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During the parallel phase, climate modelers will conduct new climate model experiments and produce new climate scenarios using the time series of emissions and concentrations from the four RCPs. The focus on a few, well-spaced RCPs will produce discernable climate change outcomes from one RCP to another, save computational resources, and thus make it possible to conduct additional new types of experiments.

Coupled Model Intercomparison Project Phase 5
A coordinated set of GCM experiments using the RCPs and other forcings was agreed by participating climate modeling groups through the Coupled Model Intercomparison Project Phase 5 (CMIP5) CMIP is a standard experimental protocol for studying the output of coupled ocean-atmosphere general circulation models (GCMs). It supports climate model diagnosis, validation, intercomparison, documentation and data access. The purpose of the CMIP5 experiments is to address outstanding scientific questions, improve understanding of climate, and provide estimates of future climate change that will be useful to those considering its possible consequences.

Two sets of climate scenarios will be developed using the RCPs, one focusing on the near term (to 2035) and the other extending to 2100 and beyond. The near-term climate projections (including ‘time-slice’ experiments for atmosphere-only models) will use the single mid-range RCP4.5 and will be run at higher resolution using more ensemble members. Another set of experiments will provide the basis for climate projections to the year 2100, with some experiments extended to 2300 for comparative analysis of the long-term climate and environmental implications of different mitigation scenarios or pathways. More information can be found in the CMIP5 Experiment Design page.

Pattern scaling
“Pattern-scaling” methods, which use the outcomes of simple climate models to scale the patterns of climate change produced by complex climate models to correspond to different emissions scenarios, will be further evaluated and developed. This method will be used in the integration phase for creating climate scenarios corresponding to new socio-economic scenarios whose radiative forcing levels are not consistent with any of the RCPs. References for pattern scaling are found below.

Status and quality control
Climate model data from CMIP3 simulations, which were featured in the 4th Assessment Report, were spot-checked for adherence to certain standards, but more comprehensive procedures for guarding against flawed data were not developed. Consequently, analysts using the data were often the first to discover any problems. For CMIP5, a more complete suite of quality control checks (on data and documentation) have been developed by DDC partners and approved by the WCRP. These checks will be run at the archive centers as the data comes in from the modeling centers. Publication of unchecked data is expected to start in late 2010, quality control checks of data will be completed shortly after data is initially published, and prospective users will not be encouraged to use data until these checks are complete. Digital Object Identifiers (DOIs) will be assigned to data that has passed all quality control checks to enable unambiguous data citation.

Initially, data will be available only from a few models, which may not represent the true range of results from the full population of models. Nevertheless, sufficient data for preliminary studies should become available by mid-2011, and all participating models are expected to contribute some results by the first quarter of 2012. Climate model data and more information on CMIP5 as it progresses can be accessed from the CMIP5 web site (

References for pattern scaling:

Mitchell, J. F. B., T. C. Johns, M. Eagles, W. J. Ingram, and R. A. Davis, 1999: Towards the construction of climate change scenarios. Climatic Change, 41, 547–581.

Mitchell, T. D., 2003: Pattern scaling. An examination of the accuracy of the technique for describing future climates. Climatic Change, 60, 217–242.

Ruosteenoja K, Tuomenvirta H, Jylhä K (2007) GCM-based regional temperature and precipitation change estimates for Europe under four SRES scenarios applying a super-ensemble patternscaling method. Climatic Change 81, 193–208.

Content last modified: 1 May 2014