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Why is the Earth heated unevenly?

To answer the question “Why is the Earth heated unevenly?”, we must first understand what is heat and how does the Earth receive energy from the Sun. Only after we answer these questions, we can understand why Earth’s surface is heated unevenly.

But in case you don’t have time for all that, here is an explanation.

To answer the question briefly, the reason Earth is heated unevenly is that light beams that come from the Sun hit the ground at lower angles and they affect larger areas around the poles. Around the equatorial regions, light beams have larger angles and they affect smaller areas.

If you already know what heat is and how do incoming light beams heat up the Earth’s surface, you can skip to the last part.

What is heat?

To understand heat, we must first understand temperature. Here is a simple definition: “Temperature is a measure of the average kinetic energy of the particles in an object.”. If the particles of an object move faster, we say it is hotter. If they move slower, we say it is colder. It is that simple.

Of course, there are more complex definitions for temperature, such as “The rate that internal energy changes with respect to entropy.”. But we don’t need such hard descriptions to answer the question “Why is the Earth heated unevenly?”.

Heat is something completely different than temperature. It is the transfer of kinetic energy from one object to another. If an object gets heated, its temperature rises. 

An object cannot have any measure of heat. Heat is merely the transfer of energy. Let’s think of a glass of water that is sitting at the table inside of your living room. It will have the same temperature as your living room. But it won’t have any measure of heat. If the temperature of your living room rises, the temperature of the glass of water will also rise. That will only happen because there is a heat transfer from your living room to the glass of water. 

So the question “Why is the Earth heated unevenly?” actually means why do some parts of Earth receive more energy than others. The question doesn’t have any relation to temperature. If you are wondering why “Some parts of Earth have different temperatures than others?”, we will slightly answer that question as well at the end of the article.

How does the Earth receive energy from the Sun?

As you may know, the Sun is a giant source of energy sitting at the centre of our Solar System. But how do we receive energy from the Sun? How does energy travel 150 million kilometres of space, and arrive here on Earth to make life as we know it possible? The answer is light, or to put it more correctly, electromagnetic waves. 

We are not going to get into the question of “What is an electromagnetic wave?”. It is an incredibly complex question that can only be answered with a physics article. For now, just think of electromagnetic waves as light beams. But you must also consider the kind of light we cannot see, such as ultraviolet light or infrared light. 

Think of how you feel when you step outside on a sunny day. You will feel the nice and relaxing feeling of getting warmer. That is because the light that is coming from the Sun interacts with the atoms on your body, making them move faster. As a result, you will receive heat from the Sun, and your temperature will rise. That is what happens to all the things on Earth when they receive light from the Sun. Buildings, roads, trees, animals, oceans, plants, air; everything gets hotter under the light.

But why does it happen unevenly? Meaning why are there icebergs on top of the Earth, and deserts in the middle? 

Why is the Earth heated unevenly?

There are two reasons why some parts of the Earth get more heat transferred than others.

Atmospheric Distance

Air molecules scatter light. So it is easy to understand why longer distances of the atmosphere cause more light to scatter, reducing the amount of energy reaching the Earth. This the exact reason why sunsets are reddish. Most of the blue and green light gets scattered in the long-distance atmosphere, leaving only red and colours close to red such as orange.

Atmospheric Distance

Now it seems really intuitive that there are deserts in the middle of the Earth and icebergs at the top. The light gets mostly scattered travelling to the poles, leaving only a tiny amount of energy to be transferred. 


The atmospheric distance is not the only reason for the decrease in heat transfer. There is also the increased area effect. The incoming light from the Sun will interact with a larger area in the upper and lower parts of Earth than the middle. 

Area effect

The effects combined will cause considerable decreases in heat transfer as you leave the equator. The incoming light will have travelled a much longer distance and will interact with a larger area. 

I hope we were able to answer the question “Why is the Earth heated unevenly?”. It is an important question that has many interesting parts of physical phenomenons and has fundamental effects on our planet.

What happens as a result?

Now the question “Why some parts of the Earth have different temperatures than others?” becomes really important. As we’ve said before, heat is not the same thing as temperature. We can clearly see this in the placement of deserts. Incredibly they are not placed around the equator.  

Desert Map

The reason for that is the direction of the winds. Since the equator receives more heat from the Sun than other regions around it, there is low atmospheric pressure. Winds flow from high-pressure to low-pressure environments. As a result, the equator receives an incredible amount of wind which also carries moisture from the oceans. The result is heavy rainfall around the equator and almost none at all around the desert region.

As we see from this example, the temperature on the Earth’s surface is a whole different story than heating of the surface.

There are many more amazing results of uneven heating on the Earth’s climate. It makes the climate much more dynamic and diverse. We all should be thankful for the incredible balance we live in and must avoid harming it in any way.