The evolution of climate over the last millennium

Knowledge of past climate variability is crucial for understanding and mode ling current and future climate trends. This article reviews present knowle dge of changes in temperatures and two major circulation features-El Nino-S outhern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)-over mu ch of the Last 1000 years, mainly on the basis of high-resolution paleoclim ate records. Average temperatures during the Last three decades were Likely the warmest of the Last millennium, about 0.2 degreesC warmer than during warm periods in the 11th and 12th centuries. The 20th century experienced t he strongest warming trend of the millennium (about 0.6 degreesC per centur y). Some recent changes in ENSO may have been unique since 1800, whereas th e recent trend to more positive NAO values may have occurred several times since 1500. Uncertainties will only be reduced through more extensive spati al sampling of diverse proxy climatic records.