Medieval warming

Data points are the high precision ( 2%c) measurements of Stuiver and Quay (9). Note the excellent agreement between the high precision data of Stuiver and the trend line generated from the lower precision (ca. 5V) data of the composite data set. Maxima occur between a.d. 1020-1080, 1290-1320, 1420-1530, 1660-1710, 1790-1830 or on the average, every ca. 190 years. The pronounced minimum between aj>. 1100 and 1240 corresponds to the Medieval Warm epoch. 

Jones 2001). According to sea level changes, the last Ice Age, centered at 18,000 years ago, was even colder than now (3-4 C) (Lamheck 2001). In contrast, the Medieval Warm Period was wanner than now (0.5 C), and both the Interglacial Period (130,000 y from now) and the Eocene Warm period (33-53 My from now) were even warmer (3-4 C) (Webb 1992). 

A young speleothem from Cold Air Cave in the Makapansgat Valley in South Africa (Holmgren et al., 1999 Tyson et al., 2000) provides a clear record of the historic period. The medieval warming (950 to 1300 AD) and the Tittle ice age from 1300 to 1800 AD are shown to be distinctive features in South Africa as well as in Europe. 

The Medieval Warm Period between ad 800 and 1,300 witnessed the expansion of... 

Fig- 7.7 Climatic changes over the last 1,400 years revealed in Greenland ice cores document periods of warmer and colder conditions than today. The Medieval Warm Period witnessed the expansion of the Vikings across the North Atlantic while the Little Ice Age documents a time of cooler conditions and declining harvests. The carbon isotope evidence from human tooth enamel shows a shift from terrestrial to marine diet during this period (data from Dansgaard et al. 1975 Arneborg et al. 1999)... 

Hughes, M.K., and H.R Diaz. 1994. Was there a Medieval Warm Period and if so, when and where Climatic Change 26 109-142. 

Figure 23.1 also shows the global temperature record of the last 1000 years, as estimated from a variety of sources. The so-called Medieval Warm Period (MWP), extending from 1000 to about 1400, was followed by a span of considerably colder climate, the Little Ice Age, (LIA) from 1450 to 1890, when the global mean temperature may have been 0.5-1,0°C lower than today. During the LIA glaciers moved into lower elevations, and rivers that rarely freeze today were often ice-covered in winter. 

Earlier studies, using considerably fewer proxy datasets, have considered the past millennium and two periods, the Little Ice Age (variously defined as 1450-1850) and the Medieval Warm Epoch (less well defined in the literature, but 900-1200 encompasses most earlier work) are often discussed. To some extent, these two periods have become accepted wisdom, but the various curves in Fig. 8 indicate only partial support. Spatial analysis of the proxy data shows that no periods in the millennium were universally colder or warmer everywhere, considerable variability being present. The latter is to be expected even by studying the instrumental period since 1850. Just as the early 1940s were warm in many parts of the world but Europe was cold, the early seventeenth century was... 

The Earth s temperature undergoes periodic variations - around AD 1000, there was what is known as a Medieval Warm Period , the warmest epoch in the past 2000 years, until today, while more recently there was a Little Ice Age centered around 1700. Average temperatures today are warmer than at any time in the past two millennia (around 0.8°C warmer in the past century and a half), and the trend is upwards. Many scientists think that the rise in CO2 levels does indeed contribute to that, not least because every transition from a glacial to a warm period in the past 420,000 years was accompanied by a substantial rise in the CO2 content of the atmosphere. 

On even shorter scales, human civilization arose in an interglacial period within an extensive period of glacial conditions. Chicago was under 1 km of ice as recently as 18,000 years ago. The medieval warming period and the little ice age that followed had important effects on recent history. 

---