REFUGE4 is an open-source tool to calculate climate impacts of emission scenarios, including changes in concentrations, radiative forcing, and temperature. The tool covers CO2, CH4, and N2O and can calculate negative emissions. It follows the calculation methods of the IPCCs sixth assessment report reproducing the main indicators from the IPCC's report. The results are printed annually up to 2500 and for user-given time intervals. The tool can be used also to study how GWP and GTP factors are calculated. REFUGE4 is a completely revised version of previous REFUGE versions. Detailed documentation and validation are presented in attached files. In addition, validation calculations can be repeated with sheets attached to the distributed version of REFUGE4, https://zenodo.org/doi/10.5281/zenodo.8220334. The link points to the latest published version. The tool is shared under Attribution 4.0 International (CC BY 4.0)