Climate Change Impacts on Africa, Asia, Australasia & Ecosystems: Summary for Policymakers, Essays (high school) of History

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WORKING GROUP II CONTRIBUTION TO THE

FIFTH ASSESSMENT REPORT OF THE

INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE

WG II

INTERGOV ERNMENTA L PA NEL ON climate change

Summary

SPM for Policymakers

This Summary for Policymakers should be cited as: IPCC , 2014: Summary for policymakers. 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. 1-32.

Drafting Authors: Christopher B. Field (USA), Vicente R. Barros (Argentina), Michael D. Mastrandrea (USA), Katharine J. Mach (USA), Mohamed A.-K. Abdrabo (Egypt), W. Neil Adger (UK), Yury A. Anokhin (Russian Federation), Oleg A. Anisimov (Russian Federation), Douglas J. Arent (USA), Jonathon Barnett (Australia), Virginia R. Burkett (USA), Rongshuo Cai (China), Monalisa Chatterjee (USA/India), Stewart J. Cohen (Canada), Wolfgang Cramer (Germany/France), Purnamita Dasgupta (India), Debra J. Davidson (Canada), Fatima Denton (Gambia), Petra Döll (Germany), Kirstin Dow (USA), Yasuaki Hijioka (Japan), Ove Hoegh-Guldberg (Australia), Richard G. Jones (UK), Roger N. Jones (Australia), Roger L. Kitching (Australia), R. Sari Kovats (UK), Joan Nymand Larsen (Iceland), Erda Lin (China), David B. Lobell (USA), Iñigo J. Losada (Spain), Graciela O. Magrin (Argentina), José A. Marengo (Brazil), Anil Markandya (Spain), Bruce A. McCarl (USA), Roger F. McLean (Australia), Linda O. Mearns (USA), Guy F. Midgley (South Africa), Nobuo Mimura (Japan), John F. Morton (UK), Isabelle Niang (Senegal), Ian R. Noble (Australia), Leonard A. Nurse (Barbados), Karen L. O’Brien (Norway), Taikan Oki (Japan), Lennart Olsson (Sweden), Michael Oppenheimer (USA), Jonathan T. Overpeck (USA), Joy J. Pereira (Malaysia), Elvira S. Poloczanska (Australia), John R. Porter (Denmark), Hans-O. Pörtner (Germany), Michael J. Prather (USA), Roger S. Pulwarty (USA), Andy Reisinger (New Zealand), Aromar Revi (India), Patricia Romero-Lankao (Mexico), Oliver C. Ruppel (Namibia), David E. Satterthwaite (UK), Daniela N. Schmidt (UK), Josef Settele (Germany), Kirk R. Smith (USA), Dáithí A. Stone (Canada/South Africa/USA), Avelino G. Suarez (Cuba), Petra Tschakert (USA), Riccardo Valentini (Italy), Alicia Villamizar (Venezuela), Rachel Warren (UK), Thomas J. Wilbanks (USA), Poh Poh Wong (Singapore), Alistair Woodward (New Zealand), Gary W. Yohe (USA)

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ASSESSING AND MANAGING THE RISKS OF CLIMATE CHANGE

Human interference with the climate system is occurring,^1 and climate change poses risks for human and natural systems (Figure SPM.1). The assessment of impacts, adaptation, and vulnerability in the Working Group II contribution to the IPCC’s Fifth Assessment Report (WGII AR5) evaluates how patterns of risks and potential benefits are shifting due to climate change. It considers how impacts and risks related to climate change can be reduced and managed through adaptation and mitigation. The report assesses needs, options, opportunities, constraints, resilience, limits, and other aspects associated with adaptation.

Climate change involves complex interactions and changing likelihoods of diverse impacts. A focus on risk, which is new in this report, supports decision making in the context of climate change and complements other elements of the report. People and societies may perceive or rank risks and potential benefits differently, given diverse values and goals.

