Editing IPCC:AR6/WGII/Chapter-10 (section)

==== 10.4.2.1 Observed Impacts ====

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===== 10.4.2.1.1 Biomes and mountain treeline =====

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Changes in biomes in Asia are compatible with a response to regional surface air temperature increase ( [[#Arias--2021|Arias et al., 2021]] ) ( ''medium agreement, medium evidence'' ). Expansion of the boreal forest and reduction of the tundra area is observed for about 60% of latitudinal and altitudinal sites in Siberia ( [[#Rees--2020|Rees et al., 2020]] ). In Central Siberia, the changes in climate and disturbance regimes are shifting the southern taiga ecotone northward ( [[#Brazhnik--2017|Brazhnik et al., 2017]] ). In Taimyr, no significant changes in the forest boundary have been observed during the past three decades ( [[#Pospelova--2017|Pospelova et al., 2017]] ). For the Japanese archipelago, it is suggested that the change in tree community composition along the temperature gradient is a response to past and/or current climate changes ( [[#Suzuki--2015|Suzuki et al., 2015]] ).

Alpine treeline position in Asian mountains in recent decades either moves upwards in North Asia or demonstrates multi-directional shifts in Himalaya ( ''high confidence'' ). Since AR5, in North Asia new evidence has appeared of tree expansion into mountain tundra and steppe, of intensive reproduction and increase in tree stands productivity in the past 30–100 years at the upper treeline in the Ural Mountains ( [[#Shiyatov--2015|Shiyatov and Mazepa, 2015]] ; [[#Zolotareva--2017|Zolotareva and Zolotarev, 2017]] ; [[#Moiseev--2018|Moiseev et al., 2018]] ; [[#Sannikov--2018|Sannikov et al., 2018]] ; [[#Fomin--2020|Fomin et al., 2020]] ; [[#Gaisin--2020|Gaisin et al., 2020]] ), in the Russian Altai Mountains ( [[#Kharuk--2017a|Kharuk et al., 2017a]] ; [[#Cazzolla%20Gatti--2019|Cazzolla Gatti et al., 2019]] ) and in the Putorana Mountains ( [[#Kirdyanov--2012|Kirdyanov et al., 2012]] ; [[#Pospelova--2017|Pospelova et al., 2017]] ; [[#Grigor’ev--2019|Grigor’ev et al., 2019]] ). Lower treelines in the southernmost ''Larix sibirica'' forests in the Saur Mountains, eastern Kazakhstan, have suffered from increased drought stress in recent decades causing forest regeneration and tree growth decrease, and tree mortality increase ( [[#Dulamsuren--2013|Dulamsuren et al., 2013]] ). In Jeju Island, Republic of Korea, recent warming has enhanced ''Quercus mongolica'' growth at its higher distribution and has led to ''Abies koreana'' (ABKO) growth reduction at all elevations, except the highest locality. Thus, the combination of warming, increasing competition and frequent tropical cyclone disturbances could lead to population decline or even extinction of ABKO at Jeju Island ( [[#Altman--2020|Altman et al., 2020]] ). In the Himalaya, the treeline over recent decades either moves upwards ( [[#Schickhoff--2015|Schickhoff et al., 2015]] ; [[#Suwal--2016|Suwal et al., 2016]] ; [[#Sigdel--2018|Sigdel et al., 2018]] ; [[#Tiwari--2018|Tiwari and Jha, 2018]] ) or does not show upslope advance ( [[#Schickhoff--2015|Schickhoff et al., 2015]] ; [[#Gaire--2017|Gaire et al., 2017]] ; [[#Singh--2018c|Singh et al., 2018c]] ), or moves downwards ( [[#Bhatta--2018|Bhatta et al., 2018]] ). In the Tibetan Plateau, the treeline either shifted upwards or showed no significant upwards shift ( [[#Wang--2019c|Wang et al., 2019c]] ). This can be explained by site-specific complex interaction of positive effect of warming on tree growth, and negative effects of drought stress, change in snow precipitation, inter- and intraspecific interactions of trees and shrubs, land-use change (especially grazing) and other factors ( [[#Liang--2014|Liang et al., 2014]] ; [[#Lenoir--2015|Lenoir and Svenning, 2015]] ; [[#Tiwari--2017|Tiwari et al., 2017]] ; [[#Sigdel--2018|Sigdel et al., 2018]] ; [[#Tiwari--2018|Tiwari and Jha, 2018]] ; [[#Sigdel--2020|Sigdel et al., 2020]] ). It is largely unknown how broader-scale climate inputs, such as pre-monsoon droughts, interact with local-scale factors to govern treeline response patterns ( [[#Schickhoff--2015|Schickhoff et al., 2015]] ; [[#Müller--2016|Müller et al., 2016]] ; [[#Bhatta--2018|Bhatta et al., 2018]] ; [[#Singh--2019b|Singh et al., 2019b]] ).

