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

==== 12.3.1.1 Mean Air Temperature ====

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Information about increasing mean annual and seasonal air temperature is relevant in the determination of suitable species range for terrestrial, freshwater and intertidal species ( [[#Thomas--2004|Thomas et al., 2004]] ; [[#Elith--2010|Elith et al., 2010]] ; [[#Hincapie--2013|Hincapie and Caicedo, 2013]] ; [[#Cooper--2014|Cooper, 2014]] ; [[#Krist--2014|Krist et al., 2014]] ; [[#Lindner--2014|Lindner et al., 2014]] ; [[#Saintilan--2014|Saintilan et al., 2014]] ; [[#Lenoir--2015|Lenoir and Svenning, 2015]] ; [[#Myers-Smith--2015|Myers-Smith et al., 2015]] ; [[#Urban--2015|Urban, 2015]] ; [[#Thorne--2017|Thorne et al., 2017]] ). Ocean ecosystems are affected by the ocean temperature CID (described in [[#12.3.6.1|Section 12.3.6.1]] ). Species redistribution and extinction studies also need information about climate velocity, a comparison of the pace of warming to geographical temperature gradients that indicates the rate at which a species would have to move to maintain its climatological temperature ( [[#Thomas--2004|Thomas et al., 2004]] ; [[#Loarie--2009|Loarie et al., 2009]] ; [[#Dobrowski--2013|Dobrowski et al., 2013]] ; [[#Burrows--2014|Burrows et al., 2014]] ; [[#Dobrowski--2016|Dobrowski and Parks, 2016]] ; [[#Sittaro--2017|Sittaro et al., 2017]] ) with some studies incorporating additional variables beyond temperature ( [[#Hamann--2015|Hamann et al., 2015]] ). Many freshwater ecosystems are strongly constrained by stream and lake temperatures ( [[#Scheurer--2009|Scheurer et al., 2009]] ; [[#Comte--2013|Comte and Grenouillet, 2013]] ; [[#Contador--2014|Contador et al., 2014]] ; [[#Knouft--2017|Knouft and Ficklin, 2017]] ). Warmer and more stratified lake temperatures are more conducive to cyanobacteria blooms with implications for ecosystem health and water resource quality ( [[#Whitehead--2009|Whitehead et al., 2009]] ; [[#Moss--2011|Moss et al., 2011]] ; [[#Jones--2014|Jones and Brett, 2014]] ; [[#Chapra--2017|Chapra et al., 2017]] ; [[#Shatwell--2019|Shatwell et al., 2019]] ). Consideration of nighttime and daytime temperature trends also elucidates different biophysical effects on vegetation ( [[#Peng--2013|Peng et al., 2013]] ). Changes in the seasonal timing caused by warming trends are critical to species ranges and ecosystem function ( [[#Pearce-Higgins--2015|Pearce-Higgins et al., 2015]] ; [[#Hughes--2017b|Hughes et al., 2017b]] ), and indices that characterize the onset of spring shed light on plant emergence and development ( [[#Ault--2015|Ault et al., 2015]] ).

Mean air temperature dictates many aspects of crop cultivation, livestock production, agroforestry and output from freshwater aquaculture and fisheries, as well as the potential for food contamination. Mean warming alters suitable cultivation zones for crop species ( [[#Bragança--2016|Bragança et al., 2016]] ; [[#Gendron%20St-Marseille--2019|Gendron St-Marseille et al., 2019]] ; [[#IPCC--2019c|IPCC, 2019c]] ) and tree species ( [[#Hanewinkel--2013|Hanewinkel et al., 2013]] ; [[#Fei--2017|Fei et al., 2017]] ). Crop and ecosystem service productivity often responds directly to mean temperatures, although this is dependent on farming systems ( [[#Bassu--2014|Bassu et al., 2014]] ; [[#Challinor--2014|Challinor et al., 2014]] ; [[#Lobell--2014|Lobell and Tebaldi, 2014]] ; [[#Rosenzweig--2014|Rosenzweig et al., 2014]] ; [[#Asseng--2015|Asseng et al., 2015]] ; [[#Li--2015|Li et al., 2015]] ; [[#Fleisher--2017|Fleisher et al., 2017]] ; [[#Zhao--2017|Zhao et al., 2017]] ; [[#Smith--2019|Smith and Fazil, 2019]] ). Many studies relate plant development (phenology), insect generation cycles and pest outbreaks to growing degree days, an aggregation of daily thermal units above a threshold (e.g., T <sub>mean</sub> &gt;5°C) that accelerates with warmer conditions ( [[#Hof--2016|Hof and Svahlin, 2016]] ; [[#Ruosteenoja--2016|Ruosteenoja et al., 2016]] ; [[#Tripathi--2016|Tripathi et al., 2016]] ). Many plants respond to changes in nighttime temperatures that affect respiration and transpiration rates (Narayanan et al., 2015; X. [[#Chen--2019|]] [[#Chen--2019|Chen et al., 2019]] ), and warming of the soil column is also relevant to determine plant sprouting ( [[#Grotjahn--2021|Grotjahn, 2021]] ). A number of indices have been developed to represent the length of the viable local growing season, including a count of days where T <sub>max</sub> &gt;5°C ( [[#Mueller--2015|Mueller et al., 2015]] ) or the period between a year’s first and last set of five consecutive days with a weighted T <sub>mean</sub> ≥10°C (G. [[#Li--2018|]] [[#Li--2018|]] [[#Li--2018|]] [[#Li--2018|]] [[#Li--2018|Li et al., 2018]] ). Warmer conditions and altered seasonality modify the range and metabolism of some pollinators, pests, diseases and weeds ( [[#Wolfe--2008|Wolfe et al., 2008]] ; [[#Bebber--2015|Bebber, 2015]] ; [[#Aljaryian--2016|Aljaryian and Kumar, 2016]] ; IPBES, 2016; [[#Ramesh--2017|Ramesh et al., 2017]] ; [[#Deutsch--2018|Deutsch et al., 2018]] ; [[#Nyangiwe--2018|Nyangiwe et al., 2018]] ) and may reduce the effectiveness of winter storage for farmers and caching species ( [[#Sutton--2016|Sutton et al., 2016]] ).

