Editing IPCC:AR6/WGII/Chapter-15 (section)

==== 15.3.4.6 Migration ====

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Climate-related migration is considered to be a particular issue for small islands because changes in extreme events and slow-onset changes affect increasingly highly exposed and vulnerable low-lying coastal populations, therefore causing a threat to small island habitability (KR9 in Figure 15.5) ( [[#Storey--2010|Storey and Hunter, 2010]] ; [[#Kumar--2015|Kumar and Taylor, 2015]] ; [[#Duvat--2017b|Duvat et al., 2017b]] ; [[#Weir--2017|Weir and Pittock, 2017]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Mycoo--2018a|Mycoo, 2018a]] ; [[#Rasmussen--2018|Rasmussen et al., 2018]] ). A typology of climate-related migration is provided in Cross-Chapter Box MIGRATE in Chapter 7. It is assumed that climate-related migration will increase in small islands; however, as is the case globally, the causes, form and outcomes are highly context specific. Types of climate-related migration occur across a continuum of agency from involuntary displacement at one end to voluntary movement to strategically reduce risks and planned resettlement at the other end ( [[#15.5.1|Section 15.5.1]] , also see Chapter 7; [[#Birk--2014|Birk and Rasmussen, 2014]] ; [[#Betzold--2015|Betzold, 2015]] ; McNamara and Des Combes, 2015; [[#Gharbaoui--2016|Gharbaoui and Blocher, 2016]] ; [[#Stojanov--2017|Stojanov et al., 2017]] ; [[#Weir--2020|Weir, 2020]] ).

Studies do not provide sufficiently robust evidence to attribute the various forms of migration to anthropogenic climate change directly on small islands or to accurately estimate the current number of climate-related migrants (see Chapter 7). Climate events and conditions strongly interact with other environmental stressors and economic, social, political and cultural reasons for migrating ( ''robust evidence, high agreement'' ) ( [[#Birk--2014|Birk and Rasmussen, 2014]] ; [[#Campbell--2014|Campbell and Warrick, 2014]] ; [[#Laczko--2014|Laczko and Piguet, 2014]] ; Marino and [[#Lazrus--2015|Lazrus, 2015]] ; [[#Connell--2016|Connell, 2016]] ; [[#Weber--2016b|Weber, 2016b]] ; [[#Stojanov--2017|Stojanov et al., 2017]] ; [[#Cashman--2019|Cashman and Yawson, 2019]] ).

Despite difficulties with attribution, the literature establishes that climate variability and extreme events and broad environmental pressures have contributed to some degree to human mobility on small islands over time ( ''medium evidence, high agreement'' ) ( [[#Birk--2014|Birk and Rasmussen, 2014]] ; [[#Campbell--2014a|Campbell, 2014a]] ; [[#Campbell--2014|Campbell and Warrick, 2014]] ; [[#Donner--2015|Donner, 2015]] ; [[#Kelman--2015a|Kelman, 2015a]] ; [[#Connell--2016|Connell, 2016]] ; [[#Stojanov--2017|Stojanov et al., 2017]] ; [[#Barnett--2018|Barnett and McMichael, 2018]] ; [[#Martin--2018|Martin et al., 2018]] ) and these studies can provide analogues from which to inform climate-migration responses ( [[#Birk--2014|Birk and Rasmussen, 2014]] ; [[#Kelman--2015a|Kelman, 2015a]] ; [[#Connell--2016|Connell, 2016]] ).

Similarly, studies do not provide robust evidence to project how the full range of climate drivers may influence migration patterns on small islands into the future, although studies are emerging that estimate populations affected as a consequence of projected SLR. [[#Rasmussen--2018|Rasmussen et al. (2018)]] estimated current populations of the world that are potentially subject to permanent inundation from projected local mean SLR associated with global mean surface temperature stabilisation targets of 1.5°C, 2.0°C and 2.5°C occurring in 2100. For the affected land area and population, this analysis included a subset of 58 SIDS, as defined by the United Nations, for which the results are shown in Table 15.4.

