Radiative Forcing of Earth's Atmosphere
This graphic was modeled after Collins, et al to depict the influences tending to drive the Earth's energy balance away from that which existed at the beginning of the industrial period. Since the net effect of human activity depicted here is a warming influence, this is the kind of quantitative analysis that is used to model global warming. The models that include the project effects of human activity do a better job of predicting the observed temperatures than do those with purely natural forcings.
Kiehl & Trenberth
Collins, et al.