Having experienced the climate of coastal California, I’m liking it well enough, but there’s room for improvement: it’s a bit too warm, too foggy and cloudy, and way too humid. I’m also missing the spectacular desert landscapes of the interior and the wide daily ranges in temperature you see in the mountains.
So what would be the ideal climate for me? I suspect I’d do well on a sea coast next to some cold water where the sun shines brightly year-round, relative humidity is no greater than around 20%, high temperatures are no greater than the sixties, and lows consistently drop to below freezing at night, perhaps as low as zero degrees Fahrenheit…which I don’t think can exist on this planet. At least not in this climate regime.
Ocean water moderates the temperature too much, especially with the range from day to night, and creates way too much humidity, fog, and cloud cover. California’s coast, especially further south, does have the raw ingredients for a climate that’s not too different from what I describe; the same ingredients create a more extreme version of the characteristic Californian climate in Namibia: on the Skeleton Coast it’s perhaps sixty degrees year-round, negligible rainfall, and very foggy. That’s getting closer, but still no cigar.
No, the closest you’ll find on this planet is in the arid reaches of the Andes, where places like La Paz, Bolivia have negligible seasonality by virtue of being on the equator, downwind of the arid beaches crafted by the cold currents sweeping down from Antarctica, and the high altitude renders the temperatures rather chilly: fifties by day and twenties by night, year-round, with low humidity and abundant sunshine. It’s only missing the sea breeze factor.
So how could you get the sea breeze factor? My first thought is, of course, to worldbuild an alien planet: the hallmark characteristic of the Andes is high altitude, meaning thinner air; at lower pressure there’s less substance to the atmosphere that permits it to hold in heat. We see this reflected in the climate of Mars, where the tropics during summer can reach as high as eighty degrees Fahrenheit by day (yes, really)…but it still plunges to a hundred degrees below zero at night. The day length is about the same: it’s just that the atmosphere is less than a hundredth as thick, so the heat of the day radiates into space very fast at night, and the sun’s power is unobstructed come morning.
Thinner atmospheres create higher daily ranges across the board: air half as thick as present-day Earth, which is still breathable with acclimatization (this pressure is currently found at 18,000 feet), might just do the trick. Brainstorming with ChatGPT suggests that such a pressure range could sustain daily ranges from 60 degrees by day down to 15 degrees at night even in mid-latitude sea coasts. To get this temperature range, which is very chilly, waters would need to be much colder than Californian or even Namibian seas: it would need to be so cold, in fact, to moderate the beach air thus, that water temperatures would likely need to be down in the twenties Fahrenheit…well below the freezing point. Oops.
But there might be a way out: already our saltwater oceans freeze at 28 degrees or so, not the 32 degrees that pure water freezes at. And helpfully human beings find salinity levels far higher than Earth seawater pleasant enough: the Dead Sea has salinity of 34% (compared to only 3% for ocean water), and can remain liquid down to -6 degrees Fahrenheit. Now we’re talking.
Don Juan Pond in Antarctica, the saltiest body of water on Earth, is even more extreme: near the saturation point of salt at over 40% salinity, it can remain liquid down to a studly -58 degrees Fahrenheit. Of course once you reach near saturation you see phenomena like salt precipitating out of the water, leaving a film on the beach, the water surface itself having a different quality to it, more viscous and overtly briny. Not very fun.
Fortunately we probably won’t need to keep the ocean liquid down to -58: if all we need is temperatures in the twenties or at worst the teens, than Dead Sea level salinity will be more than sufficient. From a human point of view water at this salinity seems pretty much the same as ocean water, the main difference being how much easier it is to float and greater irritation if the stuff gets into your eyes. No big deal; in fact if we’re building up an alien planet that should be Earth-like (i.e. alien but not too alien), it would be a neat touch.
Cold oceans emit less water vapor, and thin atmospheres can’t hold as much humidity, so such a world may plausibly be high and dry. Even coastal regions with relatively higher humidity, around the 20% range, may be hyper-arid, with quite stable weather patterns: year-round it could be sixty by day, zero by night, with bright sunshine: rainfall or snowfall, even as much as drizzle or a flurry, may be a rare event. Considerably more common would no doubt be fog, but even this wouldn’t be terribly thick or commonplace: just enough to support a desert-like ecology.
The interiors would be even more extreme: relative humidity levels perhaps in the single-digit percentages, with daily ranges expanding to eighty degrees by day and twenty below zero by night. Precipitation would be nonexistent, bar perhaps a trickle from fogs that accumulate in the deepest valleys, much like in the Noctis Labyrinthus on Mars. Oases sustained by underground water and geologically-produced hot springs would be the heart of the interiors’ ecosystems, so isolated as to resemble an open-air version of the hydrothermal vent ecologies on Earth, with many endemic species.
Daily ranges could be pushed even higher than the default interior setting dominated by plains and rolling hills if these regions were in the mountains or on a high plateau, much like we see on Earth today, but carried to an almost Martian extreme. This world’s equivalent of the Dzungarian Gate could see daily ranges exceeding 100 degrees.
