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

=== 5.2.1 Detection and Attribution of Observed Impacts ===

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Detection and attribution of climate change impacts on the food system remain challenging because many non-climate drivers are involved ( [[#Porter--2014|Porter et al., 2014]] ) but have been improved by recently developed climate model outputs tailored for impact attribution ( [[#Iizumi--2018|Iizumi et al., 2018]] ; [[#Moore--2020|Moore, 2020]] ; [[#Ortiz-Bobea--2021|Ortiz-Bobea et al., 2021]] ).

Climate change has caused regionally different, but mostly negative, impacts on crop yields and quality and marketability of products ( ''high confidence'' ) (see [[#5.4.1|Section 5.4.1]] for observed impacts). There is ''medium evidence'' and ''high agreement'' that the effects of human-induced climate warming since the pre-industrial era has had significantly negative effects on global crop production, acting as a drag on the growth of agricultural production ( [[#Iizumi--2018|Iizumi et al., 2018]] ; [[#Moore--2020|Moore, 2020]] ; [[#Ortiz-Bobea--2021|Ortiz-Bobea et al., 2021]] ). One global study using an empirical model estimated the negative effect of anthropogenic warming trends from 1961 to 2017 to be on average 5.3% for three staple crops (5.9% for maize, 4.9% for wheat and 4.2% for rice) ( [[#Moore--2020|Moore, 2020]] ). Another study using a process-based crop model found a yield loss of 4.1% (0.5–8.4%) for maize and 4.5% (0.5–8.4%) for soybean between 1981 and 2010 relative to the non-warming condition, even with CO 2 fertilisation effects ( [[#Iizumi--2018|Iizumi et al., 2018]] ). Human-induced warming trends since 1961 have also slowed down the growth of agricultural total factor productivity by 21% ( [[#Ortiz-Bobea--2021|Ortiz-Bobea et al., 2021]] ). Regionally, heat and rainfall extremes intensified by human-induced warming in West Africa have reduced millet and sorghum yields by 10–20%, and 5–15%, respectively (Sultan et al., 2019).

Methane emissions significantly impact crop yields by increasing temperatures as a greenhouse gas (GHG) and surface ozone concentrations as a precursor ( ''medium confidence'' ) ( [[#Shindell--2016|Shindell, 2016]] ; Van Dingenen, 2018; [[#Shindell--2019|Shindell et al., 2019]] ). [[#Shindell--2016|Shindell (2016)]] estimated a net yield loss of 9.5±3.0% for four major crops due to anthropogenic emissions (1850–2010), after incorporation of the positive effect of CO 2 (6.5±1.0%) and the negative effects of warming (10.9±3.2%) and tropospheric ozone elevation (5.0±1.5%). Although these estimates were not linked with historical yield changes, more than half of the estimated yield loss is attributable to increasing temperature and ozone concentrations from methane emissions, suggesting the importance of methane mitigation in alleviating yield losses ( ''medium confidence'' ) ( [[#5.4.1.4|Section 5.4.1.4]] ).

Climate change is already affecting livestock production ( ''high confidence)'' ( [[#5.5.1|Section 5.5.1]] ). The effects include direct impacts of heat stress on mortality and productivity, and indirect impacts have been observed on grassland quality, shifts in species distribution and range changes in livestock diseases (Sections 5.5.1.1–5.5.1.3). Quantitative assessment of observed impacts is still limited.

In aquatic systems, more evidence has accumulated since AR5 on warming-induced shifts (mainly poleward) of species ( ''high confidence'' ) ( [[#5.8.1|Section 5.8.1]] , Cross-Chapter Box MOVING PLATE this chapter), causing significant challenges for resource allocation between different countries and fishing fleets. Quantitative assessments of climate change impacts on production are still limited, but [[#Free--2019|Free et al. (2019)]] estimated a 4.1% global loss of the maximum sustainable yield of several marine fish populations from 1930 to 2010 due to climate change. The effects of climate change on aquaculture are apparent but diverse, depending on the types and species of aquaculture ( ''high confidence'' ) ( [[#5.9.1|Section 5.9.1]] ). Temperature increases, acidification, salt intrusion, oxygen deficiency, floods and droughts have negatively impacted production via reduced growing suitability, mortalities or damages to infrastructure ( [[#5.9.1|Section 5.9.1]] ).

The impacts of climate change on food provisioning have cascading effects on key elements of food security, such as food prices, household income, food safety and nutrition of vulnerable groups ( [[#Peri--2017|Peri, 2017]] ; [[#Ubilava--2018|Ubilava, 2018]] ; 5.11, 5.12). Climate extreme events are frequently causing acute food insecurity ( [[#5.12.3|Section 5.12.3]] , [[#FSIN--2021|FSIN, 2021]] ). There is growing evidence that human-induced climate warming has amplified climate extreme events ( [[#Seneviratne--2021|Seneviratne et al., 2021]] ), but detection and attribution of food insecurity to anthropogenic climate change is still limited by a lack of long-term data and complexity of food systems ( [[#Phalkey--2015|Phalkey et al., 2015]] ; [[#Cooper--2019|Cooper et al., 2019]] ). A recent event attribution study by Funk (2018) demonstrated that anthropogenic enhancement of the 2015/2016 El Niño increased drought-induced crop production losses in Southern Africa. Human-induced warming also exacerbated the 2007 drought in southern Africa, causing food shortages, price spikes and acute food insecurity in Lesotho ( [[#Verschuur--2021|Verschuur et al., 2021]] ).

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