Little Ice Age

The Little Ice Age (LIA) was a period of cooling that occurred after the Medieval Warm Period (Medieval Climate Optimum). While it was not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939. It has been conventionally defined as a period extending from the 16th to the 19th centuries, or alternately, from about 1350 to about 1850, though climatologists and historians working with local records no longer expect to agree on either the start or end dates of this period, which varied according to local conditions. NASA defines the term as a cold period between AD 1550 and AD 1850 and notes three particularly cold intervals: one beginning about 1650, another about 1770, and the last in 1850, each separated by intervals of slight warming. The Intergovernmental Panel on Climate Change Third Assessment Report considered the timing and 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.

Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, an inherent variability in global climate, or decreases in the human population. Lower CO₂ atmospheric concentrations found in Antarctic ice cores may have resulted from the colder global climate.