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

==== 5.4.1.4 Observed impacts of ozone on crops ====

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Tropospheric (i.e., the lowest 6–10 km of the atmosphere) ozone exacerbates negative impacts of climate change ( ''high confidence'' ) ( [[#Mattos--2014|Mattos et al., 2014]] ; [[#Chuwah--2015|Chuwah et al., 2015]] ; [[#McGrath--2015|McGrath et al., 2015]] ; [[#Bisbis--2018|Bisbis et al., 2018]] ; [[#Mills--2018|Mills et al., 2018]] ; [[#Scheelbeek--2018|Scheelbeek et al., 2018]] ). Ozone is an air pollutant and short-lived GHG that affects air quality and global climate. It is a strong oxidant that reduces physiological functions, yield and quality of crops and animals. Surface ozone concentration has increased substantially since the late 19 th century ( [[#Cooper--2014|Cooper et al., 2014]] ; Forster et al., 2021; [[#Gulev--2021|Gulev et al., 2021]] ; [[#Szopa--2021|Szopa et al., 2021]] ) and in some locations and times reaches levels that harm plants, animals and human ( ''high confidence'' ) ( [[#Fleming--2018|Fleming et al., 2018]] ).

[[#Mills--2018|Mills (2018)]] estimated global distributions of current yield losses of major crops due to ozone, pest and diseases, heat, and aridity (Figure 5.4). Ozone-induced yield losses in 2010–2012 averaged 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively. Spatial variation in yield losses is similar among different stresses; areas with a large loss due to ozone are also at high risk of yield losses due to pest and diseases and heat. Many vegetable crops are also susceptible to ozone, which will adversely impact quality and quantity ( [[#Mattos--2014|Mattos et al., 2014]] ; [[#Bisbis--2018|Bisbis et al., 2018]] ; [[#Scheelbeek--2018|Scheelbeek et al., 2018]] ).

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[[File:9cb2c3164051a26bb5ff3bf260e4b9b7 IPCC_AR6_WGII_Figure_5_004.png]]

'''Figure 5.4 |''' '''The global effects of five biotic and abiotic stresses on soybean and wheat.''' All data are presented for the 1 × 1° (latitude and longitude) grid squares where the mean production of soybean or wheat was &gt;500 tonnes (0.0005 Tg). The effect of each stress on yield is presented as a Yield Constraint Score (YCS) on a scale of 1–5, where 5 is the highest level of stress from ozone, pests and diseases, heat stress and aridity ( [[#Mills--2018|Mills et al., 2018]] ). Data are available at [[#Sharps--2020|Sharps et al. (2020)]] . See Annex I: Global to Regional Atlas for all four crops.

The estimated yield loss does not account for interactions with other climatic factors. Temperatures enhance not only ozone production but also ozone uptake by plants, exacerbating yield and quality damage. Burney (2014) estimated current yield losses due to the combined effects of ozone and heat in India at 36% for wheat and 20% for rice. [[#Schauberger--2019a|Schauberger et al. (2019a)]] found global yield losses, ranging from 2% to 10% for soybean and 0% to 39% for wheat with a model that accounts for temperature, water and CO 2 concentration on ozone uptake.

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'''Box 5.1: Evidence for Simultaneous Crop Failures Due to Climate Change'''
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Simultaneous yield losses across major producing regions can be a threat to food security but had not been quantified by the time of AR5. Large-scale sea surface temperature (SST) oscillations greatly influence global yield of major crops ( ''high confidence'' ) ( [[#Anderson--2019b|Anderson et al., 2019b]] ; [[#Najafi--2019|Najafi et al., 2019]] ; [[#Ubilava--2019|Ubilava and Abdolrahimi, 2019]] ; [[#Heino--2020|Heino et al., 2020]] ; [[#Iizumi--2021b|Iizumi et al., 2021b]] ) and food prices ( [[#Ubilava--2018|Ubilava, 2018]] ). Some studies showed that crop yields in different regions covaried with SST oscillations, suggesting occurrences of tele-connected yield failures (crop losses caused by related factors in distant regions; Table Box 5.1.1) ( ''medium confidence'' ). Evidence of synchronised crop failures increasing with ongoing climate change is still limited.

'''Table Box 5.1.1 |''' A summary of peer-review papers detecting synchronised yield losses.

{| class="wikitable"
|-
! Regions/ commodities

! Period studied

! Observed impacts

! Climate driver

! Evidence for multiple breadbasket failures

! Evidence for increasing risks due to multiple breadbasket failures

! Reference

|-
| Global breadbaskets for maize, rice, sorghum and soybean

| 1961–2013

| Not only yields of each crop covaried in many countries, but also those of different crops, maize in particular, covaried with other crops.

| SST anomalies, atmospheric and oceanic in- dices, air temperature anomalies and Palmer Drought Severity Index

| High

| NA

| Najafi et al. (2019)

|-
| Global breadbaskets for wheat, soybean and maize

| 1980–2010

| Climate modes (El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), tropical Atlantic variability (TAV) and the North Atlantic Oscillation (NAO)) account for 18%, 7% and 6% of global maize, wheat and soybean production variability, respectively. ENSO events sometimes offset yield reductions in some places by increases in other places (e.g., soybean yields in the USA and southeast South America).

Since 1961, ENSO in 1983 was the only climate mode that showed global synchronous crop failures.

| Climate modes

| Medium (1983)

| NA

| [[#Anderson--2019b|Anderson et al. (2019b)]]

|-
| Global breadbaskets for wheat, soybean and maize

|
| Climate modes induce yield variability in major breadbaskets, e.g., ENSO affects about half of maize and wheat areas. IOD and ENSO influence wheat in Australia. ENSO affects soybean in northern South America.

| Climate modes

| Medium

| NA

| [[#Heino--2020|Heino et al. (2020)]]

|-
| 67 maize producing countries

| 1961–2017

| SST anomalies from the 1980–2010 base period in the Niño3.4 region, a rectangular area bounded by 120°W–170°W and 5°S–5° is used as a driver. Maize yields are tele-connected among the southeastern tier of Sub-Saharan Africa, as well as Central America, South Asia and Australia. A 1° increase in SST reduced maize yield by up to 20% in these countries.

| Climate modes (SST), precipitation

| Medium

| NA

| [[#Ubilava--2019|Ubilava and Abdolrahimi (2019)]]

|-
| Global breadbasket (the USA, Argentina, Europe, Russia/Ukraine, China, India, Australia, Indonesia and Brazil)

| 1967–2012

| Likelihood of simultaneous climate risks increased from 1967–1990 to 1991–2012 in the global breadbasket (lower 25 th yield deviation percentile events at province level) for wheat, soybean and maize, but not rice.

Likelihood of simultaneous climate risks increased from 1967–1990 to 1991–2012 in China (lower 25 th yield deviation percentile events at province level).

| Unspecified

| Medium

| Medium

| [[#Gaupp--2020|Gaupp et al. (2020)]]

|-
| Global

| 1961–2008

| Synchronous yield losses among major breadbaskets within each commodity, such as maize and soybean, decreased between 1961 and 2008. In contrast, synchronous yield variation between crops has increased. Under a scenario of synchronisation of all four crops, the global maximum production losses for rice, wheat, soybean and maize are estimated to reach between −17% and −34%.

| Unspecified

| Medium

| Medium

| [[#Mehrabi--2019|Mehrabi and Ramankutty (2019)]]

|}

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