Editing IPCC:AR6/WGII/Chapter-16 (section)

===== 16.5.2.3.2 Risk to terrestrial and ocean ecosystems (RKR-B) =====

<div id="h3-34-siblings" class="h4-siblings"></div>

This risk refers to transformations of terrestrial and ocean/coastal ecosystems that would include significant changes in structure and/or functioning, and/or loss of a substantial fraction of species richness (commonly used to indicate loss of biodiversity). These are sourced mainly from Chapters 2 and 3, Cross-Chapter Paper 1, and reference the 1.5C report, [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] from WGII AR5, and [[IPCC:Wg2:Chapter:Chapter-4|Chapter 4]] from WGII AR4 Reports.

Severe adverse impacts on biodiversity include significant risk of species extinction (e.g., loss of a substantial fraction (one-tenth or more) of species from a local to global scale), mass population mortality (&gt;50% of individuals or colonies killed), ecological disruption (order-of-magnitude increases or abrupt reductions of population numbers or biomass), shifts in ecosystem structure and function (order-of magnitude increases or abrupt decreases in cover and/or biomass of novel growth forms or functional types) and/or a socioeconomically material increase in environmental risk (e.g., destruction by wildfire) or socioeconomically material decline in goods and services (e.g., carbon stock losses, loss of grazing, loss of pollination). Metrics relevant to SDGs are also germane.

A substantial proportion of biodiversity is at risk of being lost below 2°C of global warming (Chapter 2), due to range reductions and loss globally, with this risk amplified roughly three times in insular ecosystems and biodiversity hotspots, due to the increased vulnerability of endemic species ( [[#Manes--2021|Manes et al., 2021]] ). High-latitude, high-altitude, insular, freshwater, and coral reef ecosystems and biodiversity hotspots (Chapter 2, Cross-Chapter Paper 1) are at appreciable risk of substantial biodiversity loss due to climate change even under Low warming ( ''high confidence'' ). These systems comprise a large fraction of unique and endemic biodiversity, with species impacts often exacerbated by multiple drivers of global change (Chapter 2, Chapter 3). Roughly one-third of all known plant species are extremely rare, vulnerable to climate impacts, and clustered in areas of higher projected rates of anthropogenic climate change ( [[#Enquist--2019|Enquist et al., 2019]] ). Much evidence shows increased risk of the loss of 10% or more of terrestrial biodiversity with increasing anthropogenic climate change ( [[#Urban--2015|Urban, 2015]] ; [[#Smith--2018|Smith et al., 2018]] ) ( ''medium confidence'' ), ''likely'' with 2°C warming above pre-industrial level (Chapter 2), with consequent degradation of terrestrial, freshwater and ocean ecosystems ( [[#Oliver--2015|Oliver et al., 2015]] ) and adverse impacts on ecosystem services ( [[#Pecl--2017|Pecl et al., 2017]] ) and dependent human livelihoods ( [[#Dube--2016|Dube et al., 2016]] ). Adverse impacts on biodiversity may show lagged responses ( [[#Essl--2015|Essl et al., 2015]] ), and loss of a substantial fraction of species could occur abruptly, simultaneously across multiple taxa, below 4°C of global warming ( [[#Trisos--2020|Trisos et al., 2020]] ).

Mass population-level mortality (&gt;50% of individuals or colonies killed) and resulting abrupt ecological changes can be caused by simple or compound climate extreme events, such as exceedance of upper thermal limits by vulnerable terrestrial species ( [[#Fey--2015|Fey et al., 2015]] ), who also note reduced mass mortality trends due to extreme low thermal events; marine heatwaves that can cause mortality, enhance invasive alien species establishment, and damage coastal ecological communities and small-scale fisheries ( ''high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.7|Section 3.4.2.7]] ); and increased frequency and extent of wildfires that threaten populations dependent on habitat availability (like Koala Bears, [[#Lam--2020|Lam et al., 2020]] ). Abrupt ecological changes are widespread and increasing in frequency ( [[#Turner--2020|Turner et al., 2020]] ), and include tree mortality due to insect infestation exacerbated by drought, and ecosystem transformation due to wildfire ( [[#Vogt--2020|Vogt et al., 2020]] ). Freshwater ecosystems and their biodiversity are at high risk of biodiversity loss and turnover due to climate change (precipitation change and warming, including warming of water bodies), due to high sensitivity of processes and life histories to thermal conditions and water quality (Chapter 2) ( ''high confidence'' ). In marine systems, heatwaves cause damages in coastal systems, including extensive coral bleaching and mortality ( ''very high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.1|Section 3.4.2.1]] ), mass mortality of invertebrate species ( ''low'' to ''high confidence'' , depending on system) (Sections 3.4.2.2, [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.5|Section 3.4.2.5]] , [[IPCC:Wg2:Chapter:Chapter-3#3.4.4|Section 3.4.4.1]] ), and abrupt mortality of kelp-forest ( ''high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.3|Section 3.4.2.3]] ) and seagrass-meadow habitat ( ''high confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-3#3.4.4|Section 3.4.4.2]] ). The biodiversity of polar seas shows strong impacts of climate change on phenological timing of plankton activity, Arctic fish species range contractions and species community change (Table SM16.22) ( ''high confidence'' ). Extreme weather events and storm surges exacerbated by climate change have severe and sudden adverse impacts on coastal systems, including loss of seagrass meadows and mangrove forests ( ''high confidence'' ) (see [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.7|Section 3.4.2.7]] , [[IPCC:Wg2:Chapter:Chapter-3#3.4.2.8|Section 3.4.2.8]] , Cross-Chapter Box EXTREMES in Chapter 2).

