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

===== 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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