A-Squad

**The Carbon Cycle and Climate Change By Aileen Yang and Anna Green

The Claim**//: The carbon dioxide emitted from burning fossil fuels is about 6 to 7 billion tons anually. The oceans emit 90 billion tons of carbon dioxide each year. Thus the carbon dioxide emissions from burning fossil fuels is a small percentage of the total carbon dioxide emissions (less than 3%), so it doesn't make any difference whether we change to renewable energy.//

 **Table of Contents**
 * 1) The Carbon Cycle
 * 2) Atmospheric Carbon
 * 3) Photosynthesis
 * 4) Carbon Dioxide Dissolving in Water
 * 5) Respiration
 * 6) Oceanic Carbon
 * 7) Carbon Sinks
 * 8) Summary
 * 9) Effects of Human Activity On the Carbon Cycle
 * 10) Carbon Dioxide Flow Into and Out of the Atmosphere from Various Sources
 * 11) Future Outlook
 * 12) References


 * __The Carbon Cycle__**

The claim above shows a lack of understanding of the carbon cycle. Earth's carbon is constantly being transferred from the ocean to the soil to the atmosphere to living things. This transfer is called the carbon cycle. Depending on where it is in the cycle, carbon forms many different compounds, including carbon dioxide, calcium carbonate, carbonic acid, and large organic molecules (NASA). The diagram below shows the carbon cycle in detail.

aw;efoihaw;eifhwaw;eoirahw;eoihraweo;rih <span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirahw;eoihraweo This image of the carbon cycle is taken from nasa.gov (see references below.)

__Atmospheric Carbon__ Carbon is present in the atmosphere mostly in the form of carbon dioxide. Carbon dioxide is a <span style="color: rgb(0, 0, 0);"> greenhouse gas, meaning that it is capable of absorbing the Earth's infrared radiation and reflecting it back towards Earth, instead of letting it escape into outer space. Carbon Dioxide is released into the atmosphere via respiration, and absorbed from the atmosphere via photosynthesis (see below). Carbon Dioxide is also emitted by volcanic eruptions (Campbell), and absorbed by the oceans.

//Photosynthesis//

Carbon is removed from the atmosphere primarily through photosynthesis. Photosynthesis is a biological process employed by plants and microorganisms. Photosynthesis is a process that uses energy from the sun to convert water (from the soil) and carbon dioxide (from the atmosphere) into sugar. The equation for photosynthesis is shown below.

<span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoierahw;eoihrawasweraweo;rih <span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;e Taken from: http://harvardforest.fas.harvard.edu/research/leaves/images/photosynthesis_formula.jpg

As can be seen from this, photosynthesis also releases oxygen into the atmosphere. About 50% of the sugar produced through photosynthesis is later used by the plant cells for respiration (Campbell). The other half is used to build organic macromolecules that the plant needs to survive.

//Carbon Dioxide Dissolving in Water//

Carbon Dioxide is absorbed by the oceans, where it dissolves into bicarbonate and carbonate ions. The equation for this is shown below. <span style="color: rgb(255, 255, 255);">efoiaw <span style="color: rgb(255, 255, 255);">;eif haw;eoirahw;eoihraweo When CO2 is dissolved in water, it forms an important bicarbonate-carbonate equilibrium. This equilibrium is very important in the process of photosynthesis. Plants are able to used the dissolved CO2 for photosynthesis, thus recycling the CO2 to the bottom of the ocean when they die. (OpenLearn)

//Respiration//

Respiration is the process through which stored sugars are broken down into carbon dioxide, water, and energy. The majority of living things respire. Photosynthesizing organisms break down the sugars that they acquired through photosynthesis. Non-photosynthesizing organisms have to eat other organisms in order to obtain sugar. Either way, respiration breaks the chemical bonds in the sugar atom, providing the organism with energy and releasing carbon dioxide back into the atmosphere (Campbell). The equation for respiration is shown below:

<span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirahw;eoihraweo;rihwrewer <span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirahw;eoihraweo;rih Taken from: http://www.rogers.k12.ar.us/users/ehutches/image150.gif

When organisms die, they decompose and release much of their stored carbon into the atmosphere. This process is aided by organisms called decomposers, which break down the organic compounds in dead organisms.

__Oceanic Carbon__ The ocean contains 50 times more CO2 than the atmosphere. They are able to hold much more carbon than the atmosphere because where the CO2 is absorbed into the water, it reacts with the water and forms carbonic acid. This nongaseous form reduces the pressure of the CO2, which allows more diffusion from the atmoshere.One process that is included in the CO2 transfer to the depths of the ocean is called the "biological pump" (Shaw).

__Carbon Sinks__ Forests, soils, oceans, and the atmosphere all store carbon, which moves from one storage place to another. As a result, these storages can be sources and sinks, but they absorb and sink more carbon than they emit. The forests use the carbon dioxide as a building block for organic molecules and they then store it in the tissue of their wood. Natural carbon sinks include the absorption of it by oceans and also the process of photosynthesis by the plants and algae in the ocean. The oceans are the largest active carbon sinks on the Earth (Carbon Sinks). <span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirahw;werwereoihraweo;rih <span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirah (Picture from []) <span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirahw;eoihraweo;rih Picture above shows how oceans are the biggest carbon sinks.

