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Global climate model (GCM)

A Global Climate Model (GCM is a mathematical model of the general circulation of the planet's atmosphere or oceans based on mathematic equations that represent physical processes.

These equations are the basis for complex computer programs that simulate the atmosphere or oceans of the Earth. GCMs are widely applied for weather forecasting, understanding the climate, and projecting climate change. HadCM3 is the GCM used for the UKCP09 scenarios.

In detail

HadCM3 is a fully coupled ocean-atmosphere GCM (AOGCM) that has been used in UKCP09 for simulating 17 transient projections of climate change. This means that both the atmospheric and the oceanic processes were included in the modelling, hence providing a realistic representation of the climatological processes.

HadCM3 was developed at the Met Office Hadley Centre and is one of the models used by the IPCC and in the Coupled Model Intercomparison Project (CMIP3).

Find out more


  • More details about the climate models used in UKCP09 are given in  in the UKCP09 Climate Change Projections report. A commentary about the strengths and weaknesses of climate models is given in .
  • The 11-member RCM data is available to users. It is described in the Reports & Guidance section and in  of the UKCP09 Climate Change Projections report.
  • IPCC Fifth Assessment Report, Working Group 1 report The Physical Science Basis, Chapter 8