At http://siberiantimes.com/science/case-study/news/n0686-medieval-weapon-m… .. archaeologists chanced upon an ancient furnace after first spotting slag and clay on a roadside location. Two furnaces were subsequently unearthed, made of stone and thought to have been used to smelt iron ore. The date being aired is around 1000AD. A people known as the Kurykan were renowned for their blacksmithing skills throughout the medieval era. The site is located on a hill to take advantage of the wind when enabled the combustion process. Medieval smelting sites in Britain were also sometimes located on hill sides. The Baikal region is known to have been a metallurgical centre from the end of the first millennium BC and contemporary with the Romans (early AD).
At http://glacierhub.org/2016/06/21/1400-year-old-sledge-thawed-out-of-norw… … which is an interesting date as it suggested the sledge was frozen in around 600AD (or a bit earlier). Did this occur around the time of the sudden dip in temperatures between 536-45AD? Presumably the glacier has shrunk – but has the sledge been moved forwards by the snout of the glacier which may indicate it was originally at a different elevation? The link says the sledge was discovered on a flat area of the glacier and would have been used to transport goods across the ice – a distance of around 2km. It is also a known trade route from east to west Norway (in warm times). So, it seems the glacier existed prior to the 6th century AD but it got colder and was buried under snow that became ice. The glacier is in the process of shrinking – but bear in mind that shrinking glaciers are being sought out by archaeologists and others as they have become know to be potential sites of ancient artifacts (some of which may be valuable). Such glaciers can grow as well as shrink but ice is a moving body and can move such objects forwards as well as uncover them as they melt.
One other interesting point to bear in mind, this also means that glaciers in Scandinavia existed in the Viking era, and would have been encountered on a regular basis. This may be one reason why Vikings in Greenland were not persuaded to abandon their farms when glaciers began to grow at the end of the medieval warm period. In the end it became too cold to farm and people moved elsewhere – but they would have co-existed with glaciers without being uneasy.