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What is the Carbon Cycle & Why is it So Important?

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The carbon cycle refers to how carbon transfers between different ‘carbon reservoirs’ (or carbon sinks) located on Earth. It’s vital for maintaining a stable climate and carbon balance on our planet.


Carbon is the lifeblood of Earth and is naturally regulated by the carbon cycle. Without it, the Earth would be frozen.

Human activity plays a huge part in the carbon cycle, mainly from burning fossil fuels which are produced from crude oil and from land development – but it’s also having a detrimental effect on our planet. As humans produce more carbon dioxide (CO2) into the atmosphere, the carbon cycle is becoming overloaded. In fact, there is now more CO2 in our atmosphere than at any time during the last 800,000 years.

To illustrate just how important sustainable energy is and why everyone should be transitioning to low carbon fuels, our renewable fuel experts have put together a guide on the carbon cycle, a process that is crucial in preserving a stable climate and carbon balance on Earth.  


The importance of carbon

Carbon is the basis of all life on Earth; we are made of carbon, we consume carbon and our economies, our homes and our modes of transport are built on carbon. Whether these life forms absorb carbon to help produce food or emit carbon as part of respiration, the absorption and release of carbon is a key part of all plant and animal life.

Carbon is the fourth most abundant element in the Universe. It exists on Earth in solid, dissolved and gaseous forms. It’s a heat-trapping gas that’s produced both in nature and by human activities.

Man-made carbon dioxide is derived from burning coal, natural gas and oil to produce energy and comes from alkanes, the hydrocarbon chains that make up fuels. Whereas biological carbon is in the air as CO2 and is used by plants/photosynthetic organisms to create organic matter, which is then eventually returned to the atmosphere as CO2.

Carbon has many benefits to our planet:

  • It helps to regulate Earth’s temperature
  • It makes all living life possible
  • It is a key element in the food that sustains us
  • It provides a key source of the energy that fuels our economy

However, the substantial build up of carbon and other greenhouse gases in the atmosphere is trapping heat and contributing to climate change.

carbon cycle

What is the carbon cycle?

The carbon cycle is nature’s way of recycling carbon atoms. It refers to the process whereby carbon atoms travel continuously around the atmosphere to Earth, and then back into the atmosphere. Left alone, the carbon cycle would keep carbon dioxide concentrations in the atmosphere and global temperatures stable. But when large amounts of CO2 are released into the atmosphere at once, the cycle becomes out of balance.

Earth is a closed system, so the amount of carbon in our planet remains the same. This means that wherever carbon is located, whether that’s in the atmosphere or on Earth, it’s in a constate state of movement from place to place.

However, the amount of CO2 in a specific reservoir or carbon sink, can fluctuate over time as it transfers between reservoirs. When organisms die, volcanoes erupt, fires blaze and fossil fuels are burned, carbon is released back into the atmosphere.

What we mean here is that some of the carbon in the atmosphere may be captured by plants to produce food during photosynthesis. This carbon will then be consumed and stored in animals when they eat plants. Then, when animals die, they decompose and their remains become sediment, trapping the stored carbon in layers that eventually turn into rocks or minerals. Some of this sediment may form fossil fuels (such as coal, natural gas or oil) which release carbon back into the atmosphere when the fuel is burned, and so the cycle continues.

Therefore, we must choose sustainable alternatives to try and preserve the carbon cycle.

How does the carbon cycle work?

  • All living things contain carbon, including plants which absorb carbon dioxide to grow
  • When animals and plants die and are buried beneath the Earth’s surface, the carbon they contain can transpire into fossil fuels (oil and coal) over millions of years
  • Human activity burns these fossil fuels for industry and daily life which releases CO2 back into the atmosphere
  • Carbon dioxide is also released into the atmosphere through human and animal respiration

How is carbon stored?

Carbon is stored in a range of reservoirs, such as in plants and animals, hence why they are considered carbon life atoms. Carbon moves between them through a variety of processes, such as through photosynthesis, burning fossil fuels and simply breathing. This movement of carbon between reservoirs is the carbon cycle. 

