126
SPM
13
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.
37
[RFC 1-5]
ii) Risk of severe ill-health and disrupted livelihoods for large urban populations due to inland flooding in some regions.
38
[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.
39
[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.
40
[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.
41
[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.
42
[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.
43
[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.
44
[RFC 1, 3, and 4]
Many key risks constitute particular challenges for the least developed countries and vulnerable communities, given their limited ability to
cope.
°C
5
4
3
2
1
0
Undetectable
Very high
Level of additional risk due to climate change
Moderate
High
Unique &
threatened
systems
Extreme
weather
events
Distribution
of impacts
Global
aggregate
impacts
Large-scale
singular
events
1900
1950
2000
2050
°C
5
4
3
2
1
0
(˚
approximation of preindustrial levels)
2003–2012
2100
(˚
approximation of preindustrial levels)
6
5
4
3
2
1
0
°C
-0.61
(˚C relative to 1986–2005)
Global mean temperature change
5
4
3
2
1
0
°C
-0.61
Assessment Box SPM.1 Figure 1 | A global perspective on climate-related risks. Risks associated with reasons for concern are shown at right for increasing levels of climate
change. The color shading indicates the additional risk due to climate change when a temperature level is reached and then sustained or exceeded. Undetectable risk (white)
indicates no associated impacts are detectable and attributable to climate change. Moderate risk (yellow) indicates that associated impacts are both detectable and attributable
to climate change with at least medium confidence, also accounting for the other specific criteria for key risks. High risk (red) indicates severe and widespread impacts, also
accounting for the other specific criteria for key risks. Purple, introduced in this assessment, shows that very high risk is indicated by all specific criteria for key risks. [Figure 19-4]
For reference, past and projected global annual average surface temperature is shown at left, as in Figure SPM.4. [Figure RC-1, Box CC-RC; WGI AR5 Figures SPM.1 and SPM.7]
Based on the longest global surface temperature dataset available, the observed change between the average of the period 1850–1900 and of the AR5 reference period
(1986–2005) is 0.61°C (5–95% confidence interval: 0.55 to 0.67°C) [WGI AR5 SPM, 2.4], which is used here as an approximation of the change in global mean surface
temperature since preindustrial times, referred to as the period before 1750. [WGI and WGII AR5 glossaries]
(˚
Global mean temperature change
Observed
RCP2.6 (a low-emission mitigation scenario)
RCP8.5 (a high-emission scenario)
Overlap
Summary for Policymakers
37
5.4, 8.2, 13.2, 19.2-4, 19.6-7, 24.4-5, 26.7-8, 29.3, 30.3, Tables 19-4 and 26-1, Figure 26-2, Boxes 25-1, 25-7, and CC-KR
38 3.4-5, 8.2, 13.2, 19.6, 25.10, 26.3, 26.8, 27.3, Tables 19-4 and 26-1, Boxes 25-8 and CC-KR
39
5.4, 8.1-2, 9.3, 10.2-3, 12.6, 19.6, 23.9, 25.10, 26.7-8, 28.3, Table 19-4, Boxes CC-KR and CC-HS
40
8.1-2, 11.3-4, 11.6, 13.2, 19.3, 19.6, 23.5, 24.4, 25.8, 26.6, 26.8, Tables 19-4 and 26-1, Boxes CC-KR and CC-HS
41 3.5, 7.4-5, 8.2-3, 9.3, 11.3, 11.6, 13.2, 19.3-4, 19.6, 22.3, 24.4, 25.5, 25.7, 26.5, 26.8, 27.3, 28.2, 28.4, Table 19-4, Box CC-KR
42
3.4-5, 9.3, 12.2, 13.2, 19.3, 19.6, 24.4, 25.7, 26.8, Table 19-4, Boxes 25-5 and CC-KR
43
5.4, 6.3, 7.4, 9.3, 19.5-6, 22.3, 25.6, 27.3, 28.2-3, 29.3, 30.5-7, Table 19-4, Boxes CC-OA, CC-CR, CC-KR, and CC-HS
44 4.3, 9.3, 19.3-6, 22.3, 25.6, 27.3, 28.2-3, Table 19-4, Boxes CC-KR and CC-WE
46
SPM
Summary for Policymakers
14
Increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts.Some risks of climate
change are considerable at 1 or 2°C above preindustrial levels (as shown in Assessment Box SPM.1). Global climate change risks are high to
very high with global mean temperature increase of 4°C or more above preindustrial levels in all reasons for concern (Assessment Box SPM.1),
and include severe and widespread impacts on unique and threatened systems, substantial species extinction, 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). The precise levels of climate change sufficient to trigger tipping points
(thresholds for abrupt and irreversible change) remain uncertain, but the risk associated with crossing multiple tipping points in the earth
system or in interlinked human and natural systems increases with rising temperature (medium confidence).
