Editing IPCC:AR6/WGII/Chapter-11 (section)

===== 11.3.4.1.2 Projected impacts =====

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Australian crop yields are projected to decline due to hotter and drier conditions, including intense heat spikes ( ''high confidence'' ) ( [[#Anwar--2015|Anwar et al., 2015]] ; [[#Lobell--2015|Lobell et al., 2015]] ; [[#Prokopy--2015|Prokopy et al., 2015]] ; [[#Dreccer--2018|Dreccer et al., 2018]] ; [[#Nuttall--2018|Nuttall et al., 2018]] ; [[#Wang--2018a|Wang et al., 2018a]] ). Interactions of heat and drought could lead to even greater losses than heat alone ( [[#Sadras--2015|Sadras and Dreccer, 2015]] ; [[#Hunt--2018|Hunt et al., 2018]] ). Australian wheat yields are projected to decline by 2050, with a median yield decline of up to 30% in southwest Australia and up to 15% in southern Australia, with possible increases and decreases in the east ( [[#Taylor--2018|Taylor et al., 2018]] ; [[#Wang--2018a|Wang et al., 2018a]] ). In temperate fruit, accumulated winter chill for horticulture is projected to further decline ( [[#Darbyshire--2016|Darbyshire et al., 2016]] ). Winegrape maturity is projected to occur earlier due to warmer temperatures ( ''high confidence'' ) ( [[#Webb--2014|Webb et al., 2014]] ; [[#van%20Leeuwen--2016|van Leeuwen and Darriet, 2016]] ; [[#Jarvis--2018|Jarvis et al., 2018]] ; [[#Ausseil--2019b|Ausseil et al., 2019b]] ), leading to potential changes in wine style ( [[#Bonada--2015|Bonada et al., 2015]] ). Rice is susceptible to heat stress, and average grain yield losses across rice varieties range from 83% to 53% in experimental trials when heat stress is applied during plant emergence and grain fill stages ( [[#Ali--2019|Ali et al., 2019]] ). In Tasmania, wheat yields are projected to increase, particularly at sites presently temperature-limited ( [[#Phelan--2014|Phelan et al., 2014]] ).

New Zealand evidence on impacts across crops is very limited. Precipitation and temperature changes alone show minor effects on crop yield, and winter yields of some crops may increase (e.g., wheat, maize) ( [[#Ausseil--2019b|Ausseil et al., 2019b]] ). For temperate fruit, loss of winter chill may reduce yields in some regions and trigger impacts across supply chains ( [[#Cradock-Henry--2019|Cradock-Henry et al., 2019]] ) (11.5.1). Increased pathogens could damage the cut flower, guava and feijoa fruit growing and the honey and related industries ( [[#Lawrence--2016|Lawrence et al., 2016]] ). The combined effects of changes in seasonality, temperature, precipitation, water availability and extremes, such as drought, have the potential to escalate impacts, but understanding of these effects is limited.

Other climate-change-related factors complicate crop climate responses. When CO 2 was elevated from present-day levels of 400 to 550 ppm in trials, yields of rainfed wheat, field pea and lentil increased approximately 25% (0–70%). However, there was a 6% reduction in wheat protein that could not be offset by additional nitrogen fertilizer ( [[#O’Leary--2015|O’Leary et al., 2015]] ; [[#Fitzgerald--2016|Fitzgerald et al., 2016]] ; [[#Tausz--2017|Tausz et al., 2017]] ). Elevated CO 2 will worsen some pest and disease pressures, for example, barley yellow dwarf virus impacts on wheat ( [[#Trębicki--2015|Trębicki et al., 2015]] ). Warmer temperatures are also expanding the potential range of the Queensland fruit fly, including into New Zealand ( [[#Aguilar--2015a|Aguilar et al., 2015a]] ), threatening the horticulture industry ( [[#Sultana--2017|Sultana et al., 2017]] ; [[#Sultana--2020|Sultana et al., 2020]] ). Some crop pests (e.g., the oat aphid) are projected to be negatively affected by climate change ( [[#Macfadyen--2018|Macfadyen et al., 2018]] ), but so too are beneficial insects. There is large uncertainty in rainfall and crop projections for northern Australia (Table 11.3). For sugarcane, an impact assessment for CO 2 at 734 ppm using the A2 emission scenario at Ayr in Queensland projected modest yield increases ( [[#Singels--2014|Singels et al., 2014]] ). Climate change is projected to adversely impact tropical fruit crops such as mangoes through higher minimum and maximum temperatures, reducing the number of inductive days for flowering ( [[#Clonan--2020|Clonan et al., 2020]] ).

Climate change is projected to shift agro-ecological zones ( ''high confidence'' ) ( [[#Lenoir--2015|Lenoir and Svenning, 2015]] ; [[#Scheffers--2016|Scheffers et al., 2016]] ). This includes the climatically determined cropping strip bounded by the inner arid rangelands and the wetter coast or mountain ranges in mainland Australia ( [[#Nidumolu--2012|Nidumolu et al., 2012]] ; [[#Eagles--2014|Eagles et al., 2014]] ; [[#Tozer--2014|Tozer et al., 2014]] ). A narrowing of grain-growing regions is projected with a shift of the inner margin towards the coast under drier and warmer conditions ( [[#Nidumolu--2012|Nidumolu et al., 2012]] ; [[#Fletcher--2020|Fletcher et al., 2020]] ). The economic impact of the shift depends on adaptation ( [[#Sanderson--2015|Sanderson et al., 2015]] ; [[#Hunt--2019|Hunt et al., 2019]] ) and how resources, support industries, infrastructure and settlements adapt. Shifts in agro-ecological zones present some opportunities, for example warming is projected to be beneficial for wine production in Tasmania ( [[#Harris--2020|Harris et al., 2020]] ).

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