Editing IPCC:AR6/WGII/Chapter-16 (section)

==== 16.4.3.1 Evidence on Limits to Adaptation ====

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There is ''high agreement'' and ''medium evidence'' that there are limits to adaptation across regions and sectors. However, much of the available evidence focuses on constraints that may lead to limits at some point with little detailed information on how limits may be related to different levels of socioeconomic or environmental change ( ''high confidence'' ). Figure 16.7 assesses evidence on constraints and limits for broad categories of region and sector. Small islands and Central and South America show most evidence of constraints being linked to adaptation limits across sectors, while ocean and coastal ecosystems and health, well-being and communities show most evidence of constraints being linked to limits across regions ( ''medium confidence'' ) ''.''

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'''Figure 16.7 |''' '''Evidence on constraints and limits to adaptation by region and sector.''' Data from [[#Thomas--2021|Thomas et al. (2021)]] , based on 1682 scientific publications reporting on adaptation-related responses in human systems. See SM16.1 for methods. '''Low evidence:''' &lt;20% of assessed literature has information on limits; literature mostly focuses on constraints to adaptation. '''Medium evidence:''' between 20% and 40% of assessed literature has information on limits; literature provides some evidence of constraints being linked to limits. '''High evidence:''' &gt;40% of assessed literature has information on limits; literature provides broad evidence of constraints being linked to limits.

There are clusters of evidence with additional details on limits to adaptation, as detailed in Table 16.3. Evidence on limits to adaptation is largely focused on terrestrial and aquatic species and ecosystems, coastal communities, water security, agricultural production, and human health and heat ( ''high confidence'' ).

Beginning at 1.5°C, autonomous and evolutionary adaptation responses by terrestrial and aquatic species and ecosystems face hard limits, resulting in biodiversity decline, species extinction and loss of related livelihoods ( ''high confidence'' ). Interventionist adaptation strategies to reduce risks for species and ecosystems face soft limits due to governance, financial and knowledge constraints ( ''medium confidence'' ) ''.''

As sea levels rise and extreme events intensify, coastal communities face soft limits due to financial, institutional and socioeconomic constraints reducing the efficacy of coastal protection and accommodation approaches and resulting in loss of life and economic damages ( ''medium confidence'' ) ''.'' Hard limits for coastal communities reliant on nature-based coastal protection will be experienced beginning at 1.5°C ( ''medium confidence'' ).

Beginning at 3°C, hard limits are projected for water management measures, leading to decreased water quality and availability, negative impacts on health and well-being, economic losses in water and energy dependent sectors and potential migration of communities ( ''medium confidence'' ).

Soft and hard limits for agricultural production are related to water availability and the uptake and effectiveness of climate-resilient crops, which is constrained by socioeconomic and political challenges ( ''medium confidence'' ) ''.''

Adaptation measures to address risks of heat stress, heat mortality and reduced capacities for outdoor work for humans face soft and hard limits across regions beginning at 1.5°C and are particularly relevant for regions with warm climates ( ''high confidence'' ).

'''Table 16.3 |''' Adaptation limits and residual risks for select actors and systems. Asterisks indicate confidence level

{| class="wikitable"
|-
! Actor/system at risk

! Adaptation limits

! Residual risks

|-
| Terrestrial species in islands at risk to loss of habitat

| Hard: autonomous adaptation unable to overcome loss of habitat and lack of physical space ( c ) (Box [https://www.ipcc.ch/chapter/16#CCP1.1 CCP1.1] )

| Biodiversity decline, local extinctions, half of all species currently considered to be at risk of extinction occur on islands (Box CCP 1.1)

|-
| Terrestrial species across Africa at risk to habitat changes

| Hard: beyond 2°C, many species will lack suitable climate conditions by 2100 despite migration and dispersal ( c ) ( [[IPCC:Wg2:Chapter:Chapter-9#9.6.4.1|Section 9.6.4.1]] )

| 9% of species face complete range loss ( a ), mountaintop endemics and species at poleward boundaries of African continent at risk of range loss due to disappearing cold climates ( c ) ( [[IPCC:Wg2:Chapter:Chapter-9#9.6.4.1|Section 9.6.4.1]] )

|-
| African aquatic organisms at risk to habitat changes

| Hard: thermal changes above optimal physiological limits will reduce available habitats ( [[IPCC:Wg2:Chapter:Chapter-9#9.6.2.4|Section 9.6.2.4]] )

