Geoscience Reference
In-Depth Information
huge enterprise cannot represent power generation in other countries,
or international trade in electricity, or the interactions with the rest of
the economy, or the carbon cycle. As Leonardo da Vinci is often cited,
“Simplicity is the highest form of sophistication.” The great formulas of
physics are stunningly simple.
The central idea of climate change is also stunning in its simplicity.
It is that the average temperature of the earth changes with the rela-
tive concentration of CO
2
in the atmosphere. A doubling of CO
2
con-
centrations is expected to lead to a rise in average temperature of
around 3°C. Another doubling is expected to produce another 3°C of
warming. Unfortunately, the parallel with the law of gravity breaks
down at this point. To begin with, we don't know the exact rise in tem-
perature per doubling of CO
2
. Additionally, the effect may depend upon
other factors, especially on the time scale over which the increase takes
place.
Finally, just as maps are designed for different uses—for example,
hiking versus sailing, or driving versus fl ying—models also are designed
for different purposes. Many climate models are extremely detailed and
require supercomputers to calculate the trajectories of the components
they track. Other simplifi ed models focus on projections of specifi c out-
comes, such as impacts on agricultural output, sea level, or the geo-
graphic spread of malarial mosquitoes. Different problems require
different models.
INTEGRATED ASSESSMENT MODELS
An important approach for analysis of climate change is a class of
integrated assessment models (IAMs). These are comprehensive models
that include not only climate but other aspects of the science and eco-
nomics of climate change. IAMs combine in one package the end-to-end
processes from economic growth through emissions and climate change
to impacts on the economy and fi nally to the projected effects of policies
for slowing climate change.
IAMs also contain highly simplifi ed climate models. Like the com-
puter code in Figure 4, they attempt to capture the linkage between
