The increasingly visible impact of climatic variability on human affairs lends a sense of urgency to the task of better understanding the workings of the Earth's climatic system. Actual instrumental observations of climate are relatively short, and we must therefore turn to other sources for information about past climates to help develop and test the models that may enable us to predict climatic anomalies such as prolonged droughts or a series of severe winters. Tree -rings are one of the best sources of climatic proxy information. They can provide long, accurately dated, year-by-year records at many points around the globe, and bridge the gap between recent instrumental or historical data and the longer but more generalised geological records. Variations in the width of annual rings reflect the influence of climatic factors that limit the biological processes governing ring formation within a tree. Study of reconstructions of long records of a variety of climatic and related variables, such as temperature, precipitation, stream runoff and barometric pressure over periods of several hundred to several thousand years strongly suggests that the climate of the past century or so is not representative of the conditions that have frequently prevailed over long periods. Proxy records are thus a great help in our efforts to anticipate or predict future climate, which may be significantly different from the recent climatic past.
