My theory on what causes ice ages, and why human activity is the reason we're not in an ice age right now.

I've never heard anyone posit an explanation for why we go in and out of ice ages, so here's mine.

Look at the red line in the middle of the chart I posted, you'll see that it has peaks that come regularly, but not so regularly that it would suggest some sort of astronomical event that happens like clockwork, it looks more like a repeating process to me. It follows the same basic pattern each time, but not quite the same schedule.

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Since it's a cycle, it just keeps repeating, so I'll start at the point when the earth is coming out of an ice age. As the ice retreats in the summer, there are patches of bare ground where forest which had once been there was killed off by ice. When the sun hits these bare areas, they get warm and heat the air, causing more ice to melt. The ground exposed by the melting ice has no vegetation, so it heats up too and a feedback loop develops, warming the planet until the ice is gone. This is the big spike in temperature you see on the chart, and why it peaks higher than at any other time: the ice is no longer reflecting solar energy and there's no vegetation to cool the ground.

As plant life begins to return, it starts to consume solar energy, but the process takes a long time, since glaciers wiped away a lot of the top soil. Eventually though, forests spread across the earth, covering every piece of open ground, as forests tend to do. The trees become very large, the forests very dense, and they consume enough of the solar energy that the planet tips into a long cooling phase. Eventually ice sheets cover most of the planet, killing most of the forest, then the open ground heats the air and the whole process repeats.

That's why our present warm period just keeps going and going when previous warm periods were much more brief. This time there were humans, and not just humans, civilizations. Thousands of years ago the Middle East and North Africa were covered in forest, but ancient civilizations cut most of it down. That excess heat from that bare ground was sufficient to prevent the earth from tipping into the ice age that would normally be well underway by now. As civilization spread across the globe, so did deforestation, so we've made the earth's climate more similar to the way it normally is during the early part of a warm period.

As such, I don't think we'll be going into an ice age until or unless people stop artificially limiting the forest cover of the planet.

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Mazes avatar Science
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"why then, does the temp and sea level not follow the latest spike in CO2 level?"

If you look carefully at the chart, there are periods where temp and CO2 are trending in opposite directions, CO2 always turns to follow temperature. Based on that, it seems evident that temperature is the driver and CO2 is the passenger.

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Well, we created the last spike in CO2 by burning fossil fuels, and we've kept temperature from falling by removing forest. As far as I can tell, the only way they're related is we did both things. Normally when CO2 levels and temperature rise, it's knocked back down by plant life, we've interrupted that.

There's no way to know for sure what the long term effects of our presence will be on the climate, but based on what we know, an ice age would be a disaster for our civilization as well as much of the life on earth, so there's a solid chance we're better off with whatever is behind door number two anyway.

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But doesn't it take low temperatures in the North for the precipitation to fall as snow in the first place, and then to remain on the ground as ice for many thousands of years?

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Not where Nancy Pelosi and the other libs live.
They have walls to keep out the riff-raff. hehe smilie

@Thinkerbell Here is one recent theory. https://www2.lbl.gov/Science-Ar...sediments.html

Interesting, thanks for posting that. If it's an astronomical cycle related to the tilt of the earth, why doesn't it happen like clockwork? There's tens of thousands of years of variation in the distance between temperature peaks, that's not what I'd expect to see if that theory is correct.

@Maze Interesting, thanks for posting that. If it's an astronomical cycle related to the tilt of the earth, why doesn't...

I think this theory has to do with the tilt of the Earth's orbit rather than the tilt of the Earth itself.
I'm not sure exactly what would cause the orbit to tilt up and down with a period of about 100,000 years, unless perhaps it would be the influence of Jupiter and Saturn pulling the high side of the Earth's orbit down and the low side up, but if that happens, it would depend on the major planets being in precisely the right positions at the right time. Maybe there is some variation (depending on Jupiter's and Saturn's motions) exactly when that happens and when they are in position to actually effect the change.

@Maze Interesting, thanks for posting that. If it's an astronomical cycle related to the tilt of the earth, why doesn't...

Oh, it just occurred to me that an excellent example of a non-clockwork repetition of an astronomical phenomenon is solar eclipses, which vary widely in time and place from one eclipse to the next.  It is true that there is an approximate repetition of eclipse cycles every 18 years or so, but these repetitions do not occur at the same latitude, and they are only approximate.
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