In this post we’ll discuss worldbuilding polar ice caps, ice ages, and which flora and fauna are able to survive within the subzero climate zones.

Hey everyone, my name is Matthew, at least when I’m not totally frozen solid, and this post is part of a series where I will be going through a science-adjacent worldbuilding process step-by-step. Last time we discussed the subarctic zones of our fictional world of Locus, looking at the seasonal flora and fauna that thrive across the semi-frozen regions.

For today’s discussion, we’ll be looking at the final climate zone present across earth-like planets, the polar climates, with not-so-empty tundras and vast snow fields that dominate the furthest points of the planet.

Polar climates, according to the Koppen Climate Classification system, are classified as climates where no months have average temperatures that exceed 10 degrees Celsius. Polar climates are then divided into Tundra and Ice Cap climates, with Tundra climates referring to areas where the warmest months have average temperatures between 0 and 10 degrees Celsius, while Ice cap climates never have any monthly average temperatures above 0. These climates can also exist at high altitudes, especially within the temperate band, and though their climate conditions are identical to the above classifications, polar climates that exist due to elevation are referred to as ‘alpine climates’ for the sake of differentiation.

Tundra climates have at least one month where temperatures are high enough to melt snow, though the generally low temperatures make rates of evapotranspiration so low that terrain tends to be waterlogged, allowing wetlands of all kinds to form even in places that receive low enough precipitation that they would be considered deserts if they were at lower latitudes. Very few human settlements exist within tundra climates on earth, with Svalbard in Norway and Nuuk in Greenland being some of the more well-known inhabited tundra locations.

Ice Cap climates are sometimes referred to as ‘eternal winter’ climates, as conditions allow for ice and frost no matter the time of year. On earth, this refers to areas like Antarctica and inner Greenland, as well as the summits of tall mountains. While many people think of these climates and imagine snow, precipitation here is actually almost non-existent, as once temperatures drop below -20 degrees Celsius it is generally too cold for both rain and snow. These frozen landscapes are considered inhospitable to human life, though while there are no permanent settlements within ice cap climates on earth, some research stations such as the Summit Station in Greenland and the Amundsen-Scott Station in Antarctica can be found here.

True to their name, ice cap climates are also present in areas of the polar ocean that have frozen over, either permanently or seasonally. However, the moderating presence of the ocean means that ice caps are overwhelmingly more likely to form across polar continental areas, and so on earth our southern polar ice cap is far more expansive and frigid due to the Antarctic continent when compared to the northern ice cap that forms over the Arctic Sea.

While ice caps are reasonably well known to us, they weren’t always present on earth and aren’t necessary for any other earth-like planets either. Earth-like planets shift between two primary climate states: greenhouse and icehouse. In short, greenhouse and icehouse states refer to whether polar ice caps are present or not. While we view polar ice caps as ‘normal’, earth has actually been in a greenhouse state for around 85% of its history, and we are currently in an icehouse state. When a planet is in a greenhouse state, no continental glaciers exist anywhere on the planet, while a planet in an icehouse state has ice caps at both of its poles. More commonly, we refer to an icehouse state as an ‘ice age’, which are then divided into periods that are glacial and interglacial, which simply refer to whether ice sheets are growing or diminishing.

There are a number of factors that can cause glaciation and interglaciation, though overwhelmingly the main cause is variation in a planet’s movement around its star. Generally speaking, if a planet is trending towards being further away from its star, temperatures will drop and glaciation will occur, while the opposite is true if the planet is trending towards being closer to its star. The closer a planet gets to average surface temperatures being 0 degrees Celsius, the more expansive the ice sheets are. If a planet reaches or drops below 0 degrees, then a planet with surface water would be considered a ‘snowball planet’, with its surface having completely frozen over.

