By Gordon Noble MRSV

The northern hemisphere summer has reminded us that extreme heat events may be just around the corner. A 50°C day, which climate scenarios may have thought was still some time off, could happen any time. How well prepared is Victoria’s food system?

You have to hand it to the Europeans for creativity. As Europe’s long heatwave brought scorching temperatures, the Italian Meteorological Society gave their heatwave a name: Cerberus, after the three-headed monster featured in Dante’s Inferno.¹ Just as we name cyclones, it may be that future heatwaves are given names to communicate their severity from ordinary heatwaves.

This year has been an extraordinary year for extreme heat. On the 3rd of July, the record for the average global air temperature was broken. The record only lasted a day, being broken again on the 4th of July.^2,3 Graphic images of the impacts of extreme heat – from Canadian fires that blanketed New York in smoke, through to the fires that ripped through Maui in Hawaii with tragic consequences – provide a timely warning that Australia is a land of droughts and flooding rains.

Extreme heat is unfortunately not a surprise to climate scientists, who have detailed the fact that the frequency and intensity of hot extremes (including heatwaves) have increased on the global scale since 1950.4 The Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report states that the frequency and intensity of hot extremes will continue to increase at global and continental scales even if global warming is stabilised at 1.5°C. The intensity of extremes would be at least double at 2°C, and quadruple at 3°C of global warming, compared to changes at 1.5°C of global warming.⁴

What would a 50°C day mean for Victoria’s food system, and, perhaps most importantly, what can we do to make our system and society more resilient?

What we know is that a 50°C day is plausible. On average, between 1980 and 2009, temperatures passed 50°C about 14 days a year, somewhere in the world. The number rose to 26 days a year between 2010 and 2019.⁵ The east coast of Australia has already come close to a 50°C day: in February 2009 Melbourne reached 46.4°C, whilst Sydney (Penrith) reached 48.9°C in January 2020. Both occasions are associated with catastrophic events.

Impacts on farmed animals.

The impact of extreme heat on humans has been well studied. A recent Lancet meta-analysis reviewed 7,360 studies and found that a 1°C increase in temperature is positively associated with increased mortality and morbidity.⁶ We can expect that a 50°C day would impact on the productivity of cattle, sheep, chickens, and other farmed animals with impacts including mortality, reduced growth, and reduced fertility.

Heatwaves are known to impact dairy production and lead to mortality amongst herds.⁷ Heat stress is known to reduce egg production for chickens.⁸ For sheep, heat stress has been shown to influence feed conversion efficiency, appetite, reproduction, wool growth, and susceptibility to disease.⁹

Warming of oceans associated with prolonged heatwaves is likely to impact sea-caged Atlantic salmon, who cannot escape warmer surface waters by diving deeply.¹⁰ Research demonstrates that summer warming negatively impacts salmon growth rates, leading to increased fish disease and even death.¹¹ There are broader implications than just salmon, with research projecting that, on average, when an annual high temperature extreme occurs in an exclusive economic zone, 77% of exploited fish and invertebrates will decrease in biomass.¹²

Impacts on horticulture.

The impact of extreme heat events does not end with animal productivity. Of all the potential impacts of a 50°C day the impact on honeybees, and pollinators, is of concern. Extreme heat events can lead to a collapse of a colony.¹³ Researchers have found that with six hours at 42°C, 50 percent of male honeybees die.¹³

If a male bee survives a heat event, his fertility is likely impaired. The impact of an event which led to mass mortality of honeybees would be compounded by the impact on heat-stressed crop plants with floral outputs impacted by extreme heat. Researchers have identified the need to understand how extreme heat affects bee–crop interactions in this era of climate change.¹⁴

Another impact of extreme heat are bushfires, which produce smoke that is already associated with what the wine industry terms ‘undesirable sensory characters’ (smoky, burnt, ashy, or medicinal) that is described as ‘smoke tainted’.¹⁵ Research is examining the impact of smoke on potatoes, with McCain Foods noticing that potatoes don’t seem to store well after intense wildfire years.¹⁶

We can imagine a scenario where Victoria experiences a 50°C day that may have been preceded by a heatwave. The cumulative impacts on honeybees would then impact pollination. Impacts on chickens, sheep, cattle, and other farmed animals would be to reduce productivity with likely shortages. This will ultimately translate to higher prices for consumers.

What, then, can we do at a local level to mitigate against extreme heat events?

The actions needed. Now.

Victoria is fortunate to have levers at our disposal.

The urgent action is to green Victoria. Shaded surfaces in urban areas are known to be 11–25°C cooler than the peak temperatures of unshaded areas.¹⁷ In urban areas, research from Western Sydney University has revealed the temperatures at ground level could vary by more than 10°C due to tree coverage.¹⁸ In the United States, research has found that an increase of tree canopy shading of roadways to an average of 50% across all streets is found to reduce the estimated rate of heat mortality in 27% in Phoenix.¹⁹

The same issues apply to agriculture. There is extensive research on the benefits of shade trees for agriculture.²⁰ To create shade in the right areas there is a need for water. The challenge with water is that its value changes according to the weather. The value of an extra litre of water during extreme rainfall is negative, whilst in a drought it is exponentially high.

