today's climate the planetary emission temperature is approximately 255K,
while the average surface temperature is approximately 288K! The difference
is a result of the our atmosphere. The warming that results from
the atmosphere is referred to as the Greenhouse effect.
A simple climate
model demonstrates the effect of the atmosphere on surface temperature.
For simplicity, the atmosphere is represented as a uniform shell surrounding
the planet. In this model, the atmosphere does not absorb solar radiation;
however, the atmosphere does absorb and emit infrared radiation. As with
the first model, we assume energy balance: the absorbed radiation from
the sun must balance the outgoing infrared radiation.
An energy balance must exist at the top-of-atmosphere and at the surface.
Why does the surface temperature change
with a change in solar output?
Explain why changing the planet's albedo
modifies the planet's surface temperature.
Can the surface temperature be less than
the planet's emission temperature?
If you increase the solar output, how
can you decrease the surface temperature?
Why does surface temperature increase
with increasing atmospheric infrared emission?
How might clouds impact the surface temperature?
You control three variables of this
simple model: the atmospheric infrared emissivity, the planetary albedo,
and the energy output of the Sun. The atmospheric emissivity
is the ratio of the radiant energy emitted per unit time per unit area
by the atmosphere to the energy emitted by an ideal blackbody at the same
temperature. As you vary these parameters the emission temperature of the
planet and the temperatures of the surface and atmosphere change.
All temperatures are plotted on a graph as a function of altitude.