Is the current warming unusual compared to historical warm periods?
It has been suggested that global scale historical climate irregularities have occurred in the past, and the current situation is not unusual. Various authors throughout the 20th century compiled anecdotal and environmental evidence pointing to a ‘MEDIEVAL WARM PERIOD’ at around 900–1200 A.D. Most of this evidence, which includes the northern extent of cultivable land in Iceland and Greenland and ice-free ocean routes, comes from Western Europe. Analysis of tree stumps in lakes also reveals that parts of the western United States experienced severe and prolonged drought during this period. More recent studies demonstrate that the medieval climate probably varied heterogeneously in different regions. The evidence suggests that on the whole the Northern Hemisphere probably experienced temperatures warmer than average in a 2000-year context, and certainly warmer than the subsequent ‘LITTLE ICE AGE’ from ~1500 to ~1850 A.D. However, while some regions may have experienced warmer conditions