45
The overall risks of climate change impacts can be reduced by limiting the rate and magnitude of climate change. Risks are
reduced substantially under the assessed scenario with the lowest temperature projections (RCP2.6 – low emissions) compared to the highest
temperature projections (RCP8.5 – high emissions), particularly in the second half of the 21st century (very high confidence). Reducing climate
change can also reduce the scale of adaptation that might be required. Under all assessed scenarios for adaptation and mitigation, some risk
from adverse impacts remains (very high confidence).
46
B-2. Sectoral Risks and Potential for Adaptation
Climate change is projected to amplify existing climate-related risks and create new risks for natural and human systems. Some of these risks
will be limited to a particular sector or region, and others will have cascading effects. To a lesser extent, climate change is also projected to
have some potential benefits.
Freshwater resources
Freshwater-related risks of climate change increase significantly with increasing greenhouse gas concentrations (robust evidence,
high agreement). The fraction of global population experiencing water scarcity and the fraction affected by major river floods increase with
the level of warming in the 21st century.
47
Climate change over the 21st century is projected to reduce renewable surface water and groundwater resources significantly in
most dry subtropical regions (robust evidence, high agreement), intensifying competition for water among sectors (limited
evidence, medium agreement).In presently dry regions, drought frequency will likelyincrease by the end of the 21st century under RCP8.5
(medium confidence). In contrast, water resources are projected to increase at high latitudes (robust evidence, high agreement). Climate
change is projected to reduce raw water quality and pose risks to drinking water quality even with conventional treatment, due to interacting
factors: increased temperature; increased sediment, nutrient, and pollutant loadings from heavy rainfall; increased concentration of pollutants
during droughts; and disruption of treatment facilities during floods (medium evidence, high agreement). Adaptive water management
techniques, including scenario planning, learning-based approaches, and flexible and low-regret solutions, can help create resilience to
uncertain hydrological changes and impacts due to climate change (limited evidence, high agreement).
48
Terrestrial and freshwater ecosystems
A large fraction of both terrestrial and freshwater species faces increased extinction risk under projected climate change during
and beyond the 21st century, especially as climate change interacts with other stressors, such as habitat modification, over-
45
4.2-3, 11.8, 19.5, 19.7, 26.5, Box CC-HS
46
3.4-5, 16.6, 17.2, 19.7, 20.3, 25.10, Tables 3-2, 8-3, and 8-6, Boxes 16-3 and 25-1
47
3.4-5, 26.3, Table 3-2, Box 25-8
VB.NET PDF: Basic SDK Concept of XDoc.PDF You may add PDF document protection functionality into your VB.NET program. to edit hyperlink of PDF document, including editing PDF url links and quick
add hyperlink to pdf in; add links to pdf file
67
SPM
15
exploitation, pollution, and invasive species (high confidence). Extinction risk is increased under all RCP scenarios, with risk increasing
with both magnitude and rate of climate change. Many species will be unable to track suitable climates under mid- and high-range rates of
climate change (i.e., RCP4.5, 6.0, and 8.5) during the 21st century (medium confidence). Lower rates of change (i.e., RCP2.6) will pose fewer
problems. See Figure SPM.5. Some species will adapt to new climates. Those that cannot adapt sufficiently fast will decrease in abundance or
go extinct in part or all of their ranges. Management actions, such as maintenance of genetic diversity, assisted species migration and dispersal,
manipulation of disturbance regimes (e.g., fires, floods), and reduction of other stressors, can reduce, but not eliminate, risks of impacts to
terrestrial and freshwater ecosystems due to climate change, as well as increase the inherent capacity of ecosystems and their species to adapt
to a changing climate (high confidence).