Ecological disruption (order-of-magnitude increases or abrupt reductions of population numbers or biomass) can occur due to unprecedented inter-species interactions with unpredictable outcomes in ‘novel ecosystems’ (Chapter 2) as species shift geographic ranges idiosyncratically in response to climatic drivers (Table SM16.22). Idiosyncratic geographic shifts are now observed in an appreciable fraction of species studied (Chapter 2, Table 16.2). Commensal or parasitic diseases may infect immunologically naive hosts (e.g., chytrid fungus in amphibians). Atypical disturbance regimes may be enhanced, for example, with the spread of flammable plant species (e.g., [[#du%20Toit--2015|du Toit et al., 2015]] ), exacerbated by introduced species (e.g., [[#Martin--2015|Martin et al., 2015]] ), thus significantly increasing risk of losses and damages to infrastructure and livelihoods, as well as ecological degradation, and challenging existing management approaches.

Landscape- and larger-scale shifts in ecosystem structure and function (order-of-magnitude increases or abrupt decreases in cover and/or biomass of novel growth forms or functional types) are occurring in non-equilibrium ecosystems (systems which exist in multiple states, often disturbance-controlled) in response to changing disturbance regime, climate and rising CO 2 ( ''high confidence'' ) Woody plant encroachment has been occurring in multiple ecosystems, including subtropical and tropical fire driven grassland and savanna systems, upland grassland systems, arid grasslands and shrublands ( ''high confidence'' ), leading to large-scale biodiversity changes, albedo changes, and impacts on water delivery, grazing services and human livelihoods ( ''medium confidence'' ). Expansion of grasses (alien and native) into xeric shrublands is occurring, causing increasing fire prevalence in previous fire-free vegetation (Cross-Chapter Paper 3). In tropical forests, repeated droughts and recurrence of large-scale anthropogenic fires increase forest degradation, loss of biodiversity and ecosystem functioning ( ''high confidence'' ) ( [[#Anderson--2018b|Anderson et al., 2018b]] ; Longo et al., 2020). Accelerated growth rates and mortality of tropical trees is also adversely affecting tropical ecosystem functioning ( [[#McDowell--2018|McDowell et al., 2018]] ; [[#Aleixo--2019|Aleixo et al., 2019]] ). Projected changes in ecosystem functioning, such as via wildfire ( [[IPCC:Wg2:Chapter:Chapter-2#2.5|Section 2.5.5.2]] ), tree mortality ( [[IPCC:Wg2:Chapter:Chapter-2#2.5|Section 2.5.5.3]] ) and woody encroachment under climate change (Chapter 2) would alter hydrological processes, with adverse implications for water yields and water supplies ( [[#Sankey--2017|Sankey et al., 2017]] ; [[#Robinne--2018|Robinne et al., 2018]] ; [[#Rodrigues--2019|Rodrigues et al., 2019]] ; [[#Uzun--2020|Uzun et al., 2020]] ).

The loss of a substantial fraction of biodiversity globally, abrupt impacts such as significant local biodiversity loss and mass population mortality events, and ecological disruption due to novel species interactions have been observed or are projected at global warming levels below 2°C ( [[IPCC:Wg2:Chapter:Chapter-2|Chapter 2]] Table SM2.5, Cross Chapter Box: EXTREMES in Chapter 2, [[IPCC:Wg2:Chapter:Chapter-2#2.4.4.3.1|Section 2.4.4.3.1]] , [[IPCC:Wg2:Chapter:Chapter-2#2.4.2.3.3|Section 2.4.2.3.3]] ) ( ''medium confidence'' ). Simple and compound impacts of extreme climate events are already causing significant losses and damages in vulnerable ecosystems, including through the facilitation of important global change drivers of ecological disruption and homogenisation like invasive species ( ''high confidence'' ). Severe impacts on human livelihoods and infrastructure, and valuable ecosystem services, are all projected to accompany these changes. Adaptation potential for many of these risks is low due to the projected rate and magnitude of change, and to the requirement of significant amounts of land for terrestrial ecosystems ( [[#Hannah--2020|Hannah et al., 2020]] ). Biodiversity conservation efforts may be hampered due to climate change impacts on the effectiveness of protected areas, with high sensitivity of effectiveness to forcing scenario ( ''medium confidence'' ). In addition, climate-related risks to ecosystems pose challenges to ecosystem-based adaptation responses (‘nature-based solutions’) ( [[IPCC:Wg2:Chapter:Chapter-2#2.1|Section 2.1.3]] ) ( ''medium confidence'' ).

<div id="16.5.2.3.3" class="h4-container"></div>

<span id="risk-to-critical-physical-infrastructure-and-networks-rkr-c"></span>