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Parameterisation scheme

A set of semi-empirical or mathematical equations that are used to represent sub-grid scale physical processes that are not explicitly represented in a (climate) model, such as radiation, clouds and turbulent fluxes.

In detail

It is not always possible to incorporate every physical process that operates in the climate system into a climate model. This may be because the processes involved operate at a spatial resolution that is too fine to be incorporated into a model or due to computational constraints. Consequently, parameterisation schemes are developed to partially address this issue. A fundamental requirement in a parameterisation scheme is the specification of likely values (or a range of likely values) that a particular parameter might take. These parameterisation schemes relate the larger scale processes that are represented in the climate model to the smaller scale (or sub-grid scale) processes through mathematical equations.

Developing a parameterisation scheme to represent sub-grid scale processes involves a number of considerations, including the model configuration used, judgments on what a particular climate modelling centre considers most important to represent, the numerical optimisation schemes used and the computing power available to individual centres. As a result of these factors, different climate modelling centres implement different but equally plausible, parameterisation schemes. Consequently, different international climate models produce different projections of climate change.

  • More details about parameterisation schemes are given in in the UKCP09 Climate change projections report. A commentary about the strengths and weaknesses of climate models is given in .
  • An overview of how probabilistic projections are created and presented in UKCP09 is described in of the UKCP09 Briefing report. More details are provided in Chapter 3 of the UKCP09 Climate change projections report, including an overview of the methodology in .
  • A comparison of the UKCP09 methodology with an alternative method is described in , and summarised in of the UKCP09 Briefing report.

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