A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth’s atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth’s surface would be on average about 33 °C (59 °F) colder than at present.
However, since the beginning of the Industrial Revolution, the burning of fossil fuels has contributed to the increase in carbon dioxide in the atmosphere from 280 ppm to 390 ppm, despite the uptake of a large portion of the emissions through various natural “sinks” involved in the carbon cycle. Anthropogenic carbon dioxide (CO2 ) emissions (i.e., emissions produced by human activities) come from combustion of carbonaceous fuels, principally wood, coal, oil, and natural gas.
From Wikipedia, the free encyclopedia
Impact of a given gas on the overall greenhouse effect.
The contribution of each gas to the greenhouse effect is affected by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, on a molecule-for-molecule basis the direct radiative effects of methane is about 72 times stronger than carbon dioxide over a 20 year time frame but it is present in much smaller concentrations so that its total direct radiative effect is smaller, and it has a shorter atmospheric lifetime. On the other hand, in addition to its direct radiative impact methane has a large indirect radiative effect because it contributes to ozone formation. Shindell et al. (2005) argue that the contribution to climate change from methane is at least double previous estimates as a result of this effect.
When these gases are ranked by their direct contribution to the greenhouse effect, the most important are:
|
Gas |
Formula |
Contribution (%) |
|
Water vapor |
H2O |
36 – 72 % |
|
Carbon dioxide |
CO2 |
9 – 26 % |
|
Methane |
CH4 |
4 – 9 % |
|
Ozone |
O3 |
3 – 7 % |
Reference of picture: http://www.sabc.co.za/news/f1/f370460049439abe896dad915eb2a9f9/Graphics-on-final-road-to-Dbn-and-Greenhouse-gas-info-20111201
Global warming potential
The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. GWP is measured relative to the same mass of CO2 and evaluated for a specific timescale. Thus, if a gas has a high radiative forcing but also a short lifetime, it will have a large GWP on a 20 year scale but a small one on a 100 year scale. Conversely, if a molecule has a longer atmospheric lifetime than CO2 its GWP will increase with the timescale considered. Carbon dioxide is defined to have a GWP of 1 over all time periods.
Methane has an atmospheric lifetime of 12 ± 3 years and a GWP of 72 over 20 years, 25 over 100 years and 7.6 over 500 years. The decrease in GWP at longer times is because methane is degraded to water and CO2 through chemical reactions in the atmosphere.
Examples of the atmospheric lifetime and GWP relative to CO2 for several greenhouse gases are given in the following table:
| Atmospheric lifetime and GWP relative to CO2 at different time horizon for various greenhouse gases. | ||||||
| Gas name |
Chemical |
Lifetime |
Global warming potential (GWP) for given time horizon |
|||
|
20-yr |
100-yr |
500-yr |
||||
| Carbon dioxide |
CO2 |
See above | 1 | 1 |
1 |
|
| Methane |
CH4 |
12 | 72 | 25 |
7.6 |
|
| Nitrous oxide |
N2O |
114 | 289 | 298 |
153 |
|
| CFC-12 |
CCl2F2 |
100 | 11,000 | 10,900 |
5,200 |
|
| HCFC-22 |
CHClF2 |
12 | 5 160 | 1 810 |
549 |
|
| Tetrafluoromethane |
CF4 |
50,000 | 5,210 | 7,390 |
11,200 |
|
| Hexafluoroethane |
C2F6 |
10,000 | 8,630 | 12,200 |
18,200 |
|
| Sulphur hexafluoride |
SF6 |
3,200 | 16,300 | 22,800 |
32,600 |
|
| Nitrogen trifluoride |
NF3 |
740 | 12,300 | 17,200 |
20,700 |
|
The use of CFC-12 (except some essential uses) has been phased out due to its ozone depleting properties. The phasing-out of less active HCFC-compounds will be completed in 2030.
In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons (see IPCC list of greenhouse gases). Some greenhouse gases are not often listed. For example, nitrogen trifluoride has a high global warming potential (GWP) but is only present in very small quantities.[16]
Reference: Wikipedia
Website: http://en.wikipedia.org/wiki/Greenhouse_gas[:th]
A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth’s atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth’s surface would be on average about 33 °C (59 °F) colder than at present.
