Here is the historical timeline and effects simply summarized:
10th – 14th century: The Medieval Warm Period (MWP) or Medieval Climate Optimum
During the High Middle Ages in Europe experienced a climate slightly warmer than in the period preceding and the period following it. The summer temperatures were between 1 and 1.4 degrees higher than the average temperature of the 20th century. The winters were even warmer with an average temperature in England of 6 degrees, which is slightly warmer than for most of the 20th century. The warmer conditions were caused by the fact that the air circulation above the Atlantic changed position, as did the warm sea currents, transporting warmer water to the arctic.
In Europe the warm conditions had positive effects. Summer after summer the harvests were good and the population increased rapidly. As a result thousands of hectares were cleared of woodland and farmers expanded their fields high into the hills and on mountain slopes. It was even possible to grow successfully grapes as far north as Yorkshire.
Under these conditions, art, literature and even science were developing apace and we see the height of medieval civilisation. The most visible achievements of this period are undoubtedly the construction of the many cathedrals all over Europe. The good harvests had made Europe rich and the good weather freed people from the burden of the struggle against the elements. It created the wealth and labour force to build cathedrals. It was a golden period for European Architecture and art.
9th & 10th centuries: Vikings reach Island and Greenland during the milder condition that prevailed during Medieval Warm Period.
Norse settlers arrived in Iceland in the 9th and Greenland in the 10th century with an agricultural practice based on milk, meat and fibre from cattle, sheep, and goats. The settlers were attracted by green fields and a relatively good climate and driven there by population pressures in Scandinavia.
They were able to sail to Iceland and Greenland as well as Labrador because of a decrease in sea ice in the north Atlantic.
Beginning of Little Ice Age
Environmental upheavals linked to sever climate variability characterised the period from 1300 to 1400.
All tree ring series in northern Europe show a decline in growth rates, indicating an adverse climatic change. This marked the transition from a “Medieval Warm Period” to the “Little Ice Age” when temperatures were on average 1.5 degrees Celsius lower than before and with greater seasonal variation. The cooling trend associated with the Little Ice Age progressively moved from north-west to south-east across Europe, with the Vikings in the far North experiencing the clooing first, British Isles experiencing the effects from the 1290s and the Mediterranean after 1320.
Written records from the 14th century provide accounts of severe weather in the period from 1314 to 1317, which led in turn to crop failure and famine. This episode of failed harvests and its consequences is known as “The Great Famine”. Notwithstanding these ecological calamities, the population of northern Europe was at an all time high by the second quarter of the 14th century. However, the arrival of the Black Death, in Europe in 1347 pushed the European population into a century-long demographic decline and caused long term changes in economy and society.
See the whole timeline here:
http://www.eh-resources.org/timeline/timeline_me.html
