Adapting Agriculture to Climate Change: Preparing Australian Agriculture, Forestry and Fisheries for the Future

By CSIRO PUBLISHING

Adapting Agriculture to Climate Change is a fundamental resource for primary industry professionals, land managers, policy makers, researchers and students involved in preparing Australia’s primary industries for the challenges and opportunities of climate change.

More than 30 authors have contributed to this book, which moves beyond describing the causes and consequences of climate change to providing options for people to work towards adaptation action. Climate change implications and adaptation options are given for the key Australian primary industries of horticulture, forestry, grains, rice, sugarcane, cotton, viticulture, broadacre grazing, intensive livestock industries, marine fisheries, and aquaculture and water resources. Case studies demonstrate the options for each industry.

Adapting Agriculture to Climate Change summarises updated climate change scenarios for Australia with the latest climate science. It includes chapters on socio-economic and institutional considerations for adapting to climate change, greenhouse gas emissions sources and sinks, as well as risks and priorities for the future.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: Feb 15, 2010
• ISBN: 9780643102057

Book preview

1

INTRODUCTION

SM Howden and CJ Stokes

KEY MESSAGES:

The climate is changing and further change seems unavoidable, even if efforts are taken to reduce greenhouse gas emissions. For primary industries to continue to thrive in the future we need to anticipate these changes, be prepared for uncertainty, and develop adaptation strategies now.

Some broad generalisations can be made about how plant growth, which underpins all the primary industries addressed in this book, will be affected by climate change. Warmer temperatures may benefit perennial plants in cool climates, but annuals and plants growing in hot climates may be negatively affected. Plant productivity would be expected to increase or decrease in accordance with any changes in rainfall, while the direct effects of CO2 in stimulating plant growth and increasing water use efficiency could help by partly offsetting increases in evaporation or decreases in rainfall.

While there are some general principles about how impacts of climate change will vary geographically, regional climate change projections are currently more useful for describing the wide range of uncertainty and for probability-based risk assessment than serving as precise estimates for predictive planning and decision making.

Adaptation will need to take a flexible, risk-based approach that incorporates future uncertainty and provides strategies that will be able to cope with a range of possible changes in local climate. Initial efforts in preparing adaptation strategies should focus on equipping primary producers with alternative adaptation options suitable for the range of uncertain future climate changes and the capacity to evaluate and implement these as needed, rather than focussing too strongly yet on exactly where and when these impacts and adaptations will occur.

In the short term, a common adaptation option will be to enhance and promote existing management strategies for dealing with climate variability. This will automatically track early stages of climate change until longer term trends become clearer.

A changing climate for agriculture

Australia’s climate has many influences: seasonal synoptic circulations and frontal systems, the El Niño-Southern Oscillation (e.g. Pittock 1975), the Indian Ocean Dipole (Saji et al. 1999), the Southern Annular Mode (Marshall 2003), the Madden-Julian Oscillation (Donald et al. 2006), and the Inter-decadal Pacific Oscillation (Power et al. 1999) among others (see Table 1.1). Jointly, these have provided Australia with the world’s most variable climate. Managing the impacts of climate variability on agricultural systems has thus been a major challenge since European settlement but has been improving gradually. Now, in addition to this highly variable and challenging climate, there is increasing evidence that the climate is changing and that humans are likely to be the cause of this change (Solomon et al. 2007). Climate change will likely cause a range of impacts on Australian agriculture with a consequent need for adaptation responses to emergent risks and opportunities. This book is intended to be a first step towards effective climate change adaptation responses across Australian agriculture.

