S.M. Howden

Adapting agriculture to climate change

The strong trends in climate change already evident, the likelihood of further changes occurring, and the increasing scale of potential climate impacts give urgency to addressing agricultural adaptation more coherently. There are many potential adaptation options available for marginal change of existing agricultural systems, often variations of existing climate risk management. We show that implementation of these options is likely to have substantial benefits under moderate climate change for some cropping systems. However, there are limits to their effectiveness under more severe climate changes. Hence, more systemic changes in resource allocation need to be considered, such as targeted diversification of production systems and livelihoods. We argue that achieving increased adaptation action will necessitate integration of climate change-related issues with other risk factors, such as climate variability and market risk, and with other policy domains, such as sustainable development. Dealing with the many barriers to effective adaptation will require a comprehensive and dynamic policy approach covering a range of scales and issues, for example, from the understanding by farmers of change in risk profiles to the establishment of efficient markets that facilitate response strategies. Science, too, has to adapt. Multidisciplinary problems require multidisciplinary solutions, i.e., a focus on integrated rather than disciplinary science and a strengthening of the interface with decision makers. A crucial component of this approach is the implementation of adaptation assessment frameworks that are relevant, robust, and easily operated by all stakeholders, practitioners, policymakers, and scientists.

MODELLING GLOBAL CHANGE IMPACTS ON WHEAT CROPPING IN SOUTH-EAST QUEENSLAND, AUSTRALIA

The wheat module, I_WHEAT, from the APSIM cropping system model was used to investigate the impacts of changes in atmospheric CO2 concentrations on wheat crops by modifying radiation use efficiency, transpiration efficiency, specific leaf area and critical nitrogen concentrations. The effects of several combinations of atmospheric CO2, climate change and crop adaptation strategies on wheat production in the Burnett region were studied. Mean wheat yields were increased under doubled CO2, with the response relative to ambient CO2 greatest in dry years. Higher temperatures under the climate change scenarios moderated the yield gains achieved with increasing CO2 and in some instances reversed them under the reduced rainfall scenario. The status of the region as a producer of prime hard wheat may be at risk due to reduced grain protein levels under doubled CO2 and the increased likelihood of “heat shock” in the climate scenarios used.

Climate change and Australian livestock systems: impacts, research and policy issues

The recent changes in Australia’s climate, the likelihood of further changes over the next decades to centuries, and the likely significant impacts of these changes on the Australian livestock industries, provide increasing urgency to explore adaptation options more effectively. Climate and atmospheric changes are likely to impact on the quantity and reliability of forage production; forage quality; thermal stress on livestock; water demands for both animal needs and for growing forage; pest, disease and weed challenges; land degradation processes; and various social and economic aspects including trade. Potential adaptation options are available for moderate climate changes, with these often being variations of existing climate risk management strategies. However, to date there are few Australian examples where these adaptations have been assessed systematically on any scale (e.g. enterprise, regional, whole of industry or national). Nor have many studies been undertaken in a way that (i) effectively harness industry knowledge, (ii) undertake climate change analyses in the framework of existing operational systems, or (iii) assess climate change in the context of other socioeconomic or technical changes. It is likely that there are limits to the effectiveness of existing adaptations under more severe climate changes. In such cases more systemic changes in resource allocation need considering, such as targeted diversification of production systems and livelihoods. Dealing with the many barriers to effective adaptation will require ‘mainstreaming’ climate change into policies covering a range of scales, responsibilities and issues. This mainstreaming will facilitate the development of comprehensive, dynamic and long lasting policy solutions. The integrative nature of climate change problems requires science to include integrative elements in the search for solutions: a willingness to apply integrated rather than disciplinary science and a strengthening of the interface with decision-makers.

Global change impacts on wheat production along an environmental gradient in south Australia

Crop production is likely to change in the future as a result of global changes in CO2 levels in the atmosphere and climate. APSIM, a cropping system model, was used to investigate the potential impact of these changes on the distribution of cropping along an environmental transect in south Australia. The effects of several global change scenarios were studied, including: (1) historical climate and CO2 levels, (2) historic climate with elevated CO2 (700 ppm), (3) warmer climate (+2.4 degrees C) +700 ppm CO2, (4) drier climate (-15% summer, -20% winter rainfall) +2.4 degrees C +700 ppm CO2, (5) wetter climate (+10% summer rainfall) +2.4 degrees C +700 ppm CO2 and (6) most likely climate changes (+1.8 degrees C, -8% annual rainfall) +700 ppm CO2. Based on an analysis of the current cropping boundary, a criterion of 1 t/ha was used to assess potential changes in the boundary under global change. Under most scenarios, the cropping boundary moved northwards with a further 240,000 ha potentially being available for cropping. The exception was the reduced rainfall scenario (4), which resulted in a small retreat of cropping from its current extent. However, the impact of this scenario may only be small (in the order of 10,000-20,000 ha reduction in cropping area). Increases in CO2 levels over the current climate record have resulted in small but significant increases in simulated yields. Model limitations are discussed.

Global change impacts on native pastures in south-east Queensland, Australia

Increases in atmospheric concentrations of greenhouse gases such as carbon dioxide (CO2) are likely to impact on grazing industries through direct effects on plant growth and through possible changes in climate. Assessment of the likely direction and magnitude of these impacts requires development of appropriate modelling capacities linked with experimental work. This paper documents the adaptation of an existing soil–pasture–livestock model, GRASP, to simulate system responses to changes in CO2. The adapted model is then used to compare these responses under current climate and CO2 conditions with four possible future scenarios: (1) doubled CO2; (2) doubled CO2 and increased temperature; (3) as in the previous scenario but with a drier climate; and (4) as in (2) but with a wetter climate. These studies suggest that CO2 changes alone are likely to have beneficial effects, with increased pasture growth, increased and less variable liveweight gain, and increased ground cover. However, subsoil drainage is likely to increase. Growth responses to CO2 are likely to be greater in drier years than in wetter years partly due to nitrogen limitations in the soils of the region. Increases in temperature in combination with CO2 further increased animal production due to the increased number of growing days in the cooler months. The increased rainfall scenario had few additional positive effects but further increased subsoil drainage. In contrast, the drier scenario had reduced plant and animal production when compared with current conditions even though seasonal transpiration efficiency was increased by 20% due to increased CO2.

