According to the theory proposed by Felix, the increase in volcanic activity (along with a magnetic reversal of the poles) is linked to the onset of a new ice. This has been going on for millions of years with a new ice age occurring every 10,000 years. We are due for another one now.
Over the last 700,000 years actually the periodicity is 100,000 years, interrupted with 10,000 years,on average, of warm period,
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Ice Ages & Astronomical Causes
Figure 1-5 Climate for the last 420 kyr, from Vostok ice
From this plot, it is clear that most of the last 420 thousand years (420 kyr) was spent in ice age. The brief periods when the record peaks above the zero line, the interglacials, typically lasted from a few thousand to perhaps twenty thousand years. See also: Origin of the 100 kyr Glacial Cycle & Spectrum of 100-kyr glacial cycle: Orbital inclination, not eccentricity
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this is mainly related to astronomical factors relating to variations in the Earth's orbit more than geological reasons.
Looking back 1 million years and more, even that picture changes drastically, primarily due to continental drift and similar effects happening on the wider geological scales of time.
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Ice Ages & Astronomical Causes
The ice records take us back only to 420,000 years in the past. However, oxygen isotope records in sea floor cores allow us to go further. One of the best sets of data comes from a location in the northern Atlantic Ocean known as the Ocean Drilling Project Site 607 . This site has climate data going back three million years, and is shown in Figure 1-6. But before you look at the figure, let us warn you. In the paleoclimate community, there is a convention that time is shown backwards. That is, the present is plotted on the left-hand edge, and the past is towards the right. We are going to use this opportunity to change our convention, for the remainder of the book, so that you will have less trouble reading the literature. (The literature of "global warming" scientists, in contrast, follows the other convention, which we have used up until now.) We apologize for this change in convention, but we do not take blame for it. In Figure 1-6, the 10 kyr years of agriculture and civilization appear as a sudden rise in temperature barely visible squeezed against the left hand axis of the plot. The temperature of 1950 is indicated by the horizontal line. As is evident from the data, civilization was created in an unusual time. There are several important features to notice in these data, all of which will be discussed further in the remainder of the book. For the last million years or so (the left most third of the plot) the oscillations have had a cycle of about 100 kyr (thousand years). That is, the enduring period of ice is broken, roughly every 100 kyr, by a brief interglacial. During this time, the terminations of the ice ages appear to be particularly abrupt, as you can see from the sudden jumps that took place near 0, 120, 320, 450, and 650 thousand years ago. This has led scientists to characterize the data as shaped like a "sawtooth," although the pattern is not perfectly regular.
Figure 1-6 Climate of the last 3 million years But as we look back beyond a 1000 kyr (1 million years), the character changes completely. The cycle is much shorter (it averages 41 kyr), the amplitude is reduced, the average value is higher (indicating that the ice ages were not as intense) and there is no evidence for the sawtooth shape. These are the features that ice age theories endeavor to explain. Why did the transition take place? What are the meanings of the frequencies? (We will show that they are well-known astronomical frequencies.) In the period immediately preceding the data shown here, older than 3 million years, the temperature didn’t drop below the 1950 value, and we believe that large glaciers didn’t form – perhaps only small ones, such as we have today in Greenland and Antarctica. |
Looking back beyond the 3 million year window, we find a much different pattern of events and global temperatures which have roots in continental drift and potentially our position in the galactic arms as we swing in and out of galactic dust clouds and variations in cosmic ray flux in the disc of our Galaxy.
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Global Surface Temperature and Atmospheric CO2 over Geologic Time
Late Carboniferous to Early Permian time (315 mya -- 270 mya) is the only time period in the last 600 million years when both atmospheric CO2 and temperatures were as low as they are today (Quaternary Period ). Temperature after C.R. Scotese |
