Editing IPCC:AR6/SRCCL/Chapter-2 (section)

=== 2.2.3 The influence of climate change on food security ===

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Food security and the various components thereof are addressed in depth in Chapter 5. Climate variables relevant to food security and food systems are predominantly temperature and precipitation-related, but also include integrated metrics that combine these and other variables (e.g., solar radiation, wind, humidity) and extreme weather and climate events including storm surge (Section 5.2.1). The impact of climate change through changes in these variables is projected to negatively impact all aspects of food security (food availability, access, utilisation and stability), leading to complex impacts on global food security ( ''high confidence'' ) (Chapter 5, Table 5.1).

Climate change will have regionally distributed impacts, even under aggressive mitigation scenarios (Howden et al. 2007 <sup>[[#fn:r57|57]]</sup> ; Rosenzweig et al. 2013 <sup>[[#fn:r58|58]]</sup> ; Challinor et al. 2014 <sup>[[#fn:r59|59]]</sup> ; Parry et al. 2005 <sup>[[#fn:r60|60]]</sup> ; Lobell and Tebaldi 2014 <sup>[[#fn:r61|61]]</sup> ; Wheeler and Von Braun 2013 <sup>[[#fn:r62|62]]</sup> ). For example, in the northern hemisphere the northward expansion of warmer temperatures in the middle and higher latitudes will lengthen the growing season (Gregory and Marshall 2012 <sup>[[#fn:r63|63]]</sup> ; Yang et al. 2015b <sup>[[#fn:r64|64]]</sup> ) which may benefit crop productivity (Parry et al. 2004 <sup>[[#fn:r65|65]]</sup> ; Rosenzweig et al., 2014 <sup>[[#fn:r66|66]]</sup> ; Deryng et al. 2016 <sup>[[#fn:r67|67]]</sup> ). However, continued rising temperatures are expected to impact global wheat yields by about 4–6% reductions for every degree of temperature rise (Liu et al. 2016a <sup>[[#fn:r68|68]]</sup> ; Asseng et al. 2015 <sup>[[#fn:r69|69]]</sup> ) and across both mid- and low latitude regions, rising temperatures are also expected to be a constraining factor for maize productivity by the end of the century (Bassu et al. 2014 <sup>[[#fn:r70|70]]</sup> ; Zhao et al. 2017 <sup>[[#fn:r71|71]]</sup> ). Although there has been a general reduction in frost occurrence during winter and spring, and a lengthening of the frost free season in response to growing concentrations of GHGs (Fischer and Knutti 2014 <sup>[[#fn:r72|72]]</sup> ; Wypych et al. 2017 <sup>[[#fn:r73|73]]</sup> ), there are regions where the frost season length has increased, for example, in southern Australia (Crimp et al. 2016 <sup>[[#fn:r74|74]]</sup> ). Despite the general reduced frost season length, late spring frosts may increase risk of damage to warming induced precocious vegetation growth and flowering (Meier et al. 2018 <sup>[[#fn:r75|75]]</sup> ). Observed and projected warmer minimum temperatures have, and will continue to, reduce the number of winter chill units required by temperate fruit and nut trees (Luedeling 2012 <sup>[[#fn:r76|76]]</sup> ). Crop yields are impacted negatively by increases of seasonal rainfall variability in the tropics, sub-tropics, water-limited and high elevation environments, while drought severity and growing season temperatures also have a negative impact on crop yield (Nelson et al. 2009 <sup>[[#fn:r77|77]]</sup> ; Schlenker and Lobell 2010 <sup>[[#fn:r78|78]]</sup> ; Müller et al. 2017 <sup>[[#fn:r79|79]]</sup> ; Parry et al. 2004 <sup>[[#fn:r80|80]]</sup> ; Wheeler and Von Braun 2013 <sup>[[#fn:r81|81]]</sup> ; Challinor et al. 2014 <sup>[[#fn:r82|82]]</sup> ).

Changes in extreme weather and climate (Section 2.2.5) have negative impacts on food security through regional reductions of crop yields. A recent study shows that 18–43% of the explained yield variance of four crops (maize, soybeans, rice and spring wheat) is attributable to extremes of temperature and rainfall, depending on the crop type (Vogel et al. 2019 <sup>[[#fn:r83|83]]</sup> ). Climate shocks, particularly severe drought impact low-income small-holder producers disproportionately (Vermeulen et al. 2012 <sup>[[#fn:r84|84]]</sup> ; Rivera Ferre 2014 <sup>[[#fn:r85|85]]</sup> ). Extremes also compromise critical food supply chain infrastructure, making transport of and access to harvested food more difficult (Brown et al. 2015 <sup>[[#fn:r86|86]]</sup> ; Fanzo et al. 2018 <sup>[[#fn:r87|87]]</sup> ). There is ''high confidence'' that the impacts of enhanced climate extremes, together with non-climate factors such as nutrient limitation, soil health and competitive plant species, generally outweighs the regionally positive impacts of warming (Lobell et al. 2011 <sup>[[#fn:r88|88]]</sup> ; Leakey et al. 2012 <sup>[[#fn:r89|89]]</sup> ; Porter et al. 2014 <sup>[[#fn:r90|90]]</sup> ; Gray et al. 2016 <sup>[[#fn:r91|91]]</sup> ; Pugh et al. 2016 <sup>[[#fn:r92|92]]</sup> ; Wheeler and Von Braun 2013 <sup>[[#fn:r93|93]]</sup> ; Beer 2018 <sup>[[#fn:r94|94]]</sup> ).

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