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Model Report

Model for the Assessment of Greenhouse Gas Induced Climate Change/Scenario Generator

Last Revision Date: 10/07/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Model for the Assessment of Greenhouse Gas Induced Climate Change/Scenario Generator
Model Overview/Abstract:
MAGICC consists of a suite of coupled gas-cycle, climate and ice-melt models integrated into a single software package. The software allows the user to determine changes in greenhouse-gas concentrations, global-mean surface air temperature, and sea level resulting from anthropogenic emissions of greenhouse gases and aerosols.

SCENGEN constructs a range of geographically explicit climate change projections for the globe using the results from MAGICC together with AOGCM climate change information from the Coupled Model Intercomparison Project (CMIP3) archive. Projections of absolute (rather than relative) future climate conditions for any future date covered by the input emissions data can be obtained also. To produce these projections, SCENGEN adds the climate change information to observed baseline climate data (1980-99 means). These results are given as array files on a standard 2.5x2.5 degree latitude/longitude grid and displayed as maps.

Keywords: Climate change, model, IPCC, greenhouse gases, temperature, precipitation, aerosols, radiative forcing, sea level rise
Model Technical Contact Information:
Agency Contact
Jason Samenow

Developer Contact
Dr. Tom Wigley
National Center for Atmospheric Research

Model Homepage: http://www.cgd.ucar.edu/cas/wigley/magicc/ Exiting the EPA Site
Plans for further model development: New versions of MAGICC/SCENGEN (5.4 and 6.0) are under development

User Information Back to Top
Technical Requirements
Computer Hardware
Desktop PC
Compatible Operating Systems
Windows XP or Vista
Download Information
Fill out web form and download at:
Using the Model
Basic Model Inputs
Greenhouse Gas and Sulfur Dioxide Emissions
Basic Model Outputs
Greenhouse Gas Concentrations, Radiative Forcing, Temperature, Precipitation, and Sea Level Rise
User Support
Other User Documents
Availability of User Support
Reference user manual or contact model developer (Dr. Wigley)
User Qualifications
Requires basic understanding of climate change science (one introductory college level class in climate change science would provide a user with the requisite knowledge for running this model)

Model Science Back to Top
Problem Identification
The main aims of MAGICC are:
  • To compare the global-mean temperature and sea level implications of two different emissions scenarios.
  • To determine the sensitivity of the temperature and sea level results for any chosen emissions scenario to changes in and uncertainties in model parameters, such as the climate sensitivity. Basic uncertainty ranges and a "best-estimate" result are calculated by default. In addition, the user may select a set of model parameters that differs from the best-estimate set to examine uncertainties associated with model parameter uncertainties in more detail.

SCENGEN displays MAGICC output spatially. Beyond simple climate change scenario construction (i.e., changes in the mean climate state), SCENGEN produces spatial pattern results for: changes in inter-annual variability; two different forms of signal-to-noise ratio (to assess the significance of changes); probabilistic output (the default being the probability of an increase in the chosen climate variable); and a wide range of model validation statistics for individual models or combinations of models to assist in the selection of models for scenario development.

Summary of Model Structure and Methods
The climate model in MAGICC is an upwelling-diffusion, energy-balance model that produces global- and hemispheric-mean temperature output together with results for oceanic thermal expansion. The 5.3 version of the software is consistent with the IPCC Fourth Assessment Report, Working Group 1 (AR4). The MAGICC climate model is coupled interactively with a range of gas-cycle models that give projections for the concentrations of the key greenhouse gases. Climate feedbacks on the carbon cycle are therefore accounted for.

