Welcome to another worldbuilding post! After making posts about building your planet and filling it with land forms and water features, I got excited to start working on plant and animal life forms. But then I realized we still haven’t talked about climate. Even though I said we were going to. So let’s fix that!
Knowing the basic climate of the regions in your story can give you opportunities to make your world feel unique, diverse, and like more than a cardboard cutout with no soul. Whether your approach is to take a week to plan a unique climate for your own world or to go, “Meh, I guess this place is kind of warmish,” climate is likely to play some kind of role in your story. It might impact how sunny the days are, what kind of clothing your characters wear, what kinds of leisure activities they do, what their homes or modes of transportation look like, what kinds of plants and animals are native to the area, what kinds of weather or temperatures your characters find tolerable, and it may even impact dominant religious beliefs in the area. Even if your characters spend the entire novel inside, your climate might still play a role in what their walls are made of, how they power any devices or light the room, or maybe what they can hear through their walls. Maybe the climate is why your characters never go outside.
Basically, climate is kind of underrated.
There are many factors that influence climate, and there’s no way someone like me could ever cover everything there is to discuss, especially since I’m not a climatologist, but hopefully we can learn a few basic concepts about climate together so we can add some depth and variation to our worlds.
First, you know we’ve got to go through some disclaimers. This post is just an overview meant to get you asking questions that might lead to some interesting worldbuilding ideas. If your story requires complete scientific accuracy, please continue your research. As usual, we’ll be discussing how climate works on an Earth-like world, but if you want something different, you might think about how changing one or two things about how Earth’s climate works might have a ripple-effect that creates an entirely new and fascinating climate system for your world.
My final disclaimer is that we’re going to be covering several different things that impact the climate in your world in this post. For those who are newer to worldbuilding, this might seem overwhelming at first, but don’t panic. Take it all in. Breathe. Know that you only have to create a setting that feels real enough for your readers to suspend disbelief. As long as you write a climate that feels believable enough to suit the story you’re trying to tell, then that is enough.
With that out of the way, let’s dive into some of the aspects that will influence the climate in different regions of your world!
HOW YOUR PLANET MOVES THROUGH THE SOLAR SYSTEM: AXIAL TILT, ROTATION, AND ORBIT
I mentioned in the post on designing a planet that we’d talk more about axial tilt when we got to discussing climate, so here we are!
On Earth, the axial tilt is currently about 23.5 degrees, but this tilt changes slowly over time, varying back and forth within a degree or two. Having an axial tilt for your world can be important for many reasons. Not only will it affect how your day and night cycle looks, but Earth’s axial tilt is also one thing that keeps any one area of the planet from overheating.
But axial tilt is also the reason Earth has seasons. As the tilt changes the angle of sunlight parts of Earth receive, different hemispheres will experience hotter or cooler seasons. Another thing to note is that the greater the degree of your world’s axial tilt, the more extreme the seasons will be. Winters will be colder and summers hotter. It’s also worth mentioning that the gradual change in Earth’s axial tilt over many millennia affects glaciation. When Earth has a more extreme tilt, it leads to more glacial melt. When it has a milder tilt, however, it allows for the buildup of ice sheets, which in turn reflect sunlight back into the atmosphere and lead to more cooling of the planet. Something to consider if you’re planning on designing a world in the middle of an ice age.
Your planet’s axial tilt will also affect how much sunlight an area gets during the day. On Earth, the extreme north and south experience a period of more than 24 hours each summer where the sun never completely sets. This is known as the “midnight sun,” but even though they experience a lot of sun at this time, the angle of the sun is still less direct than it is at the equator, and the heat won’t be as extreme as if, say, northern Brazil had a day, night, and day of constant sunlight every summer. And the poles also experience a period known as “polar night” each winter where the sun never rises. Perhaps your world experiences even longer midnight suns and polar nights.
Earth’s axial tilt is maintained mostly from its gravitational relationship with other celestial bodies in the solar system, especially the moon. What would happen if some cataclysmic event in space, such as a large asteroid obliterating a moon, threw your world’s axial tilt off drastically? How fast does this change occur? How would the people on your planet deal with changes to their climate?
