Global warming potential

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The (relative) global warming potential (also global warming potential ; English Global warming potential , greenhouse warming potential , GWP ), or CO 2 equivalent of a chemical compound is a measure of their relative contribution to the greenhouse effect , so their average heating effect of the Earth's atmosphere over a certain period of time (in usually 100 years). It indicates how much a certain mass of a greenhouse gas contributes to global warming compared to the same mass of CO 2 .

For example, the CO 2 equivalent for methane over a time horizon of 100 years is 28: This means that one kilogram of methane contributes 28 times as much to the greenhouse effect as one kilogram of CO 2 within the first 100 years after its release . For nitrous oxide , this value is 265.

However, the global warming potential is not to be equated with the actual share in global warming, since the emission quantities of the various gases differ greatly. With this concept, the different contributions of individual greenhouse gases can be compared with known emission quantities.

In the first commitment period of the Kyoto Protocol , emissions are assessed using the CO 2 equivalents of the individual gases and weighted according to their global warming potential. This means that, for example, a methane emission reduction of one ton is equivalent to a CO 2 reduction of 21 tons, since in both cases there are emissions of 21 tons less CO 2 equivalent. Relevant are the figures according to the second assessment report of the Intergovernmental Panel on Climate Change (IPCC) from 1995 for a time horizon of 100 years.

However, the IPCC itself gives GWP values ​​for time horizons of 20 years, 100 years and 500 years and emphasizes that its choice is determined by political considerations. For example B. to choose a long time horizon if the containment of the long-term consequences of global warming is preferred .

Values ​​of greenhouse gas potentials

Significant greenhouse gases

Greenhouse gas Sum
formula 		source GWP according to ... atmospheric lifetime
in years
according to
IPCC AR5
IPCC AR5 Kyoto protocol
(based on 20 years) (based on 100 years) (based on 100 years)
carbon dioxide CO 2 Combustion of fossil fuels ( coal , crude oil , natural gas ) and biomass (clearing of forests / slash- and- burn ), cement production , it is also produced by external respiration 1, 0 1, 0 1, 0 - a
2,3,3,3-tetrafluoropropene (R1234yf) C 3 H 2 F 4 Refrigerants in cooling systems 4.4 0.033
methane CH 4 Rice cultivation , cattle breeding , sewage treatment plants, landfills , hard coal mining ( mine gas ), natural gas and crude oil production, decomposition of methane hydrate deposits due to global warming, wetlands 84, 0 28, 0 21st, 0 12, 000
Nitrous oxide
(laughing gas) 		N 2 O Nitrogen fertilizer in agriculture , biomass burning 264, 0 265, 0 310, 0 121, 000
1,1,1,2-tetrafluoroethane
(R-134a, HFC-134a) 		C 2 H 2 F 4 Refrigerants in cooling systems 3710, 0 1300, 0 1000, 0 13.4, 00
Chlorofluorocarbons
(CFC) 		z. B. CClF 3 Group of different compounds, propellant gases in spray cans , refrigerants in cooling systems, anesthetics , filling gases in foams . Reduction due to the Montreal Protocol . Banned in Germany since 1995. 10900, 0 13900, 0 640, 000
Fluorocarbons
(HFC, HFC) 		z. B. CHF 3 Propellants in aerosol cans, refrigerants in cooling systems, filling gases in foams 10800, 0 12400, 0 222, 000
Nitrogen trifluoride NF 3 Manufacture of semiconductors , solar cells and liquid crystal screens 12800, 0 16100, 0 500, 000
Sulfur hexafluoride SF 6 Protective gas in the technical production of magnesium. Also in the case of leaks in gas-insulated high-voltage switchgear 17500, 0 23500, 0 23900 3200, 000
a cannot be specified as a single numerical value

More gases

Despite the internationally valid protocols, including the associated improvements, there are still greenhouse gases that are not recorded and have a very high global warming potential. This applies, for example, to the substance sulfuryl difluoride, which has a global warming potential of 7642, 4780 or 1540 based on 20, 100 or 500 years with a residence time of 36 years in the atmosphere. Sulfuryl difluoride is used for pest control such as export wood (see also container fumigation ) or buildings. Due to a sharp increase in German wood exports in recent years and more restrictive import regulations in the importing countries, the uncontrolled emission of sulfuryl difluoride has also increased significantly.

