You may recall the discussion we had a few weeks ago on climate change. I picked up this link on the BBC web site about the climate in Australia, which I thought you might find interesting on how rapidly the climate can change with as yet an unknown cause and so far as I know not identified before in any part of the world.
Not having your background, whilst I noticed the absence of other references did not place any significance on it, though of course you are quite right.
Yes, lots of false trails hit the palaeontologists in the face each time. Given that eastern Siberia and what is now Alaska would still have been conjoined and had some quite balmy periods. There are fossilised tropical forest remains pre-humanity in Alaska. The native people of the northern parts of the Nordic countries, the Sami, are closely related to North American native people genetically, so that DNA sequencing works eastwards across the top of Eurasia, into North America and across to Greenland. The Sami and native Greenlanders are only distantly related although a few tens of thousands of years ago they could have migrated westward on the ice sheet (or the Greenlandic Inuit could have gone east). This is said to give a clue to climatic change direction in the north over the period of the dispersal of the native people. The North American, right down to the tip of South American people are genetically Asian. The Americas are the one 'barren land' where there was no pre-migration human beings. The reasons are not known (as yet). The Denisovans to Papua New Guinea (PNG usually) runs parallel to groups from the south of India and parts of Africa but Denisovans have contributed DNA to native Australians along with present day New Guineans and the Mamnwa indigenous tribe in the Philippines. The genetics study makes native Australians probably the oldest living population in the world and certainly the oldest outside of Africa which shows they probably have the oldest continuous culture on the planet. That culture has ancient stories about them leaving the cold lands, very certainly describing cold winds and snow on the ground among people who live in a desert area where there are no mountains, indeed it is a very long way south before they reach them and they have never heard of them anyway, which seems to be migration memory. Papuans have a gene that arises though mutation and is found at the same place on a chromosome they share with Denisovans and Australian aboriginal people, so called allenes. They have more sharing alleles than the Australian peoples though. Through that data a theory has been extrapolated that suggests that modern and archaic humans interbred somewhere in Asia before the migration to Australia. Thus you get two different migration routes in which Denisovans have direct DNA chain evidence back to Siberia from PNG whereas the Australians appear to be a convergence of African, southern Asian and Denisovan people somewhere in Asia at the same time, give or take a bit. There is no direct Neanderthal line back from the Pacific but in both cases the migratory routes would have crossed areas with a lot of evidence of modern humans and Neanderthals intermingling. The environmental picture is complicated but is there for those with time to invest in it explaining how and why the population drifts probably occurred. Lots of ice and snow plus drought and aridity over places we now know as lush tropics included.
Do I believe Richard Seager? The answer is definitely no. There is an unwritten academic rule, that whoever only gives themselves as reference material in books, articles or reports rather than a wide range of authors engaged in comparable and contrasting work is not be trusted. There is a lot of mileage in that since it is nearly always possible to try to tear anybody's work apart but those who do not even attempt to confrontationally do so can often only work that way because they lack data or materials to disprove the work of others. As it is, Seager is not a climatic change theory denier but has made some strange remarks. It is he who first said that Iraqi refugees are adding to the conditions that created IS which is part of environmental change that comes with climate change. He is rather adamant that the Gulf Stream is not changing but is almost fanatically warning the SW USA that a major, long lasting drought has already started. He is rather more of a poor USA afflicted by all of the changes caused by everybody else but never the cause type. The Gulf of Mexico being at the foot of the USA simply cannot be said to be doing anything with causality in the Americas.
I was no consciously aware of the Denisovans until your post and again reminds me how much we have to learn. One of my interests is in the spread of the Homo species throughout the world and this relatively new material obsoletes some of what has been written in the books in my library.
However, one point that does resonate is that, according to the map, they spread to New Guinea (or whatever it is called today) but not to Australia. As the "aboriginal" population seemed to have come via a separate island hopping route and are not genetically related to the "native" population of NG.
Nor did they apparently make it to N America during the same period.
So "modern" man and the Denisovans must have been around at the same time, hence the inter-breeding.
Sadly, the problem in the USA is that the genetics of the "native American" population are so mixed up with PC views that the "truth", which indeed may be out there is being distorted and/or ignored.
Thank you also for the link about the Gulf Stream. (The Independent link does not work for me!)
Do I believe him? No sure. Clearly the Gulf Stream has a major effect on sea temperatures all along the N West coast of Europe. As I recall the last vestiges keep Murmansk more or less free of sea ice during the winter. Are there other factors involved? I imagine so, as I take the view that we know very little about the climate in world and I cannot realistically assess his research then I will accept the other points he makes.
It seems to me that if the GS does slow down or stop, then that must have a significant impact on the climate in N W Europe. Another ice age I doubt it but perhaps we will become more like Canada or the N West USA in the winter months.
So the problem we now have, is if we keep on warming the world, we may delay to stop the next Ice Age but there might be an interim period when the very cold Artic water stops the Gulf Stream until the Artic water is sufficiently warm enough - where we are today - to get it going again.
I say this slightly tongue in cheek if only to make the point that we really do not understand the possible consequences of the global experiment being conducted by the Environmental lobby without our consent and subject to approval by politicians who respond to "populist angst!"
The Ice Age theory is interesting when related to human beings. Among our ancestors are Denisovans. In the Denisova cave parts of the finger bone of a young girl and molar teeth of other people including adults of various ages and a young boy who lived at least 50,000 years ago (the girl) and that two other Denisovan individuals died in the cave at least 110,000 years ago and perhaps as early as 170,000 years ago have been identified by sequencing their mitochondrial DNA. The Denisova cave is in southwestern Siberia, in the Altai Mountains near the border with China and Mongolia. The last Eurasian Ice Age was approximately 110,000 to 112,000 years ago.
