Some dynamical consequences of Greenhouse gas warming

Abstract The change in December‐February climate simulated by the CCC GCM for a doubling of CO2 is viewed from a Northern Hemisphere middle‐latitude persepctive. The simulated change in temperature is such as to reduce equator‐to‐pole and ocean‐to‐land temperature gradients in the body of the troposphere and this is expected to result in less baroclinicity and baroclinic instability, weaker eddies and transports and generally to a decrease in synoptic activity or, in other words, to more “summer‐like” conditions. The overall “rate of working” of the atmosphere, as measured by the generation of available potential energy, its conversion to kinetic energy and subsequent dissipation, decreases by some 12%. However, while the amount of available potential energy in the atmosphere decreases by about the same amount, the amount of kinetic energy is unchanged. Differences to the mean zonal, standing and transient eddy components of available potential and kinetic energies and to their rates of generation and conversion show that the energy cycle has changed in ways that might not be immediately expected. Despite the general decrease in activity, the net poleward transport of energy by the atmosphere is remarkably unchanged. This is accomplished with the expected decrease in the transport of dry static energy being off‐set by an increase in latent energy transport. This is true both for mean zonal and eddy transports. That the same amount of energy is transported by a generally less active atmosphere shows that, in a sense, the flow structures are more “efficient” in the warmer climate and calculations are made to quantify this. The transport of energy in latent form is much more efficient due to the strong increase in moisture content that accompanies the temperature increase.