| Greater risks of loss of endemic fish species than generalist fish species ( [[IPCC:Wg2:Chapter:Chapter-9#9.6.2.4|Section 9.6.2.4]] )

|-
| African coastal and marine ecosystems at risk to habitat changes

| Hard: at 2°C, bleaching of east African coral reefs ( c ) ( [[IPCC:Wg2:Chapter:Chapter-9#9.6.2.3|Section 9.6.2.3]] )

| Over 90% of east African coral reefs destroyed at 2°C ( c ) ( [[IPCC:Wg2:Chapter:Chapter-9#9.6.2.3|Section 9.6.2.3]] )

|-
| Coral reefs at risk to oceanic changes

| Hard: coral restoration and management no longer effective after 2°C ( c ), enhanced coal and reef shading no longer effective after 3°C ( b ) (Figure 3.23)

| Loss of more than 80% of healthy coral cover, loss of livelihoods dependent on coral reefs ( c ) (Figure 3.23, Table 8.7)

|-
| Cold-adapted species whose habitats are restricted to polar and high mountaintop areas at risk to loss of climate space

| Hard: evolutionary responses unable to keep pace with the rate of climate change and degraded state of ecosystems (Sections 2.6.1, [https://www.ipcc.ch/chapter/16#CCP1.2.4.2 CCP1.2.4.2] )

| Species extinctions in the case of species losing their climate space entirely on a regional or global scale (Sections 2.6.1, [https://www.ipcc.ch/chapter/16#CCP1.2.4.2 CCP1.2.4.2] )

|-
| Ecosystems in North America at risk to multiple climate hazards

| Soft: governance constraints hinder implementation of adaptation strategies

Hard: some species unable to adapt (Table 14.8)

|
|-
| Ecosystems and species at risk to multiple climate hazards

| Soft: financial and knowledge constraints lead to limits for interventionist approaches such as translocation of species or ecosystem restoration Hard: some habitats unable to be effectively restored ( [[IPCC:Wg2:Chapter:Chapter-2#2.6.6|Section 2.6.6]] )

| Species extinctions and changes, irreversible major biome shifts ( [[IPCC:Wg2:Chapter:Chapter-2#2.6.6|Section 2.6.6]] )

|-
| Coastal settlements in Australia and New Zealand at risk to sea level rise

| Soft and hard: limits in the efficacy of coastal protection and accommodation approaches as sea levels rise and extreme events intensify (Box 11.5)

| With 1–1.1 m of sea level rise, value of coastal urban infrastructure at risk in Australia is AUD 164 to &gt;226 billion, while in NZ it is NZD 43 billion. Sea level rise will also result in significant cultural and archaeological sites disturbed and increasing flood risk and water insecurity with health and well-being impacts on Australia’s small northern islands (Box 11.5)

|-
| Human settlements in

coastal areas in the 1-in-100-year floodplain at risk to coastal flooding

| Soft: socioeconomic, institutional and financial constraints may lead to soft limits well in advance of technical limits of hard engineering measures (Sections [https://www.ipcc.ch/chapter/16#CCP2.3.4 CCP2.3.2] , [https://www.ipcc.ch/chapter/16#CCP2.3.4 CCP2.3.4] ) Hard: Nature-based measures (e.g., restoration of coral reefs, mangroves, marshes) reach hard limits beginning at 1.5°C of global warming. Retreat strategies reach hard limits as availability and affordability of land decreases (CCPs 2.3.2.3, 2.3.5)

| At 3°C, globally up to 510 million people and up to USD 12,739 billion in assets at risk by 2100 (Section CCP 2.2.1)

|-
| Communities in small islands at risk to freshwater shortages

| Hard: domestic freshwater resources unable to recover from increased drought, sea level rise and decreased precipitation by 2030 (RCP8.5+ ice sheet collapse), 2040 (RCP8.5) or 2060 (RCP4.5) (Box 4.2, [[IPCC:Wg2:Chapter:Chapter-4#4.7.2|Section 4.7.2]] )

| Migration of communities due to water shortages with impacts on well-being, community cohesion, livelihoods and people–land relationships (Box 4.2)

|-
| Communities in North America at risk to poor water quality

| Soft: financial and technological constraints lead to limits in ability to treat water for harmful algal blooms (Table 14.8)

|
|-
| Communities in Western and Central Europe at risk to water shortages

| Hard: at 3°C, geophysical and technological limits reached in Southern Europe ( [[IPCC:Wg2:Chapter:Chapter-13#13.10.3|Section 13.10.3.3]] )

