of the
evolving socioeconomic context, particularly adaptation capacity, in
representing impacts and vulnerability.
19.1.2. The Special Report on Managing the Risks
of Extreme Events and Disasters to Advance
Climate Change Adaptation
The IPCC Special Report on Managing the Risks of Extreme Events and
Disasters to Advance Climate Change Adaptation (SREX; IPCC, 2012a)
provides additional insights with respect to two RFCs (risks associated
with extreme weather events and the distribution of impacts) and
particularly the distribution of capacities to adapt to extreme events
across countries, communities, and other groups, and the limitations on
implementation of these capacities. SREX emphasized the role of the
socioeconomic setting and development pathway (expressed through
exposure and vulnerability) in determining, on the one hand, the
circumstances where extreme events do or do not result in extreme
Box 19-1 | Article 2 of the United Nations
Framework Convention on
Climate Change
Article 2
OBJECTIVE: The ultimate objective of this Convention
and any related legal instruments that the Conference of
the Parties may adopt is to achieve, in accordance with the
relevant provisions of the Convention, stabilization of
greenhouse gas concentrations in the atmosphere at a level
that would prevent dangerous anthropogenic 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 economic development to
proceed in a sustainable manner.
Frequently Asked Questions
FAQ 19.1 | Does science provide an answer to the question of
how much warming is unacceptable?
No. Careful, critical scientific research and assessment can provide information to help society consider what levels
of warming or climate change impacts are unacceptable. However, the answer is ultimately a subjective judgment
that depends on values and culture, as well as socioeconomic and psychological factors, all of which influence how
people perceive risk in general and the risk of climate change in particular. The question of what level of climate
change impacts is unacceptable is ultimately not just a matter of the facts, but of how we feel about those facts.
This question is raised in Article 2 of the UNFCCC. The criterion, in the words of Article 2, is “dangerous anthropogenic
interference with the climate system”—a framing that invokes both scientific analysis and human values.
Agreements reached by governments since 2009, meeting under the auspices of the UNFCCC, have recognized “the
scientific view that the increase in global temperature should be below 2 degrees Celsius” (Section 19.1, UNFCCC,
Copenhagen Accord). Still, as informed on the subject as the scientists referred to in this statement may be, theirs
is just one valuable perspective. How each country or community will define acceptable or unacceptable levels,
essentially deciding what is “dangerous,” is a societal judgment.
Science can certainly help society think about what is unacceptable. For example, science can identify how much
monetary loss might occur if tropical cyclones grow more intense or heat waves more frequent, or identify the land
that might be lost in coastal communities for various levels of higher seas. But “acceptability” depends on how
each community values those losses. This question is more complex when loss of life is involved and yet more so
when damage to future generations is involved. These are highly emotional and controversial value propositions
that science can only inform, not decide.
The purpose of this chapter is to highlight key vulnerabilities and key risks that science has identified; however, it
is up to people and governments to determine how the associated impacts should be valued, and whether and
how the risks should be acted upon.
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Box 19-2 | Definitions
Exposure: The presence of people, livelihoods, species or ecosystems, environmental functions, services, and resources, infrastructure,
or economic, social, or cultural assets in places and settings that could be adversely affected.
Vulnerability: The propensity or predisposition to be adversely affected. Vulnerability encompasses a variety of concepts and elements
including sensitivity or susceptibility to harm and lack of capacity to cope and adapt.
A broad set of factors such as wealth, social status, and gender determine vulnerability and exposure to climate-related risk.
Impacts: (Consequences, Outcomes) Effects on natural and human systems. In this report, the term impacts is used primarily to refer
to the effects on natural and human systems of extreme weather and climate events and of climate change. Impacts generally refer
to effects on lives, livelihoods, health, ecosystems, economies, societies, cultures, services, and infrastructure due to the interaction of
climate changes or hazardous climate events occurring within a specific time period and the vulnerability of an exposed society or
system. Impacts are also referred to as consequences and outcomes. The impacts of climate change on geophysical systems, including
floods, droughts, and sea level rise, are a subset of impacts called physical impacts.
Hazard: The potential occurrence of a natural or human-induced physical event or trend or physical impact that may cause loss of life,
injury, or other health impacts, as well as damage and loss to property, infrastructure, livelihoods, service provision, ecosystems, and
environmental resources. In this report, the term hazard usually refers to climate-related physical events or trends or their physical impacts.
Stressors: Events and trends, often not climate-related, that have an important effect on the system exposed and can increase
vulnerability to climate-related risk.
