MAGICC

The Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC) is a simple climate model, also called a reduced-complexity model.^1,3 It joins a global carbon cycle to a climate model and works only at the scale of the globe and its hemispheres.^1,6 It has been developed continually for more than 30 years.¹ It has informed IPCC assessments; most recently, Working Group 3 of the Sixth Assessment Report used it to sort emissions scenarios by the warming they imply, and several integrated assessment modelling groups use it.³

Given the emissions of a scenario, MAGICC calculates concentrations of greenhouse gases and other climate drivers such as air pollutants, the radiative forcing they cause (the extra energy they trap), global annual mean surface air temperature and the heat taken up by the ocean.⁶ It is an energy-balance model with an upwelling-diffusion ocean, and reports temperature for the globe and for each hemisphere.⁶ It can run once with one set of parameters, or in a probabilistic set-up that estimates the chance of staying below a temperature level for a given emissions path.⁶ Version 6 is described by Meinshausen, Raper and Wigley in Atmospheric Chemistry and Physics, 2011.⁵ They calibrated it against the larger ocean-atmosphere models of the IPCC's Fourth Assessment Report, and for the scenarios tested its average result came within 2.2% of theirs.⁵

There are three ways in. Version 7.5.3, with the probabilistic parameter set used in the IPCC's Sixth Assessment Report, can be downloaded as a Windows or Linux program after registering.^1,2 The program is under CC BY 4.0, and the probabilistic set is under CC BY-NC 4.0, which forbids commercial use.² The makers also ask users who plan a paper or presentation to contact them at the start, not to pass copies on, and to discuss co-authorship when the model is central to the work.² A web interface at live.magicc.org runs single or probabilistic runs without installing anything or writing code.^1,2 Development from version 7.6 onward is open on GitLab.^1,2

The open code is under a 3-clause BSD licence with one added clause.^3,4 Anyone who uses or redistributes a modified version must, within a month, register the fork by a pull request to the magicc-forks repository, with a link to its code and the parameter settings behind any results.⁴ Using the model unmodified carries only the BSD terms.^3,4 The licence is issued by MAGICC7 Plus IP Co Ltd, and the website is maintained by Climate Resource.^1,3 The rewrite is somewhere between an alpha and a beta release, with little documentation yet on how to contribute.³ The latest tags are alpha releases of 7.6.0 from December 2024.⁷

MAGICC is also the climate component of IIASA's MESSAGEix-GLOBIOM framework.⁶ Like FaIR and Hector, it answers a global question: how much the world warms under a given emissions path.^1,6 A study of one city or watershed can take that path and its range of outcomes as a starting point before turning to regional projections such as the IPCC's; see Weather and climate.