Editing IPCC:AR6/WGII/Chapter-7 (section)

=== 7.3.2 Migration and Displacement in a Changing Climate ===

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''Future changes in climate-related migration and displacement are expected to vary by region and over time according to: (a) region-specific changes in climatic drivers, (b) changes in the future adaptive capacity of exposed populations, (c) population growth in areas most exposed to climatic risks and (d) future changes in mediating factors such as international development and migration policies'' ( ''high agreement, medium evidence'' ) ''( [[#Gemenne--2017|Gemenne and Blocher, 2017]] ; [[#Cattaneo--2019|Cattaneo et al., 2019]] ; [[#McLeman--2019|McLeman, 2019]] ).'' This section assesses future risks associated with changes in the frequency and/or severity of storms, floods, droughts, extreme heat, wildfires and other events assessed in Section 7.2 that currently affect migration and displacement patterns, as well as the impacts of emerging hazards, including average temperature increases that may affect the habitability of settlements in arid regions and the tropics, and sea level rise and associated hazards that threaten low-lying coastal settlements. Studies assessed here consider projected changes in future exposure to hazards over a variety of geographical and temporal periods, with some considering changes in population numbers in exposed areas. The uneven distribution of exposure of age cohorts is typically overlooked in existing research. For example, people younger than age 10 in the year 2020 are projected to experience a nearly four-fold increase in extreme events under 1.5°C of global warming and a five-fold increase under 3°C warming; such increases in exposure would not be experienced by a person of the age of 55 in 2020 in their remaining lifetime under any warming scenario ( [[#Thiery--2021|Thiery et al., 2021]] ).

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==== 7.3.2.1 Region-Specific Changes in Climatic Risks ====

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''As outlined in 7.2, the most common drivers of observed climate-related migration and displacement are extreme storms (particularly tropical cyclones), floods and droughts'' ( ''high confidence'' ) ''.'' The future frequency and/or severity of such events due to anthropogenic climate change are expected to vary by region according to future GHG emission pathways (Naik et al 2021; Regional Chapters, this report), with there being an increased potential for compound effects of successive or multiple hazards (e.g., tropical storms accompanied by extreme heat events ( [[#Matthews--2019|Matthews et al., 2019]] )). Table 7.2 summarises anticipated changes in future migration and displacement risks due to sudden-onset climate events by region (and by sub-regions for Africa and Asia, where climatic risks vary within the region).

'''Table 7.2 |''' Projected changes in sudden-onset climate events associated with migration and displacement by region.

{| class="wikitable"
|-
! '''Region'''

! '''Main directions of current migration flows (from [[#Abel--2014|Abel and Sander (2014)]] )'''

! '''Current climatic drivers of migration and displacement ( [[#7.2.6.1|Section 7.2.6.1]] )'''

! '''Expected changes in drivers (''' '''''including confidence statements''''' ''') from IPCC WGI 2021 Technical Summary, 4.3.1–4.3.2'''

|-
| Asia

| * East and Southeast Asia: within countries and between countries within same region.
* South and central Asia: within countries and between countries within same region; from south Asia to Middle East, North America, Europe.
* West Asia: within countries and between countries within the same region; to Europe

| Floods, extreme storms, extreme heat

| Increased risk of flooding in East, north, south and Southeast Asia due to increases in annual mean precipitation ( ''high confidence'' ) and extreme precipitation events in East, south, west central, north and Southeast Asia ( ''medium confidence'' ); uncertainty regarding future trends in cyclones (current trend = decreased frequency, increased intensity); higher average temperatures across region ( ''high confidence'' )

|-
| Africa

| * Within countries and between countries within the same region; to Europe and the Middle East

| Floods, droughts, extreme heat

| Decrease in total annual precipitation in northernmost and southernmost parts of Africa ( ''high confidence'' ); west-to-east pattern of decreasing-to-increasing annual precipitation in west Africa and east Africa ( ''medium confidence'' ); increased risk of heavy precipitation events that trigger flooding, across most parts of Africa ( ''medium confidence'' ); increased aridity and drought risks in north Africa, southern Africa and western parts of west Africa ( ''medium-high confidence'' )

