Reconstructed summer degree days in central Alaska and northwestern Canada since 1524

Three time series based on precisely dated annual tree-ring widths have been used to reconstruct June plus July degree days for the central Alaska and northwestern Canada region. The time series are the longest recently developed chronologies for the area and represent 57 core samples from 27 trees. The degree-day reconstruction, extending back to A.D. 1524, exhibits much year-to-year variation and extended warming and cooling trends including a general warming trend from about 1840 to 1960. The reconstruction is in agreement with some subaretic glacial information and with data of percentage melting from arctic ice cores. This and similar reconstructions can provide quantitative information to compare with general circulation and energy budget models for longer time periods than are available in recorded meteorological data.