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Multi-model ensemble (MME)

When a global climate model is run to provide a projection of future climate it produces a 'simulation'. Multiple simulations form an ensemble. A multi-model ensemble or MME, is a large number of climate model simulations created by using many different international Climate model.

The MME used to create UKCP09, is composed of climate projections from 12 different models.

In detail

Because of incomplete understanding of the physics of the climate system, different climate modelling groups around the world represent climate processes in different ways in their models. As a result, there are differences in the projections of future climate. This is therefore, a source of uncertainty in climate projections (known as structural error).

In order to address this source of uncertainty in UKCP09, single climate projections from 12 climate models that have been used in international model comparisons (such as IPCC's CMIP3) are used to generate a multi-model ensemble. These projections are then combined with the perturbed physics ensemble (created using variants of the Met Office Hadley Centre climate model HadSM3), to produce the Probabilistic climate projection in UKCP09.

An MME is distinct from a Perturbed physics ensemble (PPE), in that it emphasises structural errors between different climate models rather than parameter errors within a single model configuration.

Find out more

  • An overview of how probabilistic projections are created and presented in UKCP09 is described in Box 3 of the UKCP09 Briefing Report.
  • More details are provided in Chapter 3 of the UKCP09 Climate Change Projections report. This includes an overview of the methodology and a discussion about the interpretation of UKCP09 probabilistic projections.
  • A comparison of the UKCP09 methodology with an alternative method is described in Annex 2.3 of the climate change projections report and summarised in Box 4 of the UKCP09 Briefing Report.
  • A discussion of sources of uncertainty in the UKCP09 probabilistic projections is available in Annex 2.4 of the climate change projections report.
  • CMIP3 data is also used in UKCP09 for the marine projections, where it is used to estimate the time-mean sea level rise. An overview of how CMIP3 data was used in UKCP09 is provided in section 2.1 of the Marine & Coastal Projections report. Section 3.2 of that report describes in more detail the approach adopted in UKCP09 to provide future sea level projections.