In contrast, planets are expected to be within a greenhouse state if average surface temperatures are higher than 17.1 degrees Celsius, though it is worth noting that this is the upper more conservative estimate. Some climate scientists believe that earth-like planets can enter a greenhouse state with average surface temperatures as low as 14.7 degrees Celsius. For perspective, on earth our current average surface temperature is 13.9 degrees Celsius, and we are currently in an interglacial icehouse state, meaning that we have ice sheets present but that they are progressively getting smaller. At our current rate of interglaciation, it is expected that a complete deglaciation of the northern hemisphere will occur, which may pull earth out of its icehouse state and begin a greenhouse state.

Now that we’ve discussed tundra and ice cap climates, let’s look at where to place them on earth-like planets. This is the map of Locus, the fictional world we’re creating throughout this series. We’ve already placed all other earth-like climate zones on the map, and the tundra and ice cap climates will be the final two we have to place. If your planet is like earth, with similar surface temperatures, rotational direction and speed, then your tundra climates will form starting at the polar front at 60 degrees north and south along cold ocean currents and extend poleward up to around 80 degrees. With similar surface temperatures to earth, any earth-like planet is likely to be in an icehouse state, making any remnant areas right up to the north and south poles exist as ice cap climates.

If your planet is warmer than earth, then tundra climates start further poleward, at around 70 degrees north and south. Warmer planets must make the distinction between being in a greenhouse or an icehouse state, which as we discussed earlier cuts off somewhere between 14.7 and 17.1 degrees Celsius. Warmer planets still in an icehouse state will have ice cap coverage greatly reduced, only existing above 70 degrees north and south in continental interiors, and seasonally within polar oceans. A planet that is just below the greenhouse threshold may have ice caps that exist only in one hemisphere at a time, though a planet above the greenhouse threshold will have no ice caps at all, making tundra present all the way to the poles.

On a planet colder than earth, like Locus, we have a very different story. Tundra climates start at around 55 degrees north and south, though along areas with warm currents will exist only as thin strips, while along continental areas and areas with cold currents they will be far more expansive, reaching as far poleward as 75 degrees north and south. Ice cap climate coverage greatly expands, starting at the poles and reaching down past the polar front. How far it extends past the polar front depends on how much colder than earth the planet is, but a good rule of thumb is that for planets at or above 10 degrees Celsius, it will creep down past the polar front to 55 degrees north and south, for planets at or above 5 degrees Celsius, it will creep down to 40 degrees north and south, and for planets at or above 2 degrees Celsius, it will creep down to around 20 degrees north and south, always skewing towards areas affected by warm ocean currents. Which gives Locus a polar climate coverage of something like… this.

Notably, on this map I’ve marked out the ice caps that have formed over the polar oceans due to them being permanently present, though seasonality would still cause some growing and shrinking of these zones. On earth, the seasonality of our northern ice cap often means it is not included on maps, and as a worldbuilder it is your choice whether you include polar ocean ice caps on your maps, though my recommendation would be to exclude any areas that aren’t permanently present to avoid confusion. Also, the southern ice caps on Locus extend way closer to the polar front than they do in the northern hemisphere, and creep in towards the continents while starting further poleward out in the ocean. The reasons for these differences are that the northern continent is wider, and therefore has more expansive tundra, and that these areas out in the southern ice caps are moderated more heavily by the ocean. It is these areas that are most likely to be affected by seasons, though Locus has a lower axial tilt compared to earth, so seasonal difference won’t cause the ice sheets here to melt away to any significant degree.

Which means that we’ve completely filled in the climates of our fictional earth-like planets! Now that we’ve finished placing all our climates, I’m going to blend the map to look more realistic, so that we have something a bit more aesthetic moving forward. So, something like… this. There’s always something satisfying about having a blank map ready to go for a worldbuilding project…

Now that we’ve finished up with our map, let’s discuss the flora and fauna of the polar regions. Flora is perhaps the easier of the two to discuss, as ice cap climates distinctly have no vegetation at all, and tundras have very low biodiversity due to the harsh conditions. Much of the soil of the tundra experiences permafrost, meaning that it is frozen all year-round. Only a thin layer of this soil thaws and refreezes every year, which means plant roots must be shallow to avoid damage from the frost. This requirement effectively eliminates the possibility for trees across the tundra, and more commonly the plants of the tundra are mosses which sit close to the ground with shallow root systems. Tundras are also home to lichens, which are actually fungi, not plants, despite visually looking exceptionally similar to mosses. This is a wonderful example of convergent evolution, where mosses and lichens have evolved to end up being similar, despite being from entirely different kingdoms within the tree of life.

