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

==== 16.2.3.1 Ecosystems ====

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The collapse or transformation of ecosystems is one of the most abrupt potential tipping points associated with climate change. Climate change has started to induce such tipping points, with the first examples including mass mortality in coral reef ecosystems (e.g., [[#Donner--2017|Donner et al., 2017]] ; [[#Hughes--2018|Hughes et al., 2018]] ; [[#Hughes--2019|Hughes et al., 2019]] ) ( ''high confidence'' ), and changes in vegetation cover triggered by wildfires with climate change suppressing the recovery of the former cover ( [[#Tepley--2017|Tepley et al., 2017]] ; [[#Davis--2019|Davis et al., 2019]] ) ( ''low confidence'' because of the still limited number of studies). Another example of an abrupt change in an ecosystem triggered by a climate extreme is the shift from kelp- to urchin-dominated communities along parts of the Western North America coast ( [[#Rogers-Bennett--2019|Rogers-Bennett and Catton, 2019]] ; [[#McPherson--2021|McPherson et al., 2021]] , see ‘Marine ecosystems—Kelp forest’, Table SM16.22). The loss of kelp forests was induced by a marine heatwave where anthropogenic climate forcing has been shown to have increased the probability for an event of that duration by at least a factor of 33 ( [[#Laufkötter--2020|Laufkötter et al., 2020]] ). Many terrestrial ecosystems on all continents show evidence of significant structural transformation, including woody thickening and ‘greening’ in more water-limited ecosystems, with a significant role played by rising atmospheric CO 2 fertilisation in these trends ( ''high confidence'' ) ( [[#Fang--2017|Fang et al., 2017]] ; [[#Stevens--2017|Stevens et al., 2017]] ; [[#Burrell--2020|Burrell et al., 2020]] ). Climate change is identified as a major driver of increases in burned areas in the Western USA ( ''high confidence'' , see ‘Terrestrial ecosystems—Burned areas’, Table SM16.22).

There is also a clear footprint of climate change on species distribution, with appreciable proportions of tropical species expanding into the ranges of temperate species, and boreal species moving into Arctic regions ( ''high confidence'' , see ‘Marine ecosystems—Range reduction and shift’ and ‘Terrestrial ecosystems—Range reduction and shift’, Table SM16.22). Climate change has also shifted the phenology of animals and plants on land and in the ocean ( ''high confidence'' , see ‘Marine ecosystems—Phenology shift’ and ‘Terrestrial ecosystems—Phenology shifts’, Table SM16.22). Both processes have led to emerging hybridisation, competition, temporal or spatial mismatches in predator–prey, guest–host relationships, and the invasion of alien plant pests or pathogens ( [[#Edwards--2004|Edwards and Richardson, 2004]] ; [[#Bebber--2013|Bebber et al., 2013]] ; [[#Parmesan--2013|Parmesan et al., 2013]] ; [[#Millon--2014|Millon et al., 2014]] ; [[#Thackeray--2016|Thackeray et al., 2016]] ).

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