'''Table 15.4 |''' Global mean sea level rise (SLR) at 2100 projections and associated population of SIDS exposed to permanent inundation for global mean surface temperature stabilisation targets of 1.5°C, 2.0°C and 2.5°C. [[#Rasmussen--2018|Rasmussen et al. (2018)]] .

{| class="wikitable"
|-
! Stabilised Warming at 2100 a

! colspan="2"| 1.5°C

! colspan="2"| 2.0°C

! colspan="2"| 2.5°C

|-
! ''Percentile''

! ''50th''

! ''5th–95th''

! ''50th''

! ''5th–95th''

! ''50th''

! ''5th–95th''

|-
| Global mean SLR (cm) by percentile b

| 48

| 28–82

| 56

| 28–96

| 58

| 37–93

|-
| SIDS population exposure (thousands) by percentile c

| 400

| 300–560

| 420

| 300–640

| 430

| 320–630

|}

Notes:

(a) Above pre-industrial level.

(b) Values are centimetres above 2000 current-era baseline.

(c) Potentially affected population due to local mean SLR. Local mean SLR projections used for individual SIDS take account of variations from the global mean due to factors such as glacial isostatic adjustment, gravitational changes from ice melting, deltaic subsidence and tectonic movements.

The aggregate figures of population that could potentially be affected by permanent inundation shown in Table 15.4 and Figure 15.3 mask important differences in relative exposure between individual SIDS. Further, population affected by permanent inundation does not take into account the change in the frequency of ESL events and associated water-level attenuation (as per [[#Vafeidis--2019|Vafeidis et al., 2019]] ), nor does it account for adaptation measures that may alleviate impacts, future population growth or the extent to which populations could adaptively migrate ( [[#15.5.3|Section 15.5.3]] ). However, the analysis by [[#Rasmussen--2018|Rasmussen et al. (2018)]] shows that comparatively small changes in mean sea level can result in large increases in the frequencies of ESL events and, hence, the risk of coastal flooding of inhabited land, suggesting many areas of SIDS may become uninhabitable well before the time of permanent inundation (see also studies referenced in [[#15.3.3.1.1|Section 15.3.3.1.1]] ). A similar conclusion is drawn by [[#Kulp--2019|Kulp and Strauss (2019)]] , who show that land area home to 10% or more of the population of many SIDS is at risk of chronic coastal flooding or permanent inundation by 2100.

[[#Duvat--2021a|Duvat et al. (2021a)]] employed an integrated systems approach to analyse future risk to habitability in atoll islands, taking into account changes in various ocean and atmospheric climate drivers and a moderate adaptation scenario (i.e., adaptation responses that remain similar in nature and magnitude to currently observed responses). They found that, compared to present-day risk, additional risk to habitability in Male’, Maldives, and Fongafale, Tuvalu, is minimal under a low emissions scenario (RCP2.6) at 2050, although it may become moderate for Male and high for Fongafale by 2090. Under a worse-case emissions scenario (RCP8.5), future risk to habitability in these two urban islands may increase slightly in 2050, but may increase to moderate-to-high (for Male’) and high-to-very high (for Fongafale) by 2090.

Even where settlement locations and livelihoods remain secure, an increase in health diseases, decrease in the availability of potable water and increasing exposure to extreme events may reduce habitability ( [[#15.3.4.9.2|Section 15.3.4.9.2]] ; [[#Campbell--2014|Campbell and Warrick, 2014]] ; [[#Storlazzi--2018|Storlazzi et al., 2018]] ). For example, the Fijian coastal community of Vunidogoloa made the decision to relocate in response to regular inundation during high tides. Raising houses on stilts and constructing a seawall failed to prevent regular flood damage to buildings and the entire community eventually relocated as a ‘last resort’ adaptation measure to a site within customary land. The availability of customary land for the new site was a key factor of success in this relocation example although this will not guarantee success in every case as relocation may expose communities to new risks (McNamara and Des Combes, 2015; [[#Piggott-McKellar--2019a|Piggott-McKellar et al., 2019a]] ).

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