Changing Earth's Axial Tilt?
January 31, 2021 10:00 AM   Subscribe

This is a question for I guess planetologists or geologists? I am not asking "how to change it", but rather what would a slight change either + or - in Earth's axial tilt do to the planet, in broad strokes?

Please, any and all info is much appreciated!

More tilt makes for more extreme seasons, and the tropics become higher latitudes, right? Does it also make for more powerful and extreme weather?

Does more tilt mean a hotter core and more vulcanism?
Does the tilt have any effect on the magnetic field?
Would plate tectonics be different?
What other large scale effects am I not considering?

In terms of human civilisation is our current setup "just right", or would slightly smaller or larger tilt make for a more bountiful and more habitable planet?
posted by Meatbomb to Science & Nature (10 answers total) 2 users marked this as a favorite
 
Response by poster: And just FYI, my basic Google research prior to this question already includes

"What if our tilt was 0%?" --> sucks, very fixed climate bands
"What if our tilt was 90% / 45%?" --> super sucks, massive swings in temp and super extreme weather

So I am really more curious about how you think very slight changes would work out, like maybe +/- 0.5, or 1, or 2...
posted by Meatbomb at 10:21 AM on January 31, 2021


More tilt would mean a larger Arctic Circle and Antartic Circle, which means a larger area would experience the “midnight sun” and “polar night” (constant daylight or constant darkness for parts of the year). In places that are already within the circles, these phenemena would last longer.

An increase of 2° would bring Fairbanks, Alaska an into the Arctic Circle.

(Conversely, less tilt would mean that fewer places experience the midnight sun and polar night, and those that do would experience them for less of the year.)
posted by mbrubeck at 10:27 AM on January 31, 2021 [1 favorite]


a tilt change that happened suddenly (suddenly being anything less than geologic time scales of millions of years) would result in massive species die off - most plants are adapted to their local seasonal patterns and making their season shorter or longer, or shifting their ideal habitable zone a few degrees longitude north or south would kill them off before they could adapt. the only survivors would be those already flexible enough to grow across a wide range of temperature and moisture conditions.
posted by slow graffiti at 10:32 AM on January 31, 2021 [1 favorite]


If you tilted the Earth while keeping the moon's orbital plane fixed, then the tides would change, though I don’t know how to predict the exact effects.

On the other hand, if you tilt both the Earth and the orbit of the moon by the same amount, the relative positions of the moon and sun in the sky would change. In particular, an increase in tilt of 5.145° would align the moon’s orbital plane with the ecliptic plane, giving us solar and lunar eclipses every single month.
posted by mbrubeck at 10:38 AM on January 31, 2021 [4 favorites]


Response by poster: slow graffiti - my question is not about having it suddenly change, but what if it had always been so... like, when the moon was formed from the planetary collision 4.5 billion years ago, the tilt worked out slightly differently way back then.
posted by Meatbomb at 11:02 AM on January 31, 2021


Less tilt results in higher latitudes getting more horizontal and less vertical sunlight. For zero tilt, polar mountainous regions would have valleys of permanent darkness. Less tilt would make the poles much colder, and result in polar ice caps much larger than they are now. (I wonder if the increased polar mass might cause the planet to wobble back to a more tilted state?)

The reduced insolation will also make the polar ecologies much less productive.
posted by monotreme at 11:32 AM on January 31, 2021 [2 favorites]


We already have small changes in earth's axial tilt. from about 22 degrees to 24.5 degrees.
this is periodic occurring over 40, 000 year periods.
Milankovitch speculated that ice ages would be periodic over that time frame.

There are other variations as well. The earth wobbles or precesses every 23000 years, and
The earths orbit about the sun also changes over a 100,000 year period becoming more or less eccentric.

You might find this article interesting:
Milankovitch (Orbital) Cycles and Their Role in Earth's Climate
posted by yyz at 11:56 AM on January 31, 2021 [5 favorites]


α Ursae Minoris, the North Star, currently moves in a tiny circle relative to the apparent axis of the Primum Mobile during the ~23,000-year precession yyz describes. A different axial tilt would of course make α Ursae Minoris no longer the North Star.
posted by XMLicious at 2:25 AM on February 1, 2021 [1 favorite]


Consider the Earth as a spherical cow. You've divorced the axial tilt of the spin from the rate of the spin and the two are the same side of the coin because they are related in an inseparable way to conserve angular momentum. Now there's a whole explanation of why a giant ball of random gas (details redacted) sorta flattens into a galaxy the same way a more local bit flattens into a solar system and there's a bit of a bias because of that conservation that will end up meaning that the spherical cow of the Earth will keep rotating as it is because the amount of energy required to change it quickly is catastrophic enough to be beyond comprehension except for just making stuff up. It also narrows down the spin+axis possibilities into some things that are just mostly impossible unless aliens are doing something weird.

Now if we keep the 24 hour day for rotation and the 365.24 or whatever and just take a bit of "just like now but a bit different".

You could not have the North pole always pointing towards the sun. Angular momentum changes require catastrophic amounts of energy. At that 90 degree tilt you get a yearly cycle of one or the other hemisphere in light or dark. Winter is coming, migration to stay in the livable zone. Still a bit hard to ponder without going into fantasy.

That leaves the just slightly different than current tilt. Weather is an odd combination of the spin, texture (the atmosphere is remarkably thin when compared to mountains and oceans and landmass areas). The general principle is still energy. That's why it's climate change and not global warming/cooling. The weather happens because of the energy from the sping and the temperature differences (and moisture and other stuff).

You end up sorta like if we were at 0 degrees there would be almost totally predictable weather because.... there's not that extra randomish energy from the summer/winter. You've gone from the tilt+year change to just the year change. Smaller envelope.

As you increase the tilt, you ride that envelope to the opposite side. There's a yearly weather pattern, but still it's like summer/winter.

You should see by now that the 0 tilt gives one rotation daily patterns. The actual current minor tilt gives seasons. The full tilt give year long hell.

The rest comes down to interaction of the thin atmosphere hugging above a spinning ball and being hot in the middle and cold at the ends.

The internal magnetic bit is probably even more complicated because the Earth isn't a spherical cow and it's all sorta liquid. The North and South rotational spin poles don't even align with the Magnetic poles. And both have moved or even flipped (magnetic) in timescales that we can sorta think about.

I'm not sure there's really much of an answer beyond speculation that doesn't hit that catastrophic energy barrier that makes humans go poof or is at least weird enough that making something up is just as likely to be correct.

Eh, 0 tilt more predictable. 90 tilt still predictable but longer scale. As always the interesting bit is in the middle. If you're just and only just thinking about tilt, the difference is probably an increase in the strength/chaos of the weather because of the mid-range difference of energy distribution.
posted by zengargoyle at 7:36 AM on February 1, 2021 [2 favorites]


You could consider the case of Uranus, the odd ball of the solar system that has an axis tilt of 98 degrees -- essentially it rotates on its side.

If the earth had the same tilt it would have some extreme effects. Around the summer solstice, half the earth would be pointed directly at the sun and that half the would have 24-hour sun light and be steaming hot, much higher temperatures than exist today. And at the same time, the other half of the earth would never see the sun and be freezing cold, much colder than temperatures that exist today.
posted by JackFlash at 8:28 AM on February 1, 2021


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