Little Ice

THE LiTTLE iCE Age does not cover a clear and well-defined climatic regime and time-period upon which climate scientists agree. Glaciologists, to describe the most recent major glacial advance of the Holo-cene period, originally used the phrase. Subsequently, the Little Ice Age was associated with a period of advances of European glaciers 1450-1850. It is now often associated with a climatic regime with relatively cold temperatures. However, current research does not support a globally-synchronous period of unusual cold over this approximate period.

The Little Ice Age was originally used to denote a period of moderate glaciation covering the past 4,000 years. In more recent and seminal work on the subject by J.M. Grove, the concept refers, not directly to climate, but specifically to a time, or times, of glacial advance; more precisely, to a period lasting several centuries within the last millennium, when glaciers extended globally and remained enlarged. Pioneers of the use of historical records to reconstruct past climate, such as H.H. Lamb, were drawn to suggest a cold phase in Europe on the basis of accounts of the extent of snow and ice on land and sea 1450-1850.

Based on a variety of different types of data from many parts of the world, suggestions for the period covered by this most recent meaning of the Little Ice Age have ranged from 1200-1400, 1200-1900, 1550-1700, 1550-1800 and 1550-1850. Since some of these dates were put forward, the availability of data on the climate of the past has increased. At one time, it was believed that the Little Ice Age was a global phenomenon, but

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this is now less apparent. Spatial climatic patterns of the past 1,000 years are beginning to be mapped for large parts of the world, and the early 21st century have seen the development of multiple climate-proxy averages providing year-by-year estimates of average temperatures. These new series challenge the idea of global synchrony, often assumed when terms such as Little Ice Age and Medieval Warm Period are used.

Climate model results using best estimates of forcing factors over the past 1,000 years also show no clearly-defined global-scale warm or cold periods during this time, suggesting that any signals that exist are largely masked by the noise of shorter timescale variability. Although the concept of a global-scale cold climatic regime in the later half of the last millennium, lasting for several hundred years, is now outdated, there were episodes of relatively cold climate in many parts of the world during the past millennium. That glaciers advanced in the 1650s, for example, in the Swiss Alps, is well-known. However, while continental

Europe suffered cold temperatures in the 1600s, Iceland enjoyed a relatively mild period with infrequent sea ice 1640-80. Particularly cold periods occurred in Iceland in the 1780s and 1880s. In the United States, winter 1780 was notably cold, and New York harbor froze, allowing people to walk on the ice.

A cold Little Ice Age climate has been suggested as a causal factor in a number of episodes in human history. However, in these cases, it is likely that several elements were involved, not just climate. A case in point is the loss of the Norse settlements in Greenland (1350 and 1450), where it is clear that many factors contributed to their demise, including a possible reluctance on the part of the settlers to learn from their environment and their Inuit neighbors.

The concept of the Little Ice Age has now evolved from the idea of a simple, centuries-long period of lower temperatures, to a more complex view of temporal and spatial climate variability. There were, nevertheless, distinct phases of cold and variable climate

General George Washington crossing the Delaware on the evening before the Battle of Trenton, December 25,1776. The American revolutionary period experienced the effects of colder temperatures, particularly during the winter of 1780.

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