Greenhouse effect

What is greenhouse effect

Greenhouse gases warm the atmosphere, thermal radiation is absorbed by the planet and the temperature increases. This phenomenon is called greenhouse effect as its mechanisms are similar to the processes which occur in a greenhouse. In this case the atmosphere of the planet functions as glass which enables to heat the surface from one side and from the other side it absorbs heat emitted by the surface thereby causing global increase in temperature. To be brief, the atmosphere and gases it includes allow the radiation emitted by the Sun to get inside; however, at the same time, they trap the radiation of the heated Earth and do not allow it to escape and direct it towards the surface again. We receive the same amount of energy but the accumulation of the compounds which trap the Earth radiation in the atmosphere favors the increase in temperature.

Gases and aerosols are responsible for this.

Greenhouse effect is a thoroughly natural phenomenon which was observed not only on the Earth but also on other celestial bodies in our solar system, namely on Mars, Venus and Titan (moon of Saturn).

Natural greenhouse effect

The greenhouse effect is essential to life on our planet. Due to the ability to absorb and trap part of heat, it was possible for life to be created and survive. The greenhouse effect, owing to the specific role of atmosphere on every planet, is a natural phenomenon. Only on the Earth it takes on alarming proportions due to human activity. Natural heating of the planet is the effect of heat exchange. This process looks as follows: solar radiation carries thermal energy, when it reaches the Earth, it heats the atmosphere and the surface; water, forests and whole environment are heated as well. The Earth does not absorb the whole radiation, some of it is reflected; every light surface which reflects light also reflects thermal energy. This process is increased by some compounds and formations contained in the air (clouds, some aerosols). On the other hand, clouds and some gases let in and absorb energy thereby increasing temperature. Heating is not a one-way process. Ultraviolet objects heated by radiation emit all or part of radiation in a reverse process - long-wave infrared radiation. But for the atmosphere and the presence of compounds limiting the emission outside, all radiation would be transmitted to space. Nevertheless, the returned emission is stopped, heat balance of the Earth is positive, i.e. the amount of heat which reaches the Earth exceeds the amount of heat which leaves the Earth. This process leads to increase in temperature.

The causes of the greenhouse effect

The atmosphere of our planet is the air which is the mixture of various gases and aerosols. The composition of the atmosphere depends on the height. To put it simply, this is a composite mixture of gases. The most common gases are nitrogen (over 78%) and oxygen (28%). Other gases constitute only a fraction of the whole mixture; however, we cannot ignore their importance.

The main greenhouse gas is water vapour. According to scientists, it is responsible for the greenhouse effect in 30 to 60 per cent. The amount of the vapour in the atmosphere is not fixed and it fluctuates depending on a time of the day, season or area. Clouds are made of vapour, its presence can be easily stated with our own eyes. The vapour is also significant due to the fact that, on one hand, it absorbs perfectly some solar radiation and, on the other hand, it substantially limits heat return in the form of infrared radiation. Its presence in the atmosphere is the result of evaporating water: seas, lakes, oceans and also evaporating water from ground, plants and other organisms. The atmosphere is cleaned by rainfall and the process of vapour exchange and water cycle in the nature is dependant on temperature: the higher temperature the higher water evaporation rate; as a result the content of water vapour in the air increases and so does the greenhouse effect.

Another greenhouse gas is carbon dioxide. It was discovered in the atmosphere a long time ago and it is one of the factors responsible for life-friendly temperature. However, as the result of the emission of carbon dioxide in the process of fuel burning and forest burning, its greenhouse effect increases and so does its influence on climate. Carbon dioxide is responsible for the greenhouse effect at about 9 to 26% and the ability to absorb infrared radiation is 1. Methane has a considerable influence on climate warming. This gas is produced in natural processes, mainly by bacteria which decompose organic matter (remains of plants and animals). The excess of methane in the air and thereby enhancing the greenhouse effect are caused by mining industry and stockpiles of organic waste (dumps). The ability of methane to absorb infrared radiation is thirty times higher than the ability of carbon dioxide.