Global-mean temperatures from MAGICC are used to drive SCENGEN. SCENGEN uses a version of the pattern scaling method described in Santer et al. (1990) to produce spatial patterns of change from a data base of atmosphere/ocean GCM (AOGCM) data from the CMIP3/AR4 archive. The pattern scaling method is based on the separation of the global-mean and spatial-pattern components of future climate change, and the further separation of the latter into greenhouse-gas and aerosol components. Spatial patterns in the data base are normalized and expressed as changes per 1°C change in global-mean temperature. These normalized greenhouse-gas and aerosol components are appropriately weighted, added, and scaled up to the global-mean temperature defined by MAGICC for a given year, emissions scenario and set of climate model parameters. For the SCENGEN scaling component, the user can select from a number of different AOGCMs for the patterns of greenhouse-gas-induced climate.

Santer, B.D., Wigley, T.M.L., Schlesinger, M.E. and Mitchell, J.F.B., 1990: Developing Climate Scenarios from Equilibrium GCM Results. Max-Planck-Institut für Meteorologie Report No. 47, Hamburg, Germany, 29 pp.

Model Evaluation
A key aspect of MAGICC is that it is able to emulate the global-mean temperature results of more complex AOGCMs. This is done via calibration of MAGICC parameters (such as the climate sensitivity) to obtain best fits to the more complex models. In this mode, MAGICC has been used in all IPCC reports to date to extend and generalize AOGCM results. Technical details of MAGICC, details of AOGCM calibrations, and a range of sensitivity analyses are given in:

Meinshausen, M., S. C. B. Raper and T. M. L. Wigley (2008). "Emulating IPCC AR4 atmosphere-ocean and carbon cycle models for projecting global-mean, hemispheric and land/ocean temperatures: MAGICC 6.0." Atmospheric Chemistry and Physics Discussions 8: 6153–6272.

(Note this reference is to a beta version of the model,v6.0, which has not been publicly released. The description/discussion/analysis is germane to the current publicly available version, v5.3. The carbon cycle model in version 6.0 is able to emulate results for any of the models in the C4MIP archive. Version 5.3’s carbon cycle model has been calibrated to give results consistent with the mean of the models in this archive.)

Key Limitations to Model Scope
For some areas, there are still significant developments to be expected in the realism of both climate and carbon cycle models. For example, the current state-of-the-art carbon cycle models themselves face substantial uncertainties, related to, for example, nitrogen-fertilization, modeling of fire regimes, ocean chemistry, etc.

A second limitation (for SCENGEN) arises from the incomplete knowledge on the patterns of climate model response to aerosol forcing, particularly indirect forcing. The limitation here is that the required AOGCM ‘single forcing’ experiments have not yet been done with state-of-the-art AOGCMs.

Thirdly, there are uncertainties as to how AOGCM and carbon cycle models would behave for scenarios outside the tested range.

Case Studies
Santer, B.D., T.M.L. Wigley, M.E. Schlesinger, and J.F.B. Mitchell. 1990. Developing Climate Scenarios from Equilibrium GCM Results. Max-Planck-Institut für Meteorologie Report No. 47, Hamburg, Germany.

Wigley, T.M.L. and S.C.B. Raper. 1992. Implications for climate and sea level of revised IPCC emissions scenarios. Nature 357:293-300.

Wigley, T.M.L. 1993. Balancing the carbon budget. Implications for projections of future carbon dioxide concentration changes. Tellus 45B:409-425.

Raper, S.C.B., T.M.L. Wigley, and R.A. Warrick. 1996. Global sea level rise: past and future. In Sea-Level Rise and Coastal Subsidence: Causes, Consequences and Strategies, J. Milliman and B.U. Haq (eds.). Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 11-45.

Wigley, T.M.L. and S.C.B. Raper. 2001. Interpretation of high projections for global-mean warming. Science 293:451-454.

Wigley, T.M.L. and S.C.B. Raper. 2002. Reasons for larger warming projections in the IPCC Third Assessment Report. Journal of Climate 15:2945-2952.

Other information is given in the atmospheric chemistry, climate projections, and sea level chapters of the IPCC TAR Working Group 1 report, Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, D. Xiaosu, and K. Maskell (eds.). 2001. Climate Change 2001: The Scientific Basis. Cambridge University Press, New York.

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