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

== CCP1.2 Assessment ==

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Specific hotspot numbers (H) are indicated in this chapter text to aid their identification in Table CCP1.1 and Figures CCP1.1 and CCP1.2.

'''Table CCP1.1 |''' List of biodiversity hotspots names from ( [[#Olson--2002|Olson and Dinerstein, 2002]] ) as mapped in Figures CCP1.1 for terrestrial (numbered 1 to 142) and CCP1.2 for freshwater (143 to 195) and marine (196 to 238). Hotspots containing islands (&gt;100 km 2 ) are indicated with an asterisk.

{| class="wikitable"
|-
| # 1 Hawaii Moist Forest*

| # 81 Drakensberg Montane Woodlands and Grasslands

| # 161 Danube River Delta

|-
| # 2 Hawaii Dry Forest*

| # 82 Ural Mountains Taiga and Tundra

| # 162 Balkan Rivers and Streams*

|-
| # 3 Alaskan North Slope Coastal Tundra*

| # 83 Taimyr and Russian Coastal Tundra*

| # 163 Anatolian Freshwater

|-
| # 4 Canadian Boreal Taiga*

| # 84 Altai-Sayan Montane Forests

| # 164 Upper Guinea Rivers and Streams*

|-
| # 5 Canadian Low Arctic Tundra*

| # 85 Central and Eastern Siberian Taiga

| # 165 Niger River Delta*

|-
| # 6 Muskwa/Slave Lake Boreal Forests

| # 86 Chukhote Coastal Tundra*

| # 166 Cameroon Crater Lakes

|-
| # 7 Pacific Temperate Rainforests*

| # 87 Central Asian Deserts

| # 167 Gulf of Guinea Rivers and Streams*

|-
| # 8 Northern Prairies

| # 88 Middle Asian Montane Woodlands and Steppe

| # 168 Congo River and Flooded Forests

|-
| # 9 Klamath-Siskiyou Coniferous Forests

| # 89 Kamchatka Taiga and Grasslands*

| # 169 Congo Basin Piedmont Rivers and Streams

|-
| # 10 Sierra Nevada Coniferous Forests

| # 90 Russian Far East Broadleaf and Mixed Forests*

| # 170 Cape Rivers and Streams

|-
| # 11 California Chaparral and Woodlands*

| # 91 Daurian/Mongolian Steppe

| # 171 Rift Valley Lakes

|-
| # 12 Sonoran-Baja Deserts*

| # 92 Tibetan Plateau Steppe

| # 172 Madagascar Freshwater Ecosystem*

|-
| # 13 Chihuahuan-Tehuacan Deserts

| # 93 Hengduan Shan Conifer Forests

| # 173 Lena River Delta

|-
| # 14 Sierra Madre Oriental and Occidental Pine-Oak

| # 94 Southwest China Temperate Forests

| # 174 Lake Baikal

|-
| # 15 Southern Mexican Dry Forests*

| # 95 Western Himalayan Temperate Forests

| # 175 Russian Far East Rivers and Wetlands*

|-
| # 16 Mesoamerican Pine-Oak Forests

| # 96 Rann of Kutch Flooded Grasslands

| # 176 Lake Biwa*

|-
| # 17 Appalachian and Mixed Mesophytic Forests

| # 97 Terai-Duar Savannas and Grasslands

| # 177 Indus River Delta*

|-
| # 18 Southeastern Conifer and Broadleaf Forests*

| # 98 Eastern Himalayan Alpine Meadows

| # 178 Western Ghats Rivers and Streams

|-
| # 19 Everglades Flooded Grasslands

| # 99 Eastern Himalayan Broadleaf and Conifer Forests

| # 179 Southwestern Sri Lanka Rivers*

|-
| # 20 Greater Antillean Moist Forests*

| # 100 Eastern Deccan Plateau Moist Forests*

| # 180 Salween River

|-
| # 21 Greater Antillean Pine Forests*

| # 101 Chhota-Nagpur Dry Forests

| # 181 Lake Inle

|-
| # 22 Talamancan-Isthmian Pacific Forests

| # 102 Southwestern Ghats Moist Forest

| # 182 Sundaland Rivers and Swamps*

|-
| # 23 Choco-Darien Moist Forests*

| # 103 Sri Lankan Moist Forest*

| # 183 Yangtze River and Lakes

|-
| # 24 South American Pacific Mangroves*

| # 104 Sundarbans Mangroves

| # 184 Xi Jiang Rivers and Streams

|-
| # 25 Galapagos Islands Scrub*

| # 105 Naga-Manapuri-Chin Hills Moist Forests*

| # 185 Yunnan Lakes and Streams

|-
| # 26 Northern Andean Páramo

| # 106 Kayah-Karen/Tenasserim Moist Forests

| # 186 Mekong River*

|-
| # 27 Northern Andean Montane Forests

| # 107 Indochina Dry Forests*

| # 187 Philippines Freshwater*

|-
| # 28 Tumbesian-Andean Valleys Dry Forests*

| # 108 Cardamom Mountains Moist Forests*

| # 188 Central Sulawesi Lakes*

|-
| # 29 Napo Moist Forests

| # 109 Peninsular Malaysia Lowland and Montane Forests*

| # 189 New Guinea Rivers and Streams*

|-
| # 30 Southwestern Amazonian Moist Forests

| # 110 Sumatran Islands Lowland and Montane Forests*

| # 190 Lakes Kutubu and Sentani*

|-
| # 31 Atacama-Sechura Deserts

| # 111 Western Java Montane Forests*

| # 191 Kimberley Rivers and Streams

|-
| # 32 Central Andean Dry Puna

| # 112 Nusu Tenggara Dry Forests*

| # 192 Southwest Australia Rivers and Streams

|-
| # 33 Central Andean Yungas

| # 113 Southeast China-Hainan Moist Forests

| # 193 New Caledonia Rivers and Streams*

|-
| # 34 Chilean Matorral

| # 114 North Indochina Subtropical Moist Forests

| # 194 Central Australian Freshwater*

|-
| # 35 Valdivian Temp. Rain Forests Juan Fernandez*

| # 115 Annamite Range Moist Forests

| # 195 Eastern Australia Rivers and Streams

|-
| # 36 Patagonian Steppe*

| # 116 Kinabalu Montane Shrublands*

| # 196 Bering Sea*

|-
| # 37 Amazon-Orinoco-Southern Caribbean Mangroves*

| # 117 Borneo Lowland and Montane Forests*

| # 197 California Current*

|-
| # 38 Coastal Venezuela Montane Forests

| # 118 Greater Sundas Mangroves*

| # 198 Hawaiian Marine*

|-
| # 39 Llanos Savannas

| # 119 Nansei Shoto Archipelago Forests*

| # 199 Gulf of California*

|-
| # 40 Guianan Highlands Moist Forests

| # 120 Taiwan Montane Forests*

| # 200 Mesoamerican Reef*

|-
| # 41 Rio Negro-Jurua Moist Forests

| # 121 Philippines Moist Forests*

| # 201 Panama Bight*

|-
| # 42 Guianan Moist Forests

| # 122 Palawan Moist Forests*

| # 202 Galapagos Marine*

|-
| # 43 Atlantic Dry Forests

| # 123 Sulawesi Moist Forests*

| # 203 Fiji Barrier Reef*

|-
| # 44 Cerrado Woodlands and Savannas

| # 124 Moluccas Moist Forests*

| # 204 Tahitian Marine*

|-
| # 45 Pantanal Flooded Savannas

| # 125 New Guinea Mangroves*

| # 205 Rapa Nui*

|-
| # 46 Chiquitano Dry Forests

| # 126 Southern New Guinea Lowland Forests*

| # 206 Humboldt Current*

|-
| # 47 Atlantic Forests*

| # 127 Central Range Subalpine Grasslands*

| # 207 Grand Banks*

|-
| # 48 Fenno-Scandia Alpine Tundra and Taiga*

| # 128 New Guinea Montane Forests*

| # 208 Chesapeake Bay

|-
| # 49 Caucasus-Anatolian-Hyrcanian Temp. Forests

| # 129 Solomons-Vanuatu-Bismarck Moist Forests*

| # 209 Greater Antillean Marine*

|-
| # 50 European Mediterranean Montane Forests

| # 130 Northern Australia and Trans-Fly Savannas*

| # 210 Southern Caribbean Sea*

|-
| # 51 Mediterranean Forests, Woodlands, Scrub*

| # 131 Great Sandy-Tanami-Central Ranges Desert

| # 211 Northeast Brazil Shelf Marine*

|-
| # 52 Sudd-Sahelian Flooded Grasslands and Savannas

| # 132 Carnavon Xeric Shrubs*

| # 212 Patagonian Southwest Atlantic*

|-
| # 53 Guinean Moist Forests

| # 133 Southwestern Australia Forests and Scrub*

| # 213 Antarctic Peninsula and Weddell Sea*

|-
| # 54 Gulf of Guinea Mangroves*

| # 134 Southern Australia Mallee and Woodlands*

| # 214 Barents-Kara Seas*

|-
| # 55 Cameroon Highlands Forests*

| # 135 Queensland Tropical Forests*

| # 215 Northeast Atlantic Shelf Marine*

|-
| # 56 Congolian Coastal Forests*

| # 136 New Caledonia Moist Forests*

| # 216 Mediterranean Sea*

|-
| # 57 Sudanian Savannas

| # 137 New Caledonia Dry Forests

| # 217 Canary Current*

|-
| # 58 Western Congo Basin Moist Forests

| # 138 Lord Howe and Norfolk Island Forests*

| # 218 Benguela Current

|-
| # 59 Northeastern Congo Basin Moist Forests

| # 139 New Zealand Temperate Forests*

| # 219 Arabian Sea*

|-
| # 60 Central Congo Basin Moist Forests

| # 140 Eastern Australia Temperate Forests*

| # 220 Red Sea*

|-
| # 61 Albertine Rift Montane Forests

| # 141 Tasmanian Temperate Rainforests*

| # 221 West Madagascar Marine*

|-
| # 62 Central and Eastern Miombo Woodlands

