Overview of Energy

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Overview

Energy is the ability to do work or cause change. It’s what makes things happen—whether it’s moving objects, heating up your food, lighting up a room, or even allowing you to run or think. Energy comes in many forms, like heat, light, electricity, and motion, and it can change from one form to another. For example, when you eat food, your body converts the energy stored in that food into the energy you need to move, grow, and stay warm. Without energy, nothing can move or change in the world around us.

When talking about energy to understand why the climate system behaves like it does, there are three fundamental principles we need to understand: 

1. Energy can be stored.
2. Energy can move from one piece of matter to another. 
3. Energy can exist in different types and can transform between these types. 

These three concepts also lay the groundwork for the First Law of Thermodynamics. According to this law, the total amount of energy within a closed system remains constant during all processes of energy movement and transformation.

Hmmm. That’s a bit of a mouthful – how can we frame this more simply? Let’s try this: Energy is never created nor destroyed, but it can move around and change forms. You may have also heard this called the “conservation of energy.” It’s worth noting the language “closed system” – this means a hypothetical box where energy cannot enter or exit. The grandest way to think about this is the universe – if we could place it in a giant box (a funny -- and very optional -- Futurama episode to watch), all energy within the box must remain constant because we assume no energy can enter or escape the universe.

Types of Energy

In the study of energy, we encounter a diverse array of “types” (sometimes referred to in textbooks as “forms”), each with unique characteristics and roles in the physical world. There are numerous forms of energy (ask a physicist for some of the more complicated ones!), but we will focus on four important ones here.

1. Radiant Energy – the energy associated with electromagnetic radiation. As humans, we generally consider this manifesting as light – after all, it is the energy form that allows us to perceive the world around us (think visible light to our eyes, infrared heat from a fireplace, etc.). But as we will see very soon, it will also be critically important for getting energy into and out of (and moving it long distances around) the Earth system.
2. Kinetic Energy - associated with motion, is evident in everything from the swaying of leaves in the wind to the bustling activity of a city. Any bit of matter, no matter how big or small or how light or how dense, possesses kinetic energy when it moves.
3. Gravitational Potential Energy - determined by an object's height above the Earth's surface. It is called potential because it could be converted to kinetic energy if it starts falling toward the ground. Roller coaster aficionados know how potential energy and kinetic energy can be converted back and forth between one another – coasters tend to move slowly when very high and then move faster as they are closer to the ground.
4. Internal energy - a composite of factors about a piece of matter itself (i.e., the atmosphere), such as its temperature, pressure, and chemical makeup.

What ties these diverse forms of energy together in the Earth system is their propensity for transfer and conversion. These transfers and conversions among various types of energy are the driving forces behind virtually every natural phenomenon. Therefore, we need to understand this to understand the climate system. While the First Law of Thermodynamics assures us that the total amount of energy in a system remains constant, it is important to recognize that not all energy is equally likely to undergo transfer or conversion. This leads us to the Second Law of Thermodynamics. According to this law, heat always flows spontaneously from hotter to colder regions of matter. A way to think about this that I think is somewhat intuitive is that heat always flows “downhill” if you think of a hill where the top represents warmth, and the valley represents cold.

What does this mean in practice? Let’s say I have a glass of ice cubes on my kitchen table. We know from personal experience that over time, those ice cubes will melt, and the resulting liquid will eventually become lukewarm. That is because the surrounding energy of the room – which is hopefully above freezing -- flows “downhill” to heat the ice cubes, melt them, and bring the water’s temperature in equilibrium with everything else around it. Left by itself, energy will always try to reduce its own order or organization itself, a concept known as “entropy.”

A hot cup of coffee sitting on a counter will never get hotter -- so says the 2nd law of thermodynamics. But I know I can heat up coffee in a microwave, so what gives? Read the next paragraph!

Julius Schorzman from Wikimedia CC BY-SA 2.0

But wait a minute, maybe you should be skeptical of that. After all, if that’s the case, how do air conditioners and refrigerators function? After all, the whole reason they exist is to keep things cold, even when everything else around them is hot! Well, they can exist because they keep things cold (make heat flow “uphill” away from the inside of the freezer) by rearranging energy elsewhere (in their case, using electrical energy to push this heat up the hill). Similarly, we know that parts of the planet are cold and parts of the planet are warm. I know if -- for some reason -- I really, really, really want to feel an icy wind blow in my face, I can be essentially guaranteed that if I head to the South Pole. The second law of thermodynamics tells me that for this temperature imbalance between balmy Cancun, Mexico and frigid Antarctica to be maintained, energy must be being actively rearranged within the Earth system. While we will discuss all these forms of energy throughout this course, we start by focusing on radiant energy. Essentially, all the energy-sustaining life on our planet arrives in the form of radiation from our nearest star – the sun. All five components of the climate system consistently release radiation: 24 hours a day, 7 days a week. How this radiant energy is received, stored, moved, and transformed can teach us so much about the Earth’s climate! Read on.