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Vermont Climate Change Indicators

We develop climate change indicators 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 fifty years, provide useful information for climate change adaptation planning for the state. The freeze period has got shorter and the growing season for frost-sensitive plants has got longer by about 3.7 (±1.1) days per decade; as the date of the last spring freeze has come earlier by 2.3 (±0.7) days per decade, and the first autumn freeze has come later by 1.5 (±0.8) days per decade. The frozen period for small lakes, which depends on mean temperatures over longer periods, has decreased faster by 6.9 (±1.5) days per decade. Lake freeze-up has occurred later by 3.9 (±1.1) days per decade, while ice-out has come earlier by 2.9 (±1.0) days per decade. Lilac first leaf has also been coming earlier by 2.9 (±0.8) days per decade, while lilac first bloom has advanced more slowly by 1.6 (±0.6) days per decade. The first leaf of Vermont lilacs, an indicator of early spring, is closely correlated with the ice-out of our small reference lake, Stile’s Pond, because both are related to temperatures in March, April and May. In the past forty years, the growing season for frost-sensitive plants has increased by 2 weeks, and the growing season for frost-hardy plants may have increased more.

Plain English Discussion

The climate of Vermont is warming rapidly along with the rapid warming of the Earth at northern latitudes. Spring is coming earlier and the growing season is getting longer by several days every decade. Winter is warming twice as fast as summer, and the winter frozen period for small lakes is shrinking by one week every decade. What we are seeing now in Vermont will likely continue for the next few decades. Understanding local climate change may inspire us to confront the accelerating warming trends that are being driven by the burning of fossil fuels.

A recording of a presentation of this paper at the 2011 annual meeting of the AMS in Seattle is available at (no sound for first 90 secs)

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Full Citation

Betts, A.K. (2011): Vermont Climate Change Indicators. Weather, Climate and Society, 3, 106-115, doi: 10.1175/2011WCAS1096.1