49
Within this century, magnitudes and rates of climate change associated with medium- to high-emission scenarios (RCP4.5, 6.0,
and 8.5) pose high risk of abrupt and irreversible regional-scale change in the composition, structure, and function of terrestrial
and freshwater ecosystems, including wetlands (medium confidence). Examples that could lead to substantial impact on climate are the
boreal-tundra Arctic system (medium confidence) and the Amazon forest (low confidence). Carbon stored in the terrestrial biosphere (e.g., in
peatlands, permafrost, and forests) is susceptible to loss to the atmosphere as a result of climate change, deforestation, and ecosystem
degradation (high confidence). Increased tree mortality and associated forest dieback is projected to occur in many regions over the 21st
century, due to increased temperatures and drought (medium confidence). Forest dieback poses risks for carbon storage, biodiversity, wood
production, water quality, amenity, and economic activity.
50
Trees
Herbaceous
plants
Split-hoofed
mammals
Carnivorous
mammals
Rodents
Primates
Plant-feeding
insects
Freshwater
mollusks
Maximum speed at which species can move (km per decade)
Lower
bound
Upper
bound
Median
0
20
40
60
80
100
RCP8.5 flat areas
Average climate velocity
2050–2090
RCP6.0 flat areas
RCP6.0 global average
RCP8.5 global average
RCP2.6 flat areas and global average
RCP4.5 flat areas
RCP4.5 global average
Figure SPM.5 | Maximum speeds at which species can move across landscapes (based on observations and models; vertical axis on left), compared with speeds at which
temperatures are projected to move across landscapes (climate velocities for temperature; vertical axis on right). Human interventions, such as transport or habitat fragmentation,
can greatly increase or decrease speeds of movement. White boxes with black bars indicate ranges and medians of maximum movement speeds for trees, plants, mammals,
plant-feeding insects (median not estimated), and freshwater mollusks. For RCP2.6, 4.5, 6.0, and 8.5 for 2050–2090, horizontal lines show climate velocity for the
global-land-area average and for large flat regions. Species with maximum speeds below each line are expected to be unable to track warming in the absence of human
intervention. [Figure 4-5]
Summary for Policymakers
48
3.2, 3.4-6, 22.3, 23.9, 25.5, 26.3, Table 3-2, Table 23-3, Boxes 25-2, CC-RF, and CC-WE; WGI AR5 12.4
49
4.3-4, 25.6, 26.4, Box CC-RF
50
4.2-3, Figure 4-8, Boxes 4-2, 4-3, and 4-4
100
SPM
Summary for Policymakers
16
Change in maximum catch potential (2051–2060 compared to 2001–2010, SRES A1B)
> 100 %
< –50 %
–21 to –50 %
–6 to –20 %
–1 to –5 %
20 to 49 %
50 to 100 %
5 to 19 %
0 to 4 %
no data
Mollusk and crustacean fisheries
(present-day annual catch rate
≥
0.005 tonnes km-2)
Cold-water
corals
Warm-water
corals
Change in pH (2081–2100 compared to 1986–2005, RCP8.5)
Positive effect
No effect
Negative effect
pCO
2
(μatm)
(A)
40 16 15 31
Control
500–650
651–850
851–1370
0
20
40
60
80
100
Mollusks
1371–2900
29
37 4 9 18
Control
500–650
651–850
851–1370
0
20
40
60
80
100
Crustaceans
1371–2900
23
Cold-water corals
7 4 7 5
Control
500–650
651–850
851–1370
0
20
40
60
80
100
3
1371–2900
Species (%)
26 9 15 23
Control
0
20
40
60
80
100
20
500–650
651–850
851–1370
1371–2900
Warm-water corals
(B)
–0.05
–0.10
–0.15
–0.20
–0.25
–0.30
–0.35
–0.40
–0.45
–0.50
–0.55
–0.60
54
SPM
17
Coastal systems and low-lying areas
Due to sea level rise projected throughout the 21st century and beyond, coastal systems and low-lying areas will increasingly
experience adverse impacts such as submergence, coastal flooding, and coastal erosion (very high confidence).The population and
assets projected to be exposed to coastal risks as well as human pressures on coastal ecosystems will increase significantly in the coming
decades due to population growth, economic development, and urbanization (high confidence). The relative costs of coastal adaptation vary
strongly among and within regions and countries for the 21st century. Some low-lying developing countries and small island states are expected
to face very high impacts that, in some cases, could have associated damage and adaptation costs of several percentage points of GDP.