The situation could become even more extreme than this and still remain human-habitable: Earth’s atmosphere at the pressure experienced at 18,000 feet is near the limit for long-term living without supplemental oxygen, but keep in mind Earth’s atmosphere is only 21% oxygen, with the rest being nitrogen and various trace elements that are irrelevant to the human body. Strip away all the other components bar the ones we breathe, and you’re left with an atmosphere only 21% as thick but still just as breathable as Earth at sea level, because the “partial pressure” of oxygen is exactly the same!
Given a 100% (or nearly 100%) oxygen atmosphere (which could realistically occur, according to recent scientific research!), and the human ability to adapt to about half of Earth sea level pressure, in principle an atmosphere an atmosphere only a tenth as thick as Earth’s could still be breathable! That would be half of the partial pressure of oxygen at Earth sea level, with that being the (nigh) sole component of the atmosphere. Imagine how dry the air could be and how wide the temperature could get from day to night on that world! The climate could be positively Martian.
More extreme than what I’m after, but this goes to show there are some fascinating possibilities that are realistic but often overlooked, even in science fiction.
The geology would also be more Martian than Terran: without water to enrich the soil and the process of erosion from rain and snow to smooth the rocks, only wind erosion ablates rock into small particles, almost as sharp and angular as lunar regolith. On such a world, particularly in the interior, true topsoil would be absent, especially given the desertified conditions that lead to a lack of plant cover. Thermal expansion and contraction, given the wide daily temperature ranges, would be another large factor. Chemical weathering, which in our world is driven by water, would be almost nonexistent; rocks would maintain their original composition for far longer.
Fields of rock debris, flat solid plates of volcanic origin, rocky outcrops, and vast dune seas would dominate the landscape on such a world, even right next to the sea coast.
The otherworldly vibes would continue: given the hyper-aridity, depressions of oceanic crust or tectonic rifts like the Caspian Sea and Lake Baikal (respectively) would be exposed to the open air as dry land, leading to unique low-altitude and high-pressure climates that would feature much warmer conditions with less variation from day to night in temperature.
Briny water flowing underground from aquifers could emerge at the cliff faces that lead into these depressions, forming streams, rivers, and waterfalls, and fog could be quite extensive, being trapped at low altitude, condensing onto rock surfaces and supporting colonies of organisms. Saltwater lakes could form at the very bottom of these depressions, leading to evaporite rock formations such as salt pillars and mineral-encrusted cliffs, amid vast salt flats and sinkholes. Salt dust and salt fogs carried by the wind could create an alien haze in and around these depressions, perhaps joined (in the more extreme scenarios with even thinner air) ice fogs that accumulate every night before burning off in the heat of the day.
In a Baikal-scale depression with an atmosphere a fifth or even a tenth as thick as Earth, daytime temperatures could exceed a hundred degrees Fahrenheit even as the nights plunge to forty below zero, more than cold enough to support ice fog. In permanently shadowed regions ice could condense onto the rocks; especially in caves it would never burn off during the daytime, leading to entire cave systems encrusted in ice, subglacial melt rendering them as underwater ice caves, tongues resembling glaciers flowing out at veritably Martian velocities into the sunlit areas of the depression, creating rare standing bodies of liquid water in the interior before the harsh sun and dry air evaporate them away.
It’s a desert world, this place I’m imagining; shades of “Dune”, but with its own twist…including an internal contrast. While the land is harsh, the cold salty oceans might be just the opposite: desert dust blown off during sandstorms helps to fertilize the oceans of the Earth, and on this world that factor would be multiplied a hundredfold, nourishing a vast and thriving ecosystem of marine life, which tends to do better in the coldest of waters due to icewater being able to hold more dissolved oxygen than warmer water (hence why the poles are very productive in the marine realm even as land life starts to die back in the face of the cold).
Any land-based life that can take to the water and live off the sea would: even fairly deep in the interior the dominant life-form may well be birds, evolved to shelter themselves out of the way of any potential competitors. Their guano would provide fertile ground and perhaps even some much-needed water for various plant and animal life.
Desert-like plant life would no doubt cling to the coast, nourished by sea breezes and the odd fog or two throughout the year.
But the most exotic life-forms of all might be in the interior, evolved to cling to hot springs and aquifers for dear life. Picture something like a saguaro cactus: thick and insulated so as to hold in water, but with extremely deep root systems, designed to dig into even the hardest-to-access water underground, and with formidable scales, thorns, plates, designed to protect against any potential predators, or even the harsh winds that no doubt would sweep through the interior on a regular basis. Photosynthesis might be accomplished by protrusions from the very top of these perhaps very tall structures (greater size means more insulation, a valuable commodity in a place where it can be a hundred by day and forty below by night), much like the giant baobab trees of Madagascar.
In extreme cases these plants, or a colony of them, could grow so large as to entirely capture a hot spring or some such water source within themselves, their branches perhaps growing so large as to form a vertical forest over these oases, several hundred meters tall, much like the redwoods of California, their towering expanse harboring a rich ecosystem unto itself.
Alien, yet familiar. One wonders what sort of sapient life-forms or civilization could emerge in such a place, particularly on the harsher land side as opposed to the sea side; a fascinating possibility, but it might make an even better site for human colonization in some kind of science-fiction story. Maybe one I could write up sometime… 😀