However, since the beginning of the Industrial Revolution, the burning of fossil fuels has contributed to the increase in carbon dioxide in the atmosphere from 280 ppm to 390 ppm, despite the uptake of a large portion of the emissions through various natural “sinks” involved in the carbon cycle. Anthropogenic carbon dioxide (CO2 ) emissions (i.e., emissions produced by human activities) come from combustion of carbonaceous fuels, principally wood, coal, oil, and natural gas.
From Wikipedia, the free encyclopedia
Impact of a given gas on the overall greenhouse effect.
The contribution of each gas to the greenhouse effect is affected by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, on a molecule-for-molecule basis the direct radiative effects of methane is about 72 times stronger than carbon dioxide over a 20 year time frame but it is present in much smaller concentrations so that its total direct radiative effect is smaller, and it has a shorter atmospheric lifetime. On the other hand, in addition to its direct radiative impact methane has a large indirect radiative effect because it contributes to ozone formation. Shindell et al. (2005) argue that the contribution to climate change from methane is at least double previous estimates as a result of this effect.
When these gases are ranked by their direct contribution to the greenhouse effect, the most important are:
|
Gas |
Formula |
Contribution (%) |
|
Water vapor |
H2O |
36 – 72 % |
|
Carbon dioxide |
CO2 |
9 – 26 % |
|
Methane |
CH4 |
4 – 9 % |
|
Ozone |
O3 |
3 – 7 % |
Reference of picture: http://www.sabc.co.za/news/f1/f370460049439abe896dad915eb2a9f9/Graphics-on-final-road-to-Dbn-and-Greenhouse-gas-info-20111201
Global warming potential
The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. GWP is measured relative to the same mass of CO2 and evaluated for a specific timescale. Thus, if a gas has a high radiative forcing but also a short lifetime, it will have a large GWP on a 20 year scale but a small one on a 100 year scale. Conversely, if a molecule has a longer atmospheric lifetime than CO2 its GWP will increase with the timescale considered. Carbon dioxide is defined to have a GWP of 1 over all time periods.
Methane has an atmospheric lifetime of 12 ± 3 years and a GWP of 72 over 20 years, 25 over 100 years and 7.6 over 500 years. The decrease in GWP at longer times is because methane is degraded to water and CO2 through chemical reactions in the atmosphere.
Examples of the atmospheric lifetime and GWP relative to CO2 for several greenhouse gases are given in the following table:
| Atmospheric lifetime and GWP relative to CO2 at different time horizon for various greenhouse gases. | ||||||
| Gas name |
Chemical |
Lifetime |
Global warming potential (GWP) for given time horizon |
|||
|
20-yr |
100-yr |
500-yr |
||||
| Carbon dioxide |
CO2 |
See above | 1 | 1 |
1 |
|
| Methane |
CH4 |
12 | 72 | 25 |
7.6 |
|
| Nitrous oxide |
N2O |
114 | 289 | 298 |
153 |
|
| CFC-12 |
CCl2F2 |
100 | 11,000 | 10,900 |
5,200 |
|
| HCFC-22 |
CHClF2 |
12 | 5 160 | 1 810 |
549 |
|
| Tetrafluoromethane |
CF4 |
50,000 | 5,210 | 7,390 |
11,200 |
|
| Hexafluoroethane |
C2F6 |
10,000 | 8,630 | 12,200 |
18,200 |
|
| Sulphur hexafluoride |
SF6 |
3,200 | 16,300 | 22,800 |
32,600 |
|
| Nitrogen trifluoride |
NF3 |
740 | 12,300 | 17,200 |
20,700 |
|
The use of CFC-12 (except some essential uses) has been phased out due to its ozone depleting properties. The phasing-out of less active HCFC-compounds will be completed in 2030.
In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons (see IPCC list of greenhouse gases). Some greenhouse gases are not often listed. For example, nitrogen trifluoride has a high global warming potential (GWP) but is only present in very small quantities.[16]
Reference: Wikipedia
