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

==== 12.4.4.1 Heat and Cold ====

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'''Mean air temperature:''' New literature confirms a continuous warming since the beginning of the 20th century in the majority of the eight sub-regions (Atlas.7). However, observational datasets in several areas are still short and trend estimation is hindered by year-to-year and interannual variability. [[IPCC:Wg1:Chapter:Atlas|Atlas]] projections point to a ''virtually certain'' warming across all sub-regions, with the largest increases taking place in the Amazon basin (NSA and SAM; Atlas.7.2.4). A consistent increase in temperature-related indices linked to several climate-sensitive sectors (e.g., growing degree days, cooling degree days) is found across CMIP5, CMIP6 and CORDEX-CORE projections, with smaller increases for cooling degree days in mid-latitude regions than in SCA and the Amazon ( [[#Coppola--2021b|Coppola et al., 2021b]] ). Daily mean temperature exceedances of a typical 21.5°C threshold for a successful incubation of disease pathogens inside many mosquito vectors ( [[#Lambrechts--2011|Lambrechts et al., 2011]] ; [[#Blanford--2013|Blanford et al., 2013]] ; [[#Mordecai--2013|Mordecai et al., 2013]] , 2017) will be crossed much more frequently, potentially driving increases in the incidence of vector-borne diseases ( [[#Laporta--2015|Laporta et al., 2015]] ; [[#Messina--2019|Messina et al., 2019]] ).

'''Extreme heat:''' [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] found ''high confidence'' of increased heatwaves in all regions except SSA over the past decades. There is evidence of increasing heat stress over summer in much of SES and SWS using the wet bulb globe temperature (WBGT) index for the period 1973–2012, and this has been attributed to human influence on the climate system ( [[#Knutson--2016|Knutson and Ploshay, 2016]] ). Climate change projections point to major increases in several heat indices across the region for all scenarios ( ''high confidence'' ). Largest increases in the frequency of hot days (maximum temperatures, Tx &gt; 35°C) are projected for the Amazon basin under SSP5-8.5 with more than 200 days per year at the end of the century under SSP5-8.5 relative to 1995-2014, while such increases remain moderate (50–100 days) in SSP1-2.6. For the dangerous heat threshold of HI &gt; 41°C, increases in frequency are similar to that in Tx &gt; 35°C (Figure 12.4 and Figures 12.SM.1 and 12.SM.2; [[#Coppola--2021b|Coppola et al., 2021b]] ; [[#Schwingshackl--2021|Schwingshackl et al., 2021]] ).

'''Cold spell and frost:''' A decreasing frequency of cold days and nights has been observed in many sub-regions (Table 11.13). There is ''medium confidence'' ( ''limited agreement'' ) of a decrease in frost days in SWS, SES and SSA. Projections consistently suggest a general decrease in the frequency of cold spells and frost days in the region as indicated by several indices based on minimum temperature ( [[#Chou--2014|Chou et al., 2014]] ; [[#López-Franca--2016|López-Franca et al., 2016]] ; [[#Li--2021|]] [[#Li--2021|C. Li et al., 2021]] ). Heating degree days are consistently projected to decrease by 5 degree days per year in the Amazon region, and up to 20–30 degree days per year in NWS, SWS and SES, under RCP8.5/SSP5-8.5 by mid century ( [[#Coppola--2021b|Coppola et al., 2021b]] ).

'''In conclusion, it is''' virtually certain '''that warming will continue everywhere in Central and South America and there is''' high confidence '''that by the end of the century most regions will undergo extreme heat stress conditions much more often than in recent past (e.g., increase of dangerous heat with HI &gt; 41°C, or Tx &gt; 35°C) with more than 200 additional days per year under SSP5-8.5, while such conditions will be met typically 5''' '''0–1''' '''00 more days per year under SSP1-2.6 over the same regions. Cold spells and frost days will have a decreasing trend''' ( high confidence ''').'''

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