Any change in the cycle that shifts carbon out of one reservoir, puts more carbon in other reservoirs. Changes that put carbon gases into the atmosphere result in warmer temperatures on Earth. 

On Earth, the majority of carbon is found in rocks and sediments (around 65,500 billion metric tonnes) while the rest is in the ocean, the atmosphere, plants, soil and fossil fuels:

  • Plants use carbon to build leaves and stems which are then digested by animals and used for cellular growth
  • In the atmosphere, carbon is stored in the form of gases such as CO2
  • It is stored in oceans and captured by many types of marine organisms
  • The majority of carbon is stored in rocks, minerals and other sediment buried beneath the planet’s surface
carbon cycle

Why is the carbon cycle important?

A stable carbon cycle is essential to life on Earth. Maintaining a carbon balance allows the planet to remain habitable for life. Without it, life on Earth as we know it would be in danger of being destroyed.


Key terms surrounding the carbon cycle

To comprehend the carbon cycle in greater detail, it’s important to understand following terms:

Greenhouse gases; circulating carbon; carbon sink; carbon emissions; carbon sequestration; carbon neutral; carbon negative.

Greenhouse gases

Greenhouse gases (GHG) trap heat in the atmosphere through absorbing and emitting radiant energy within the thermal infrared range, resulting in the greenhouse effect (warming global temperatures). It’s not just Earth that contains greenhouse gases, Venus, Mars and Titan also have GHG in their atmosphere.

Primary GHG are: carbon dioxide (CO2) and nitrogen oxide (N2O) water vapour (H2O), methane (CH4) and ozone (O3).

Without greenhouse gases, the Earth’s surface temperature would be on average -18oC instead of the current average of 15oC.

A change in average temperatures is causing unpredictable weather patterns: hotter summers and milder winters, as well as higher sea levels and melting ice caps.

Circulating carbon

Carbon is omnipresent; whether that’s in living organisms or as CO2 in the air, there is always carbon in circulation. The carbon cycle is the circulation of carbon in various forms through nature.

Carbon sink

A carbon sink is anything that absorbs more carbon from the atmosphere than it releases, such as plants, the ocean and soil. This is also known as a carbon reservoir.  

Forests are typically known as net carbon sinks as they absorb more carbon than they release through the process of photosynthesis. This temporary reduction of CO2 is known as negative emissions.

The ocean is another example of a carbon sink; it absorbs large amounts of CO2 from the atmosphere.

Carbon sources

Many processes release more CO2 into the atmosphere than they absorb; these are known as carbon sources. Anything that uses fossil fuels such as burning coal and producing electricity releases substantial amounts of carbon into the atmosphere.

Carbon stored in fossil fuels is static, remaining trapped outside the atmosphere for hundreds of thousands of years. Therefore, carbon sinks will never be able to cancel or offset emissions from fossil sources.

Carbon emissions

Carbon emissions (CO2) are the release of carbon into the atmosphere; the main contributors to climate change. Natural processes result in CO2 emissions such as through volcanic activity, and plant and animal activity through respiration or decomposition. However, the main causes of carbon emissions are from burning fossil fuels and manufacturing cement.

Carbon sequestration

Carbon sequestration, also known as carbon capture, is a method to remove carbon from the atmosphere and the ocean and put it back into storage in plants, soils, geological formations and the ocean. It secures carbon dioxide to prevent it from entering the Earth’s atmosphere with the goal of reducing climate change.

Carbon sequestration works by stabilising carbon in solid and dissolved forms to prevent the atmosphere from warming.

There are three main types of carbon sequestration: biological, technological and geological.

The Kyoto Protocol under the United Nations Framework Convention on Climate Change gives countries credits for their carbon sequestration activities in the area of land use, land use change and forestry. Activities can include afforestation, reforestation, improved forestry or agricultural practices and revegetation.

Did you know? Although we mostly associate removing CO2 from the environment through trees, most carbon sequestration takes place on the sea bed – in fact, the ocean holds 50 times more CO2 than the atmosphere [ – iaea.org].