It is very likely that human-influenced emissions of greenhouse gases are affecting the global climate (Solomon et al. 2007). Global mean temperatures have risen approximately 0.76°C since the mid-1800s. The last decade is the warmest ever recorded instrumentally (0.42°C above the 1961–1990 baseline: Brohan et al. 2006) followed by the previous two decades (0.18 and 0.05°C respectively) while the last 100 years were the warmest of the millennium. This warming plus changes in continental-scale temperatures, rainfall patterns, wind fields, climate extremes and sea levels cannot be explained by natural causes alone: there is a strong human ‘fingerprint’ (Solomon et al. 2007). Additionally, rates of glacial and ice-field retreat and many other observations of physical and biological responses are consistent with expectations of ‘greenhouse’ climate change. It seems likely that these changes will continue for the foreseeable future due to ongoing, and even accelerating (Canadell et al. 2008) emissions of carbon dioxide and other greenhouse gases. Indeed, past greenhouse gas emissions alone are estimated to have committed the globe to a warming of about 0.2°C per decade for the next several decades (Solomon et al. 2007). The most up-to-date climate projections are for an increase in global average temperatures of 1.1–6.4°C by the end of the present century along with a large range of other climate changes (see Chapter 2). To place these temperature rises in perspective, a 1°C rise in average temperature will make Melbourne’s climate something like that currently experienced by Wagga Wagga, a 4°C rise like that of Moree and a 6°C rise like that just north of Roma in Queensland (corresponding to shifts in latitude of 2.5°, 8° and 11° towards the equator respectively). Intuitively, it is hard to conceive that such changes will not have implications for Australia’s agricultural industries. Unfortunately, at the moment the rate of greenhouse gas emissions, the build-up of atmospheric carbon dioxide, the global temperature increase and the rate of sea level rise are all at or above the worst-case scenario of the IPCC (Rahmstorf et al. 2007; Canadell et al. 2008) and thus the higher end of the range of change seems more likely than the lower.

Agricultural adaptation to climate change: a new need

Agricultural systems in Australia are well known to be sensitive to both long-term climatic conditions and year-to-year climate variability. This is evident in the systems used in a given geographic location or season type, average production and production variability, product quality, relative preferences for different agricultural activities, preferred soil types, the management systems and technologies used, input costs, product prices and natural resource management. Consequently, if the climate changes, there are likely to be systemic changes (or adaptations) in agricultural systems. Here we use the term ‘adaptation’ to include the actions of adjusting practices, processes and capital in response to the actuality or threat of climate change, as well as responses in the decision environment, such as changes in social and institutional structures, or altered technical options, that can affect the potential or capacity for these actions to be realised (Howden et al. 2007).

Adaptation is not new. Australian farmers have always adapted to past changes in prices, technologies and climate variations as well as institutional factors (e.g. McKeon et al. 2004). The rationale for having a focus on adaptation to climate change is that the changes are likely to be far-reaching, systemic and to some extent, able to be foreseen, and so there is a case for advanced preparation. For example, the recent IPCC Fourth Assessment Report concludes that Australian agriculture and the natural resource base on which it depends has significant vulnerability to the changes in temperature and rainfall projected over the next decades to 100 years (Hennessy et al. 2007). Climate change will add to the existing, substantial pressures on Australia’s agricultural industries and will interact strongly with the food security challenge over the next decades: that is, to effectively double food production while reducing greenhouse gas emissions, reducing impact on biodiversity and the natural resource base while facing competition for land and water from urban encroachment and biofuel use. To be prepared for this challenge, we argue here that there is a need to start developing and implementing adaptation strategies now. This book is aimed at assisting such efforts.

Table 1.1: Major components of the climate system relevant to climatic variability and land management in Australia’s agricultural systems. The cited reference indicates examples of the influence of components on Australian rainfall, controlling climate systems and vegetation response (after Meinke and Stone 2005; McKeon et al. 2009).

The importance of developing effective strategies for adapting to climate change has been recognised by the governments of the Commonwealth, States and Territories. Initiatives such as the Garnaut Climate Change Review (http://www.garnautreview.org.au), the National Climate Change Adaptation Research Facility (www.nccarf.edu.au) and the CSIRO Climate Adaptation Flagship (www.csiro.au/org/ClimateAdaptationFlagship.html) are seeking to more fully understand the implications of climate change and the actions that could be taken to address this challenge. It is now recognised that in order to assess the costs (and benefits) of climate change, we need to include the costs (and benefits) of mitigation, the costs (and benefits) of impacts and the costs (and benefits) of adaptation (Howden et al. 2007). Several of these interact with each other. For example, we would expect the size of the adaptation task to be lower if there is effective, but perhaps costly, mitigation and higher if mitigation is foregone. Similarly, the benefits of effective adaptation are likely to be greater if the climate change itself is large. Achieving this complex task of effectively informing public policy development will be challenging in its own right and this book is also a step towards that goal. In this we are building on several decades of research into the management of climate variability and approximately two decades of intermittent research into the impacts of climate change on Australian agricultural systems. However, there is relatively little prior research on climate change adaptation, with only relatively few options analysed in a practical, participatory way with industry for their utility in reducing the risks or taking advantage of any opportunities arising from climate change. Even fewer adaptations have been evaluated in relation to the broader costs and benefits of their use. These few analyses show that practicable and financially viable adaptations will have very significant benefits in ameliorating risks of negative climate changes and enhancing opportunities where they occur. The benefit-to-cost ratio of undertaking research and development into these adaptations appears to be very large (indicative ratios greatly exceed 100:1, Howden and Jones 2004). In response to the growing demand from industry, government and the general public (including the recent National Climate Change Research Strategy for Primary Industries review), we prepared reports drawing together expertise from across Australia to identify prospective adaptation options (Howden et al. 2003; Stokes and Howden 2008). This book updates and expands these options drawing on more recent studies.

