Geoscience Reference
In-Depth Information
12
CLIMATE SIMULATION
AND PREDICTION
The feedback processes discussed in the previous chapter, along with many
others, are triggered when a forcing is applied to the climate system. How can
all these processes, and interactions among these processes, be accounted for to
evaluate the resulting climate change? How do we know which processes are
relatively important, either globally or regionally, and which are ineffective at
changing climate? Computer climate models based on the equations and prin-
ciples discussed in previous chapters are used to keep track of the feedbacks
and interactions.
Climate models range from very simple representations of the earth system
to very complex models that are run on the world's fastest computers. The
most complete climate models are a comprehensive compilation of our knowl-
edge of how the climate system works, cast in computer language to allow for
numerical solution.
However complex, all climate models consist of a set of governing equa-
tions accompanied by a set of assumptions. We begin with the simplest climate
model.
12.1 ZERO-DIMENSIONAL CLIMATE MODEL
The simplest climate model has zero dimensions—it treats the whole earth sys-
tem as one point and is based on the concept of radiative equilibrium discussed
in chapter 4. Two equations are solved simultaneously for two unknowns, the
radiative equilibrium temperature ( T E ) and the surface temperature ( T S ). From
section 4.2, the steady-state radiation balance at the top of the atmosphere is
given by
(1
α
)
S
0
4
E
=
σ
T
.
(12.1)
4
The second equation, which relates T S and T E , is generated from observations
of today's climate, which indicate that the globally and annually averaged sur-
face temperature of the earth is (roughly) 35 K warmer than the radiative
equilibrium temperature:
=+
(12.2)
TT K.
S
35
The set of assumptions that accompany the equations to define a climate
model are important for defining the context of the model, including the
 
Search WWH ::




Custom Search