At present, the Arctic climate is changing much more rapidly than the rest of the globe, and yet the observational data density in the region is low. Permafrost is an important element of the terrestrial Cryosphere, which is strongly affected by changes in Arctic energy and water cycle. There is an urgent need to realistically incorporate permafrost in global modelling frameworks, such as Earth System Models. Evaluating and parameterising these process-based models especially requires simultaneous measurements of interacting variables. Here we present an example of such a long-term data set, from the Bayelva site at Ny-Ålesund, Svalbard, where meteorology, energy balance components and subsurface observations have been made for the last 20 years. Since the data provide observations of temporally variable parameters that mitigate energy fluxes between permafrost and atmosphere, such as snow depth and soil moisture content, they are suitable for use in integrating, calibrating and testing permafrost simulations at a range of scale The data show that mean annual, summer and winter soil temperature data from shallow to deeper depths have been warming over the period of record, indicating the degradation of permafrost at this site. The air temperature in Ny-Ålesund has increased over the past 20 years by about 1.46°C (+/0.05°C) per decade. The active layer has doubled in thickness from 0.9 m in 1998 to more than 1.5m in 2018. The freezing period starts later now compared to 20 years ago, leading to a shortening of the period where the soil is frozen of 31 days per decade. We present examples how the Bayelva data sets is employed to improve global models. Applications not only comprise Earth System Models, but also new high-resolution data sets on the permafrost thermal state compiled in the ongoing CCI Permafrost project by the European Space Agency.