Activity 4

Carbon Dioxide

Carbon dioxide keeps cropping up whenever we discuss global warming and climate change – so what role does it play, and why has it become such an issue?

What role does Carbon Dioxide play?  

Respiration:

All living things need oxygen to survive. They take in oxygen, use it to keep themselves alive, then release carbon dioxide into the atmosphere as a by product. This process is called respiration.  For example, we breathe in ( or take in)  oxygen from the atmosphere and when we breathe out, we release carbon dioxide in our breath.

Photosynthesis:

Plants, in addition to using carbon dioxide as part of respiration, also use it in another process.  Plants cannot move and gather or hunt for food, so they have developed an ingenious process called photosynthesis which enables them to create food from carbon dioxide. They take in carbon dioxide from the atmosphere or the soil, transform it into food,  then release oxygen into the air as a by product.

See the diagrams below

This efficient recycling of oxygen and carbon dioxide is key to life on Earth and ensures that the planet and its living organisms never run out of oxygen or carbon dioxide.  Carbon dioxide is made up of 1 part  carbon and 2 parts oxygen.  Carbon and oxygen are two chemicals that are necessary for life on Earth – and  they have both been around on the planet since life on Earth began.  An important fact about these chemicals is that there is the same amount of oxygen and carbon on Earth now as there was millions of years ago.  This means that these chemicals are recycled over and over again.

 

Carbon storage.   While much of the carbon dioxide  is in the atmosphere, to be used in processes of photosynthesis and respiration, a great deal is stored in rocks, the soil and the oceans. For example, when plants or animals die much of the carbon goes into the soil where it is stored, or in the case of sea animals the carbon goes into the ocean.

This stored carbon dioxide is slowly released into the atmosphere, for example, rocks gradually get worn away and the carbon dioxide then escapes into the atmosphere, or the carbon dioxide in sea water gradually travels to the surface and into the atmosphere. This is a cycle which is more or less in balance : the total amount going into store is roughly the same as the amount being released.

Balance  This balancing act – the carbon cycle - ensures that the overall levels of carbon dioxide in the atmosphere are kept more or less constant. And up until about 200 years ago, this balancing act worked.  However, since the Industrial Revolution we have been using fossil fuels – coal, oil  and gas - for manufacturing ( factories ), heat ( e.g. central heating ) and electricity ( e.g. power stations). And that has upset the balance.

Fossil Fuels:  Coal, oil and gas all release large amounts of carbon dioxide into the atmosphere when they are burned. Burning fossil fuels releases about 20 time more carbon into the atmosphere than would occur naturally. So where does all that extra carbon dioxide go?  The answer is in the atmosphere.   In the past the oceans stored all the excess carbon dioxide as part of the carbon cycle, but now so much carbon dioxide is being released as a result of the burning of fossil fuels that the oceans cannot absorb it. The gas now just builds up in the atmosphere.

Why is this an issue?   You read earlier in Activity 3 that carbon dioxide is one of the Greenhouse gases, and that it has the important function of keeping the Earth warm. However,  like so much in Nature, this is about balance: the right amount of carbon dioxide ensures that we trap a certain amount of the sun’s heat - sufficient to keep the surface of the Earth warm enough for life to survive. The more carbon dioxide in the atmosphere, the greater the Greenhouse effect, and the warmer the surface of the Earth. 

While there is still some debate on the exact impact higher temperatures could have on life on Earth, there is nevertheless a consensus that even a couple of degrees difference could have quite devastating consequences.

Questions:

1. What happens during respiration?
2. What is photosynthesis?
3. Some carbon dioxide is in the atmosphere but much of it is stored. Where?
4. What are fossil fuels?
5. How has the burning of fossil fuels created a problem?