| # 142 Southern Pacific Islands Forests*

| # 222 East African Marine*

|-
| # 63 Zambezian Flooded Savannas

| # 143 Gulf of Alaska Coastal Rivers*

| # 223 Agulhas Current

|-
| # 64 Namib-Karoo-Kaokoveld Deserts and Shrublands*

| # 144 Pacific Northwest Coastal Rivers

| # 224 Maldives-Chagos-Lakshadweep Atolls*

|-
| # 65 Fynbos

| # 145 Colorado River

| # 225 Andaman Sea*

|-
| # 66 Arabian Highlands Woodlands and Shrublands*

| # 146 Chihuahuan Freshwater

| # 226 Banda-Flores Sea*

|-
| # 67 Socotra Island Desert*

| # 147 Mexican Highland Lakes

| # 227 Western Australia Marine*

|-
| # 68 Ethiopian Highlands

| # 148 Mississippi Piedmont Rivers and Streams

| # 228 Southern Australian Marine

|-
| # 69 Horn of Africa Acacia Savannas

| # 149 Lower Mississippi River

| # 229 Okhotsk Sea*

|-
| # 70 East African Coastal Forests*

| # 150 Southeastern Rivers and Stream s*

| # 230 Yellow Sea*

|-
| # 71 East African Moorlands

| # 151 Greater Antillean Freshwater*

| # 231 Nansei Shoto*

|-
| # 72 Eastern Arc Montane Forests

| # 152 Orinoco River and Flooded Forests

| # 232 Sulu-Sulawesi Seas

|-
| # 73 East African Mangroves*

| # 153 Upper Amazon Rivers and Streams

| # 233 Palau Marine*

|-
| # 74 East African Acacia Savannas

| # 154 Brazilian Shield Amazonian Rivers and Streams

| # 234 Bismarck-Solomon Seas

|-
| # 75 Southern Rift Montane Woodlands

| # 155 High Andean Lakes

| # 235 New Caledonia Barrier Reef*

|-
| 76 Madagascar Mangroves*

| 156 Guianan Freshwater

| 236 Great Barrier Reef*

|-
| 77 Madagascar Dry Forests*

| 157 Amazon River and Flooded Forests*

| 237 Lord Howe-Norfolk Islands Marine

|-
| 78 Seychelles and Mascarenes Moist Forests*

| 158 Upper Paraná Rivers and Streams

| 238 New Zealand Marine*

|-
| 79 Madagascar Forests and Shrublands*

| 159 Volga River Delta

|
|-
| 80 Madagascar Spiny Thicket*

| 160 Mesopotamian Delta and Marshes*

|
|}

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[[File:708e3d374fd72414485e87d3edac7bc3 IPCC_AR6_WGII_Figure_CCP1_001.png]]

'''Figure CCP1.1 |''' '''Recent human impacts on the terrestrial biodiversity hotspots (coloured, grey is non hotspot)''' '''(Table CCP1.''' '''SM.1).''' Impacts are scaled in five equal 20% categories. '''(a)''' North and Central America; '''(b)''' South America; '''(c)''' Southeast Asia; '''(d)''' Europe and North Africa; '''(e)''' Africa and Arabia; '''(f)''' North Asia; '''(g)''' Southeast Asian archipelagos, Australia and New Zealand. See Table CCP1.1 for key to hotspot numbers.

<div id="_idContainer009" class="Figure"></div>

[[File:a5d3fe4213076d628589e37a0b07bc8d IPCC_AR6_WGII_Figure_CCP1_002.png]]

'''Figure CCP1.2 |''' '''Recent human impacts from multiple factors on''' '''(a)''' '''freshwater hotspots since 2000, based on Janse et''' '''al.''' '''(2015) and (b) marine hotspots based on [[#Halpern--2015|Halpern et al. (2015)]] .''' Human impacts in freshwater areas refer to the remaining wilderness. Marine impacts represent land-based, fishing, climate change and ocean-based stressors. Impacts are scaled into five equal 20% categories. See Table CCP1.1 for the key to hotspot numbers.

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=== CCP1.2.1 Global Perspective ===

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==== CCP1.2.1.1 Observed Impacts ====

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<span id="ccp1.2.1.1.1-observed-climatic-hazards"></span>
===== CCP1.2.1.1.1 Observed climatic hazards =====

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Terrestrial and freshwater hotspots have been warming less over the last 50 years than non-hotspot areas, whereas marine hotspots have been warming more ( [[#Kocsis--2021|Kocsis et al., 2021]] ). The warming inside terrestrial hotspots is 0.91°C (Myers) and 1.04°C (G200), respectively, while for freshwater hotspots it is 0.89°C, compared to 1.08°C warming outside ( [[#Kocsis--2021|Kocsis et al., 2021]] ). In contrast, mean annual sea surface temperatures in the G200 marine biodiversity hotspots have warmed 41% more than the regions outside (0.53°C compared with 0.38°C) ( [[#Kocsis--2021|Kocsis et al., 2021]] ). Thus, terrestrial biodiversity hotspots have been warming slightly less, and marine hotspots considerably more than non-hotspots ( ''medium confidence'' ).

Climate velocity, the direction and pace of movement in climate variables (typically temperature) in space, is key to understanding the origin and fate of biodiversity hotspots under climate change ( [[#Loarie--2009|Loarie et al., 2009]] ; [[#Burrows--2011|Burrows et al., 2011]] ). Climate trajectories generally predict the direction and pace of past and future species range shifts ( [[#Pinsky--2013|Pinsky et al., 2013]] ; [[#Brito-Morales--2018|Brito-Morales et al., 2018]] ), although there are exceptions ( [[#Fuchs--2020|Fuchs et al., 2020]] ). Spatial patterns of climate trajectories show regions where species are expected to leave, pass through, and/or arrive under climate change ( [[#Burrows--2014|Burrows et al., 2014]] ). Regions of high climate velocities are those with low topographic relief on land, particularly flooded grasslands and deserts ( [[#Loarie--2009|Loarie et al., 2009]] ), and tropical as well as offshore and polar sea regions ( [[#Burrows--2011|Burrows et al., 2011]] ; [[#Burrows--2014|Burrows et al., 2014]] ; [[#García%20Molinos--2016|García Molinos et al., 2016]] ; [[#Brito-Morales--2018|Brito-Morales et al., 2018]] ; [[#Brito-Morales--2020|Brito-Morales et al., 2020]] ).

On millennial time scales, some areas of low climate velocity have more endemic species and can be considered climate refugia, at least on land ( [[#Sandel--2011|Sandel et al., 2011]] ) and, for marine species, around Antarctica (H213) ( [[#Costello--2010|Costello et al., 2010]] ). This suggests that, if these areas are subject to increased velocities, they will lose species that are not able to disperse fast enough to cope with the pace of climate change ( ''medium confidence'' ) ( [[#Sandel--2011|Sandel et al., 2011]] ; [[#Brito-Morales--2018|Brito-Morales et al., 2018]] ).

Climate velocities are 47% (Myers), 29% (G200, terrestrial) and 10% (G200, freshwater) lower inside biodiversity hotspots than outside, respectively ( [[#Kocsis--2021|Kocsis et al., 2021]] ), but are 69% higher inside marine hotspots than outside ( ''medium confidence'' ). Climate velocities from 1970 to 2019 ranged from 3–4 km per decade (terrestrial and freshwater) to ~11 km per decade in marine ( [[#Kocsis--2021|Kocsis et al., 2021]] ).

For terrestrial and freshwater hotspots, the highest climate velocities are in central South America, including the Amazon (H153, 154) (Figure CCP1.3). Terrestrial hotspots also have high velocities in the Arctic (H196, 214) and east of the Caspian Sea, while freshwater hotspots have low velocities in the eastern European Mediterranean and eastern Australia.

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[[File:c0bd1751c9399491c25b2ebc32c80076 IPCC_AR6_WGII_Figure_CCP1_003.png]]

'''Figure CCP1.3 |''' '''Climate velocities in terrestrial''' '''(a)''' ''', freshwater''' '''(b)''' '''and marine''''(c)''' '''hotspots between 1970–2019.''' Values are presented in kilometres per decade and derived using the analytical package VoCC ( [[#García%20Molinos--2019|García Molinos et al., 2019]] ) from gridded temperature data, sea surface temperatures for marine ( [[#Rayner--2003|Rayner et al., 2003]] ) and near-surface air temperatures on land and freshwater ( [[#Harris--2020|Harris et al., 2020]] ). Positive and negative velocities indicate warming and cooling, respectively.