51
Marine systems
Due to projected climate change by the mid 21st century and beyond, global marine-species redistribution and marine-biodiversity
reduction in sensitive regions will challenge the sustained provision of fisheries productivity and other ecosystem services (high
confidence). Spatial shifts of marine species due to projected warming will cause high-latitude invasions and high local-extinction rates in the
tropics and semi-enclosed seas (medium confidence). Species richness and fisheries catch potential are projected to increase, on average, at
mid and high latitudes (high confidence) and decrease at tropical latitudes (medium confidence). See Figure SPM.6A. The progressive expansion
of oxygen minimum zones and anoxic “dead zones” is projected to further constrain fish habitat. Open-ocean net primary production is
projected to redistribute and, by 2100, fall globally under all RCP scenarios. Climate change adds to the threats of over-fishing and other non-
climatic stressors, thus complicating marine management regimes (high confidence).
52
For medium- to high-emission scenarios (RCP4.5, 6.0, and 8.5), ocean acidification poses substantial risks to marine ecosystems,
especially polar ecosystems and coral reefs, associated with impacts on the physiology, behavior, and population dynamics of
individual species from phytoplankton to animals (medium to high confidence). Highly calcified mollusks, echinoderms, and reef-building
corals are more sensitive than crustaceans (high confidence) and fishes (low confidence), with potentially detrimental consequences for fisheries
and livelihoods. See Figure SPM.6B. Ocean acidification acts together with other global changes (e.g., warming, decreasing oxygen levels) and
with local changes (e.g., pollution, eutrophication) (high confidence). Simultaneous drivers, such as warming and ocean acidification, can lead
to interactive, complex, and amplified impacts for species and ecosystems.
