Observed and modelled changes in the seasonal temperature cycle in Stockholm

Abstract

The increasing temperatures on Earth is a great threat to sustainability for both the environment and life. The Arctic region and adjacent places such as Stockholm are warming faster than equatorial areas due to the Arctic Amplification (AA). The Urban Heat Island (UHI) is a phenomenon heating cities and is important to account for observational temperatures from cities. The aim of this study is to investigate the historical seasonal changes in surface air temperatures (TAS) and the seasonal TAS for CMIP6 Global Climate Model (GCM) simulations for two scenarios (SSP245 and SSP585). The aim is also to test the reliability of the GCMs to examine if they are useful. This was carried out by using Python to create daily climatologies, maximum and minimum temperature and their respective day of year (DOY), as well as calculating ratios for checking which GCMs are accurate for the area, and a time series for sea ice extent. The result revealed that the TAS has increased between 1756 and 2025, with a longer warm period in early year. The TAS is projected to increase for both SSP245 and SSP585, but no seasonal warming was projected. The GCMs were revealed to be somewhat reliable, as some of them were calculated to have a ratio far from the observed temperature ratios. Excluding these specific GCMs may be the key to project warming in the patterns of historical data. In conclusion the TAS has been increasing during winter in Stockholm, and although an overall increase in TAS is projected for the future, no seasonal warming is present. This could be caused by the use of illfitted GCMs for Stockholm.