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

=== 2.6.6 Limits to Adaptation Actions by People ===

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The evidence summarised above (Sections 2.6.2–2.6.4) shows that by restoring ecosystems it is possible to increase their resilience to climate change, including the resilience of the populations of species they support and of human communities. However, changes to healthy ecosystems and biodiversity are already happening as described in this chapter ( ''robust evidence'' , ''high agreement'' ) and further changes are inevitable even in scenarios of low GHG emissions ( ''robust evidence'' , ''high agreement'' ). Planning to manage the consequences of inevitable changes and prioritise investments in conservation actions where they have the best chance of succeeding (e.g., [[#2.6.5.6|Section 2.6.5.6]] ) will be an increasingly necessary component of adaptation ( ''robust evidence'' , ''high agreement'' ) (Table 2.6).

It is possible to help species survive by active interventions such as translocation, but, as described above ( [[#2.6.5.1|Section 2.6.5.1]] ), this is not straightforward, is not suitable for all species and is resource-intensive. Modifying local microclimate or hydrological conditions can work for some species (Sections 2.6.2, 2.6.5.5), but is likely to be less effective at higher levels of climate change. It will also be less successful for larger species and more mobile ones. The microclimate of a tree is much more closely coupled with wider atmospheric conditions than that of a small plant or animal in the boundary layer, and mobile species like birds and large mammals range over large areas rather than being confined to discrete locations where conditions can be manipulated.

There is potential for using evolutionary changes to enhance the adaptive capacity for target species, as is being done on the Great Barrier Reef where symbionts and corals that have survived recent intense heat-induced bleaching events are being translocated into areas that have had large die-off. However, known limitations to genetic adaptations preclude species-level adaptations to climates beyond their ecological and evolutionary history (Sections 2.2.4.6; 2.6.1). All of these interventionist approaches are constrained by requiring significant financial resources and expertise. They also require a high level of understanding of individual species autecology, which can take years to acquire, even when resources are available. ''Ex situ'' conservation (e.g., seed banks) may be the only option to conserve some species, especially as levels of warming increase, but this will not be feasible for all species.

While the science of restoration has generated many successes, some habitats are very difficult to restore, making certain decisions effectively irreversible. For example, ''Acacia nilotica'' was introduced into Indonesia in the 1850s for gum arabic, with planting expanded for fire breaks in the 1960s. This tree became invasive and has already replaced &gt;50% of the savanna habitat in the Baluran National Park, with complete replacement expected in the near future. This shift from savanna to acacia forest is causing large declines in native species, including the charismatic wild banteng, ''Bos javanicus'' , and the wild dog (dhole, ''Cuon alpinus'' ) ( [[#Caesariantika--2011|Caesariantika et al., 2011]] ; [[#Padmanaba--2017|Padmanaba et al., 2017]] ; [[#Zahra--2020|Zahra et al., 2020]] ). Multiple approaches to controlling the spread of this acacia have been ineffective, highlighting the difficulty of reversing the decision to plant this tree ( [[#Zahra--2020|Zahra et al., 2020]] ). Another example is the difficulties in restoring the tropical peat forests of SEA ( [[#2.6.5.10|Section 2.6.5.10]] ).

EbA, when implemented well, can reduce risks to people but there are limits. For example, an extreme flood event may exceed the capacity of natural catchments to hold water or slow its flow ( [[#Dadson--2017|Dadson et al., 2017]] ), and urban shade trees and green spaces can make a few degrees difference to temperatures experienced by people but this may not be enough in the hottest conditions.

In general, adaptation measures can substantially reduce the adverse impacts of 1°C–2°C of global temperature rise, but beyond this losses will increase ( [[#IPCC--2018b|IPCC, 2018b]] ), including species extinctions and changes like major biome shifts which cannot be reversed on human time scales. Some adaptation measures will also become less effective at higher temperatures. Whilst adaptation is essential to reduce risks, it cannot be regarded as a substitute for effective climate change mitigation ( ''robust evidence'' , ''high agreement'' ).

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