Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.2.1 Heat and Cold ====

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'''Mean air temperature:''' A long-term warming trend in annual mean surface temperature has been observed across Asia during 1960–2015, and the warming accelerated after the 1970s ( ''high confidence'' ) ( [[#Davi--2015|Davi et al., 2015]] ; [[#Aich--2017|Aich et al., 2017]] ; [[#Cheong--2018|Cheong et al., 2018]] ; S. [[#Dong--2018|]] [[#Dong--2018|Dong et al., 2018]] ; [[#IPCC--2018|IPCC, 2018]] ; [[#Krishnan--2019|Krishnan et al., 2019]] ; M. [[#Zhang--2019|]] [[#Zhang--2019|]] [[#Zhang--2019|]] [[#Zhang--2019|Zhang et al., 2019]] ). Records also indicate a higher rate of warming in minimum temperatures than maximum temperatures in Asia, leading to more frequent warm nights and warm days, and less frequent cold days and cold nights ( ''high confidence'' ) ( [[#Supari--2017|Supari et al., 2017]] ; [[#Akperov--2018|Akperov et al., 2018]] ; [[#Cheong--2018|Cheong et al., 2018]] ; [[#Rahimi--2018|Rahimi et al., 2018]] ; [[#Khan--2019a|Khan et al., 2019a]] ; L. [[#Li--2019|]] [[#Li--2019|Li et al., 2019]] ; M. [[#Zhang--2019|]] [[#Zhang--2019|]] [[#Zhang--2019|]] [[#Zhang--2019|Zhang et al., 2019]] ).

Projections show continued warming over Asia in the future with contrasted regional patterns across the continent ( ''high confidence'' ) (Figure 4.19). For RCP8.5/SSP5-8.5 at the end of the century, the mean estimated warming exceeds 5°C in WSB, ESB and RFE and 7°C in some parts ( ''high confidence'' ). In most areas of ARP and WCA, 5°C is exceeded ( [[#Ozturk--2017|Ozturk et al., 2017]] ), but EAS, SAS and SEA have a lower projected warming of less than 5°C ( [[#Basha--2017|Basha et al., 2017]] ; [[#Lu--2019|]] [[#Lu--2019|C. Lu et al., 2019]] ; [[#Almazroui--2020|Almazroui et al., 2020]] ; Atlas.5). Under SSP1-2.6, the warming remains limited to 2°C in most areas except Arctic regions, where it exceeds 2°C (Figure 4.19).

'''Extreme heat:''' There is increased evidence and ''high confidence'' of more frequent heat extremes in the recent decades than in previous ones in most of Asia ( [[#Acar%20Deniz--2015|Acar Deniz and Gönençgil, 2015]] ; [[#Rohini--2016|Rohini et al., 2016]] ; [[#Mishra--2017|Mishra et al., 2017]] ; [[#You--2017|You et al., 2017]] ; [[#Imada--2018|Imada et al., 2018]] ; [[#Khan--2019b|Khan et al., 2019b]] ; [[#Krishnan--2019|Krishnan et al., 2019]] ; [[#Rahimi--2019|Rahimi et al., 2019]] ; [[#Yin--2019|Yin et al., 2019]] ; Chapter 11) due to the effects of anthropogenic global warming, El Niño and urbanization ( [[#Luo--2017|Luo and Lau, 2017]] ; [[#Thirumalai--2017|Thirumalai et al., 2017]] ; [[#Imada--2019|Imada et al., 2019]] ; Y. [[#Sun--2019|]] [[#Sun--2019|]] [[#Sun--2019|Sun et al., 2019]] ; [[#Zhou--2019|Zhou et al., 2019]] ). But there is ''medium confidence'' of heat extremes increasing in frequency in many parts of India ( [[#Rohini--2016|Rohini et al., 2016]] ; [[#Mazdiyasni--2017|Mazdiyasni et al., 2017]] ; [[#van%20Oldenborgh--2018|van Oldenborgh et al., 2018]] ; [[#Sen%20Roy--2019|Sen Roy, 2019]] ; [[#Kumar--2020|Kumar et al., 2020]] ) partly due to the alleviation of anthropogenic warming by increased air pollution with aerosols and expanding irrigation ( [[#van%20Oldenborgh--2018|van Oldenborgh et al., 2018]] ; [[#Thiery--2020|Thiery et al., 2020]] ).

