Impact of climate change on southern farming systems

Take home messages

• It is important to consider both climate variability and climate change.
• The projections show a continuation of the warming and drying that has been seen in the southern grains belt. The confidence in the trends and projections is higher for temperature than rainfall.
• Adaptable, information-rich farming systems are needed. This includes understanding phenology, making the most of rainfall that falls at any time of the year, responding to seasonal variability, vigilance for pests and disease and an appropriate level of optimism.

Background

In 2019, Australia experienced the driest year on record (drier than 1902) and warmest year on record (half a degree hotter than 2013 and 2 degrees hotter than 1961-90 reference period). Many in the southern grains region have been through a series of very difficult years. This poses the obvious question as to what to expect in the coming decades? Should the recent past be interpreted as the challenges of our variable climate or how much is a manifestation of what is to come with climate change? The simple answer is that there are components of both variability and change with higher confidence for trends and projections of warming than drying. It is important to think clearly about the interaction between climate variability and climate change, cycle and trend, hot spell and warming, drought and drying, a run of poor seasons and increased aridity.

As a general observation, rural communities are much more aware of year-to-year and decade –to-decade variability in climate compared to urban communities. Some commentators remarked that, for urban communities, water restrictions during the Millennium drought (2002 to 2009) provided an abrupt realisation of vulnerability to climate. Following from this shock, there seemed to be greater acceptance of climate change. For rural communities, the deep understanding of past runs of poor years and good years leads to a greater emphasis on variability and a caution or suspicion about attributing events to climate change. This is mainly because variability is part of lived experience and understanding passed down from parents. An additional factor is that because the climate plays such an important part in livelihoods, discussing a negative trend is confronting. While some might say that when a crop runs out of water or is hit by a heat event that the distinction between variability and change doesn’t matter, I disagree. A neighbour saying that they have had enough and are selling up because of drought (variability) is quite different to saying they are leaving due to increased aridity (long term and ongoing change). The central point for the grains industry (and wider society) is that we need to shift the conversation from either variability or change, waves or tides to a respectful conversation on variability and change, waves and tides.

Climate variability and climate change – waves and tides; cycles and trends

Climate variability is the year-to-year changes in seasonal conditions due to the internal forcing of the climate system (for example, El Nino Southern Oscillation (ENSO) or Indian Ocean Dipole (IOD)). Many grain growers are aware of these major drivers of climate. GRDC has invested in the Climate4Profit and the R&D for Profit project, working with the Bureau of Meteorology (BoM) on climate extremes. More effective management of seasonal variability is well recognised as one of the most effective ways to manage long term risk.

Climate change is manifested as a longer-term trend due to external forcing that comes from astronomy (distance from the sun), volcanoes and changes to levels of green-house gases. Human induced climate change or the enhanced greenhouse effect refers to the changes in the radiative properties of the atmosphere due to human activity. Earlier reports of the Intergovernmental Panel on Climate Change (IPCC) stated that the warming of the climate system is unequivocal. The fifth and most recent assessment report states; ‘Human influence on the climate system is clear’ and assess that there is a 95 to 100% probability that human influence was the dominant cause of global warming in the last 50 years. The attribution of the cause of warning increases confidence in the trend and indicates that the future depends on choices made by the global community.

A simple but powerful analogy used by the late eminent climate scientist Stephen Schneider is to consider a vulnerable system (like a grain crop) being impacted as a sandcastle with waves (climate variability) and tides (climate change). Following any damaging climate event such as drought, fire, heatwave or flood, the question is often posed as to how much can be attributed to climate change (the tide) and how much to climate variability (the wave). It is almost always the wave that destroys the sandcastle, but on a rising tide the waves do more damage. Another analogy for the same purpose is a man walking in a consistent direction (trend) with a dog on a lead (variation) - (From Dog Walking to Weather and Climate - Climate.gov)

Although Guy Debelle, deputy governor of the Reserve Bank didn’t use analogies of sandcastles or dogs, in 2019 in his speech on monetary policy that distinguished between shocks and trends he noted that economists were used to considering climate shocks (such as a cyclone destroying most of the banana crop or low production due to drought). These climate shocks are treated as temporary and discrete rather than a trend. He posed the question ‘What if droughts are more frequent, or cyclones happen more often? The supply shock is no longer temporary but close to permanent. That situation is more challenging to assess and respond to.' (Climate Change and the Economy - Speech - Reserve Bank of Australia).This involves looking back to interpret the recent past and accessing information on what climate science is projecting for the future.