Marine hotspots have a wider range of climate velocities than terrestrial and freshwater environments (Figure CCP1.3), being faster in equatorial, Mediterranean (H216), Baltic (H215), North and Okhotsk (H229), and Arctic hotspots (H196, 214), and slow in the Antarctic hotspot (H213). Marine species tend to follow climate velocities more closely than terrestrial species ( ''high confidence'' ) ( [[#Sunday--2012|Sunday et al., 2012]] ; [[#Pinsky--2019|Pinsky et al., 2019]] ; [[#Lenoir--2020|Lenoir et al., 2020]] ). The reasons may be smaller thermal safety margins in the seas or greater human impacts on land impeding species range shifts. Climate velocities are particularly fast in equatorial seas (Figure CCP1.3; ( [[#Burrows--2011|Burrows et al., 2011]] ), which are therefore expected to be source areas for species shifting their ranges towards the subtropics ( [[#Burrows--2014|Burrows et al., 2014]] ). The subtropics are then source areas of species that shift to temperate latitudes and so forth, such that observed impacts in marine biodiversity hotspots are largely attributable to species range shifts ( ''high confidence'' ) ( [[#Pecl--2017|Pecl et al., 2017]] ). Because marine climate velocities are significantly greater within than outside hotspots, marine hotspots are especially prone to species redistributions ( ''medium confidence'' ) (Figure CCP1.3; ( [[#Kocsis--2021|Kocsis et al., 2021]] ).

While species from lower latitudes may shift their geographic ranges to higher latitudes to adapt to changing climate, there are no species to replace low latitude species. Thus, as already observed in the oceans around the equator, the loss of species in low latitudes will continue with future climate warming ( ''high confidence'' ) ( [[#Yasuhara--2020|Yasuhara et al., 2020]] ; [[#Chaudhary--2021|Chaudhary et al., 2021]] ). The issue also extends to altitudinal ranges in terrestrial environments, with species moving to higher elevations where surface area generally declines with increasing elevation; mountaintop species may have nowhere to go ( [[#Flousek--2015|Flousek et al., 2015]] ; [[#Freeman--2018|Freeman et al., 2018]] ; [[#Kidane--2019|Kidane et al., 2019]] ).

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<span id="ccp1.2.1.1.2-observed-impacts-on-biodiversity"></span>
===== CCP1.2.1.1.2 Observed impacts on biodiversity =====

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Although conservation status has only been assessed globally for about 6% of all species ( [[#Costello--2019|Costello, 2019]] ) and most confirmed extinctions and threatened species are terrestrial, a higher proportion of freshwater species are threatened. This is reflected in the higher proportion of freshwater hotspots impacted by humans ( [[#Collen--2014|Collen et al., 2014]] ; [[#Costello--2015|Costello, 2015]] ; [[#Harrison--2018|Harrison et al., 2018]] ). The rate of species endemicity is exceptionally high in freshwater biogeographic realms (i.e., large regions of distinct species composition and endemicity), at 89–96% for fish in all but one realm, compared to 11–98% for terrestrial vertebrate groups ( [[#Leroy--2019|Leroy et al., 2019]] ) and 17–84% for marine realms ( [[#Costello--2017|Costello et al., 2017]] ). Already, one-third of wetlands have been lost and 9000 freshwater species are threatened with extinction without considering the effects of climate change ( [[#Darwall--2018|Darwall et al., 2018]] ), and only 13% of world rivers were recently classified as least impacted ( [[#Su--2021|Su et al., 2021]] ).

Globally, observed climate-driven changes in biodiversity are typically of species distributions shifting to higher latitudes ( ''virtually certain'' ) ( [[#Lenoir--2020|Lenoir et al., 2020]] , Ch.2, Ch. 3.4). Since the 1950s, marine species richness has shifted poleward in the Northern Hemisphere, increased in mid-latitudes and declined at the equator in concert with ocean warming ( ''medium confidence'' ) ( [[#Chaudhary--2021|Chaudhary et al., 2021]] ). Climate-driven altitudinal shifts are common on land ( ''high confidence'' ) ( [[#Lenoir--2015|Lenoir and Svenning, 2015]] ; [[#Steinbauer--2018|Steinbauer et al., 2018]] ), and depth shifts in the ocean may occur but are little studied ( ''low confidence'' ) ( [[#Burrows--2019|Burrows et al., 2019]] ; [[#Jorda--2020|Jorda et al., 2020]] ). While climate-induced range expansions can be viewed as opportunities for increasing regional biodiversity, range contractions adversely affect biodiversity through regional extirpations ( ''high confidence'' ) ( [[#Cahill--2013|Cahill et al., 2013]] ; [[#Chaudhary--2021|Chaudhary et al., 2021]] ).

Both of the two climate change associated global species extinctions to date support the predictions that endemic species on mountains and islands are at the greatest risk of extinction ( [[#Manes--2021|Manes et al., 2021]] ). The golden toad ( ''Bufo periglenes'' ) became extinct after some years of decline associated with changes in climate warming and precipitation in the Talamancan-Isthmian Pacific Forests biodiversity hotspot (H22) ( [[#Pounds--1999|Pounds et al., 1999]] ; [[#Cahill--2013|Cahill et al., 2013]] , WGII Ch2.4.2.2). The Bramble Cay melomys ( ''Melomys rubicola'' ) '','' a rodent endemic to an island between Australia and Papua New Guinea and closely related to a mainland Australian species, became extinct due to habitat loss arising from climate change-related sea level rise and cyclone activity ( [[#Fulton--2017|Fulton, 2017]] ; [[#Roycroft--2021|Roycroft et al., 2021]] , WGII Ch.11).

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<span id="ccp1.2.1.2-projected-impacts"></span>
==== CCP1.2.1.2 Projected Impacts ====

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<span id="ccp1.2.1.2.1-projected-climatic-hazards"></span>
===== CCP1.2.1.2.1 Projected climatic hazards =====

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Comparison of climate warming projected for air and sea temperature shows biodiversity hotspots will continue to experience the greatest net increases in temperature at higher Northern Hemisphere latitudes, particularly in tundra regions (Figures CCP1.4; CCP1.5; Table CCP1.1). Generally, terrestrial and freshwater hotspots are projected to continue to warm more than marine (Figure CCP1.3). Modelled temperatures are projected to continue to be the highest in the tropics, indicating where there are more thermally stressful conditions for more species ( ''high confidence'' ) ( [[#Stuart-Smith--2015|Stuart-Smith et al., 2015]] ; [[#Stuart-Smith--2017|Stuart-Smith et al., 2017]] ; [[#Foster--2018|Foster et al., 2018]] ; [[#Waldock--2019|Waldock et al., 2019]] ). By the end of this century, all terrestrial biodiversity hotspots in Central and South America, Africa, India and southern and eastern Asia (including the Indo–West Pacific islands) are projected to experience climates unprecedented in their species’ evolutionary history ( ''medium confidence'' ) ( [[#Williams--2007|Williams et al., 2007]] ).

Based on WGI ''Interactive Atlas'' data (Gutiérrez et al., 2021), global warming is projected to affect terrestrial hotspots less than non-hotspot areas: 80% less for Myers and 95–96% less for G200 terrestrial and freshwater hotspots at global warming of 1.5°C–3°C ( ''medium confidence'' ) ( [[#Kocsis--2021|Kocsis et al., 2021]] ). In contrast, warming is projected to be 12–13% greater inside than outside marine hotspots ( ''medium confidence'' ) ( [[#Kocsis--2021|Kocsis et al., 2021]] ). Precipitation is generally projected to increase more in terrestrial and freshwater biodiversity hotspots compared to outside them ( ''low confidence'' ) ( [[#Kocsis--2021|Kocsis et al., 2021]] ). The exception is Myers hotspots, which are projected to have, on average, ~28% less precipitation at 1.5°C warming, but ~33% more at 2°C and ~65% more at 3°C ( ''low confidence'' ). However, precipitation changes are often difficult to assess as many hotspots cover large areas, with some areas projected to be wetter and some drier with wide differences between different climate models.

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[[File:66c272609ea8772bf06a6ccbd8ce0a6b IPCC_AR6_WGII_Figure_CCP1_004.png]]

'''Figure CCP1.4 |''' '''Projected loss of climatically suitable area in terrestrial biodiversity hotspots for a global average of 1.''' '''5°C (upper row, a–b), 2°C (middle, c–d) and 3°C (lower, e–f).''' Left-hand column displays the projected human impact using the five equal 20% categories of present-day impact (Figure CCP1.1). The right-hand column indicates the changes of impact categories compared to present-day impact. See Table SMCCP1.1 for more details.

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[[File:6d2cf0fcb752770752634eb91e0d66d3 IPCC_AR6_WGII_Figure_CCP1_005.png]]

'''Figure CCP1.5 |''' '''Projected future warming in degrees Celsius for freshwater (left column, near-surface air temperature, panels''' '''a''' ''',''' '''c''' '''and''' '''e''' ''') and marine (right column as sea surface temperature, panels''' '''b''' ''',''' '''d''' '''and''' '''f''' ''')''' '''hotspots for a global average warming of +1.''' '''5°C (a, b), +2°C (c, d) and +3°C''' '''(e, f) compared to pre-industrial conditions.''' Values in text boxes in the figures indicate temperature increase from present-day (2005–2014) settings. Projected temperatures were calculated with averages of multi-model, yearly means across Shared Socioeconomic Pathways (SSP) 1.26 (only for +1.5°C), SSP2-45, SSP3-70 and SSP5-85.