Risk: The potential for consequences where something of value is at stake and where the outcome is uncertain, recognizing the
diversity of values. Risk is often represented as probability of occurrence of hazardous events or trends multiplied by the impacts if
these events or trends occur.
Risk = (Probability of Events or Trends) × Consequences
Risk results from the interaction of vulnerability, exposure, and hazard (see Figure 19-1). In this report, the term risk is used primarily
to refer to the risks of climate-change impacts.
Key vulnerability, key risk, key impact: A vulnerability, risk, or impact relevant to the definition and elaboration of “dangerous
anthropogenic interference (DAI) with the climate system,” in the terminology of United Nations Framework Convention on Climate
Change (UNFCCC) Article 2, meriting particular attention by policymakers in that context.
Key risks are potentially severe adverse consequences for humans and social-ecological systems resulting from the interaction of
climate-related hazards with vulnerabilities of societies and systems exposed. Risks are considered “key” due to high hazard or high
vulnerability of societies and systems exposed, or both.
Vulnerabilities are considered “key” if they have the potential to combine with hazardous events or trends to result in key risks.
Vulnerabilities that have little influence on climate-related risk, for instance, due to lack of exposure to hazards, would not be
considered key.
Key impacts are severe consequences for humans and social-ecological systems.
Continued next page
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impacts and disasters, and on the other hand, when non-extreme events
may also result in extreme impacts and disasters.
19.1.3. New Developments in this Chapter
With these frameworks already established, and a long list of impacts and
key vulnerabilities enumerated and categorized in previous assessments,
the current chapter has three goals: first, to recognize and assess risks that
arise out of complex interactions involving climate and socio-ecological
systems, called emergent risks (see Boxes 19-2, CC-KR; Table 19-4). In many
cases, scientific literature sufficient to permit assessment of such risks
has become available largely since AR4. In this chapter, we consider
only those emergent risks that are relevant to interpreting Article 2 or
have the potential to become relevant (see criteria in Section 19.2.2)
as additional understanding accumulates. For example, since AR4,
sufficient literature has emerged to allow initial assessment of the
potential relationship between climate change and conflict. The second
goal is to reassess and reorganize the existing frameworks (based on
RFCs and KVs) for evaluating the literature pertinent to Article 2 of the
UNFCCC to address the deficiencies cited in Section 19.1.1, particularly
in light of the advances in SREX and the current report’s discussions of
vulnerability and human security (Chapters 12 and 13) and adaptation
(Chapters 14 to 17 and 20). From this perspective, the objective stated
in Article 2 may be viewed as aiming in part to ensure human security
in the face of climate change. Third, this chapter assesses recent literature
pertinent to additional frameworks for categorizing risk and vulnerability,
focusing on indirect impacts and interaction and concatenation of risk,
including geographic areas of compound risk (Section 19.3).
To clarify the relative roles of characteristics of the physical climate system,
such as increases in temperature, precipitation, or storm frequency, and
Box 19-2 (continued)
Extract from WGII AR4 Chapter 19:
Many impacts, vulnerabilities and risks merit particular attention by policy-makers due to characteristics that might make them ‘key’.
The identification of potential key vulnerabilities is intended to provide guidance to decision-makers for identifying levels and rates of
climate change that may be associated with ‘dangerous anthropogenic interference’ (DAI) with the climate system, in the terminology
of United Nations Framework Convention on Climate Change (UNFCCC) Article 2 (see Box 19-1). Ultimately, the definition of DAI
cannot be based on scientific arguments alone, but involves other judgments informed by the state of scientific knowledge.
Emergent Risk: A risk that arises from the interaction of phenomena in a complex system, for example, the risk caused when
geographic shifts in human population in response to climate change lead to increased vulnerability and exposure of populations in
the receiving region. Many of the emergent risks discussed in this report have only recently been analyzed in the scientific literature
in sufficient detail to permit assessment. In this chapter, the only emergent risks discussed are those that have the potential to become
key risks once sufficient understanding accumulates.
Reasons for Concern: Elements of a classification framework, first developed in the IPCC Third Assessment Report, which aims to
facilitate judgments about what level of climate change may be “dangerous” (in the language of Article 2 of the UNFCCC) by
aggregating impacts, risks, and vulnerabilities.
