An international group of scientists, which included Ural dendrochronologists, found out that during the Late Antique Ice Age (from 536 to 550) the air temperature decreased only in the Northern Hemisphere. The researchers obtained these data from trees in Eurasia, the Western Hemisphere and the Southern Hemisphere.
The climatic and social cataclysms that began in 536 have long attracted the attention of volcanologists, climatologists and historians. Byzantine sources describe a mystical fog that covered a vast area in the years 536-537. Cold and drought led to the death of crops in Italy and Mesopotamia, causing famine and other disasters in the following years. The Justinian Plague, the first historically known pandemic, fell victim to millions of people.
Unusual phenomena were also recorded in Chinese sources. In many provinces of China in July and August of 536 frost and snow were observed, which ruined grain crops and caused famine among the population, which lasted until 538. In the northern part of China at that time about 80 percent of the population died. UrFU historians have shown: these events were the reason why the Turks neighboring China began to strengthen their position and subjugate their neighbors, leading to the formation of the Turkic Kaganate.
The results of their new research have been published in the journal Science Bulletin. The work was supported by the Russian Science Foundation. "We estimated the spatial scale of the events of the 536-540s using tree rings. We used 'abnormal' rings as markers. One advantage of this approach is that the width of annual rings responds to temperature changes mainly only in polar regions and high mountains, but abnormal rings are formed during extreme cooling in trees in many areas of the Earth.
Therefore, the work was able to include data on 23 different points, including the Southern Hemisphere, that is, much more than when using the width of the rings, "- says the co-author of the work, a leading researcher in the laboratories of dendrochronology IERizh Ural Branch of the Russian Academy of Sciences and natural science methods in humanities research UrFU Rashit Khantemirov.
Scientists analyzed three types of anomalies: frost rings - rings with a layer of cells deformed due to freezing; light rings - with thin cell walls of late wood; blue rings - with reduced lignin content in cell walls. All three types of anomalies are formed by a sharp and, as a rule, short-term (from several hours to several days) drop in temperature during the summer period. So, as a result, the scientists found that no trees in the Southern Hemisphere developed anomalies between 530 and 550.
"In the Northern Hemisphere trees synchronously responded with the formation of tree ring anomalies to the event of 536. Moreover, the peak of cooling, according to the annual rings, occurred at the end of July - beginning of August. In some areas the anomalies were formed in the next year. And the cooling after the eruption of 540 was not synchronous. And its duration was different in different areas. For example, in Mongolia, as well as in Yamal, the peak of the extremum fell on 543 years, in the U.S. - on 541-543 years, in Fennoscandia - on 541-542 years", - adds Rashit Khantemirov.
Recall, scientists have long discussed the causes of climatic cataclysms of 530-550 years. The most plausible reason is considered a large volcanic eruption. However, for a long time in the ice cores of Greenland and Antarctica traces of eruption were not found. This was probably due to sketchy data on the content of sulfates, which are markers of volcanic eruptions, and shortcomings in dating the ice layers. But in 2008, an international group of researchers, including Danish glacier researchers and dendrochronologists from Europe and Russia, including Ekaterinburg, published data based on the width of annual rings of trees.
Dendrochronologists have established: the cooling, which began in 536, covered all of Eurasia and lasted about 15 years. That is quite unusual, as even very large volcanic eruptions reduce the temperature only for 3-5 years. Scientists later found out that a few years later there was another eruption that was one of the most powerful in the last two millennia.
"A very powerful eruption occurred four years later, in 540, and triggered a climate response due to the formation of a film of aerosol in the stratosphere. Therefore, its effects began to be felt in different parts of the Earth with a delay of 1-4 years. Further research showed that the most likely source of the 540 eruption was the Ilopango volcano in central America. Such a double volcanic impact led to an unusually long cooling," explains Rashit Khantemirov.