Search site

Modelling uncertainty

Modelling uncertainty refers to the imperfect representation of the earth's climate system by climate models.

In detail

Models provide a mathematical representation of many of the processes in the climate system, which are based on a mixture of theory, observations and experimentation. A level of uncertainty in climate models is unavoidable.

Different modelling groups seek to represent climate processes in the best possible way in their models and, because this is to an extent a subjective judgement, this leads to different groups adopting different representations. Not surprisingly, this leads to different strengths (and even, in the case of clouds, directions) of feedbacks in the models, and hence different projections of future changes. This is the structural error component of modelling uncertainty.

It is not possible to explicitly incorporate every physical process operative in the climate system, into a climate model. This is often because the processes involved operate at too fine a spatial resolution, to be incorporated into a model, due to computational constraints. Consequently, parameters are assigned to represent these processes, involving a mixture of theory, observations, experimentation and expert judgement. Definition of parameter values is seldom precise enough to be able to assign accurate values. This is the parameter error component of modelling uncertainty.

Find out more


  • An overview of the uncertainties associated with climate modelling is described in  of the UKCP09 Briefing Report.
  • More details about uncertainties are provided in  of the UKCP09 Climate Change Projections report. A discussion of sources of uncertainty in the UKCP09 probabilistic projections is available in .
  • IPCC Fifth Assessment Report, Working Group 1 report The Physical Science Basis , Chapter 9.