Summary of Reasons for Concern (revised from WGII TAR Chapter 19; see also Sections 1.2.3, 18.6.4):
“Reasons for Concern may aid readers in making their own determination about what is a “dangerous” climate change. Each Reason
for Concern is consistent with a paradigm that can be used by itself or in combination with other paradigms to help determine what
level of climate change is dangerous. The reasons for concern are the relations between global mean temperature increase and:
1. Risks to unique and threatened systems
2. Risks associated with extreme weather events
3. Risks associated with the distribution of impacts
4. Risks associated with global aggregate impacts
5. Risks associated with large-scale singular events
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c
haracteristics of the socioeconomic and biological systems with which
these interact (vulnerability and exposure) to produce risks of particular
consequences (the latter term used interchangeably here with “impacts
and “outcomes”), we rely heavily on a concept used sparingly in the TAR
and AR4, key risks (see Box 19-2). Furthermore, we emphasize recent
literature pointing to the dynamic character of vulnerability and exposure
based on their intimate relationship to development.
Section 19.2 describes the framework used here for identifying key
vulnerabilities, key risks, and emergent risks. We consider a variety of
types of emergent risks, including in Section 19.3 those arising from
multiple interacting systems and stresses, and in Section 19.4, those
arising from indirect impacts, trans-boundary impacts, and impacts
occurring at a long distance from the location of the climate change
that causes them. One example that illustrates all of these properties
is the extent to which climate change impacts on agriculture, water
resources, and sea level affect human migration flows. These shifts entail
both risks of harm and potential benefits for the migrants, for the regions
where they originate, and for the destination regions (see Sections 12.4,
19.4.2.1). Associated risks include indirect impacts, like the effect of
land use changes on ecosystems occurring at the new locations of
settlement, which may be near the location of the original climate
impact or quite distant. Such distant, indirect effects would compound
the direct consequences of climate change at the locations receiving
the incoming migrants. In Section 19.5, we discuss other risks newly
assessed here, including those arising from ocean acidification. Section
19.6 assesses key risks and vulnerabilities in light of the criteria discussed
here (Section 19.2.2) and in the context of the RFCs, and Section 19.7
assesses response strategies aimed at avoiding key risks.
19.2. Framework for Identifying
Key Vulnerabilities, Key Risks,
and Emergent Risks
19.2.1. Risk and Vulnerability
Definitions and frameworks that systematize hazards, exposure,
vulnerability, risk, and adaptation in the context of climate change are
multiple, overlapping, and often contested (see, e.g., Burton et al., 1983;
Blaikie et al., 1994; Twigg, 2001; Turner et al., 2003a,b; UNISDR, 2004;
Schröter, 2005; Adger, 2006; Birkmann, 2006b; Füssel and Klein, 2006;
Thomalla et al., 2006; Tol and Yohe, 2006; Villagrán de León, 2006; IPCC,
2007a; Cutter and Finch, 2008; Cutter et al., 2008; ICSU-LAC, 2010a,b;
Cardona, 2011; DEFRA, 2012; IPCC, 2012a; Kienberger, 2012; Birkmann
et al., 2013a; Costa and Kropp, 2013). Today, key reports and most
authors differentiate among hazards, vulnerability, risk, and impacts (see,
e.g., Hutton et al., 2011; IPCC, 2012a; Birkmann et al., 2013a). The recent
literature underscores that risks from climate change are not solely ex-
ternally generated circumstances or changes in the climate system to
which societies respond, but rather the result of complex interactions
among societies or communities, ecosystems, and hazards arising from
climate change (Susman et al., 1983; Comfort et al., 1999; Birkmann et
al., 2011a, 2013a; UNISDR, 2011; IPCC, 2012a). The differentiation of
the various aspects of these interactions is an important improvement
since AR4 because it exhibits the social construction of risk through the
concept of vulnerability (IPCC, 2012a). This new framework, growing
o
ut of SREX, translates information more easily into a risk management
approach that facilitates policy making (de Sherbinin, 2013). The following
section advances this framework in the context of Article 2 of the UNFCCC.
We refer to the characteristics of climate change and its effects on
geophysical systems, such as floods, droughts, deglaciation, sea level
rise, increasing temperature, and frequency of heat waves, as hazards.
In contrast, vulnerability refers primarily to characteristics of human or
social-ecological systems exposed to hazardous climatic (droughts,
floods, etc.) or non-climatic events and trends (increasing temperature,
sea level rise) (UNDRO, 1980; Cardona, 1986, 1990; Liverman, 1990;
Cannon, 1994, 2006; Blaikie et al., 1996; UNISDR, 2004, 2009;
Birkmann, 2006a; Füssel and Klein, 2006; Thywissen, 2006; IPCC, 2012a).
