From hot to cold

We have all read about the Medieval Warm Period and the Little Ice Age in the newspapers and books. These terms, which are now commonly used, were introduced by the climate-historian Hubert Lamb in 1965 and by the glaciologist Francois Matthes in 1939, respectively. Climate historians and paleoclimatologists,  however, do not agree on the time and duration of these periods and also the estimates of the variations in the temperature that characterized them are different. Furthermore the climate change in these periods did not vary only from one year to the another but also from one area to another of the Planet. Lamb positioned the Medieval Warm Period between 950 and 1200 for European Russia and Greenland, while for Europe he indicated the period between 1150 and 1300, with temperatures that were 1-2°C higher than in the first years of the Twentieth Century. Some experts disagreed with these statements and concluded that “in some part of the Globe, at some time of the year, relatively warm conditions could have prevailed”.  The Little Ice Age, instead, is a period of relative cooling, that regarded the Northern Hemisphere from 1300 to 1850. Even this cold period was not constant and global, and according to Fagan “there never was a monolithic deep freeze”, but a “climatic seesaw”, in other words an alternation of warm and cold periods often accompanied by disastrous climatic phenomena.
The different theories proposed by the scientists with regard to the Medieval Warm Period and the Little Ice Age have led to the diffusion of not very precise information which has often been used as proof that the current climate changes have not been caused by humans. For a clearer explanation , refer to the chapter on “Paleoclimate” in the Fourth IPCC-WG1 Report, an authoritative source that states that the Medieval Warm Period and the Little Ice Age were respectively warmer and colder than the periods that preceded and followed them. Furthermore they were local phenomena that did not influence global climate and did not affect the entire planet at the same time And, in particular, they cannot be compared with the current rise in temperature. In fact the climatic data indicate that up to 1900  the variations in temperature were limited to  a few tenths of a degree.

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