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

===== Observed Impacts =====

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'''Multiple lines of evidence, combined with the strong and consistent trends observed on every continent, make it''' '''''very likely''''' [[#footnote-001|2]] '''that many''' '''observed changes in the ranges, phenology, physiology and morphology of terrestrial and freshwater species can be attributed to regional and global climate changes, particularly increases in the frequency and severity of extreme events (''' '''''very high confidence''''' [[#footnote-000|3]] ''')''' {2.3.1; 2.3.3.5; 2.4.2; 2.4.5; Table 2.2; Table 2.3; Table SM2.1; Cross-Chapter Box EXTREMES in this chapter} . The most severe impacts are occurring in the most vulnerable species and ecosystems, characterised by inherent physiological, ecological or behavioural traits that limit their abilities to adapt, as well as those most exposed to climatic hazards ( ''high confidence'' ) {2.4.2.2; 2.4.2.6; 2.4.2.8; 2.4.5; 2.6.1; Cross-Chapter Box EXTREMES in this chapter} ''.''

'''New studies since the IPCC 5th Assessment Report (AR5) and the Special Report on Global Warming of 1.5°C (SR1.5) (with data for &gt;12,000 species globally) show changes consistent with climate change. Where attribution was assessed (&gt;4,000 species globally),''' '''approximately half of the species had shifted their ranges to higher latitudes or elevations and two-thirds of spring phenological events had advanced, driven by regional climate changes (''' '''''very high confidence''''' ''')''' '''''.''''' Shifts in species ranges are altering community make-up, with exotic species exhibiting a greater ability to adapt to climate change than natives, especially in more northern latitudes, potentially leading to new invasive species ''(medium confidence)'' {2.4.2.3.3; 2.4.2.7} . New analyses demonstrate that prior reports underestimated impacts due to the complexity of biological responses to climate change ( ''high confidence'' ). {2.4.2.1; 2.4.2.3; 2.4.2.4; 2.4.2.5; 2.4.5; Table 2.2; Table SM2.1; Table 2.3}

'''Responses of freshwater species are strongly related to changes in the physical environment (''' '''''high confidence''''' ''')''' {2.3.3; 2.4.2.3.2} . Global coverage of quantitative observations in freshwater ecosystems has increased since AR5. Water temperature has increased in rivers (up to 1°C per decade) and lakes (up to 0.45°C per decade) {2.3.3.1; Figure 2.2} . The extent of ice cover has declined by 25% and duration by &gt;2 weeks {2.3.3.4; Figure 2.4} . Changes in flow have led to reduced connectivity in rivers ( ''high confidence'' ) {2.3.3.2; Figure 2.3} . Indirect changes include alterations in river morphology, substrate composition, oxygen concentrations and thermal regime in lakes ( ''very high confidence'' ) {2.3.3.2; 2.3.3.3} . Dissolved oxygen concentrations have typically declined and primary productivity has increased with warming. Warming and browning (increase in organic matter) have occurred in boreal freshwaters, with both positive and negative repercussions on water temperature profiles (lower vs. upper water) ( ''high confidence'' ) and primary productivity ( ''medium confidence'' ) as well as reduced water quality ( ''high confidence'' ) {2.4.4.1; Figure 2.5} .

'''Climate change has increased wildlife diseases (''' '''''high confidence''''' ''').''' Experimental studies provide ''high confidence'' in the attribution of observed increased disease severity, outbreak frequency and the emergence of novel vectors and their diseases into new areas to recent trends in climate and extreme events. Many vector-borne diseases and those caused by ticks, helminth worms and the chytrid fungus ( ''Batrachochytrium dendrobatidis'' , Bd) have shifted polewards and upwards and are emerging in new regions ( ''high confidence'' ) ''.'' In the high Arctic and at high elevations in Nepal, there is ''high confidence'' that climate change has driven the expansion of vector-borne diseases (VBDs) that infect humans. {2.4.2.7, 7.2.2.1, 9.8.2.4, 10.4.7.1, 12.3.1.4, 13.7.1.2, 14.4.6.4; Cross-Chapter Box ILLNESS in this chapter}

'''Forest insect pests have expanded northward, and the severity and extent of outbreaks have increased in northern North America and northern Eurasia due to warmer winters reducing insect mortality and longer growing seasons favouring more generations per year (''' '''''high confidence''''' ''')''' '''{2.4.2.1; 2.4.4.3.3} .'''