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===== 10.4.2.1.2 Species ranges and biodiversity =====

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Since AR5, new evidence has appeared of alterations in terrestrial and freshwater species, populations and communities in line with climate change across Asia ( ''medium to high confidence'' ) ( [[#Arias--2021|Arias et al., 2021]] ). In North Asia, temperature increase and droughts have promoted spread northward of the current silk moth outbreak (has affected nearly 2.5 × 10 6 ha) in Central Siberia dark taiga since 2014 ( [[#Kharuk--2017b|Kharuk et al., 2017b]] ; [[#Kharuk--2020|Kharuk et al., 2020]] ). The climatic range of the Colorado potato beetle ( ''Leptinotarsa decemlineata'' ) in 1991–2010 expanded east- and northward in Siberia and the Russian Far East compared with the 1951–1970 range ( [[#Popova--2014|Popova, 2014]] ). The climatic range of ''Ixodes ricinus'' , a vector of dangerous human diseases, expanded into Central Asia and south of the Russian Far East ( [[#Semenov--2020|Semenov et al., 2020]] ). A butterfly ( ''Melanargia russiae'' ) in the Middle Urals moved northward ( [[#Zakharova--2017|Zakharova et al., 2017]] ). Thrush birds in West Siberia penetrated northward up to the limits of the sparse woodlands ( [[#Ryzhanovskiy--2019a|Ryzhanovskiy, 2019a]] ). The increase in the length of frost-free period observed in the Ilmen Nature Reserve, Middle Urals, during recent decades is supposed to be interlinked with changes in the amplitude and frequency of population waves of bank vole ( [[#Kiseleva--2020|Kiseleva, 2020]] ). In Katunskiy Biosphere Reserve, Russian Altai, in the period 2005–2015, alpine plant species have shifted towards higher altitudes by 5.3 m on average ( [[#Artemov--2018|Artemov, 2018]] ). Wild reindeer herds in Taimyr, north of Central Siberia, migrated northward to the Arctic Sea coast in hot summers between 1999–2003 and 2009–2016 because of an earlier massive emergence of bloodsucking insects ( [[#Pospelova--2017|Pospelova et al., 2017]] ). In Yakutia, the ranges of red deer, elk and the northern pika are expanding, and the winter survival of the mouse-like rodents has increased ( [[#Safronov--2016|Safronov, 2016]] ). In the Chukchi Sea, in recent decades the average duration polar bears spent onshore increased by 30 d ( [[#Rode--2015b|Rode et al., 2015b]] ) in line with global warming and the rapid decline of their sea ice habitat ( [[#Derocher--2013|Derocher et al., 2013]] ; [[#Jenssen--2015|Jenssen et al., 2015]] ; [[#Rode--2015a|Rode et al., 2015a]] ).

In Central Kazakh Steppe, in line with warming, in 2018 there were more ‘southern’ sub-arid species in the communities and fewer relatively ‘northern’ boreal and polyzonal species of ground beetles (Carabidae) and black beetles (Tenebrionidae) than in 1976–1978 ( [[#Mordkovich--2020|Mordkovich et al., 2020]] ). The present distribution of Asian black birch ( ''Betula davurica'' Pall.) in East and North Asia was formed as a result of northward expansion during post-Last Glacial Maximum global warming ( [[#Shitara--2018|Shitara et al., 2018]] ). Both upper and lower limits of avifauna of two New Guinean mountains, Mt. Karimui and Karkar Island, have been shifting upslope since 1965 ( [[#Freeman--2014|Freeman and Freeman, 2014]] ). In Republic of Korea, for the past 60 years, the northern boundary line of 63 southern butterfly species has moved further north ( [[#Bae--2020|Bae et al., 2020]] ). The change in the butterflies’ occurrence in this period has been influenced mostly by large-scale reforestation, not by climate change ( [[#Kwon--2021|Kwon et al., 2021]] ). Warming-driven geographic range shift was recorded in 87% of 124 endemic plant species studied in the Sikkim Himalaya in the periods 1849–1850 and 2007–2010 ( [[#Telwala--2013|Telwala et al., 2013]] ). In Darjeeling, India, significant change in lichen community structure was shown in response to climate change and anthropogenic pollution ( [[#Bajpai--2016|Bajpai et al., 2016]] ).