Neanderthal remains have also be found interspersed with Denisovans. The Neanderthals in habited Europe and southwestern to central Asia about 400,000 - 40,000 years ago. We know far more about them than Denisovans and have established they did not necessarily hang around to wear lots of animal skins during a number of periods of ice age, that means they migrated to warmer climes which explains the time dispersal of quantities of remains found.
Despite that part of Central Asia now being a notably barren and incredibly cold climate much of the time, the reason Denisovans and Neanderthals were there would have been the relatively temperate climate and abundance of food. Ice ages heavily reduce that potential, especially the general lack of vegetable matter. They would have evolved to a dead end, indeed they did die out, but most Europeans have a large percentage of inherited DNA from Neanderthals particularly with some evidence of Denisovan ancestry, particularly as one goes eastward. However, modern Central Asian and Siberian indigenous people have far less. The other palaeontological evidence shows that around 50,000 years ago there were at least four human groups: modern humans, Neanderthals, Denisovans and small , often called 'hobbits' who were found in Indonesia who actually carry Denisovan DNA similar to western Europeans, appearing roughly 95,000 years ago but dying out around 17,000 years ago. Their DNA is found in parts of Indonesia but even some in East and Central Africa, very little though.
All of this tells us about both human and climatic ecology with the key to timing some events showing lines of probable early human migration. In Africa it was the success of early modern Homo Sapiens along with a period of aridity that made food scarce, probably water as well. Europeans are probably the outcome of two or three groups coming together in a temperate and fertile area where food was plentiful then interbreeding rather than moderns killing off Neanderthals as the theory used to be pre DNA sequencing. If we take the remains, the artefacts and such things as 'cave art' we get a fairly precise picture of each group in its location. That also tells us a lot about the physical world.
Climatic changes we learn about alongside all of the above were rapid and radical. In some places we can see that in a single millennium a rich, fertile place could have become desert or tundra. However, we know from the marginal areas of deserts that desertification is a rapid process. The highest rate measured was in the 1980s where one place measured over 2km, that place is not nearly 5km into desert. Synonymously we can look at Greenland that was recorded as only ice cap early in the 20 century with very little vegetation against now large areas of forest and tundra, with some meadowland that are permanently ice free that is increasing rapidly.
So we know that there are climatic cycles and that a European ice age is 'due' but not exactly next week. We also see that ice ages are sometimes preceded by periods that are hot and arid, reducing vegetation that to an extent holds back ice capping. What is unique this time is that human activity has distorted climatic change thus the present global warming has happened too fast and all the wrong time so that instead of ice caps 'moving' to take ice ages to other parts of the world, we have polar cap melting that would happen normally during a period of far more volcanic activity where not so much the actual ambient temperature as the gases released led to melting. Measuring human migration is naturally difficult in the modern world for obvious reasons but being very recent in real terms we can predict that had we not reached our present evolutionary state that European species of homo sapiens might have migrated out leaving the rest of the group to go the route of Neanderthal and Denisovan humans into extinction.
All superb stuff but very dry reading. I am into it because my academic starting point was human migration and somehow I have become both professionally involved and personally interested again in the last two years. However, it helps inform me on the physical science parts that I do not understand. As for predictions, well they are very imprecise and even then usually in thousands of years so that we really do not need think about our own direct descendants who will adapt anyway as changes happen but for who we will be as obscure as Romans are to us.
Very interesting link, thanks...
This capacity and likelihood for (extremely),rapid change I remember being discussed when scientists had made the discovery/observed that the course and trajectory of the Gulf Stream had already altered considerably...I think travelling across the Atlantic off the coast of the US at a much lower latitude, so that places like Nova Scotia were remaining iced up for far longer....and of course this has implications for northern Europe...
One (rather alarming), prediction, is if the Gulf Stream continues to travel acsoss at a lower and lower latitude, then at some point, almost overnight, Northern Europe would be plunged into another Ice Age.....although there is still alot of debate about whether this is the case...thankfully...
Yes, Brian and of course that part of Africa is "due" to split away as a new "minor" plate, if the projections turn out to be correct. Not all proto tectonic plates actually form, also for reasons as yet unknown.
My point is only that as you say with your example and this one I did not know about from Australia is that there are "frequent" and apparently rapid changes in climate and we should be very careful not to confuse what we are (maybe) doing to the climate and what is "natural"
I read it too. Interesting isn't it when put alongside other comparable situations. The Great Rift Valley is about 6000 km long from Lebanon's Beqaa Valley in Asia to Mozambique in SE Africa but the part in Kenya is famous as what the Leakeys identified as the 'birthplace' of Homo Sapiens (no longer so certain, but irrelevant here). What one finds when visiting there is a very arid, quite climatically unfriendly place. However, palaeontologists, archaeologists and other experts have established that at the time early humans were found there it was very much unlike now. It was probably a place where the diversity of nutrition that gave the primate species that leg up toward being hominid then 'human' was a given because evidence of climate, vegetation and (edible) animal species found along with geological indicators shows that. In climatic terms when Homo Erectus appeared a little short of two million years ago.
The evidence shows it happened several times and recently even, less than 2000 years ago there was a period of 'ideal' conditions. So we know there are cycles, but we need a far better global overview before we can conclude too much.