ABSTRACT
Temperature is the fundamental measure of the state of the climate system. Past periods, especially in mid-latitudes, are generally referred to as cold or warm epochs (e.g., Ice Age, Hypsithermal, Medieval Warm Epoch and Little Ice Age). Changes in temperature, when sustained over a period of time, therefore tell us something about changes in the functioning of the climate system. Chapter 7 looked at the history of meteorological instrumentation and observations, indicating the key figures and developments over the last 400 years. While the geographical variations in temperature over the British Isles have been described in Chapter 3, this chapter considers what the historical measurements reveal about the variation of temperature since the seventeenth century. Trends in British Isles temperatures will also be compared with those for other land areas of the Northern Hemisphere, and the causes of colder and warmer years discussed in relation to larger-scale changes in the atmospheric circulation (cf. Chapter 2). How this most important period of our climatic history relates to the Holocene and to the medieval period has been addressed, respectively, in Chapters 5 and 6.