Compared to past WGII reports, the WGII AR5 assesses a substantially larger knowledge base of relevant scientific, technical, and socioeconomic literature. Increased literature has facilitated comprehensive assessment across a broader set of topics and sectors, with expanded coverage of human systems, adaptation, and the ocean. See Background Box SPM.1. 2

Section A of this summary characterizes observed impacts, vulnerability and exposure, and adaptive responses to date. Section B examines future risks and potential benefits. Section C considers principles for effective adaptation and the broader interactions among adaptation, mitigation,

EMISSIONS

and Land-use Change

Vulnerability

Exposure

Hazards RISK

Anthropogenic Climate Change

Socioeconomic Pathways

Adaptation and Mitigation Actions

Governance

IMPACTS

Natural Variability

SOCIOECONOMIC

CLIMATE PROCESSES

R

Figure SPM.1 | Illustration of the core concepts of the WGII AR5. 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. Changes in both the climate system (left) and socioeconomic processes including adaptation and mitigation (right) are drivers of hazards, exposure, and vulnerability. [19.2, Figure 19-1]

(^1) A key finding of the WGI AR5 is, “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.” [WGI AR5 SPM Section D.3, 2.2, 6.3, 10.3-6, 10.9] (^2) 1.1, Figure 1-

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and sustainable development. Background Box SPM.2 defines central concepts, and Background Box SPM.3 introduces terms used to convey the degree of certainty in key findings. Chapter references in brackets and in footnotes indicate support for findings, figures, and tables.

A: OBSERVED IMPACTS, VULNERABILITY, AND ADAPTATION IN A COMPLEX AND CHANGING WORLD

A-1. Observed Impacts, Vulnerability, and Exposure

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans. Evidence of climate-change impacts is strongest and most comprehensive for natural systems. Some impacts on human systems have also been attributed 5 to climate change, with a major or minor contribution of climate change distinguishable from other influences. See Figure SPM.2. Attribution of observed impacts in the WGII AR5 generally links responses of natural and human systems to observed climate change, regardless of its cause. 6

In many regions, changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality (medium confidence). Glaciers continue to shrink almost worldwide due to climate change (high confidence), affecting runoff and water resources downstream (medium confidence). Climate change is causing permafrost warming and thawing in high- latitude regions and in high-elevation regions (high confidence).^7

Many terrestrial, freshwater, and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interactions in response to ongoing climate change (high confidence). See Figure SPM.2B. While only a few recent species extinctions have been attributed as yet to climate change (high confidence), natural global climate change at rates slower than current anthropogenic climate change caused significant ecosystem shifts and species extinctions during the past millions of years (high confidence).^8

Based on many studies covering a wide range of regions and crops, negative impacts of climate change on crop yields have been more common than positive impacts (high confidence). The smaller number of studies showing positive impacts relate mainly to

Background Box SPM.1 | Context for the Assessment

For the past 2 decades, IPCC’s Working Group II has developed assessments of climate-change impacts, adaptation, and vulnerability. The WGII AR5 builds from the WGII contribution to the IPCC’s Fourth Assessment Report (WGII AR4), published in 2007, and the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), published in

2012. It follows the Working Group I contribution to the AR5 (WGI AR5). 3

The number of scientific publications available for assessing climate-change impacts, adaptation, and vulnerability more than doubled between 2005 and 2010, with especially rapid increases in publications related to adaptation. Authorship of climate-change publications from developing countries has increased, although it still represents a small fraction of the total. 4

The WGII AR5 is presented in two parts (Part A: Global and Sectoral Aspects, and Part B: Regional Aspects), reflecting the expanded literature basis and multidisciplinary approach, increased focus on societal impacts and responses, and continued regionally comprehensive coverage.

(^3) 1.2- (^4) 1.1, Figure 1- (^5) The term attribution is used differently in WGI and WGII. Attribution in WGII considers the links between impacts on natural and human systems and observed climate change, regardless of its cause. By comparison, attribution in WGI quantifies the links between observed climate change and human activity, as well as other external climate drivers. (^6) 18.1, 18.3- (^7) 3.2, 4.3, 18.3, 18.5, 24.4, 26.2, 28.2, Tables 3-1 and 25-1, Figures 18-2 and 26- (^8) 4.2-4, 5.3-4, 6.1, 6.3-4, 18.3, 18.5, 22.3, 24.4, 25.6, 28.2, 30.4-5, Boxes 4-2, 4-3, 25-3, CC-CR, and CC-MB

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or other components of food security. See Figure SPM.2C. Since AR4, several periods of rapid food and cereal price increases following climate extremes in key producing regions indicate a sensitivity of current markets to climate extremes among other factors (medium confidence). 11

At present the worldwide burden of human ill-health from climate change is relatively small compared with effects of other stressors and is not well quantified. However, there has been increased heat-related mortality and decreased cold-related mortality in some regions as a result of warming (medium confidence). Local changes in temperature and rainfall have altered the distribution of some water- borne illnesses and disease vectors (medium confidence).^12

