New evidence for climate impacts on ancient societies

An international research team of archaeologists, climatologists, geographers and historians led by Willy Tegel (University of Freiburg, Institute for Forest Growth) and Ulf Büntgen (Swiss Federal Research Institute WSL) compared variations in European summer climate with conspicuous events and episodes in human history.

Their study, published Jan. 13, 2011 in the online version of the journal Science, provides new evidence that agrarian wealth and overall economic growth may was impacted by climate change.

The researchers reconstructed the history of central Europe's summer precipitation and temperature for the past 2,500 years, extending the record more than 1,000 years further than previous studies into the past. Their results are based on measurements of annual tree-rings from thousands of sub-fossil, archaeological, historical and living tree samples from Germany, France, Italy and Austria.

The climate information stored in these trees allows comparison of natural precipitation and temperature fluctuations with the development of European societies. European summer climate during the Roman Era about 2,000 years ago was relatively warm and wet and characterized by less variability. Increased climate variations from around 250-600 A.D. coincided with the demise of the Western Roman Empire and the exceptional turmoil of the Migration Period during which the continent's population was substantially reordered.

The new study also revealed that humid and mild summers paralleled the rapid cultural and political growth of Medieval Europe, whereas unfavorable climate may have played a role in the underlying health conditions that contributed to the devastating economic crisis that arose in connection with the Black Death plague pandemic in the 14th century. More recently, temperature minima in the early 17th and 19th centuries coincided with large-scale settlement abandonment during the Thirty Years' War and the modern mass migrations from Europe to America.

Past hydroclimatic variations may have exceeded the magnitude and duration of variations seen in modern times. The situation is different for temperature though, as the recent warming in the late 20th and early 21st century appears unprecedented with respect to the past 2,500 years."

The authors, however, note that such comparative studies cannot be used to indicate a direct and simple relationship between climate variability and human history. Their detailed palaeoclimatic history, however, lends new credence to the idea that climate variability can impact human society. Sounding a cautionary note, the researchers suggest that projected global climate change may affect human societies more than is currently expected, and that complex causal links between past climate changes and human responses urgently require more investigation.