Decadal-scale variability and global warming affect spring timing and forest growth across the western Great Lakes region

Abstract

Abstract The Great Lakes region of central North America has warmed by 1–2 degrees Celsius on average since pre-industrial times, with the bulk of warming occurring in winter and spring. Within the continental interior, the multi-decadal warming trend is modulated by long-range teleconnections to centers of ocean-atmosphere variability in the North Pacific and high Arctic, which affect atmospheric dynamics across the mid-latitude. Variability in spring temperatures affects regional ecosystems by altering growing season length and growth phenology, and different ecotypes and species may exhibit unique or diverging responses to climatic changes. Determining the relative influence of natural ocean-atmosphere variability versus the ‘secular’ warming trend on spring temperatures is necessary to estimate the range of potential ecological responses to future warming scenarios. This study examines shifts in Great Lakes climate by evaluating the role of warming and major ocean atmosphere climate patterns on interannual variability and multi-decadal trends in spring climatology in long observational records and leading modes of ocean-atmosphere circulation over the Arctic and North Pacific. From the analysis of climatology, this study also measures the sensitivity of regional forests to variation and trend in temperature using long-term growth records from tree-rings and satellite data. Using a modeling approach designed to test for regime shifts in time series data, this research shows that mid-continent spring climatology is strongly influenced by winter phases-changes in the North Pacific, and that regional forests show a strengthening response to the trend in spring climate during the last half-century.