Warming raises accumulated seasonal heat indices used in livestock production, especially when humidity is high ( [[#Key--2014|Key et al., 2014]] ; [[#Lallo--2018|Lallo et al., 2018]] ), determines aquaculture suitability and is important for wild fish species migration ( [[#Tripathi--2016|Tripathi et al., 2016]] ; [[#Brander--2017|Brander et al., 2017]] ). Agricultural planners may also calculate how overall warming trends alter the accumulation of vernalization units or chilling hours for agricultural or horticultural crops (often accumulated temperature deficit below a given daily or hourly threshold; [[#Dennis--2009|Dennis and Peacock, 2009]] ; [[#Luedeling--2012|Luedeling, 2012]] ; [[#Tripathi--2016|Tripathi et al., 2016]] ; [[#Grotjahn--2021|Grotjahn, 2021]] ). Warming in the post-harvest is also important for the determination of spoilage and waste ( [[#Stathers--2013|Stathers et al., 2013]] ) as well as food-borne diseases ( [[#Kovats--2004|Kovats et al., 2004]] ; [[#Mbow--2019|Mbow et al., 2019]] ).

Warming affects road degradation rates ( [[#Chinowsky--2012|Chinowsky and Arndt, 2012]] ; [[#Espinet--2016|Espinet et al., 2016]] ) and warming rates inform designs for long-term energy efficiency of buildings ( [[#Kalvelage--2014|Kalvelage et al., 2014]] ). Mean temperature drives seasonal energy demand, often expressed using winter heating degree days (the accumulated deficit of daily temperatures below a ‘comfortable’ indoor temperature, e.g., 15.5°C) and summer cooling degree days (the accumulated excess of temperature above a ‘comfortable’ level, e.g., 18°C; [[#Spinoni--2015|Spinoni et al., 2015]] ; [[#Arnell--2019|Arnell et al., 2019]] ). Energy resources may also need information on warming trends to determine suitable zones and overall productivity for biofuels and solar panels, the efficiency of which decreases with higher temperatures ( [[#Schaeffer--2012|Schaeffer et al., 2012]] ; [[#Wild--2015|Wild et al., 2015]] ; [[#Solaun--2019|Solaun and Cerdá, 2019]] ).

Health impacts and risk studies compare seasonal temperature conditions to limiting thresholds to understand range shifts and incubation rates for pathogens, disease vectors and zoonotic hosts (e.g., mosquitoes, ticks; [[#Caminade--2012|Caminade et al., 2012]] , 2014; [[#Eisen--2013|Eisen and Moore, 2013]] ; [[#Lima--2016|Lima et al., 2016]] ; [[#Ogden--2017|Ogden, 2017]] ; [[#Monaghan--2018|Monaghan et al., 2018]] ) and warming of surface ocean and lake waters conducive to bacterial outbreaks ( [[#Baker-Austin--2013|Baker-Austin et al., 2013]] ; [[#Jacobs--2015|Jacobs et al., 2015]] ; [[#Vezzulli--2015|Vezzulli et al., 2015]] ). Warmer conditions can also affect tourism ( [[#Kovács--2017|Kovács et al., 2017]] ) and impact human health by lengthening the allergy season and increasing pollen concentration ( [[#Hamaoui-Laguel--2015|Hamaoui-Laguel et al., 2015]] ; [[#Kinney--2015a|Kinney et al., 2015a]] ; [[#Lake--2017|Lake et al., 2017]] ; [[#Upperman--2017|Upperman et al., 2017]] ; [[#Sapkota--2019|Sapkota et al., 2019]] ; [[#Ziska--2019|Ziska et al., 2019]] ).

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