Hammitt et al. Model

In a series of papers, Hammitt and his colleagues have presented a simple integrated model that represents policy choices in two periods: the present, under uncertainty, and at a future time when certain relevant uncertainty has been resolved.

The model includes a base-case trajectory for emissions of greenhouse gases, expressed in CO2 equivalents, from which emissions can be reduced by two classes of abatement measures: energy conservation, which is represented as a low-cost decline over time to a lower limit in energy intensity (modeled as a logistic function); and fuel-switching, represented as the replacement of emitting capital equipment by higher-cost non-emitting equipment. Both classes of measures can be enacted at various levels.

Concentrations are modeled by a linear impulse-response function and global-average temperature by a simple model incorporating energy-balance and a simple ocean with upwelling and diffusion, which allows specification of various levels of climate sensitivity. Damages are modeled in two ways: either by specifying a maximum permissible change in global-average temperatures or by hypothesizing a simple convex damage function, whose parameters can be varied to match the assumptions of other work.

The Hammitt et al. model has been employed to examine two-period decision problems with one or two world regions. One study examined a single-actor sequential decision problem, in which current-period abatement decisions are revised in a future period, when uncertainty regarding climate sensitivity and maximum temperature has been resolved ( Hammitt, Lempert, and Schlesinger 1992). Another examined interactive decisions by two world regions, setting abatement strategies independently in the first period while knowing that in a future period, with more knowledge about sensitivity, they will abate to meet a specified temperature target with a fixed burden-sharing rule Hammitt 1995; Hammitt and Adams 1995).

The next section is The DICE Model.

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Sources

Parson, E.A. and K. Fisher-Vanden, Searching for Integrated Assessment: A Preliminary Investigation of Methods, Models, and Projects in the Integrated Assessment of Global Climatic Change. Consortium for International Earth Science Information Network (CIESIN). University Center, Mich. 1995.

Suggested Citation

Consortium for International Earth Science Information Network (CIESIN). 1995. Thematic Guide to Integrated Assessment Modeling of Climate Change [online]. University Center, Mich.
CIESIN URL: http://sedac.ciesin.org/mva/iamcc.tg/TGHP.html

Acknowledgement

This work, including access to the data and technical assistance, is provided by CIESIN, with funding from the National Aeronautics and Space Administration under Contract NAS5-32632 for the Development and Operation of the Socioeconomic Data and Applications Center (SEDAC).

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