Input data set: Atmospheric composition (ISIMIP4a)

The atmospheric greenhouse gas concentration dataset provides observed atmospheric CO₂ and CH₄ concentrations for ISIMIP4a impact simulations. It combines the CMIP7 historical greenhouse gas concentration dataset with recent observations from NOAA to provide continuous concentration time series extending beyond the CMIP7 historical period.

The dataset contains atmospheric greenhouse gas mole fractions expressed as dry-air mixing ratios. It includes both CO₂ (ppm) and CH₄ (ppb) concentration time series at annual and monthly temporal resolution.

The time series are compiled from two periods:

1850–2022: Historical concentrations from the CMIP7 Input4MIPs greenhouse gas concentration dataset CR-CMIP-1-0-0 (v20250228).
2023 onwards: Observed atmospheric greenhouse gas concentrations from the NOAA Global Monitoring Laboratory (GML).

The resulting dataset provides continuous annual and monthly concentration time series for both greenhouse gases, suitable for impact models requiring either annual or monthly atmospheric forcing.

Atmospheric greenhouse gas concentrations are compiled from two complementary sources:

Historical period (1850–2022): The CMIP7 Input4MIPs greenhouse gas concentration dataset CR-CMIP-1-0-0 (v20250228), developed by the Climate Resource consortium and distributed through the Input4MIPs infrastructure:
https://input4mips-cvs.readthedocs.io/en/latest/dataset-overviews/greenhouse-gas-concentrations/
Recent observations (2023 onwards): Atmospheric greenhouse gas observations provided by the NOAA Global Monitoring Laboratory (GML):
https://gml.noaa.gov/ccgg/trends/gl_data.html and https://gml.noaa.gov/ccgg/trends_ch4/

For both CO₂ and CH₄, the historical Input4MIPs records are extended with the corresponding NOAA observations to produce continuous annual and monthly greenhouse gas concentration time series for ISIMIP4a.

For ISIMIP participants, these files are available for download on the DKRZ server:
/work/bb0820/ISIMIP/ISIMIP4a/InputData/climate/atmosphere_composition/