ARTICLES
An Online Climate Model to facilitate Depth-studies and Science Extension (continued)
Box 1 – How do climate models work? Box 2 – How does carbonator work?
State-of-the-art climate models are complex constructions in
which the climate system is divided into a three-dimensional
array of grid cells – Figure 2 shows this for the atmosphere
component of a model. As a model simulation steps forward in
time, relevant properties of each cell (e.g. air temperature, wind
humidity for an atmospheric cell, water temperature, currents and
salinity for an ocean cell) are modified according to mathematical
equations representing physical and biogeochemical processes.
These equations govern how properties in a cell are affected by
neighbouring cells (e.g. by currents transporting heat around the
ocean) or are modified within the cell (e.g. by the formation of
clouds). The equations enshrine fundamental laws, such as the
conservation of mass, energy and momentum, in the model. At the heart of a state-of-the-art climate model lies the principle
of the conservation of energy. Any imbalance between the
energy entering and leaving the climate system will cause the
temperature to change (until an equilibrium is reached). Regional
imbalances in the build-up of energy require the redistribution of
heat through the climate system (i.e. between grid boxes) via the
simulated movement of air and water. However, to understand the
first order response of the climate system to energy imbalances
– i.e., the globally averaged response – we can do away with the
array of grid cells needed to resolve regional changes. Instead
we can treat the climate system as a homogenous body – such
as a box - that warms or cools via energy imbalances. Carbonator
treats the climate as two interconnected boxes that respond to
energy imbalances on different timescales. The “surface climate”
includes the lower atmosphere, the land surface and the well-
mixed surface ocean (~ top 50m). These regions interact rapidly
and so can be represented by a single temperature. The surface
temperature responds rapidly to changes in energy input as it has
a relatively small heat capacity.
These workhorses of climate science typically require hundreds
of person-years to develop, are made up of millions of lines of
computer code and are run on tens to thousands of processors on
large supercomputers. The complexity of the models means that
their outputs can be almost as difficult to analyse and understand
as observations of the real world.
Figure 2 Schematic of the three-dimensional grid of the
atmosphere of a climate model (Image attribution: CCRC, UNSW
Sydney (NonCommercial-ShareAlike (CC BY-NC-SA 2.0 AU)))
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SCIENCE EDUCATIONAL NEWS VOL 68 NO 3