Dr John Church is the pre-eminent authority on the rate of 20th century sea-level rise. He was a pioneer in what is now a standard approach to the use of observations to detect climate change in the ocean. He provided substantial improvements in estimates of ocean heat uptake, resolving discrepancies between observations and models and the long-standing conundrum about the causes of 20th century sea-level rise. Church elucidated the dynamical balances at work in some of the major current systems surrounding Australia. His multi-disciplinary work remains a model of the application of oceanographic information to biological fisheries issues.