'''Local population extinctions caused by climate change have been widespread among plants and animals, detected in 47% of 976 species examined and associated with increases in the hottest yearly temperatures (''' '''''very high confidence''''' ''') {2.4.2.2} .''' Climate-driven population extinctions have been higher in tropical (55%) than in temperate (39%) regions, higher in freshwater (74%) than in marine (51%) or terrestrial (46%) habitats, and higher in animals (50%) than in plants (39%). Extreme heat waves have led to local fish dying out in lakes and mass mortality events in birds, bats, mammals and fish {2.3.3.5, 2.4.2.7.2, Cross-Chapter Box EXTREMES in this chapter} . Intensification of droughts contributes to the disappearance of small or ephemeral ponds that often harbour rare and endemic species. {2.4.2.2; Cross-Chapter Box EXTREMES in this chapter}

'''Global extinctions or near-extinctions have been linked to regional climate change in three documented cases''' {2.4.2.2} . The cloud forest-restricted golden toad ( ''Incilius periglenes'' ) was extinct by 1990 in a nature preserve in Costa Rica following successive extreme droughts ( ''medium confidence'' ). The white sub-species of the lemuroid ringtail possum ( ''Hemibelideus lemuroides'' ) in Queensland, Australia, disappeared after heat waves in 2005 ( ''high confidence'' ): intensive censuses found only 2 individuals in 2009. The Bramble Cay melomys (BC melomys, ''Melomys rubicola'' ) was not seen after 2009 and was declared extinct in 2016, with sea-level rise (SLR) and increased storm surge associated with climate change being the most probable drivers ( ''high confidence'' ) ''.'' Additionally, the interaction of climate change and chytrid fungus (Bd) has driven many of the observed global declines in amphibian populations and the extinction of many species ( ''high confidence'' ) {2.4.2.7.1} .

A growing number of studies have documented genetic evolution within populations in response to recent climate change ( ''very high confidence'' ) ''.'' To date, genetic changes remain within the limits of known variation for species ( ''high confidence'' ). '''Controlled selection experiments and field observations indicate that evolution would not prevent a species becoming extinct if its climate space disappears globally (''' '''''high confidence''''' ''')''' '''''.''''' Climate hazards outside of those to which species have adapted are occurring on all continents ( ''high confidence'' ). More frequent and intense extreme events, superimposed on longer-term climate trends, have pushed sensitive species and ecosystems towards tipping points that are beyond the ecological and evolutionary capacity to adapt, causing abrupt and possibly irreversible changes ( ''medium confidence'' ). {2.3.1; 2.3.3; 2.4.2.6; 2.4.2.8; 2.6.1; Cross-Chapter Boxes ILLNESS and EXTREMES in this chapter}

'''Since AR5, biome shifts and structural changes within ecosystems have been detected at an increasing number of locations, consistent with climate change and increasing atmospheric CO''' 2 '''(''' '''''high confidence''''' ''')''' '''''.''''' New studies are documenting the changes that were projected in prior IPCC reports have now been observed, including upward shifts in the forest/alpine tundra ecotone, northward shifts in the deciduous/boreal forest ecotones, increased woody vegetation in the sub-Arctic tundra and shifts in the thermal habitat in lakes ''(high confidence)'' . A combination of changes in grazing, browsing, fire, climate and atmospheric CO 2 is leading to observed woody encroachment into grasslands and savannah, consistent with projections from process-based models driven by precipitation, atmospheric CO 2 and wildfires ( ''high confidence'' ) {2.4.3; Table 2.3; Table SM2.1; Box 2.1; Figure Box 2.1.1; Table Box 2.1.1} . There is ''high agreement'' between the projected changes in earlier reports and the recent trends observed for areas of increased tree death in temperate and boreal forests and woody encroachment in savannas, grasslands and tundra {2.5.4; Box 2.1; Figure Box 2.1.1; Table Box 2.1.1} . Observed changes impact the structure, functioning and resilience of ecosystems as well as ecosystem services, such as climate regulation ( ''high confidence'' ) {2.3; 2.4.2; 2.4.3; 2.4.4, 2.5.4, Figure 2.11, Table 2.5, Box 2.1; Figure Box 2.1.1; Table Box 2.1.1} .