Differences in vulnerability and exposure arise from non-climatic factors and from multidimensional inequalities often produced by uneven development processes (very high confidence). These differences shape differential risks from climate change. See Figure SPM.1. People who are socially, economically, culturally, politically, institutionally, or otherwise marginalized are especially vulnerable to climate change and also to some adaptation and mitigation responses (medium evidence, high agreement). This heightened vulnerability is rarely due to a single cause. Rather, it is the product of intersecting social processes that result in inequalities in socioeconomic status and income, as well as in exposure. Such social processes include, for example, discrimination on the basis of gender, class, ethnicity, age, and (dis)ability. 13

Impacts from recent climate-related extremes, such as heat waves, droughts, floods, cyclones, and wildfires, reveal significant vulnerability and exposure of some ecosystems and many human systems to current climate variability (very high confidence). Impacts of such climate-related extremes include alteration of ecosystems, disruption of food production and water supply, damage to infrastructure and settlements, morbidity and mortality, and consequences for mental health and human well-being. For countries at all levels of development, these impacts are consistent with a significant lack of preparedness for current climate variability in some sectors.^14

Climate-related hazards exacerbate other stressors, often with negative outcomes for livelihoods, especially for people living in poverty (high confidence). Climate-related hazards affect poor people’s lives directly through impacts on livelihoods, reductions in crop

Background Box SPM.3 | Communication of the Degree of Certainty in Assessment Findings^10

The degree of certainty in each key finding of the assessment is based on the type, amount, quality, and consistency of evidence (e.g., data, mechanistic understanding, theory, models, expert judgment) and the degree of agreement. The summary terms to describe evidence are: limited, medium, or robust; and agreement: low, medium, or high.

Confidence in the validity of a finding synthesizes the evaluation of evidence and agreement. Levels of confidence include five qualifiers: very low, low, medium, high, and very high.

The likelihood, or probability, of some well-defined outcome having occurred or occurring in the future can be described quantitatively through the following terms: virtually certain, 99–100% probability; extremely likely, 95–100%; very likely, 90–100%; likely, 66–100%; more likely than not, >50–100%; about as likely as not, 33–66%; unlikely, 0–33%; very unlikely, 0–10%; extremely unlikely, 0–5%; and exceptionally unlikely, 0–1%. Unless otherwise indicated, findings assigned a likelihood term are associated with high or very high confidence. Where appropriate, findings are also formulated as statements of fact without using uncertainty qualifiers.

Within paragraphs of this summary, the confidence, evidence, and agreement terms given for a bold key finding apply to subsequent statements in the paragraph, unless additional terms are provided.

(^10) 1.1, Box 1- (^11) 7.2, 18.4, 22.3, 26.5, Figures 7-2, 7-3, and 7- (^12) 11.4-6, 18.4, 25. (^13) 8.1-2, 9.3-4, 10.9, 11.1, 11.3-5, 12.2-5, 13.1-3, 14.1-3, 18.4, 19.6, 23.5, 25.8, 26.6, 26.8, 28.4, Box CC-GC (^14) 3.2, 4.2-3, 8.1, 9.3, 10.7, 11.3, 11.7, 13.2, 14.1, 18.6, 22.3, 25.6-8, 26.6-7, 30.5, Tables 18-3 and 23-1, Figure 26-2, Boxes 4-3, 4-4, 25-5, 25-6, 25-8, and CC-CR

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ARCTIC

Distribution change (km per decade)

(90)

(20) (^) (46) (29)^ (9)

(3)

(13)

(29) (9)

(111) (359)

Cooler

Warmer

Benthic algae Benthic cnidariansBenthic mollusksBenthic crustacea Benthic invert. (other)

PhytoplanktonZooplanktonLarval bony fishesNon-bony fishesBony fishes

All taxa

75 th^ percentile

90 th^ percentile

10 th^ percentile

Median 25 th^ percentile

Standard error Mean Standard error

EUROPE

verylow low med high veryhigh

Glaciers, snow, ice, and/or permafrost

indicates confidence range

Rivers, lakes, floods, and/or drought

Terrestrial ecosystems (^) Regional-scale impacts Coastal erosionand/or sea level effects Marine ecosystems