As identified in previous issues of Science Victoria, Victoria is in the fortunate position of producing excess water, but it is literally poured down the drain. Currently around 140 billion litres of Class C recycled water are discharged into Port Phillip Bay each year.²¹ The Eastern Treatment Plant in Carrum discharges around 123 billion litres into Bass Strait.²² The volume of recycled water is linked to the size of the city, due to Melbourne’s desalination plant, and we can expect this volume to grow. Population growth in Melbourne’s north, west, and inner city will translate into increased flows of Class C recycled water into Port Phillip Bay. It is projected that the population of the north and west of the city alone will grow by 1 million in coming years.²³

The challenge is that the recycled water we have is not where we need it. In the Victorian era, engineers solved this problem by establishing the dams that supply our water today, investing in the pipes across our urban networks and building a sewage treatment facility that meant that Melburnians could forget that we were once called ‘Smell-Bourne’.

Today, the science informs us of the risk. The actions we take are up to us.

References:

1. Cerberus heatwave: Hot weather sweeps across southern Europe. (2023, July 12). BBC News. bbc.com/news/world-europe-66183069
2. Osborne, M. (2023). Earth Faces Hottest Day Ever Recorded—Three Days in a Row. Smithsonian Magazine. Retrieved September, 2023, from smithsonianmag.com/smart-news/earth-faces-hottest-day-ever-recorded-three-days-in-a-row-180982493/
3. Cuff, M. (2023, July 4). Record for hottest day ever recorded on Earth broken twice in a row [Review of Record for hottest day ever recorded on Earth broken twice in a row]. New Scientist. newscientist.com/article/2381069-record-for-hottest-day-ever-recorded-on-earth-broken-twice-in-a-row/
4. Intergovernmental Panel on Climate Change (IPCC). (2023). Weather and Climate Extreme Events in a Changing Climate. In Climate Change 2021 – The Physical Science Basis: Working Group I Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 1513-1766). Cambridge: Cambridge University Press. doi:10.1017/9781009157896.013
5. Climate change: World now sees twice as many days over 50C. (2021, September 13). BBC News. bbc.com/news/science-environment-58494641
6. Liu, J., et al. (2022). Heat exposure and cardiovascular health outcomes: a systematic review and meta-analysis. The Lancet Planetary Health, 6(6), e484–e495. doi.org/10.1016/S2542-5196(22)00117-6
7. Meyer, C., Vogel, E., & Eckard, R. (2017). Severe heatwaves show the need to adapt livestock management for climate. The Conversation. theconversation.com/severe-heatwaves-show-the-need-to-adapt-livestock-management-for-climate-73447
8. Li, G.-M., et al. (2020). Heat stress decreases egg production of laying hens by inducing apoptosis of follicular cells via activating the FasL/Fas and TNF-α systems. Poultry Science, 99(11), 6084–6093. doi.org/10.1016/j.psj.2020.07.024
9. Masters, D. G., et al. (2023). Shelter and shade for grazing sheep: implications for animal welfare and production and for landscape health. Animal Production Science. doi.org/10.1071/an22225
10. Nuez-Ortín, W. G., et al. (2018). Liver proteome response of pre-harvest Atlantic salmon following exposure to elevated temperature. 19(1). doi.org/10.1186/s12864-018-4517-0
11. Meng, H., et al. (2022). Benefits and detrimental effects of ocean warming for Tasmanian salmon aquaculture. Continental Shelf Research, 246, 104829. doi.org/10.1016/j.csr.2022.104829
12. Cheung, W. W. L., et al. (2021). Marine high temperature extremes amplify the impacts of climate change on fish and fisheries. Science Advances, 7(40). doi.org/10.1126/sciadv.abh0895
13. McAfee, A. (2022). Extreme heat waves threaten honeybee fertility and trigger sudden death. The Conversation. theconversation.com/extreme-heat-waves-threaten-honeybee-fertility-and-trigger-sudden-death-178504
14. Walters, J., et al. (2022). Heat of the moment: extreme heat poses a risk to bee–plant interactions and crop yields. Current Opinion in Insect Science, 52, 100927. doi.org/10.1016/j.cois.2022.100927
15. Smoke taint. (n.d.). The Australian Wine Research Institute. www.awri.com.au/industry_support/winemaking_resources/smoke-taint/
16. Wildfire Smoke’s Affect on Potato Crops Being Studied. (2022, September 12). University of Idaho. Retrieved September, 2023, from uidaho.edu/news/news-articles/news-releases/2022/091222-wildfiresmoke
17. US EPA. (2014, June 17). Using Trees and Vegetation to Reduce Heat Islands. US EPA. https://www.epa.gov/heatislands/using-trees-and-vegetation-reduce-heat-islands
18. Amin, M. (2019, November 21). This Sydney street stays cooler than others during a heatwave — here’s why. ABC News. abc.net.au/news/2019-11-21/western-sydney-heatwave-alleviated-by-tree-cover/11721698
19. Stone, B., et al. (2023). How Blackouts during Heat Waves Amplify Mortality and Morbidity Risk. doi.org/10.1021/acs.est.2c09588
20. Shade Trees – an overview | ScienceDirect Topics. (n.d.). ScienceDirect. sciencedirect.com/topics/agricultural-and-biological-sciences/shade-trees
21. Gell, R. (2022, October 10). What’s in the Water? Part One. Science Victoria. rsv.org.au/whats-in-the-water-part-one/
22. Purple Pipeline Project | Port Phillip & Western Port Regional Catchment Strategy. (n.d.). portphillipwesternport.rcs.vic.gov.au/prospectus/dingley-cheltenham-sandringham-recycled-water-scheme/
23. Victoria in Future 2019 (2019). planning.vic.gov.au/guides-and-resources/data-and-insights/victoria-in-future