Editing IPCC:AR6/WGII/Chapter-2 (section)

=== 2.6.1 Limits to Autonomous (Natural) Adaptation ===

<div id="h2-16-siblings" class="h2-siblings"></div>

Natural ecosystems often have a high degree of resilience and can, to some extent, adjust to change. Species can adjust through evolutionary adaptation, distribution change, behavioural change, developmental plasticity and ecophysiological adjustment. There are, however, limits to autonomous adaptation, because of intrinsic limitations, the rate at which the climate is changing and the degraded state of many ecosystems.

None of the evolutionary changes either documented or theorised would enable a species to survive and reproduce in climate spaces that it does not already inhabit. It is very improbable that evolutionary responses would be sufficient to prevent species extinctions in the case of that species losing its climate space entirely on a regional or global scale (section 2.4.2.8) ( [[#Parmesan--2015|Parmesan and Hanley, 2015]] ). At the highest risk are the world’s most cold-adapted species (whose habitats are restricted to polar and high mountain-top areas). Examples include the polar bear ( [[#Regehr--2016|Regehr et al., 2016]] ), ‘sky-island’ plants in the Tropics ( [[#Kidane--2019|Kidane et al., 2019]] ), mountain-top amphibians in Spain ( [[#Enriquez-Urzelai--2019|Enriquez-Urzelai et al., 2019]] ), mountain-top lichens in the Appalachians (USA) ( [[#Allen--2016|Allen and Lendemer, 2016]] ) and silverswords in Hawaii ( [[#Krushelnycky--2013|Krushelnycky et al., 2013]] ). However, there is potential for using evolutionary changes to enhance the adaptive capacity of target species, as is being done on the Great Barrier Reef by translocating symbionts and corals that have survived recent intense heat-induced bleaching events into areas that have had large die-off ( [[#Rinkevich--2019|Rinkevich, 2019]] ). Multiple studies have assessed when and how evolution might be able to help wild species adapt to climate change ( [[#Ratnam--2011|Ratnam et al., 2011]] ; [[#Sgro--2011|Sgro et al., 2011]] ).

Some of the reasons cited in the literature as limits to autonomous adaptation are:

# Genetic changes in populations require many generations and, for many species, operate on longer timescales than those on which the climate is currently changing. In addition, experiments indicate there are strong constraints to ability to evolve beyond current climatic limits.
# Many species are moving to higher latitudes as the climate warms, but not all are keeping pace with changes in suitable climate space ( [[#Valladares--2014|Valladares et al., 2014]] ; [[#Mason--2015|Mason et al., 2015]] ). Such ‘climate debt’ (see sections 2.4.2.3.1, 2.4.2.8, 2.5.1.3.1) indicates an inability for non-genetic autonomous adaptation (e.g., evidence of limited ability for plastic responses, like those stemming from dispersal limitations, behavioural restrictions or physiological constraints).
# Some species have a low capacity for dispersal, which, combined with increased fragmentation of habitats, creates barriers to range shifts to match climate warming. Studies have shown that changes in the distribution of species and composition of communities are limited by the presence of intensively managed agricultural land fragmenting natural habitats ( [[#Oliver--2017|Oliver et al., 2017]] ).

There are a variety of mechanisms which promote the resilience of ecosystems through persistence, recovery and reorganisation ( [[#Falk--2019|Falk et al., 2019]] ). Changes in the balance of different plant species within a community can maintain the persistence of the community itself, maintaining its value as a habitat for other species and providing ecosystem services. In some cases, there are negative feedback mechanisms between biological and physical processes; for example, in peatlands, lowered water tables resulting from drier conditions can lead to reduced permeability of peat, increasing rates of water loss ( [[#Page--2016|Page and Baird, 2016]] ). There are limits to this resilience and the concept of tipping points beyond which ecosystems change state, and returning to the original state has been subject of much recent research ( [[#van%20Nes--2016|van Nes et al., 2016]] ). There is clear evidence that the degradation of ecosystems has reduced their resilience and that restoration can help to reduce risks to biodiversity and ecosystem services, discussed below (see [[#2.6.2|Section 2.6.2]] , 2.6.3). However, as the rate of climate change increases, the limits of this approach will start to be reached, and losses (including some with potentially catastrophic consequences) cannot be prevented; this is discussed further in [[#2.6.6|Section 2.6.6]] .

<div id="2.6.2" class="h2-container"></div>

<span id="adaptation-for-biodiversity-conservation"></span>