The Top Ten Problems of the New-and-Improved ECHAM6 Model
Stevens, B., Giorgetta, M., Esch, M., Mauritsen, T., Crueger, T., Rast, S., Salzmann, M., Schmidt, H., Bader, J., Block, K., Brokopf, R., Fast, I., Kinne, S., Kornblueh, L., Lohmann, U., Pincus, R., Reichler, T. and Roeckner, E. 2013. Atmospheric component of the MPI-M System Model: ECHAM6. Journal of Advances in Modeling Earth Systems 5: 146-172.
Although Stevens et al. say that "ECHAM6 better simulates many aspects of the present climate as compared to ECHAM5," they acknowledge that "a number of stubborn biases endure." These biases are said by them to be the facts that (1) "there has been relatively little improvement in the representation of precipitation since the introduction of ECHAM3, (2) "precipitation over land is too weak," (3) "there is a global tendency of precipitation features, from the South Pacific Convergence Zone to precipitation over the Gulf Stream, to be shifted too far northward," (4) "biases in the representation of marine boundary layer clouds remain large," (5) "cloud layers appear too infrequently in the simulations," but are (6) "too bright when they do appear," (7) "ECHAM6 continues to have large (3 K) cold biases in upper tropospheric temperatures," (8) "tropical temperature biases only vanish with very high (300-m) vertical resolution in the upper troposphere," (9) "the tropical and mid-latitude convective stability of the troposphere remains more unstable relative to observations, particularly in the southern Hemisphere in its summer season," and (10) "the extra-tropical jets maximize at somewhat lower latitudes than observed."
Once again, it appears that state-of-the-art climate models still have a long way to go in simulating many important aspects of Earth's climate.