A chemical structure for carbon dioxide

Carbon dioxide must be one of the most talked about molecules in recent years. You hear about it on the news or newspapers, or in blogs or social media online. Most of the time carbon dioxide is labelled as a bad, terrible molecule But what is carbon dioxide, and why is it such a problem? 

In the beginning…

Carbon dioxide is believed to have existed on Earth since it was formed 4.6 billion years ago. If you were able to go back to that time then the early atmosphere would have been mostly made of carbon dioxide. Back then the Earth was a very hot place, full of volcanoes and lava – toasty! It was these volcanoes that released huge amounts of carbon dioxide into the air.  

A mysterious gas

Despite being around for millions of years, carbon dioxide was not discovered until 1640 by a scientist named Jan Baptiste van Helmont. It was when he was burning some charcoal that Van Helmont realised that some of the charcoal was being changed to a new substance he called a gas. This gas was actually carbon dioxide, but Van Helmont did not quite know this. 

In 1754, a scientist named Joseph Black was heating a substance known as calcium carbonate. He noted that this process produced a gas. The gas was heavier than air and that fire would not burn in it. Black called this new gas “fixed air”, but it was really carbon dioxide.

Simple, but complicated

Carbon dioxide is a small and simple molecule. It is made from two atoms of oxygen and an atom of carbon. As a result, carbon dioxide can be written in a much simpler way as CO2. The image below shows what a molecule of CO2 looks like. Unlike a molecule of a water, the atoms in carbon dioxide are all in a straight line. The scientific name for this is linear.

A chemical structure for carbon dioxide
Carbon dioxide – a carbon atom with two oxygen atoms double bonded to it.

Carbon dioxide is normally found in the air as a colorless gas. It has no smell, although very high concentrations and said to smell and taste slightly acidic.

Ice, Ice Maybe

Like water, carbon dioxide can be frozen into something known as dry ice. Unlike water, dry ice does not melt into a liquid. It goes directly from a solid to a gas, a process known as sublimation. The only way to obtain carbon dioxide as a liquid is under high pressure, and so it is not commonly found.  

Because dry ice changes directly from a solid to a gas, it can be used to create fog. The spooky fog you may see in theatres or shows may be dry ice changing from solid to gas! Dry ice can also be used to help keep items cold and preserve food. 

Dry ice forms at the cool temperature of -78.5 ℃. It must be used carefully as skin contact can cause frostbite.

Carbon Dioxide is a vital molecule

Carbon dioxide is very important to all life on Earth. Many plants use carbon dioxide in a process called photosynthesis to produce their food. The process also releases oxygen gas, which is vital for all animals, including humans.

In humans and other animals, the opposite process occurs. Oxygen is used in a process called respiration that produces all our energy. However, this process produces carbon dioxide, which is released when you breathe out. It should be noted that plants also respire and so do also release carbon dioxide.

Natural CO2

Carbon dioxide is naturally released during volcanic eruptions, or when certain types of rock are dissolved. Carbon dioxide is also trapped in ice and glaciers. As these melt, the carbon dioxide they contain is released. 

An erupting volcano
An erupting volcano, spewing out lots of carbon dioxide, rocks and lava. The very early Earth was full of these so would not have been an easy place to live!

Carbon dioxide is also produced when substances containing carbon are burned. Fossil fuels such as natural gas, gasoline, diesel, coal and wood all produce carbon dioxide and water when burnt. Because the modern world burns a very large amount of these fuels, then lots of carbon dioxide is constantly being produced.

Turn up the heat

Substances called carbonates also produce carbon dioxide. The most well known carbonate is calcium carbonate, also called limestone. When calcium carbonate is heated, it can break down to produce calcium oxide and carbon dioxide. Calcium oxide is also called lime. 

Calcium carbonate can also react with acids. The reaction produces several products including water and carbon dioxide. 

What’s in air?

A small amount of carbon dioxide can be found in the Earth’s atmosphere. It is the fourth most abundant substance in the atmosphere after nitrogen, oxygen and argon. However, over the last two hundred years the amount of carbon dioxide in the atmosphere has increased. It is this increase in the amount of CO2 that is a problem. 

Keeping warm

Let’s first look at how the Earth is kept warm. The Earth is heated by the sun. Certain types of light from the sun pass through our atmosphere and reach the surface of the Earth. Once there some of the light is absorbed by the surface and helps to warm our planet. The remainder of the light is reflected back towards space. 

