Monitoring climate at Jungfraujoch in the high Swiss Alpine region Christof Appenzeller a, ⁎ , Michael Begert a , Evelyn Zenklusen a , Simon C. Scherrer b a Federal Office of Meteorology and Climatology MeteoSwiss, Krähbühlstrasse 58, CH-8044 Zürich, Switzerland b National Center for Atmospheric Research, Climate Analysis Section, Climate and Global Dynamics Division, P.O. Box 3000, Boulder CO, 80307, USA ARTICLE INFO ABSTRACT A homogenized temperature record measured at Jungfraujoch, the highest permanently manned meteorological station in Europe at 3580 m asl, is presented based on almost 70 years of record (1937–2005). The observed decadal variability as well as the overall trend (1.8 °C/69 years) in the homogenized data is comparable to other homogenized Swiss time series at other altitudes. A detailed analysis of seasonal mean temperature trends revealed no significant height dependence for the period 1961–2005. The dominant trend features are the weaker trends in autumn, significant only at low altitudes. Temperature indices such as thawing days, derived from newly homogenized minimum temperature series, exhibit strong vertical and seasonal trend dependence. Strongest relative trends occur in winter at an altitude around 1000 and 1600 m asl. For the summer season relative trends in thawing days are strongest at the highest stations, as expected. At Jungfraujoch an increase of about 50% is observed for the period 1961–2005 even when the extraordinary warm summer of 2003 is excluded. © 2007 Elsevier B.V. All rights reserved. Keywords: Jungfraujoch Temperature Homogeneity Trends Thawing Alpine region 1. Introduction In recent years climate change has gained substantial atten- tion in the media and on the political agenda. In terms of global mean surface temperature, the years in the 1990s and the beginning of the 21st century have been the warmest years, at least since the beginning of instrumental measurements (Houghton et al., 2001). In central Europe eight of the ten warmest years of the 1851–2004 temperature record have been observed from 1989 to 2003 (Scherrer et al., 2005). Climate model simulations show that most of the observed trend can only be explained when the anthropogenic greenhouse gas emissions are taken into account (Houghton et al., 2001). In the Alpine region similar temperature increases have been observed over the last ∼150 years (e.g. Begert et al., 2005; Böhm et al., 2001; Kunz et al., 2007). The amplitudes of these trends are twice or even three times as large as the global average figures for the last few decades (Philipona et al., 2004; Böhm et al., 2001). Some studies find indications for larger increases in temperature at high altitude stations (e.g. Diaz and Bradley, 1997). Many economical, ecological and geophysical sectors in the Alpine region are sensitive in one or the other way to temperature changes (Houghton et al., 2001; Haeberli and Beniston, 1998; Studer et al., 2005; Walther et al., 2002; Scherrer et al., 2004). For such studies the vertical distribution of the observed and expected temperature changes, as will be explored in this paper, are of crucial importance. In Switzerland a high density near surface measurement network (SwissMetNet: Fig. 1, Frei, 2003) provides long term observations at altitudes ranging from 197 to 3580 m asl. The later altitude is the one of the station at Jungfraujoch operated by the Federal Office of Meteorology and Climatology MeteoSwiss. It is the highest permanently manned meteorological station in Europe. Measurements have been carried out since 1922 when the access by railroad was completed and the Jungfraujoch Commission was founded. Today, long term data series of Jungfraujoch and other stations on such altitudes are of great value to address questions of the current global change debate. SCIENCE OF THE TOTAL ENVIRONMENT 391 (2008) 262 – 268 ⁎ Corresponding author. Tel.: +41 44 256 93 88. E-mail address: christof.appenzeller@meteoswiss.ch (C. Appenzeller). 0048-9697/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2007.10.005 available at www.sciencedirect.com www.elsevier.com/locate/scitotenv