A 120-year cold spell that spanned the Northern Hemisphere during the 6th and 7th centuries was so profound that it deserves its own name, according to a new study. Analyses of tree rings from more than 150 living trees in the Russian Altai-Sayan Mountains, as well as more than 500 older trees that have fallen to the ground there, provide a complete chronicle of climate stretching from 359 B.C.E. to the year 2011. Of the 20 coldest summers in that region in the last 2000 years, 13 occurred in the 6th century after the year 536, which a recent study of ice cores has pinned down as the date of a massive volcanic eruption somewhere at high latitude in the Northern Hemisphere. Two more large eruptions (in the years 540 and 547) helped render the 540s the coldest decade in more than 2300 years, with an average temperature of about 11.8°C (53.2°F), researchers report today in Nature Geoscience. (For comparison, 2015’s global average temperature was 14.8°C, or 58.6°F.) Particles spewed high into the atmosphere by those eruptions scattered sunlight back into space, thus cooling Earth substantially, the researchers explain. The extraordinary cold spell was probably strengthened and lengthened by the resulting increase in sea ice at high latitudes, as well as an unusually low number of sunspots in the middle of the 7th century. The poor climate may been one of many factors contributing to societal changes of the era, including widespread crop failures and famines in Central Asia that may have triggered migrations from the area to China and Eastern Europe, thus helping spread an episode of plague (depicted in this 15th century painting) that originated there. The researchers’ proposed name for the event is the Late Antique Little Ice Age, a nod to the interval’s falling within the last phases of a period many cultural researchers call the Age of Antiquity.