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In message , Adrian D. Shaw
Not that I ever studied A level geology, but as far as I remember the
normal pattern over (recent) geological history has been 100,000 years
of ice age followed by 10,000 years of milder climate. It's something
like 12,000 years since the last ice age.
That's just for very recent dates, the planet's vastly older than that
 and has been ice-free for almost all its history. There are just
two short periods where you get any ice at all, one in the Precambrian
and the other in the Recent. Geologist call those ice ages; during them
there are colder and warmer phases when the ice advances and retreats,
called glaciations or stades or whatever, but there's always quite a lot
of ice around the poles.
What these two periods have in common is that the continents were mostly
gathered around a pole - around the S pole in the Precambrian, around
the N pole in the Recent.
For the rest of geological time (a few thousand million years) the
continents have been distributed in other ways and there hasn't been any
ice.  Two episodes is not a large sample to base conclusions on, but
it's considered eccentric to argue that the placing of continents
doesn't cause the ice.
The planet is warmer overall when ice-free, but there's also less
difference between the climate at the poles and at the equator.
The continents have smaller land areas and wide continental shelves
where the fossil sea creatures swam in warm shallow seas (geology is
heavy on warm shallow seas because they produce the best fossils).
Skiing means sand skiing, but there's lots of scope for snorkelling.
It seems likely that the buildup of ice is made possible by the
continents obstructing the movement of ocean currents. The warm water
from the equator can't reach the poles and keep them warm, so ice forms
there. Then the ice reflects sunlight and makes the poles colder still,
and the sea level drops because so much water is piled up on land,
exposing the continental shelf and increasing the land area available
for accumulating ice.
Nobody knows exactly what the continents have to do to keep the poles
iced up. So we don't know whether our Recent ice age is set to continue
for another few million years or whether it could end overnight.
We do know that if people keep pumping out ever-increasing amounts of
CO2, the North West Passage will become a reality within twenty years.
That means you'll be able to sail a boat from the Atlantic to the
Pacific across the Arctic Sea, above the remains of Cold War nuclear
submarines that hunted each other under the ice. Dedicated researchers
are working night and day on funding applications to buy supercomputer
time to try to predict the effects of this on ocean currents and hence
on the climate.
The small, low-lying nations of the Pacific see each year's storms
coming further up the beach; they're planning their evacuations and
making bets on which whole country will be the first to disappear.
Large countries with huge populations living on low ground (Bangladesh,
Britain) are not making plans, perhaps because they can't think of any
to make - I think I've suddenly gone off the idea of devolution for
Scotland and Wales though.
 unless you're a religious fundie in which case it was created a few
thousand years ago with thousands of millions of years' worth of fake
geology built in, just to fool us. Half of all USA voters believe this
version, thanks to only about 10% who are fundies and control what US
schools and media are allowed to say.
 The continents move around, albeit slowly. For instance, the
Atlantic ocean is getting wider from the middle at a few centimetres a
century. The famous San Andreas Fault is the scrape between the Pacific
Ocean moving one way and North America moving the other way.
BTW the ice advances and retreats simultaneously at both poles although
only one has the continents.
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