Lack of Correlation between CO2 Levels and Antarctica Ice Sheet over Past 400 Million Years
In the previous part of this series, I wrote that over the past 540 million years, there hasn't been much correlation between atmospheric levels of CO2 and average global temperatures. Believers in the secular religion of global warming might attribute this to the continents having different relative and absolute positions in the past due to plate tectonics. Therefore, I urge you to have a look at this YouTube clip (see below) of the reconstructed positions and movements of continents over that period. As you will notice pretty quickly, the relative and absolute positions of many continents does change a lot over that period. FYI- the relative positions of these continents, more precisely their constituent cratons, over that time-span has been deduced through a combination of classical geology, paleontology, paleomagnetism, isotope analysis etc.
The fact that atmospheric levels of C02 ranging from 20x to 2-3x those seen today had little effect on average global temperature over such a long time-span and variety of continental arrangements, if anything, bolsters the argument about those levels being a relatively minor player in the larger scheme of things. Also note that most modern continental landmasses, except India and Australia and to some extent South America were near their current latitudes by 80 million years (at 5:10 in first clip) or about 15 million years before dinosaurs went extinct. Furthermore, Eocene Thermal Maximum (at 5:38) occurred when most continents were fairly close to their current latitude and longitude. Also, the most recent cycle of ice ages began about 6 million years ago (6:24-6:34) when all continents were, for practical purposes, at their present location.
Let us move to how long the ice-sheet currently covering Antarctica has been around. As you will soon see, the answer is more complicated and surprising than you might have expected. So let us first talk about the position of that specific continent relative to the geographical south pole for the past 540 million years, as shown in second clip. Long story short, some part of the modern Antarctic continent has been within the southern polar circle (south of 66.5 degrees South) for past 400 million years-which is, geologically speaking, a pretty long time. More surprisingly, the geographical south pole has been within the land mass of Antarctica for at two extended periods within those 400 million years- from 0 to 120 million years ago and 260 to 350 million years ago. To put it another way, Antarctica has been the south polar continent (often along with Australia) for a bit longer than vertebrates first crawled on dry land.
So how was the climate in Antarctica during the past 400 million years? Well.. for a good portion of that period, it was what we would today classify as temperate, albeit with an interesting twist due to being located at extreme southern latitudes. It may have been even warmer (subtropical) during the period between 240-400 million years ago, but once again with that peculiar seasonality. More importantly, it has been close to its current position for past 80 million years and had a cool temperate climate for at least half that period. In other words, long dark winters and long bright summers did not cause that continent to become a frozen wasteland for many ten millions of years.
The first evidence of some glaciation on that continent in the past 200 million years seems to have occurred around 40-35 million year ago. So what caused this cooling? Well.. the current explanation is that it was due to the Antarctic Circumpolar Current (see figure below) which started up after both South America and Australia separated from Antarctica to a point where such a current could form. The popular conventional view is that ACC created a cold barrier around Antarctica about 35 million years ago and it hasn't ever gotten warmer since then. Indeed, most official information sources on the internet try to endlessly repeat this lie. To be clear, nobody is denying that the ACC has been there in its current form for the past two million years. But evidence for the climate of Antarctica for past 35 million years is more complicated than most "experts" are willing to admit in public for reasons that will soon be obvious.
As many of you might have guessed, our knowledge about geology and paleontology of Antarctica is much sparser than for other continents. Nevertheless, a number of surveys for plant and animal fossils have revealed evidence which simply does not fit with the popular version of Antarctica being a frigid wasteland for the past 35 million years. For example, there is decent evidence that parts of Antarctica had extensive tundra like vegetation throughout the Oligocene to the mid Miocene (24-14 million years ago). Even conifers existed on that continent 15 million years ago. But the most striking evidence concerns the last forests on Antarctica, which existed as late as 2.3-2.6 million years ago- and I have written about in a previous post.
To be clear, the last forests on that continent were restricted to certain regions and their tree biome was largely made up some of most cold-resistant species. Having said that, we can use the types of tree and micro fossils found at those sites to estimate the contemporary climatic conditions. A cold-resistant tree genus known as Nothofagus aka southern beeches are well represented in those fossils. Luckily, living members of that genus can be found in the southern Andes, parts of Australia and New Zealand. To make another long story short, the region of Antarctica where those fossils were found would have to be about at least 30 degrees Celsius warmer than today for even the most cold-tolerant species in that genus to exist. Furthermore, there is a lower temperature limit for vascular plants- which is why there are only one or two species of vascular shrubs on that continent today.
There are also other independent lines of evidence to support the contention that Antarctica looked and felt a lot like certain parts of Northern Canada and Siberia as late as 2.3-2.6 million years ago. But such streams of evidence also create a massive problem for the popular model of Antarctica being an icebox for the past 35 million years. I mean.. why did Antarctica go through pretty large and incomplete cycles of partial glaciation and deglaciation within the past 40 million years, when it was close to its current location, physically isolated from other continents and the levels of atmospheric CO2 were in current range or lower. Also, why did the continent become a frozen icebox only in the past 2.3 million years?
What do you think? Comments?