The talk begins with a general overview of observed changes to the climate system over the past century or so, and the evidence that these changes are primarily due to the human emission of greenhouse gases. We then focus on the changes to the global water cycle that are associated with climate change, including changes in atmospheric water vapour content, in precipitation patterns and in evapotranspiration. The focus then shifts to Australia, where we explore the observed changes to the hydrological cycle in Australia, examining the evidence for the influence of climate change on many of the observed changes. We then turn to the future and outline the range of projections for alternations to Australia’s water cycle through the rest of this century, depending on the amount of additional greenhouse gases that are emitted into the atmosphere. The emphasis then turns more directly to the relationship between human societies and the water cycle; that is, the distribution of our population, agriculture, industries etc. is, in large part, determined by the nature of the water cycle. As the water cycle changes, this is already putting generic pressures on human societies, as clearly evident in several parts of the world. Finally, we conclude with a brief examination of climate change in a broader, long-term Earth System perspective.