While some of this light escapes from the atmosphere, not all of it can. Gases in the atmosphere, known as greenhouse gases, can either absorb this light or reflect it back to Earth. Because of this, the air and the Earth are heated even more.

ozone layer protect from uv sunlight
Greenhouse gases in the atmosphere trap thermal energy and heat up the Earth. The more greenhouse gases, the more thermal energy trapped and the more the Earth heats up.

Carbon dioxide isn’t the only gas that changes how our atmosphere behaves. We have to keep the balance between all of them to keep our planet green and healthy! Another gas to think about is ozone and you can read about that in a previous molecule of the month post.

Natural Heating

A small amount of greenhouse gas in our atmosphere is normal. In fact, they are very important for keeping the Earth warm. It is estimated that without greenhouse gases, the average surface temperature on Earth would be -18℃.

Too much can be a bad thing

However, an increase in the amount of greenhouse gases is also a problem. Too much and the temperature of the Earth will increase, causing a process known as global warming. 

Global warming is one of the greatest challenges the world faces. One effect of global warming is climate change. Together, global warming and climate change is destroying the habitats of many animals. Changes in when and where rain falls is making wet places drier, and dry places wetter. 

Hot, hot, hot

How does this relate to carbon dioxide? Well, one of the major greenhouse gases is carbon dioxide. As the amount of carbon dioxide is increasing, then the amount of greenhouse gas in our atmosphere has also increased. Put simply, the more carbon dioxide produced, the more greenhouse gas in the atmosphere and so the higher the temperature of Earth becomes. 

It is because of this that many countries around the world are trying to reduce the amount of CO2 they produce. One way to achieve this is to reduce the amount of fossil fuels being burnt. Using our vehicles less or finding different ways to generate electricity can all help to reduce the amount of CO2 produced. 

In addition, methods to capture and store carbon dioxide are being tested. Natural methods include planting trees, which take in carbon dioxide and release oxygen. Scientists are also developing new materials that can capture carbon dioxide and store it. 


Unfortunately, global warming is not the only problem caused from the increase in carbon dioxide levels.

Greater amounts of carbon dioxide is also a problem for the oceans. Carbon dioxide can dissolve in water forming an acid called carbonic acid. The more carbon dioxide there is, the more that can dissolve in the oceans and the more acidic they become. 

Many living things such as corals and shellfish are badly affected by oceans becoming more acidic.

Not good! 

Global warming and ocean acidification are two reasons why many countries are trying to reduce the amount of carbon dioxide they produce. 

Even though carbon dioxide is a problem and often labeled as a bad molecule, it does have many uses.

The good side

Carbon dioxide has many uses. When baking foods like cake or bread, the release of carbon dioxide helps the food to rise. 

The reason soft drinks are fizzy is because they contain carbon dioxide. When the bottle is opened, the bubbles and hissing sound is carbon dioxide gas escaping. Some drinks are fermented and the carbon dioxide molecules in them are made by bacteria or yeast.

While the carbon dioxide molecule is one of the chemicals produced by fire, CO2 can also be used to put out fires. There are some fires where water will not work or is too dangerous. For these fires, carbon dioxide can be used instead. It works by removing oxygen from the area around the fire. With no oxygen present, the fire cannot burn anymore. 

A red fire extinguisher
There are many different fire extinguishers – some of them work by spraying carbon dioxide gas to smother the fire.

Not all fire extinguishers use carbon dioxide. Some use foam to extinguish oil-based fires for example. Percy Lavon Julian actually discovered a way to make fire extinguishers with waste products from the soybean industry – how’s that for sustainability? Certainly helps to keep carbon dioxide emissions down.

From start to end?

Carbon dioxide has been on Earth from the very start. It will also likely stay on Earth until the very end. Without this molecule, life would be very different. However, some might argue that life will be very different because of this molecule. 

Like water and oxygen, it is the small molecules that are so important to life on Earth. As a greenhouse gas, carbon dioxide has played an important role in warming the Earth and preventing it from being too cold to live on. 

But, the increase in levels of carbon dioxide and causing the Earth to heat up too much. Global warming is one of the biggest issues facing us right now. The increase in carbon dioxide is also affecting our oceans.  As a result, the world is trying to reduce the amount of carbon dioxide it produces. 

Carbon Dioxide: A Misunderstood Molecule?

Despite this, the carbon dioxide molecule has many uses. It can be found in fun items such as dry ice or soft drinks. Cakes and bread would not rise without help from the carbon dioxide being produced. It can also keep us safe through its use in fire extinguishers.


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