Editing IPCC:AR6/WGII/Chapter-5 (section)

==== 5.4.1.1 Observed impacts on major crops ====

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AR5 [[IPCC:Wg2:Chapter:Chapter-7|Chapter 7]] ( [[#Porter--2014|Porter et al., 2014]] ) stated with confidence that warmer temperatures have benefited agriculture in the high latitudes, and more evidence has been published to support this statement. Typical examples include pole-ward expansion of growing areas and reduction of cold stress in East Asia and North America (Table SM5.1).

Recent warming trends have generally shortened the life cycle of major crops ( ''high confidence'' ) ( [[#Zhang--2014|Zhang et al., 2014]] ; [[#Shen--2015|Shen and Liu, 2015]] ; [[#Ahmed--2018|Ahmed et al., 2018]] ; [[#Liu--2018c|Liu et al., 2018c]] ; [[#Tan--2021|Tan et al., 2021]] ). Some studies, however, observed prolonged crop growth duration despite the warming trends ( [[#Mueller--2015|Mueller et al., 2015]] ; [[#Tao--2016|Tao et al., 2016]] ; [[#Butler--2018|Butler et al., 2018]] ; [[#Zhu--2018b|Zhu et al., 2018b]] ) because of shifts in planting dates and/or adoption of longer-duration cultivars in mid-to-high latitudes. Conversely, in mid-to-low latitudes in Asia, a review study found that farmers favoured early maturing cultivars to reduce risks of damages due to drought, flood and/or heat ( [[#Shaffril--2018|Shaffril et al., 2018]] ), suggesting that region-specific adaptations are already occurring in different parts of the world ( ''high confidence'' ).

Global yields of major crops per unit land area have increased 2.5- to 3-fold since 1960. Plant breeding, fertilisation, irrigation and integrated pest management have been the major drivers, but many studies have found significant impacts from recent climate trends on crop yield ( ''high confidence'' ) (Figure 5.3; see [[#5.2.1|Section 5.2.1]] for the change attributable to anthropogenic climate change).

Climate impacts for the past 20–50 years differ by crops and regions. Positive effects have been identified for rice and wheat in Eastern Asia, and for wheat in Northern Europe. The effects are mostly negative in Sub-Saharan Africa, South America and Caribbean, Southern Asia, and Western and Southern Europe. Climate factors that affected long-term yield trends also differ between regions. For example, in Western Africa, 1°C warming above preindustrial climate has increased heat and rainfall extremes, and reduced yields by 10–20% for millet and 5–15% for sorghum (Sultan et al., 2019). In Australia, declined rainfall and increased temperatures reduced yield potential of wheat by 27%, accounting for the low yield growth between 1990 and 2015 ( [[#Hochman--2017|Hochman et al., 2017]] ). In Southern Europe, climate warming has negatively impacted yields of almost all major crops, leading to recent yield stagnation ( [[#Moore--2015|Moore and Lobell, 2015]] ; [[#Agnolucci--2020|Agnolucci and De Lipsis, 2020]] ; [[#Brás--2021|Brás et al., 2021]] ).

[[#Ortiz-Bobea--2021|Ortiz-Bobea et al. (2021)]] analysed agricultural total factor productivity (TFP), defined as the ratio of all agricultural outputs to all agricultural inputs, and found that, while TFP has increased between 1961 and 2015, the climate change trends reduced global TFP growth by a cumulative 21% over a 55-year period relative to TFP growth under counterfactual non-climate change conditions. Greater effects (30–33%) were observed in Africa, Latin America and the Caribbean (Figure 5.3).

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[[File:dbf41cc585e3e4c6655b7bef7aa97b71 IPCC_AR6_WGII_Figure_5_003.png]]

'''Figure 5.3 |''' '''Synthesis of literature on observed impacts of climate change on productivity by crop type and region.''' The figure draws on &gt;150 articles categorized by: agriculture total factor productivity including literature estimating all agricultural outputs in a region; major crop species including literature assessing yield changes in the four major crops; crop categories including productivity changes (yield, quality and other perceived changes) in a range of crops with different growth habits. The assessment uses literature published since AR5, although the timespan often extends prior to 2014. The direction of the effect and the confidence are based on the reported impacts and attribution, and on the number of articles. See SM5.1 and SM5.2 for details.

Climate variability is a major source of variation in crop production ( [[#Ray--2015|Ray et al., 2015]] ; [[#Iizumi--2016|Iizumi and Ramankutty, 2016]] ; [[#Frieler--2017|Frieler et al., 2017]] ; [[#Cottrell--2019|Cottrell et al., 2019]] )(Table SM5.1). Weather signals in yield variability are generally stronger in productive regions than in the less productive regions ( [[#Frieler--2017|Frieler et al., 2017]] ), where other yield constraints exist such as pests, diseases and poor soil fertility ( [[#Mills--2018|Mills et al., 2018]] ; 5.2.2). Nevertheless, yield variability in less productive regions has severe impacts on local food availability and livelihood ( ''high confidence'' ) ( [[#FAO--2021|FAO, 2021]] ).

Climate-related hazards that cause crop losses are increasing ( ''medium evidence'' , ''high agreement'' ) ( [[#Cottrell--2019|Cottrell et al., 2019]] ; [[#Mbow--2019|Mbow et al., 2019]] ; [[#Brás--2021|Brás et al., 2021]] ; [[#FAO--2021|FAO, 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). Drought-related yield losses have occurred in about 75% of the global harvested area ( [[#Kim--2019b|Kim et al., 2019b]] ) and increased in recent years ( [[#Lesk--2016|Lesk et al., 2016]] ). Heatwaves have reduced yields of wheat ( [[#Zampieri--2017|Zampieri et al., 2017]] ) and rice ( [[#Liu--2019b|Liu et al., 2019b]] ) ''.'' The combined effects of heat and drought decreased global average yields of maize, soybeans and wheat by 11.6%, 12.4% and 9.2%, respectively ( [[#Matiu--2017|Matiu et al., 2017]] ). In Europe, crop losses due to drought and heat have tripled over the last five decades ( [[#Brás--2021|Brás et al., 2021]] ), pointing to the importance of assessing multiple stresses. Globally, floods also increased in the past 50 years, causing direct damages to crops and indirectly reduced yields by delaying planting, which cost 4.5 billion USD in the 2010 flood in Pakistan and 572 million USD in the 2015 flood in Myanmar ( [[#FAO--2021|FAO, 2021]] ).

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