Other gases which cause and enhance the greenhouse effect (as a result of emission caused by people) are nitric oxides, including nitrous oxide, ozone and CFCs. The ability of nitrous oxide to absorb thermal radiation is 150 higher than the ability of carbon dioxide; this gas is produced in the emission of exhaust fumes and while using nitric fertilizers in farming.

Ozone, which is the protective ozone sphere in upper layers, in lower layers prevents heat produced on the Earth from escaping and its absorbency is 200 times higher than the same abilities of carbon dioxide. The content of greenhouse ozone increases due to chemical reactions of carbon monoxide, hydrocarbons and nitric oxides emitted in industrial burning processes.

And finally CFCs which are not natural as they were produced by people. Although there are not many CFCs in the air, their ability to trap radiation is from ten to twenty thousand higher than the ability of carbon dioxide.

Greenhouse effect and global warming

The issue of the greenhouse effect on climate change is debatable even in a scientific environment. Nevertheless, it is widely assumed that the greenhouse effect or its intensification resulting from human activity, has impact on global warming. The facts are clear: within the space of one century, i.e. from the beginning of the 20th century to the beginning of the 21st century, average temperature increased by 0.7%. What is more, there was a rise in the emission of carbon dioxide and other greenhouse gases. The estimated probability that it was caused by human activity and not by natural reasons is 90% (data from IV Report of the Intergovernmental Panel on Climate Change). Scientists who are skeptical about this theory claim that this change was caused by change in the activeness of the Sun which always influenced our planet, even before the intensification of human industrial activity.

There are other examples of climate change, such as a rise in average temperature on poles (the Arctic - average yearly temperature increased by 3oC and by 7oC in winter), changes in a moderate climate - which can be observed in hot summers and relatively warm winters. Furthermore, climatic zones are shifting to the Equator and, as a result, areas on which droughts occur are extending.

If this process continues, in the next century the consequences will be much more worrying: permafrost melting will cause the creation of bogs which consequently will increase the emission of methane and carbon dioxide. Due to the increase in the amount of carbon dioxide and methane in the air, the temperature of the Earth will rise by about 2oC which will influence ice melting and cause level of water to rise, as a result vast areas of the Earth will be threatened with flooding. From 1880 to 1990 the level of seas and oceans increased by about 11 cm.

Air circulation may be disturbed, climatic zones will shift, we will lose huge areas of farming lands and forest areas. Paradoxically global warming may lead to another Ice Age (ice melting will prevent warm sea currents).

To sum up, scientists agree that the greenhouse effect enhanced by people will speed up the process of global warming and global climate changes which may lead to unpredictable consequence in the future - even extermination of humankind and life on the Earth.

Forests and greenhouse effect

One of the main greenhouse gases responsible for the greenhouse effect, i.e. gases which absorb heat and trap it in the Earth atmosphere, is carbon dioxide. It is widely known that this gas is converted into oxygen by plants (photosynthesis). It means that the presence of carbon dioxide in the air is closely associated with the condition of plants on the Earth. Being a treasure trove of plants and lungs of our planet, forests are of great importance.

Most of forest areas have been destroyed and some of them are still being destroyed due to territorial expansion. They are cut down and burnt down. As a result of both processes we lose vast areas of forests which regulate gas and thermal economy of our planet. By burning forests we contribute to increase in the emission and concentration of carbon dioxide in the atmosphere.

Forests also absorb humidity thereby protecting the air from the excess of carbon dioxide. High humidity facilitates storing carbon dioxide in lower layers of the atmosphere owing to which it is kept in forests and does not escape to higher layers where it could cumulate heat. According to scientists' opinion, about 15% of the emission of carbon dioxide to the atmosphere is the effect of the destruction of forest areas.

Another problem connected with the greenhouse effect is destruction of rain forests. Not only are these huge green areas the treasure trove of nature and a place where oxygen is produced, they also regulate the amount of heat and light absorbed and reflected by the Earth. The ration of light reflection is called albedo. The colors of forests are dark so they absorb light radiation. If forests are destroyed, the light is reflected. Significant changes in the albedo ration influence winds, sea currents and rainfall, in other words, they cause climatic changes.

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