Global temperatures have warmed in the past 100 years and this trend is likely to continue. What changes in climate can Australian growers expect in the future?
Climate change refers to any long-term trends or shifts in climate over many decades. It differs from ‘climate variability’, which describes the differences in climate experienced from year to year.
The difference between weather and climate is a measure of time. Weather consists of short-term changes in the atmosphere that produce rapid changes in factors like temperature and humidity, whereas climate describes the more stable average weather patterns experienced at a location over time. In other words, climate is what you expect and weather is what you get.
Understanding changes in climate is important
Climate change will affect the productivity and profitability of apple and pear orchards in a range of ways, including through the impacts of warming temperatures on winter chill and fruit quality. Orchard blocks planted this year are likely to be at peak production in 2030 and beyond. Understanding how regional climates are likely to change can inform decisions around investment in netting or lower-chill cultivars, for example, at the time of site establishment.
Changes in temperatures over time
To make sense of future climate projections it is useful to consider how the climate has changed over time using historical temperature records from the Bureau of Meteorology.
Since 1970 much of Australia has experienced consistently warmer minimum and maximum temperatures in both winter and summer, with more extreme heat days over 35°C. These long-term warming trends in temperature occur on top of the normal yearly, or cyclical, variations that are experienced.
A convenient way to distinguish between consistent climate change trends and normal variation is with graphs of temperature anomalies. A temperature anomaly is the difference between the observed temperature and the long-term average. In our study, observed temperatures in each year were compared with the 30-year average from 1981 to 2010.
Autumn and winter
Autumn and winter temperatures have increased in Applethorpe (Qld), Shepparton (Vic), Manjimup (WA) and Mount Barker (SA) since 1968. In Huonville (Tas) and Orange (NSW), the warming trend is more apparent in minimum temperatures than maximums over this period.
Since 1968 the milder growing regions of Applethorpe, Manjimup and Mount Barker have experienced a decline in the number of chill portions accumulated each year. Eight out of the 10 years from 2006 to 2016 in Manjimup have had less winter chill than the long-term average. Shepparton has seen a small reduction in winter chill over this period, while the colder regions of Huonville and Orange have not changed.
Spring and summer
Maximum spring and summer temperatures have warmed in most locations since 1968, except for Huonville. Shepparton and Mount Barker have experienced an increase in the number of extreme heat days per year (where maximum temperature exceeded 35°C) and Manjimup have received more extreme heat days than the long-term average every year for the last six years. Maximum temperatures have rarely exceeded 35°C in Applethorpe and Huonville, and these sites have not seen much change in the number of extreme heat days.
Climates for growing regions to 2050
Across Australia’s growing regions the climate was projected to warm by 2050. Winter minimum temperatures were projected to warm by between 0.5°C and 2°C and summer maximum temperatures by between 0.5°C and 3°C. Winter chill accumulation declined under both the medium-case scenario and a worst-case scenario. The highest declines were projected for the warmer growing regions like Manjimup and Applethorpe, and the smallest declines were in the coldest winter regions such as Orange and Huonville.
The number of extreme heat days was projected to increase in all growing regions, with potential impacts on fruit quality likely to be greatest in areas currently experiencing the hottest summers. By 2050 Manjimup was likely to receive a similar number of heat days to that which Shepparton had now, while Shepparton was projected to double the number of extreme heat days over the same period.
Climate change and the apple and pear industry
Climate change is likely to add substantial variability to apple and pear production, particularly flowering and fruit quality. Australian growers are already dealing with some level of variability and it seems likely that impacts on flowering and fruit quality may be within the range of grower experience up to about 2030 but that by 2050 growers in some regions will be operating outside of current experience. This will present challenges for the Australian industry in the consistency of fruit supply and in maintenance of the uniform orchard blocks needed for mechanisation.
For access to all historical climate graphs and information on how the climate scenarios were developed, go to the AP12029 final report. Our study looked at changes in temperature only; information on changing rainfall and bushfire risk can be found in the State of the Climate reports and the ‘climate change in Australia’ website.
This research was undertaken for the project Understanding apple and pear production systems in a changing climate (AP12029) and is a strategic investment under the Hort Innovation Apple and Pear Fund. It is funded by Hort Innovation using the apple and pear levy and funds from the Australian Government. Additional financial support was contributed by the Department of Agriculture and Fisheries (Qld), the Department of Economic Development, Jobs, Transport and Resources (Vic), the Department of Agriculture and Food Western Australia, Pomewest (WA) and the University of Tasmania.
About the authors
Dr Heidi Parkes and Neil White work with Queensland’s Department of Agriculture and Fisheries, and Rebecca Darbyshire is with the NSW Department of Primary Industries.