The Carbon Cycle

The atmosphere contains 0.03% by volume of carbon dioxide.
This represents a huge reservoir of carbon, which is continually being removed from and returned to the atmosphere by a variety of processes.

Defination:

The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.

adapted from http://en.wikipedia.org/wiki/Carbon_cycle

How is Carbon Dioxide produced?

There are two main processes which produce Carbon Dioxide.

1.Respiration
All Living things respire. During respiration, carbon and hydrogen compounds in food are converted into carbon dioxide and water. Energy is released during respiraton.

glucose + oxygen ---(in living cells)--> carbon dioxide + water + energy
C6H12O6(aq) + 6 O2(g) ---> 6CO2(g) + 6H2O(l) + energy

2.Combustion of fuels
Coal, petroleum and natural gas are examples of fuels. Most fuels contain both carbon and hydrogen. When these fuels are burnt, carbon dioxide and water are produced. In the combustion of natural gas, which contains mainly methane, the equation for the reaction can be written as

methane + oxygen --> carbon dioxide + water vapour + heat energy
CH4(g) + 2O2(g) --> CO2(g) +2H2O(g) + heat energy

However, if a limited supply of air is used, carbon particles in the form of soot and carbon monoxide, a odourless but colorless gas is given out. This is known as incomplete combustion. The chemical equation can be written as:

Methane + oxygen --> carbon monoxide + water vapour + carbon + heat energy

4CH4(g) + 5O2(g) ---> 2CO(g) + 8 H2O(g) + 2C(s) + heat energy


How is Carbon Dioxide removed?

Planes are important as they help to remove carbon dioxide from the atmosphere. This process is known as photosynthesis, whereby plants absorb raw materials such a water, and carbon dioxide in the presence of sunlight to form glucose and oxygen.

The simplified version of the chemical equation for photosynthesis is shown below.

carbon dioxide + water ---> glucose + oxygen

6CO2(g) + 6H2O(l) --(sunlight + chlorophyll)--> C6H12O6(aq) + 6O2(g)

Therefore, the carbon cycle exists to help regulate the amount of carbon (which exists as Carbon dioxide) in the atmosphere.
The supply of oxygen will always be renewed by plants through photosynthesis and oxygen will be used up in the process of respiration and combustion of fuels.

Greenhouse Effect

Carbon Dioxide and water vapour have important roles to play in maintaining a fairly uniform temperature on the Earth's surface.
These gases allow the visible radiation from the sun to reach the Earth's surface but trap some of the infrared radiation which is emitted by the Earth. Energy is thus retained in the atmosphere.
This produces a warming effect known as the greenhouse effect, and gases which encourage or cause this process are known as greenhouse gases.

Defination:

Greenhouse gases are gaseous constituents of the atmosphere that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared radiation emitted by the Earth’s surface, the atmosphere itself, and by clouds.

adapted from http://en.wikipedia.org/wiki/Greenhouse_gas

Therefore, from the defination, we can also infer that water vapour, which is present in clouds, is a greenhouse gas.
Carbon Dioxide and Methane are greenhouse gases as well.

Because of industralization, human activities have added greenhouse gases to the atmosphere, mainly through the burning of fossil fuels and clearing of forests.
This causes a phenomenon known as global warming, whereby there is an excess of greenhouse gas such as carbon dioxide building up in the atmosphere at an higher rate than photosynthesis can remove. This causes an increase in the Earth's average temperature.

Sources of these greenhouse gases can be from cars and factories, where combustion of fossil fuels is needed.

Consequences of an increase in global warming:

1.Melting of large quantities of ice in the North and South Pole, which will cause levels of oceans to rise and flood low lying countries.

2.Decrease in crop yields world-wide, due to change in climate.
Areas currently covered by vegetation may become deserts.

3.Rapid Evaporation of water from the Earth's surface. When this happens, carbon dioxide dissolved in the oceabs will be driven out into the atmosphere, which adds on further to the greenhouse effect.