Figure 1.4. (a) Differences between the mean onset of spring (days) in Europe for the 10 years with the highest (1990, 1882, 1928, 1903, 1993, 1910, 1880, 1997, 1989, 1992) and the lowest (1969, 1936, 1900, 1996, 1960, 1932, 1886, 1924, 1941, 1895) NAO winter and spring index (November to March) drawn from the period 1879 to 1998. After Menzel et al. (2005b). (b) Anomalies of different phenological phases in Germany (mean spring passage of birds at Helgoland, North Sea; mean egg-laying of pied flycatcher in Northern Germany; national mean onset of leaf unfolding of common horse-chestnut (Aesculus hippocastanum) and silver birch (Betula pendula) (negative = earlier)), anomalies of mean spring air temperature T (HadCRUT3v) and North Atlantic Oscillation index (NAO) (http://www.cru.uea.ac.uk/cru/data/). Updated after Walther et al. (2002).