John Raven has devoted most of his working life to studying algae that float in the upper levels of the ocean. He has explored how resources such as carbon dioxide, light and trace minerals interact to limit primary productivity in these evolutionarily ancient organisms, which underpin marine ecosystems and recycle carbon.

His work combines theoretical and laboratory studies, and extends from processes in individual plant cells to the biogeochemical exchanges that sustain the water and carbon cycles. His models have made it possible to test the effect of raised concentrations of atmospheric carbon dioxide at the ocean surface.

John has also examined the evolution of land plants, developing models to predict the likelihood of plant life on other planets and the biological signals that might reveal their presence. In 2005, he led a Royal Society review of the increasing acidity of the oceans with rising atmospheric carbon dioxide.