Assessing dangerous climate change impacts on Australia's wheat industry

Atmospheric carbon dioxide (CO₂) concentrations and global and regional climates are already changing as a result of human activities. More change seems likely. Historical climate variations, particularly in rainfall, have had significant impacts on the Australian cropping industries and consequently we would anticipate additional impacts from future climate change. However, the magnitude of these changes is highly uncertain at regional levels especially for rainfall. To deal with this uncertainty a systematic assessment approach is described here that separates the effects of changed temperatures, rainfall and CO₂ concentration on regional and national wheat yields, including the effects of management adaptations in response to the above changes. This allows addressing questions such as 'Are there beneficial effects of moderate warming?' 'If so, at what point does further warming become negative?' and 'What is the benefit of management adaptation to climate changes?' Furthermore, the approach allows recombination of the components in a risk assessment approach to investigate questions such as 'What level of CO ₂ increase is required to offset deleterious changes in rainfall and temperature ?' or 'What is the probability of reductions in the value of the wheat industry ?' A key aspect of the international debate on climate change is in regard to what constitutes 'dangerous' climate change. Some preliminary assessments suggest that a global temperature increase of more than 2°C will have increasingly deleterious net effects. This study provides some additional support (albeit limited) to this emerging view. In southerly sites and also at a national level, small increases in temperature (up to 1°C) are simulated to slightly increase regional yields. Adaptations can extend the beneficial effects of higher temperatures out to 3°C but only in scenarios where rainfall increases. In drier scenarios, temperature increases above 1°C are deleterious. In more northerly sites in contrast, any increase in temperature reduces regional yields. Management adaptations (changed varieties, changed planting windows) can significantly offset the negative impacts of climate changes. These adaptations were most effective with small temperature increases (1 to 2°C), raising yields by 6 to 12%. At higher temperatures, further benefit was limited, particularly under scenarios with reduced rainfall. The greatest benefit from adaptations arose from positive management responses in higher rainfall scenarios where benefits of up to 16% were simulated. The beneficial effects of elevated CO₂ concentrations on yield can also substantially offset small climate changes. An increase in CO₂ concentration to about 650ppm is calculated as needed to offset either a 20% reduction in rainfall alone or a temperature increase of 4°C. Smaller increases in CO₂ are required to maintain yields when adaptation is practiced. (Graph Presented) In a preliminary attempt to address the issue of 'dangerous' climate change, we calculate the probability (risk) of the value of the national wheat crop dropping below the historical average in response to scenarios of global CO₂ increase and associated climate change. The likelihood increases with CO₂ level and climate changes, increasing to about 45% with changes feasible within 60 years (Fig 1). The adaptations assessed in this study more than halve that risk.