Extreme heat events are ''very likely'' to become more intense and/or more frequent in SAS, WCA, ARP, EAS, and SEA by the end of 21st century, especially under RCP6.0 and RCP8.5 (Figure 12.4a–c and Chapter 11; [[#Lelieveld--2016|Lelieveld et al., 2016]] ; [[#Pal--2016|Pal and Eltahir, 2016]] ; [[#Guo--2017|Guo et al., 2017]] ; [[#Mishra--2017|Mishra et al., 2017]] ; [[#Dosio--2018|Dosio et al., 2018]] ; [[#Lin--2018|Lin et al., 2018]] ; [[#Nasim--2018|Nasim et al., 2018]] ; [[#Shin--2018|Shin et al., 2018]] ; [[#Hong--2019|Hong et al., 2019]] ; [[#Su--2019|Su and Dong, 2019]] ; [[#Khan--2020|Khan et al., 2020]] ; [[#Kumar--2020|Kumar et al., 2020]] ). The exceedance of the dangerous heat stress 41°C threshold of the HI is expected to increase by about 250 days in SEA and by 50–150 days in SAS, WCA, ARP and EAS for SSP5-8.5 at the end of the century (Figure 12.4d–f and Figure 12.SM.2). Under SSP1-2.6, the increase would be restricted to less than 30 days in many of these regions except SEA, where the number of exceedance days increases by about 100 days in some areas. Such increases are already present in the middle of the century (Figure 12.4d–f; [[#Schwingshackl--2021|Schwingshackl et al., 2021]] ). In these regions, the increase in number of days with exceedance of 35°C of high heat stress is also expected to increase substantially for the mid-century under SSP5-8.5 (typically by 10–50 days except in Arctic and Siberian regions), and by more than 60 days in areas of SEA, and a large difference is found between low- and high-end scenarios in the end of the century ( ''high confidence'' ) (Figure 12.4b). Over WSB, ESB and RFE also, an increase of extreme heat durations and frequency is expected in all scenarios ( ''high confidence'' ) ( [[#Kattsov--2017|Kattsov et al., 2017]] ; [[#Khlebnikova--2019b|Khlebnikova et al., 2019b]] ).

'''Cold spell and frost:''' Cold spells intensity and frequency, as well as the number of frost days, in most Asian regions have been decreasing since the beginning of the 20th century ( ''high confidence'' ) (Chapter 11; [[#Sheikh--2015|Sheikh et al., 2015]] ; [[#Donat--2016|Donat et al., 2016]] ; [[#Erlat--2016|Erlat and Türkeş, 2016]] ; S. [[#Dong--2018|]] [[#Dong--2018|Dong et al., 2018]] ; [[#Liao--2018|Liao et al., 2018]] , 2020; [[#Lu--2018|Lu et al., 2018]] ; [[#van%20Oldenborgh--2019|van Oldenborgh et al., 2019]] ), except for the central Eurasian regions, where there was a cooling trend during 1995–2014, which is linked to sea ice loss in the Barents–Kara Seas ( ''medium confidence'' ) (Atlas.5.2; [[#Wegmann--2018|Wegmann et al., 2018]] ; [[#Blackport--2019|Blackport et al., 2019]] ; [[#Mori--2019|Mori et al., 2019]] ).

It is ''very likely'' that cold spells will have a decreasing frequency in all future scenarios across Asian regions (J. [[#Guo--2018|]] [[#Guo--2018|Guo et al., 2018]] ; [[#Sui--2018|Sui et al., 2018]] ; L. [[#Li--2019|]] [[#Li--2019|Li et al., 2019]] ), as well as frost days (L. [[#Wang--2017|]] [[#Wang--2017|]] [[#Wang--2017|Wang et al., 2017]] ; [[#Fallah-Ghalhari--2019|Fallah-Ghalhari et al., 2019]] ) except in tropical Asia (Chapter 11).

'''In Asia, temperatures have warmed during the last century''' ( high confidence '''). Extreme heat episodes have become more frequent in most regions''' ( high confidence '''), and are''' very likely '''to increase in all regions of Asia under all warming scenarios during this century. Dangerous heat stress thresholds such as HI &gt; 41°C will be crossed much more often (typically 5''' '''0–1''' '''50 days per year more than the recent past) in many southern Asia regions at the end of the century under SSP5-8.5 while these numbers should remain limited to a few tens under SSP1-2.6''' ( high confidence '''). It is''' very likely '''that cold spells and frost days will decrease in frequency in all future scenarios across Asian regions during the century.'''

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