Results of a 100-year run of the Hadley Centre general circulation model are used to compute monthly values of the three components of atmospheric torque on the Earth and of the associated atmospheric angular momentum series. All these results are compared with equivalent ones from the National Center for Environmental Prediction/National Center for Atmospheric Research reanalyses for the overlap period since 1948. We find some important differences; consequently, our results should be taken as an order of magnitude of the effect. We also compute the effect of the atmosphere on length of day (LOD) and polar motion by the use of both the torque and the angular momentum approaches. We find comparable amplitude with both torque and angular momentum for the polar motion; the axial torque, however, related to LOD, appears to be unphysical. The excitation of long-period LOD variation is in phase with the observed variation but much smaller. The low-frequency polar motion is only coherent with the observation at certain particular periods.