Global climate projections are climate model simulations which have been generated by multiple independent climate research centres in an effort coordinated by the World Climate Research Program (WCRP) and assessed by the Intergovernmental Panel on Climate Change (IPCC). These climate projections underpin the conclusion of the IPCC 5th Assessment Report (published in 2013) that “Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems”.
The Climate Model Intercomparison Project (CMIP) was established in 1995 by the World Climate Research Program (WCRP) to provide climate scientists with a database of coupled Global Circulation Model (GCM) simulations.
The CMIP process involves institutions (such as national meteorological centres or research institutes) from around the world running their climate models with an agreed set of input parameters. The modelling centres produce a set of standardised output, when combined these produce a multi-model dataset that can be shared internationally between modelling centres and the results compared.
Analysis of the CMIP data allows for improving understanding of
Comparison of different climate models allows for
The fifth phase of Coupled Model Intercomparison Project (CMIP5, 2008-2012) involved 24 modelling centres running their climate models under the prescribed conditions to produce the multi-model dataset designed to advance our knowledge of climate (Taylor et al. 2012). The scientific analyses from CMIP5 were used extensively in the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (IPCC AR5), published in September 2013.
The CMIP5 data archive is distributed through the Earth System Grid Federation (ESGF) though many national centres have either a full or partial copy of the data for their scientists to utilise. A quality-controlled subset of CMIP5 data are made available through the Climate Data Store (CDS) for the users of the Copernicus Climate Change Service (C3S).
To obtain full details of the whole CMIP5 data archive please refer to the full documentation at the Program for Climate Model Diagnosis & Intercomparison (PCMDI). An introductory factsheet for an overview of an IPCC subset also provides a useful guide to the CMIP5 data.
The sixth phase of the Coupled Model Intercomparison Project (CMIP6) is in progress. Approximately 40 modelling centres are participating in this phase of CMIP. During the period 2019-2020 modelling centres are standardising and releasing their data to be distributed internationally through the Earth System Grid Federation (ESGF). It is expected that the Climate Data Store (CDS) will begin making CMIP6 data available from 2021.
The global climate projections in the Climate Data Store (CDS) are a quality-controlled subset of the wider CMIP5 data. These data represent only a small subset of CMIP5 archive. A set of 50 core variables from the CMIP5 archive were identified for the CDS. These are the most used of the CMIP5 data. These variables are provided from seven of the most popular CMIP5 experiments.
The CDS subset of CMIP5 data have been through a metadata quality control procedure which ensures a high standard of reliability of the data. It may be for example that similar data can be found in the main CMIP5 archive however these data come with no quality assurance and may have metadata errors or omissions. The quality-control process means that the CDS subset of CMIP5 data is further reduced to exclude data that have metadata errors or inconsistencies. It is important to note that passing of the quality control should not be confused with validity: for example, it will be possible for a file to have fully compliant metadata but contain gross errors in the data that have not been noted. In other words, it means that the quality control is purely technical and does not contain any scientific evaluation (for instance consistency check).
The CDS-CMIP5 subset consists of the following CMIP5 experiments
The models included in the CDS-CMIP5 subset are detailed in the table below, these include most of the models from the main CMIP5 archive. However a small number of models were not included as the data from the models have a research-only restriction on their use, all data in the CDS are released without restriction, therefore, the MIROC and MRI models from Japan are not included.
The following table contains a list of the global climate models in use in the CDS and a brief description of the model where this information is readily available, further details can be found on the Earth System Documentation site.
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For pressure level data the model output is available on the pressure levels according to the table below. Note that not all models provide the same pressure levels.
Frequency | Number of Levels | Pressure Levels (hPa) |
Daily | 8 | 1000., 850., 700., 500., 250., 100., 50., 10. |
Monthly | 17 | 1000., 925., 850., 700., 600., 500., 400., 300., 250., 200., 150., 100., 70., 50., 30., 20., 10. |
Each modelling centre typically run the same experiment using the same model several times to confirm the robustness of results and inform sensitivity studies through the generation of statistical information. A model and its collection of runs is referred to as an ensemble. Within these ensembles, three different categories of sensitivity studies are done, and the resulting individual model runs are labelled by three integers indexing the experiments in each category.
Each member of an ensemble is identified by a triad of integers associated with the letters r, i and p which index the “realization”, “initialization” and “physics” variations respectively. For instance, the member "r1i1p1" and the member "r1i1p2" for the same model and experiment indicate that the corresponding simulations differ since the physical parameters of the model for the second member were changed relative to the first member.
It is very important to distinguish between variations in experiment specifications, which are globally coordinated across all the models contributing to CMIP5, and the variations which are adopted by each modelling team to assess the robustness of their own results. The “p” index refers to the latter, with the result that values have different meanings for different models, but in all cases these variations must be within the constraints imposed by the specifications of the experiment.
For the scenario experiments, the ensemble member identifier is preserved from the historical experiment providing the initial conditions, so RCP 4.5 ensemble member “r1i1p2” is a continuation of historical ensemble member “r1i1p2”.
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Data Format
The CDS subset of CMIP5 data are provided as NetCDF files. NetCDF (Network Common Data Form) is a file format that is freely available and commonly used in the climate modelling community. See more details: What are NetCDF files and how can I read them
A CMIP5 NetCDF file in the CDS contains:
The metadata provided in NetCDF files adhere to the Climate and Forecast (CF) conventions (v1.4 for CMIP5 data). The rules within the CF-conventions ensure consistency across data files, for example ensuring that the naming of variables is consistent and that the use of variable units is consistent.
When you download a CMIP5 file from the CDS it will have a naming convention that is as follows:
<variable>_<cmor_table>_<model>_<experiment>_<ensemble_member>_<temporal_range>.nc
Where
Please note that the CIMP5 filenames in the CDS do not contain a version tag as opposed to the file names used for the corresponding data in the ESGF nodes, where you have the versioning information. In the CDS we serve the latest version of the CMIP5 data which is now complete (no new version expected). To find the version number of this latest version published in the CDS, see the metadata of the netcdf file. This contains a track identity of the file and an http address for each file from where the version number information may be checked.
The CDS subset of the CMIP5 data have been through a set of quality control checks before being made available through the CDS. The objective of the quality control process is to ensure that all files in the CDS meet a minimum standard. Data files were required to pass all stages of the quality control process before being made available through the CDS. Data files that fail the quality control process are excluded from the CDS-CMIP5 subset or if possible the error is corrected and a note made in the history attribute of the file. The quality control of the CDS CMIP5 subset checks for metadata errors or inconsistencies against the Climate and Forecast (CF) Conventions and a set of CMIP5 specific file naming and file global metadata conventions.
Various software tools have been used to check the metadata of the CDS CMIP5 data:
The data within the files were not individually checked however where it was known that a variable from a given model had a gross error, e.g in the sign convention of a flux, then these data were also omitted from the CDS-CMIP5 subset.
It is important to note that passing of these quality control tests should not be confused with validity: for example, it will be possible for a file to be fully CF compliant and have fully compliant CMIP5 metadata but contain gross errors in the data that have not been noted.
For a detailed description of all the quality control of the data please see the accompanying documentation
This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation Agreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |