ICE AGE OR GLOBAL WARMING?
he 'reindeer' cave art we saw in chapter 8 was located in
southern France and there are certainly no reindeer there
now. Reindeer are caribou, a sub-arctic animal. So as the
big-brained human-like fossils go back some 300,000 years perhaps
we should look at what our scientists tell us about the last ice age
and its ending.
No one seems to know why it ended when it did; in fact there are
various theories about how and why ice ages come and go. It has
been recognized that oxygen isotope ratios vary with the volume of
glacial ice. The earth also has magnetic field reversals from time to
time, which can be identified. By taking deep sea cores and
checking the oxygen isotope fluctuations against the magnetic
polarity reversals, we get this:
I prefer to read the scale horizontally as shown here, although it was
originally vertical. Our present time is now at the right. Warm is up,
cold is down. The horizontal time span is almost 2 million years. You
can see that we are now reaching a peak of temperature after a
climb from the last ice age. That climb is longer than any other in the
last 1.9 million years, which suggests we are in for falling
temperatures towards another ice age fairly soon. Temperatures
have on average been in decline over the last 300,000 years. We
can also note that the swings between warm and cold spells are
becoming much more severe than they were earlier in the last two
million years or so.
Present conventional wisdom tells us the last ice age
ended about 10,000 BP or at most started its decline about 12,000
years ago. If so, this chart may be of limited value
unless the 10-12,000 BP change was too small or too recent to register,
because by actual measurement it appears
to me from the time scale given that the low point occurred at just over
30,000 BP and temperature has been rising since then.
As the interglacial ages advance, the amount of water in the oceans
and elsewhere becomes correspondingly greater, producing a
terraced effect, like this:
When the ice increases the sea levels go back down.
What this means is that as the planet is at present in a warm spell with sea
levels rising, much low lying land is flooded that was inhabited during or soon after
the end of the last ice age. Even Roman docks and wharves in the
Mediterranean can be seen under water today. Land also rises when
the weight of ice melts off it, and continents are always drifting about.
So our planet has plenty of change and surface movement.
When we consider the time scale of ice ages against the known
specimens of big-brained individuals, say back to about 300,000
years ago, we see they can be traced to the peak of a
warm period and their history since then has spanned three ice ages
and three warm periods. But during all that time it is apparently only in the last
5,000 to 6,000 or so years that urban civilizations have arisen.
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