Manabe contributed many pivotal works to the broad domain of planetary and atmospheric physics in the 1960's. The word "model" in reference to his work is substantially more than just computer simulations; really, it's referring to some of his seminal contributions providing "models" in the sense of physical frameworks for understanding the responses and evolution of planetary atmospheres (broadly speaking - with relevance far beyond the terrestrial atmosphere) to particular forcings. See Manabe and Weatherald (1967) [1] for perhaps one of the most critical contributions that he made.

[1]: https://journals.ametsoc.org/view/journals/atsc/24/3/1520-04...