Looking back at trends in the climate

In 2019 the BoM, CSIRO and FarmLink were funded by the Commonwealth Government in a $2.7M project to develop regional weather and climate guides for all natural resource management regions across Australia. These guides compared the weather records of the last 30 years (1989 to 2019) with the previous 30 years (1959 to 1989) (Australian Regional Weather and Climate Guides - BOM). GRDC was consulted on the design of the information.
(Southern NSW Growers get up to date Climate Outlooks - GROUNDCOVER)

The main conclusions for the Northern and Yorke Peninsula regions of South Australia (SA) are as follows:

• Annual rainfall has been relatively stable.
• There have been seven years drier than average and nine wetter.
• There has been a decrease in rainfall in the autumn months.
• Winter rainfall has been reliable; summer rainfall has been unreliable.
• There have been more frosts and they have been coming later.
• There have been more hot days, with more consecutive days above 40°C.

The recent past has been dominated by the extensive Millennium Drought (2002 to 2009) which can be shown in Figure 1 rainfall across South East Australia. The drought ended with widespread rain from the 2010 La Nina. The only other wet year since the Millennium Drought has been the negative IOD of 2016. The wet springs of 2010 and 2016 were reasonably well forecast in winter by the BoM. Some, but not all of the dry springs were forecast.

Figure 1. April to November rainfall for south eastern Australia (line from Newcastle to Ceduna) (Source: Bureau of Meteorology).

GRDC has invested in a large project titled ‘Forewarned is Forearmed’ with the BoM to improve the forecast and management of extreme events on a multi-week to seasonal time scale. Another investment in a project led by Agriculture Victoria with input from SARDI and Federation University has funded the Break newsletters and produced a local climate tool where anyone can check the impact of climate drivers on their rainfall.

Looking forward with climate change projections

The first climate change projections for Australia were prepared for the Greenhouse 1987 conference and since then projections have been released by CSIRO in 1990, 1991, 1992, 1996 and 2001, 2007 and 2015 (Whetton et al. 2016). Current projections for Australia are available at the Climate Change in Australia website. The SA Government also provides climate change projections.

Key findings from the Climate Change in Australia report for the southern grains belt include:

• Average temperatures will continue to increase in all seasons (very high confidence).
• More hot days and warm spells are projected with very high confidence. Fewer frosts are projected with high confidence.
• By late in the century, less rainfall is projected during the cool season, with high confidence. There is medium confidence that rainfall will remain unchanged in the warm season.
• Even though mean annual rainfall is projected to decline, heavy rainfall intensity is projected to increase, with high confidence.
• A harsher fire-weather climate in the future (high confidence).
• On annual and decadal basis, natural variability in the climate system can act to either mask or enhance any long-term human induced trend, particularly for rainfall in the next 20 years.

The Climate Change in Australia report compared 70 global climate models. All models show future warming in all seasons of the year. In contrast, there is a disagreement between model projections for annual and seasonal rainfall. Figure 2 shows the number of models in different categories of wetter or drier futures. Using the annual columns for the Murray Basin as an example; the white bar represents no change (-5% to +5% by 2050) and this is the result for about a third of the 70 models. The bars to the left of the white bar show a third projecting moderate drying (-5% to -15%), eight models show severe drying (>15%). The bar to the right of the white bar indicates 12 of the 70 models show a moderate wetting (+5% to 15%). Summer (DJF) and autumn (MAM) show the widest spread but there are more models showing drying than wetting. Winter and spring show more pronounced drying with the strongest projection of drying in spring. The SA grains belt to the west of the Mt Lofty Ranges is covered by the Southern and South West Flatlands (SSWF). There are more models showing drying for this region.