Managing Murray-Darling Basin livestock systems in a variable and changing climate: challenges and opportunities.

The key biophysical impacts associated with projected climate change in the Murray–Darling Basin (MDB) include: declines in pasture productivity, reduced forage quality, livestock heat stress, greater problems with some pests and weeds, more frequent droughts, more intense rainfall events, and greater risks of soil degradation. The most arid and least productive rangelands in theMDBregion may be the most severely impacted by climate change, while the more productive eastern and northern grazing lands in theMDBmay provide some opportunities for slight increases in production. In order to continue to thrive in the future, livestock industries need to anticipate these changes, prepare for uncertainty, and develop adaptation strategies now. While climate change will have direct effects on livestock, the dominant influences on grazing enterprises in the MDB will be through changes in plant growth and the timing, quantity and quality of forage availability. Climate change will involve a complex mix of responses to rising atmospheric carbon dioxide levels, rising temperatures, changes in rainfall and other weather factors, and broader issues related to how people collectively and individually respond to these changes. Enhancing the ability of individuals to respond to a changing climate will occur through building adaptive capacity. We have, via secondary data, selected from the Australian Agricultural and Grazing Industries Survey, built a national composite index of generic adaptive capacity of rural households. This approach expresses adaptive capacity as an emergent property of the diverse forms of human, social, natural, physical and financial capital from which livelihoods are derived. Human capital was rated as ‘high’ across the majority of theMDBcompared with the rest of Australia, while social, physical and financial capital were rated as ‘moderate’ to ‘low’. The resultant measure of adaptive capacity, made up of the five capitals, was ‘low’ in the northern and central-west regions of the MDB and higher in the central and eastern parts possibly indicating a greater propensity to adapt to climate change in these regions.

Global change and the mulga woodlands of southwest Queensland: greenhouse gas emissions, impacts, and adaptation

The possibility of trading greenhouse gas emission permits as a result of the Kyoto Protocol has spurred interest in developing land-based sinks for greenhouse gases. Extensive grazing lands that have the potential to develop substantial woody biomass are one obvious candidate for such activities. However, such activities need to consider the possible impacts on existing grazing and the possible impacts of continuing CO2 buildup in the atmosphere and resultant climate change. We used simulation models to investigate these issues in the mulga (Acacia aneura) woodlands of southwest Queensland. The simulation results suggest that this system can be managed to act as either a net source or a net sink of greenhouse gases under current climate and CO2 and under a range of global change scenarios. The key component in determining source or sink status is the management of the woody mulga. The most effective means of permanently increasing carbon stores and hence reducing net emissions is to exclude both burning and grazing. There are combinations of management regimes, such as excluding fire with light grazing, which, on average, allows productive grazing but transient carbon storage. The effects of increased CO2 on ecosystem carbon stores were unexpected. Carbon stores increased (7-17%) with doubling of CO2 only in those simulations where burning did not occur, but decreased when burnt. This occurred because the substantial increases in grass growth with doubling of CO2 (34-56%) enabled more fires, killing off the establishing cohorts needed to ensure continued carbon accumulation. On average, the doubling of atmospheric CO2 concentration increased grass growth by 44%, which is identical with mean literature values, suggesting that this result may be applicable in other ecosystems where fire has a similar function. A sensitivity analysis of the CO2 response of mulga showed only minor impacts. We discuss additional uncertainties and shortcomings.

The dynamics of grazed woodlands in southwest Queensland, Australia and their effect on greenhouse gas emissions

This study outlines the development of an approach to evaluate the sources, sinks, and magnitudes of greenhouse gas emissions from a grazed semiarid rangeland dominated by mulga (Acacia aneura) and how these emissions may be altered by changes in management. This paper describes the modification of an existing pasture production model (GRASP) to include a gas emission component and a dynamic tree growth and population model. An exploratory study was completed to investigate the likely impact of changes in burning practices and stock management on emissions. This study indicates that there is a fundamental conflict between maintaining agricultural productivity and reducing greenhouse gas emissions on a given unit of land. Greater agricultural productivity is allied with the system being an emissions source while production declines and the system becomes a net emissions sink as mulga density increases. Effective management for sheep production results in the system acting as a net source (approximately 60-200 kg CO2 equivalents/ha/year). The magnitude of the source depends on the management strategies used to maintain the productivity of the system and is largely determined by starting density and average density of the mulga over the simulation period. Prior to European settlement, it is believed that the mulga lands were burnt almost annually. Simulations indicate that such a management approach results in the system acting as a small net sink with an average net absorption of greenhouse gases of 14 kg CO2 equivalents/ha/year through minimal growth of mulga stands. In contrast, the suppression of fire and the introduction of grazing results in thickening of mulga stands and the system can act as a significant net sink absorbing an average of 1000 kg CO2 equivalents/ha/year. Although dense mulga will render the land largely useless for grazing, land in this region is relatively inexpensive and could possibly be developed as a cost-effective carbon offset for greenhouse gas emissions elsewhere. These results also provide support for the hypothesis that changes in land management, and particularly, suppression of fire is chiefly responsible for the observed increases in mulga density over the past century.