Ever wonder why the charts like to begin at about 1850?
http://en.wikipedia.org/wiki/Little_Ice_Age
The Little Ice Age (LIA) was a period of cooling that occurred after the Medieval Warm Period (Medieval Climate Optimum). [1] While it was not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939. [2] It has been conventionally defined as a period extending from the sixteenth to the nineteenth centuries, [3][4][5] or alternatively, from about 1350 to about 1850, [6] 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 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. [7] 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. [8]
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.
http://en.wikipedia.org/wiki/Medieval_Warm_Period
The Medieval Warm Period (MWP), Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region that may also have been related to other climate events around the world during that time, including in China [1] and other countries, [2][3][3][4][5][6][7] lasting from about AD 950 to 1250. [8] It was followed by a cooler period in the North Atlantic termed the Little Ice Age. Some refer to the event as the Medieval Climatic Anomaly as this term emphasizes that effects other than temperature were important. [9][10]
Despite substantial uncertainties, especially for the period prior to 1600 for which data are scarce, the warmest period of the last 2,000 years prior to the 20th century very likely occurred between 950 and 1100, but temperatures were probably between 0.1 °C and 0.2 °C below the 1961 to 1990 mean and significantly below the level shown by instrumental data after 1980. Proxy records from different regions show peak warmth at different times during the Medieval Warm Period, indicating the heterogeneous nature of climate at the time. [11] Temperatures in some regions matched or exceeded recent temperatures in these regions, but globally the Medieval Warm Period was cooler than recent global temperatures. [8]
(I recently read an article that brings that last sentence, and sweeping conclusion into great question)
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