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

==== 2.4.2.2 Observed Local Population and Global Species’ Extinctions Driven by Climate Change ====

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Disappearances of local populations within a species range are more frequent and better documented than whole species’ extinctions, and attribution to climate change is possible for sites with minimal confounding non-climatic stressors. Changes of temperature extremes are often more important to these local extinction rates than changes of mean annual temperature ''(high confidence)'' (see Sections 2.3.1, 2.3.2, 2.3.3.5, 2.4.2.6, Cross-Chapter Box EXTREMES in this chapter) ( [[#Parmesan--2013|Parmesan et al., 2013]] ). A global meta-analysis of 236 species of birds, mammals, amphibians, fish, invertebrates and plants across 132 independent studies found that changes in population abundances were strongly related to temperature variability globally, and significantly related to precipiation variability in lower latitudes ( [[#Pearce-Higgins--2015|Pearce-Higgins et al., 2015]] ). In a global study of 538 diverse plant and animal species, sites with local extinctions were associated with smaller changes of mean annual temperature but larger and faster changes of hottest yearly temperatures than sites where populations persisted ( [[#Román-Palacios--2020|Román-Palacios and Wiens, 2020]] ). Near warm range limits, 44% of species had suffered local extinctions. In both temperate and tropical regions, sites with local extinction had greater increases in maximum temperatures than those without: a T max increase of 0.456°C and 0.316°C versus a T mean increase of 0.153°C and 0.061°C for temperate ( ''n'' = 505 sites) and tropical ( ''n'' = 76 sites), respectively (P &lt; 0.001) ( [[#Román-Palacios--2020|Román-Palacios and Wiens, 2020]] ).

[[#Wiens--2016|Wiens (2016)]] assumed that population extinctions were primarily driven by climate change when they occurred at elevational or latitudinal ‘warm edge’ range limits, and were at relatively undisturbed sites stated by the authors to be under increasing climatic stress. By this criterion, climate-caused local extinctions were widespread among plants and animals globally, detected in 47% of 976 species examined. The percentage of species suffering these extinctions was higher in the Tropics (55%) than in temperate habitats (39%), higher in freshwater (74%) than in marine (51%) or terrestrial (46%) habitats, and higher in animals (50%) than in plants (39%). The difference between plants and animals varied with latitude; in the temperate zone, a much higher proportion of animals than plants suffered range-limit extinctions (38.6% of 207 animal species vs. 8.6% of 105 plants, P &lt; 0.0001) while at tropical sites, local extinction rates were (nonsignificantly) higher in plants (59% of 155 species) than in animals (52% of 349 species), the reverse of their temperate-zone relationship. Rates varied across animal groups from 35% in mammals, to 43% in birds, 56% in insects and 59% in fish ( [[#Wiens--2016|Wiens, 2016]] ).

Freshwater population extinctions are mainly due to habitat loss, the introduction of alien species, pollution, over-harvesting ( [[#Gozlan--2019|Gozlan et al., 2019]] ; [[#IPBES--2019|IPBES, 2019]] ) and climate change-induced epidemic diseases ( [[#Pounds--2006|Pounds et al., 2006]] )(see [[#2.4.2.7.1|Section 2.4.2.7.1]] ). Climate warming, particularly through the intensification and severity of droughts, contributes to the disappearance of small ponds which hold rare and endemic species ( [[#Bagella--2016|Bagella et al., 2016]] ). Systematic data on the extent and biology of small ponds is, however, lacking on the global scale. Extreme heat waves can lead to large local fish kills in lakes (see [[#2.3.3|Section 2.3.3.5]] ), when water temperature and oxygen concentrations surpass critical thresholds and threatening cold-water fish and amphibians ( [[#Thompson--2012|Thompson et al., 2012]] ). Evidence of a local extinction of some invertebrate species with a 1.4°C–1.7°C rise in mean annual stream winter temperature from 1981 to 2005 was reported in [[#Abrahams--2013|Abrahams et al. (2013)]] . Population declines of specialist species in glacier-fed streams, such as the non-biting midge ''Diamesa davisi'' (Chironomidae), can be attributed to climate-change-driven glacier retreat ( [[#Cauvy-Fraunié--2019|Cauvy-Fraunié and Dangles, 2019]] ), and the flatworm ''Crenobia alpina'' (Planariidae) has been reported as locally extinct in the Welsh Llyn Brianne river ( [[#Durance--2010|Durance and Ormerod, 2010]] ; [[#Larsen--2018|Larsen et al., 2018]] ).

