Coupled model intercomparison project
In climatology, the Coupled Model Intercomparison Project (CMIP) is a collaborative framework designed to improve knowledge of climate change, being the analog of Atmospheric Model Intercomparison Project (AMIP) for global coupled ocean-atmosphere general circulation models (GCMs). It was organized in 1995 by the Working Group on Coupled Modelling (WGCM) of the World Climate Research Programme’s (WCRP). It is developed in phases to foster the climate model improvements but also to support national and international assessments of climate change.
The Program for Climate Model Diagnosis and Intercomparison at Lawrence Livermore National Laboratory has been supporting the several CMIP phases by helping WGCM to determine the scope of the project, by maintaining the project's data base and by participating in data analysis. CMIP has received model output from the pre-industrial climate simulations ("control runs") and 1% per year increasing-CO2 simulations of about 30 coupled GCMs. More recent phases of the project (20C3M, ...) include more realistic scenarios of climate forcing for both historical, paleoclimate and future scenarios.
CMIP Phases 1 and 2
According to Lawrence Livermore National Laboratory PCMDI, the response to the CMIP1 announcement was very successful and up to 18 global coupled models participated in the data collection representing most of the international groups with global coupled GCMs. In consequence, at the September 1996 meeting of CLIVAR NEG2 in Victoria, Canada, it was decided that CMIP2 will be an inter-comparison of 1% per year compound CO2 increase integrations (80 years in length) where CO2 doubles at around year 70.
CMIP Phase 3
During 2005 and 2006, a collection of climate model outputs was coordinated and stored by PCMDI. The climate model outputs included simulations of past, present and future climate scenarios This activity enabled those climate models, outside the major modeling centers to perform research of relevance to climate scientists preparing the IPCC Fourth Assessment Report (IPCC-AR4). For the CMIP3 a list of 20 different experiments were proposed, and the PCMDI kept the documentation of all the global climate model involved. Additional information and data-sets are in.
CMIP Phase 5
The most recently completed phase of the project (2010-2014) is CMIP5. CMIP5 included more metadata describing model simulations than previous phases. The METAFOR project created an exhaustive schema describing the scientific, technical, and numerical aspects of CMIP runs which was archived along with the output data.
A main objective of the CMIP5 experiments is to address outstanding scientific questions that arose as part of the IPCC AR4 process, improve understanding of climate, and to provide estimates of future climate change that will be useful to those considering its possible consequences. The IPCC Fifth Assessment Report summarizes information of CMIP5 experiments, while the CMIP5 experimental protocol was endorsed by the 12th Session of the WCRP Working Group on Coupled Modelling (WGCM). Additional information and data-sets are in.
CMIP Phase 6
Planning meetings for Phase 6 began in 2013, and an overview of the design and organization was published in 2016. By 2018 CMIP6 had endorsed 23 Model Intercomparison Projects (MIPs) involving 33 modeling groups in 16 countries. A small number of common experiments were also planned. The deadline for submission of papers to contribute to the IPCC 6th Assessment Report Working Group I is early 2020.
The structure of the CMIP6 has been extended with respect to CMIP5 by providing an equivalent framework named CMIP Diagnostic, Evaluation and Characterization of Klima (DECK), together with a set of Endorsed MIPs to improve the description of aspects of climate models beyond the core set of common experiments included in DECK. However, CMIP-Endorsed Model Intercomparison Projects (MIPs) are still built on the DECK and CMIP historical simulations, therefore their main goal is just to address a wider range of specific questions . This structure will be kept in future CMIP experiments.
CMIP6 also aims to be consistent regarding common standards and documentation. To achieve that it includes methods to facilitate a wider distribution and characterization of model outputs, and common standard tools for their analyses. A number of guides has been created  for data managers, modelers and users.
A set of official/common forcings datasets are available for the studies under DECK, as well as several MIPS. That allows for more sensible comparisons on the model ensemble created under the CMIP6 umbrella.
- Historical Short-Lived Climate Forcers (SLCF) and GHG (CO2 and CH4) Emissions
- Biomass Burning Emissions
- Global Gridded Land-use Forcing Datasets: data are available from 
- Historical greenhouse gases (GHG) concentrations: a full description is published  via the CMIP6 Special Issue publication 
- Ozone Concentrations and Nitrogen (N)-Deposition: additional information at , while the description of ozone radiative forcing based on this dataset is published.
- Aerosol Optical Properties and Relative Change in Cloud Droplet Number Concentration: Data are available as supplement to Stevens et al. (2016) at  
- Solar Forcing: Datasets are available from  and the description published 
- Stratospheric Aerosol Data Set: data are available from 
- AMIP Sea Surface Temperature and Sea Ice Datasets
Beyond these historical forcings, CMIP6 also has a common set of future scenarios comprising land use and emissions as required for the future Shared Socio-economic Pathway (SSP) and Representative Concentration Pathways (RCPs).
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- Checa-Garcia, Ramiro; Hegglin, Michaela I.; Kinnison, Douglas; Plummer, David A.; Shine, Keith P. (2018-04-06). "Historical Tropospheric and Stratospheric Ozone Radiative Forcing Using the CMIP6 Database". Geophysical Research Letters. 45 (7): 3264–3273. doi:10.1002/2017gl076770. ISSN 0094-8276.
- Stevens, B.; Fiedler, S.; Kinne, S.; Peters, K.; Rast, S.; Müsse, J.; Smith, S. J.; Mauritsen, T. (2017-02-01). "MACv2-SP: a parameterization of anthropogenic aerosol optical properties and an associated Twomey effect for use in CMIP6". Geosci. Model Dev. 10 (1): 433–452. doi:10.5194/gmd-10-433-2017. ISSN 1991-9603.
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