Figure 2. Climate projections for seasonal and annual rainfall changes for 2050 using a high emission Representative Concentration Pathway (RCP) 8.5 for the Murray Basin region (left) and SA to the west of Mt Lofty Ranges (right). Y-axes show data as the % of models (primary) and number of models (secondary) from the full 70 models. Data from the Climate Change in Australia website.

In 2018, the National Environmental Science Programme (NESP) built on the 2015 Climate Change in Australia Report producing a summary document on long term trends and future projections for rainfall in Southern Australia.The report concludes that the general drying trend over southern Australia over the past 50 or so years is likely to continue in the future. Key findings are as follows:

1. The intensification of the subtropical ridge (Pepler et al. 2018)– the pattern of cooler wetter winters and hot dry summers is driven by annual progression of the subtropical ridge from a summer position of 40°S (between mainland and Tasmania) and a winter position of 30°S (Maree SA, Bourke NSW). There is more confidence in the intensification (higher pressures) across southern Australia than a consistent latitudinal shift.
2. A trend towards positive Southern Annular Mode (SAM) (Lim et al. 2016). A positive SAM indicates a contraction of westerly winds and reduced winter rainfall for southern mainland Australia (and wetter summers). The impact of SAM on winter drying is more pronounced on the southern edge of the continent.
3. An increase in extreme ENSO and IOD events leading to greater variability (Power et al. 2018).
4. After assessing the 70 models used in the Climate Change in Australia report, Gross et al. (2017) used 15 models that best represented rain-bearing circulation for southern Australia. These 15 models showed a stronger drying especially in the winter.

In late October 2019 a group of 15 Australian climate scientists held a workshop on the science of extreme event attribution. In this context, attribution addresses the role of anthropogenic climate change in modifying the likelihood, intensity, duration or frequency of a particular extreme event. Table 1 is a qualitative assessment of the ability of the latest climate models to represent specific extremes (model capability), the quality and length of the observational record for extremes (observations) and the level of physical understanding of how anthropogenic forcing influenced the extreme (understanding). The percent of disagreement amongst the 15 workshop participants represents approximately the number of participants expressing ‘strong disagreement’
(BAMOS Vol 32 No.4 December 2019 - The Bulletin of Australian Meteorological and Oceanographic Society)

Table 1. Qualitative assessment of the ability of the latest climate models to represent model capability, observations and understanding.

It is important to note that these are qualitative rankings from a workshop and are more usefully interpreted as relative rankings rather than objective ratings of confidence. The lower level of understanding of the process of drought and the high level of disagreement with the rankings on drought indicate that this in an area of active debate and research. It would be a mistake to interpret the lack of understanding or agreement as an indication that rainfall won’t change.

The role of human induced climate change in the catastrophic bushfire summer of 2019/20 has gained worldwide attention. There is widespread acceptance of the warming, but there is less clarity on the lack of rainfall. The extreme drought leading up to the summer was consistent with the positive IOD and the positive SAM and these can be considered drivers of variability or waves. However, there may be some indication of longer-term trends or a tide. In a response to the Guardian newspaper on 13 January 2020, Professor Matthew England, UNSW Climate Change Research Centre said: ‘These modes of variability are not changing in a way that’s good for south-east Australia… we are stacking the dice for the chances of these extreme drought years because of the changes in the [IOD and SAM] modes. '
' Explainer: what are the underlying causes of Australia's shocking bushfire season? - The Guardian '

Exposure, sensitivity and adaptive capacity of the southern grains industry

Returning to the earlier analogy of a sandcastle by the beach, some sandcastles are more vulnerable than others. The vulnerability of a natural or managed system to climate can be considered as the difference between impact and adaptive capacity (Figure 3). In this simple diagram (Figure 3), the impact of climate is the result of exposure and sensitivity. A high value horticultural crop in a glass house is sensitive to climate, but not exposed whereas a slow growing rangeland shrub is exposed but less sensitive. Recent seasons have highlighted that the grains industry in Australia is both exposed and sensitive to adverse climatic conditions such as drought, frost and heat. In a managed system such as cropping, adaptive capacity includes the varieties, equipment, chemicals and know-how in dealing with the variable and changing climate. Impressive crops produced under difficult circumstances in recent years show the high degree of adaptive capacity within the Australian grains industry.