Many high montane possums in Australia have low physiological tolerance to heat waves, with death occuring due to heat-driven dehydration at temperatures exceeding 29°C–30°C for &gt;4–5 h over several days ( [[#Meade--2018|Meade et al., 2018]] ; [[#Turner--2020|Turner, 2020]] ). Major declines have been recorded for several species, population extinctions have occured at lower elevations since the early 2000s, and the white sub-species of the lemuroid ringtail possum ( ''Hemibelideus lemuroides'' ) in Queensland, Australia, disappeared after heat waves in 2005 ( ''high confidence'' ): intensive censuses found only 2 individuals in 2009 ( [[#Chandler--2014|Chandler, 2014]] ; [[#Weber--2021|Weber et al., 2021]] ).

Two terrestrial and freshwater species have become extinct in the wild, with climate change implicated as a key driver. The cloud forest-restricted golden toad ( ''Incilius periglenes'' ) was extinct by 1990 in a nature preserve in Costa Rica, driven by successive extreme droughts. This occurred in the absence of chytridiomycosis infection, caused by the fungal pathogen Bd, verified during field censuses of golden toad populations in the process of extinction as well as genetic analyses of museum specimens, although Bd was present in other frog species in the region ( ''medium evidence'' , ''high agreement'' ) ( [[#Pounds--1999|Pounds et al., 1999]] ; [[#Pounds--2006|Pounds et al., 2006]] ; [[#Puschendorf--2006|Puschendorf et al., 2006]] ; [[#Richards-Hrdlicka--2013|Richards-Hrdlicka, 2013]] ). The interaction between expansion of chytrid fungus globally and local climate change is implicated in the extinction of a wide range of tropical amphibians ''(high confidence)'' (see [[#2.4.2.7.1|Section 2.4.2.7.1]] Case Study 2 Chytrid fungus and climate change).

The BC melomys ( ''Melomys rubicola'' ), the only mammal endemic to the Great Barrier Reef, inhabited a small (5-hectare) low-lying (&lt;3-m-high) cay in the Torres Strait Islands, Australia. Recorded as having a population size of several hundred in 1978, this mammal has not been seen since 2009 and was declared extinct in 2016 ( [[#Gynther--2016|Gynther et al., 2016]] ). SLR and documented increases in storm surge and in tropical cyclones, driven by climate change, led to multiple inundations of the island in the 2000s. Between 1998 and 2014, herbacious vegetation, the food resource for the BC melomys, declined by 97% in area (from 2.2 down to 0.065 hectares), and from 11 plant species down to two ( [[#Gynther--2016|Gynther et al., 2016]] ; [[#Watson--2016|Watson, 2016]] ; [[#Woinarski--2016|Woinarski, 2016]] ; [[#Woinarski--2017|Woinarski et al., 2017]] ). The island was unihabited with few non-climatic threats, providing ''high confidence'' in the attribution of extinction of the BC melomys to climate change-driven increases in the frequency and duration of island inundation ( [[#Turner--2007|Turner and Batianoff, 2007]] ; [[#Woinarski--2014|Woinarski et al., 2014]] ; [[#Gynther--2016|Gynther et al., 2016]] ; [[#Watson--2016|Watson, 2016]] ; [[#Woinarski--2017|Woinarski et al., 2017]] ).

In the IUCN Red List ( [[#IUCN--2019|IUCN, 2019]] ), 16.2% of terrestrial and freshwater species ( ''n'' = 3,777 species) that are listed as endangered, critically endangered or extinct in the wild ( ''n'' = 23,251 species) list climate change or severe weather as one of their threats.

In summary, local population extinctions caused by climate-change-driven increases in extreme weather and climate events have been widespread among plants and animals ''(very high confidence),'' and the first clear documentations of entire species driven extinct by recent climate change is emerging ''(medium confidence).''

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