Model Source Code for the MAGICC Coupled Carbon–Nitrogen Cycle Model – CNit

MAGICC_CNit.py is the main Python source code for CNit v2.0 — the coupled carbon–nitrogen cycle model in MAGICC. The other Python files included in this repository provide essential supporting functions for MAGICC_CNit.py. para_df_CMIP6.csv contains parameter names, units, and calibrated values from 15 CMIP6 Earth system models. The previous CNit v1.0 model and its calibrated parameters are available at https://doi.org/10.5281/zenodo.12204421 (Tang et al., 2024). A detailed description and calibration of CNit v1.0 are published in: Tang, G., Nicholls, Z., Norton, A., Zaehle, S., and Meinshausen, M.: Synthesizing global carbon–nitrogen coupling effects – the MAGICC coupled carbon–nitrogen cycle model v1.0, Geosci. Model Dev., 18, 2193–2230, https://doi.org/10.5194/gmd-18-2193-2025, 2025. MAGICC homepage: https://magicc.org MAGICC Fortran source code (open access): https://gitlab.com/magicc/magicc CNit homepage: https://github.com/gangtang-au/cnit CNit documentation: https://cnit.readthedocs.io/en/latest/ Update 1 Jan 2026: New model version (CNit v2.1) and calibration released: GitHub public repository: https://github.com/gangtang-au/cnit (a ready-to-use Python package) Tang, G. (2026). CNit Model Calibration and Results [Data set]. Zenodo. https://doi.org/10.5281/zenodo.18116573 (CNit v2.1 calibrated against TRENDY DGVMs) 2. This page may no longer be maintained, as the source code has been moved to the public GitHub repository and the documentation is now hosted on Read the Docs. Going forward, we will continue to maintain the model source code on GitLab and archive calibration and related results at Zenedo.