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Imagine the Earth's axis of rotation were to precess in synch with the orbit of earth around the sun so the north pole always pointed towards the sun (same current axial tilt of about 23 degrees). Inside the arctic circle it would always be day light. Between the tropics and the arctic circle daylight hours would vary from slightly greater than 12 hours to much greater than 12 hours.

This would obviously wreak havoc on jet streams and thermohaline currents, but eventually things would stabilize and you'd reach a max temperature (ish) relative to latitude.

How scorchingly hot would the high arctic get and what would more temperate zones like 35 and 45 degrees latitude max out at for daily highs?

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  • $\begingroup$ Hello D, welcome to Worldbuilding. When you have a moment, please take our tour and read these two pages (help center and help center) to better understand how this Stack works. I'm not sure it's possible for a world to be tidally locked (which is what you're asking about) and have any axial tilt. I'm hoping the astronomers/celestial mechanics on the Stack chime in on that. $\endgroup$
    – JBH
    Commented Aug 1, 2021 at 2:22
  • $\begingroup$ Yeah, I have to confirm what @JBH said-- if you had the Earth with a rotation time equal to its orbital period, but also had an axial tilt, there would still be seasons, since the axis wouldn't change inclination to face the sun. I don't think it would even be referred to as "tidal locking" because it's not a situation that would come about by the natural pull of tides-- that would push the planet toward being zero inclination. $\endgroup$ Commented Aug 1, 2021 at 2:27
  • $\begingroup$ On our sister site Astronomy I found this question: Can a tidally-locked planet maintain an obliquity, which isn't quite as authoritative as I'd prefer, but has enough supporting information to suggest that you can't have a (significant) axial tilt and be tidally locked, and I suspect the planet would need to be tidally locked to answer your question. $\endgroup$
    – JBH
    Commented Aug 1, 2021 at 2:29
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    $\begingroup$ Setting aside the physical possibility of the orbital mechanics, the hypothetical is not meant to describe tidal locking. The rotation about its own axis is still 24 hours... it's just an endless summer in the northern hemisphere. Given season lag under current conditions en.wikipedia.org/wiki/Seasonal_lag the hottest average summer days are weeks from the solstice largely because the oceans take longer to absorb heat. If the mid latitude oceans were absorbing those extra couple of hours of sunlight per day during that lag, the max must be higher but how much?..... $\endgroup$
    – D to the P
    Commented Aug 1, 2021 at 16:09
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    $\begingroup$ Never mind the north.. I'm a bit concerned about the south. Antarctica would definitely get cold enough to start depositing CO2 ice, and might very well get cold enough to start condensing nitrogen. That would be.... interesting. It's a bit similar to considering the case of a tidally-locked world. $\endgroup$
    – PcMan
    Commented Oct 20, 2021 at 8:27

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Perhaps I am oversimplifying the question in my head, or I shouldn't be answering at midnight.

However, if I were to assume you're effectively asking what the daily highs would be if there was eternal summer on the northern hemisphere? Then I would advise you look to the tropics where there is very little, if any, variation between daily highs heedless of season. Sure, where I am there's a 'hot season' and a 'rainy season', but the highs are pretty constantly tropical.

Then of course, you need to contend with how this would affect the polar region. It would no longer experience its 3 months of night during winter, giving the ice sheets little time to 'regrow'.

That could have major ramifications for the polar regions. Enough to melt them and spike the temperatures further? Possibly. More so than the tropics? Doubtful. So you're still looking at tropical weather, just further north than currently is the case. And that would lock the southern hemisphere into perma-winter--something you shouldn't ignore, because that would have a lasting impact as well.

(In case that was unclear, that means you're looking at between 25-35 degrees Centigrade as highs, depending on local weather conditions)

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  • $\begingroup$ Pushing the upper and lower bounds by 25-35 C from their current average sounds fairly plausible. The Hadley Cell and other jet-stream behavior would be wild to see in a high-powered computer model. $\endgroup$
    – D to the P
    Commented Nov 5, 2023 at 16:21
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If the Earth had an almost horizontal axis of rotation, rather than an almost vertical one, it would have a very complicated day/night cycle that would probably wreak havoc on the atmosphere and climates.

If the planet is spinning about its horizontal axis, it cannot be tidally locked with the Sun due to the law of conservation of angular momentum. With a 360ish "day" year, the planet would rotate one degree, about its vertical axis, per day.

For one quarter of the year, points north of the equator would receive 24 hours of sun per day, and points south of the equator would receive 24 hours of dark. For the next quarter, there would be a "normal"ish day/night cycle. For the third quarter, points south of the equator would receive 24 hours of sun per day, and points north of the equator would receive 24 hours of dark. For the final quarter, there would,again, be a "normal"ish day/night cycle.

This would probably cause the north and south poles to alternate between desert and tundra. This would, in turn, cause all winds to blow strongly and continuously north for one quarter of the year, and south for one quarter. And God knows what it would do in between.

With two, short, growing seasons and two winters the planet would probably be nigh uninhabitable.

On the other hand, due to a quirk with gravity, the planet would probably, eventually, stop rotating and one side would burn as the other side froze.

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    $\begingroup$ So the intention is not to be a horizontal rotation of axis. It's still 23 degrees off vertical, but in such a way that the 23 degree tilt is always towards the sun for the northern hemisphere. Every day of the year, it's the summer equinox in the northern hemisphere, and the spin period is still 24 hours. So again, set aside whether that's possible from an orbital mechanics standpoint, I'm just speculating about what that means given the lag of the seasons (the hottest part of summer is weeks after the solstice) in our current progression of solstices and equinoxes. $\endgroup$
    – D to the P
    Commented Sep 21, 2021 at 16:27

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