Can you calculate the CO2 emissions for your city now or for the future? Ubigu Ltd, Tietotakomo, Gispo Ltd, Finnish Environment Institute and City of Tampere in Finland have crafted an open source climate tool during spring 2019. It was created using QGIS, PostGIS, GeoServer and Oskari map service for detecting what areas have more CO2 emissions than others taking into account also carbon sinks. The climate tool is used to do better land use planning to achieve CO2 neutral city. The base of the calculation comes from 250*250 m urban zone grid by Finnish Environment Institute where we have information about workplaces, demography and buildings. The tool utilizes also different climate parameters and combines the information to the grids. The user interface was created with QGIS and where analysis was driven with algorithms stored to PostGIS database. The tool also provides CO2 visualisation of the analysis results via GeoServer and in the end Oskari map service. In this presentation we will go through the background and demonstrate the use of the tool.