53
Food security and food production systems
For the major crops (wheat, rice, and maize) in tropical and temperate regions, climate change without adaptation is projected to
negatively impact production for local temperature increases of 2°C or more above late-20th-century levels, although individual
locations may benefit (medium confidence). Projected impacts vary across crops and regions and adaptation scenarios, with about 10% of
projections for the period 2030–2049 showing yield gains of more than 10%, and about 10% of projections showing yield losses of more than
Figure SPM.6 | Climate change risks for fisheries. (A) Projected global redistribution of maximum catch potential of ~1000 exploited fish and invertebrate species. Projections
compare the 10-year averages 2001–2010 and 2051–2060 using SRES A1B, without analysis of potential impacts of overfishing or ocean acidification. (B) Marine mollusk and
crustacean fisheries (present-day estimated annual catch rates ≥0.005 tonnes km-2) and known locations of cold- and warm-water corals, depicted on a global map showing the
projected distribution of ocean acidification under RCP8.5 (pH change from 1986–2005 to 2081–2100). [WGI AR5 Figure SPM.8] The bottom panel compares sensitivity to
ocean acidification across mollusks, crustaceans, and corals, vulnerable animal phyla with socioeconomic relevance (e.g., for coastal protection and fisheries). The number of
species analyzed across studies is given for each category of elevated CO
2
. For 2100, RCP scenarios falling within each CO
2
partial pressure (pCO
2
) category are as follows:
RCP4.5 for 500–650 μatm (approximately equivalent to ppm in the atmosphere), RCP6.0 for 651–850 μatm, and RCP8.5 for 851–1370 μatm. By 2150, RCP8.5 falls within the
1371–2900 μatm category. The control category corresponds to 380 μatm. [6.1, 6.3, 30.5, Figures 6-10 and 6-14; WGI AR5 Box SPM.1]
Summary for Policymakers
51
5.3-5, 8.2, 22.3, 24.4, 25.6, 26.3, 26.8, Table 26-1, Box 25-1
52
6.3-5, 7.4, 25.6, 28.3, 30.6-7, Boxes CC-MB and CC-PP
53
5.4, 6.3-5, 22.3, 25.6, 28.3, 30.5, Boxes CC-CR, CC-OA, and TS.7
61
SPM
Summary for Policymakers
18
25%, compared to the late 20th century. After 2050 the risk of more severe yield impacts increases and depends on the level of warming. See
Figure SPM.7. Climate change is projected to progressively increase inter-annual variability of crop yields in many regions. These projected
impacts will occur in the context of rapidly rising crop demand.
54
All aspects of food security are potentially affected by climate change, including food access, utilization, and price stability (high
confidence). Redistribution of marine fisheries catch potential towards higher latitudes poses risk of reduced supplies, income, and employment
in tropical countries, with potential implications for food security (medium confidence). Global temperature increases of ~4°C or more above
late-20th-century levels, combined with increasing food demand, would pose large risks to food security globally and regionally (high
confidence). Risks to food security are generally greater in low-latitude areas.
55
Urban areas
Many global risks of climate change are concentrated in urban areas (medium confidence). Steps that build resilience and enable
sustainable development can accelerate successful climate-change adaptation globally. Heat stress, extreme precipitation, inland and
coastal flooding, landslides, air pollution, drought, and water scarcity pose risks in urban areas for people, assets, economies, and ecosystems
(very high confidence). Risks are amplified for those lacking essential infrastructure and services or living in poor-quality housing and exposed
areas. Reducing basic service deficits, improving housing, and building resilient infrastructure systems could significantly reduce vulnerability
and exposure in urban areas. Urban adaptation benefits from effective multi-level urban risk governance, alignment of policies and incentives,
strengthened local government and community adaptation capacity, synergies with the private sector, and appropriate financing and
institutional development (medium confidence). Increased capacity, voice, and influence of low-income groups and vulnerable communities
and their partnerships with local governments also benefit adaptation.
56
Figure SPM.7 | Summary of projected changes in crop yields, due to climate change over the 21st century. The figure includes projections for different emission scenarios, for
tropical and temperate regions, and for adaptation and no-adaptation cases combined. Relatively few studies have considered impacts on cropping systems for scenarios where
global mean temperatures increase by 4°C or more. For five timeframes in the near term and long term, data (n=1090) are plotted in the 20-year period on the horizontal axis
that includes the midpoint of each future projection period. Changes in crop yields are relative to late-20th-century levels. Data for each timeframe sum to 100%. [Figure 7-5]
0 to –5%
–5 to –10%
–10 to –25%
–25 to –50%
–50 to –100%
0 to 5%
5 to 10%
10 to 25%
25 to 50%
50 to 100%
Range of yield change
increase
in yield
decrease
in yield
Color Legend
Percentage of yield projections
2010–2029
2030–2049
2090–2109
0
20
40
60
80
100
2070–2089
2050–2069
54
7.4-5, 22.3, 24.4, 25.7, 26.5, Table 7-2, Figures 7-4, 7-5, 7-6, 7-7, and 7-8
55
6.3-5, 7.4-5, 9.3, 22.3, 24.4, 25.7, 26.5, Table 7-3, Figures 7-1, 7-4, and 7-7, Box 7-1
56 3.5, 8.2-4, 22.3, 24.4-5, 26.8, Table 8-2, Boxes 25-9 and CC-HS
53
SPM
19
Rural areas
Major future rural impacts are expected in the near term and beyond through impacts on water availability and supply, food
security, and agricultural incomes, including shifts in production areas of food and non-food crops across the world (high
confidence). These impacts are expected to disproportionately affect the welfare of the poor in rural areas, such as female-headed households
and those with limited access to land, modern agricultural inputs, infrastructure, and education. Further adaptations for agriculture, water,
forestry, and biodiversity can occur through policies taking account of rural decision-making contexts. Trade reform and investment can improve
market access for small-scale farms (medium confidence).
