In gauging the relative climatic significance of different forcings, an important question is whether they have similar climate sensitivities. As discussed in Section 6.2.1, while models indicate a reasonable similarity of climate sensitivities for spatially homogeneous forcings (e.g., CO2 changes, solar irradiance changes), it is not possible as yet to make a generalisation applicable to all the spatially inhomogeneous forcing types. In some cases, the climate sensitivity differs significantly from that for CO2 changes while, for some other cases, detailed studies have yet to be conducted. A related question is whether the linear additivity concept mentioned above can be extended to include all of the relevant forcings, such that the sum of the responses to the individual forcings yields the correct total climate response. As stated above, such tests have been conducted only for limited subsets of the relevant forcings