Phosphorus (P) losses from land to water will be impacted by climate change and land management for food production, with detrimental impacts on aquatic ecosystems. Here we use a unique combination of methods to evaluate the impact of projected climate change on future P transfers, and to assess what scale of agricultural change would be needed to mitigate these transfers. We combine novel high frequency P flux data from three representative catchments across the UK, a new high spatial resolution climate model, uncertainty estimates from an ensemble of future climate simulations, two P transfer models of contrasting complexity and a simplified representation of the potential intensification of agriculture based on expert elicitation from land managers. We show that the effect of climate change on average winter P loads (predicted increase up to 30% by 2050s) will be limited only by large scale agricultural changes (e.g. 20-80% reduction in P inputs).