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

== Executive Summary ==

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Geographic areas that are exceptionally rich in species, ecologically distinct and/or show high endemism (species occurring in that defined geographic area and nowhere else) are broadly recognised as biodiversity hotspots and prioritised for conservation. Here, we assess the impacts and vulnerability to climate change of terrestrial, freshwater and marine regions considered to be biodiversity hotspots. {CCP1.1}

'''Species in biodiversity hotspots already show changes in response to climate change (''' '''''high confidence''''' [[#footnote-000|1]] ''').''' The geographic ranges of the animal and plant species assessed have shifted from low to high latitudes in response to climate warming on land and in the ocean ( ''very high confidence'' ). On land, climate change-induced shifts towards higher elevations are also common in biodiversity hotspots ( ''high confidence'' ); while, in the ocean, climate-induced shifts to greater water depths are little studied. In the ocean, abrupt mortality of habitat-forming species on coral reefs and kelp forests, especially following heatwaves, are increasing in frequency in biodiversity hotspots ( ''high confidence'' ). {CCP1.2.1; 1.2.2; 1.2.4}

'''All biodiversity hotspots are impacted, to differing degrees, by human activities (''' '''''very''''' '''''high confidence''''' ) '''.''' Climate change impacts are compounded by other anthropogenic impacts. These include habitat loss and fragmentation, hunting, fishing and its bycatch, over-exploitation, water abstraction, nutrient enrichment, pollution, human introduction of invasive species, pests and diseases. All of these reduce climate resilience ( ''very high confidence'' ), complicating the attribution of observed changes to climate change. {CCP1.2.1}

'''Observed climate velocities are approximately 20% lower inside than outside of terrestrial and freshwater biodiversity hotspots, but 69% higher inside than outside marine hotspots (''' '''''high confidence''''' ''').''' In spite of the lower climate velocities inside terrestrial hotspots, these areas are not projected to serve as effective climate refugia from the effects of global warming, especially for endemic species (unique to a hotspot) ( ''medium confidence'' ). The greater climate velocities inside marine hotspots exposes their species to greater climate-induced pressures inside than outside hotspots ( ''high confidence'' ). The differences between temperatures inside and outside of hotspots narrow with increasing warming ( ''medium confidence'' ). {CCP1.2.2}

'''The risk of species extinction increases with warming in all climate change projections for native species studied in hotspots (''' '''''high confidence''''' '''), being about 10-times greater for endemic species from 1.5°C to 3°C above pre-industrial levels (''' '''''medium confidence''''' ''').''' Of the 6116 projections for more than 2700 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 ( ''medium confidence'' ). Very high extinction risk in biodiversity hotspots due to climate change is more common for endemic species than other native species ( ''high confidence'' ). For these endemic species, considering all scenarios and time periods evaluated, ~100% on islands, ~84% on mountains, ~12% on continents ( ''medium confidence'' ) and ~54% in the ocean (notably the Mediterranean) ( ''low confidence'' ) are projected to be threatened with extinction due to climate change. With further warming, increasingly high risks of local and global extinctions are projected in biodiversity hotspots from climate-related stressors ( ''high confidence'' ). {CCP1.2.1; Figure CCP1.7; Figure CCP1.6}

Adaptation options can enhance the persistence of biodiversity in hotspots (high confidence). Noting that over 3 billion people live within biodiversity hotspots, reduction of existing (non-climatic) pressures due to human activities is critical for building resilience within hotspots. Adaptation options for biodiversity (e.g., expanding fully protected areas, restoration and sustainable use practices) are as applicable inside biodiversity hotspots as outside (high confidence). Nevertheless, the protection of biodiversity hotspots is key to preventing a substantial global biodiversity decline from climate change. {CCP1.3; 2.6; 3.6; Table CCP1.2; Cross-Chapter Box NATURAL in Chapter 2} .

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