Vermont Climate Change Indicators

Climate change indicators are developed for Vermont in recent decades based on the trends in freeze dates, the length of the growing season, the frozen period of small lakes, and the onset of spring. These trends, which show a consistent pattern of a warming climate in Vermont during the past 50 yr, provide useful information for climate change adaptation planning for the state. The freeze period has become shorter and the growing season for frost-sensitive plants has become longer by about 3.7 (±1.1) days decade−1, the date of the last spring freeze has come earlier by 2.3 (±0.7) days decade−1, and the first autumn freeze has come later by 1.5 (±0.8) days decade−1. The frozen period for small lakes, which depends on mean temperatures over longer periods, has decreased faster by 6.9 (±1.5) days decade−1. Lake freeze-up has occurred later by 3.9 (±1.1) days decade−1, while ice-out has come earlier by 2.9 (±1.0) days decade−1. Lilac first leaf has also been coming earlier by 2.9 (±0.8) days decade−1, while lilac first bloom has advanced more slowly, by 1.6 (±0.6) days decade−1. The first leaf of Vermont lilacs, an indicator of early spring, is closely correlated with the ice-out of the small reference lake, Stile’s Pond, because both are related to temperatures in February–April. In the past 40 yr, the growing season for frost-sensitive plants has increased by 2 weeks, and the growing season for frost-hardy plants may have increased more.