So, I assigned the intro to Lynas's
Six Degrees to one of my classes. Someone in the class pointed to the passage that talks about how, even though 6C may not sound like much, it was the difference between today's relatively temperate NYC and an iceage era NYC area with a mile of glacier over it.
But someone else pointed out that you could probably go a couple hundred miles north of NYC and the temperatures on average would be that much colder than NYC today, but it (say, Nova Scotia) is not under a mile of ice. (She actually didn't quite say it that clearly, but that was the gist.)
I kind of waffled at the time. But when I looked into it, I found something unexpected (to me at least--probably completely 'duh' obvious to the rest of you):
First of all, apparently the cooling distributed evenly over the surface of the earth. There was less or none of it over the equatorial/tropical regions, especially over water. (So that's the first question--Is that anywhere near the ball park? It makes sense to me, but lots of things end up being rather counter intuitive in this field, I find.)
Second (and this was the part that I found a bit surprising), the distribution of the cooling across the
year was also not evenly distributed: the winters over much of the norther hemisphere were actually a bit warmer than current averages. I always thought of the ice age as unimaginably cold. But over much of the north it may have been a bit warmer (but longer) than what we experience in MN. All you need to freeze things is for temps to be generally below 0 C enough of the time that warming spells don't totally thaw it.
So a longer, though warmer, winter combined with a shorter and much cooler summer was enough to tip the balance in much of the NoHem so that more ices was formed every winter than was melted every summer...and then it's just a matter of piling on the years and the ice layers.
Does that sound about right? I foraged this from a number of sources that I can't recall right now. So if anyone has any points where I'm off (or especially if I'm completely full of bollocks!) or if you can point me to any (perhaps slightly user friendly?) sources to shore up my weak understanding of these things, it would be greatly appreciated.
Those effects have to do with how the sun hits the earth and affects the seasons when the tilt of the axis goes closer to straight up and down; so far northern and far southern climes are not tipped as directly toward the sun during their summers, hence the cooler summers. But conversely they are tipped closer to the sun during their winters, hence the warmer winters.
Thanks ahead of time for any corrections, pointers, or even face palms

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