Carbon Dioxide
Carbon dioxide (chemical formula CO2), is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in the Earth’s atmosphere in this state. Carbon dioxide is an important greenhouse gas because it transmits visible light but absorbs infrared.
Carbon dioxide is produced by all animals, plants and micro-organisms during respiration and is used by plants during photosynthesis to make sugars which may either be consumed again in respiration or used as raw material for plant growth. It is, therefore, a major component of the carbon cycle. Carbon dioxide is generated as a by-product of the combustion of fossil fuels or vegetable matter, among other chemical processes. Inorganic carbon dioxide comes from the output of volcanoes and other geothermal processes such as hot springs.
Carbon dioxide has no liquid state at pressures below 5.1 atm, but is a solid at temperatures below -78˚C and in its solid state, carbon dioxide is commonly called dry ice.
Due to human activates such as the combustion of fossil fuels and deforestation, the concentration of atmospheric carbon dioxide has increased by approximately 35 % since the start of the Industrial Revolution. 500 000 000 years ago the concentration of carbon dioxide was 20 times more prevalent than today, decreasing to 4-5 times during the Jurassic period and then maintaining a slow decline until the start of the Industrial Revolution.
As a direct result of electric energy generation the United States are annually estimated to produce an average of 2.250.000.000 metric tons of CO2.
Volcanic activity is estimated to release between 150-200 million tonnes of CO2 into the atmosphere each year. Emissions from human activities are estimated to be 130 times greater than the quantity emitted by volcanoes, amounting to 27 billion tonnes of CO2 each year.
Carbon Dioxide in the Oceans
There is about 50 times as much carbon dissolved in the oceans of the World in the form of CO2 than exists in the atmosphere. The oceans act as an enormous carbon sink having already absorbed about ⅓ of all human-generated CO2 emissions to date. Generally speaking, gas solubility decreases with water temperatures and accordingly CO2 is released from the oceans water into the atmosphere as the temperatures of the World’s oceans rise.
Global Warming
Global warming is the increase pf the average temperature of the Earth’s near-surface air and oceans in recent decades and its projected continuation.
Greenhouse Gases
Greenhouse gases are components of the atmosphere that contribute to the greenhouse effect. Without the greenhouse effect the Earth would be uninhabitable. In its absence the average mean temperature of the Earth would be approximately -20˚C rather than the present average standard atmospheric temperature of approximately +15˚C.
Greenhouse gases include in their order of abundance: water vapour, carbon dioxide, methane, nitrous oxide and ozone. Greenhouse gases come from natural sources and human activity.
Human Activity
Human activity may increase the greenhouse effect through the release of carbon dioxide, but human influences on other greenhouse gases can also be important. Some of the main sources of greenhouse gases due to human activity are:
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Deforestation leading to higher concentrations of CO2
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The burning of fossil fuels leading to higher CO2 concentrations. Here is a breakdown showing the distribution and amount of fossil fuel emissions in percent:
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Solid fuels (e.g. coal): 35 % |
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Liquid fuels (e.g. petrol): 36 % |
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Gaseous fuels (e.g. natural gas): 20 % |
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Cement production: 3 % |
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International shipping and aviation bunker fuels: 4 % |
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Other activities: 1 % |
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Livestock leading to higher methane atmospheric concentrations:
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The use of chlorofluorocarbons in refrigeration systems and in halon in fire suppression systems and manufacturing processes |
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Agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide concentrations |
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Global Temperature Increase
Increasing global temperature will cause the sea level to rise, and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation. Other effects of global warming can include changes in agricultural yields, glacier retreat, extinction of some species of animals and an increase in the limits and boundaries of known diseases.