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<span id="ccp1.2.1.2.2-projected-impacts-on-biodiversity"></span>
===== 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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[[File:6ebf947924b09444582937f9f5f27bd8 IPCC_AR6_WGII_Figure_CCP1_006.png]]

'''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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<span id="ccp1.2.1.3-compounding-and-cascading-effects"></span>
==== CCP1.2.1.3 Compounding and Cascading Effects ====

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All biodiversity hotspots are already impacted, to differing degrees, by human activities ( ''high confidence'' ) (Table CCP1.1, Figures CCP1.1, CCP1.2, [[#Myers--2000|Myers et al., 2000]] ; [[#Le%20Roux--2019|Le Roux et al., 2019]] ). At present, over three billion people live within terrestrial and (catchments of) freshwater biodiversity hotspots, many of which border marine hotspots (Figures CCP1.1; CCP1.2; Table SMCCP1.1; Gutiérrez et al., 2021). Thus, climate change impacts on biodiversity hotspots are compounded by other anthropogenic impacts, increasing the vulnerability and reducing the resilience of biodiversity to climate change ( ''very high confidence'' ). Projections of changing climate alone may overestimate or underestimate the impacts on biodiversity ( ''medium evidence, high agreement'' ). The additional risk of the combined effects of climate change and other impacts (e.g., land use change, overhunting, pollution and invasive species) on species has been raised since the Third Assessment Report. The terrestrial hotspots projected to be most affected by global warming are, in general, those already being impacted by loss of habitat due to land use change (Figure CCP1.4; Table SMCCP1.1) ( [[#Warren--2018a|Warren et al., 2018a]] ). This remains a trend in the recent literature, although most studies still address only one stressor ( [[#Titeux--2016|Titeux et al., 2016]] ). For example, [[#Mantyka-Pringle--2015|Mantyka-Pringle et al. (2015)]] show that when the interaction between projected climate change and habitat loss is taken into account, the extinction risk of birds and mammals in 15–32% of terrestrial biodiversity hotspots changes. Similarly, [[#Bellard--2014b|Bellard et al. (2014b)]] found different results when examining the impact of climate change, invasive species and land use change independently, as opposed to synergistically. When combining those three impacts they identified the Atlantic Forest (H47), Cape Floristic Region (H65) and Polynesia-Micronesia (H1, 2, 138, 139, 142) as particularly vulnerable.

In a global assessment of the threat of climate change to river fish biodiversity, [[#Tedesco--2013|Tedesco et al. (2013)]] projected that current extinction rates of species may be 7% greater due to climate change. The main threat is due to the effects of drought and reduced river flows, which would be 18 times greater than without climate change. However, just 20 of the 110 river basins studied would experience sufficient climate-driven water loss to cause fish extinctions by 2090. Moreover, the present rates of species loss due to human activities are 130 times greater than those projected under future climate change ( ''medium confidence'' ) ( [[#Tedesco--2013|Tedesco et al., 2013]] ).

Marine systems are also vulnerable to cumulative human impacts, which can be direct (e.g., pollution, overfishing) and indirect (altered food webs) ( ''very high confidence'' ) ( [[#Halpern--2008|Halpern et al., 2008]] ; [[#Halpern--2015|Halpern et al., 2015]] ). The marine hotspots most currently threatened by non-climate-related human impacts are all situated in the Northern Hemisphere, specifically along the northern European, Mediterranean and Asian coasts, where the overlap of overfishing and pollution is especially large (Figure CCP1.2 b; [[#Halpern--2008|Halpern et al., 2008]] ; [[#Halpern--2015|Halpern et al., 2015]] ; [[#Ramírez--2018|Ramírez et al., 2018]] ). Although there is a strong overlap of non-climatic and climatic impacts in marine ecosystems ( [[#Blowes--2019|Blowes et al., 2019]] ; [[#Bowler--2020|Bowler et al., 2020]] ), the effects suggest that climate change impacts are most severe in tropical and northern high-latitude seas ( ''high confidence'' ) ( [[#Doney--2012|Doney et al., 2012]] ; [[#Gattuso--2015|Gattuso et al., 2015]] ; [[#Cheung--2018|Cheung et al., 2018]] ; [[#IPCC--2019b|IPCC, 2019b]] ). Temperature-driven range shifts and range expansions are projected to also lead to cascading effects on marine biodiversity through ecological interactions ( ''high confidence'' ) ( [[#Pecl--2017|Pecl et al., 2017]] ; [[#Vergés--2019|Vergés et al., 2019]] ). Cascading effects may be especially pronounced in temperate reefs, where tropicalisation could lead to the arrival of herbivorous fish and predators previously absent ( [[#Vergés--2019|Vergés et al., 2019]] ). However, how these indirect effects of climate change on species may change food webs and ecosystem function, including carbon sequestration, is unknown. Direct and indirect human impacts due to fisheries and pollution can also lead to cascading effects that may be additive to climate impacts on biodiversity. Destruction of marine biogenic habitats due to trawling and dredging and loss of large proportions of marine megafauna, particularly fish, mammals, birds and reptiles, alter food webs and reduce resilience to additional disturbances, such as those caused by climate change ( ''medium evidence, high agreement'' ) ( [[#Brander--2007|Brander, 2007]] ; [[#Wernberg--2011|Wernberg et al., 2011]] ; [[#Ramírez--2017|Ramírez et al., 2017]] ; [[#Cheung--2018|Cheung et al., 2018]] ; [[#Bates--2019|Bates et al., 2019]] ; [[#Costello--2021|Costello, 2021]] ).

The following sections report observed and projected climate change impacts on terrestrial, freshwater and marine environments.

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<span id="ccp1.2.2-terrestrial"></span>
=== CCP1.2.2 Terrestrial ===

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The 177 terrestrial hotspots assessed here (including 142 G200) cover about 61,000,000 km 2 (41% of global land area), with a 37% overlap with freshwater hotspots (Table CCP1.1; Figure CCP1.2). They include wet and dry forests, woodland and scrub, highlands, mangroves, deserts, steppe, savanna, grasslands, moorlands and tundra (Figures CCP1.8-1.11). Over 77% of publications on climate change impacts on hotspots since AR5 have been on terrestrial ecosystems, most on projected (as opposed to observed) impacts ( [[#Manes--2021|Manes et al., 2021]] ).

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[[File:951fa65620c6986412a4bb97b7bd07c4 IPCC_AR6_WGII_Figure_CCP1_011.png]]

'''Figure CCP1.1 1 |''' '''Island biodiversity hotspots.''' Photos by Galice Hoarau (top two) and Mark Costello (other four).

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[[File:8da323292c35ed04f7913b65380bfbf0 IPCC_AR6_WGII_Figure_CCP1_010.png]]

'''Figure CCP1.1 0 |''' '''African biodiversity hotspots.''' Photos by Denis Costello (top row and left second row) and Mark Costello (with elephant) for Drakensberg region, and Frank Zachos (lower four).

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[[File:b057b402bae7d35cedd20bbcc0c77972 IPCC_AR6_WGII_Figure_CCP1_009.png]]

'''Figure CCP1.9 |''' '''Polar and boreal biodiversity hotspots in the Arctic (Norway) taiga.''' Photos by Galice Hoarau (top three) and Mark Costello (bottom two).

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[[File:173e831942ff16e2f1c247fb5ed06fb6 IPCC_AR6_WGII_Figure_CCP1_008.png]]

'''Figure CCP1.8 |''' '''Terrestrial biodiversity hotspots in the Americas, Asia and New Zealand.''' Photos by Denis Costello (top four), Mariana M. Vale (Brazil), and Mark Costello (other three).

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<span id="ccp1.2.2.1-observed-impacts"></span>
==== CCP1.2.2.1 Observed Impacts ====

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There is ''high confidence'' that climate change has already had impacts in North American hotspots. Phenological and range shifts have been reported for bird and mammal species within the boreal forest hotspot ( [[#Davidson--2020|Davidson et al., 2020]] ), and earlier egg laying in birds in tundra hotspots (H3, 5) owing to changes in snowmelt ( [[#Grabowski--2013|Grabowski et al., 2013]] ). Woody vegetation is already shifting north into the tundra ( [[#Larsen--2014|Larsen et al., 2014]] ).

In Central and South America, observed impacts within Mesoamerica (H15, 16) and the Tropical Andes hotspots (H26, 27, 28, 32, 33) comprise upward altitudinal range shifts of birds, frogs, beetles and butterflies ( [[#Narins--2014|Narins and Meenderink, 2014]] ; [[#Molina-Martínez--2016|Molina-Martínez et al., 2016]] ; [[#Moret--2016|Moret et al., 2016]] ; [[#Freeman--2018|Freeman et al., 2018]] ) ( ''medium confidence'' ). A shift of the Guianan-Amazon mangroves (H37) to higher grounds inland was attributed to the effects of observed sea level rise ( ''low confidence'' ) ( [[#Cohen--2018|Cohen et al., 2018]] ).

