2.4.5.6 Assessment of the Cloud Albedo Radiative Forcing

As in the TAR, only the aerosol interaction in the context of liquid water clouds is assessed, with knowledge of the interaction with ice clouds deemed insufficient. Since the TAR, the cloud albedo effect has been estimated in a more systematic way, and more modelling results are now available. Models now are more advanced in capturing the complexity of the aerosol-cloud interactions through forward computations. Even though major uncertainties remain, clear progress has been made, leading to a convergence of the estimates from the different modelling efforts. Based on the results from all the modelling studies shown in Figure 2.14, compared to the TAR it is now possible to present a best estimate for the cloud albedo RF of –0.7 W m^–2 as the median, with a 5 to 95% range of –0.3 to –1.8 W m^–2. The increase in the knowledge of the aerosol-cloud interactions and the reduction in the spread of the cloud albedo RF since the TAR result in an elevation of the level of scientific understanding to low (Section 2.9, Table 2.11).