Temperature regimes, climate extremes, and the waning of Minnesota’s winter

Abstract

Minnesota, a state known for its extreme winter climate, is undergoing rapid changes to what may be its most iconic season. While Minnesota’s winter warming trend is widely known, an extended analysis on the exact nature of these changes is largely unexplored in the climate literature. The research in this thesis addresses the gap in existing literature by investigating the Minnesota winter climate record from multiple statistical approaches, including linear regression, 30-year means analysis, and change point detection, on several levels of data, including statewide, climate division, and station winter minimum temperature records. The linear regression analysis reveals consistent warming since the beginning of the record, with the greatest warming occurring between 1961 to 2020, and an absence of warming from 1991 to 2020. Investigation from the 30-year means analysis finds significant warming in the 1971–2000 and 1981–2010 periods compared to all previous 30-year mean periods in the Minnesota observational winter record, and that the 1991–2020 period is the warmest of any 30-year mean analyzed. Change point detection is implemented to provide further understanding of where a shift in the mean state could have occurred. The combined results of these three statistical approaches indicate that the Minnesota winter climate underwent an abrupt adjustment to a new regime in the early to mid-1980s. This new regime, consisting of winters with unprecedented winter warmth, has been remarkably constant since. These findings parallel literature that points to the 1980s as a period of dramatic climate variability, where regime shifts are found in climate records across the globe.