MAGICC_CN.py is the model source code (Python) for the coupled carbon-nitrogen cycle in MAGICC. para_dict_A is a dict of parameters and their values for the calibration. MAGICC homepage: https://magicc.org/ 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. Update 18 Jun 2025: 1. New model version (CNit v2.0) and calibration released: CNit v2.0 model description and calibration preprint: Tang, G., Zaehle, S., Nicholls, Z., Norton, A., Ziehn, T., & Meinshausen, M. Understanding the Drivers of Carbon-Nitrogen Cycle Variability in CMIP6 ESMs with MAGICC CNit v2.0: Model and Calibration Updates. ESS Open Archive. June 16, 2025. https://doi.org/10.22541/essoar.175008280.09297369/v1 CNit v2.0 model source code and calibration: Tang, G., Zaehle, S., Nicholls, Z., Norton, A., Ziehn, T., & Meinshausen, M. (2025). Model Source Code for the MAGICC Coupled Carbon–Nitrogen Cycle Model – CNit. Zenodo. https://doi.org/10.5281/zenodo.15569387 2. CNit v1.0 model description and calibration paper: 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. Update 30 Jan 2025: Add the custom Python modules required for MAGICC_CN.py, including exceptions.py, unit_registry.py, timeseries.py, utils.py, and maths.py. Update 19 Dec 2024: Revised paper title: Synthesizing Global Carbon-Nitrogen Coupling Effects – the MAGICC Coupled Carbon-Nitrogen Cycle Model v1.0 Add a para_dict_A.csv in case the .pkl file cannot be opened.