Wildfire Livelihoods, health,and/or economics

Food production

Physical systems Biological systems Human and managed systems

Filled symbols = Major contribution of climate change

Outlined symbols = Minor contribution of climate change

Confidence in attribution to climate change

Observed impacts attributed to climate change for

SMALL ISLANDS

AUSTRALASIA

AFRICA

CENTRAL & SOUTH AMERICA

NORTH AMERICA ASIA

ANTARCTIC

(B) (C)

(A)

−

−

0

2

0

20

400

100

Temperate Wheat Soy Rice Maize Region Crop type

Tropical

(19) (27) (18) (10) (13) (12)

Yield impact (% change per decade)

Figure SPM.2 | Widespread impacts in a changing world. (A) Global patterns of impacts in recent decades attributed to climate change, based on studies since the AR4. Impacts are shown at a range of geographic scales. Symbols indicate categories of attributed impacts, the relative contribution of climate change (major or minor) to the observed impact, and confidence in attribution. See supplementary Table SPM.A1 for descriptions of the impacts. (B) Average rates of change in distribution (km per decade) for marine taxonomic groups based on observations over 1900–2010. Positive distribution changes are consistent with warming (moving into previously cooler waters, generally poleward). The number of responses analyzed is given within parentheses for each category. (C) Summary of estimated impacts of observed climate changes on yields over 1960–2013 for four major crops in temperate and tropical regions, with the number of data points analyzed given within parentheses for each category. [Figures 7-2, 18-3, and MB-2]

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• In the Arctic, some communities have begun to deploy adaptive co-management strategies and communications infrastructure, combining traditional and scientific knowledge. 24
• In small islands, which have diverse physical and human attributes, community-based adaptation has been shown to generate larger benefits when delivered in conjunction with other development activities.^25
• In the ocean, international cooperation and marine spatial planning are starting to facilitate adaptation to climate change, with constraints from challenges of spatial scale and governance issues.^26

A-3. The Decision-making Context

Climate variability and extremes have long been important in many decision-making contexts. Climate-related risks are now evolving over time due to both climate change and development. This section builds from existing experience with decision making and risk management. It creates a foundation for understanding the report’s assessment of future climate-related risks and potential responses.

Responding to climate-related risks involves decision making in a changing world, with continuing uncertainty about the severity and timing of climate-change impacts and with limits to the effectiveness of adaptation (high confidence). Iterative risk management is a useful framework for decision making in complex situations characterized by large potential consequences, persistent uncertainties, long timeframes, potential for learning, and multiple climatic and non-climatic influences changing over time. See Figure SPM.3. Assessment of the widest possible range of potential impacts, including low-probability outcomes with large consequences, is central to understanding the benefits and trade-offs of alternative risk management actions. The complexity of adaptation actions across scales and contexts means that monitoring and learning are important components of effective adaptation. 27

Adaptation and mitigation choices in the near term will affect the risks of climate change throughout the 21st century (high confidence). Figure SPM.4 illustrates projected warming under a low-emission mitigation scenario and a high-emission scenario [Representative Concentration Pathways (RCPs) 2.6 and 8.5], along with observed temperature changes. The benefits of adaptation and mitigation occur over different but overlapping timeframes. Projected global temperature increase over the next few decades is similar across emission scenarios (Figure SPM.4B).^28 During this near-term period, risks will evolve as socioeconomic trends interact with the changing climate. Societal

Scoping

Implementation

Review & learn

Implement decision

Monitor

Assess risks

Identify options

Evaluate tradeoffs

Analysis

Scopppinggg Identify risks, vulnerabilities, & objectives

Establish decision- making criteria

Figure SPM.3 | Climate-change adaptation as an iterative risk management process with multiple feedbacks. People and knowledge shape the process and its outcomes. [Figure 2-1]

(^24) 28.2, 28. (^25) 29.3, 29.6, Table 29-3, Figure 29- (^26) 30. (^27) 2.1-4, 3.6, 14.1-3, 15.2-4, 16.2-4, 17.1-3, 17.5, 20.6, 22.4, 25.4, Figure 1- (^28) WGI AR5 11.

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Observed Temperature Change

Based on trend over

1901–2012 (˚ C over period)

Diagonal Lines Trend notstatistically significant White Insufficientdata

Solid Color Significanttrend

Projected Temperature Change

–0.5 0 2 4 6 11.

–0.5 0 2 4 6 11.

