What are the climatic effects of increases in carbon dioxide and other anthropogenic trace gases? Suki Manabe pioneered the resolution of this important problem about four decades ago using numerical models - first, constructing the one-dimensional radiative-convective and, then, developing the three-dimensional general circulation climate models. His careful cultivation of the models and judicious design of the numerical experiments over the years, together with insightful and rigorous diagnoses of the simulations, have carved out major scientific milestones in our understanding of anthropogenic global climate change. This talk will review some prominent results from Suki's research on this subject. The manner in which his works have enabled a robust platform for the modern scientific assessments of climate change shall also be highlighted.