Decarbonization Avenue C2V - CO2 to Value All about CO2

CO2 history & lifecycle

This section of All about CO2 provides insights on the sources of and processes that emit CO2 emissions, the history of CO2 emissions from the earliest stages of earth, and specific stages CO2 passes over its lifecycle.

Knowing more about CO2’s origins and an understanding of its evolution in earth’s historical context can enable readers to get a better contextual perspective of what CO2 really is, beyond just a gas.

1. What are the sources of CO2 emissions?

CO2 emissions can be a result of natural phenomena or human-induced activities, also called anthropogenic emissions.

2. How much CO2 was present in earth's atmosphere during different periods?

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3. How do human bodies produce CO2?

Our cellular respiration converts food and oxygen taken in by the body to energy in the form of adenosine triphosphate (ATP).

CO2 is produced as a byproduct of this reaction.

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4. How much CO2 do plants and trees give out during respiration?

During daylight hours, plants take in carbon dioxide and release oxygen through photosynthesis, and at night about half that carbon is then released through respiration. The total amount of CO2 given out by plants during respiration is much higher than CO2 emitted by all human breathing - as much as ten times higher. While that's a lot of CO2 given out, the plants are taking in twice the amount at the start.

All appears to be well.

But perhaps we should start getting a bit more concerned because, as the world becomes warmer, plants and trees could respire more, releasing more CO2 and even higher temperatures, triggering a hazardous feedback loop.

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5. Why does combustion release CO2?

During combustion, the heat of combustion releases gases.

When these gases are hot enough, carbon molecules react with oxygen from the air to make carbon dioxide.

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6. What does CO2 turn into after its life in the atmosphere?

Between 65% and 80% of CO2 released into the atmosphere dissolves into the ocean over a period of 20–200 years.

The remaining CO2 is removed by slower processes that take up to several thousands, or even hundreds of thousands of years. These processes include chemical weathering and rock formation.

All these imply that once CO2 enters the atmosphere, at least some portions of it will continue to affect climate for many hundreds of years.

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7. Can CO2 emissions be recycled infinitely such that it is never released into the atmosphere? 

While many avenues are available to utilize CO2 by converting it into products or using it in applications - some of which could even sequester it for a very long time - this is not the same as recycling. 

Strictly speaking, CO2 recycling refers to a concept in which CO2 is captured at source from a production process emissions and is utilized back in the process in some manner. For instance, in the steel industry, it is possible to use syngas (a mixture of CO and H2) as the reducing agent for iron ore, in place of coke. In the process, where both H2 and CO act as reducing agents, CO2 is emitted. It is possible to capture the CO2 and through reaction with green hydrogen produced from renewable powered electrolysis, produce syngas (a mixture of CO and H2) which can be fed back into the iron ore reduction process, and thus the carbon gets infinitely recycled in this process. Note that such a CO2 recycling, though technically possible, is only being currently piloted in the steel industry (as of 2021).

Another almost perfect example of CO2 recycling happens in the plant domain. Biomass - which is derived from CO2 captured from air - can be converted to biochar which can be used to enhance soil fertility by helping soil retain nutrients like nitrogen and phosphorus, resulting in better plant growth and thus increased CO2 capture from the atmosphere, resulting in a virtuous cycle.

It might be more challenging to find many such avenues for perfect recycling of CO2. However, if one were to broaden the definition of “recycling” and allow for carbon emitted to be converted to a product that sequesters the carbon but could be used in a different location, many recycling possibilities emerge. CO2 emitted from power plants could be used to cure concrete and thus get sequestered for long periods. CO2 captured from breweries and wineries could be converted to durable plastics that can sequester carbon for long time periods.

8. What if there were no CO2 in the atmosphere?

As a greenhouse gas, CO2 traps the heat radiated from the earth and reflects some of it back to earth.

At high levels of CO2 in the atmosphere, this phenomenon creates global warming. While high levels of CO2 is a problem, having very low levels of CO2 or no CO2 will result in a much colder world because some heat had not been sent back to earth. So very low levels or zero CO2 is not an acceptable solution either!

Very low levels or no CO2 in the atmosphere will also mean plants will not be able to produce their - and our - food.

It's all about maintaining a balance.


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