Difference from

1986–2005 mean ( ˚ C)

Solid Color Very strongagreement Strongagreement Little or Gray (^) no change Divergent changes Diagonal Lines

White Dots

(A)

(B)

(C)

RCP2.6 2081–2100 RCP8.5 2081–

Global mean temperature change

(^ C relative to 1986–2005)˚^

1900 1950 2000 2050 2100

6

4

2

0

Figure SPM.4 | Observed and projected changes in annual average surface temperature. This figure informs understanding of climate-related risks in the WGII AR5. It illustrates temperature change observed to date and projected warming under continued high emissions and under ambitious mitigation.

Observed

RCP2.

RCP8. Overlap

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high probability, or irreversibility of impacts; timing of impacts; persistent vulnerability or exposure contributing to risks; or limited potential to reduce risks through adaptation or mitigation. Key risks are integrated into five complementary and overarching reasons for concern (RFCs) in Assessment Box SPM.1.

The key risks that follow, all of which are identified with high confidence, span sectors and regions. Each of these key risks contributes to one or more RFCs.^36

(^33) WGI AR5 SPM, 2.2, 6.3, 10.3-6, 10. (^34) 18.6, 19.6; observed warming from 1850–1900 to 1986–2005 is 0.61°C (5–95% confidence interval: 0.55 to 0.67°C). [WGI AR5 2.4] (^35) Current estimates indicate that this threshold is greater than about 1°C (low confidence) but less than about 4°C (medium confidence) sustained global mean warming above preindustrial levels. [WGI AR5 SPM, 5.8, 13.4-5] (^36) 19.2-4, 19.6, Table 19-4, Boxes 19-2 and CC-KR

Assessment Box SPM.1 | Human Interference with the Climate System

Human influence on the climate system is clear.^33 Yet determining whether such influence constitutes “dangerous anthropogenic interference” in the words of Article 2 of the UNFCCC involves both risk assessment and value judgments. This report assesses risks across contexts and through time, providing a basis for judgments about the level of climate change at which risks become dangerous.

Five integrative reasons for concern (RFCs) provide a framework for summarizing key risks across sectors and regions. First identified in the IPCC Third Assessment Report, the RFCs illustrate the implications of warming and of adaptation limits for people, economies, and ecosystems. They provide one starting point for evaluating dangerous anthropogenic interference with the climate system. Risks for each RFC, updated based on assessment of the literature and expert judgments, are presented below and in Assessment Box SPM.1 Figure 1. All temperatures below are given as global average temperature change relative to 1986–2005 (“recent”).^34

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.

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).

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).

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.

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,^35 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.

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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 (^1900 1950 2000 2050) events °C

5 4 3 2 1 0

(^ C relative to˚^

1850–

, as an

approximation of preindustrial levels)

2003 –

2100

(^ C relative to˚^

1850–

, as an

approximation of preindustrial levels)

6 5 4 3 2 1 0

°C

-0.

(^ C relative to˚^

1986–

)

Global mean temperature change

5 4 3 2 1 0

°C

-0.

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]

(^ C relative to˚^

1986–

)

Global mean temperature change

Observed

RCP2.6 (a low-emission mitigation scenario)

RCP8.5 (a high-emission scenario) Overlap

(^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

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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 mammalsRodentsPrimates 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–

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]

(^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. (^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-

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Change in maximum catch potential (2051–2060 compared to 2001–2010, SRES A1B) < –50 % –21 to –50 % –6 to –20 % –1 to –5 % no data 0 to 4 % 5 to 19 % 20 to 49 % 50 to 100 % > 100 %

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

Control500–650651–850851–

0

20

40

60

80

100

Mollusks

1371–

29 37 4 9 18

Control500–650651–850851–

0

20

40

60

80

100

Crustaceans

1371–

23

Cold-water corals 7 4 7 5

Control500–650651–850851–

0

20

40

60

80

100 3

1371–

Species (%)

26 9 15 23

Control

0

20

40

60

80

100 20

500–650651–850851–13701371–

Warm-water corals

(B)

–0.60–0.55–0.50–0.45–0.40–0.35–0.30–0.25–0.20–0.15–0.10–0.

SPM

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–

2050–2069 2070–

(^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- (^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- (^56) 3.5, 8.2-4, 22.3, 24.4-5, 26.8, Table 8-2, Boxes 25-9 and CC-HS

SPM

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

(^57) 9.3, 25.9, 26.8, 28.2, 28.4, Box 25- (^58) 3.5, 10.2, 10.7, 10.10, 17.4-5, 25.7, 26.7-9, Box 25- (^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.