The observed loss of biodiversity and habitat of animals and plants has been linked to climate change in some parts of Asia ( ''high confidence'' ). Climate change, together with human disturbances, have caused local extinction of some large and medium-sized mammals during the past three centuries in China ( [[#Wan--2019|Wan et al., 2019]] ). Climate change has shown significant impacts on subalpine plant species at low altitudes and latitudes in Republic of Korea and may impose a big threat to these plant species ( [[#Adhikari--2018|Adhikari et al., 2018]] ; [[#Kim--2019c|Kim et al., 2019c]] ). Climate change has caused habitat loss of amphibians ( [[#Surasinghe--2011|Surasinghe, 2011]] ) and extinction of some endemic species in Sri Lanka ( [[#Kottawa-Arachchi--2017|Kottawa-Arachchi and Wijeratne, 2017]] ).

There is evidence that climate change can alter species interaction or spatial distribution of invasive species in Asia ( ''high confidence'' ). Climate warming has enhanced the competitive ability of the native species ( ''Sparganium angustifolium'' ) against the invasive species ( ''Egeria densa'' ) in China under a mesocosm experiment in a greenhouse ( [[#Yu--2018e|Yu et al., 2018e]] ). It has also increased the non-target effect on a native plant ( ''Alternanthera sessilis'' ) by a biological control beetle ( ''Agasicles hygrophila'' ) in China due to range expansion of the beetle and change of phenology of the plant ( [[#Lu--2015|Lu et al., 2015]] ). Climate warming has expanded the distribution of invasive bamboos ( ''Phyllostachys edulis'' and ''P. bambusoides'' ) northward and upslope in Japan ( [[#Takano--2017|Takano et al., 2017]] ), while soil dry-down rates have been a key driver of invasion of dwarf bamboo ( ''Sasa kurilensis'' ) in central Hokkaido above and below the treeline ( [[#Winkler--2016|Winkler et al., 2016]] ).

Climate change along with land-use and land-cover change influences soil organic carbon content, microbial biomass C, microbial respiration and the soil carbon cycle in the Hyrcanian forests of Iran ( [[#Soleimani--2019|Soleimani et al., 2019]] ; [[#Francaviglia--2020|Francaviglia et al., 2020]] ). In the fir forest ecosystems of the Tibetan Plateau, winter warming affects the ammonia-oxidising bacteria and archaea, thus altering the nitrogen cycle ( [[#Huang--2016|Huang et al., 2016]] ). Ecosystem carbon pool in the spruce forests of the northeast Tibetan Plateau was reduced by about 25% by deforestation due to recent decades of climate warming as well as wood pasture and logging ( [[#Wagner--2015|Wagner et al., 2015]] ). In Mongolia’s forest steppe, recent decades of drought- and land-use-induced deforestation has reduced the ecosystem carbon stock density by about 40% ( [[#Dulamsuren--2016|Dulamsuren et al., 2016]] ). In Inner Mongolia, the predicted decreases in precipitation and warming for most of the temperate grassland region could lead to a pH change, which would contribute to a soil C-N-P decoupling that could reduce plant growth and production in arid ecosystems ( [[#Jiao--2016|Jiao et al., 2016]] ).

In Central Asia, in the Vakhsh, Kafirnigan and Kyzylsu river basins, Tajikistan, it has been shown that temperature stimulates algal species diversity, while precipitation and altitude suppress it ( [[#Barinova--2015|Barinova et al., 2015]] ). In line with the warming of Lake Baikal, Russia, since the 1990s in the lake’s south basin, there have been shifts in diatom community composition towards higher abundances of the cosmopolitan ''Synedra acus'' and a decline in endemic species, mainly ''Cyclotella minuta'' and ''Stephanodiscus meyerii'' , and to a lesser extent ''Aulacoseira baicalensis'' and ''A. skvortzowii'' ( [[#Roberts--2018|Roberts et al., 2018]] ). In Gonghai Lake, North China, diatom biodiversity has increased remarkably from 1966, but began to decline after 1990 presumably in response to rapid climate warming ( [[#Yan--2018|Yan et al., 2018]] ).

