[WIP] Building a world from tectonics onward

[MrBragg]

Regarding the test you ran with Antarctica, there should indeed be a significant difference there--and you'd be surprised how warm polar regions can get without ice thanks to constant sunlight in summer.

That it was warmer made sense, but the magnitude seemed off. As a followup here I removed the ice from Greenland and saw qualitatively similar but somewhat less crazy warming of Greenland / Siberia / northern Canada. My guess is that's due to the moderating effect of water near the pole, though removing half the land from an ice-free Antarctica still gives temperatures nearing 30 C in the summer.

Ice-free Greenland
lastmap.png

As a point of comparison, I'd actually be really curious to know what ExoPlaSim predicts for the temperature of your southern continent in the summer to see how that compares to the >40 C predicted by Clima-sim. Even with its systematic issues, I'd be much more inclined to trust the output from ExoPlaSim given how much more explicitly it treats things.

[worldbuilding pasta]

As a point of comparison, I'd actually be really curious to know what ExoPlaSim predicts for the temperature of your southern continent in the summer to see how that compares to the >40 C predicted by Clima-sim. Even with its systematic issues, I'd be much more inclined to trust the output from ExoPlaSim given how much more explicitly it treats things.

I checked and it reached about 20-25 C in summer, but that's with years about 1/3 the length of Earth's (and various other tweaked parameters) so it's not a direct comparison to clima-sim's model. I've also recently been running a range of models of Earth at different temperatures (there will be a post up about it soon) and for Earth 10 C hotter than today on average, with fully melted ice caps (though topography not adjusted to account for that because it'd be a ton of effort) Antarctica reached around 30-40 C in summer. So all in all, yes, there's probably something funky going on with clima-sim here, likely because it's just not really designed to handle heat flowing away from the poles.

A question however about the elevation: it seems that at the poles, elevation and the presence of ice sheets are somewhat endogenous to each other. For instance, most of Greenland would be below 1000 meters above sea level if it weren't for the presence of the Greenland Ice Sheet, which is 2-3 kilometers thick. The high elevation brings temperatures down, which allows for a continuing ice sheet- a feedback loop basically. I'm assuming that Clima-sim or ExoPlasim would give us ice cap climates near the poles if we were to include 2000-meter-thick ice caps in our elevation map inputs. So barring a detailed history of atmospheric CO2 for the world, maybe the presence of an ice sheet is a decision we have to make ahead of time as we're building the planet, rather than assuming from our geology that doesn't take into account the potential presence of thick ice sheets at some of the poles.

There is a valid point there, but if your ultimate concern is the extent of the ice sheets, then it doesn't really matter. The extent of a glacier is determined by its edges, where it's fairly thin; if those edges melt away, the interior will melt down towards the land surface, and if the edges are stable, the interior will be as well regardless of whether it's 10 meters or 4 kilometers thick.

Of course in reality, flow of ice from the glacier interior to the edges has a cooling effect that helps the glacier expand, and that will depend on the internal structure of the glacier, but glacial flow isn't modeled in ExoPlaSim (or clima-sim for that matter, but it's a bit easier to adjust glacial extent on the fly there) so it's a moot point. You kind of just have to accept that the model will underestimate the extent of glaciers in most cases. However, if your intent is to have an Earth-like world emerging from a recent ice age, it does help to run the model to balance first at something like 5-10 C colder than your intended temperature, and then warm it up from there. (Also ExoPlaSim does have the capacity to model the presence of deep glaciers on top of the topography, but doing so would require messing around with the running files and probably be more effort than it's worth).

Also, ExoPlaSim can run on mac, though it takes a bit more fiddling around; there's some notes on it in the readme on its github