Climate Mini-Exploration: Shifted Poles
Hey everyone, a short one today: Throughout these posts I've been using Earth's geography mostly just for demonstration purposes. The idea hasn't been so much to show what Earth specifically would look like under different conditions, but rather to demonstrate more generally how these conditions might influence Earth-like planets, with Earth's topography serving as a convenient point of reference. As such I generally haven't been too concerned with scenarios like Earth with a retrograde rotation or different arrangements of continents, because these don't really show any fundamental difference in the state and mechanisms of the climate independent of Earth's particular topography, and so don't often carry lessons we could carry into predicting the climates of other worlds (though where other people have already modelled retrograde Earth or climates of Earth's past I'm perfectly willing to pull their data and make climate maps, and in the future I might run some models with "toy" topography like land covering all of one hemisphere or only between certain latitudes, where we might be able to derive some general lessons on how land distribution impacts climate).
But I was recently contacted by someone who did want to see what the climate of Earth with shifted continents was like and was willing to commission me for the modelling time, and expressed a wish that the results should be made available on the blog, which is a fairly delightful task to be commissioned for. Let's take look at the results:
For the first one, I shifted the Earth's axis by 90°, placing the north pole at to sit at (0, 0) latitude and longitude, just off the African coast. Note that for these models I haven't attempted to replace the glacial topography of Greenland and Antarctica with any sort of ice-free reconstruction of the actual land surface, so they appear here with high, cool internal plateaus despite sitting near the equator, though this isn't actually too far off from what we might expect for them after isostatic rebound (and really a lot of regions would probably have substantially different topography if Earth had always had this orientation; much of the northern coastlines of Eurasia and North America have been shaped by glacial action and even long-term patterns of mantle convection and continent drift may be influenced in some way by the planet's rotational axis).
I also haven't altered any other parameters like axial tilt or CO levels from the baseline, but with no large glaciated landmasses, the overall climate is about 3 °C warmer than our Earth and there are no permanent ice caps. There are some clear winners and losers here in terms of overall hospitability and biodiversity: North America and Antarctica sport vast rainforests while Asia and South America have dried out; Australia has ended up a tad cooler and wetter; Europe sports much the same range of climates as in real life but shuffled around; and Africa has lost its arid belts but substantially cooled down, and might be expected to support a single vast boreal forest.
There are some interesting patterns over Asia I think are worth highlighting.
The large, equator-spanning continent experiences pretty strong temperature swings, which leads to large shifts in wind patterns and the tropical rain belt; a monsoon-type wind pattern, which we've seen before but usually think about in terms of drawing moisture from an equatorial ocean onto a subtropical landmass. Here, the landmass is equatorial and the ocean (the Arctic) lies to the east, but we still see a pattern of wetter summers and intensely dry winters as the winds off that ocean shift direction.
Meanwhile, a patch of the west coast remains conspicuously wet year-round, despite appearing to lie in the rainshadow of the Himalayas if we assume generally west-blowing tropical winds; to some extent this is helped by the monsoon pattern (as it brings winds from the north and south rather than exclusively from the east across the mountains) but it's also likely a result of lee cyclogenesis; the tendency for large mountain ranges with winds blowing directly across them to form a low-pressure zone on their lee (downwind) side, which can form cyclones that draw in moisture from nearby seas.
For the second model, we were looking to see what the impact of a large polar continent would be, so placed the north pole at (45° N, 80° E) latitude and longitude, near the China-Kazakhstan border, in order to place most of Asia in the Arctic circle. Oddly enough, this one only came out a tad cooler than the last model, and despite my attempts to encourage glaciers, they haven't spread out from Tibet (a trick I've been experimenting with a bit has been to start models with 1 meter of initial global ice cover, which helps slow its initial warming; for our Earth with its true arrangement of continents this does a better job of replicating the true ice cover, but more generally there seems to be a fairly narrow range of parameters where this works without the ice just promptly melting away anyway, like here, or failing to melt at all and locking the planet into a snowball state). A more complex approach of balancing at a lower CO level first and then warming might be more successful, but I may be overthinking things here.
