HR: 09:15h
AN: A51D-06 INVITED     [Abstracts]
TI: Earth's Albedo in GCMs - Model Performance and Impact of Model Tuning
AU: * Bender, F A
EM: frida@misu.su.se
AF: Stockholm University, Svante Arrhenius vag 12, Stockholm, 10691, Sweden
AB: Albedo estimates from coordinated simulations with 20 different GCMs, performed in support of the IPCC 4th assessment report, and measurements obtained from ERBE (Earth Radiation Budget Experiment) and CERES (Clouds and the Earth's Radiant Energy System) are compared and evaluated. Study of seasonal anomalies, temporal trends and spatial distribution of albedo and model-to-observation correlations, shows that models and observations differ in many aspects. Deviations are especially pronounced in certain regions, for instance marine subtropical areas dominated by stratocumulus clouds. While the models display similar albedo characteristics in terms of e.g. absolute values and geographical distribution, inter-model differences in albedo-determining cloud properties such as cloud water content are large. This indicates that at least some models fail to realistically reproduce cloud-albedo interactions, which limits the extent to which these models can be used to further understand such relationships. The modelled global mean TOA albedo is found to be systematically higher than the observed, and the models deviate more from the more recent CERES measurements than from the older ERBE measurements, most likely as a consequence of being tuned to agree with ERBE TOA fluxes. Tuning the NCAR CAM3.1 (Community Atmosphere Model) to CERES TOA radiative fluxes instead of ERBE is found to give a small but statistically significant difference in the model's equilibrium climate sensitivity. This elucidates the fact that climate sensitivity calculations are indirectly based on parameters that are not well restricted by observations and makes clear the need for more restricting measurements to avoid arbitrariness in climate sensitivity estimates and future climate predictions.
DE: 1626 Global climate models (3337, 4928)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3309 Climatology (1616, 1620, 3305, 4215, 8408)
DE: 3337 Global climate models (1626, 4928)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly