Editing IPCC:AR6/WGII/Cross-Chapter-Paper-1 (section)

===== CCP1.2.1.2.2 Projected impacts on biodiversity =====

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Biodiversity hotspots are expected to be especially vulnerable to climate change because their endemic species have smaller geographic ranges ( ''high confidence'' ) ( [[#Sandel--2011|Sandel et al., 2011]] ; [[#Brown--2020|Brown et al., 2020]] ; [[#Manes--2021|Manes et al., 2021]] ). [[#Manes--2021|Manes et al. (2021)]] reviewed over 8000 projections of climate change impacts on biodiversity in 232 studies, including 6116 projections on endemic, native and introduced species in terrestrial (200 studies), freshwater (14 studies) and marine (34 studies) environments in biodiversity hotspots. Only half of the hotspots had studies on climate change impacts. All measures of biodiversity were found to be negatively impacted by projected climate change, namely, species abundance, diversity, area, physiology and fisheries catch potential ( ''medium confidence'' ). However, introduced species’ responses were neutral to positive ( ''medium confidence'' ). Land areas were projected to be more negatively affected by climate warming than marine. Land plants, insects, birds, reptiles and mammals were all projected to be negatively affected ( ''medium confidence'' ), as well as fish, coral reef, benthic, planktonic and other marine species ( ''medium confidence'' ).

Of the 6116 projections for more than 2,700 species assessed in biodiversity hotspots, ~44% were found to be at high extinction risk, and ~24% at very high extinction risk due to climate change ( [[#Manes--2021|Manes et al., 2021]] ) ( ''medium confidence'' ). Risks of extinction were estimated based on the projections for all warming levels combined, showing that endemic species were about 2.7 times more at very high risk of extinction compared to non-endemic native species ( [[#Manes--2021|Manes et al., 2021]] ). Extinction risks were highest for endemic species of both land and ocean ( ''medium confidence'' ), and were higher for those living on islands (~100%, ''medium confidence'' ) and mountains (~84%, ''medium confidence'' ) than in the ocean (~54%, ''low evidence, medium agreement'' ; ''low confidence'' ) and on continents (~12%, ''robust evidence, medium agreement, medium confidence'' ) (Figure CCP1.6). Extinction risks for non-endemic natives were ~20% for both terrestrial and marine species, with introduced species projected to become more rather than less invasive. At 1.5°C warming, ~2% of both terrestrial and marine species and at 3°C, ~20% and ~32% respectively, were projected to be at very high risk of extinction in the hotspots (Figure CCP1.6). Thus, a doubling of warming results in a roughly 10-fold increase in species at very high extinction risk.

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'''Figure CCP1.6 |''' '''A summary of''' '''the projected risks of species extinction at global warming levels of &lt;1''' '''.''' 5°C, 1.5–2.0°C and &gt;3°C in terrestrial and marine biodiversity hotspots. Data from [[#Manes--2021|Manes et al. (2021)]] .

[[#Manes--2021|Manes et al. (2021)]] found that any benefits to species (e.g., range or abundance increase) were projected to be localised and transient (e.g., Arctic, H196, 214). This and previous assessments indicate that, while climate change varies spatially and taxa may respond differently, a loss of biodiversity is projected across all terrestrial hotspots ( ''high confidence'' ) ( [[#Foden--2013|Foden et al., 2013]] ; [[#Warren--2018a|Warren et al., 2018a]] ; [[#Manes--2021|Manes et al., 2021]] ). Abrupt changes across species assemblages may occur under all scenarios: in 9% of assemblages at 1.75°C and 35% at 4.4°C on both land and sea ( [[#Trisos--2020|Trisos et al., 2020]] ). However, species losses may be reduced if species have thermal microclimate refugia and behavioural thermoregulation, or greater due to extreme events, such as heatwaves.

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