Climate varies on all scales of time and space, bya large variety of reasons. However, before any discussion of reasons can be performed it is necessary to realize the very facts of climate variability by means of observations or reconstructions, respectively. In this book we focus on observed long-term trends of selected climate elements (tempera ture, precipitation, humidity, pressure ) as revealed by direct measurements of the Euro pean station network within the recent 100 years. Of course, there are a number of problems in detail: Reliability and accuracy of data, time series...