| At 3°C, two-thirds of the population of Southern Europe at risk to water security with significant economic losses in water- and energy-dependent sectors ( b ) (Sections 13.2.2, 13.6, 13.10.2.3)

|-
| Communities in Central and South America at risk to water shortages

| Soft: improved water management as an adaptation strategy unable to overcome lack of trust and stakeholder flexibility, unequal power relations and reduced social learning ( [[IPCC:Wg2:Chapter:Chapter-12#12.5.3.4|Section 12.5.3.4]] )

| Increasing competition and

conflict associated with high economic losses ( b ); glacier shrinkage leading to loss of related livelihoods and cultural values ( [[IPCC:Wg2:Chapter:Chapter-12#12.5.3.1|Section 12.5.3.1]] , Table 8.7)

|-
| Agricultural production in Europe at risk to heat and drought

| Soft: above 3°C, unavailability of water will limit irrigation as an adaptation response ( c ) (Sections 13.5.1, 13.10.2.2)

| At 3–4°C, yield losses for maize may reach up to 50% ( b ) (Sections 13.5.1, 13.10.2.2)

|-
| Crops at risk to temperature increase

| Soft: socioeconomic and political constraints limit uptake of climate-resilient crops ( [[IPCC:Wg2:Chapter:Chapter-5#5.4.4.3|Section 5.4.4.3]] ) Hard: after 2°C, cultivar changes unable to offset global production losses ( [[IPCC:Wg2:Chapter:Chapter-5#5.4.4.1|Section 5.4.4.1]] )

| Costs of adaptation and residual damages are USD 63 billion at 1.5°C. USD 80 billion at 2°C and USD 128 billion at 3°C, with greater risks and damages in tropical and arid regions ( [[IPCC:Wg2:Chapter:Chapter-5#5.4.4.1|Section 5.4.4.1]] )

|-
| Human health in Europe at risk to heat

| Soft: many adaptation measures will not be able to fully mitigate overheating in buildings with high levels of global warming ( c ) ( [[IPCC:Wg2:Chapter:Chapter-13#13.6.2.3|Section 13.6.2.3]] ) Hard: above 3°C, people and health systems unable to adapt ( c ) (Sections 13.6.2.3, 13.7.2, 13.7.4, 13.10.2.1, 13.8)

| At 1.5°C, 30,000 annual deaths due to extreme heat with up to 90,000 annual deaths at 3°C in 2100 ( c ) ( [[IPCC:Wg2:Chapter:Chapter-13#13.7.1|Section 13.7.1]] ); at 3°C, thermal comfort hours during summer will decrease by as much as 74% in locations in southern Europe ( c ) ( [[IPCC:Wg2:Chapter:Chapter-13#13.6.1.5|Section 13.6.1.5]] )

|-
| Human health at risk to heat

| Soft: socioeconomic constraints limit adaptation responses to extreme heat ( [[IPCC:Wg2:Chapter:Chapter-7#7.4.2.6|Section 7.4.2.6]] , Table 8.7)

| Globally, the impact of projected climate change on temperature-related mortality is expected to be a net increase under RCP4.5 to RCP8.5, even with adaptation, particularly for regions with warm climates ( d ) ( [[IPCC:Wg2:Chapter:Chapter-7#7.3.1|Section 7.3.1]] , Table 8.7)

|-
| South Asian settlements at risk to coastal flooding, drought, sea level rise and heatwaves

| Soft and hard: at 4.5°C, maximum temperature is expected to exceed survivability threshGold across most of South Asia, particularly relevant for outdoor work ( a ) (Table 10.6)

| At RCP4.5, 25–50% of population affected; at RCP8.5, more than 50% of population affected; at 4.5°C of warming, increase in heat-related deaths of 12.7% in South Asia ( a ) (Table 10.6)

|-
| Tourism in Europe reliant on snow at risk to higher levels of warming

| Soft: at 3°C, snowmaking as an adaptation measure limited by biophysical and financial constraints ( c ) (Sections 13.6.1.4, 13.6.2.3)

| Damages in European tourism with larger losses in Southern Europe ( c ) ( [[IPCC:Wg2:Chapter:Chapter-13#13.6.1.4|Section 13.6.1.4]] )

|-
| Rapidly growing towns/cities and smaller cities at risk to range of climate hazards

| Soft: governance and financial constraints lead to limits in ability to adapt (Sections 6.3, 6.4)

|
|}

Notes:

(a) ''low confidence''

(b) ''medium confidence''

(c) ''high confidence''

(d) ''very high confidence.''

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