Scope of the book

In this book we cover all the major agricultural industries in Australia: grains (Chapter 3), cotton (Chapter 4), rice (Chapter 5), sugarcane (Chapter 6), winegrapes (Chapter 7), horticulture and vegetables (Chapter 8), forestry (Chapter 9), broadacre grazing (Chapter 10), intensive livestock (Chapter 11) and fisheries and aquaculture (Chapter 13). For each of these industries we consider the likely implications of projected climate change (as described in Chapter 2) and what actions industries might consider taking to adapt to these new challenges and opportunities. The total gross value of production of these industries is about $40 billion per year and it has been increasing at about 3.3% per year over the past decade (ABARE 2007). In the year 2006–7, exports from these industries were about $31.4 billion (about 15% of total exports). Hence, agriculture makes a substantial contribution to the national balance of trade. Throughout this chapter terms such as ‘agriculture’, ‘enterprise’, ‘land use’ and ‘primary producer’ are used to refer more broadly to the full range of industries that Australia’s renewable natural resources support.

Past experience demonstrates that all these agricultural sectors have sensitivity to climate variations ranging from minor to substantial. Consequently, there are many management responses to climate variability and these will likely provide the basis of many initial adaptation strategies. This aspect is covered in each of the industry chapters along with other adaptation options these industries might use in responding to climate change and the uncertainties that need to be addressed to start developing adaptation strategies. We have also included cross-cutting issues of water resources and pests/diseases as previous work has suggested that these are highly sensitive to potential climate changes and they have significant implications for components of the agricultural sector. The material on pests and diseases is integrated into each sector as this will be how the impacts are largely expressed, while water resources are dealt with in a separate chapter (Chapter 12). Greenhouse gas emissions from agriculture and how to reduce these are dealt with in Chapter 14, and human dimensions of adaptation are covered in Chapter 15. The concluding chapters include a summary and an analysis of prospective ways ahead to make adaptation effective in a variable and changing climate.

There are several impacts of climate and atmospheric composition that are common across agricultural sectors as they impact on plant production, the primary driver for agriculture and fisheries. To reduce repetition in the subsequent chapters we deal with these common responses below. We then address issues of managing uncertainty.

Direct impacts of atmospheric and climatic change

The almost certain increases in atmospheric CO2 concentrations, the high likelihood of increases in temperatures and the possibility of changes in rainfall averages, seasonality and intensity (Chapter 2) are all likely to affect plant production directly. The broad nature of likely changes in these three factors (CO2, temperature and rainfall) are described below followed by the likely impacts on plant production and marine systems.

Direct effects of rising atmospheric CO2

Pre-industrial atmospheric concentrations of CO2 were about 280 parts per million (ppm) and these have risen almost exponentially to their current level of about 389 ppm (a 37% increase). The IPCC developed sets of emissions scenarios about a decade ago, describing different economic, population and technology trajectories (Nakicenovic and Swart 2000). The low-emissions scenarios indicated a small rise in emissions followed by a sustained reduction, whereas the high-emissions scenarios involved almost exponential increases in emissions. Even the lowest emissions scenario stabilised CO2 concentration at about 550 ppm (almost double pre-industrial levels) whereas the high-end scenarios had CO2 levels exceeding 900 ppm at 2100. As noted earlier, emissions are now higher than the worst-case scenario (Canadell et al. 2008) and are growing rapidly (3.5% p.a.) with limited immediate prospect for global reductions in emission rates. Consequently, plants will increasingly be growing in high CO2 environments and this will directly affect the resource use efficiency, productivity, and product quality of plant production in agriculture.

