I think that anyone who has taken an interest in climate change is aware of the role that our ever-changing climate has played in the rise and fall of civilisations and the prosperity and suffering of ordinary people ranging from anecdotes about the Greenland settlements and the considerably more detailed material available about the effect of the degradation of the European climate during the so-called Little Ice Age.
Writing in the Science Online a team of researchers (led by Willy Tegel, University of Freiburg, Institute for Forest Growth and Ulf Büntgen, Swiss Federal Research Institute) have produced what they say is the first annual-resolved European summer climate data for the past 2,500 years. The climate data comes from tree rings obtained from living trees, historical timber and sub-fossil wood of Stone Pine and European Larch from Germany, France, Italy and Austria. In all they say they examined some 9000 pieces of wood collected over 30 years.
The researchers say their analysis reveals possible links between past climate variability and changes in human history, although they are clearly not the first to make this link. Climate change, they maintain, coincided with periods of socioeconomic, cultural and political turmoil associated with the Barbarian Migrations, the Black Death and Thirty Years’ War.
They find that European summer climate during the Roman Era about 2,000 years ago was relatively warm and wet and characterised by less variability than today. Increased climate variations from around 250-600 A.D. coincided with the demise of the Western Roman Empire and the exceptional turmoil of the so-called Migration Period.
The new study revealed that humid and mild summers accompanied the rapid cultural and political growth of Medieval Europe, whereas unfavorable climate may have played a role in the 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.
However my interest, and indeed confidence, in this study, is somewhat undermined when I looked at the temperature estimates derived from the tree ring data and a comment in the paper’s abstract that warming in the late 20th and early 21st century appears unprecedented with respect to the past 2,500 years. The comment seems inserted for political correctness and seems out of place.
In addition, looking at their Fig 4 (click on image to enlarge) shows the expected Medieval Warm Period and the Little Ice Age, but what is the 2 degree rise in temperature seen in the 20th century when other databases show a rise substantially less than half that? I think that point should have been address in the paper.
Looking at the graph another thing strikes me. Bad things, such as wars, plagues and famines, as well as mass migrations, only happen during a downturn in global temperature. Does this mean our modern, warmer world is a safer one? Lessons from the past are useful but limited. In our populous, demarcated world mass migrations are no longer possible meaning that our brains will have to tackle climate change, not our feet.