Since the earth is spherical, the Simple Greenhouse Model does not
adequately include latitudinal effects. As shown here, the angle
of incidence of the sun's radiation in the polar regions is very
different than with the sun high overhead in the tropics. Since
absorption of solar radiation is relative to the locally flat surface
of earth (i.e. the local horizontal "tangent plane"), the amount of solar radiation
per unit surface area absorbed in polar latitudes is much less than the amount
per unit area absorbed in tropical latitudes. This means that there is
an imbalance of solar heating of earth between these latitudinal regions,
illustrated by the yellow curve varying from high values at the equator to
much lower values at polar latitudes.
The earth's infrared emission also has systematic latitudinal variations.
The emission in the tropics is also
larger than emission at polar latitudes, illustrated by the red curve which
has higher values in the warm tropics than in the much colder polar region.
But actual surface temperature data teaches scientists that there is not a radiative balance
in either the tropical or polar regions. There is a net radiant energy input to tropical latitudes
(solar radiational input exceeds infrared radiation loss) while the opposite
occurs at the polar latitudes. Thus, the earth system must find a way to equalize
this latitudinal energy imbalance. This is generally accomplished by the systematic
movement of wind and ocean currents.
|
