carbon cycle and climate

short term cycling of carbon

The short term cycling of carbon begins with carbon dioxide (CO2 ) in the atmosphere.

the carbon cycle

Carbon is a very important element to living things. As the second most common element in the human body, we know that human life without carbon would not be possible. Protein, carbohydrates, and fats are all part of the body and all contain carbon. When your body breaks down food to produce energy, you break down protein, carbohydrates, and fat, and you breathe out carbon dioxide. Carbon occurs in many forms on Earth. The element moves through organisms and then returns to the environment. When all this happens in balance, the ecosystem remains in balance too.

why the carbon cycle is important

Why is such a small amount of carbon dioxide in the atmosphere even important? Carbon dioxide is a greenhouse gas. Greenhouse gases trap heat energy that would otherwise radiate out into space, which warms Earth. These gases were discussed in the chapter Atmospheric Processes.

atmospheric carbon dioxide

Remember that the amount of CO2 in the atmosphere is very low. This means that a small increase or decrease in the atmospheric CO2 can have a large effect. By measuring the composition of air bubbles trapped in glacial ice, scientists can learn the amount of atmospheric CO2 at times in the past. Of particular interest is the time just before the Industrial Revolution, when society began to use fossil fuels. That value is thought to be the natural content of CO2 for this time period; that number was 280 parts per million (ppm). By 1958, when scientists began to directly measure CO2 content from the atmosphere at Mauna Loa volcano in the Pacific Ocean, the amount was 316 ppm (Figure 1.2). In 2014, the atmospheric CO2 content had risen to around 400 ppm. The amount of CO2 in the atmosphere has been measured at Mauna Loa Obser- vatory since 1958. The blue line shows yearly averaged CO2 . The red line shows seasonal variations in CO2 . This is an increase in atmospheric CO2 of 40% since the before the Industrial Revolution. About 65% of that increase has occurred since the first CO2 measurements were made on Mauna Loa Volcano, Hawaii, in 1958.


human actions impact the carbon cycle

Humans have changed the natural balance of the carbon cycle because we use coal, oil, and natural gas to supply our energy demands. Fossil fuels are a sink for CO2 when they form, but they are a source for CO2 when they are burned. The equation for combustion of propane, which is a simple hydrocarbon looks like this: The equation shows that when propane burns, it uses oxygen and produces carbon dioxide and water. So when a car burns a tank of gas, the amount of CO2 in the atmosphere increases just a little. Added over millions of tanks of gas and coal burned for electricity in power plants and all of the other sources of CO2 , the result is the increase in atmospheric CO2 seen in the Figure 1.2. The second largest source of atmospheric CO2 is deforestation (Figure 1.3). Trees naturally absorb CO2 while they are alive. Trees that are cut down lose their ability to absorb CO2 . If the tree is burned or decomposes, it becomes a source of CO2 . A forest can go from being a carbon sink to being a carbon source. This forest in Mexico has been cut down and burned to clear forested land for agri- culture.


longterm carbon cycling

carbon sinks and carbon sources

Places in the ecosystem that store carbon are reservoirs. Places that supply and remove carbon are carbon sources and carbon sinks, respectively. If more carbon is provided than stored, the place is a carbon source. If more carbon dioxide is absorbed than is emitted, the reservoir is a carbon sink. What are some examples of carbon sources and sinks? Carbon sinks are reservoirs where carbon is stored. Healthy living forests and the oceans act as carbon sinks. Carbon sources are reservoirs from which carbon can enter the environment. The mantle is a source of carbon from volcanic gases. A reservoir can change from a sink to a source and vice versa. A forest is a sink, but when the forest burns it becomes a source. The amount of time that carbon stays, on average, in a reservoir is the residence time of carbon in that reservoir.


Through photosynthesis, the inorganic carbon in carbon dioxide plus water and energy from sunlight is transformed into organic carbon (food) with oxygen given off as a waste product. The chemical equation for photosynthesis is:


Plants and animals engage in the reverse of photosynthesis, which is respiration. In respiration, animals use oxygen to convert the organic carbon in sugar into food energy they can use. Plants also go through respiration and consume some of the sugars they produce. The chemical reaction for respiration is: C6 H12 O6 + 6 O2 6 CO2 + 6 H2 O + useable energy Photosynthesis and respiration are a gas exchange process. In photosynthesis, CO2 is converted to O2 ; in respiration, O2 is converted to CO2 . Remember that plants do not create energy. They change the energy from sunlight into chemical energy that plants and animals can use as food (Figure 1.1).


instructional diagrams

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which statement is not true about carbon?

-->  a) it is the most common element in the human body

b) diamonds are made of carbon

c) it is part of co2

d) fats contain carbon

you breathe in oxygen and breathe out carbon dioxide.

-->  a) true

b) false

the waste product of photosynthesis is

a) glucose

b) carbon dioxide

-->  c) oxygen

d) all of the above

respiration and photosynthesis are gas exchange processes with the exchange being between co2 and o2.

-->  a) true

b) false

in photosynthesis, plants change this into chemical energy that plants and animals can use as food.

-->  a) sunlight

b) oxygen

c) sugar

d) all of the above

this is an example of a carbon source.

a) forest

b) ocean

c) fault

-->  d) volcano

the amount of carbon dioxide in the atmosphere is very low, but small changes make a big difference.

-->  a) true

b) false

some things are sinks for co2 until they are burned or warmed and then they become sources, including:

a) forests

b) fossil fuels

c) oceans

-->  d) all of these

on mauna loa volcano in the pacific ocean, co2 content has changed from _ in 1958 to around _ in 2014.

-->  a) 316 ppm; 400 ppm

b) 316 ppm; 350 ppm

c) 416 ppm; 420 ppm

d) 416 ppm; 500 ppm

diagram questions

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