Carbon neutral

Carbon neutral, also known as net zero carbon, refers to when there is a balance between emitting carbon and absorbing carbon from the atmosphere in carbon sinks.

To achieve net zero carbon emissions, global emissions must be counterbalanced by carbon sequestration (removing CO2 from the atmosphere and storing it).

Carbon negative

Carbon negative takes the concept of carbon neutral one step further and describes a system that removes more carbon from the environment than you emit. Vegetation, algae and other photosynthetic organisms are all inherently carbon negative.

Aside from natural CO2 capturing mechanisms, direct CO2 capturing machines (Direct Air Capture DAC) are also available. However, they are energy-intensive currently and cannot remove carbon dioxide from the air at scale.


How can we reduce carbon emissions?

  • Adopt low carbon fuels such as HVO fuel in transport, data centres, rail and all other industries
  • Use non-mineral based lubricants in engines
  • Use solar energy where possible
  • Reduce flights
  • Use rail and public transport where possible
  • Cycle or walk instead of driving
  • Use electric vehicles
carbon cycle

Renewable fuels and the carbon cycle

Switching to renewable fuels provides a tool to keep more carbon in the carbon sink – by reducing the demand for fossil fuels through their low contributions to the carbon cycle and in some cases, such as with HVO fuel, by offering up to a 90% reduction in net CO2 greenhouse gas (GHG) emissions.

Using the Department for Business, Energy & Industrial Strategy’s (BEIS) data on Scope 1 CO2 emissions, we can calculate the CO2 emissions for various diesel fuels – both renewable and mineral-based – to quickly understand the benefits of using renewable fuels in terms of the carbon cycle:

Fuel consumed (litres)Scope 1 Emissions (kg CO2e)
HVO diesel (0.03558 per litre)FAME biodiesel (0.16751 per litre)B7 Diesel (2.51233 per litre)100% mineral diesel (2.70553 per litre)
1.000.040.172.512.71
1,000361682,5122,706
5,00017883812,56213,528
10,0003561,67525,12327,055
15,0005342,51337,68540,583
20,0007123,35950,24754,111
25,0008904,18862,80867,638
30,0001,0675,02575,37081,166
35,0001,2455,86387,93294,694

The table shows that HVO fuel delivers 98% lower carbon emissions compared to road diesel, however that amount is reduced to closer to 90% when accounting for additional greenhouse gases that are not included. You can understand more about this in our HVO fuel FAQ.

These significant savings in CO2 emissions are just some of the many reasons why many businesses are beginning to switch to HVO fuel. BEIS’s own data also shows that the UK National Grid’s own CO2 emissions are similar to that of diesel, which is why many fleet-operating businesses are choosing renewable fuels over EVs.


Crown Oil’s steps towards sustainability

At Crown Oil, we’ve been delivering a wide range of fuels and oils for almost 75 years. But times are changing for the fuel industry and businesses have a duty to reduce their harmful emissions to help the UK achieve net zero carbon.

During the last two years, we’ve been focusing our efforts on renewable fuel alternatives and are passionate about helping businesses in their clean energy transition. We’ve even recently won the UKIFDA’s Green Award for 2021 which commemorates just how committed we are to tackling climate change!

Carbon sustainability is the right thing to do. That’s why we’ve taken active steps towards a greener future –  our entire fuel tanker delivery fleet now runs on Crown HVO fuel, and we’re helping other businesses do the same with our sustainable fuel solutions.



As well as using HVO fuel in fleets and the benefits HVO fuel brings, we’re helping to pioneer the use of HVO fuel in home heating to help reduce the UK’s reliance on fossil fuel-based home heating oil.

We’re also helping data centres to reduce their environmental impact by using HVO diesel in their backup power generators.

Other industries that benefit from using HVO fuel are:

  • Festivals
  • Construction
  • Rail
  • Hospitals
  • Agriculture
  • Tourism

Call Crown Oil today on 0330 123 1444 to learn how your business can reduce its impact on the carbon cycle.

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