CAMS global forecast test data is available from 05-2025 onwards from the MARS catalogue. A daily updated test dataset is also available for the most recent 3 days on the FTP server.

MARS 

If you have access and you can retrieve data from the MARS catalogue, please use the following keywords for the CAMS global forecast test data:

class=mc
expver=0080

Here the link to directly access the data in the MARS catalogue (please remember that ecCodes version 2.44.0 or later is required to handle the full range of parameters of current CAMS data).

Atmosphere Data Store (ADS)

If you cannot retrieve data from the MARS catalogue, you can retrieve the data from the cams-global-atmospheric-composition-forecasts-test dataset using the API.

If you haven't done it yet, you will need to create an ECMWF account and accept the terms of use.

The test data is only accessible through the ADS API service, and it is not possible to use the interactive web interface to download it.

You can use existing requests for the CAMS global atmospheric composition dataset by replacing the dataset name with "cams-global-atmospheric-composition-forecasts-test".

API Example

Select only European domain, 10 dates and day 1 forecast (from hour 0 to 24):

import cdsapi
 
c = cdsapi.Client()
 
c.retrieve(
    'cams-global-atmospheric-composition-forecasts-test',
    {
        'date':          '2026-01-01/2026-01-10',
        'type':          'forecast',
        'format':        'netcdf_zip',
        'model_level':   '137',                    # Lowest model level only
        'variable':    [ 'biogenic_secondary_organic_aerosol_mass_mixing_ratio',
                         'anthropogenic_secondary_organic_aerosol_mass_mixing_ratio',
                         'glyoxal',
                         'secondary_organic_aerosol_optical_depth_550nm',
                         'total_column_glyoxal' ], # See other variables at:
        'time':          '00:00',                  # https://ads.atmosphere.copernicus.eu/datasets/cams-global-atmospheric-composition-forecasts?tab=download
        'leadtime_hour': [h for h in range(0,25,3)],
        'area':          [70, -35, 35, 60]         # [N,W,S,E] Europe area boundaries
    },
    'cams_test_20260101_10.nc.zip')

ECMWF data portal (aux.ecmwf.int; SFTP/FTP/HTTPS data access)

The test dataset is available through ECMWF data portal (aux.ecmwf.int; SFTP/FTP/HTTPS data access) in these directories:

/DATA/CAMS_GLOBAL_TEST
/DATA/CAMS_GLOBAL_ADDITIONAL_TEST
/DATA/CAMS_EUROPE_BC_TEST

You can use your normal FTP account to access the data. Details about filenames convention or list of available parameters can be found at CAMS Knowledge Base.

If everything else fails ...

... you can always contact us on ECMWF Support Portal creating a ticket "Request for CAMS global test dataset" as a subject and specify:

• which parameters and levels
• which time period
• forecast step / time frequency
• which geographical area
• which data format you require

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