Another aspect of your planet that will affect your climate is its rotation: the length of its days. A really short day means the sun won’t have a lot of time to heat up the nearest side of the planet, nor will the side in darkness have time to cool down too much. Maximum and minimum temperatures won’t be as extreme. Really long days and nights, however, will allow for higher maximum temperatures during the day and lower minimum temperatures during the night. For reference, Earth is considered to have shorter days than many other planets.
The last aspect of your planet’s relationship to the sun that I wanted to discuss is its orbit. Your planet’s orbit doesn’t affect what seasons parts of your world experience. If it did, everyone on Earth would experience winter at the same time of year, as Earth’s orbit is actually slightly elliptical. If its orbit affected what seasons Earth had, the entirety of the planet would be in the middle of summer in January and the middle of winter in July. Which is obviously not the case.
However, an eccentric orbit can impact the length of the seasons. A perfectly circular orbit will have an even number of days of winter, spring, summer, and fall (at least for places that experience four seasons). An orbit more eccentric than Earth’s, however, may mean the northern hemisphere of your world experiences an entire extra month of winter while your southern hemisphere gets an extra month of summer.
If your planet has an eccentric orbit, the sun can also have an impact on daily temperature variations. When your planet is closer to the sun, the sun will have a larger impact on daily temperatures, but when your planet is farther from the sun, the sun will have less impact on day-to-day temperature fluctuations.
ATMOSPHERE AND WIND PATTERNS
The makeup of your planet’s atmosphere will regulate how much sunlight gets through to the planet’s surface and therefore how much heat enters and leaves the atmosphere. A thin atmosphere will allow for wider temperature variations while a denser atmosphere will stabilize temperature. Earth’s atmosphere has a moderate density, allowing it to both keep out excess heat while letting enough in. It also helps trap some of that heat throughout the night.
Keep in mind that your planet’s size and gravitational force are likely to contribute to the density of your planet’s atmosphere. Very large planets will have strong gravitational forces, which in turn will trap more gasses around them, creating a denser atmosphere.
As your planet turns on its axis, it will also create what are called “wind belts,” which form the dominant wind circulation patterns across the grove. As hot air rises from the equator toward the upper limits of the lower atmosphere, it moves eastward and toward the poles. But as it moves toward the poles, that air then cools. Before it ever has a chance to reach the poles, it cools enough to sink down toward the earth’s surface where it then moves westward. These east-to-west winds form the major wind patterns in the tropical latitudes. But as we extend northward and southward from these equatorial winds, we find this pattern flips around and repeats, with a second pair of wind belts forming between approximately 30 and 60 degrees and having dominant wind patterns that flow from west to east, and a third pair of belts at the polar regions extending from 60 degrees north or south and having dominant winds that again flow from east to west.
These are your wind patterns, but there are a few important things to note. First, these are not the only way wind circulates. Depending on other factors, your winds can shift direction throughout the day or seasons. In fact, even these wind belts shift on Earth as different latitudes get nearer or farther from the sun than the equator, thanks to Earth’s axis. When the northern hemisphere experiences summer, part of it gets closer to the sun than the equator, and some of these wind belts shift toward the north. Likewise when the southern hemisphere experiences summer, part of it gets closer to the sun than the equator and these wind belts shift toward the south. Since land heats and cools more easily than water, places in your world where you have open ocean will have more stable wind belts, but where you have large land masses, wind belts may shift even further north or south across the seasons.
Also note that these wind patterns are only true for planets that turn counter-clockwise and have a twenty-four hour day like Earth. If your planet turns clockwise, these wind patterns will be reversed. (Also: a reminder that if your planet turns clockwise, your sun will rise in the west and set in the east.) If your planet turns slower and has a longer day than Earth does, you will have less wind cycles. More if your planet spins faster.
These winds, together with other factors, will impact where wet and dry regions or warm and cold regions can be found on your world. Expect these major wind patterns to also affect everything from precipitation, storms, where certain species of vegetation might be found, sea trade routes, and even sometimes where people might choose to set up a new city or outpost.
