Global climate change in the instrumental period

The instrumental period of climate history began in the 18th century with the commencement of routine weather observations at fixed sites. Estimates of global-mean climate (e.g. temperature and precipitation) were not possible, however, until the establishment of extensive observing networks midway through the 19th century. This paper reviews our knowledge of global climate change in the instrumental period. Time series of global-mean temperature and precipitation are examined and a comparison is made between two independent 30-year climatologies: 1931-1960 and 1961-1990. Examples are also provided of regional-scale climate changes. Such assessments are important for two reasons. First, they establish the variability of climate on the time-scale of decades, time-scales upon which it is reasonable to plan economic and socio-political activities. Second, and more specifically, they enable us to quantify the magnitude of global-mean climate change which has occurred over this period. Such detailed diagnostic climate information is a necessary, although not sufficient, prerequisite for the detection of global-scale warming which may have occurred due to the enhanced greenhouse effect. Some attention is given to explanations of the observed changes in global-mean climate.