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===== 10.4.2.1.3 Wildfires =====

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Climate change, human activity and lightning determine increases in wildfire severity and area burned in North Asia (high detection with medium-to-low attribution to climate change). In North Asia, the extent of fire-affected areas in boreal forest can be millions of hectares in a single extreme fire year ( [[#Duane--2021|Duane et al., 2021]] ) and nearly doubled between 1970 and 1990 ( [[#Brazhnik--2017|Brazhnik et al., 2017]] ). During recent decades, the number, area and frequency of forest fires increased in Putorana Plateau (north of Central Siberia), in larch-dominated forests of Central Siberia and in Siberian forests as a whole. This increase is in line with an increase in the average annual air temperature, air temperature anomalies, droughts and the length of fire season ( [[#Ponomarev--2016|Ponomarev et al., 2016]] ; [[#Kharuk--2017|Kharuk and Ponomarev, 2017]] ; [[#Pospelova--2017|Pospelova et al., 2017]] ). The number of forest fires and damaged areas in Gangwon Province and the Yeongdong area in the 2000s increased by factors of 1.7 and 5.6, respectively, compared with the 1990s ( [[#Bae--2020|Bae et al., 2020]] ). Climate change is not the sole cause of the increase in forest fire severity ( [[#Wu--2014|Wu et al., 2014]] ; [[#Wu--2018d|Wu et al., 2018d]] ). Ignition is often facilitated by lightning ( [[#Canadell--2021|Canadell et al., 2021]] ), and over 80% of fires in Siberia are ''likely'' anthropogenic in origin (e.g., ( [[#Brazhnik--2017|Brazhnik et al., 2017]] ). Gas field development and Indigenous tundra burning practices that may get out of control contribute to fire frequency in the forest–tundra of West Siberia ( [[#Adaev--2018|Adaev, 2018]] ; [[#Moskovchenko--2020|Moskovchenko et al., 2020]] ). Climate change in combination with socioeconomic changes has resulted in an increase in fire severity and area burned in South Siberia, and illegal logging increases fire danger in forest–steppe Scots pine stands ( [[#Ivanova--2010|Ivanova et al., 2010]] ; [[#Schaphoff--2016|Schaphoff et al., 2016]] ).

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===== 10.4.2.1.4 Phenology, growth rate and productivity =====

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In East and North Asia, satellite measurements and ground-based observations in recent decades demonstrate either an increase in the length of plant growth season over sub-regions or in some territories in line with climate warming, or do not show any significant trend in other territories ( ''high confidence'' ). In recent decades in China, there has been an increasing trend in annual mean grassland net primary production (NPP), average leaf area index and lengthening of the local growing season ( [[#Piao--2015|Piao et al., 2015]] ; [[#Zhang--2017b|Zhang et al., 2017b]] ; [[#Xia--2019|Xia et al., 2019]] ). Nevertheless, phenology patterns vary across different studies, species and parts of China. In most regions of Northeast China, start date and length of land surface phenology from 2000 to 2015 had advanced by approximately 1 d yr −1 , except in the needle-leaf and cropland areas ( [[#Zhang--2017d|Zhang et al., 2017d]] ). For Inner Mongolia, it has been shown that neither the start of growing season (SOS) nor the end of growing season (EOS) presented detectable progressive patterns at the regional level in 1998–2012, except for the steppe–desert (6% of the total area) ( [[#Sha--2016|Sha et al., 2016]] ). In the Tianshan Mountains in China, the NPP of only 2 out of 12 types of vegetation increased in spring, and the NPP of only one type increased in autumn from 2000–2003 to 2012–2016 ( [[#Hao--2019|Hao et al., 2019]] ). In Republic of Korea, from 1970 to 2013, the SOS has advanced by 2.7 d per decade, and the EOS has been delayed by 1.4 d per decade ( [[#Jung--2015|Jung et al., 2015]] ). During the past decade, leaf unfolding has accelerated at a rate of 1.37 d yr −1 , and the timing of leaf fall has been delayed at a rate of 0.34 d yr −1 ( [[#Kim--2019d|Kim et al., 2019d]] ). Cherry blossoms are predicted to flower 6.3 and 11.2 d earlier after 2090 according to scenarios RCP4.5 and RCP8.5, respectively ( [[#Bae--2020|Bae et al., 2020]] ). On the Tibetan Plateau, it was found that the SOS has advanced and the EOS has been delayed over the past 30–40 years ( [[#Yang--2017|Yang et al., 2017]] ). Using normalised difference vegetation index (NDVI) datasets and ground-based Budburst data ( [[#Wang--2017c|Wang et al., 2017c]] ) found no consistent evidence that the SOS has been advancing or delaying over the Tibetan Plateau during the past two to three decades. The discrepancies among different studies in the trends of spring phenology over the Tibetan Plateau could be largely attributed to the use of different phenology retrieval methods. An uncertainty exists with the relationship between land-surface phenology and climate change estimated by satellite-derived NDVI because these indices are usually composite products of a number of days (e.g., 16 d) that could fail to capture more details. Besides, due to lack of ''in situ'' observations, the SOS and EOS at large areas cannot be easy defined ( [[#Zhang--2017d|Zhang et al., 2017d]] ).