But to understand more about how wind patterns can affect climate, we have to understand how they interact with other features of your world, like:
OCEAN CURRENTS
One of my more recent worldbuilding posts was about designing the water features for your world, and in that post I gave ocean currents a very brief mention, but they play an important part in climate. The ocean absorbs a lot of heat from the sun, and both warm and cold ocean currents act to distribute that heat more evenly. If your world doesn’t have much in the way of oceans, how does it regulate temperature for life to survive? How does life adapt?
There are three layers of ocean currents: deep ocean, upper ocean, and—what we’re going to focus on today—surface currents. Your deep ocean and upper ocean currents are affected mostly by the density of the water. Colder, saltier water is denser and circles downward into deep ocean basins. As it sinks into these basins, it forces older water out, which wells upward and continues this exchange of not only water, but also nutrients necessary for the survival of many ocean species.
It’s a good thing we already discussed wind patterns, because you’re going to need them if you’re interested in figuring out where the surface currents in your world will end up, because surface currents, those currents in the upper 400 metres of the ocean, are primarily driven by wind.
A very general rule of thumb is that a surface current is going to travel with the prevailing winds until it meets the continental shelf of any land you’ve designed for your world. At that point, the current will split with warm ocean currents flowing away from the equator and cold currents flowing toward it. Once either cold or warm currents meet a new wind belt, they’ll then follow the direction of that wind until they meet a continental shelf and, once again, split into warm currents that flow away from the equator and cold currents that flow toward it. You’ll note that this means ocean currents next to each other will flow in opposite directions: one clockwise and the other counter-clockwise.
Right at your equator, however, you will have two currents headed in the direction of the major wind pattern, but between them they’ll create a narrow current going in the opposite direction. Form these currents into their respective loops, and there you go!
If you don’t have any land masses at your poles, expect to see one big current circling the pole in the direction of the major wind pattern there.
Even if you don’t want to draw in wind patterns and ocean currents for your map, you might at least want to decide where there will be warm or cold ocean currents running near your land masses, as that will impact the temperature of the air and winds in the area as well as precipitation levels. Warm currents allow for more evaporation, which means that lands or seas in the path of the prevalent winds are likely to see more rain. And likewise, seas and lands near cold currents are likely to see less of it.
And, just like with wind patterns, your ocean currents are likely to affect sea trade routes. Even if you’ve got ships with the power to go against the wind and surface currents, that ship is going to go through far more fuel to do so.
TEMPERATURE
If you’ve ever watched a weather forecaster on television offer daily high and low temperatures for major settlements in the area, you’ll know that temperature isn’t set in stone and even neighbouring towns can experience cold and hot differently on different days. But we can speak about temperature trends to help you figure out what parts of your world are most likely to have sweltering summers and which will freeze your breath to your eyelashes in the winter.
As we already discussed, temperatures will vary between the parts of your planet experiencing daytime and the parts experiencing nighttime, but how much temperature varies between day and night can depend on axial tilt or how short the days are.
The next most obvious place to look for higher temperatures on a planet with a similar axial tilt to Earth is the equator. While equatorial regions will still vary in distance from the sun throughout the year, that shift in distance is smaller, and they receive a steadier, more direct supply of sunlight and heat throughout the year. As we move to latitudes farther north or south from the equator, those regions will see less heat, but much of these regions will also see wider variations in temperature between summer and winter.
But you don’t want to consider only latitude but also altitude, because high-altitude regions will experience less heat than those living at sea level due to the air being thinner.
One more thing to take into account is that land heats and cools more easily than water does, which you’re probably aware of if you’ve ever taken a dip in a lake on a hot summer’s day. The earth or rocks under your bare feet might almost burn you, but the water still feels cool to the touch. As we already mentioned, the sea currents will have an impact on temperatures of coastal regions and may make the temperatures more moderate. But inland regions will see higher temperatures as well as greater temperature variations than coastal regions as the land heats and cools more rapidly.