|-
| Europe

| * Within countries and between countries in same region

| Floods

| Increased risk of floods across all areas of Europe except Mediterranean areas ( ''high confidence'' ); higher risks of drought and fire weather in Mediterranean areas ( ''high confidence'' )

|-
| North America

| * Within countries and between countries in same region

| Floods, tropical cyclones (US Atlantic and Caribbean coast), tornadoes, wildfires

| Increased frequency of heavy precipitation events across most areas ( ''high confidence'' ); tropical cyclones to become more severe ( ''medium confidence'' ); increased risk of drought and fire weather in central and western North America

|-
| Central and

South America

| * Within countries and between countries in same region; to North America, Europe

| Floods (Central and South America), extreme storms (Central America)

| Increases in mean annual precipitation and extreme precipitation events with higher risks of floods in most areas of South America ( ''medium confidence'' ); increased risk of droughts in northeastern and southern South America and northern Central America ( ''medium confidence'' ); tropical cyclones becoming more extreme ( ''medium confidence'' )

|-
| Australasia

| * Displacement within countries

| Wildfires

| Increases in fire weather across Australia and New Zealand ( ''medium confidence'' )

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| Small island states

| * Within and between countries in same region (e.g., Pacific Islands to Australia and New Zealand; Caribbean islands to USA)

| Extreme storms

| Potentially fewer but more extreme tropical cyclones ( ''medium confidence'' )

|}

''In low-lying coastal areas of most regions, future increases in mean sea levels will amplify the impacts of coastal hazards on settlements, including erosion, inland penetration of storm surges and groundwater contamination by salt water, and eventually lead to inundation of very low-lying coastal settlements'' ( ''high confidence'' ) ''( [[#Diaz--2016|Diaz, 2016]] ; [[#Hauer--2016|Hauer et al., 2016]] ; [[#Neumann--2015|Neumann et al., 2015]] ; [[#Rahman--2019|Rahman et al., 2019]] ; [[#IPCC--2019a|IPCC, 2019a]] )'' . Projections of the number of people at risk of future displacement by sea level rise range from tens of millions to hundreds of millions by the end of this century, depending on (a) the sea level rise scenario or RCP selected, (b) projections of future population growth in exposed areas and (c) the criteria used for identifying exposure. These latter measures can include estimates of populations situated within selected elevations above sea level (with 1 m, 2 m and 10 m being common parameters), populations situated in 1-in-100 year floodplains or populations in areas ''likely'' to be entirely inundated under specific RCPs ( [[#Neumann--2015|Neumann et al., 2015]] ; [[#Hauer--2016|Hauer et al., 2016]] ; [[#Merkens--2018|Merkens et al., 2018]] ; [[#McMichael--2020|McMichael et al., 2020]] ; [[#Hooijer--2021|Hooijer and Vernimmen, 2021]] ). As an illustrative example, an estimated 267 million people (error range = 197–347 million at 68% confidence level) worldwide lived within 2 m of sea level in 2020, 59% of whom reside in tropical regions of Asia ( [[#Hooijer--2021|Hooijer and Vernimmen, 2021]] ). At a 1 m increase in sea level and holding coastal population numbers constant, the number of people worldwide living within 2 m of sea level expands to 410 million (error range = 341–473 million). However, it is ''unlikely'' that coastal population growth rates will remain constant at global or regional scales in future decades. At present, coastal cities in many regions have relatively high rates of population growth due to the combined effects of in-migration from other regions and natural increase, with coastal areas of Africa having the highest projected future population growth rates ( [[#Neumann--2015|Neumann et al., 2015]] ; [[#Hooijer--2021|Hooijer and Vernimmen, 2021]] ; Box 7.5). Further complicating future estimates is that many large coastal cities are situated in deltas with high rates of subsidence, meaning that locally experienced changes in relative sea level may be much greater than sea level rise attributable to climate change, thereby further increasing the number of people exposed ( [[#Edmonds--2020|Edmonds et al., 2020]] ; [[#Nicholls--2021|Nicholls et al., 2021]] ).

