climates of coldsun
This whole things starts with my love affair with maps, my admiration and envy for Chris Wayans’ Planetocopia, and the desire for a setting whose most distinctive features are visible by looking at the map. So here’s a rough, very first-draft planetary map of Coldsun - a world where exposure to sunlight cools things down, rather than heats them up.
(Caveats: don’t worry about the exact shape of the continents above, because it’ll change; don’t worry about the microphysics yet either. This is just about the general biomes and climate - and even there, imagery that appeals to me can get a pass as long as there’s some sort of baseline plausibility.) So!
The move obvious consequence is that things are colder near the equator than at the poles, the reverse of the usual situation.
However, the tropical regions aren’t packed with ice and snow because it’s actually pretty hard for ice and snow to form. This is because ice and snow have a high albedo, meaning they bounce back a lot of sunlight. In our world, with sunlight that heats things up, this means that ice and snow are somewhat self-reinforcing, leading to both snow piles that last longer than they otherwise would and to glacial feedback loops that lead to ice ages/hothouse periods - geological time periods where lots of ice cover, high albedo, and high temperature (or the reverse of those) reinforce one another. The world of Coldsun, by contrast, is homeostatic on this front.
(Except, of course, if you’re dealing with massive fields and glaciers of sooty black ice! Burning coal can’t just cool things down by damaging the equivalent of the ozone layer (if there’s an equivalent of an ozone layer? idk yet) but by creating ice formations with a much lower and thus can last, maybe even spread under the right conditions. The civilizations here used to operate at a higher level of technology, but these factors (combined with a bunch of others less relevant to this post) led to a crash period.)
Coldsun’s climate bands reverse the wet/dry alteration of Earth. An Intertropical Divergence Zone near the equator starts things off with its falling, cold air and hence low levels of precipitation. A Subtropical Low around our own horse latitudes features rising air and high levels of precipitation, followed by a band of desert. And the hot polar zones feature high precipitation, rather than the cold desert conditions of our own poles.
Around this Subtropical Low, with its abundant water and sunlight, but cold conditions, we get evergreen jungles. Shaggy, warmblooded mammals occupy niches here that tropical frogs and other jungle denizens might in our own world. Snow and ice (with fewer climactic consequences) can form in the canopy, melting to nurse rivers in the winter.
Fungal forests bloom in the poles, where the heat and precipitation would be ideal for life if not for the long sun-droughts. Photosynthesis-based plants grow crazy-quilt and kuzu-like in the summer before being devoured by mushrooms in the winter.
And the thick cactal forest region? That’s just a personal caprice - with the excuse being some sort of vast but deep aquifer supporting a dense growth of phreatophytes - rather than anything that flows out of the “cold sun” thing.