On Locus, the most prevalent flora in the tundra are Stralux and Straestus, members of the folia and pilea kingdoms, which are analogous to plants and fungi respectively. Like mosses and lichens on earth, the two have convergently evolved similar adaptations for their environment, though also have a unique symbiotic relationship with each other. Both are capable of a fictional process called synthesis, which you can find a video outlining linked in the corner. In simple terms, synthesis is the process of energy creation, and as organisms capable of synthesis, Stralux and Straestus are able to generate their own energy. Specifically, Stralux is capable of generating light energy, while Straestus generates thermal energy. In the long winters of the polar climates, there are months with no sunlight and temperatures can be the coldest present across the entire planet. The Stralux and Straestus keep each other safe in the winter, with one generating warmth and the other generating light. These synthetic traits are only active in darkness and come winter these two organisms are a glowing source of refuge across the frigid tundra, making them keystone species, and turning the tundras of Locus into frozen glowing expanses.

Now that we’ve looked at the iconic polar flora, let’s look at the creatures of the tundras and ice caps. Due to the lack of abundant flora within the polar climates, herbivores aren’t particularly common. Arctic hares, reindeer, and muskox are some of the more iconic and prevalent herbivores on earth, and arctic foxes, wolves and of course polar bears are some of the more iconic carnivores. Unsurprisingly, all of these creatures have means of cold resistance in order to survive, and many migrate away from the polar climates in the winter. Many also have white fur to help with camouflage across the consistently snowy landscape.

On Locus, the Leonix have body structures not dissimilar to large cats on earth, though are far larger with denser fur to keep them warm. Their fur also secretes oils that allow for Leonix to swim across frigid waters, and has adapted a white appearance, helping to camouflage from their prey. Leonix are apex predators, migrating between polar climates and subarctic climates, though in a pattern reversed to those of many other land-dwelling creatures. In the fall when temperatures start to drop, Leonix migrate into polar climates all the way into the ice caps, with the increased ice coverage providing greater areas for hunting. Throughout the winter, they will prey mostly on water-dwelling creatures that must come to the surface to breathe, though they are also capable of swimming short distances at high speeds if necessary to catch prey. However, they are at most semi-aquatic, and are not suited for lengthy periods of swimming. When they migrate away from the poles in the spring, they generally avoid competition with other large predators like Velatrox by preying on larger sea creatures than the Velatrox fish for. In the rare instances where the two giant predators do come into conflict, it is a clash of the titans, and is one of the most dangerously spectacular sights on the planet.

So, to recap, polar climates are separated into tundra and ice cap climates, though ice caps are only expected to be present when a world is in an icehouse state, which we more commonly refer to as an ice age. Flora here is exceptionally non-diverse, and creatures are not only cold resistant but tend to be migratory. Polar climates are the final climate type within the koppen climate classification system, and therefore the final earth-like climate of this series.

Join me next time when we’ll be looking at how creatures establish intelligence, specifically the kind of intelligence that will lead them to establish civilisations that we can worldbuild for. We’ll be lining up the creatures we’ve created so far and putting them through the crucible that will launch some of them into the spotlight as the fantasy races of our worldbuilding stage.

You can find all the information for this video as well as other resources for worldbuilding in general over at worldbuildingcorner.com, and if you enjoyed this video don’t forget to like and subscribe to follow the world-building journey. And until next time… stay awesome!