Future Snow Scenarios for Northern Europe Based on Coupled Model Intercomparison Project Phase 6 Data

The ongoing climate change alters the snow conditions. This paper evaluates these changes in Northern Europe including Fennoscandia and the Baltic Sea region, based on data from the newest generation of global climate models (Coupled Model Intercomparison Project phase 6; CMIP6). Thirteen CMIP6 models are selected for the analysis based on the availability of daily snow data and the models' performance in simulating global and Northern European climate and snow conditions in Finland. The analysis focuses on four quantities: the largest daily value of snow water equivalent during the winter SWE_max, and the length, start day and end day of the longest continuous snow period. The models project an overall shift towards less snowy conditions with progressing warming: reduced SWE_max and shorter snow seasons that start later and end earlier. This is seen already in recent (1951–2023) trends, with largest simulated trends in southern Fennoscandia and in the Baltic countries and smaller trends in the northern inland regions. ERA5-Land reanalysis data mainly agree with this spatial pattern, although with some notable differences. The decrease of snow continues into the future (2023–2100), with larger trends projected for Shared Socioeconomic Pathways (SSP) scenarios with larger radiative forcing. Also, larger changes are projected for southern than northern Fennoscandia. For example, for the moderate emission scenario SSP245, snow seasons around 2090 are projected to be nearly 50 days shorter than in 1981–2010 in southern Finland but only 30 days shorter in Finnish Lapland. However, there is substantial quantitative uncertainty in the trends in snow conditions, even for a fixed emission scenario. For example, for SSP245, the one-sigma uncertainty due to natural variability alone is estimated to be at least 30%–50% of the multi-model mean trends in 2023–2100 for all snow-season metrics considered.