Editing IPCC:AR6/WGII/Chapter-14 (section)

=== 14.2.2 Projected Changes in North American Climate ===

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Climate changes related to warming temperature, including more intense heatwaves over land and in the ocean, diminished snowpack, sea ice reduction and SLR, are projected with ''high confidence'' and are strongly sensitive to future GHG concentrations (Figure 14.2). Climatic hazards affected by hydrological change, including humidity-inclusive heat stress, extreme precipitation and more intense storms, are projected to intensify.

Pronounced amplification of warming across the Arctic and continental intensification of warming (Figure 14.2B,C) is projected with ''high confidence'' ( [[#Doney--2007|Doney et al., 2007]] ; [[#Vose--2017|Vose et al., 2017]] ). Extreme heatwaves are projected to intensify, particularly in MX-NW, MX-N, MX-NE, US-SW, US-NP and US-SP (Figure 14.2F,G) and become more frequent and longer in duration as average temperature rises across North America ( [[#Seneviratne--2021|Seneviratne et al., 2021]] ). Extreme cold events are projected to decrease in severity ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Wuebbles--2014|Wuebbles et al., 2014]] ).

Total precipitation is projected to increase across the northern half of North America ( ''very high confidence'' ) and decrease in southwest North America (MX-SW, MX-NW, US-SW) ( ''medium confidence'' ) (Figure 14.2D,E; [[#Gutiérrez--2021b|Gutiérrez et al., 2021b]] ). Further increases in the intensity of locally heavy precipitation are ''very likely'' across the continent, as a greater fraction of precipitation falls in intense events ( [[#Easterling--2017|Easterling et al., 2017]] ; [[#Prein--2017a|Prein et al., 2017a]] ; [[#Zhang--2019a|Zhang et al., 2019a]] ).

High-humidity hazards are projected to increase ( ''medium confidence'' ) in regions around the Gulf of Mexico and southeast North America (US-SE, US-SP, MX-NE, MX-SE) ( [[#Zhao--2015|Zhao et al., 2015]] ). In subtropical regions that are less influenced by moisture from the Gulf of Mexico (including US-SW, US-SP, MX-NW and MX-N), the combination of higher temperature and less total precipitation leads to projections of increased aridity: drier surface conditions, higher evaporative demand by plants and more intense droughts ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Jones--2016|Jones and Gutzler, 2016]] ; [[#Easterling--2017|Easterling et al., 2017]] ; [[#Escalante-Sandoval--2017|Escalante-Sandoval and Nuñez-Garcia, 2017]] ).

As temperatures rise, snow extent, duration of snow cover and accumulated snowpack are ''virtually certain'' to decline in subarctic regions of North America (Gutierrez et al., 2021a; [[#McCrary--2019|McCrary and Mearns, 2019]] ; [[#Mudryk--2021|Mudryk et al., 2021]] ), with corresponding effects on snow-related hydrological changes ( ''high confidence'' ). These changes include declines in snowmelt runoff ( [[#Li--2017|Li et al., 2017]] ), increased evaporative losses during snow ablation ( [[#Foster--2016|Foster et al., 2016]] ; [[#Milly--2020|Milly and Dunne, 2020]] ), as well as increases in the frequency of rain-on-snow events ( [[#Jeong--2018a|Jeong and Sushama, 2018a]] ) and consecutive snow drought years in western North America ( [[#Marshall--2019a|Marshall et al., 2019a]] ).

Climate change is projected to magnify the impact of tropical cyclones in US-NE, MX-NE, US-SP, and US-SE by increasing rainfall ( [[#Patricola--2018|Patricola and Wehner, 2018]] ) and extreme wind speed ( ''high confidence'' ) and slowing the speed of land-falling storms ( ''limited evidence, low confidence'' ) ( [[#Seneviratne--2021|Seneviratne et al., 2021]] ; [[#Kossin--2018|Kossin, 2018]] ) ''.'' The coastal region at severe risk from tropical storms is projected to expand northward within US-NE ( ''medium confidence'' ) ( [[#Kossin--2017|Kossin et al., 2017]] ).

Additional reduction in polar sea ice is ''virtually certain'' ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Mudryk--2021|Mudryk et al., 2021]] ), with the North American Arctic projected to be seasonally ice free at least once per decade under 2°C of global warming ( ''high confidence'' ) ( [[#IPCC--2019b|IPCC, 2019b]] ; [[#Mioduszewski--2019|Mioduszewski et al., 2019]] ; [[#Mudryk--2018|Mudryk et al., 2018]] ). Duration of freshwater lake ice across the northern USA and southern Canada is projected to diminish ( ''high confidence'' ) ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Dibike--2012|Dibike et al., 2012]] ; [[#Mudryk--2018|Mudryk et al., 2018]] ; [[#Sharma--2019|Sharma et al., 2019]] ).

Ocean surface temperature is ''very likely'' to increase in future decades in waters around North America ( [[#Jewett--2017|Jewett and Romanou, 2017]] ; [[#Greenan--2018|Greenan et al., 2018]] ), but at a slower rate than air temperature over the continent. Rates of change are projected to be relatively higher in northern latitudes, with most rapid warming in summer in the Arctic and Bering Sea (US-AK, CA-NW) ( [[#Wang--2015|Wang and Overland, 2015]] ; [[#Wang--2018a|Wang et al., 2018a]] ; [[#Hermann--2019|Hermann et al., 2019]] ).

Sea level rise is ''virtually certain'' to continue along North American coastlines except for parts of US-AK and around Hudson Bay (HB) with geographically variable rates of rise ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; see Box 14.4). Relatively greater SLR is projected along the US-SE and MX-SW coastlines and relatively less along CA-BC and US-NW ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; see Box 14.4) ( [[#Fasullo--2018|Fasullo and Nerem, 2018]] ; [[#Greenan--2018|Greenan et al., 2018]] [[#IPCC--2019b|IPCC, 2019b]] ).

Ocean acidification (OA) along North American coastlines is projected to increase ( ''very high confidence'' ) ( [[#Jewett--2017|Jewett and Romanou, 2017]] ). The frequency and extent of oxygen minimum and hypoxic zones are projected to increase, with less confidence, exacerbated by climate-driven eutrophication and increasing stratification ( [[#Altieri--2015|Altieri and Gedan, 2015]] ; [[#IPCC--2019b|IPCC, 2019b]] ).

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