In Europe, the Mediterranean hotspot (H216) has seen increases in wildfires and droughts attributed to anthropogenic climate change ( [[#Gudmundsson--2017|Gudmundsson et al., 2017]] ; [[#Barbero--2020|Barbero et al., 2020]] ). Range shifts in birds have been observed at higher elevations ( ''medium confidence'' ) ( [[#Tellería--2020|Tellería, 2020]] ).

In Africa, multiple lines of evidence suggest woody plants are increasing in area, density and cover in previously lightly wooded savanna and grassland hotspots (H65, 82) ( [[#Poulsen--2015|Poulsen and Hoffman, 2015]] ; [[#Stevens--2017|Stevens et al., 2017]] ). Significant vulture and cheetah range reductions in these hotspots are at least partially attributable to bush encroachment ( [[#Nghikembua--2016|Nghikembua et al., 2016]] ; [[#Wolter--2016|Wolter et al., 2016]] ; [[#Santangeli--2018|Santangeli et al., 2018]] ). Thus, climate-driven bush encroachment has adversely affected unique mammal and bird diversity ( ''robust evidence, medium agreement, medium confidence'' ). Warming and drying trends have historically been shown to reduce the range of the Ethiopian wolf ( ''Canis simensis'' ), and they interact with land use pressures in the Ethiopian hotspot (H68) ( [[#Sintayehu--2018|Sintayehu, 2018]] ) and plant species richness in the Cape Fynbos (H65) of southern Africa to reduce post-wildfire recruitment ( ''low confidence'' ) ( [[#Slingsby--2017|Slingsby et al., 2017]] ).

Observed impacts in Asia were mostly restricted to the Himalaya (H95, 98, 99), Sundaland (H109, 110, 111, 112, 117, 118) and Indo-Burma (H105, 106, 107, 114, 115) hotspots, showing negative impacts through increased invasion by exotic plants, decreased suitable area for endemic species and significant changes in phenology ( ''medium confidence'' ) ( [[#Telwala--2013|Telwala et al., 2013]] ; [[#Braby--2014|Braby et al., 2014]] ; [[#Padalia--2015|Padalia et al., 2015]] ; [[#Lamsal--2017|Lamsal et al., 2017]] ). In the Central Asian mountain landscape (H87), studies have shown increased aridity induced by climate change impacts on several shrub species ( [[#Seim--2016|Seim et al., 2016]] ). Some positive effects were observed for native species in terms of an increase of suitable habitat ( ''limited evidence, low agreement'' ) ( [[#Priti--2016|Priti et al., 2016]] ; [[#Tang--2017|Tang et al., 2017]] ; [[#Rathore--2019|Rathore et al., 2019]] ).

In Australia, climate change has been implicated in: drought-induced canopy dieback across a range of forest and woodland types due to decades of declining rainfall in the southwestern hotspot (H133); fires in the palaeo-endemic pencil pine forests (Tasmania H142); declines in vertebrates in the Australian Wet Tropics World Heritage Area, which overlaps with the eastern part of the northern Australia hotspot (H131), related to warming and increased length of the dry season; and declines in grass and increases in shrubs in the Bogong High Plains ( ''high confidence'' ) ( [[#Hoffmann--2019|Hoffmann et al., 2019]] ). The Australian Alps have seen increased species diversity following retreat of the snow line ( [[#Slatyer--2010|Slatyer, 2010]] ), replacement of long-lived trees by short-lived shrubs following multiple wildfires ( [[#Zylstra--2018|Zylstra, 2018]] ), and changing ecological interactions due to climate-related snow loss, drought and fires ( ''high confidence'' ) ( [[#Hoffmann--2019|Hoffmann et al., 2019]] ). While warming is allowing mangroves to expand their range in coastal hotspots of Asia and Australia ( [[#Ward--2016|Ward et al., 2016]] ; [[#Hughes--2019a|Hughes et al., 2019a]] ), drought and associated salinity stress has killed mangroves in northern Australia hotspots ( [[#Babcock--2019|Babcock et al., 2019]] ).

Approximately 76% of biodiversity hotspots within this assessment either contain, or are comprised of islands &gt;100 km 2 (Table CCP1.1). However, just 0.08% of these hotspots were represented in post-AR5 literature examining climate change impacts on terrestrial biodiversity. Most observed impacts were assessed with ''low evidence'' , but ''high agreement'' , and focused on plants and insects. Impacts described included abundance changes and extirpations ( [[#Jenouvrier--2014|Jenouvrier et al., 2014]] ), altitudinal range shifts ( [[#Koide--2017|Koide et al., 2017]] ), increased invasive alien species’ abundance and extent in Madagascar (H76, 77), Balearic (H51) and Pacific islands ( [[#Ghulam--2014|Ghulam, 2014]] ; [[#Silva-Rocha--2015|Silva-Rocha et al., 2015]] ; [[#Goulding--2016|Goulding et al., 2016]] ; [[#Dawson--2017|Dawson et al., 2017]] ), increased temperature affecting physiology, body size and behaviour of frogs in the Caribbean (H20) ( [[#Narins--2014|Narins and Meenderink, 2014]] ) and phenological alterations ( [[#Fontúrbel--2018|Fontúrbel et al., 2018]] ). One positive observation was the high resilience to recovery of intact forest ecosystems to tropical cyclones within Caribbean (H20) and Pacific islands ( ''medium confidence'' ) ( [[#Keppel--2014|Keppel et al., 2014]] ; [[#Marler--2014|Marler, 2014]] ; [[#Shiels--2014|Shiels et al., 2014]] ).

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<span id="ccp1.2.2.2-projected-impacts"></span>
==== CCP1.2.2.2 Projected Impacts ====

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Most terrestrial species in biodiversity hotspots in North America have been projected to be negatively impacted by climate change ( ''medium evidence, medium agreement'' , ''medium confidence'' ). About ~80% of projections for assessed species showed a negative impact of climate change, with ~25% at very high risk of extinction (Figure CCP1.7; [[#Manes--2021|Manes et al., 2021]] ). Alterations to vegetation that would have ecosystem-wide impacts, such as a shift from oak-dominated forests to predominantly hickory and maple species in the Appalachian Forests (H17) ( [[#Ma--2016|Ma et al., 2016]] ) or the continued shrinking of tundra ecosystems, have also been projected. Range shifts have been projected for a variety of plants ( [[#Beltrán--2014|Beltrán et al., 2014]] ; [[#Riordan--2014|Riordan and Rundel, 2014]] ) and vertebrate taxa ( [[#Warren--2014|Warren et al., 2014]] ; [[#Stralberg--2015|Stralberg et al., 2015]] ; [[#McKelvy--2017|McKelvy and Burbrink, 2017]] ). Sizeable range loss, which particularly affects endemic species, is projected with higher levels of climate change. Adaptation in the agricultural sector poses an additional risk to remaining wildlife habitat (e.g., wine in California: [[#Roehrdanz--2016|Roehrdanz and Hannah, 2016]] ).

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[[File:c5a38e6af612d0c08d27ef9cec118839 IPCC_AR6_WGII_Figure_CCP1_007.png]]

'''Figure CCP1.7 |''' '''The projected impacts of climate change on species in 232 studies''' '''(a)''' '''terrestrial and''' '''(b)''' '''marine hotspots (adapted from Manes e''' '''t al.''' ''', 2021), illustrating the number and percentage of species showing positive (blue) and negative (orange) responses to climate change, and threatened with extinction (red).''' Note Oceania includes Australia, New Zealand, Wallacea, New Guinea, New Caledonia, Polynesia and Micronesia and overlaps the global Small Islands category, which excludes Australia. The Small Islands category represents oceanic and continent-associated small islands, and thus overlaps with Oceania and continental data.

In Central and South America, risks have been assessed in at least 24 terrestrial hotspots, especially within the Atlantic Forest, Cerrado, Mesoamerica and the Caribbean, the most studied hotspots in the world in terms of climate change impacts (H47, 44, 15, 16, 20, respectively) ( [[#Manes--2021|Manes et al., 2021]] ). About 85% of projections for assessed species showed a negative impact of climate change ( ''high confidence'' ), with ~26% projecting species extinctions (Figure CCP1.7; [[#Manes--2021|Manes et al., 2021]] ). Projected impacts include contraction or loss of species’ geographic range, loss of diversity and high species turnover ( ''high confidence'' ). Most studies had focused on vertebrates and plants in the Atlantic Forest (H47) and Cerrado (H44) ( [[#Loyola--2014|Loyola et al., 2014]] ; [[#de%20Oliveira--2015|de Oliveira et al., 2015]] ; [[#Vale--2018|Vale et al., 2018]] ; [[#Vasconcelos--2018|Vasconcelos et al., 2018]] ; [[#Hidasi-Neto--2019|Hidasi-Neto et al., 2019]] ; [[#Lima--2019|Lima et al., 2019]] ; [[#Lourenço-de-Moraes--2019|Lourenço-de-Moraes et al., 2019]] ; [[#Vasconcelos--2019|Vasconcelos and Prado, 2019]] ; [[#Velazco--2019|Velazco et al., 2019]] ). Several insect species are projected to lose suitable climatic conditions, including moths in Cerrado (H44) ( [[#Khormi--2014|Khormi and Kumar, 2014]] ). There were projected negative impacts on vegetation such as rupestrian grasslands in Cerrado (H44) ( [[#Fernandes--2018|Fernandes et al., 2018]] ) and tropical and temperate forests in Mesoamerica (H15, H16) ( [[#Mendoza-Ponce--2018|Mendoza-Ponce et al., 2018]] ; [[#Mendoza-Ponce--2019|Mendoza-Ponce et al., 2019]] ). Endemic species face consistent risks of decrease in suitable habitat in the Atlantic Forest (H47) ( [[#Vale--2018|Vale et al., 2018]] ), Cerrado (H44) ( [[#Vasconcelos--2014|Vasconcelos, 2014]] ), Tumbes-Chocó-Magdalena (H28, H23) ( [[#Hermes--2018|Hermes et al., 2018]] ), and Mesoamerica (H15, H16) ( [[#Garcia--2014|Garcia et al., 2014]] ; [[#Ramírez-Amezcua--2016|Ramírez-Amezcua et al., 2016]] ). Climate change may also benefit invasive plant species in terms of range expansion ( [[#Wang--2017|Wang et al., 2017]] ) and physiology ( [[#de%20Faria--2018|de Faria et al., 2018]] ) in the region.

