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

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

<div id="h3-9-siblings" class="h3-siblings"></div>

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]] ).

<div id="CCP1.3" class="h1-container"></div>

<span id="ccp1.3-adaptation-and-solutions"></span>