The so-called greenhouse effect of the earth's atmosphere is vital: a layer of air enveloping the planet lets about 70 percent of incoming sun rays pass through, but retains a large part of the heat reflected by the Earth's surface.
This effect makes sure that the planet always has a comfortable median temperature of 15 degrees Celsius. Without the greenhouse effect we would be freezing at minus 18 degrees.
The greenhouse effect is caused by certain traces of gases in the atmosphere that let short-wave radiation, such as sunlight pass through easily, but holds back long-wave heat radiation.
Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O, known as laughing gas) are among the main greenhouse gases after steam.
Since the beginning of industrialization, these gases, especially CO2, have been entering the atmosphere in large amounts through the burning of fossil fuels like coal, oil and gas.
Agriculture is another source of greenhouse gases.
With more intensive farming practices, deforestation, increasing numbers of cars on our roads, rising industrial production in developed countries and the industrialization of developing nations, the situation is getting worse by the day.
As humans produce more greenhouse gases, the atmosphere absorbs more heat, causing global warming and changing the Earth's climate.
Some visible effects of global warming are melting glaciers, rising sea levels, and worsening weather conditions such as heat waves and stronger storms.
CO2, methane and nitrous oxide make up nearly 90 percent of man- made greenhouse gases, says the United Nations World Meteorological Organization (WMO). With the emission of those gases, humans increase the natural greenhouse effect.
Compared to measurements taken around 1750 - before industrialization - figures at the end of 2005 had increased as follows: Carbon dioxide up 35.4 per cent, nitrous oxide up by 18.2 per cent and methane up by 154.7 per cent
The average CO2 concentration in 2005 was 379.1 ppm (parts per million particles of air). The average for methane was 1.78 ppm, for nitrous oxide 0.32 ppm. At the beginning of industrialization, the CO2 concentration stood at 280 ppm.