John Alexander Church AO (born 1951) is an expert on sea level and its changes.

[1] He was co-convening lead author (with Jonathan M. Gregory) for the chapter on Sea Level in the IPCC Third Assessment Report.

He is currently a professor with the University of New South Wales' Climate Change Research Centre.

On an international level, Church has been the Principal Investigator for the NASA/CNES TOPEX/Poseidon Extended Satellite Mission.

[citation needed] Currently, Church is chair of the scientific committee of the World Climate Research Programme studying sea-level rise, and is leader of the Sea level Rise Project at the Antarctic Climate and Ecosystems Cooperative Research Centre.