Sustainable Tourism
Anatomy of global warming
CO2 is the second most important greenhouse gas.
The Greenhouse Effect
The following five substances play direct or indirect parts in the greenhouse effect:
Carbon dioxide (CO2)
CO2 is the second most important greenhouse gas after water vapour. Its pre-industrial concentration in the atmosphere was about 280ppm (parts per million), but nowadays this concentration has risen to more than 370 ppm. CO2 is created during the combustion of petroleum products (such as petrol and kerosene), natural gas, coal and wood, etc. The reduction or decomposition of atmospheric carbon dioxide proceeds very slowly - the average period for which it remains in the atmosphere is of the order of 100 years.
Water Vapor (H2O)
The largest proportion (about 60%) of the natural greenhouse effect is due to atmospheric water vapour. When hydrocarbons (such as petrol and kerosene, etc.) are burned, water vapour is generated as a waste product (about 1.1 kg per litre of kerosene). The greenhouse effect becomes important when a condensation trail is produced from the water vapour. This happens when water vapour from the jet engines and the surrounding air condenses on the aerosols that are emitted at the same time and then freezes to form ice particles.
Aerosols
Aerosols are particles that are suspended in the air. These particles may be solid or also liquid - sulphuric acid droplets, for instance. Sulphuric acid is produced from the sulphur dioxide which is a product of burning kerosene.
Aerosols have two conflicting effects on the climate. A significant direct effect is that aerosols reflect the solar radiation in the atmosphere. This causes a reduction of irradiation which leads to cooling of the Earth's surface.
However, there is also an indirect effect which is more significant than this cooling: as so-called condensation nuclei, aerosols provide a reaction surface for the water vapour that is present, so they encourage the formation of condensation trails and clouds. In turn, this leads to warming of the Earth's surface. The characteristics of the aerosol determine when the formation of water droplets takes place.
Ozone
Ozone is not a direct product of burning kerosene - it is a reaction product of the nitrogen oxides. Ozone's importance in relation to humans varies depending on the altitude at which it occurs.
Ozone formation directly on the ground is encouraged by nitrogen oxides from car engines and industrial processes. It is particularly troublesome during summer and in cities, because it irritates our mucous membranes. At an altitude of about 10 km, where most aircraft fly, ozone is a strong greenhouse gas. Its contribution towards the greenhouse effect is about the same as that of carbon dioxide.
At even greater altitudes, ozone takes on a protective function. It filters the harsh UV radiation from the sun, which protects us against skin cancer.
Nitrogen oxides (NOx)
The effect of the nitrogen oxides on various chemical reactions is indirect and altitude-dependent: at a flying height of about 10 km, NOX increases the ozone content. This is important because ozone acts as a greenhouse gas at this altitude. On the other hand, nitrogen oxides reduce methane (another greenhouse gas in the atmosphere) again. Nevertheless, the net residual effect is a climatic warming.
Other greenhouse gases included in the Kyoto Protocol are: methane (caused by keeping farm animals, rice cultivation, and waste dumps), laughing gas (caused by agriculture), and chlorofluorocarbons (CFCs, cooling agents that are now banned internationally).
Carbon dioxide (CO2)
CO2 is the second most important greenhouse gas after water vapour. Its pre-industrial concentration in the atmosphere was about 280ppm (parts per million), but nowadays this concentration has risen to more than 370 ppm. CO2 is created during the combustion of petroleum products (such as petrol and kerosene), natural gas, coal and wood, etc. The reduction or decomposition of atmospheric carbon dioxide proceeds very slowly - the average period for which it remains in the atmosphere is of the order of 100 years.
Water Vapor (H2O)
The largest proportion (about 60%) of the natural greenhouse effect is due to atmospheric water vapour. When hydrocarbons (such as petrol and kerosene, etc.) are burned, water vapour is generated as a waste product (about 1.1 kg per litre of kerosene). The greenhouse effect becomes important when a condensation trail is produced from the water vapour. This happens when water vapour from the jet engines and the surrounding air condenses on the aerosols that are emitted at the same time and then freezes to form ice particles.
Aerosols
Aerosols are particles that are suspended in the air. These particles may be solid or also liquid - sulphuric acid droplets, for instance. Sulphuric acid is produced from the sulphur dioxide which is a product of burning kerosene.
Aerosols have two conflicting effects on the climate. A significant direct effect is that aerosols reflect the solar radiation in the atmosphere. This causes a reduction of irradiation which leads to cooling of the Earth's surface.
However, there is also an indirect effect which is more significant than this cooling: as so-called condensation nuclei, aerosols provide a reaction surface for the water vapour that is present, so they encourage the formation of condensation trails and clouds. In turn, this leads to warming of the Earth's surface. The characteristics of the aerosol determine when the formation of water droplets takes place.
Ozone
Ozone is not a direct product of burning kerosene - it is a reaction product of the nitrogen oxides. Ozone's importance in relation to humans varies depending on the altitude at which it occurs.
Ozone formation directly on the ground is encouraged by nitrogen oxides from car engines and industrial processes. It is particularly troublesome during summer and in cities, because it irritates our mucous membranes. At an altitude of about 10 km, where most aircraft fly, ozone is a strong greenhouse gas. Its contribution towards the greenhouse effect is about the same as that of carbon dioxide.
At even greater altitudes, ozone takes on a protective function. It filters the harsh UV radiation from the sun, which protects us against skin cancer.
Nitrogen oxides (NOx)
The effect of the nitrogen oxides on various chemical reactions is indirect and altitude-dependent: at a flying height of about 10 km, NOX increases the ozone content. This is important because ozone acts as a greenhouse gas at this altitude. On the other hand, nitrogen oxides reduce methane (another greenhouse gas in the atmosphere) again. Nevertheless, the net residual effect is a climatic warming.
Other greenhouse gases included in the Kyoto Protocol are: methane (caused by keeping farm animals, rice cultivation, and waste dumps), laughing gas (caused by agriculture), and chlorofluorocarbons (CFCs, cooling agents that are now banned internationally).
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