The concentration of important gases, like carbon dioxide (CO2) and methane (CH4) are measured continuously since a few decades. Furthermore we have the opportunity to analyse the composition of air bubbles trapped in very ancient ice layers, from which we can derive the composition of the troposphere in the past, thousands of years ago.
The experimental record is unambiguous: CO2, CH4 and many other gases display a spectacular increase since the beginning of the industrial period, i.e. the early 19th century.
Causes of increased emissions of gaseous pollutants
Human activities are responsible for the emissions of various chemical compounds into the atmosphere. The main source of pollutants is:
- burning of fossil fuels (oil, coal, natural gas)
- vegetation (savannah and forest fires)
The gases include mostly CO2, CO, NO2 and NO, hydrocarbons, chlorofluorocarbons, etc.. The burning of fossil fuels is largest in the industrialised areas in our latitudes, while forest and savannah fires are more important in the tropical areas.
In particular, the production and use of energy is the main cause of the observed increase of numerous gasses in the atmosphere.
Intensive agriculture also causes important emissions. Cattle and the rice paddies form important sources of methane. The intensive use of fertilisers considerably increases the natural production of nitrogen oxide from the soil.
This is why it is now believed that on a global scale, anthropogenic sources (i.e. sources controlled by Man) dominate the natural sources for most polluting gases. Not surprisingly, the amount of these gases in the atmosphere has mainly increased during the last century.
Consequences of increased emissions of polluting gases
- On an urban scale
The pollution is generally intense; the gases and particles emitted by industry and fuel burning are harmful for human health; they also reduce visibility and damage buildings.
- On a larger scale (e.g. Western Europe)
Pollutants increase rain acidity and lead to photochemical "smog" episodes, primarily in the summertime. This pollution by ozone and other species is harmful for our respiratory system, for forests and for agricultural production.
- On a planetary scale
Gases like methane and tropospheric ozone can contribute to the global warming of the Earth because of the "greenhouse effect". On top of that, the emission of sulphur compounds and microscopic particles, the so-called "aerosols", can disturb the formation of clouds and rainfall.