Elevated atmospheric CO2 concentration increases the efficiency of use of light and water (Gifford 1979; Morison and Gifford 1984), nitrogen (Drake et al. 1997) and possibly efficiency or effectiveness of uptake of other minerals like soil phosphorus (Campbell and Sage 2002). In Australia where water, nitrogen and phosphorus are major limiting factors in production, this is an important first order, and generally positive feature of the response of agriculture to global atmospheric change. It is sometimes termed the ‘CO2 fertilisation effect’. The other, less certain, components of climate change such as rising temperature and changed rainfall will be superimposed on this primary response. As such it is appropriate to understand it and to consider how the benefits might be maximised.

The increase in light use efficiency in ‘temperate’ C3 species, like wheat, barley, rice, cotton, oats, oil seeds, trees, and cool-season pasture species, derives substantially from the suppression of the process of photorespiration by elevated CO2: photorespiration is essentially an inefficiency. The increase in light use efficiency can be substantial – 30% or more at the crop level with doubling of CO2. The ‘tropical’ C4 species (maize, sorghum, sugarcane and tropical grasses) lack photorespiration and the effect of CO2 on increasing light use efficiency is correspondingly much lower in these species.

The increase in water use efficiency with elevated CO2 results from partial closure of stomata (the small pores, mostly on the undersides of leaves, that allow CO2 into the leaf but simultaneously let water vapour out). Higher concentrations of CO2 in the atmosphere increase the rate that CO2 diffuses into the leaf for photosynthesis relative to the rate of water loss through stomatal pores. This tends to increase water use efficiency expressed as: (1) an increase in photosynthesis while transpiration rates stay the same; (2) reduced transpiration while photosynthesis remains the same, or (3) an intermediate combination of increased photosynthesis and reduced transpiration. In the field, this may be observed as an increase in growth rate while soil water depletion remains unaltered (e.g. Samarakoon and Gifford 1995) or reduced soil water depletion with little growth effect or an intermediate combination (e.g. Stokes et al. 2008). This increase in plant dry matter production per unit of water used by plants occurs in both C3 and C4 species (Morison and Gifford 1984). In good growing conditions, under elevated CO2 there is a tendency in some but not all plants for the decrease in water use per unit leaf area to almost match the increase in leaf area, resulting in almost identical time-course of water use to that found in lower CO2 conditions (e.g. Samarakoon and Gifford 1995). However, in nutrient-poor situations, there is limited capacity to increase leaf area but the stomatal response still occurs, resulting in increased soil moisture contents in the subsoil and extension of the period when water is available for growth in the surface soil. This may significantly benefit trees and shrubs in savanna communities and also alter grass species dynamics (e.g. Stokes and Ash 2006). The increased efficiency with which plants use water can potentially be exploited in developing adaptation strategies and could be used to partly offset the effects of reduced rainfall or increased evaporative demand.

The increase in nitrogen (N) use efficiency (here referring to the capacity to grow more dry matter with the same amount of nitrogen) can occur in both C3 and C4 species. In C3 species in particular this appears to occur as a result of the increased efficiency and hence lowered production of ‘rubisco’, a key photosynthetic enzyme that contains a large fraction of leaf nitrogen. Leaf and grain N-concentrations can also be reduced via passive ‘dilution’ whereby elevated CO2 stimulates carbon fixation, and storage of carbohydrates but this is not matched by corresponding increases in uptake of N by plant roots. These changes in nitrogen (i.e. protein) and storage carbohydrates have implications for plant product quality such as herbage forage quality and grain quality. Adaptive management measures may be needed to compensate for these impacts where they are problematic, for example via application of nitrogenous fertilisers etc. (see Chapter 3), but in some circumstances these impacts can be beneficial (e.g. in livestock where growth is energy limited not N-limited, see Chapter 10).

In legume species that have symbiotic N-fixation in the roots, elevated CO2 concentration has frequently been shown to increase the rate of N-fixation per plant or per unit ground area by increasing the size of the root system and mass of nodules (Chapter 10). Additionally, the growth response of legumes to elevated CO2 concentration is generally greater than that of grasses. Thus in mixed farming systems the need for artificial fertiliser, to maintain grain protein levels for example, may be reduced by using legume-based leys (all else being equal).

