Editing IPCC:AR6/SROCC/Chapter-1 (section)

=== 1.6.2 Adaptation in Natural Systems, Ecosystems, and Human Systems ===

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In AR5, a range of changes in ocean and cryosphere natural systems were linked with ''medium'' to ''high confidence'' to pressures associated with climate change (Cramer et al., 2014 <sup>[[#fn:r287|287]]</sup> ). Climate change impacts on natural ecosystems are variable in space and time. The multiplicity of pressures these natural systems experience impedes attribution of population or ecosystem responses to a specific ocean and/or cryosphere change. Moreover, the interconnectivity of populations within ecosystems means that a single ‘adaptive response’ of a population, or the aggregate response of an ecosystem (the adaptive responses of the interconnected populations), is influenced not just by direct pressures of climate change, but occurs in concert with the adaptive responses of other species in the ecosystem, further complicating efforts to disentangle specific patterns of adaptation.

Notwithstanding the network of pressures and adaptations, much effort has gone into resolving the mechanisms, interactions and feedbacks of natural systems associated with the ocean and cryosphere. Chapters 4, 5 and 6, as well as Cross-Chapter Box 9, assess new knowledge on the adaptive responses of wetlands, coral reefs, other coastal habitats, and the populations of marine organisms encountering ocean-based risks, including. Likewise, Chapters 2 and 3 describe emerging knowledge on how ecosystems in high-mountain and polar areas are adapting to cryosphere decline.

AR5 and SR15 have highlighted the importance of evolutionary adaptation as a component of how populations adapt to climate change pressures (e.g., Pörtner et al., 2014; Hoegh-Guldberg et al., 2018 <sup>[[#fn:r288|288]]</sup> ). Acclimatisation (variation in morphology, physiology or behaviour) can result from changes in gene expression but does not involve change in the underlying DNA sequence. Responses related to acclimatisation can occur both within single generations and over several generations. In contrast, evolution requires changes in the genetic composition of a population over multiple generations; for example, by differential survival or fecundity of different genotypes (Sunday et al., 2014 <sup>[[#fn:r289|289]]</sup> ). Adaptive evolution is the subset of evolution attributable to natural selection, and natural selection may lead to populations becoming more fit (Sunday et al., 2014) or extend the range of environments where populations persist (van Oppen et al., 2015 <sup>[[#fn:r291|291]]</sup> ). The efficacy of natural selection is affected by population size (Charlesworth, 2009 <sup>[[#fn:r292|292]]</sup> ), standing genetic variation, the ability of a population to generate novel genetic variation, migration rates and the frequency of genetic recombination (Rice, 2002 <sup>[[#fn:r293|293]]</sup> ). Many studies have shown evolution of traits within and across life stages of populations (Pespeni et al., 2013 <sup>[[#fn:r294|294]]</sup> ; Hinners et al., 2017 <sup>[[#fn:r295|295]]</sup> ), but there are fewer studies on how evolutionary change can impact ecosystem or community function, and whether trait evolution is stable (Schaum and Collins, 2014 <sup>[[#fn:r296|296]]</sup> ). Although acclimatisation and evolutionary adaptation are separate processes, they influence each other, and both adaptive and maladaptive variation of traits can facilitate evolution (Schaum and Collins, 2014 <sup>[[#fn:r297|297]]</sup> ; Ghalambor et al., 2015 <sup>[[#fn:r298|298]]</sup> ). Natural evolutionary adaptation may be challenged by the speed and magnitude of current ocean and cryosphere changes, but emerging studies investigate how human actions may assist evolutionary adaptation and thereby possibly enhance the resilience of natural systems to climate change pressures (e.g., Box 5.4 in Section 5.5.2). Through acclimatisation and evolutionary adaptation to the pressures from climate change (and all other persistent pressures), populations, species and ecosystems present a constantly changing context for the adaptation of human systems to climate change.

