Page 513 - Environment: The Science Behind the Stories

THE SCIENCE BEHIND THE STORY

How Do Climate models more sophisticated, they are to make them behave realistically in

Models Work? incorporating more and more of the space and time. In the real climate
factors—major and minor, direct and
system, time is continuous and spatial
indirect—that affect climate. effects reach down to the level of
To handle the complexity, gener- molecules interacting with one another.
ally a model is composed of multiple But the virtual reality of climate models
submodels. Essentially, submodels cannot be so deep and precise—there
for components of the Earth sys- is simply not enough computer power
tem—ocean waters, sea ice, gla- available. Instead, modelers approxi-
ciers, forests, deserts, troposphere, mate reality by dividing time up into
stratosphere—are each built and are periods (called time steps) and by
then combined into a global model. dividing the Earth’s surface up into cells
a researcher manipulates a 3d cloud Years ago when models first coupled or boxes according to a grid (called grid
simulator to help in modeling the atmosphere and ocean components
climatic influence of clouds. boxes) (Figure 2).
together, they were called “coupled” Each grid box contains land,
models. This is standard in today’s far ocean, or atmosphere, much like a digi-
Climate models are indispensable for more complex general circulation mod- tal photograph is comprised of discrete
modern climate science—and they are els, or global climate models (which pixels of certain colors. The grid boxes
increasingly vital for our society as they share the acronym GCM). are arrayed in a three-dimensional layer
allow us to make informed predictions For a model to function, all the by latitude and longitude, or in equal-
about what conditions will confront us building blocks must be given equations sized polygons.
in the future. Yet to most of us, a cli-
mate model is a mysterious black box.
So how exactly do scientists go about
creating a climate model? Incoming Outgoing
heat
solar energy
The output we often see from
Transition
climate models are colorful maps or from solid
data-rich graphs and charts, but the to vapor
scientist puts into the model a long Evaporative Cumulus
series of mathematical equations. These and heat Snow clouds Cirrus
equations describe how various compo- exchanges cover clouds
nents of Earth’s systems function. Some
equations are derived from physical laws
such as those on the conservation of Vegetation, Stratus
topography,
clouds
mass, energy, and momentum (p. 41). reflectivity layers Atmospheric
Others are derived from observational Precipitation
and
and experimental data on the physi- evaporation
cal, chemical, and biological aspects of Runoff
our planet. Converted into computing Winds Heat
language, these equations are integrated Soil exchange
with information about Earth’s landforms, moisture Ocean Sea Ocean currents, layers Ocean
hydrology, vegetation, and atmosphere bathymetry ice temperature,
and salinity
(Figure 1). All these types of infor-
mation are the building blocks of a Upwelling and
climate model. downwelling
The number of these building
blocks determines the complexity of
the model. Earth’s climate system is
mind-bogglingly complex, and model-
ers will never capture all the factors
that influence climate. Yet as com- Figure 1 climate models incorporate a diversity of natural factors and processes.
puters become more powerful and Anthropogenic factors can then be added in.

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