The more I learn about climate the more I realize I've been taking weather and climate for granted by just going through life being like "ahh such a sunny day", "will this rain ever stop???", "brr hate winter gotta dig out my car again" without thinking too much about the specifics.
Actually there's a lot going on behind the scenes. It's a pretty complex system, and the fact that we've managed to screw it up is both impressive and kinda unsurprising. But I want to leave the climate change part for the next essay and focus on the basics of the climate system itself here.
Keep in mind that I'm actively learning about climate, so my writing might not be 100% scientifically accurate. But I'm doing my best to make it as accurate as I can!
Anyway, the main components of the Earth's climate system are air, water, earth, fire, and aether. J/k these are the classical elements. The actual components of the climate system are the atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere (to an extent). No aether. Wouldn't it be cool if it existed?
The Sun ties our climate system together, so I'll start with it.
The Sun is pretty cool. And kinda hot. Like 15,000,000°C hot (at its core). The Sun powers all life on Earth and is the main reason we exist.
Without going into too much detail, here's how the Sun affects our climate system:
The Sun emits shortwave radiation (mostly visible light and ultraviolet), which travels through space and hits the Earth. Some of the rays get reflected back into space, but a lot gets absorbed by the Earth's surface, warming it up.
The Earth then emits longwave radiation (infrared, or heat) to maintain a stable surface temperature. This is called the Earth's energy budget and is basic thermodynamics, which I totally flunked in high school.
Some of that emitted radiation gets trapped by certain gases in our atmosphere, keeping Earth warm enough for life. That's the greenhouse effect – without it, the average surface temperature on Earth would be like -18°C, and I would totally hate it here and have to move elsewhere.
The equator receives more radiation than the poles, so the excess heat gets transferred to the poles via atmospheric and oceanic circulation. This heat transfer is a key driver of our climate system.
The atmosphere is also pretty neat. It's another important reason we exist and consists of a mix of gases: 78.08% nitrogen, 20.95% oxygen, 0.93% argon, and trace gases – some 13 of them.
Earth's atmosphere can be divided into five main layers based on altitude: troposphere, stratosphere, mesosphere, thermosphere, and exosphere. (There's also the ionosphere and magnetosphere, but they aren't true layers.)
When it comes to climate, we generally care about the troposphere (where most of the weather happens) and the stratosphere (where the ozone layer absorbs and scatters the incoming ultraviolet radiation, meaning we get less cancer).
The boundary between these two layers is called the tropopause. That's where the weather ends as the temperature starts to increase with altitude in the stratosphere, inhibiting vertical air movement. So it's like the lid on top of the weather system.
So far, so good. But the air isn't static. It constantly moves around due to Earth's rotation and the temperature and pressure difference between different regions. This movement is called atmospheric circulation and there are two types of it:
First, there's the latitudinal circulation. That's the air moving between different latitudes in a circular vertical pattern, called a circulation cell. There are three distinct circulation cells in each hemisphere: the Hadley cell near the equator, the Ferrel cell in mid-latitudes, and the polar cell near the poles.
The physics within each cell is a little different:
- The Hadley cell is driven by the intense Earth's surface heating at the equator. This causes the air to warm, expand, and rise all the way up to the tropopause. With no way further up, it starts moving poleward, gradually cooling down, becoming denser, and descending back to the surface in mid-latitudes.
- The Polar cell works in a similar manner but is driven by the cooler and denser polar air moving along the surface toward lower latitudes. At about 60 degrees, it meets the warm air of the Ferrel cell, which is forced up and back to the poles at higher altitudes.
- The Ferrel cell sits between the Hadley and Polar cells and is driven by their temperature and pressure like a gear inside a massive atmospheric gearbox.
Circulation cells are where we get some of our weather from:
- The rising air motion creates a low-pressure zone, which leads to rainfalls as the air cools down and the water vapor in it condenses.
- The descending air motion creates a high-pressure zone, which leads to a lack of precipitation.
These circulation patterns are relatively stable, but they do shift north and south with the seasons. The equatorial region (known as the Intertropical Convergence Zone) typically sees high precipitation, while certain regions in mid-latitudes experience drier conditions due to the high-pressure area created by the descending air from the Hadley and Ferrel cells.
Second, there's the longitudinal (or lateral) circulation. This is where the air moves along the East-West axis due to the Coriolis effect (caused by the Earth's rotation) and the pressure and temperature difference between different regions. That's where winds come from!
There are two types of winds: surface winds and jet streams.
Surface winds are the East-West winds closer to the surface. As the Earth rotates, the air flows from east to west near the equator and the poles (trade winds and polar easterlies) and from west to east in mid-latitudes (westerlies). And by the way the naming's kinda confusing here since the winds are named for where they come from, not where they're going.
