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

==== 12.4.9.1 Heat and Cold ====

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'''Mean air temperature:''' Atlas.11.2 shows ''high confidence'' in warming of the Arctic in observations and projections, measuring among the fastest-warming places at more than twice the global mean, with substantially higher temperature increases in the cold season (see also [[#AMAP--2017|AMAP, 2017]] ; [[#Meredith--2019|Meredith et al., 2019]] ). Atlas.11.1 assessed ''very likely'' warming in observations of West Antarctica from 1957 to 2016, but ''limited evidence'' of mean air temperature change across East Antarctica even as there is ''high confidence'' in future warming across the continent (Figure Atlas.29; [[#Meredith--2019|Meredith et al., 2019]] ).

'''Extreme heat, cold spell and frost:''' Ecosystem and societal temperature thresholds in polar regions often reflect lower tolerance to heat and higher tolerance to cold. Extreme heat events have increased around the Arctic and Iceland since 1979, including increases in cold season warm days and nights, melt days, and Arctic winter warm events (T &gt; –10°C) as well as decreases in cold days and nights ( [[#Mernild--2014|Mernild et al., 2014]] ; [[#Matthes--2015|Matthes et al., 2015]] ; [[#Vikhamar-Schuler--2016|Vikhamar-Schuler et al., 2016]] ; [[#Graham--2017|Graham et al., 2017]] ; [[#Sui--2017|Sui et al., 2017]] ; [[#Dobricic--2020|Dobricic et al., 2020]] ; [[#Peña-Angulo--2020|Peña-Angulo et al., 2020]] ). Heatwaves causing high temperature records have been recently documented in West and East Antarctica ( [[#Wille--2019|Wille et al., 2019]] ; [[#Robinson--2020|Robinson et al., 2020]] ). There is ''high confidence'' that polar amplification will drive increases in Arctic heat extremes as well as continuing declines in the magnitude and frequency of cold extremes ( [[#Matthes--2015|Matthes et al., 2015]] ; [[#Kharin--2018|Kharin et al., 2018]] ), although dynamical effects will still bring substantial cold air anomalies over the Arctic ( [[#Wu--2019|Wu and Francis, 2019]] ). There is ''medium confidence'' for equivalent changes in extreme heat in Antarctica based primarily on higher mean temperatures, with J.R. [[#Lee--2017|]] [[#Lee--2017|Lee et al. (2017)]] projecting more than 50 additional degree days above freezing (2098 RCP8.5 compared with 2014) over parts of the Antarctic Peninsula but smaller changes over mainland Antarctica.

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