TOPOGRAPHY
So, not only do things like your planet’s axis, wind patterns, ocean currents, and expected temperature ranges affect the climate of your world, so will its topography, and there’s one bit of topography in particular we need to discuss: mountains.
Your mountain ranges, particularly if they’ve sprouted perpendicular to the course of your major wind patterns, will have a windward and leeward side. The windward side of your mountain range is the side that faces into the wind. This side of your mountains, and the land around it, will see higher levels of precipitation and is likely to see lusher vegetation as well. And this will be especially true if you’re mountains are anywhere near a warm ocean current, like the west coast of Canada is. This area is home to Canada’s temperate rainforest.
But as winds carry rain-bearing clouds higher up the mountains, much of that precipitation is lost, meaning that the leeward side of the mountain range, as well as the geography past it, will be drier than the windward side. Instead of rainforests and lush greenery, you might find grasslands or deserts.
As a rule of thumb, the taller your mountain ranges are, the more extreme the difference in precipitation and climate is likely to be between the windward and leeward sides. A range of hills might make a minimal difference, but enormous mountains may form a barrier between a flourishing wetland and empty plains of scorched earth or sand dunes.
A good example of this comes from The Wheel of Time book series by Robert Jordan. In the books, a mountain range known as “The Spine of the World” or the “Dragonwall” stretches from north to south. These mountains are described as being very, very tall. So tall, in fact, the journey to the other side of the mountain range is considered very difficult and, for some, near-impossible. This has affected the climate. One side of the mountain range is greener, with rivers, forests, and farmlands, and the other side is known as the Aiel Waste: a vast desert where the rarity of water means the people who live there will wage war over control of even very small sources of drinking water.
PROJECT: NOVELJUTSU
Now it's time to figure out some basic climate information for Project: Noveljutsu.
Here I've taken my map of basic landforms and water features, and I've figured out where the main wind belts are. The story of Project: Noveljutsu takes place over a wide area of land, but it doesn't cover the whole planet, so it's enough to depict only a few wind belts rather than all the belts that would cover the planet.
Here we've got a tropical region on the northern side of the equator, a temperate region where most of the story will take place, and just a tiny sliver where some polar winds can impact climate and weather. I'm going with a regular sun-rises-in-the-east-and-sets-in-the-west pattern, which means that the direction of these major wind patterns will match what we have on Earth.
From there I've figured out where the major ocean currents should go and whether those currents nearest the land will be warm or cold. On the western side of the mainland and the eastern side of the lower islands we have warm currents, and on the opposite sides we have our cold currents. Since areas of land near those warm ocean currents are likelier to have warmer, wetter weather, these are the areas most likely to be affected, whereas regions near the cold currents are more likely to have cooler, drier climates. (At least so far as the oceans impact their climates).
But as we learned, ocean currents aren't the only thing that will impact average temperatures. The interior of this continent will heat and cool more rapidly than the parts nearer the ocean, seeing wider variations in temperature throughout the days and seasons. The mountain regions will see cooler average temperatures than areas closer to sea level. The west side of the mainland mountains and the east side of the island mountains will also see more precipitation than the sides in the rain shadow, which will be drier.
All this should be enough to give me a good start in figuring out what the seasons, precipitation, and average temperatures of these regions will look like as I develop this world further.
CHALLENGE
There are even more factors than what we’ve gone over today that can contribute to the climate of your world, but having a basic idea of wind patterns, ocean currents, and your taller mountain ranges should really help you in deciding the most likely climates for different regions in your made-up world.
For this post’s challenge, try figuring out the directions of the winds for your world and at least whether the ocean currents along the edges of your continent will be warm or cold. From there, figure out how winds moving precipitation toward or away from your shorelines, inland regions, and mountain ranges will affect what areas are likely to get the most and least precipitation. Consider your planet’s axis, rotation, and orbit to figure out how average temperatures and precipitation levels might alter throughout the year. Do you want your world’s climate to be like the one you’re familiar with? Or do you want to set your story in a climate like a different one on Earth, or maybe in a climate not like one on Earth at all?
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