Figure 3. Vulnerability is determined by impacts and adaptation. (see Turner 2013 for review and critique of frameworks).

In Table 2 the broad concept of climate change is broken down into components of seasonal heat, extreme heat, frost, seasonal rainfall, extreme rain events and changes to carbon dioxide (CO2) levels. This allows comment on the level of confidence from climate science on the exposure, confidence on crop science on sensitivity, and agronomy on management (Hayman, O’Leary and Meinke, 2019).

Table 2. Components of climate change and commentary regarding exposure, sensitivity and adaptive capacity (Source: Hayman, O’Leary and Meinke, 2019).

There are some changes such as increase in mean temperature where the confidence from both climate science on projections and agricultural science on impacts are high. This contrasts with changes to rainfall where the confidence in the projections is lower, but the impacts on cropping of changes to rainfall are very well understood. The interaction between these six aspects of climate change is important but uncertain. For example, elevated carbon dioxide is likely to partially offset some of the impacts of a decline in rainfall, but it is less clear how a drier, but carbon dioxide enriched future will respond to a heat wave.

Conclusion

The southern grains industry will continue to deal with a climate that varies year to year and has a warming and most likely a drying trend. Adaptable, information-rich farming systems are needed. Some of the important steps for agronomists and leading farmers are:

• Understand crop phenology –matching variety to environment. GRDC is investing in projects to better characterise phenology.
• Make the most of out of season rainfall.
• Manage the variable seasons through soil moisture monitoring and the use of seasonal climate information.
• Be vigilant for changes to pests and disease.
• Be an informed user of climate science.

Being an informed user of climate science is not easy as there is a vast amount of information. It is also difficult to come to terms with a message that increasingly points to a more challenging future. The southern grains industry is exposed and sensitive to climate, but it also has a high level of adaptive capacity. Not only has there been substantial performance in good seasons, the capacity to produce in difficult seasons is impressive. It is important to maintain an appropriate level of optimism. As Puri and Robinson (2007) put it, ‘optimism is like red wine, a glass a day is good for you, but a bottle a day can be hazardous’. From my observations, one of the most effective ways to achieve the appropriate level of optimism, learning and social support is through farming systems groups.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support. Bronya Cooper assisted with preparation of the paper.

References

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Hayman PT, O’Leary GL and Meinke H 2019 Australian Agronomy in the Anthropocene: The challenge of Climate. Chapter 25 in Pratley J and Kirkegaard J (eds) Australian agriculture in 2020: From conservation to automation. Agronomy Australia, 2019. 405-418. Australian Agronomy in the Anthropocene: the challenges of climate - Peter Hayman, Garry O’Leary and Holger Meinke - Australian Agriculture in 2020

Lim E-P, Hendon HH, Arblaster JM, et al. (2016) Interaction of the recent 50-year SST trend and La Niña 2010: amplification of the Southern Annular Mode and Australian springtime rainfall. Climate Dynamics 47, 2273-2291.

Pepler A, Dowdy A and Hope A (2018) A global climatology of surface anticyclones, their variability, associated drivers and long-term trends. Climate Dynamics.

Power SB, Delage FPD (2018) El Niño Southern oscillation and associated climatic conditions around the world during the latter half of the twenty-first century. Journal of Climate 31, 6189- 6207.

Puri, Manju & Robinson, T. David. Optimism and economic choice. Journal of Financial Economics. 86, No 1, 71-99, 2007

Turner, B.L., Kasperson, R.E., Matson, P.A., McCarthy, J.J., Corell, R.W., Christensen, L., Eckley, N., Kasperson, J.X., Luers, A., Martello, M.L. and Polsky, C., 2003. A framework for vulnerability analysis in sustainability science. Proceedings of the National Academy of Sciences, 100(14), pp.8074-8079.

Contact details

Peter.Hayman@sa.gov.au
0401996448