Changes in minimum and maximum temperatures at the Pic du Midi in relation with humidity and cloudiness, 1882–1984

In an attempt to contribute to the investigation on a global climate change, a historical series of minimum and maximum temperature data at the Pic du Midi, a mountain observatory at 2862 m a.s.l. in the French Pyrenees, is updated after correction of a systematic deviation due to a relocation of the station in 1971. These data, which now cover the 1882–1984 period, are examined in parallel with humidity and cloud cover data for the same period. From the beginning to the end of this period, observations show that the mean night-time temperature has increased by 2.39°C100 yr while the mean daytime temperature has decreased by 0.50°C100 yr. In consequence, the mean annual diurnal temperature range has dropped by 36%100 yr. The maximum seasonal decrease is 46%100 yr in spring. Season-to-season and year-to-year inter-relationships between minimum temperature, maximum temperature, relative humidity and cloud cover suggest that the decrease in maximum temperature is related to a concomitant increase of 15%100 yr in both relative humidity and cloud cover.