Editing IPCC:AR6/WGII/Chapter-2 (section)

===== Projected Risks =====

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'''Climate change increases risks to fundamental aspects of terrestrial and freshwater ecosystems, with the potential for species’ extinctions to reach 60% at 5°C global mean surface air temperature (GSAT) warming (''' '''''high confidence''''' '''), biome shifts (changes in the major vegetation form of an ecosystem) on 15% (at 2''' '''°''' '''C warming) to 35% (at 4''' '''°''' '''C warming) of global land (''' '''''medium confidence''''' '''), and increases in the area burned by wildfire of 35% (at 2''' '''°''' '''C warming) to 40% (at 4''' '''°''' '''C warming) of global land (''' '''''medium confidence''''' ''').''' {2.5.1; 2.5.2; 2.5.3; 2.5.4; Figure 2.6; Figure 2.7; Figure 2.8; Figure 2.9; Figure 2.11; Table 2.5; Table SM2.2; TableSM2.5; Cross-Chapter Box DEEP in Chapter 17; Cross-Chapter Paper 1}

'''Extinction of species is an irreversible impact of climate change, with increasing risk as global temperatures rise''' '''''(very high confidence)''''' '''.''' The median values for percentage of species at ''very high risk'' of extinction (categorized as “critically endangered” by IUCN Red List categories)( [[#IUCN--2001|IUCN, 2001]] ) are 9% at 1.5°C rise in GSAT, 10% at 2°C, 12% at 3.0°C, 13% at 4°C and 15% at 5°C ''(high confidence)'' , with the ''likely'' range of estimates having a maximum of 14% at 1.5°C and rising to a maximum of 48% at 5°C (Figure 2.7). Among the groups containing the largest numbers of species at a ''very high risk'' of extinction for mid-levels of warming (3.2°C) are: invertebrates (15%, and specifically pollinators at 12%), amphibians (11% overall, but salamanders are at 24%) and flowering plants (10%). All groups fare substantially better at lower warming of 2°C, with extinction projections reducing to &lt;3% for all groups, except salamanders that reduced to 7% ( ''medium confidence'' ) (Figure 2.8a) ''.'' Even the lowest estimates of species’ extinctions (median of 9% at 1.5°C rise GSAT’) are 1000 times the natural background rates. Projected species’ extinctions at future global warming levels are consistent with projections from AR4, but assessed for many more species with much greater geographic coverage and a broader range of climate models. {2.5.1.3; Figure 2.6; Figure 2.7; Figure 2.8; Cross-Chapter Box DEEP in Chapter 17; Cross-Chapter Paper 1}

'''Species are the fundamental unit of ecosystems, and the increasing risk of local losses of species increases the risks of reduced ecosystem integrity, functioning and resilience with increasing warming (''' '''''high confidence''''' ''')''' . As species become rare, their role in the functioning of the ecosystem diminishes ( ''high confidence'' ). Loss of species locally reduces the ability of an ecosystem to provide services and lowers its resilience to climate change ( ''high confidence'' ). At 1.58°C GSAT warming, &gt;10% of species are projected to become endangered (median estimate, with “endangered” equating to a ''high risk'' of extinction, sensu IUCN), and at 2.07°C this rises to &gt;20% of species, representing a ''high'' and ''very high'' risk of biodiversity loss, respectively ( ''medium confidence'' ) {2.5.4; Figure 2.8b, Figure 2.11; Table 2.5; Table SM2.5} . Biodiversity loss is projected for more regions with increasing warming, and will be worst in northern South America, southern Africa, most of Australia and at northern high latitudes ( ''medium confidence'' ) {2.5.1.3; Figure 2.6} .

'''Climate change increases risks of biome shifts on up to 35% of global land at ≥4''' '''°''' '''C GSAT warming, that emission reductions could limit to &lt;15% for &lt;2''' '''°''' '''C warming (''' '''''medium confidence''''' '''). Under high-warming scenarios, models indicate shifts of extensive parts of the Amazon rainforest to drier and lower-biomass vegetation (''' '''''medium confidence''''' '''), poleward shifts of boreal forest into treeless tundra across the Arctic, and upslope shifts of montane forests into alpine grassland (''' '''''high confidence''''' ''').''' Area at high risk of biome shifts from changes in climate and land use combined can double or triple compared to climate change alone ( ''medium confidence'' ). Novel ecosystems, with no historical analogue, are expected to become increasingly common in the future ( ''medium confidence'' ). {2.3, 2.4.2.3.3, 2.5.2; 2.5.4, Figure 2.11; Table 2.5; Table SM2.4; Table SM2.5}

'''The risk of wildfire increases along with an increase in global temperatures (''' '''''high confidence''''' ''')''' '''''.''''' '''With 4°C GSAT warming by 2100, wildfire frequency is projected to have a net increase of ~30% (''' '''''medium confidence''''' ''')''' '''''.''''' Increased wildfire, combined with soil erosion due to deforestation, could degrade water supplies ( ''medium confidence'' ) ''.'' For ecosystems with an historically low frequency of fires, a projected 4°C global temperature rise increases the risk of fires, with potential increases in tree mortality and the conversion of extensive parts of the Amazon rainforest to drier and lower-biomass vegetation ( ''medium confidence'' ). {2.5.3.2; 2.5.3.3}

'''Continued climate change substantially increases the risk of carbon stored in the biosphere being released into the atmosphere due to increases in processes such as wildfire, tree mortality, insect pest outbreaks, peatland drying and permafrost thaw (''' '''''high confidence''''' ''').''' These phenomena exacerbate self-reinforcing feedbacks between emissions from high-carbon ecosystems (that currently store ~3000–4000 GtC) and increasing global temperatures. Complex interactions of climate change, land use change (LUC), carbon dioxide fluxes and vegetation changes, combined with insect outbreaks and other disturbances, will regulate the future carbon balance of the biosphere. These processes are incompletely represented in current earth system models (ESMs). The exact timing and magnitude of climate–biosphere feedbacks and potential tipping points of carbon loss are characterised by large uncertainty, but studies of feedbacks indicate that increased ecosystem carbon losses can cause large temperature increases in the future ( ''medium confidence'' ). (section 5.4, Figure 5.29 and Table 5.4 in ( [[#Canadell--2021|Canadell et al., 2021]] )), {2.5.2.7; 2.5.2.8; 2.5.2.9; 2.5.3.2; 2.5.3.3; 2.5.3.4; 2.5.3.5; Figure 2.10; Figure 2.11; Table 2.4; Table 2.5; Table SM2.2 Table SM2.5}

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