Abstract/Summary

This paper reviews the status of our understanding of the Earth's annual, global mean energy balance, the hemispheric energy balances and the symmetry observed about the equator, and explores the influence of latitudinal changes of energy both on the annual mean and seasonal transports of energy from low latitudes to higher latitudes. Based on the best available information we show that our planet continues to be out of balance with additional heat being added to it at the rate of 0.6 ±0.4Wm−2. This heat appears to be taken up primarily by the oceans of the SH and perhaps mostly equatorward of 37 S. The nature of the adjustments applied to our best estimates of individual, annual mean fluxes of energy to produce a balance are described and the results of applying a more formal constraint for these adjustments are discussed. The energy balances of the Southern and Northern Hemispheres are then shown to be practically identical which in turn suggests the transport of energy across the equator in the net is close to zero. In fact the hemispheres are not identically symmetrical with the SH being slightly out of balance absorbing the additional heat and transporting a small amount of net heat across the equator to the balanced NH. The symmetry in absorbed solar and the near symmetry in OLR are remarkable in their own right and are a result of the effects of clouds both on solar reflection and OLR that act to offset land–ocean interhemispheric differences. We then demonstrate important interhemispheric seasonal influences on the heat transported to the winter pole that conspire to make these seasonal transports lopsided. This asymmetry is a direct result of the eccentricity of the Earth's orbit that induces larger energy losses from the southern winter hemisphere. This in turn produces a latitudinal asymmetry in the location of on the tropical trough zone, a region from which energy is always moved to the winter pole, requiring it be located deeper into the NH.