Tree-ring measurements have revealed a period of extreme cold in Eurasia between 536 and around 660 CE. It coincides strikingly with the Justinian plague, migrations of peoples and political turmoil in both Europe and Asia... WSL dendroclimatologist Ulf Buntgen and his fellow researchers were able for the first time to precisely reconstruct the summer temperatures in central Asia for the past 2,000 years. This was made possible by new tree-ring measurements from the Altai mountains in Russia. The results complement the climatological history of the European Alps, stretching back 2,500 years, that Buntgen and collaborators published in 2011 in the...