Little Ice Age
The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region.[2] It was not a true ice age of global extent.[3] The term was introduced into scientific literature by François E. Matthes in 1939.[4] The period has been conventionally defined as extending from the 16th to the 19th centuries,[5][6][7] but some experts prefer an alternative timespan from about 1300[8] to about 1850.[9][10][11]
For the most recent period that was much colder than present with significant glaciation, see Last Glacial Period.
The NASA Earth Observatory notes three particularly cold intervals. One began about 1650, another about 1770, and the last in 1850, all of which were separated by intervals of slight warming.[7] The Intergovernmental Panel on Climate Change Third Assessment Report considered that the timing and the areas affected by the LIA suggested largely independent regional climate changes, rather than a globally synchronous increased glaciation. At most, there was modest cooling of the Northern Hemisphere during the period.[3]
Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, variations in Earth's orbit and axial tilt (orbital forcing), inherent variability in global climate, and decreases in the human population (such as from the massacres by Genghis Khan, the Black Death and the epidemics emerging in the Americas upon European contact[12][13]).
There is no consensus on when the Little Ice Age began,[15][16] but a series of events before the known climatic minima have often been referenced. In the 13th century, pack ice began advancing southwards in the North Atlantic, as did glaciers in Greenland. Anecdotal evidence suggests expanding glaciers almost worldwide. Based on radiocarbon dating of roughly 150 samples of dead plant material with roots intact that were collected from beneath ice caps on Baffin Island and Iceland, Miller et al. (2012)[8] state that cold summers and ice growth began abruptly between 1275 and 1300, followed by "a substantial intensification" from 1430 to 1455.[8]
In contrast, a climate reconstruction based on glacial length[17][18] shows no great variation from 1600 to 1850 but a strong retreat thereafter.
Therefore, any of several dates ranging over 400 years may indicate the beginning of the Little Ice Age:
The Little Ice Age ended in the latter half of the 19th century or in the early 20th century.[21][22][23]
The 6th report of the IPCC describes the coldest period in the last millennium as:[24]