Down-scaled global circulation modelling is combined with wheat growth simulation modelling to generate yield responses to times of sowing under current and projected climatic conditions for several locations in the grainbelt of Western Australia. A model for investment in crop sowing machinery draws on these simulated yield relationships at each location and is used to determine a farmer’s optimal investment in crop sowing work rate capacity under current and projected climate regimes. The key finding is that at most locations the projected change in climate has marked impacts on profit distributions from grain production, yet mostly modest changes in the farmer’s investment in machinery work rate form part of the profit-maximising response to climate change at each location. There is also a divergence in machinery investment response between high versus low rainfall locations, with increases and decreases in work rates respectively being forecast. However, as illustrated for a few locations, the changes in investment in work rate within a broadly similar rainfall region are not uniform; principally due to climate change differently affecting the pattern of yield response to time of sowing at each location.