At present, the Arctic climate is changing much more rapidly than the rest of the globe, and yet observational data available in the region is poor. The positive feedback between climate warming a nd permafrost carbon emissions depends on changing land - atmosphere energy and mass exchanges. There is thus a great need to understand links between the energy balance, which can vary rapidly over hourly to annual time scales, and permafrost, which changes over longer time periods. This understanding mandates long - term observational data sets. There is also a need to realistically incorporate permafrost into global modelling frameworks such as Earth System Models. Evaluating and parameterising of process - based models require 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, and testing permafrost as a component in Earth System Models. There is a great need for continuous monitoring at more sites, to span the full range of permafrost conditions. 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.