That'll do for today, then. I may do more mini-explorations like this in the future, for quick model runs that don't necessarily merit the deep analysis or rigor of the main explorations, but for now work continues on the next main post, on the impact of eccentricity (and I'm also still working on the main series, I'm just a bit held up by probably getting a bit too obsessive about perfecting the process for generating the topography).
I imagine the continentality of Asia inhibits ice formation even right at the pole, reinforced by exoplasim's undershooting of ice caps. Perhaps cooler temperatures could be achieved if the north pole were somewhere around SEA or China -incidentally, yielding a south pole somewhere around South America. Apart from that I notice some interesting climate patterns, like tundra in india directly south of a boreal climate, or that little band of Dfa nestled right against the tibetan plateau
ReplyDeleteThe Indian tundra I think is the Deccan plateau.
DeleteIt is well known that too large a continent is always too dry for glaciers. In the Quaternary glacial periods, lowland Siberia and all of Manchuria escaped glaciation, whereas corresponding latitudes of North America were entirely glaciated. Even in Antarctica, the moisture to support the glaciation of the South Pole comes from the coastal mountains, and that to support Greenland does too. If Antarctica were the area of Eurasia, the ice would become much, much thinner and sublimation of snow during the summer would be much greater
DeleteWhat is now the coast from the Urals to the Taymyr Peninsula did become ice-covered. At least during the last three ice ages. I don’t know how much research has been put into the maximum extent of the ice sheet in Siberia. But here in Europe the ice never reached as far south as it did in North America. In the lowlands its largest extent was in northern Germany. This was somewhere around 51 degrees north. All permanent ice further south was limited to mountain chains.
DeleteLooking at the second map, one wonders what it would be like to have a large continental pole (larger than Antarctica) with a 90° axial tilt.
ReplyDeleteI always thought continents crowding the equator tended to cool the planet, since they are more reflective than open ocean.
ReplyDeleteWhere would you put the poles if you wanted the warmest, wettest global climate possible?
All else being equal I suppose more equatorial land would have some cooling effect, but the lack of ice caps is clearly the stronger factor. For a warm wet climate, you'd probably want to experiment to find a particular orientation that placed as much land as possible in the tropical and temperate rain belts (~0-20 and 40-60 latitude) while avoiding the poles and desert belts. Orientation of mountain ranges would also matter too, though.
DeleteReminds me of a study? article? that I read a couple of years ago- you can get major glaciation with either a polar sea surrounded by land, or a polar continent surrounded by ocean. But otherwise? No I’ve caps. Your model doesn’t do deep-sea currents, so probably a different source, but still.
ReplyDeleteMakes me wonder what would have happened if you’d put both Asia and South America directly on the pole itself, rather than close-but-not-quite.
Still interesting to read, though. Whole project reminds me a little of Planetcopia.
The first example is similar to Cris Wayan’s Seapole.
DeleteIn the second model, do I see a small patch of tropical rainforest in Iceland? There must be a significant warm current running up the eastern side of North America, as that is quite far poleward for a tropical rainforest (even though substantially lower latitude than Iceland in the real world.)
ReplyDeleteExoPlaSim doesn't fully model ocean currents, there is some degree of heat exchange between adjacent ocean cells but it's not really modelled as a fluid--fortunately ocean currents turn out to be a less critical factor in global climate than is often supposed. In this case it probably comes down to the world as a whole being a tad warmer and iceland being well-positioned to pick up some warm winds from North America in summer but benefit from the heat capacity of the Atlantic ocean in winter.
DeleteI wonder what would happen to the climate of a habitable planet with dense rocky rings. From what I do know, the rings would reflect quite a lot of heat and light into the summer nights, and block the star's light in the winter daytime.
ReplyDeleteI did recently come across one old paper attempting to model the effect of a ring's shadow and did find pretty substantial cooling https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001JD001230, but they model that ring as completely opaque, which isn't terribly realistic, didn't model any reflection of light back onto the surface (though I doubt that would amount to much), and is just about old enough that I'd be hesitant to trust any of the specifics of their computer model (it's also arguing for debris rings from past impacts being a major influence on Earth's climate at several points which is not an idea that ever caught on).
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