Annual Zonal Mean Radiation Budget
When globally averaged over a year, net energy gains are balanced by energy losses, or nearly so. This is not the case when the radiation gains and losses are averaged as a function of latitude (see above figure). Regions between approximately 30°N and 30°S gain radiant energy while the polar regions are losing energy through radiation processes. Since the tropics are not observed to be continually heating and the polar regions continually cooling, energy must be transported from the tropics to the poles. This transportation is accomplished by the atmosphere and ocean currents and is the reason we have weather!
Monthly mean regional radiation budgets.