Ecosystems or geographic areas can be classified as vulnerable, which
is of particular concern if human vulnerability increases as a result of
potential impairment of the related ecosystem services. The Millennium
Ecosystem Assessment (MEA), for example, identified ecosystem services
that affect the vulnerability of societies and communities, such as
provision of freshwater resources and air quality (Millennium Ecosystem
Assessment, 2005a,b). Examples in this chapter and other chapters in this
report include the vulnerability of warmwater coral reefs and respective
ecosystem services for coastal communities (see Table 19-4; Box CC-KR).
The new framework used here also underscores that the development
process of a society has significant implications for exposure, vulnerability,
and risk. Climate change is not a risk per se; rather climate changes and
related hazards interact with the evolving vulnerability and exposure
of systems and therewith determine the changing level of risk (see
Figure 19-1; Table 19-4). Identifying key vulnerabilities facilitates
estimating key risks when coupled with information about evolving
hazards associated with climate change. This approach provides the
basis for criteria developed in the following sections.
19.2.2. Criteria for Identifying
Key Vulnerabilities and Key Risks
Vulnerability is dynamic and context specific, determined by human
behavior and societal organization, which influences for example the
susceptibility of people (e.g., by marginalization) and their coping and
adaptive capacities to hazards (see IPCC, 2012a). In this regard coping
mainly refers to capacities that allow a system to protect itself in the
face of adverse consequences, while adaptation—by contrast—denotes
a longer term process that also involves adjustments in the system itself
and refers to learning, experimentation, and change (Yohe and Tol, 2002;
Pelling, 2010; Birkmann et al., 2013a). Perceptions and cognitive
constructs about risks and adaptation options as well as cultural contexts
influence adaptive capacities and thus vulnerability (Grothmann and
Patt, 2005; Rhomberg, 2009; Kuruppu and Liverman, 2011; see Section
19.6.1.4). SREX stressed that the consideration of multiple dimensions
(e.g., social, economic, environmental, institutional, cultural), as well as
different causal factors of vulnerability, can improve strategies to reduce
risks to climate change (see IPCC 2012c, p. 17; Cardona et al., 2012, pp.
17, 67–106).
Key vulnerability and key risk are defined in Box 19-2. Vulnerabilities
that have little influence on overall risk are not considered key. Similarly,
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t
he magnitude or other characteristics of climate change-related
hazards, such as glacier melting, sea level rise, or heat waves, are not
by themselves adequate to determine key risks, as the consequences of
climate change also will be determined by the vulnerability of the
exposed society or social-ecological system. Key vulnerabilities and key
risks embody a normative component because different societies might
rank the various vulnerability and risk factors and actual or potential
types of loss and damage differently (see Schneider et al., 2007, p. 785;
Lavell et al., 2012, p. 45). Generally, vulnerability merits particular
attention when the survival of societies, communities, or ecosystems is
threatened (see UNISDR, 2011, 2013; Birkmann et al., 2011a). Climate
change will influence the nature of the climatic hazards people and
ecosystems are exposed to and also contribute to deterioration or
improvement of coping and adaptive capacities of those exposed to
these changes. Consequently, many studies (Wisner et al., 2004; Cardona,
2010; Birkmann et al., 2011a) focus with a priority on the vulnerability
of humans and societies as a central feature, rather than solely on the
level of climatic change and respective hazards.
19.2.2.1. Criteria for Identifying Key Vulnerabilities
We reorganize and further develop criteria for identifying vulnerabilities
as “key” used in AR4 based on the literature (Blaikie et al., 1994; Bohle,
2001; Turner et al., 2003a,b; Birkmann, 2006a, 2011a; Villagrán de León,
2006; Cutter et al., 2008; Cutter and Finch, 2008; ICSU-LAC, 2010a,b;
Cardona, 2011; UNISDR, 2011; IPCC, 2012a; Birkmann et al., 2013a)
and the differentiation of hazard, exposure, and vulnerability presented
here. The criteria in this and succeeding sections were used to identify
key vulnerabilities, key risks, and emergent risks in Sections 19.4 and
19.6.1-2, and in Table 19-4. Not all of the criteria need to be fulfilled to
characterize a vulnerability or risk as key but the characterization of a
phenomenon as a KV or key risk is usually supported by more than one
criterion.
The following five criteria are used to judge whether vulnerabilities are
key:
1) Exposure of a society, community, or social-ecological system to
climatic stressors. While exposure is distinct from vulnerability,
exposure is an important precondition for considering a specific
vulnerability as key. If a system is neither at present nor in the future
exposed to hazardous climatic trends or events, its vulnerability to
such hazards is not relevant in the current context. Exposure can
be assessed based on spatial and temporal dimensions.
