ABSTRACT
As noted in Section 2.2, the term "greenhouse effect" refers to the reduction in outgoing infrared radiation to space due to the presence of the atmosphere. It can be and has been directly measured, based on the surface emission (which depends only on temperature) and the emission at the top of the atmosphere as observed by satellites. In this chapter the underlying physics of this effect is explained in very simple terms. This is followed by a discussion of the heating perturbation that occurs when GHG or aerosol concentrations change - the so-called "radiative forcing". The concept of fast and slow feedbacks and of climate sensitivity is then introduced, followed by a discussion of the relationship between radiative forcing and climate sensitivity for a variety of important radiative forcing mechanisms.