Sea level rise is not presently a significant driver of migration in comparison with hazards assessed in [[#7.2.6|Section 7.2.6]] , but it has been attributed as a factor necessitating the near-term resettlement of small coastal settlements in Alaska, Louisiana, Fiji, Tuvalu and the Carteret Islands of Papua New Guinea ( [[#Marino--2015|Marino and Lazrus, 2015]] ; [[#Connell--2016|Connell, 2016]] ; [[#Hamilton--2016|Hamilton et al., 2016]] ; [[#Nichols--2019|Nichols, 2019]] ). In coastal Louisiana, communities tend to resist leaving exposed settlements until approximately 50% of available land has been lost ( [[#Hauer--2019|Hauer et al., 2019]] ). Movements away from highly exposed areas may have longer-term demographic implications for inland settlements ( [[#Hauer--2017|Hauer, 2017]] ), but this requires further study. Based on the available empirical evidence, sea level rise does not appear to currently be a primary motivation for international migration originating in small island states in the Indian and Pacific Oceans; rather, economic considerations and family reunification appear to be the dominant drivers ( [[#McCubbin--2015|McCubbin et al., 2015]] ; Stojanov and Du, 2016; [[#Heslin--2019|Heslin, 2019]] ; [[#Kelman--2019|Kelman et al., 2019]] ). However, climatic drivers of migration are anticipated to take on a much greater causal role in migration decisions in coming decades ( [[#Thomas--2020|Thomas et al., 2020]] ) and may discourage return migration to small island states ( [[#van%20der%20Geest--2020|van der Geest et al., 2020]] ). Even under best-case sustainable development scenarios, rising sea levels and associated hazards create risks of involuntary displacement in low-lying coastal areas and should be expected to generate a need for organised relocation of populations where protective infrastructure cannot be constructed (Horton and de Sherbinin, 2021; [[#Hamilton--2016|Hamilton et al., 2016]] ). In high emissions scenarios, low-lying island states may face the long-term risk of becoming uninhabitable, creating the potential for a new phenomenon of climate-induced statelessness ( [[#Piguet--2019|Piguet, 2019]] ; [[#Desai--2021|Desai et al., 2021]] ).

''Increased frequency of extreme heat events and long-term increases in average temperatures pose future risks to the habitability of settlements in tropical and subtropical regions, and may in the long term affect migration patterns in exposed areas, especially under high emissions scenarios'' ( ''medium agreement, low evidence'' ) ''.'' Greater research into the specific dynamics between extreme heat and population movements is required in order to make an accurate assessment of this risk. Recent studies suggest that future increases in average temperatures could expose populations across wide areas of the tropics and subtropics to ambient temperatures for extended periods each year that are beyond the threshold for human habitability ( [[#Pal--2016|Pal and Eltahir, 2016]] ; [[#Im--2017|Im et al., 2017]] ; [[#Xu--2020|Xu et al., 2020]] ). This effect would be amplified in urban settings where heat-island effects occur and create a heightened need for air conditioning and other adaptation measures. In addition to risks associated with average temperature changes, [[#Dosio--2018|Dosio et al. (2018)]] project that at 1.5°C warming, between 9% and 18% of the global population will be regularly exposed to extreme heat events at least once in five years, with the exposure rate nearly tripling with 2°C warming. How these changes in exposure to high temperatures will affect future migration patterns, particularly among vulnerable groups, will depend heavily on future adaptation responses (Horton and de Sherbinin, 2021). Multiple country-level studies assessed in Section 7.2 observe existing associations between extreme heat, its impacts on agricultural livelihoods and changes in rural-to-urban migration flows in parts of south Asia and sub-Saharan Africa. A study conducted in Indonesia, Malaysia and the Philippines suggests that an increased risk of heat stress would ''likely'' influence migration intentions of significant numbers of people ( [[#Zander--2019|Zander et al., 2019]] ).