The video below explains the greenhouse effect, and explains that fossil fuels burned today are products of photosynthesis performed thousands of years ago.

<span style="color: rgb(255, 255, 255);">aw;efoihaw;eifhaw;eoirahw;eoihraweo;rih media type="youtube" key="5e0o_7o24HY" height="344" width="425" __Summary__

Carbon flows to and from the atmosphere because of the processes of photosynthesis and respiration. Carbon also dissolves into and is emitted by the oceans. Carbon is used by organisms to build their bodies, and then is released back into the atmosphere when those organisms die and are decomposed or burned. The carbon cycle is so active that a single carbon dioxide molecule will remain in the atmosphere for only five years (Wolfson). However, it will remain in this cycle for a very long time, because it will be constantly absorbed and released by organisms and the ocean.

Some of the carbon absorbed by organisms reaches locations called carbon sinks. When marine organisms die, they sink to the bottom of the deep ocean, where their bodies become part of the sediment. When terrestrial organisms die, some of their carbon is absorbed into the soil. When carbon reaches one of these sinks, it is effectively removed from the carbon cycle.


 * __Effects of Human Activity on the Carbon Cycle__**

The burning of fossil fuels takes the carbon stored in these permanent sinks--the soil and ocean sediments--and returns it to the atmosphere. This carbon would have remained stored beneath the Earth's surface for thousands of years.

__Carbon Flow Into and Out Of the Atmosphere from Various Sources__ This table was made from the NASA diagram of the carbon cycle shown above. As can be seen from this table, the burning of fossil fuels causes the net carbon flow into the atmosphere to be positive. However, without the burning of fossil fuels, the net flow of carbon into the atmosphere would be negative. This can be attributed partly to the fact that the oceans absorb more carbon dioxide it becomes more abundant in the atmosphere. Plants also absorb more carbon dioxide as more becomes available. So, the environment is effectively compensating for the atmospheric increase in carbon dioxide, but it its not able to keep up with the rate at which carbon dioxide is being burned.
 * **Source** || **Carbon Dioxide In (Gt)** || **Carbon Dioxide Out (Gt)** || **Net (GtC)** ||
 * Ocean || 92 || 90 || -2 ||
 * Soils || 0 || 60 || 60 ||
 * Vegetation || 121.8 || 61.6 || -60.2 ||
 * Fossil Fuels || 0 || 5.5 || 5.5 ||
 * Total Net CO2 ||  ||   || 3.3 ||
 * Total Net CO2 (Without ||  ||   ||   ||
 * Fossil Fuel Burning) ||  ||   || -2.2 ||
 * Total Net CO2 (Without ||  ||   ||   ||
 * Fossil Fuel Burning) ||  ||   || -2.2 ||

__Future Outlook__ So, the increase in atmospheric carbon dioxide is being caused by human activity. Humans are disturbing the carbon cycle by removing carbon from permanent sinks and releasing it into the atmosphere. What can be done to stop this?

The immediate answer is to stop emitting carbon dioxide into the atmosphere. However, the carbon that we have already injecting into the carbon cycle won't go away immediately. It will continue to cycle between the surface ocean and organisms on the planet for thousands of years. A new study by scientists from the Proceedings of National Academy of Sciences shows that carbon dioxide levels in the atmosphere won't return to pre-industrial conditions even if humans stop burning fossil fuels all-together (Solomon et al., 2008). However, this doesn't mean that we shouldn't stop releasing fossil fuels. The sooner we stop emissions, the less our planet will have to adjust to the increase in carbon. An increase in carbon would affect not only the temperature of the earth, but also the oceans and most of the organisms on the planet.

"Carbon sinks." __FERN - Home__. 20 Mar. 2009 <http://www.fern.org/pages/climate/carbon.html>.
 * __References__**

__OpenLearn - The Open University__. 20 Mar. 2009 [].

Shaw, Jonathon. "The Ocean Carbon Cycle |." __Harvard Magazine__. 2002. 20 Mar. 2009 [].

Solomon, Susan, Plattner, Gian-Kasper, Knutti, Reto, & Friendlingstein, Pierre. "Irreversible Climate Change Due to Carbon Dioxide Emissions." __Proceeding of National Academy of Sciences,__ vol. 106 no. 6, pgs 1704-1709. 18 Dec. 2008.

__The Carbon Cycle__. National Aeronautics and Space Association: Earth Observatory. 19 Mar 2009. []

Wolfson, Richard. __Energy, Environment, and Climate__. New York, NY: W. W. Norton & Co., 2008.

Campbell, Neil A. and Reece, Jane B. __Biology: 7th Edition (International Edition)__ San Fransisco, CA: Benjamin Cummings, 2004.