Greenhouse Gases

Not every gas in the atmosphere absorbs intensely long-wave radiation from the ground. The greenhouse gases in the earth’s atmosphere are called greenhouse gases, mainly carbon dioxide (CO2), methane, ozone, nitrous oxide, freon and water vapor. They absorb almost all the long-wave radiation emitted from the ground, and only a very narrow region absorbs very little, so they are called “window region”. It is through this window that the earth returns 70% of the heat from the sun to the space in the form of long-wave radiation, thus maintaining the ground temperature unchanged. The greenhouse effect is mainly due to the increase in the number and variety of greenhouse gases by human activities, which makes the 70% value decrease and the remaining heat makes the earth warm.

What is greenhouse gas?

However, although CO2 and other greenhouse gases have a strong ability to absorb long-wave radiation from the ground, their amount in the atmosphere is very small. If the atmospheric state of pressure as a atmospheric pressure and temperature of 0 C is called the standard state, then the whole atmosphere of the earth is compressed to this standard state, its thickness is 8000 meters. At present, the content of CO 2 in the atmosphere is 355 ppm, or 355 parts per million. Converting it to the standard state, it will be 2.8 meters thick. This is 2.8 meters thick in the atmosphere of 8,000 meters thick. Methane content is 1.7 ppm, corresponding to 1.4 cm thick. The ozone concentration is 400 ppb (ppb is one thousandth of ppm), which is only 3 mm thick after conversion. Nitrous oxide is 310 ppb, 2.5 mm thick. There are many kinds of freon, but the most abundant Freon 12 in the atmosphere is only 400 ppt (ppt is one thousandth of ppb), converted to the standard state of only 3 microns. This shows that there are few greenhouse gases in the atmosphere. It is also for this reason that human release without restrictions can easily lead to rapid global warming.

History of development

As early as 1938, British meteorologist Carlinda pointed out that CO2 concentration had risen by 6% since the beginning of the century after analyzing sporadic CO2 observations around the world at the end of the 19th century. He also found that there was a warming tendency in the world from the end of last century to the middle of this century, which caused great repercussions in the world. To this end, Kellin of Scripps Oceanographic Research Institute established an observatory in 1958 at an altitude of 3,400 meters in the Maunaroya Mountains of Hawaii, and began the precise observation of atmospheric CO2 content. Because Hawaii is located in the middle of the North Pacific Ocean. Therefore, it can be considered that it is not affected by terrestrial air pollution and the observation results are reliable.

From April 1958 to June 1991, the atmospheric CO2 concentration in the Maunaroya Mountains was observed. It was found that the atmospheric CO2 content in 1958 was only about 315 ppm, which reached 355 ppm in 1991. The seriousness of the problem also lies in the fact that only about half of the 5.5 billion tons of fossil fuels (about 4 tons of CO2 per ton) that humans burn annually (1996) enter the atmosphere and the rest are mainly absorbed by marine and terrestrial plants. Once the ocean is saturated with CO2, the atmospheric CO2 content will increase exponentially. In addition, they also found seasonal variations in CO2 content, with a difference of 6 ppm between winter and summer. This is mainly due to the winter drought and summer glory of vegetation on the vast continents of the Northern Hemisphere, that is, plants absorb CO2 in summer, which makes the atmospheric CO2 concentration relatively lower.


According to the determination of CO2 concentration in the air of sealed bubbles in the Antarctic and Greenland continental ice sheets, the CO2 content in the atmosphere has been relatively stable for a long time in the past, about 280 ppm. Only from the mid-18th century, before and after the Industrial Revolution began to rise steadily. That is to say, it took 240 years for human beings to increase the atmospheric CO2 concentration from 280 ppm to 355 ppm.

Methane is the second most important greenhouse gas after CO2. Although its concentration in the atmosphere is much lower than CO2, its growth rate is much higher. According to the Second Climate Change Assessment Report issued by the Intergovernmental Panel on Climate Change (IPCC) in 1996, CO2 increased by 30% in 240 years from 1750 to 1990, while methane increased by 145% in the same period. Methane, also known as biogas, is produced when organic matter decays under anoxic conditions. For example, paddy fields, compost and animal manure all produce biogas. Nitrogen monoxide is also known as laughing gas, because inhaling a certain concentration of this gas can cause facial muscle spasm, which looks like laughing. It is mainly produced by burning fossil fuels and organisms using chemical fertilizers. Although the ozone content in the atmosphere decreases in the stratosphere, it increases in the troposphere, which will be discussed later. Freon gases are compounds of chlorine, fluorine and carbon; they do not exist in nature and are entirely human-made. Because of its low melting point and boiling point, non-flammable, non-explosive, odorless, harmless and excellent stability, it is widely used in the manufacture of refrigerants, foaming agents and cleaners. Although the highest concentrations of Freon 12 and 11 in the earth’s atmosphere are very few, their growth rates have been very high in the past, both of which are 5% per year. Because of its severe destruction of the ozone layer in the atmosphere, its concentration in the atmosphere is expected to decrease gradually from the beginning of the 21st century according to the 1987 International Montreal Protocol.

It should be noted that although the atmospheric concentration of greenhouse gases other than CO2 is much lower than that of CO2, some of them are several orders of magnitude smaller, their greenhouse effect is much stronger than that of CO2. Therefore, their contribution to atmospheric greenhouse effect, according to the second IPCC Report, is only one order of magnitude lower than that of CO2. If their total contribution to the greenhouse effect of the Earth’s atmosphere is small compared with CO2 before 1960, it is not negligible that in the near future they will go hand in hand with CO2 and even exceed CO2.
April 2, 2018, DOE Labor

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