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Thematic Guide to Integrated Assessment Modeling
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Population Growth
The other dominant long-term driver of emissions, along with technological change, is population growth. In the long term, population growth drives paths of global greenhouse emissions, but its fundamental determinants are not understood. Currently developed nations have undergone demographic transitions when fertility rates fell sharply, but the primary causes are not understood, nor are whether, when, and how they can be projected to occur in nations that are now developing.With so little knowledge on which to build causal models, the standard method in integrated assessment is to take external scenarios of population growth rates, either global or specific to particular regions, normally specifying several distinct scenarios. As with any other important parameter, it would be possible to collapse multiple scenarios into a probability distribution and propagate its effects through a modeling exercise. No present integrated assessment project for climate change takes explicit account of inter-regional migration. As with technology, population growth and movement is ultimately dependent upon economics, policies, and environmental changes, but the determinants of these are not known. Using a variety of scenarios as inputs helps compensate for ignorance of these relationships.
The next section is Land Use.
