In the light of our current worries about climate change and global warming, this is the first a series of articles for Deposits that will cover significant climate changes that have occurred in the geological past and times when the earth’s climate was hugely different from what we know today. However, this first one covers a slightly more recent event – the Medieval Warm period.
The twenty-first century has had some of the hottest temperatures on record, but there was another period that was just as warm or warmer. The Medieval Warm Period (approximately 900–1300 AD), refers to the time when temperatures in Europe and nearby regions of the North Atlantic are thought to have been similar to, or in some places exceeded, temperatures of the late twentieth century. Researchers believe changes in the circulation of the Atlantic Ocean brought warmer waters to the North Atlantic and neighbouring regions, causing warming temperatures. The Medieval Warm Period was followed by the Little Ice Age (approximately 1300-1850 AD), a period of cooling that brought colder winters and advancing glaciers to parts of Europe and North America that lasted well into the nineteenth century.
Scientists have evidence of this unusual warming period through indirect estimates of temperatures based on climate indicators that include tree rings, Greenland ice cores, ocean sediments and, in certain regions, written evidence of crop yields. There are even recorded dates when leaves come out and when flowers bloom in the spring. Records show that Norse people colonised ice free areas of Greenland because of the unusually warm weather. In England, grapes were grown several hundred kilometres north beyond their current growth range.