Large scale forest plantations in the Murray-Darling Basin may be embraced as a carbon sequestration mechanism under a Carbon Pollution Reduction Scheme. However, increased tree plantation will be associated with reduced inflows to river systems because of increased transpiration, interception and evaporation. Therefore, an unregulated change in land management is most likely to have a dramatic impact on the water availability. This will exacerbate the impacts of climate change projected in the Garnaut Review. This paper examines the implications of unrestricted changes in land use. These results should suggest the true costs to society from carbon sequestration by determining the tradeoffs between timber production and agricultural products.