Effects of increased temperature

The primary climatic effect of increasing concentrations of greenhouse gases is an increase in the average temperature of the terrestrial and ocean surface and the lower atmosphere. The rate of development of many agricultural plants is approximately linearly dependent on cumulative air temperature (‘heat sum’) above a base temperature at which development rate is essentially zero. In addition, plant growth rate often shows a flat bell-shaped response to temperature with each species having its own ‘optimum’ temperature characteristics. The optimum is, however, subject to acclimation such that plants within a species growing in high temperatures have a higher optimum than those growing in low temperatures. Generally speaking, most agricultural crops are grown in areas where average temperatures are below their acclimated optimum. Thus, as temperatures rise (and assuming all else being equal), we might expect both dry weight growth rates and rates of progression through developmental phases to increase with the effect on rate of development being the stronger of the two. However, plant responses to possible changes in frequency of occasional high temperature or frost stress make generalisation very problematic. For annual crops, warmer conditions tend to reduce yields owing to any faster growth rate not being sufficient to compensate for the earlier attainment of maturity reducing the opportunity to accumulate sunlight and hence biomass. Higher temperatures also increase respiration, decreasing yields (e.g. Manunta and Kirkham 1996).

For perennials such as trees and pasture species in regions where cool winters slow growth, it might be anticipated that warming would increase winter growth and extend the more rapid growth period. However, for the perennial subterranean clover, it was found that 3.5°C continuous warming of the atmosphere in a field experiment did not increase winter growth and for the whole year decreased herbage growth by almost 30%, offsetting a positive response to concurrent elevated CO2 concentration (Lilley et al. 2001). The temperature responses of productivity are clearly complex, involving interdependent effects on photosynthesis, respiration, transpiration, nutrition and plant development.

In addition to the above effects, minimum temperature is inversely related to vapour pressure deficit (VPD: the ‘dryness’ of the air), which is in turn linearly related to evaporation rates. High vapour pressure deficits also result in lower water use efficiencies. Thus if VPD increases there are two compounding negative impacts (higher water demand and lower water use efficiency). VPD is likely to increase with higher temperatures provided that there is not a marked asymmetry between the increases in night-time and daytime temperatures. An additional effect on VPD and water use efficiency may arise from the influence of elevated CO2 in reducing stomatal aperture, which would reduce evaporative cooling of the leaf from transpiration, increase the temperature differential between the leaf boundary layer and the air and thus increase effective VPD. Reduced transpiration (with reduced evaporative cooling) would also create an additional daytime warming of plant leaves above and beyond the leaf temperature increases associated with warming of the lower atmosphere.

Increases in night-time temperatures are known to affect numerous developmental and product quality attributes of protected horticultural crops such as on flowering, plant height, seed and flower set and fruit quality. Similarly, in rice, increasing night temperatures can increase spikelet sterility, reducing yields (Ziska and Manalo 1996). Thus adapting to higher night-time temperatures may need to take into account situation-specific responses created by species (or genotype) by environment interactions.

Low night-time temperatures are necessary for some annual and perennial plants via the process of vernalisation or provision of chilling units. Increases in temperature are already reducing the achievement of chilling units in industries such berry-growing and apple and stonefruits. Further warming will likely require much more significant adaptations such as changes in location, varieties or species and use of chemical or other control options. In contrast, for many industries such as viticulture, horticulture and some grains, frost is a significant risk. In some regions such as central Queensland, frost risk is already declining with warming conditions, but the reverse trend is occurring in southern Australia. There remains some uncertainty as to the likely changes in frost risk in southern Australia under climate change.

Interactions between elevated CO2 concentration and temperature are complex. Although there seemed to be solid theoretical reasons why the magnitude of the CO2 growth response of C3 species would increase with temperature (Gifford 1992), synthesis of experimental evidence from the literature indicated no trend of increased CO2 sensitivity with increasing temperature (Morison and Lawlor 1999). Hence, we cannot assume that the responsiveness of plant growth to CO2 will become greater with global warming.

