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

=== 16.3.1 Adaptation-Related Responses by Natural Systems ===

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There is growing evidence of shifts in species distributions and ecosystem structure and functioning in response to climate change (Chapter 2). While many species are increasingly responding to climate change, there is ''limited evidence'' that these responses will be fully adaptive, and for many species the rate of response appears insufficient to keep pace with the rate of climate change under mid- and high-range emissions scenarios ( ''medium confidence'' ). There is relatively limited, but growing, empirical data to document adaptation of natural systems in the absence of human interventions. For example, [[#Scheffers--2016|Scheffers et al. (2016)]] reviewed climate responses across diverse species, reporting widespread and extensive observed changes in organisms (genetics, physiology, morphology), populations (phenology, abundance and dynamics), species (distributions) and ecosystems. A systematic review by Franks et al. (2014) synthesised evidence from 38 empirical studies of changes in terrestrial plant populations, finding evidence to support a mix of plastic and evolutionary responses. [[#Boutin--2014|Boutin and Lane (2014)]] similarly reviewed adaptive responses in mammals, finding most species’ responses to be due to phenotypic plasticity. [[#Charmantier--2014|Charmantier and Gienapp (2014)]] reviewed responses to climate change among birds, finding emerging evidence that birds from a range of taxa show advancement in their timing of migration and breeding in response to warming. [[#Aragão--2018|Aragão et al. (2018)]] reviewed adaptation responses in marine systems, including 12 studies of live marine mammals. They observed widespread evidence of shifting distributions and timing of biological events (Chapter 2, Chapter 3, and Cross-Chapter Paper 1).

'''''Some ecosystems and species’ responses may be insufficient to keep pace with rates of climate change.''''' It is difficult to distinguish whether adaptations are due to genotypic change or to phenotypic plasticity. Long-term natural adaptations will require the former, but the latter may provide short-term coping mechanisms to ‘buy time’ to respond to climate changes or lay foundations for evolutionary adaptation. There is mixed evidence regarding evolutionary versus plastic responses, with relatively limited evidence of longer-term evolutionary responses of species that can be associated with climate change. Similarly, it is difficult to assess whether responses are indeed potentially adaptive (e.g., coping, shifting, migrating) or simply reflective of impacts (e.g., stress, damage). Among mammal responses reviewed by [[#Boutin--2014|Boutin and Lane (2014)]] , for example, only 4 of 12 studies found some evidence that responses were adaptive. Even where adaptive responses are occurring, they may not be sufficient to keep pace with the rate of climate change. found, for example, that, among the 12 studies in their review that directly assessed the sufficiency of responses to keep pace with the rate of climate change, 8 concluded that responses would be insufficient to avert extinction.

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