Evidence of Climate Change Declines with Elevation Based on Temperature and Snow Records from 1930s to 2006 on Mount Washington, New Hampshire, U.S.A

Mount Washington, New Hampshire, has the longest northeastern U.S. mountain climatological record (1930s to present), both at the summit (1914 m) and at Pinkham Notch (612 in). Pinkham's homogenized daily temperature exhibits annual (mean = +0.07 degrees C/decade, p = 0.07 min +0.11 degrees C/decade, p = 0.01), winter (min = +0.18 degrees C/decade, p = 0.07), spring (max +0.13 degrees C/decade, p = 0.10), and summer (min = +0.11 degrees C/decade, p = 0.01) warming trends. Though suggesting annual, winter, and spring warming (0.05 to 0.12 degrees C/decade), mean summit temperature trends were not significant. Pinkham shows no significant change in date of first and last snow, however, the summit does but its period of record is shorter. Onset of continuous snow cover has not changed significantly at either site. Thawing degree days trended earlier at the summit (2.8 days/decade; p = 0.01) and Pinkham Notch (1.6 days/decade, p < 0.01), but end of continuous snow cover trended significantly earlier (1.6 days/decade; p = 0.02) only at Pinkham. Growing degree days showed no significant trends at either location. Pinkham exhibits more climatic change than the summit but less than regional lower elevations. Thermal inversions and high incidence of cloud fog commonly at or above the regional atmospheric boundary layer may explain the summit's resistance to climate warming. Caution is needed when extrapolating climate change trends from other Mountains or proximate lower elevation climate data to upper elevations.