Milankovitch cycles: What are they and how do they affect Earth?

I think this article does a good job for the aspects of this topic, relating the parameters of Earth's orbit and rotation to the habitability of our planet. and also bringing in our unusually large moon's stabilizing influence. That is all pertinent to the questions we have discussed on other threads about the probability of finding another planet like ours.

But, from the perspective of those of us who also think about climate problems here on Earth, I think this article is somewhat lacking. At least it did not try to claim that the Earth's climate can be predicted adequately just by looking at the Milankovitch cycle. For one thing, the calculations for solar energy hitting the northern hemisphere do not seem to show the biggest peaks having the same frequency as the ice age cycle s, and the timing seems to drift out of sync the way we currently estimate the periods of the various Milankovitch cycles.

I have suggested previously that the periods of some of those cycles might be altered by the gigantic shifts in water mass from the equatorial oceans into ice masses on the higher latitudes of the northern continents, so there may be some ability to better tune the cycle predictions.

But, it still looks like the climate has a chaotic component, and that may well have to do with circulation patterns of ocean currents and their effects on atmospheric circulation patterns. For instance, see and .

Some propose that the closing of the ocean passage through Central America a few million years ago set the ice age cycles in motion by stopping ocean currents from exchanging between the Pacific and Atlantic Oceans. And that happened about the same time that crust upheavals (which are what created the Central American Peninsula and separated the oceans) exposed a lot of new rock surfaces, which seem to have pulled a lot of CO2 out of the atmosphere by the process of rock weathering. Some have proposed using that same process to remove extra carbon, now, see https://www.anthropocenemagazine.or...-overlooked-but-tantalizing-climate-solution/ .

Even though (last I read) we are not currently able to make computer models that can "backcast" the ice ages to match their geologically derived behavior, the geological evidence of atmospheric CO2 levels does provide reasonably good evidence that Earth's climate will be more like warmer periods of the more distant past, when atmospheric CO2 levels were about as high as they are now or are predicted to reach in this century.

Besides shifting the locations of terrestrial forests and steppes and deserts, the end of ice ages will probably mean that sea level will eventually rise by something like 300 feet. If that seems unimaginable, consider that it has already risen about 325 feet since the peak of the last ice age, only about 20,000 years ago, and it did nearly all of that in only a few thousand years. Also, consider that the sea level high point in the last interglacial warm period was about 25 feet higher than it is right now. And, in the previous periods of high CO2 levels in our atmosphere, there were much higher sea levels than now, but the continents were also positioned differently.

So, the idea that humans can stabilize our climate and sea level to remain within a few feet of where it is right now seems remote. We will have to adapt to some pretty substantial changes, at least until we can learn a lot more about how our planet's climate really operates - and get a lot more control over our own collective behaviors.
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Another interesting link:
Note the part about the center part of Antarctica being open water about 120,000 years ago. That would have been in the last warm period between the last ice age and the one before. And, it could explain 10 feet of the 25 feet of additional sea level that seems to have occurred then, compared to now.

With the current state of the Milankovitch cycles putting more heat into the southern hemisphere than the northern hemisphere, there is some question in my mind how much of the warming in the Antarctic is human-induced, and how much is cyclic. Of course, there is also ice lost in the Arctic, now, too. The problem with figuring that out is that the climate does not seem to be in lockstep with the solar energy cycle calculations. There seem to be other factors that make the response more chaotic.


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