In North Asia, in Central Siberia and south of West Siberia, the growth index of Siberian larch based on tree-ring width increased with the onset of warming and changed in antiphase with aridity in the 1980s ( [[#Kharuk--2018|Kharuk et al., 2018]] ). In Mongolia and Kazakhstan, the temperature increase over the previous decade promoted radial stem increment of the Siberian larch. However, the simultaneous influence of increased temperature, decreased precipitation and increased anthropogenic pressure resulted in widespread declines in forest productivity and reduced forest regeneration, and increased tree mortality ( [[#Dulamsuren--2013|Dulamsuren et al., 2013]] ; [[#Lkhagvadorj--2013a|Lkhagvadorj et al., 2013a]] ; [[#Lkhagvadorj--2013b|Lkhagvadorj et al., 2013b]] ; [[#Dulamsuren--2014|Dulamsuren et al., 2014]] ; [[#Khansaritoreh--2017|Khansaritoreh et al., 2017]] ). In Eastern Taimyr, growing season, the number of flowering shoots, annual increment, success of seed ripening and vegetation biomass have increased considerably in recent decades ( [[#Pospelova--2017|Pospelova et al., 2017]] ). In Vishera Nature Reserve, northern Ural Mountains, annual temperature has increased in recent decades in parallel with a summer temperature drop and an increase in summer frost numbers. As a result, trends in vegetation change are mostly unreliable ( [[#Prokosheva--2017|Prokosheva, 2017]] ).

In Asia, the date of arrival of migrant birds to nesting areas and the date of departure from winter areas are changing consistently with climate change ( ''medium confidence'' ). Time of arrival of the grey crow to the Lower Ob river region, northwest Siberia, shifted to earlier dates in the period 1970–2017, which is consistent with an increase in the daily average temperatures on the day of arrival ( [[#Ryzhanovskiy--2019b|Ryzhanovskiy, 2019b]] ). In Ilmen Nature Reserve, Urals, an earlier arrival of the majority of nesting bird species has not been observed in recent decades. This is explained by the fact that other factors, such as the weather of each spring month of particular years, population density in the previous nesting period, the seed yield of the main feeding plants and migration of wintering species from adjacent areas, determinate the long-term dynamics of bird arrival ( [[#Zakharov--2016|Zakharov, 2016]] ; [[#Zakharov--2018|Zakharov, 2018]] ). In Yokohama, Japan, observations since 1986 have revealed that the arrival of six winter bird species came later and the departure earlier than in the past, due to warmer temperatures ( [[#Kobori--2012|Kobori et al., 2012]] ; [[#Cohen--2018|Cohen et al., 2018]] ). Some papers corroborate that earlier start and later end of phenological events in Asia are associated with global warming; however, other papers do not confirm such a connection. Comparison and synthesis of results is impeded by usage of different metrics, measurement methods and models (e.g., [[#Hao--2019|Hao et al., 2019]] ). Relative contribution of climatic stress and other factors to phenology and plant growth trends are poorly understood (e.g., [[#Andreeva--2019|Andreeva et al., 2019]] ).

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