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==== 7.3.2.2 Interactions with Non-climatic Determinants and Projections of Future Migration Flows ====

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Only a very small number of studies have attempted to make systematic projections of future regional or global migration and displacement numbers under climate change. Key methodological challenges for making such projections include the availability of reliable data on migration within and between countries, definitional ambiguity in distinguishing climate-related migration from migration undertaken for other reasons, and accounting for the future influence of non-climatic factors. The most reliable example of such studies to date is a World Bank report by [[#Rigaud--2018|Rigaud et al. (2018)]] that generated projections of future internal population displacements in south Asia, sub-Saharan Africa and Latin America by 2050 using multiple climate and development scenarios, resulting in a very large range of possible outcomes (from 31 to 143 million people being displaced, depending on assumptions). An important outcome is the study’s emphasis on how the potential for future migration and displacement will be strongly mediated by socioeconomic development pathways in low- and middle-income countries. [[#Hoffmann--2020|Hoffmann et al. (2020)]] used meta-regression-based analyses to project that future environmental influences on migration are ''likely'' to be greatest in low- and middle-income countries in Latin America and the Caribbean, sub-Saharan Africa, the Middle East and most of continental Asia.

''Research reviewed in AR4 and AR5 observed that at higher rates of socioeconomic development, the'' in situ ''adaptive capacity of households and institutions rises, and climatic influences on migration correspondingly decline. Recent evidence adds further support for such conclusions'' ( ''high confidence'' ) ''( [[#Kumar--2018b|Kumar et al., 2018b]] ; [[#Mallick--2019|Mallick, 2019]] ; [[#Gray--2020|Gray et al., 2020]] ; Box 7.5)'' . Population growth rates are currently highest in low-income countries (UN DESA Population Division, 2019), many of which have high rates of exposure to climatic hazards associated with population displacement, further emphasising the importance of socioeconomic development and adaptive capacity-building. Although country-specific scenarios for socioeconomic development and population are embedded in SSPs, research into future migration flows under climate change has not made great use of these. One of the few studies to do so found that safe and orderly international migration tends to increase wealth at regional and global scales in all SSP narratives, which in turn reduces income inequality between countries ( [[#Benveniste--2021|Benveniste et al., 2021]] ). International barriers to safe and orderly migration may potentially impede progress towards attainment of the objectives described in the SDGs and increase exposure to climatic hazards in low- and middle-income countries ( [[#McLeman--2019|McLeman, 2019]] ; [[#Benveniste--2020|Benveniste et al., 2020]] ).

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'''Box 7.5 | Uncertainties in projections of future demographic patterns at global, regional and national scales'''
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Projections of future numbers of people exposed to climate change-related hazards described in this chapter and elsewhere in this report are heavily influenced by assumptions about population change over time at global, regional and national scales. One challenge concerns global and regional variability of baseline data for current populations, which is typically aggregated from national censuses that vary considerably in terms of frequency, timing and reliability, especially in low-income countries. A number of gridded mapping dataset initiatives emerged in recent years to support population–environment modelling research at global and regional levels, common ones being the Gridded Population of the World, the Global Rural Urban Mapping Project, and LandScan Global Population dataset ( [[#McMichael--2020|McMichael et al., 2020]] ). For future population projections at national levels, researchers commonly draw upon data generated by the Population Division of the United Nations Department of Economic and Social Affairs, which publishes periodic projections for future fertility, mortality, and international migration rates for over 200 countries, the most recent projections being for the 2020 to 2100 period (UN DESA Population Division, 2019). There have been debates among demographers regarding the precision of DESA projections, and whether these overestimate or underestimate future population growth in some regions ( [[#Ezeh--2020|Ezeh et al., 2020]] ). Population growth rates are highly influenced by socioeconomic conditions, meaning that future population levels at local, national and regional scales are ''likely'' to respond to relative rates of progress towards meeting the Sustainable Development Goals ( [[#Abel--2016|Abel et al., 2016]] ). The Shared Socioeconomic Pathways (SSPs) used in climate impacts and adaptation research include a variety of assumptions about future mortality, fertility and migration rates and provide a range of population growth scenarios that diverge after the year 2030 according to future development trajectories ( [[#Samir--2017|Samir and Lutz, 2017]] ) and are then further modified and downscaled by researchers for national-level studies. Understanding future risks of climate change will benefit from continued efforts by the international community to collect and share data on observed population numbers and trends, and to work towards better projected data for population characteristics that strongly influence vulnerability to climate risks, such as gender, age and indigeneity.

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