Page 514 - Environment: The Science Behind the Stories

The finer-scale the grid, the greater Figure 3 Models
resolution the model will have, and the 1.0 Observed data that incorporate
better it will be able to predict results All factors both natural and
region by region. However, more 0.8 Anthropogenic factors anthropogenic
resolution means more computing power Natural factors factors predict
is needed, and climate models already 0.6 observed climate
strain the most powerful supercomputing 0.4 trends best.
networks. The best climate models today Global temperature change (°C) Adapted from U.S.
feature dozens of grid boxes piled up 0.2 Global Change
from the bottom of the ocean to the top Research Program,
of the atmosphere, with each grid box 0.0 2013. National climate
measuring a few dozen miles wide, and assessment. Draft for
public review.
time measured in periods of just minutes. –0.2
Once the grid is established, the
processes that drive climate are assigned
to each grid box, with their rates parceled 1850 1900 1950 2000
out among the time steps. The model Year
lets the grid boxes interact through time
by means of the flux of materials and may predict future climate accurately observations the best (Figure 3). This
energy into and out of each grid box. as well. supports the idea that human activities
Once modelers have input all this A number of studies have com- are influencing our climate.
information, learned from our study pared model runs that include only nat- The major human influence on
of Earth and the climate system, they ural processes, model runs that include climate is our emission of greenhouse
let the model run through time and only human-generated processes, gases, and modelers need to select
simulate climate, from the past through and model runs that combine both. values to enter for future emissions
the present and into the future. If Repeatedly these studies have found if they want to predict future climate.
the computer simulation accurately that the model runs that incorporate Generally they will run their simula-
reconstructs past and present climate, both human and natural processes are tions multiple times, each time with
then that gives us confidence that it the ones that fit the real-world climate a different emission amount accord-
ing to a specified scenario. Differ-
ences between the results from such
scenarios tell us what influence these
different actions would have. You can
see results from such a comparison in
Figure 18.24 (p. 525).
Throughout this chapter, you will see
figures that show results of various mod-
els. In crafting its assessment reports, the
IPCC consults nearly two dozen major
models, considers the strengths and
weaknesses of each, and presents the
best summary its authors can muster.
Researchers are constantly testing
and evaluating their climate models. They CHAPTER 18 • Glob al Cli M aT e Chan G e
continually improve them by incorporat-
Figure 2 climate models divide earth’s
surface into a layered grid. Each grid box ing what is learned from new research
represents land, air, or water, and interacts and by taking advantage of what increas-
with adjacent grid boxes via the flux of ingly powerful computing technologies
materials and energy. Adapted from Bloom, will allow. As their work proceeds, we
Arnold J., 2010. Global climate change: Conver- can expect better and better predictions
gence of disciplines. Sinauer Associates, Sunderland, about what climate conditions we will
Mass. encounter in the future.

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