These winds have been known to sailors and used for trade and exploration for centuries. Fun fact: the regions between the easterlies and westerlies with little to no wind are called the doldrums, and you generally don't want to end up there as a sailor relying on the wind.
Jet streams are strong winds in the upper layer of the troposphere near the tropopause. These form at the boundaries of adjacent air masses with significant temperature contrast, typically between circulation cells. There are two main jet streams in each hemisphere: polar and subtropical jets.
Jets are where we get more of our weather from since they move high and low-pressure zones around, causing heat waves and monsoons. They're also crucial for air travel as they can speed up planes flying from west to east. So jet streams slowing down due to climate change isn't a great thing for more than one reason.
The hydrosphere is yet another reason we exist. Water's good for you! About 71% of the Earth's surface is covered by water, 96.5% of which is ocean saltwater. And just like air, water in the oceans also moves around constantly in two main ways.
First, there's the thermohaline circulation. It's the deep oceanic circulation primarily driven by differences in temperature (thermo-) and salinity (-haline), which in turn affect water density. As part of this process, cold, dense, and salty water from the polar regions sinks to the ocean floor and is transported towards the equator, where it warms up, rises to the surface, and ends up back at the poles.
Thermohaline circulation is a pretty slow process that can take hundreds to thousands of years and is sometimes referred to as the great ocean conveyor belt.
Second, there's surface circulation. That's the horizontal circulation of the ocean water caused by the wind and the Coriolis force, which forms the major oceanic gyres like the Gulf Stream and Kuroshio.
Just like with the air circulation cells, one of the key aspects of ocean circulation is the transfer of heat from the equator to the poles, so it plays a big role in past and future climate changes.
Then there's the cryosphere: the snow and ice cover of the Earth. It consists of polar ice and glaciers, ice shelves, ice sheets, ice caps, frozen ground, and even seasonal snow cover.
The cryosphere is an important part of the climate system:
- Its high albedo makes it reflect solar radiation at a much higher rate than the rest of the Earth's surface, causing less of it to be absorbed, thus generating less heat.
- It's an important freshwater reservoir. For example, the Antarctic ice sheet contains about 61% of all fresh water and is the largest single mass of ice on Earth.
- It provides essential habitat for a variety of species ranging from microbes (meh) to polar bears (cool!) and is used by humans for transportation and recreation.
Furthermore, the cryosphere is scientifically significant as the ice cores extracted from glaciers and ice sheets provide valuable information about past climates.
Unfortunately, ice has a tendency to melt under warmer conditions, which can lead to a range of problems - from relatively manageable ones to pretty catastrophic and irreversible ones.
Finally, there's the biosphere. These are the living organisms on Earth, such as plants, animals, microorganisms, and humans, which are also technically animals.
The biosphere has a critical role in the climate system in a few ways:
- Carbon cycle. Plants, algae, and certain microorganisms absorb carbon dioxide and release oxygen into the atmosphere through photosynthesis. When they die and decompose, some of this carbon stays in the soil or ocean sediment, which is a crucial mechanism for controlling atmospheric CO2 levels.
- Albedo. Vegetation affects the reflective properties of the Earth's surface, generally making it less reflective and contributing to warming.
- Transpiration. Plants also affect climate through their role in the water cycle as water is absorbed by plant roots and evaporated through the leaves.
And then there's human activity. We are the primary drivers of the current climate change due to activities such as fossil fuel burning, deforestation, and intensive farming, which increase our greenhouse gas emissions and disrupt the natural carbon cycle. Good job, everyone!
The lithosphere is the Earth's crust and the upper part of the mantle. It's a more indirect component of the climate system compared to the others and its effects are generally observed over much larger timescales (millions of years), but it's still worth mentioning.
The layout of Earth's surface, shaped by tectonic activity, has an effect on climate by affecting atmospheric circulation and ocean currents. Mountain ranges can alter wind patterns and precipitation distribution, and large-scale geographic changes like the formation of the Isthmus of Panama around 3 million years ago can even reshape ocean circulation - as it did with the Gulf Stream.
The lithosphere also plays a role in the carbon cycle. Weathering processes draw carbon dioxide out of the atmosphere and into rocks, and tectonic activity can release it back. This slow carbon cycle takes place over millions of years.
Volcanic activity is a primary way the lithosphere affects climate over shorter timescales. In addition to greenhouse gas emissions, large volcanic eruptions can release enough sunlight-blocking sulfates into the atmosphere to create a temporary cooling effect. For example, the 1991 Mount Pinatubo eruption in the Philippines resulted in a temporary 0.5°C drop in global temperatures, which is pretty significant.
That's the climate system in a nutshell.
At least that's what I think it is based on a couple weeks of learning about it, so don't quote me on it. But stay tuned for my next essay where I'll cover the change part of climate change – and butcher it in a similar manner.
Just kidding. This is pretty accurate. Quote me on it.