IAM Modeling Overview

photo shows cars braking in heavy traffic

The iPETS model is an integrated assessment model under development in NCAR's IAM group that links three component models: a demographic model, an energy-economic model (PET), and a climate and greenhouse gas cycle model (ISAM). The name iPETS derives from the original PET and ISAM models.

PET model

The PET model (Population-Environment-Technology model) is a global energy-economic model that provides the economic core of the iPETS model. It is a multi-region, multi-sector computable general equilibrium (CGE) model with forward looking behavior. The PET model has its origin in a DOE-funded project led by economist Larry Goulder at Stanford University in the 1990s that also included current NCAR collaborator Michael Dalton, now at NOAA. Continued development of the model by Dalton and colleagues, including those at the Population and Climate Change program at IIASA, focused in particular on disaggregating the household sector in order to better represent demographic changes such as aging and urbanization. Currently the standard configuration of the model has nine global regions, five production sectors, and four types of consumer goods. However the level of disaggregation is flexible, and the number of production sectors is being expanded to provide a more detailed representation of energy and agricultural industries.

Fortran source code for version 1.0 of the PET model is available here. This version was used to generate all of the scenarios in the 2010 PNAS paper on demographic influences on global carbon emissions. Documentation for the model can be found in the online supporting information to that paper, as well as in Dalton et al. (2008).

[PET v1.0] [PNAS 2010 input/output files] [PET v1.0 readme]


ISAM is the Integrated Science Assessment Model, a global model of greenhouse gas cycles and the climate system, developed by Atul Jain at the University of Illinois and colleagues. There are several versions of ISAM with varying degrees of complexity. The simplest version includes a simple climate model and globally aggregated carbon cycle model, with reduced form representations of other greenhouse gases. The most complex version includes a spatially explicit terrestrial model that includes both carbon and nitrogen cycles, and a 2.5-dimensional ocean model with representations of ocean biogeochemistry and sea ice. Currently iPETS links the PET model with the simpler version of ISAM, with work underway to link to the spatially explicit terrestrial model.

Demographic model

The demographic model under development will project population by age, sex, urban/rural residence, and household type for at least nine world regions. The population and urbanization model uses a multi-state, cohort component methodology. The household model is based on household headship rates specified by region, age, household size, and urban/rural residence. The demographic projections serve as an input to the PET model. We are also developing a method for downscaling regional population projections to the level of grid-cells, so that we can explore the implications of alternative spatial population scenarios for emissions and impacts.

The population, urbanization, and household scenarios developed for use in the 2010 PNAS paper are available here. Documentation for these scenarios can be found in the online supporting information to that paper, as well as in Jiang & O'Neill (2009).

[PNAS 2010 demographic scenarios]




CGD | Climate & Global Dynamics