Editing IPCC:AR6/WGII/Chapter-16 (section)

==== 16.2.3.4 Food system ====

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Crop yields respond to weather variations but also to increasing atmospheric CO 2 , changes in management (e.g., fertilizer input, changes in varieties), diseases and pests. However, the weather signal is clearly detectable in national and subnational annual yield statistics in main production regions (see ‘Food system—Crop yields’, Table SM16.23). Over the last decades, crop yields have increased nearly everywhere mainly due to technological progress (e.g., [[#Lobell--2007|Lobell and Field, 2007]] [global]; [[#Butler--2018|Butler et al., 2018]] [USA]; [[#Hoffman--2018|Hoffman et al., 2018]] [Sub-Saharan Africa]; [[#Agnolucci--2019|Agnolucci and De Lipsis, 2019]] [Europe]), with only minor areas not experiencing improvements in maize, wheat, rice and soy yields. However, meanwhile, stagnation or decline in yields is also observed in parts of the harvested areas ( ''high confidence'' ) (~20–40% of harvested areas of maize, wheat, rice and soy with wheat being most affected) ( [[#Ray--2012|Ray et al., 2012]] ; [[#Iizumi--2018|Iizumi et al., 2018]] ). Evidence on the contribution of climate change to recent trends is still limited (see ‘Food system—Crop yields’, Table SM16.22). Current global-scale process-based simulations forced by simulated historical and pre-industrial climate lack an evaluation to what degree simulations reproduce observed yields ( [[#Iizumi--2018|Iizumi et al., 2018]] ). Global-scale empirical approaches do not explicitly account for extreme weather events but growing season average temperatures and precipitation (e.g., [[#Lobell--2011|Lobell et al., 2011]] ; [[#Ray--2019|Ray et al., 2019]] ). In addition, studies are constrained by only fragmented information about changes in agricultural management such as growing season adjustments. Some of these limitations have been overcome in regional studies indicating a climate-induced increase (28% of observed trend since 1981) in maize yields in the USA ( [[#Butler--2018|Butler et al., 2018]] , based on a detailed accounting of impacts of extreme temperatures and growing season adjustments) and a climate-induced decrease in millet and sorghum yields (10–20% for millet and 5–15% for sorghum in 2000–2009 compared with pre-industrial conditions) in Africa and a negative effect of historical climate change on potential wheat yields (27% reduction from 1990 to 2015) in Australia ( [[#Hochman--2017|Hochman et al., 2017]] ; [[#Sultan--2019|Sultan et al., 2019]] based on detailed process-based modelling including a dedicated evaluation against observed yield fluctuations). These findings need additional support by independent studies. Results are relatively convergent that climate change has been an important driver of the recent declines in wheat yields in Europe ( ''medium confidence'' ) ( [[#Moore--2015|Moore and Lobell, 2015]] ; [[#Agnolucci--2019|Agnolucci and De Lipsis, 2019]] ; [[#Ray--2019|Ray et al., 2019]] ).

Due to complex interactions with socioeconomic conditions, climate-induced trends in crop yields and production do not directly transmit to crop prices, availability of food, or nutrition status. This complexity, in addition to the limited availability of long-term data, has so far impeded the detection and attribution of a long-term impact of climate change on associated food security indicators. However, in a few cases, observed crop prices (e.g., domestic grain price in Russia and Africa, [[#Götz--2016|Götz et al., 2016]] ; [[#Mawejje--2016|Mawejje, 2016]] ; [[#Baffes--2019|Baffes et al., 2019]] ) are shown to be sensitive to fluctuations in local weather through its impact on production (see ‘Food system—Food prices’, Table SM16.23). In addition, there is growing evidence that ''climate extremes'' (in particular, droughts) have led to malnutrition (in particular, stunting of children) in the historical period ( ''medium confidence'' , see ‘Food system—Malnutrition’, Table SM16.23) but without an attribution of changes to long-term climate change.

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