In European biodiversity hotspots, about 75% of projections for assessed species showed a negative impact of climate change, with ~30% at very high risk of extinction ( ''medium confidence'' ) (Figure CCP1.7; [[#Manes--2021|Manes et al., 2021]] ). These threats are projected to be worse under higher levels of warming. Increased wildfire size and frequency is projected to have a strong effect on the Mediterranean basin (H216) ecosystems ( ''medium confidence'' ) ( [[#Lozano--2017|Lozano et al., 2017]] ). Range reductions have been projected for endemic plants ( [[#Pérez-García--2013|Pérez-García et al., 2013]] ; [[#Casazza--2014|Casazza et al., 2014]] ), reptiles ( [[#Ahmadi--2019|Ahmadi et al., 2019]] ), birds ( [[#Abolafya--2013|Abolafya et al., 2013]] ) and insects ( [[#Sánchez-Guillén--2013|Sánchez-Guillén et al., 2013]] ) ( ''medium confidence'' ).

In African biodiversity hotspots, about 80% of projections for assessed species showed a negative impact of climate change, with ~10% at very high risk of extinction, especially of endemic species including birds, plants, bees across several taxa and hotspots if warming exceeds 2°C ( ''high confidence'' ) (Figure CCP1.7; [[#Huntley--2012|Huntley and Barnard, 2012]] ; [[#Kuhlmann--2012|Kuhlmann et al., 2012]] ; [[#Baker--2015|Baker et al., 2015]] ; [[#Lee--2016|Lee and Barnard, 2016]] ; [[#Young--2016|Young et al., 2016]] ; [[#Hannah--2020|Hannah et al., 2020]] ; [[#Manes--2021|Manes et al., 2021]] ).

In Asia, there is a bias in studies towards Indo-Burma (H105, 106, 107, 114, 115), followed by Himalaya (H95, 98, 99) and Southeast Asian montane tropical and temperate forests. About ~70% of projections for assessed species showed a negative impact of climate change, with ~30% at very high risk of extinction ( ''medium confidence'' ) (Figure CCP1.7; [[#Manes--2021|Manes et al., 2021]] ). Impacts include species’ range changes, habitat loss for endemic plants, expansion of invasive species, decreased connectivity and overall species richness decline ( ''high confidence'' ) ( [[#DasGupta--2013|DasGupta and Shaw, 2013]] ; [[#Telwala--2013|Telwala et al., 2013]] ; [[#Sridhar--2014|Sridhar et al., 2014]] ; [[#Zomer--2014|Zomer et al., 2014]] ; [[#Ali--2015|Ali and Begum, 2015]] ; [[#Aryal--2016|Aryal et al., 2016]] ). A projected decrease in habitat suitability for large species like the Asiatic black bear ( ''Ursus thibetanus'' ) is of concern as alternative habitats are outside protected areas, and may lead to human–wildlife conflicts ( [[#Farashi--2018|Farashi and Erfani, 2018]] ). The few positive impacts of climate change were projected as increases in suitable habitat and distribution range for a few endangered plants and mammals ( ''medium confidence'' ) ( [[#Banag--2015|Banag et al., 2015]] ; [[#Shrestha--2018|Shrestha et al., 2018]] ). Animals benefiting from increased fruit and seed production in Southeast Asian forests during warm El Niño cycles were also projected to increase with climate warming ( [[#Corlett--2011|Corlett, 2011]] ).

All projections for assessed species in Australia and New Zealand terrestrial biodiversity hotspots showed a negative impact of climate change, with half at very high risk of extinction ( ''low confidence'' ) ( [[#Manes--2021|Manes et al., 2021]] ). Observed impacts in the Australian Alps were projected to continue under future climate change ( [[#Zylstra--2018|Zylstra, 2018]] ). The northern Australia savanna (H131) may experience increased rainfall and carbon dioxide due to climate change ( [[#Scheiter--2015|Scheiter et al., 2015]] ), and the range of exotic grasses was projected to be reduced under climate warming ( [[#Gallagher--2009|Gallagher et al., 2009]] ). In Australian tropical wet forests, ground-living vertebrates may be more sensitive than arboreal species to unstable climates ( [[#Scheffers--2017|Scheffers et al., 2017]] ). [[#Bellard--2016|Bellard et al. (2016)]] projected losses of land due to sea level rise in the East Australian Forest hotspot (H140), and [[#González-Orozco--2016|González-Orozco et al. (2016)]] projected the contraction of eucalyptus species towards the coast of the Southwest Australia hotspot (H134), exposing them to sea level rise. In New Zealand forests (H139), native plants may be replaced by more fire-resistant introduced species following climate change-related fires ( [[#Perry--2014|Perry et al., 2014]] ). While forest growth is projected to potentially increase due to carbon dioxide fertilization, this may be compromised by drought ( ''low confidence'' ) ( [[#Ausseil--2013|Ausseil et al., 2013]] ). Seed production in native New Zealand beech forests is projected to increase due to climate warming, fuelling the abundance of invasive rats and stoats, which then predate native species and lead to loss of endemic fauna and flora ( ''medium confidence'' ) ( [[#Tompkins--2013|Tompkins et al., 2013]] , Ch. 11).

About 80% of projections for assessed terrestrial species within insular biodiversity hotspots showed a negative impact of climate change, with ~50% at very high risk of extinction, including 100% of endemic species ( ''medium confidence'' ) (Figure CCP1.7; [[#Manes--2021|Manes et al., 2021]] ). In addition to habitat loss and species range reductions, changes in precipitation are projected to be a major driver impacting tropical and subtropical island species ( ''medium confidence'' ) ( [[#Maharaj--2013|Maharaj and New, 2013]] ; [[#Harter--2015|Harter et al., 2015]] ; [[#Struebig--2015|Struebig et al., 2015]] ; [[#Vogiatzakis--2016|Vogiatzakis et al., 2016]] ; [[#Maharaj--2018|Maharaj et al., 2018]] ). Compared to continents, island species are projected to undergo greater impacts from changing climate, especially birds and amphibians ( ''high confidence'' ) ( [[#Fortini--2015|Fortini et al., 2015]] ; [[#Holmes--2015|Holmes et al., 2015]] ; [[#Manes--2021|Manes et al., 2021]] , Box CCP1.1). Of all biodiversity hotspots, island species face the highest proportion of extirpation risk at high elevations due to decreasing habitat area (e.g., [[#Brown--2015|Brown et al., 2015]] ) and at low elevations from sea level rise, habitat loss and introduced species ( ''medium confidence'' ) ( [[#Bellard--2014a|Bellard et al., 2014a]] ).

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<span id="ccp1.2.3-freshwater"></span>
=== CCP1.2.3 Freshwater ===

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The 53 hotspots in freshwater ecosystems assessed here cover about 32,830,000 km 2 (17% of global freshwater habitats and 22% of the global land area), with a 68% overlap with terrestrial ecosystems (Table CCP1.1; Figure CCP1.2). They include lakes, rivers and streams (Figure CCP1.1 2).

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[[File:836f4c70f5ee51621c6e95f45cd5d097 IPCC_AR6_WGII_Figure_CCP1_012.png]]

'''Figure CCP1.1 2 |''' '''Photographs of freshwater biodiversity hotspots.''' Photos by Will Darwall '''(b, c)''' , Pablo Tedesco '''(a, d)''' , and Mark Costello '''(e, f)''' .

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==== CCP1.2.3.1 Observed Impacts ====

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An analysis of trends in 190 river basins in Australia found that stream-flows have been declining, including in the Central Australian (H194) and Kimberley (H191) hotspots, due to greater terrestrial plant uptake of water in response to climate-related increases in carbon dioxide ( ''low confidence'' ) ( [[#Ukkola--2016|Ukkola et al., 2016]] ). We did not find any other publications providing evidence of impacts of climate change on freshwater biodiversity within the hotspots. Whether this is because freshwater temperatures tend to be cooler due to inputs from groundwater and/or mountain streams ( [[#Knouft--2017|Knouft and Ficklin, 2017]] ), resilience of freshwater species or lack of research is unclear.