57
Key economic sectors and services
For most economic sectors, the impacts of drivers such as changes in population, age structure, income, technology, relative prices,
lifestyle, regulation, and governance are projected to be large relative to the impacts of climate change (medium evidence, high
agreement). Climate change is projected to reduce energy demand for heating and increase energy demand for cooling in the residential and
commercial sectors (robust evidence, high agreement). Climate change is projected to affect energy sources and technologies differently,
depending on resources (e.g., water flow, wind, insolation), technological processes (e.g., cooling), or locations (e.g., coastal regions, floodplains)
involved. More severe and/or frequent extreme weather events and/or hazard types are projected to increase losses and loss variability in
various regions and challenge insurance systems to offer affordable coverage while raising more risk-based capital, particularly in developing
countries. Large-scale public-private risk reduction initiatives and economic diversification are examples of adaptation actions.
58
Global economic impacts from climate change are difficult to estimate. Economic impact estimates completed over the past 20 years
vary in their coverage of subsets of economic sectors and depend on a large number of assumptions, many of which are disputable, and many
estimates do not account for catastrophic changes, tipping points, and many other factors.
59
With these recognized limitations, the incomplete
estimates of global annual economic losses for additional temperature increases of ~2°C are between 0.2 and 2.0% of income (±1 standard
deviation around the mean) (medium evidence, medium agreement). Losses are more likely than not to be greater, rather than smaller, than
this range (limited evidence, high agreement). Additionally, there are large differences between and within countries. Losses accelerate with
greater warming (limited evidence, high agreement), but few quantitative estimates have been completed for additional warming around 3°C
or above. Estimates of the incremental economic impact of emitting carbon dioxide lie between a few dollars and several hundreds of dollars
per tonne of carbon
60
(robust evidence, medium agreement). Estimates vary strongly with the assumed damage function and discount rate.
61
Human health
Until mid-century, projected climate change will impact human health mainly by exacerbating health problems that already exist
(very high confidence). Throughout the 21st century, climate change is expected to lead to increases in ill-health in many regions
and especially in developing countries with low income, as compared to a baseline without climate change (high confidence).
Examples include greater likelihood of injury, disease, and death due to more intense heat waves and fires (very high confidence); increased
likelihood of under-nutrition resulting from diminished food production in poor regions (high confidence); risks from lost work capacity and
reduced labor productivity in vulnerable populations; and increased risks from food- and water-borne diseases (very high confidence) and
Summary for Policymakers
57 9.3, 25.9, 26.8, 28.2, 28.4, Box 25-5
58
3.5, 10.2, 10.7, 10.10, 17.4-5, 25.7, 26.7-9, Box 25-7
59
Disaster loss estimates are lower-bound estimates because many impacts, such as loss of human lives, cultural heritage, and ecosystem services, are difficult to value and
monetize, and thus they are poorly reflected in estimates of losses. Impacts on the informal or undocumented economy as well as indirect economic effects can be very
important in some areas and sectors, but are generally not counted in reported estimates of losses. [SREX 4.5]
60
1 tonne of carbon = 3.667 tonne of CO
2
61 10.9
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