|Cool North European summers and possible links to explosive volcanic eruptions
Tree-ring-width reconstructions summer temperatures in northern Fennoscandia reveal a number of extremely cool summers over the last 6000 years. Long observational temperature records, which extend back to about 1780 for this region, reveal very few of the markedly cool summers that are reconstructed. Slightly longer instrumental records for northwestern Europe reveal some well-known dates such as the year-without-a-summer in 1816. The two coolest summers in the CE part of the long reconstruction occurred in 536 and 1601, well before instrumental records began. In the pre-CE part of the reconstruction reveal a similar number, 6 similar magnitude events previous 3000 years. There appears to be a clear link for 1601 event to the eruption of Huaynaputina eruption in Peru the year before and a volcanic cause has been postulated for the event in 536. Presumably the earlier 6 events have similar causes, but the link to volcanic layers in the Greenland Ice Cores is tenuous as the earlier known exactly dated layer is that from Vesuvius in 79 CE. This paper will discuss several issues relating to the tree-ring evidence, suggesting that we need more of the multimillennial reconstructions in other high-latitude regions of Northern Eurasia and Northern North America to ensure that what is being seen in Fennoscandia is not just a local response and whether the tree-ring effects are simply due to cool summer temperatures, or are more climatic variables or direct deposition involved.