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==== CCP1.2.3.2 Projected Impacts ====

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Cold-water species are projected to lose habitat in Canada and this may apply in the Alaskan river (H143) and Russian Far East Lake Inle (H181) hotspots ( ''medium confidence'' ) ( [[#Comte--2013|Comte et al., 2013]] ). Water abstraction is significant in the Colorado river hotspot (H145) and reduces its resilience to climate change effects on flow rates ( [[#Grafton--2013|Grafton et al., 2013]] ).

In South America, in the Brazilian Amazon hotspot (H153, 154, 157), half the assessed fish species were considered sensitive to increased temperatures and reduced oxygen due to climate change ( ''low confidence'' ) ( [[#Frederico--2016|Frederico et al., 2016]] ). The use of protected areas was recommended to reduce the impacts of deforestation and water pollution ( [[#Jézéquel--2020|Jézéquel et al., 2020]] ). El Niño-related floods have led to declines in numbers of caiman, a top predator in the Brazilian Paraná river hotspot (H158), which indicates that increased floods due to climate change may reduce its population and alter food webs ( [[#Herrera--2015|Herrera et al., 2015]] ).

In Europe, including the Mediterranean freshwater hotspots, climate change is projected to result in reduced river flow, low oxygen in summer, salinity incursions, further eutrophication and spread of invasive species, compromising the survival of native biodiversity ( ''medium confidence'' ) ( [[#Moss--2009|Moss et al., 2009]] ). The longer growth season in the boreal and Arctic latitudes is projected to aid the invasion of exotic species, and increase lake stratification resulting in lower oxygen below the hypolimnion ( ''medium confidence'' ). In addition, strict cold-water species are projected to lose suitable habitat ( [[#Moss--2009|Moss et al., 2009]] ). An analysis of 1648 species of freshwater fish, amphibians, turtles, plants, molluscs, crayfish and dragonflies, projected ~6% of common and ~77% of rare species to lose 90% of their geographic range ( ''low confidence'' ) ( [[#Markovic--2014|Markovic et al., 2014]] ). Even if some species can spread to other areas and follow the climate, [[#Markovic--2014|Markovic et al. (2014)]] projected a loss of species, especially molluscs, from the southeastern Mediterranean, including the Balkan biodiversity hotspot (H162) ( ''medium confidence'' ). Similarly, within Europe, Mediterranean fish ( [[#Jarić--2019|Jarić et al., 2019]] ) and insects ( [[#Conti--2014|Conti et al., 2014]] ) are the most threatened by climate warming, droughts and floods. The fish species of the Danube river delta hotspot (H161) are less susceptible to climate change than in the Balkans (H162) and Anatolian (H163) hotspots. The rest of Europe, from the Iberian Peninsula to Scandinavia is not classified as a biodiversity hotspot. Thus, the areas where freshwater biodiversity is most threatened by climate change in Europe are in two of the three hotspots ( ''high confidence'' ).

The African Rift Valley Lakes (H171), including Lakes Tanganyika and Turkana, are suffering from climate change influenced drought, potentially impacting freshwater biodiversity ( ''medium confidence'' ) ( [[#Dudgeon--2006|Dudgeon et al., 2006]] ). Africa and Madagascar (H172) are projected to see a climate-driven 10% reduction in freshwater flow that is projected to threaten the survival of ~9% of freshwater-dependent fish and birds ( ''low confidence'' ) ( [[#Thieme--2010|Thieme et al., 2010]] ). Climate change is projected to increase the extinction vulnerability of most freshwater fish in the western South Africa Cape hotspot (H170) ( ''low confidence'' ) ( [[#Shelton--2018|Shelton et al., 2018]] ).

In Asia, although climate change impacts on the Yangtze (H183) and Mekong river (H186) biodiversity hotspots have not been reported, they are subject to the range of human impacts of over-exploitation, pollution, water abstraction, altered flow regimes, habitat loss and spread of invasive species, which makes them more vulnerable to climate effects ( ''medium confidence'' ) ( [[#Dudgeon--2006|Dudgeon et al., 2006]] ). The release of water from shrinking glaciers in Asia to some extent protects downstream freshwaters against drought, but half of these glaciers are projected to disappear by 2100 ( ''medium confidence'' ) ( [[#Pritchard--2019|Pritchard, 2019]] ).

In Australia, the Murray-Darling river basin occupies much of the Eastern Rivers hotspot (H195) and climate-related drought exacerbated by water abstraction is projected to drive declines in freshwater birds, fish and invertebrates ( ''high confidence'' ) ( [[#Grafton--2013|Grafton et al., 2013]] ). However, a national scale analysis projected climate change to cause freshwater species range shifts, but no losses of species in this hotspot ( ''low confidence'' ) ( [[#James--2017|James et al., 2017]] , WG2 Ch. 11).

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=== CCP1.2.4 Marine ===

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The 43 hotspots in marine ecosystems cover 46,600,000 km 2 , representing 9% of the ocean area (Table CCP1.1; Figure CCP1.2). They include coral reef ecosystems, kelp forests, seagrass meadows, polar and upwelling zones (Figures CCP1.1 3; CCP1.1 4).

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[[File:374dd1148a2f8894380e9bc4486a4168 IPCC_AR6_WGII_Figure_CCP1_014.png]]

'''Figure CCP1.1 4 |''' '''Species in island coral and rocky reef biodiversity hotspots.''' Photos by Galice Hoarau (top four Sulawesi), and Mark Costello (other nine).

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[[File:1a93016095b44e38aebd92fedd64e46a IPCC_AR6_WGII_Figure_CCP1_013.png]]

'''Figure CCP1.1 3 |''' '''High-latitude marine biodiversity hotspots.''' Northeast Atlantic temperate seagrass beds, soft-corals, and kelp forests in Norway (photos by Galice Hoarau). South African fynbos and Agulhas current and Antarctic Peninsula and Weddell Sea (photos by Denis Costello). In the Americas, the Humboldt Current Chile and Chesapeake Bay (photos by Mark Costello).

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==== CCP1.2.4.1 Observed Impacts ====

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Observed impacts attributable to climate change are strongly biased geographically, with most data from the temperate Northern Hemisphere, followed by subtropical to temperate Australia and few long-term data in the tropics ( [[#Poloczanska--2013|Poloczanska et al., 2013]] ; [[#Poloczanska--2016|Poloczanska et al., 2016]] ). Marine heatwaves have increased over the past century, causing mass mortalities in the hotspots of the Mediterranean (H216), Great Barrier Reef (H236), western and southern Australia (H227, 228), northwest Atlantic (H207) and northeast Pacific (H197) ( ''high confidence'' ) ( [[#Hobday--2018|Hobday et al., 2018]] ; [[#Oliver--2018|Oliver et al., 2018]] ). The shift of thousands of species from equatorial latitudes since the 1950s has been attributed to climate warming ( ''medium confidence'' ) ( [[#Chaudhary--2021|Chaudhary et al., 2021]] ).

Climate change-related hazards, particularly marine heat events, have caused widespread coral bleaching and mass mortalities as the time between consecutive bleaching events decreases ( ''high confidence'' ) ( [[#IPCC--2018|IPCC, 2018]] ; [[#Bindoff--2019|Bindoff et al., 2019]] ; [[#IPCC--2019b|IPCC, 2019b]] ). Coral reefs in some Indian Ocean hotspots (H230, 234) already exhibit net loss of coral reefs ( ''low confidence'' ) ( [[#Perry--2018|Perry et al., 2018]] ). While coral bleaching is a visible symptom of heat stress, warming has also induced restructuring of associated fish and invertebrate communities in the Great Barrier Reef (H236) ( ''medium confidence'' ) ( [[#Stuart-Smith--2018|Stuart-Smith et al., 2018]] ).

Although the number of coral species that are both exposed and vulnerable to climate hazards is greatest in the central Indo-Pacific, the proportion of corals at risk is greater in the lower diversity Caribbean hotspots (H209) ( ''medium confidence'' ) ( [[#Foden--2013|Foden et al., 2013]] ). Some reef corals are able to acclimate to heatwaves ( ''low confidence'' ) ( [[#DeCarlo--2019|DeCarlo et al., 2019]] ), and some have expanded their latitudinal ranges polewards ( ''high confidence'' ), up to 14 km yr –1 in the northwest Pacific ( [[#Yamano--2011|Yamano et al., 2011]] ). Although future latitudinal expansions may be limited by winter light availability ( [[#Muir--2015|Muir et al., 2015]] ), new coral reefs are already emerging in Japan ( [[#Kumagai--2018|Kumagai et al., 2018]] ).

The Mediterranean Sea hotspot (H216) is negatively affected by climate change ( ''high confidence'' ) (Cross-Chapter Paper 4). Species entering via the Suez Canal from the Red Sea (H220) are facilitated by warming and lead to profound community changes ( ''high confidence'' ) ( [[#Yeruham--2015|Yeruham et al., 2015]] ; [[#Rilov--2016|Rilov, 2016]] ; [[#Vasilakopoulos--2017|Vasilakopoulos et al., 2017]] ; [[#Givan--2018|Givan et al., 2018]] ; [[#Bianchi--2019|Bianchi et al., 2019]] ). In contrast, the more open coastal seas of the Atlantic and Pacific coasts of North America have had increasing species richness since the 1970s ( [[#Batt--2017|Batt et al., 2017]] ).