Increased intensity of the hydrological cycle

Implicit in the theory of global warming is a positive feedback of increasing greenhouse gas concentrations, increasing temperatures, increasing evaporation and thus atmospheric water vapour that will further increase temperatures and so on. This intensification of the hydrologic cycle means (on average across the globe) higher evaporation rates, higher absolute atmospheric humidity and higher rainfall (Solomon et al. 2007). However, the places where evaporation may increase are not necessarily the same as those where rainfall may increase. Across the globe, climate change scenarios indicate a tendency for increased rainfall in the equatorial and cool-temperate to polar regions but decreased rainfall in the subtropics and Mediterranean mid-latitude climate zones (Solomon et al. 2007). This tendency for lower rainfall and more droughts in southern Australia in particular is discussed in detail in the following chapter but, if realised, it will affect agriculture and water resource management across the continent. However, it is important to note that whereas we can have high confidence in CO2 increases, there are major increases in the uncertainty as we consider temperature and particularly rainfall changes and as we move from global to local scales (Giorgi 2005). Consequently, local-scale rainfall changes in particular are fraught with uncertainty due to the large range of factors that affect them as well as the effectiveness of descriptions of the underlying climatic processes. Nevertheless, there appears to be more certainty in relation to changes in the intensity of rainfall. Even in regions where average rainfalls may decrease, rainfall intensities may increase through more rainfall falling as a result of thunderstorm-type activity rather than frontal rainfall (which tends to be of lower intensity). Similarly, high intensity rainfall may increase from cyclones as these are likely to increase in intensity and severity but not necessarily in frequency or latitudinal distribution (Solomon et al. 2007). Increased rainfall intensity will require management responses to reduce erosion risk across a broad range of agricultural industries (e.g. McKeon et al. 1988).

Marine system changes

The dominant climate change influences on marine environments will be warming of the oceans, sea level rises, changes in circulation patterns and changes in ocean chemistry. Increasing temperatures in oceans are likely to threaten coral reefs with more frequent bleaching episodes, cause fish species to migrate towards the poles, reduce the viability of southern kelp forests and threaten many important fisheries that have specific ecological, physiological or temperature requirements, such as abalone, rock lobster and Atlantic salmon (Hennessy et al. 2007; Hobday et al. 2008). Oceans serve as a strong buffer for atmospheric CO2 levels and have been estimated to have absorbed about a third of all anthropogenic CO2 emissions to date. However, this buffering already appears to be decreasing with the fraction of total CO2 emissions absorbed by the ocean decreasing from about 31.5% in 1960 to only 25.5% now (Canadell et al. 2008). Further decreases seem likely as the oceans warm (CSIRO 2007). Rising levels of CO2 in oceans are increasing their acidity and reducing the availability of calcium carbonate, which is required by many creatures with calcium carbonate-based shells: evidence from the Southern Ocean suggests this decline has already begun (Moy et al. 2009, Chapter 13). Increased stratification of oceans will potentially reduce overturning and nutrient cycling and this could alter productivity, particularly in upwelling regions with subsequent effects on fisheries (Chapter 13). Estuaries, which are important nurseries, are likely to be affected by rising sea levels and changes in flows of freshwater from rivers, often positively.

Adapting to uncertain changes

There are many sources of climate change uncertainties that form a cascade, each compounding one after another. As a result, there is a broad spread in the range of projected climate changes over the next decades to centuries (see Chapter 2). To illustrate this, there is substantial uncertainty about what actions humans will take globally to reduce future greenhouse gas emissions. For any given emissions scenario, there are uncertainties about how the greenhouse emissions will influence global climate and how feedbacks from the biosphere in response to these climate changes will further increase or decrease the atmospheric greenhouse gas levels. As we move from global climate to management scales (regional to local) the climate projections become less reliable. For any given climate change projection, there are then further uncertainties as to what the impact will be on current land (and ocean) use practices and the underpinning natural resources. There is further uncertainty as to the effectiveness of adaptations by affected industries, and whether their responses will or will not increase emissions, thus feeding back to climate change. How to deal with this cascade of uncertainty is a key challenge for adaptation.

There is a general view that the agricultural sectors in Australia are highly adaptive, developing management, technologies and other responses to a range of challenges and opportunities. Often, these have been in the face of fairly well-defined single factors such as changes in relative price of inputs or outputs, market access or change in consumer preference. In contrast, as indicated earlier and also in Chapter 2, climate change is, in many respects, highly uncertain in both the nature and degree of the change and it has multiple related dimensions. These are not only through potential changes in climate (and hence productivity) at local, regional and global scales, but also through the emerging carbon economy that may affect input prices and potential new products such as carbon storage (Keating et al. 2008). For example, it is important that adaptations do not increase emissions, thus increasing the size of the mitigation task (Howden et al. 2007). There is also the prospect of maladaptation that could arise from either under-adapting or over-adapting, or by adapting too quickly or too slowly.

