Geoscience Reference
In-Depth Information
engines that allow governments and businesses to project events for
purposes such as planning the federal budget.
Climate models, similarly, use algebraic or numerical equations to
represent the dynamics of the atmosphere, oceans, ice, and other related
tation of the earth, with different layers of the atmosphere and oceans,
running in short time steps of minutes to hours. They are very large
models, deploying hundreds of thousands of lines of computer code
that have been developed by dozens of teams of scientists in many
countries. Many good descriptions of how models are developed are
available in topics and also online.
4
You might wonder whether climate models are simplifi ed. That is
actually their purpose—to simplify, but not to oversimplify. After all,
reality is enormously complex. The U.S. economy, for example, includes
more than 300 million people, each making hundreds of decisions ev-
ery day. There is no way to represent this system “accurately” in the
sense of “literally.” What we need for economic and climate modeling is
to simplify the picture for the purpose at hand. We need the relevant
details, not all the details.
Figure 4 illustrates the difference between a simplifi ed model and
the full reality. The left-hand side shows a photograph of a high-voltage
transmission line that moves electricity from generators to customers.
This is the “reality.” The right-hand side shows the computer code in
GAMS language for the energy system and the economy (actually, it is
the DICE model discussed shortly). The model is a conceptual represen-
tation of the complex interactions of the electricity sector along with
the rest of the energy system. Which do you prefer? An architect might
choose the picture, while someone interested in dealing with climate
change would prefer the computer program.
A good model, whether of a transmission tower, an economy, or the
earth's climate, should capture the essence of the process without over-
whelming the user with unnecessary clutter. In economics we build
models of output and incomes, for example, to help the government
forecast its revenues and spending and to provide an informed basis for
