# Climates if Earth had large axial tilt (45 or 90 degrees)

Has anybody made any serious calculations of what the climates on Earth would be if our planet had a larger axial tilt? The most interesting are the cases of 45 and 90 degrees.

90 degrees is easier to calculate here, so I'm going to talk about that, as we have a prime example existing in our current solar system (the planet Uranus)

With an axial tilt of 90 degrees, the magnetic and rotational north and south poles would be at the "equator" of the planet. This means that the planet would spin about in the 'Z' axis and thus the range of climate would be very much reduced to what we experience here on Earth.

We'd have no such concepts as seasons as, for 6 months of the year, we'd be in darkness, no sunlight to speak of and freezing cold temperatures (-40c or less) then, for the next 6 months, we'd be bathed in sunshine 24 hours a day pushing temperatures to extreme heats (50c or more) such temperatures are nearly fatal for us humans and quite possibly most other animals save extremophiles.

(Example ONLY)

However, there is a penumbral area, a band between the side facing the sun and the side away from the sun that could potentially be suitable for life. We'd experience a constant twilight there, never quite day nor night-time and as the planet moves throughout its orbit, this area would change positions.

This nature of a moving habitable area would probably mean that very little plant-life would be able to survive for long, either freezing to death or boiling. (save for the most hardy of plants such as cacti)

The fact that the tilt would be 90 degrees also means that along longitudinal lines there'd be no variation in the amount of "day time" throughout the year you'd get as you get closer to the geographical north.

EDIT: If anyone else wants to do 45 degrees, they're more than welcome to.

• Actually climate will be fairly moderate half of the year, as around the equinoxes day/night patterns will be close to what we have today. It definitely wouldn't be as bad as it would if the solar year was as long as on Uranus. Aug 25 '16 at 11:15
• Also, a big omission in regards to climate patterns - the differential of temperatures around the solstices would give rise to a new global wind pattern, with cold low altitude winds blowing towards the hot parts, and hot high altitude winds going the other way, in contrast with today, where low altitude winds are based on micro climate thermal day night dynamics and high altitude winds being steady product of interaction of the upper atmosphere with solar wind. This may have a number of implications, but it would require a simulation to get more detailed. Aug 25 '16 at 11:16
• @ddriver - You have some good points here. I just used Uranus as the example as it's the only planet we know of so far to have such a large angle of rotation (91 degrees) Aug 25 '16 at 12:31
• [duplicate] found in astronomy.se A good animation of 90° tilt can be seen here.
– rek
Aug 25 '16 at 13:36
• Directly at the poles will experience such extremes as seemingly endless winter nights and summer days (as the sun spirals around the sky toward the center and then back to the horizon), but there will still be days and 4 seasons everywhere else. A little off the poles will see a long night winter, then through a spring where days begin and grow ever longer, until summer with seemingly endless days, then autumn where nights begin and grow longer until winter (the long night). The equator will be much more 'normal' in terms of day/night cycles. Aug 25 '16 at 15:50

Thinking the 90 degree case @Raisus put a picture of. The most suitable place place for living like @Raisus pointed would be in the new equator. There during spring and autumn equinoxes the diurnal cycle of sunlight would be essentially the same as in current earth equator. While sunlight would come from lower angels when moving towards winter and summer solstices and then in mid summer finally in twilight mode for a while. So @Raisus is wrong there wouldn't be an eternal twilight anywhere.

Worse living conditions occur when moving from the equator to either poles everywhere but near the equator there would be darkness half a year and sunlight the other.

Like @ddriver commented climate patterns would be completely different than current earth. The greatest zonal temperature gradient would definitely be in the equator (current earth it is in both hemispheres in the mid-latitudes) and stronger than in anywhere in current earth. This would generate strong potential for warm air to blow to cold areas and cold to warm areas. Strong potential would lead to probably very large high and low pressure areas more effectively transporting and leveling heat between hot and cold sides of the earth. Stormy earth where it is livable.¨

I also disagree with the cacti, they in current earth endure great diurnal temperature changes, whereas evergreen trees are better in annual changes. So evergreens would probably prevail in areas away from equator but not too close to poles.

• I think in a world of extreme climate dynamics, mushrooms will prevail, as they always have throughout the history of the planet, their actual organism can bury deep underground, where the temperature is more suitable, they don't need sunlight, and they can survive on the carcasses of everything that doesn't make it. Aug 25 '16 at 12:36

There have been a couple studies about the climates of planets with high obliquities. See here: http://adsabs.harvard.edu/abs/2003IJAsB...2....1W and here: http://arxiv.org/abs/0807.4180

The main result is that the seasonal variations are much higher on planets with large obliquities. This is not too surprising since the obliquity is the main driver of seasons on Earth.

Orbital eccentricity can also drive seasons, especially in concert with obliquity. For instance, here is one simple climate model of a planet on an eccentric orbit with a large obliquity such that it only thaws once per year at the south pole (Details here: https://planetplanet.net/2014/10/06/real-life-sci-fi-worlds-1-the-eccentric-earth/).

Finally, it's worth noting that a planet's obliquity can oscillate in time (and its orbital eccentricity too). This will have a strong effect on modulating the climate (perhaps in extreme ways). See here: https://planetplanet.net/2014/10/08/real-life-sci-fi-worlds-3-the-oscillating-earth/

A paper on this topic just appeared: Multiple Climate States of Habitable Exoplanets: The Role of Obliquity and Irradiance

They describe a new kind of climate a so-called Uncapped Cryoplanet which is only possible for high obliquities. Such a planet has sea-ice around the equator and a permanent open ocean at the higher latitudes.

The following figure shows the temperature, the mass stream function, the zonal wind, and the meridional energy transport for a planet with 90 deg obliquity in southern summer. Depending on the initial condition of the planet either an Uncapped Cryoplanet or an Aquaplanet state exists (for further details see paper).

• If you could flash out the answer some more it would be better. Else it risks deletion.
– L.Dutch
Aug 6 '17 at 10:03
• The mentioned paper exactly answer this question. I think, you even haven't checked the paper. Figure 10 shows the climate including the atmospheric circulation and meridional energy transport for a Earth-like habitable planet with an obliquity of 90 deg. Aug 6 '17 at 16:41