Hi guys, welcome to my channel! My name's Rosh, and today we'll be investigating how just three processes are responsible for governing the global climate. Watch on to find out more!
If there's one thing that climate sceptics, scientists and activists can all agree on, it's that throughout Earth's history, the global climate has continuously changed. Sometimes quite dramatically. At different times, the Earth has looked like a giant snowball, a tropical greenhouse, and everything in between. In fact, looking at Earth's history, it becomes quite apparent that the climate system is inherently unstable and vulnerable to change.
But why exactly does the climate change? You probably know that climate is the long-term average of weather. But what is weather?
You might think of temperature, wind, rain, and cloud, and you'd be right. But all of these result from something far more fundamental, the transfer of energy within the atmosphere. For example, rain is formed when water vapour which has evaporated into the air cools, condenses and releases energy in the process.
Wind is caused by hot air rising and cooler, dense air rushing in to fill its place. And here's the crucial point. If the weather is a result of the energy moving within the atmosphere, we can think of the global climate as a result of the total energy within the system.
Just as a change in the weather can be thought of as a shift in the energy at a given place and a given time. Global climate change can be thought of as a shift in the total energy in the system. So what causes these shifts in energy?
To understand this we have to look at where the energy comes from in the first place. I don't think it would surprise anyone to find that practically all this energy comes from the sun. Fusing approximately 600 million tonnes of hydrogen every second, the surface of the sun is 5800 kelvin.
which is about five times the temperature required to vaporize a diamond. Now for a little physics. There are two key principles to understand here.
The first is that the hotter an object is, the more energy it will radiate or lose in a given period of time. And the second is that the type of radiation emitted by an object depends on its temperature. The hottest things in the universe emit radiation with very short wavelengths like gamma rays and x-rays.
Cooler objects emit radiation mostly with much longer wavelengths such as visible light, infrared, radio waves and microwaves. Our sun, while hot, is nowhere near the hottest thing in the universe, and most of its energy is emitted as visible light or ultraviolet radiation, which is great for those of us who like to see. The earth, being much cooler, emits mostly infrared radiation, or heat as normal people call it.
Now the climate will always try and move towards a stable state. And this can only exist when the amount of energy in the system is also stable. For this to happen, the amount of energy leaving the Earth must equal the amount coming in. This state of balance is known as a dynamic equilibrium.
But how does this happen? Well, energy leaves the planet in two principal ways. By being directly reflected off the surface, and by being absorbed and then re-emitted as heat into space.
Bright surfaces like ice, clouds or sandy deserts have high reflectivity or albedo and they bounce sunlight off their surfaces. Dull surfaces like oceans or forests absorb more energy than they reflect and this absorbed energy is emitted as heat. In order for the planet to reach a dynamic equilibrium the amount of energy reflected off the surface combined with the amount of energy emitted as heat must equal the amount of energy coming in from the sun. As we discussed the climate is largely determined by the amount of energy in the atmosphere. and oceans.
If all the energy that reached the surface was immediately radiated back out again, the planet would be a frozen wasteland. Clearly this doesn't happen, and that's where the greenhouse effect comes in. Greenhouse gases are transparent to invisible light and let the energy from the sun pass straight through. However, they absorb the heat from the earth's surface and emit it in random directions.
Some is lost to space, but much of it gets re-emitted back into the atmosphere or down towards the surface. This effectively reduces the proportion of energy escaping to space. But if greenhouse gases are reducing the amount of energy leaving the planet, then how do we get a dynamic equilibrium?
Remember that means the amount of energy leaving must equal the amount coming in. Well, all that extra energy trapped in the atmosphere also raises its temperature. And if we remember our basic physics principles, we know that hotter things radiate and lose more energy.
This means that the greenhouse effect causes the atmosphere to warm up until it reaches a temperature warm enough to radiate enough heat into space to equal the energy coming in. In other words, the temperature of the atmosphere adjusts to ensure that the amount of energy leaving equals the amount coming in. As long as there are no changes in the energy received from the sun, the albedo, or the greenhouse effect, the total amount of energy in the climate system, and therefore the climate itself, will remain stable. Anything that changes this balance is known as a radiative forcing, and forcings nearly always trigger chain reactions called feedbacks which further alter the energy balance.
There are dozens of forcings which could affect the planet. Forcings which affect the energy from the sun like solar cycles. Forcings which affect the albedo like volcanic dust, asteroid impacts, or the movement of tectonic plates. And forcings which affect the greenhouse gas concentration like volcanic activity, the weathering of rocks, or the combustion of organic carbon. This means that all climate change, natural or otherwise, is a result of changes in just three things Energy from the sun, albedo, and the greenhouse effect So that is why the climate changes, in as brief and concise a video as I could make Obviously I've simplified the science here, but hopefully that's cleared up the basic principles of what governs the climate system and what causes it to change If you're interested in finding out about the forcings operating today, and how they affect the modern climate then don't forget to subscribe, hit the bell and stay tuned for a video on exactly that subject.
That's all for today folks! As always, links and sources are in the description below. Once again, thanks for watching and don't forget to like and subscribe, it really helps the channel grow.
Until next time, goodbye!