The following chapters address these and other points such as costs, benefits and barriers to adaptation and likely adaptive capacity to provide an industry-by-industry perspective on adapting to climate change. These accounts are then synthesised in the Summary (Chapter 16) into a region-by-region overview of adaptation options.

A consistent theme that emerges throughout this book is that the impacts of climate change are only partly certain. This theme is revisited towards the end of the book in considering the human dimension of adaptation, where a suggested approach for dealing with this uncertainty is presented (Chapter 15). A related theme is that adaptation should be viewed as an ongoing process that is part of good risk management, whereby drivers of risk are identified and their likely impacts on systems under alternative management are assessed. In this respect, adaptation to climate change is similar to adaptation to climate variability, changes in market forces (cost/price ratios, consumer demands, etc.), institutional or other factors. Isolating climate change from other drivers of risk may be helpful, especially during the initial stages of assessment when awareness of the relative importance of this risk factor is still low.

Operationally, however, translating adaptation options into adaptation actions requires consideration of a more comprehensive risk management framework. This would allow exploration of quantified scenarios dealing with all the key sources of risk (not just climate change), providing more effective decision making and learning for farmers, policy-makers and researchers: an increase in the ‘climate knowledge’ (Howden et al. 2007). Importantly this framework should not be limited to technical approaches to risk assessment, which tend to assume that people are ‘locked in’ to the existing enterprise mix or management systems. It is highly likely that incremental adaptations applied to existing systems will have limits to their effectiveness under more severe climate changes. Hence, more systemic, transformational changes in resource allocation need considering, such as targeted diversification of production systems and livelihoods. We hope that this book is a step on the pathway to an Australian primary industries sector that is flexible, forward-looking and more able to adapt to a variable and changing climate.

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2

CLIMATE PROJECTIONS

KJ Hennessy, PH Whetton and B Preston

KEY MESSAGES:

Warming of the climate system over the past century is beyond doubt, and it is partly due to anthropogenic increases in atmospheric concentrations of greenhouse gases.

Since 1950, Australia has become warmer, with less rainfall in the south and east, and more rainfall in the north-west.

Further global warming and climate change is expected due to projected increases in greenhouse gases.

Australia is likely to become warmer and drier in the future.

Small changes in average climate can have large effects on extreme weather events.

Extremely hot years and days are likely to occur more often, with fewer frosts, more heavy rainfall in summer and autumn, less heavy rainfall in winter and spring in the south, more droughts, more fires, more intense tropical cyclones, less hail in the south and more hail along the east coast.

Introduction

Warming of the climate system over the past century is beyond doubt, and it is partly due to increases in greenhouse gases (IPCC 2007a). Further climate change is expected due to projected increases in greenhouse gases (IPCC 2007a). The consequences of such climate change will vary across regions and sectors (IPCC 2007b). While global warming can be slowed through large reductions in greenhouse gas emissions, some warming is unavoidable and adaptation will be needed to reduce damages and take advantage of opportunities (IPCC 2007b). A key part of planning for climate change is having access to reliable and relevant regional projections of climate change.

This chapter summarises the latest information about the climate change that has been observed in Australia since the early 20th century and its attribution to natural and anthropogenic causes. In addition, this chapter presents projections of global climate change over the 21st century as well as regional projections for Australia. This information is based on international climate change research, including conclusions and data from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), and builds on a large body of climate research that has been undertaken for Australia in recent years. More detail is available in a technical report (CSIRO and Australian Bureau of Meteorology 2007).

Observed climate variability and change

Internal and external factors drive climate variability on a range of timescales. Internal factors are natural in origin and arise from complex interactions within the climate system, such as the El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole, the Southern Annular Mode and the Inter-decadal Pacific Oscillation (CSIRO and Bureau of Meteorology 2007). A number of natural external factors also influence climate variability including the Earth’s rotation, variations in the energy from the Sun, volcanic eruptions and changes in the Earth’s orbital parameters. However, some external factors are human-induced, such as changes in land use, emissions of greenhouse gases and aerosols and stratospheric ozone depletion.