There are several human adaptation options for climate change impacts on the ocean and cryosphere. Adaptive responses include nature- and ecosystem-based approaches (Renaud et al., 2016 <sup>[[#fn:r299|299]]</sup> ; Serpetti et al., 2017 <sup>[[#fn:r300|300]]</sup> ). Additionally, more social-based approaches for human adaptation range from community-based and infrastructure-based approaches to managed retreat, along with other forms of internal migration (Black et al., 2011 <sup>[[#fn:r301|301]]</sup> ; Hino et al., 2017 <sup>[[#fn:r302|302]]</sup> ). Building on AR5 (Wong et al., 2014 <sup>[[#fn:r303|303]]</sup> ), Chapter 4 describes four main modes of adaptation to mean and extreme sea level rise: protect, advance, accommodate, and retreat. This report demonstrates that all modes of adaptation include mixes of institutional, individual, socio-cultural, engineering, behavioural and/or ecosystem-based measures (e.g., Section 4.4.2).

The effectiveness and performance of different adaptation options across spatial and social scales is influenced by their social acceptance, political feasibility, cost-efficiency, co-benefits and trade-offs (Jones et al., 2012 <sup>[[#fn:r304|304]]</sup> ; Adger et al., 2013 <sup>[[#fn:r305|305]]</sup> ; Eriksen et al., 2015 <sup>[[#fn:r306|306]]</sup> ). Scientific evaluation of past successes and future options, including understanding barriers, limits, risks and opportunities, are complex and inadequately researched (Magnan and Ribera, 2016 <sup>[[#fn:r307|307]]</sup> ). In the end, adaptation priorities will depend on multiple parameters including the extent and rate of climate change, the risk attitudes and social preferences of individuals and institutions (and the returns they may gain) (Adger et al., 2009 <sup>[[#fn:r308|308]]</sup> ; Brügger et al., 2015 <sup>[[#fn:r309|309]]</sup> ; Evans et al., 2016 <sup>[[#fn:r310|310]]</sup> ; Neef et al., 2018 <sup>[[#fn:r311|311]]</sup> ) and access to finances, technology, capacity and other resources (Berrang-Ford et al., 2014 <sup>[[#fn:r312|312]]</sup> ; Eisenack et al., 2014 <sup>[[#fn:r313|313]]</sup> ).

Since AR5, transformational adaptation (i.e., the need for fundamental changes in private and public institutions and flexible decision-making processes to face climate change consequences) has been increasingly studied (Cross-Chapter Box 2 in Chapter 1). The recent literature documents how societies, institutions, and/or individuals increasingly assume a readiness to engage in transformative change, via their acceptance and promotion of fundamental alterations in natural or human systems (Klinsky et al., 2016 <sup>[[#fn:r314|314]]</sup> ). People living in and near coastal, mountain and polar environments often pioneer these types of transformations, since they are at the forefront of ocean and cryosphere change (e.g., Solecki et al., 2017). Community led and indigenous led adaptation research continues to burgeon (Ayers and Forsyth, 2009 <sup>[[#fn:r315|315]]</sup> ; David-Chavez and Gavin, 2018 <sup>[[#fn:r316|316]]</sup> ), especially in many mountain (Section 2.3.2.3), Arctic (Section 3.5), and coastal (Section 4.4.4.4, 4.4.5.4, Cross-Chapter Box 9) areas, and demonstrate potential for enabling transformational adaptation (Dodman and Mitlin, 2013 <sup>[[#fn:r317|317]]</sup> ; Chung Tiam Fook, 2017 <sup>[[#fn:r318|318]]</sup> ). Similarly, the concepts of scenario planning and ‘adaptation pathway’ design have expanded since AR5, especially in the context of development planning for coastal and delta regions (Section 4.4, Cross-Chapter Box 9; Wise et al., 2014 <sup>[[#fn:r319|319]]</sup> ; Maier et al., 2016 <sup>[[#fn:r320|320]]</sup> ; Bloemen et al., 2018 <sup>[[#fn:r321|321]]</sup> ; Flynn et al., 2018 <sup>[[#fn:r322|322]]</sup> ; Frame et al., 2018 <sup>[[#fn:r323|323]]</sup> ; Lawrence et al., 2018 <sup>[[#fn:r324|324]]</sup> ).

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