I'm trying to design a planet with two continents where one is always warm/hot and the other is cool/cold. The continents should be directly opposite each other (so not a pole and an equatorial one). They should by separated by some kind of barrier that is very hard but not impossible to cross (I'm imagining a large ocean but it could be anything that works, high mountains, expanse of volcanic fields, extreme weather, etc). Each continent can be either one large landmass or several smaller ones clustered together.

I don't want a tidally locked planet because a) I want day/night cycles and b) I don't want extreme heat and cold. Both continents should be habitable by human societies that have adapted to their climate without major technological intervention.

Basically one continent should have a constant Scandinavian winter climate with lots of snow but where you can still go outside wearing normal winter gear, and the other should have a constant hot climate, say Mediterranean or southern US summer. The hot continent can be tropical or dry or a mix, it doesn't matter as long as it's habitable (i.e. not just one massive desert). The continents can have seasons as long as they are mild - the hot continent's winter should still be warmer than the cold continent's summer.

Would it be enough to just make the cold continent at a much higher altitude than the hot one? Or is there a way to tilt the axis of the planet so that one hemisphere has very long hot summers and short mild winters while the other has long cold winters and short cool summers (not long enough to melt the snow)?

The climate difference is necessary for aesthetic/plot reasons but this is not a hard sci-fi world so a certain amount of fudging would be OK. I just want to figure out in my own head roughly how it could work.

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    $\begingroup$ I'm curious about the need to have the continents be exactly antipodal. Unless the story involves tunneling straight down through the earth, I can't think of a reason why that would come up. For most purposes, I'd expect near-antipodes on opposite sides of the planet but at different latitudes would function the same. $\endgroup$ – Nuclear Hoagie Dec 2 '20 at 21:54
  • $\begingroup$ If on your wintry continent it is always winter... how do people grow food? $\endgroup$ – Erik Dec 3 '20 at 7:57
  • $\begingroup$ Nuclear Hoagie - for aesthetic/symbolic reasons. As I said, this is not a hard sci-fi world. $\endgroup$ – チェズ Dec 3 '20 at 11:36
  • $\begingroup$ Erik - their culture has adapted to the climate in similar ways as real human societies living in cold climates e.g. they eat a lot of fish and meat, berries and root vegetables, seaweed etc. They don't grow summer crops. It's not constantly ice and blizzards, just always cold. $\endgroup$ – チェズ Dec 3 '20 at 11:38

Of course changing the elevation would work. Let's look at our Earth:

Lhasa is located at about 30° north, elevation 3.6km. The average high temperature is 23°C during summer, average low -10°C during winter (and that's average). Quite a cool climate. Now, 30°N is about the latitude of Tripoli - with definitely hotter-than-Mediterranean climate, average high 32°C, average low 9°C.

Then take the Bouvet Island, located at 54°S, with an average high 10°C during summer (i.e. no summer as we know it), average low -6°C during winter and covered in a glacier.

54°N is the latitude of Copenhagen - while not a Mediterranean city, the climate is quite pleasant, with average summer high 25°C and anverage winter low 0°C.

So our Earth comes close, there are just no suitable sized continents at just the correct places. Keep our Gulf Stream to warm up the regions above the *Mediterranean, Antarctic Circumpolar Current to cool down the *Antarctica and have a Tibet-like elevated continent at the place of our Bouvet Island.

  • $\begingroup$ In fact there's very little land at all directly opposite any other land on this planet, climatically similar or otherwise. $\endgroup$ – Darrel Hoffman Dec 2 '20 at 21:24
  • $\begingroup$ Thanks, accepted as this seems like the simplest way to achieve what I want. $\endgroup$ – チェズ Dec 3 '20 at 11:39

One way which gets your continents strictly opposite from each other is by giving your planet a tilted axis and an elliptical orbit.

If, say, the Cold Place is centred at 45° north you just need to make sure that it has summer (i.e. that it's tilted towards the sun) when the planet is the furthest away from the its sun. This way, the tilt and the distance would counteract each other on the northern hemisphere, while they combine in the south. The opposite is true in the northern summer.

By varying the latitudes, the eccentricity of the orbit and the tilt you could get many levels of difference. I don't have time to run the numbers now, but I could try later.

Also, you could cheat a little bit by placing one continent slightly closer to the equator if you need to to get the difference you want.

Note though, that this configuration likely isn't totally stable, in that the difference would probably vary or even reverse over sufficiently long time scales. Within the life of a civilisation it should be stable enough though.

  • $\begingroup$ What effect would this have on day length, specifically how much day length differs between summer and winter in each place? Would a more severe tilt lead to very long summer days and very long winter nights? $\endgroup$ – チェズ Dec 3 '20 at 11:46

A Simple way to create this sort of Climat would be to place both Continents roughly where Europe is in the real world. Then you can use a Underwater Stream to heat up one Contienent. You could for example say that this Continent is exactly where pretty much all Underwater streams of the entire planet meet. That would heat up the Place. Remember that Europe would be more or less like Finland if it wasnt for some Streams. At least the parts in the north.

The next thing you could add would be a lot of Geothermal activity and a one sided high Mountain range. This Mountain Range would capture Hot air for Air Streams to heat the place up even more.

Finally you could make a lot of the Surface of the Continent some black Material like Obsidian or Ash. That too would capture a lot of Heat.

  • $\begingroup$ I like the idea of using obsidian in the hot continent to absorb heat, especially as it ties in nicely with a geothermally active area. I'm confused about the one-sided mountain range though - how can a mountain range have only one side? And where would it be? $\endgroup$ – チェズ Dec 3 '20 at 11:42
  • $\begingroup$ Ah yes sorry that was a bit missleading. I meant to say that there is one Mountain Range one one side of the Continient. For Example, lets say the West side has a giant wall of Mountains while North, East and south dont. The idea is that the Air Currents have to travel accros the Continent and then get stopped by the Mountains. $\endgroup$ – Erik Hall Dec 3 '20 at 11:58

Air Currents

On Earth, there are several global air-currents which are reasonably consistent - e.g. the Gulf Stream, which, for example, warm up countries which are North enough that one would expect a lot of snow. e.g. warm air flowing up the Atlantic warms up Western Europe.

So heat in an area isn't just down to how much time you get in the sun. You could have an exaggerated version of this - i.e. Your global air currents move in such a way that the warm air from the equatorial areas generally hit the warm continent, whereas the cold air from the polar areas are more likely to flow into the cold continent.

  • $\begingroup$ Very useful to add to the altitude solution and increase the difference, thank you. $\endgroup$ – チェズ Dec 3 '20 at 11:43

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