Kelp forests are in decline in mid-latitudes due to warming and associated increased herbivory ( ''medium confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.3|Section 3.4.2.3]] , Chapter 11). South and southeastern (H228), and southwestern (H227) Australia have experienced a climate-related decline of kelp forests ( [[#Wernberg--2011|Wernberg et al., 2011]] ; [[#Vergés--2016|Vergés et al., 2016]] ; [[#Wernberg--2016|Wernberg et al., 2016]] ). West Australia (H227) has been affected by extreme climate events characterised by the replacement of kelp and sessile invertebrates by algal turfs and warm-water fish species ( [[#Wernberg--2013|Wernberg et al., 2013]] ; [[#Wernberg--2016|Wernberg et al., 2016]] ). Australia’s Great Barrier Reef (H236), kelp forests, seagrass meadows and mangroves (due to drought), have suffered mortalities due to climate change ( ''medium confidence'' ) ( [[#Babcock--2019|Babcock et al., 2019]] ). Climate warming driven changes in seaweed assemblages have been reported not only in Australia, but in the marine biodiversity hotspots of Atlantic Canada, Japan, Mediterranean, New Zealand ( [[#Laffoley--2016|Laffoley and Baxter, 2016]] ; [[#Thomsen--2019|Thomsen et al., 2019]] ; [[#Thomsen--2019|Thomsen and South, 2019]] ) and California (H207, 231, 216, 238, 199) ( [[#Arafeh-Dalmau--2019|Arafeh-Dalmau et al., 2019]] ; [[#McPherson--2021|McPherson et al., 2021]] ). However, while climate change is having measurable effects on kelp, the dominant effects on kelp projected to 2025 are fishing, through its effects on herbivores and predators ( ''medium confidence'' ) ( [[#Steneck--2002|Steneck et al., 2002]] ). Although fishing affected Atlantic cod in the Barents Sea (H214) and Gulf of Maine (H207) biodiversity hotspots, it was also affected by climate change, but negatively and positively, respectively ( [[#Kjesbu--2014|Kjesbu et al., 2014]] ; [[#Pershing--2015|Pershing et al., 2015]] ).

Range expansions out of the Nansei Shoto (H231) hotspot south of Japan has led to the replacement of temperate kelp forests by tropical coral and herbivorous fishes on Japanese coasts ( [[#Kumagai--2018|Kumagai et al., 2018]] ). The Yellow Sea (H230) is one of the most exploited marine hotspots, with decreasing ecosystem services compounded by climate change but there is ''low confidence'' for climate change contributing substantially to ecological degradation ( [[#Wang--2016|Wang et al., 2016]] ; [[#Song--2019|Song and Duan, 2019]] ).

Upwelling systems are best known for bringing nutrients to the surface. These stimulate phytoplankton blooms, which in turn support important fisheries ( [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.1|Section 3.4.2.1]] 1). However, this deep water also tends to be low in oxygen, which can be further depleted by respiration and surface warming. Prolonged marine heatwaves in the Californian Current hotspot (H197) drove major shifts in the geographic range of birds, mammals, fish, crustaceans, molluscs and other species, and toxic algal blooms ( [[#Sanford--2019|Sanford et al., 2019]] ).

In both the Antarctic (H213) and Arctic (H196, 214), the loss of ice impacts on the behaviour and foraging ability of marine mammals and birds ( [[#Doney--2012|Doney et al., 2012]] ). The retreat of sea ice in the Bering Sea (H196) hotspot has been followed by a reorganisation of the seabed and fish communities, a northward shift in species, and greater species’ biomass and richness ( [[#Mueter--2008|Mueter and Litzow, 2008]] ; [[#Grebmeier--2018|Grebmeier et al., 2018]] ). In the Eurasian Arctic (H214), species richness has similarly been increasing ( [[#Węsławski--2011|Węsławski et al., 2011]] ; [[#Kortsch--2012|Kortsch et al., 2012]] ; [[#Certain--2015|Certain and Planque, 2015]] ; [[#Fossheim--2015|Fossheim et al., 2015]] ; [[#Węsławski--2018|Węsławski et al., 2018]] ), as has phytoplankton productivity ( [[#Arrigo--2008|Arrigo et al., 2008]] ). The distribution of krill has already contracted with ocean warming in the Southern Ocean ( ''medium confidence'' ) ( [[#Cox--2018|Cox et al., 2018]] ; [[#Atkinson--2019|Atkinson et al., 2019]] ).

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==== CCP1.2.4.2 Projected Impacts ====

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Tropical extirpations, already underway ( [[IPCC:Wg2:Chapter:Chapter-1#1.2|Section 1.2.4.1]] ), are projected to reduce hotspot diversity especially in the Coral Triangle (H226, 232, 234), Maldives (H224) and, to a lesser extent, in the Caribbean (H200, H210) ( [[#Jones--2015|Jones and Cheung, 2015]] ; [[#García%20Molinos--2016|García Molinos et al., 2016]] ) and Persian Gulf (H219) ( [[#Wabnitz--2018|Wabnitz et al., 2018]] ). Paleo evidence supports projections of tropical biodiversity loss under high global warming ( ''high confidence'' ) ( [[#Kiessling--2012|Kiessling et al., 2012]] ; [[#Yasuhara--2020|Yasuhara et al., 2020]] ).

Warm-water coral reefs are expected to decline with 1.5°C warming ''(very high confidence'' ) ( [[#King--2017|King et al., 2017]] ; [[#Bindoff--2019|Bindoff et al., 2019]] ) leading to systems with reduced biodiversity and structural complexity ( ''high confidence'' ) (Chapters 3; 11; Box 11.2). In the Coral Triangle, marine heatwaves are projected to have the same effect as an added mean annual 0.5°C sea surface temperature increase ( [[#McManus--2020|McManus et al., 2020]] ). While some corals are expected to survive in deep ‘mesophotic’ reefs ( [[#Laverick--2019|Laverick and Rogers, 2019]] ), the shallow coral reefs of today will not last the century if climate warming continues without mitigation ( ''high confidence'' ) ( [[#Hughes--2018a|Hughes et al., 2018a]] ; [[#Hughes--2018b|Hughes et al., 2018b]] ; [[#IPCC--2018|IPCC, 2018]] ; [[#Bindoff--2019|Bindoff et al., 2019]] ; [[#Hughes--2019b|Hughes et al., 2019b]] ).

In the Mediterranean, ocean acidification has been projected to lead to increases of fleshy algae at the expense of calcifying algae ( [[#Zunino--2017|Zunino et al., 2017]] ). However, seagrass has been projected to decline ( [[#Chefaoui--2018|Chefaoui et al., 2018]] ) and increase ( [[#Zunino--2017|Zunino et al., 2017]] ) in the Mediterranean Sea hotspot (H216). Kelp forests are expected to decline in the northwest Atlantic (Grand Banks, H207), whereas gains and losses are projected to be approximately balanced in the Northeast Atlantic Shelf (H215) under Representative Concentration Pathway (RCP) 8.5 ( [[#Assis--2018|Assis et al., 2018]] ; [[#Wilson--2019|Wilson et al., 2019]] ), but may lead to impoverished benthic assemblages ( [[#Teagle--2018|Teagle and Smale, 2018]] ).

Projected climate caused changes in biodiversity in coastal upwelling regions are uncertain. While productivity in the California Current (H197) system is projected to increase with future climate change, nonlinear plankton responses and uncertain interactions with food web dynamics hinder predictions of ecosystem responses ( [[#Xiu--2018|Xiu et al., 2018]] ). In addition, this hotspot is projected to suffer from ocean acidification by 2050 ( [[#Gruber--2012|Gruber et al., 2012]] ).

Around Antarctica (H213), almost half of all species are endemic ( [[#Costello--2010|Costello et al., 2010]] ), and warming during this century is projected to cause a reduction in suitable thermal environment for 79% of its species (RCP8.5) ( ''low confidence'' ) ( [[#Basher--2016|Basher and Costello, 2016]] ; [[#Griffiths--2017|Griffiths et al., 2017]] ). The previously mentioned declines in Southern Ocean krill due to climate change contribute to projected declines in baleen whales there ( [[#Tulloch--2019|Tulloch et al., 2019]] ).

Species richness in the northern polar hotspots is expected to increase substantially ( ''high confidence'' ) ( [[#Cheung--2015|Cheung et al., 2015]] ). However, population sizes of presently occurring native species are expected to decline, especially in the Barents Sea (H214) ( [[#Koenigstein--2018|Koenigstein et al., 2018]] ). Ocean acidification is projected to continue globally, and while its impact is uncertain and projected to be less than the effect of warming, it may lead to changes in marine food webs due to varying effects on marine species ( [[#Terhaar--2020|Terhaar et al., 2020]] ). Hotspots in temperate latitudes are projected to have assemblages modified by immigration from the tropics and emigration to polar waters. Where land barriers and other geographical limits to range shifts occur, limited dispersal and habitat fragmentation may also limit the capacity of some species to track climate velocities, such as in the Baltic Sea (H215) ( [[#Jonsson--2018|Jonsson et al., 2018]] ), Mediterranean Sea (H216) ( [[#Burrows--2014|Burrows et al., 2014]] ; [[#Arafeh-Dalmau--2021|Arafeh-Dalmau et al., 2021]] ) and Antarctica (H213) ( ''medium confidence'' ) ( [[#Cristofari--2018|Cristofari et al., 2018]] ).

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