'''Regional increases in the area burned by wildfire (up to double natural levels), tree mortality of up to 20%, and biome shifts of up to 20 km latitudinally and 300 m up-slope have been attributed to anthropogenic climate change in tropical, temperate and boreal ecosystems around the world (''' '''''high confidence''''' '''), damaging key aspects of ecological integrity.''' This degrades the survival of vegetation, habitat for biodiversity, water supplies, carbon sequestration, and other key aspects of the integrity of ecosystems and their ability to provide services for people ( ''high confidence'' ). {2.4.3.1; 2.4.4.2; 2.4.4.3; 2.4.4.4; Table 2.3; Table SM2.1}

Fire seasons have lengthened on one-quarter of vegetated areas since 1979 as a result of increasing temperature, aridity and drought ( ''medium confidence'' ). '''Field evidence shows that anthropogenic climate change increased area burned by wildfire above natural levels in western North America in the period 1984–2017: a doubling above natural for the western USA and 11 times higher than natural in one extreme year in British Columbia (''' '''''high confidence''''' ''')''' '''''.''''' In the Amazon, the Arctic, Australia and parts of Africa and Asia, burned area has increased, consistent with, although not formally attributed to, anthropogenic climate change. Wildfires generate up to one-third of ecosystem carbon emissions globally, a feedback that exacerbates climate change ( ''high confidence'' ). Deforestation, draining of peatlands, agricultural expansion or abandonment, fire suppression, and inter-decadal cycles such as the El Niño-Southern Oscillation (ENSO), can exert a stronger influence than climate change on increasing or decreasing wildfire in some regions {2.4.4.2; Table 2.3; Table SM2.1; FAQ 2.3} . Increase in wildfire from the levels to which ecosystems are adapted degrades vegetation, habitat for biodiversity, water supplies and other key aspects of the integrity of ecosystems and their ability to provide services for people ( ''high confidence'' ). {2.4.3.1, 2.4.4.2, 2.4.4.3, 2.4.4.4; Table 2.3; Table SM2.1}

'''Drought-induced tree mortality attributed to anthropogenic climate change has caused up to 20% loss of trees in the period 1945–2007 in three regions in Africa and North America''' '''''(high confidence)''''' '''.''' It has also potentially contributed to over 100 other cases of drought-induced tree mortality across Africa, Asia, Australia, Europe, and North and South America ( ''high confidence'' ) ''.'' Field observations have documented post-mortality vegetation shifts ( ''high confidence'' ) ''.'' Timber cutting, agricultural expansion, air pollution and other non-climate factors also contribute to tree death. Increases in forest insect pests driven by climate change have contributed to tree mortality and shifts in carbon dynamics in many temperate and boreal forest areas ( ''very high confidence'' ). The direction of changes in carbon balance and wildfires following insect outbreaks depends on the local forest insect communities ( ''medium confidence'' ). {2.4.4.3; Table 2.3; Table SM2.1}

'''Terrestrial ecosystems currently remove more carbon from the atmosphere, 2.5–4.3 Gt yr''' -1 ''', than they emit (+1.6 ± 0.7 Gt y-1), and so are currently a net sink of -1.9 ± 1.1 Gt y-1. Intact tropical rainforests, Arctic permafrost, peatlands and other healthy high-carbon ecosystems provide a vital global ecosystem service of preventing the release of stored carbon (''' '''''high confidence''''' ''')''' '''''.''''' Terrestrial ecosystems contain stocks of ~3500 GtC in vegetation, permafrost, and soils, three to five times the amount of carbon in unextracted fossil fuels ( ''high confidence'' ) and &gt;4 times the carbon currently in the atmosphere ( ''high confidence'' ). Tropical forests and Arctic permafrost contain the highest ecosystem carbon stocks in aboveground vegetation and in soil, respectively, in the world ( ''high confidence'' ). Deforestation, draining, burning or drying of peatlands, and thawing of Arctic permafrost, due to climate change, has already shifted some areas of these ecosystems from carbon sinks to carbon sources ( ''high confidence'' ). {2.4.3.6; 2.4.3.8; 2.4.3.9; 2.4.4.4}

'''Evidence indicates that climate change is affecting many species, ecosystems and ecological processes that provide ecosystem services connected to human health, livelihoods, and well-being (''' '''''medium confidence''''' ''').''' These services include climate regulation, water and food provisioning, pollination of crops, tourism and recreation. It is difficult to establish full end-to-end attribution from climatic changes to changes in a given ecosystem service and to identify the location and timing of impacts. The lack of attribution studies may delay specific adaptation planning, but there is evidence that protection and restoration of ecosystems builds resilience of service provision. {2.2; 2.3; 2.4.2.7; 2.4.4; 2.4.5; 2.5.3; 2.5.4; 2.6.3; 2.6.4; 2.6.5; 2.6.6; 2.6.7; Cross-Chapter Boxes NATURAL, ILLNESS and EXTREMES in this chapter; Cross-Chapter Box COVID in Chapter 7; Cross-Chapter Box MOVING PLATE in Chapter 5; Box 5.3; section 5.4.3.4}

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