Energy and Carbon Dioxide
The present atmospheric concentration of CO2 is about 383 parts per million by volume. Imagine we took a box of air and divided it into one million equal parts, or pieces. We would find that CO2 only takes up 383 of those one million pieces. However, 200 years ago, CO2 would have filled only 283 of the one million pieces. By 2100, scientists expect that CO2 will take up 550 of the one million pieces. What is being replaced in this process of adding more CO2? Oxygen (O2), mainly. We breathe oxygen into our lungs, process it, and breathe out CO2. The green parts of plants (where there is chlorophyll) breathe in CO2 and breathe out oxygen: thus, the plants give animals oxygen, and the animals give the plants CO2.
Also, oxygen is used to burn things. In the process of burning, a chemical reaction takes place and the oxygen in the air combines with the carbon in the fuel (wood, gas, coal) to create CO2. It is this very process that gives us the heat that we use to produce other forms of energy. If you've ever started a campfire you know that to get it going you sometimes need to fan the small flames to get big flames. When you fan the fire and the flames get bigger, you are adding oxygen to the fire more quickly than if it just burned the oxygen in the air around it. In a simple way, this is why we breathe harder when we run fast for a long time.
So, where did all of the extra CO2 come from? Well, first from burning a lot of trees. Trees contain a huge amount of carbon, which is why trees form such a good fuel when heated and combined with oxygen in the air. Since 1850, however, humans have happened upon other things that work even better than wood. Gasoline, natural gas, and coal also contain a lot of carbon, and in a form that mixes very easily with oxygen, and thus generates lots of energy. This same energy is used to cook our food and move the wheels on our cars, and since about 1950, to create fertilizers for our crops. All of these processes use oxygen and release CO2.
It has only been since about 1950 that we've seen significant increases in burning gasoline, coal, and natural gas. Unlike wood, however, the carbon contained in these fuels was once deep below ground. We pulled the carbon out of the ground in the form of these fuels, combined it with oxygen, and released it into our air as CO2. The more we burn, the more we put up into our atmosphere.
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