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

===== 2.5.1.3.1 Overview =====

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This assessment of current findings is of studies across a range of taxa and modelling techniques. Extinction risk estimates whether or not a particular species may be at risk of extinction over the coming decades if climatic trends continue, and usually does not take into account other human-induced stressors (e.g., invasive species or pollution). It is not a prediction that a species will definitely become extinct because, even when complete loss of a species’ range is projected, the scale of the model cannot estimate persistence in very small-scale micro-climatic refugia (that can be on the order of metres in size) ( [[#Suggitt--2015|Suggitt et al., 2015]] ; [[#Suggitt--2018|Suggitt et al., 2018]] ). Individuals and populations can survive after the conditions for successful reproduction are gone, leading to a lagged decline, called ‘extinction debt’ (see section 2.4.2.8) ( [[#Alexander--2018|Alexander et al., 2018]] ). Therefore, range loss is an established criterion for assessing endangerment status and risk of extinction. As a species range becomes smaller and occupied habitats become more isolated, the likelihood of a single stochastic event causing extinction increases. It is this combination of projected loss of climatically suitable space and additional stressors (especially LULCC of critical habitat) that is expected to drive future extinctions.

The IUCN Red List Criteria ( [[#IUCN--2019|IUCN, 2019]] ) classifies a species as ‘critically endangered’ if it has suffered a range loss of ≥80%, with a resulting likelihood of extinction of &gt;50% in the near term (10–100 yrs, depending upon generation length). A species is classified as ‘endangered’ if it has suffered a range loss of ≥50%, with a resulting likelihood of extinction of &gt;20% in the near term (10–100 years). In this assessment, a species that is projected to become classified as ‘endangered’ is deemed to be at ''‘high risk’'' of extinction, and becoming classified as ‘critically endangered’ is deemed at ''‘very high risk’'' of extinction.

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