Saturday, 23 November 2013

A Human History of Climate Change in Europe Part I - 45,000 to 20,000 BP

After noticing this guest post by Andy May on Anthony Watts' WUWT blog - well worth a read - I was reminded that I've been meaning to write something similar with respect to the human impact of (natural) climate change in Europe (more specifically NW Europe) which, for obvious reasons, is historically, archaeologically and geologically rather better documented than elsewhere.

May's timeline starts at 18,000 years ago. I want to go back much further, starting at around 40-45,000 BP, in the depths of the last Ice Age, when anatomically modern humans first appeared in Northern Europe. A very long time, relatively speaking, during which average temperatures in Europe have fluctuated by as much as 15 degrees Celsius, sometimes dramatically and in a matter of just decades, as during the Dryas stadials/interstadials immediately prior to the Holocene. A period when, for much of the time, agriculture and large scale settlements were not even invented. A period during which much of Northern Europe was covered by huge ice sheets up to a mile thick, when a piffling 0.3C 'global warming', supposedly due to human CO2 emissions over the last 50/60 years, would have meant diddly squat to your average caveman and to the climate in general.

Worrying about incremental environmental changes, the evidence for which is often made possible to observe only because of advanced instrumentation, is a distinctly modern phenomenon. The temptation to attribute such changes to human beings probably goes back much further to the murky origins of anthropocentric thinking. Humans have, it seems, always preferred to reside at the centre of their very own universe.

The point is, and people often overlook this fact - the vast majority of the history of human habitation in Europe has been during Ice Age conditions. Only relatively recently (approx. 12,000 BP onwards) have Europeans basked in the warmth of the current interglacial - and civilisation has thrived in the process, made possible by the development of large-scale agriculture. Only even more recently (circa 5500 BC) has human civilsation really taken off and the population exploded. For the past 12,000 years, and particularly during the last 5000, global warming has been extraordinarily beneficial to mankind. Only now are we asked to believe that another possible 2-4C warming in the coming centuries, supposedly due to anthropogenic CO2, if it ever happens, will be catastrophic for the environment and for human civilisation.

It was originally thought that modern humans did not appear in Europe until well after 30-35,000 BP when the last Neanderthals died out. However, recent archaeological discoveries put back the date for the arrival of modern humans in Europe to 40-45,000BP. They were probably able to migrate north overland from Africa to Europe, across terrain which nowadays forms the sea-bed - sea levels being very much lower during the Ice Age. Therefore early modern humans and Neanderthals must have coexisted in Europe for many thousands of years. This 2011 paper in Nature confirms the discovery of the earliest known modern human remains in Devon, dated to between 41,000 and 43,000 years BP.

Did Climate Change Kill off the Neanderthals?

Neanderthals are said to be our closest extinct relatives and, indeed, Homo neanderthalensis and Homo sapiens diverged along separate evolutionary paths from a common African ancestor only 400,000 years ago. Neanderthals moved north to Europe whilst our direct ancestors stayed put in Africa for over 300,000 years. The reasons for the demise of Neanderthals in Europe have been fiercely debated for many years now and theories have come and gone with no definitive answer to the question 'Why did Neanderthals become extinct approx. 28,000 years ago?'

Climate change has been mooted as a possible cause on several occasions, with volcanic eruptions suggested as one driver of such climatic variability, but nothing really substantive has ever come out of these arguments. To understand why climate change 30 or 40,000 years ago is unlikely to have done for Homo Neanderthalensis we need only look at the evidence of repeated glaciations over the last 400,000 years, as revealed by the Vostok ice core:

Neanderthals thrived in Europe for 200-300,000 years, during which they endured repeated ice ages followed by warmer inter-glacials. Cooling is unlikely to have sent them over the edge as they were well adapted to enduring a frigid climate, more so than Homo sapiens who spent most of their time evolving in Africa during the period when Neanderthals reigned supreme in a much colder Europe. Neanderthals disappeared during the peak of the last glacial maximum. They had been gone for many thousands of years before the retreat of the great European ice sheets starting approximately 20,000 years BP. If anyone was going to suffer from the severe cold, one would have thought it would have been our direct ancestors, having only relatively recently arrived from sunnier climes further south.

The most likely reason for the demise of the Neanderthals is not climate-related but rather due in no small measure to the arrival of modern humans on the scene. Before Homo sapiens appeared, the European offshoot of our common African hominid ancestor was doing just fine. After we arrived, the original Europeans went into rather rapid decline and disappeared totally within several thousand years. Competition is a possibility. Transmission of disease from modern humans is another. As an interesting and somewhat wry historical observation, Europeans are often slated for their past colonialist behaviour, particularly in Africa. But in actual fact, it was 'Africans' who, directly or indirectly, probably wiped out the original Europeans - the Neanderthals - and it was their ancestors - modern white northern-latitude adapted Homo sapiens - who went back to Africa thousands of years later to impose colonialist rule!

Another intriguing suggestion is that the domestication of dogs played a significant part in the downfall of Neanderthals. It is now thought that dogs were first domesticated from an extinct lineage of European wolf some 19,000 to 32,000 years ago. Previously, it was believed that they were domesticated much later in the Middle East (as suggested in Andy May's WUWT essay) or even in China. This introduces the real possibility that canines were domesticated in Europe at the time when Neanderthals and modern humans co-existed. Accordingly, there have been suggestions that the companionship of dogs, who were supposedly domesticated by modern humans, afforded modern humans a crucial advantage over their Neanderthal cousins, especially when it came to assistance in hunting prey. Hence, with the help of canines, Homo sapiens were far better placed to out-compete their Neanderthal rivals, bereft as the latter were of the assistance, protection and early warning provided by Man's best friend.

Early domestic dog remains have only been found in human encampments, not Neanderthal, so it seems likely that Neanderthals did not originally domesticate wild wolves. However, Neanderthals and early humans did interbreed, hence there are remnants of ancient Neanderthal DNA in our genome. Only human females impregnated by Neanderthal males were able to produce viable offspring as evidenced by the lack of mitochondrial Neanderthal DNA in modern humans. My personal theory is that these cross-breeds, who naturally would have been raised in human encampments with their human mothers, uniquely possessed the ability to interact with 'friendly' wolves who would linger around human encampments looking for food and perhaps protection from other wolves. Domestication of dogs was thus achieved via two hominid species, but our direct human ancestors were the only ones to really benefit. Neanderthal communities lost out because the 'dog-friendly' hybrids were brought up in human groups.

Perhaps this might also explain why humans were able to endure the icy cold despite their recent African ancestry. Dogs have a natural body temperature a few degrees higher than ours. Long-haired species are supremely adapted to the cold. The Inuit have an expression 'three dog night' - meaning a very cold night when snuggling up to sleep with three dogs would be the equivalent of a modern high tog rating duvet!

Whatever the case, modern humans survived the worst vagaries of the last great Ice Age in Europe. They survived and then they thrived, hunting for big game on the vast dry open grasslands of the Late Pleistocene just beyond the edges of the great ice sheets, no doubt also supplementing their diet with plants and herbs, berries and nuts. Then, after the dramatic and damaging series of climatic upheavals associated with the ending of the Ice Age proper (notably the Younger Dryas) human population exploded into the relatively warm and benign Holocene.

Jaime Jessop   2013