2) Importance of the vulnerable system(s). Views on the importance of
different aspects of societies or ecosystems can vary across regions
and cultures (see Kienberger, 2012). However, the identification of
KVs is less subjective when it involves characteristics that are crucial
for the survival of societies or communities or social-ecological
systems exposed to climatic hazards. Defining key vulnerabilities in
the context of particular societal groups or ecosystem services also
takes into account the conditions that make these population
groups or ecosystems highly vulnerable, such as processes of social
marginalization or the degradation of ecosystems (Leichenko and
O’Brien, 2008; O’Brien et al., 2008; IPCC, 2012a).
3) Limited ability of societies, communities, or social-ecological systems
to cope with and to build adaptive capacities to reduce or limit the
a
dverse consequences of climate-related hazard. Coping and adaptive
capacities are part of the formula that determines vulnerability (see
IPCC, 2012a; Birkmann et al., 2013a). While coping describes actions
taken within existing constraints to protect the current system and
institutional settings, adaptation is a continuous process that
encompasses learning and change of the system exposed, including
changes of rule systems or modes of governance (Smithers and Smit,
1997; Pielke Jr., 1998; Frankhauser et al., 1999; Smit et al., 1999;
Kelly and Adger, 2000; Yohe and Tol, 2002; Adger et al., 2005; Smit
and Wandel, 2006; Pelling et al., 2008; Pelling, 2010; Tschakert and
Dietrich; 2010; IPCC, 2012a; Birkmann et al., 2013a; Garschagen,
2013). Severe limits of coping and adaptation provide criteria
for defining a vulnerability as key, as they are core factors that
increase vulnerability to climatic hazards (see, e.g., Warner et al.,
2012).
4) Persistence of vulnerable conditions and degree of irreversibility of
consequences. Vulnerabilities are considered key when they are
persistent and difficult to alter. This is particularly the case when the
susceptibility is high and coping and adaptive capacities are very
low as a result of conditions that are hard to change. Irreversible
degradation of ecosystems (e.g., warmwater coral reefs), chronic
poverty and marginalization, and insecure land tenure arrangements
are drivers of vulnerability that in combination with climatic hazards
determine risks that often persist over decades (see Box CC-KR), for
example, as observed in the Sahel Zone. In this way, communities
or social-ecological systems (e.g., coastal communities dependent
on fishing or mountain communities dependent on specific soil
conditions) may reach a tipping point (or critical threshold) that
would cause a partial or full collapse of the system, including
displacement (see Renaud et al., 2010; Section 19.4.2.1). Inability
to replace such a system or compensate for potential and actual
losses and damages (i.e., irreversibility) is a critical criterion for
determining what is “key.”
5) Presence of conditions that make societies highly susceptible to
cumulative stressors in complex and multiple-interacting systems.
Conditions that make communities or social-ecological systems
highly susceptible to the imposition of additional climatic hazards
or that impinge on their ability to cope and adapt, such as violent
conflicts (e.g., during drought disaster in Somalia (see Menkhaus,
2010)) are considered under this criterion. Also, the critical
dependence of societies on highly interdependent infrastructures
(e.g., energy/power supply, transport, and health care) (see Rinaldi
et al., 2001; Wang, S. et al., 2012; Atzl and Keller, 2013) leads to key
vulnerabilities regarding multiple-interacting systems where capacity
to cope or adapt to their failure is low (see Copeland, 2005; Reed
et al., 2010; Section 19.6.2.1; Table 19-4).
19.2.2.2. Criteria for Identifying Key Risks
Risks are considered key” due to high hazard or high vulnerability
(“key vulnerability”) of societies and systems exposed, or both. Criteria
for determining key risks build on the criteria for key vulnerabilities, as
vulnerability is a component of risk. As such, risk is strongly determined
by coping and adaptive capacities. However, the criteria for identifying
key risks also take into account the magnitude, frequency, and intensity
of hazardous events and trends linked to climate change to which
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v
ulnerable systems are exposed. Accordingly, the following four
additional criteria are used to judge whether risks are key:
1) Magnitude. Risks are key if associated harmful consequences have
a large magnitude, determined by a variety of metrics including
human mortality and morbidity, economic loss, losses of cultural
importance, and distributional consequences (see Schneider et al.,
2007; IPCC, 2012a). Magnitude and frequency of the hazard as well
as socioeconomic factors that determine vulnerability and exposure
contribute.
2) Probability that significant risks will materialize and their timing.
Risks are considered key when there is a high probability that the
hazard due to climate change will occur under circumstances where
societies or social-ecological systems exposed are highly susceptible
and have very limited capacities to cope or adapt and consequently
potential consequences