Climate sensitivity

The terra "climate sensitivity" was defined in Section 3.6 as the ratio of the steady-state change in the global and annual mean surface air temperature to the global and annual mean radiative forcing. Only the fast feedback processes, involving atmospheric water vapour and temperature structure, clouds, and seasonal ice and snow, are accounted for in this definition. As discussed in Section 3.7, the climate sensitivity is believed to be approximately constant for radiative forcing perturbations of up to a few Wm^-2 and to be largely independent of the specific combination of forcings that add up to a given total forcing when changes in the concentration of different well-mixed greenhouse gases, in non-absorbing aerosols, and in solar luminosity are combined. Thus, if the climate sensitivity is known, the steady-state global mean temperature response can be scaled up or down as the magnitude of the total forcing changes. A commonly computed indicator of climate sensitivity is the global mean temperature response for a doubling in the atmospheric concentration of CO₂.