Long-Term Climate Change at Four Rural Stations in Minnesota, 1920-2010

Temperature data from 1920-2010 from four rural Minnesota stations were classified into three 30-year timeframes and examined for differences and trends in temperature (Tmax and Tmin), precipitation, and growing season variables: start of season (SOS), end of season (EOS) and length of season (LOS). These variables were subjected to an ANOVA, and Tukey test to ascertain statistical differences between the 30-year datasets. Subsequently, a Change Point analysis was applied pursuant to temperature and precipitation trends to determine the start and termination of temporal trends occurring within the dataset without the imposition of 30-year timeframes. The main findings were: (1) precipitation has increased significantly in May and June since 1985 and that the last 30-year timeframe possessed more precipitation (69-206 mm/2.7-8.1") than the first 30 years, (2) mean Tmin increased significantly at all four stations during the last 30-year period relative to the middle period but not the initial period, (3) Tmax proved significantly warmer at only two stations during the initial 30-year period (1920-1949), (4) the length of growing season increased with an earlier onset or start being the chief variable at three of the four stations. Our Change Point analysis further highlights differences and trends superimposed over the 30-year bracketing of climate data. The regional role of water vapor as a greenhouse gas and landuse/cover factors, along with anthropogenic CO2 loading at a planetary scale, are argued to be partially causative, albeit specific weights were not assigned to each criterion as this task proved outside the scope of this study.