A probabilistic view on recent and near future climate change in Sweden

The decade 1991–2000 was warm and wet in Sweden, with 10-station mean temperature 0.8 ◦C above and 20-station mean precipitation 6% above the mean for 1961–1990. Here we study the question if such changes should be seen as a symptom of anthropogenic climate change or if they might be of purely natural origin. Using the control simulations of 19 atmosphere–ocean general circulation models and taking into account differences between the simulated and observed interannual variability, we estimate that the recent increase in temperature and that in precipitation had both about a 6–7% chance to occur solely as a result of natural variability. Using the corresponding simulations with increasing CO2, we further estimate that the anthropogenic forcing raised the probability of the observed changes to occur to 23% for the increase in temperature and to 14% for the increase in precipitation. About half of the warming and about 30% of the increase in precipitation appear to be explained by anthropogenic forcing. The seasonal aspects of observed and simulated climate change are also discussed, with special emphasis on winter, when the observed warming has been much larger than expected from the model simulations. Finally, a probabilistic forecast for the Swedish climate in the first decade of the 21st century suggests a 95% (87%) possibility of warmer (wetter) annual mean conditions than in 1961– 1990 on the average. One of the caveats in our analysis is that the model simulations exclude variations in solar and volcanic activity, the effects of which might not be fully covered by our rescaling of interannual variability.