The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Since the Industrial Revolution (around 1750 AD) the atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased by 35%, 148% and 18%, respectively (IPCC 2007a). The increases in CO2 are mainly due to fossil fuel use and land use change, while those of CH4 and N2O are mainly due to agriculture (IPCC 2007a).

The Earth’s average surface temperature has increased by 0.7°C since the beginning of the 20th century (IPCC 2007a). Most of the warming since 1950 is very likely due to increases in atmospheric greenhouse gas concentrations associated with human activities, and it cannot be explained by natural variability alone (IPCC 2007a). The warming has been linked to more heatwaves, changes in precipitation patterns, reductions in sea ice extent and rising sea levels (IPCC 2007a).

Australian climate change

Australian average annual temperatures have increased by 0.9°C since 1910. Most of this warming has occurred since 1950 (see Figure 2.1, page 41), with the greatest increases in the east and a slight cooling in the far north-west (Figure 2.2, page 41) associated with increased rainfall. The warmest year on record for the whole of Australia is 2005, but 2007 was the warmest year for southern Australia (Australian Bureau of Meteorology 2008c). The number of hot days (maximum temperature greater than 35°C) and nights (minimum temperature greater than 20°C) has increased and the number of cold days (maximum temperature less than 15°C) and nights (minimum temperature less than 5°C) has declined (CSIRO and Australian Bureau of Meteorology 2007).

Since 1950, most of eastern and south-western Australia has become drier (see Figure 2.3, page 42). Across New South Wales and Queensland, rainfall trends partly reflect a very wet period around the 1950s, though recent years have been unusually dry. In contrast, north-western Australia has become wetter over this period, mostly during summer. Since 1950, the number of very heavy rainfall events of over 30 millimetres per day (mm/day) and the number of wet days (at least 1 mm/day) have decreased in the south and east but increased in the north (CSIRO and Australian Bureau of Meteorology 2007).

Australian rainfall shows considerable year-to-year variability, partly in association with the ENSO. El Niño events tend to be associated with hot and dry years in Australia, and La Niña events tend to be associated with mild and wet years (Power et al. 2006). There has been a marked increase in the frequency of El Niño events and a decrease in La Niña events since the mid-1970s (Power and Smith 2007). The frequency of tropical cyclones in the Australian region has decreased in recent decades, largely due to the increasing frequency of El Niños. However, the number of severe cyclones has not declined.

Causes of Australian climate change

Most of the Australian warming since the mid-20th century is very likely due to increases in greenhouse gases (IPCC 2007a). The 40% decline in south-east Australian snow depths in early spring over the past 40 years is due to warming rather than a decline in precipitation (Nicholls 2005). About 50% of the rainfall decrease in south-western Australia since the late 1960s is likely to be due to increases in greenhouse gases (Cai and Cowan 2006). The autumn rainfall decline in south-eastern Australia since the late 1950s may be partly due to increases in greenhouse gases (Cai and Cowan 2008). Increased rainfall in the north-west since 1950 may be due to increased aerosol particles produced by human activity (Rotstayn et al. 2008). However, the extent to which natural versus human causes have altered patterns of drought in Australia remains uncertain (Nicholls 2007; Hennessy et al. 2008).

Climate change projections

The IPCC developed forty scenarios of greenhouse gas and sulphate aerosol emissions for the 21st century based on various assumptions about demographic, economic and technological change (Naki enovi and Swart 2000). The scenarios are grouped into four ‘storylines’: B1, B2, A1 and A2, each of which has a number of variants. Six of these variants were utilised as ‘illustrative’ scenarios, designed to represent the broad range of uncertainty in emissions trajectories over the 21st century (see Figure 2.4, page 42). The climatic effects of projected changes in emissions can be simulated using climate models. These models are mathematical representations of the Earth’s climate system based on well-established laws of physics, but involving simplifications of biophysical processes. Projections derived from climate models are not predictions because they are conditional on the emission scenarios and on the reliability of climate models.

Australian climate change simulations for the 20th and 21st centuries are currently available for 23 global climate models. Each model has been given a score based on its ability to simulate average observed (1961–1990) patterns of temperature, rainfall and mean sea level pressure in the Australian region (CSIRO and Bureau of Meteorology 2007). Models with higher scores are given greater emphasis in developing future climate projections.

The projections