Chapter 4 Climate Impacts and Responses

Impacts of Climate Change on Australia > Agriculture and Forestry

Approximately 40% of the 70 million hectares of forest existing in Australia at the time of European settlement has been cleared, and a similar amount has been logged.

CSIRO Plant Industry researchers are applying their knowledge about the impacts of drought on availability of soil nutrients for crops. Nitrogen and phosphorous concentrations are generally high following a drought. Careful nutrient management can assist in reducing drought recovery times. Underestimating nitrogen levels can lead to growers sowing an inappropriate crop. Calculations of nitrogen need to include residual nitrogen from fertiliser applied the previous year, subsoil and topsoil nitrogen mineralisation – which can be accelerated after a drought – and nitrogen removed by the previous year’s crops.

Climate change is already affecting Australian cropping systems and the way they are managed, according to scientists from the Queensland Department of Primary Industries. Continuing increases in the concentration of atmospheric carbon dioxide will affect growth patterns of crops, trees and pastures while changes in rainfall patterns will influence production. Temperature increases are already leading to changes such as the planting dates for wheat. For example, in Emerald, in Central Queensland, there are around three weeks each year of frost, compared with 10 weeks each year in 1900 (Figure 4.6). Further temperature increases will also affect rotations, limiting canola's spread north into Queensland, or supporting cotton production further south than it is grown today. Farmers in marginal regions now might need to switch from their current grain/grazing mixed operations to grazing or even plantation forestry. Management changes recommended to farmers could include changes in varieties and planting dates, changes in crop species, erosion and salinity management, pest and disease management, and greater use of seasonal forecast information.

CSIRO researchers have shown that under climate change in Australian viticultural regions – likely warming with drier conditions particularly in winter and spring – earlier ripening and possible reductions in grape quality are expected. In cooler, southern regions higher temperatures may allow for new varieties. Higher carbon dioxide concentrations may lead to more canopy growth and shading, leading to decreased fruitfulness. Water supplies for irrigation may decrease.

Researchers at Queensland Department of Natural Resources and Mines (Crimp et al 2002) used the pasture production model GRASP to explore the impact of climate change on native grasses. With a small increase in temperature and a decrease in rainfall, pasture growth was reduced by 10- 50%, with larger reductions by 2070. With a small increase in temperature and an increase in rainfall, pasture growth increased. With larger increases in temperature and increases in rainfall pasture production increased by 2030 in the north, but not in the south, and results were not as positive by 2070. With large increases in temperature and decreased rainfall, average pasture growth across Australia was reduced by between 30-70% by 2030, with reductions increasing to 30-100% by 2070.

On clear, sunny days a plant’s top leaves cast strong shadows over the rest of the plant, say researchers at the Australian National University and Cooperative Research Centre for Greenhouse Accounting. Plants photosynthesise more effectively when sunlight is diffused through cloud or haze, rather than when it hits the plant canopies directly. Their research suggests that plants would respond to greater cloudiness and more pollution by growing more.

CSIRO scientists have undertaken research into the impact of increases in atmospheric concentrations of carbon dioxide and climate change (specifically increased temperature and water stress) on the Australian wheat industry. The wheat industry is particularly important as it represents Australia’s major crop in terms of both value and volume. Yields and areas cropped are strongly influenced by climate. The scientists employed a statistical method to build likelihoods and ranges of future grain yields, value of production and value of exports. They found that by 2030, there is an 88% chance of production being above current levels. By 2070, there is a 64% chance that average national grain production will be higher than current levels. Markedly different regional climate changes are likely to result in large differences in regional production, particularly by the year 2070. Climate variation causes change in long-term yields by about + 10% for Queensland and +6% or lower for the other states. In cropping regions of Western Australia, there is a strong chance that productivity and value will be below current levels in both 2030 and 2070.

Pragmatic adaptation strategies such as changing varieties and planting times can offset some of the negative impacts, especially in Western Australia, while enhancing the positive impacts. Changing wheat varieties and planting dates alone for example could save the industry between $100M and $500M each year (in current dollar terms) by maintaining productivity in the face of change. An overview of the adaptive capacity of the Australian agricultural sector to climate change (options, costs and benefits) was undertaken for the Australian Greenhouse Office. CSIRO researchers worked with industry groups to deal effectively with their key concerns, draw on their valuable expertise and also contribute to enhanced knowledge in the agricultural community. A clear conclusion from this overview was that investment in adaptation is extremely worthwhile for the agricultural sector.