The possibility that future climate change may affect agriculture has attracted considerable attention(1,2). As a step towards evaluating such influences, the effect of climate trends over the past few decades(3) needs to be assessed. Here I estimate the contribution of climate trends in Australia(4,5) to the substantial increase in Australian wheat yields since 1952. Non-climatic influences-such as new cultivars and changes in crop management practices-are removed by detrending the wheat yield and climate variables and using the residuals to calculate quantitative relationships between variations in climate and yield. Climate trends appear to be responsible for 30-50% of the observed increase in wheat yields, with increases in minimum temperatures being the dominant influence. This approach should be applicable in other regions for which sufficient data exist.