Influencing variables

The relative global warming potential (GWP) of a greenhouse gas is determined by various factors, namely its residence time in the atmosphere and the radiative forcing caused by an increase in concentration from an existing background concentration. Changes in the assessment of the residence time and lower radiative forcing due to increasing background concentrations are reasons why the IPCC regularly updates the values ​​for the global warming potential in its reports.

Contrary to an objection that is occasionally raised, carbon dioxide ( CO 2 ) additionally emitted into the atmosphere is able to intensify the greenhouse effect, although the existing CO 2 within its absorption bands already practically completely absorbs the thermal radiation.

The earth's atmosphere radiates heat into space at an average altitude of 5500 m, not at sea level. An increase in atmospheric greenhouse gas concentrations causes the area in which the earth radiates its heat into space to move upwards. So that the heat radiation remains the same as the radiation, the radiation area must also shift upwards. The temperature near the ground then rises according to the atmospheric temperature gradient .

Influence of the absorption behavior

The effect of a greenhouse gas is based on its ability to absorb the heat radiation emitted by the earth's surface and air layers close to the ground in the mid- infrared range (3 to 50 micrometers) and partially reflect it back to the earth and thus hinder the cooling of the atmosphere (greenhouse effect). Since the additional warming effect of the gas is considered here, its absorption behavior is particularly important in those spectral ranges in which the naturally occurring greenhouse gases (especially water vapor and carbon dioxide) do not or only slightly absorb. This is particularly the so-called atmospheric window in the range of 8-13 micrometers wavelength .

Influence of concentration and molecular geometry

The radiative forcing of a greenhouse gas depends non-linearly on its concentration. This non-linear dependence is approximately a logarithmic function . This means that a change in concentration from, for example, 2 to 3  ppm has the same effect as a change in concentration from 20 ppm to 30 ppm (or 200 ppm to 300 ppm, etc.). In addition to the larger number of possible vibration forms of complex molecules compared to, for example, CO 2 , this is another reason why the change in the concentration of a trace gas that absorbs in the atmospheric window, which of course does not exist or only exists in extremely small concentrations, has such a strong effect as in the table shown.

The absorption behavior of a greenhouse gas, i.e. the wavelength ranges in which it can absorb heat radiation, depends on the molecular structure of the gas in question.

Influence of the residence time

The mean residence time of the gas in the atmosphere is also of decisive importance . The time horizon chosen also plays an important role here. Greenhouse gases containing fluorine have a significantly higher GWP than greenhouse gases without fluorine atoms in the molecule due to their long residence time (e.g. 3200 years for SF 6 ) in the atmosphere. Methane (residence time approx. 12 years), on the other hand, has a short-term effect; its GWP is therefore much greater for short time horizons than for long ones. As a comparison, the residence time of CO 2 is estimated at approx. 120 years, whereby it should be noted that this concerns the solution equilibrium for carbon dioxide from the atmosphere and the upper sea layers. If water masses containing CO 2 sink into the deep sea , the dwell time in the ocean intermediate storage increases to a few thousand years.

Current Values

Since 1835, the concentration of carbon dioxide in the earth's atmosphere has increased from around 280  ppm to 400 ppm in 2015. The methane content more than doubled from 0.8 to 1.75 ppm in 1750–2000. This corresponds to an increase in the CO 2 equivalent from 24 ppm to around 50 ppm. Together with the increase in the concentration of many other greenhouse gases, this results in a total radiative forcing for 2015 that corresponds to a CO 2 equivalent of 485 ppm. The concentration of most other greenhouse gases was almost zero pre-industrial. Nitrous oxide (laughing gas) has recently come into focus.

See also

  • The ozone depletion potential is the analog measure to the GWP for describing the relative effect of the depletion of the ozone layer (ozone hole).

Web links

Individual evidence

  1. ↑ a b c G. Myhre, D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nalajima, A. Robock, G. Stephens, T. Takemura, H. Zhang et al .: Climate Change 2013: The Physical Science Basis . Working Group I contribution to the IPCC Fifth Assessment Report. Ed .: Intergovernmental Panel on Climate Change. September 30, 2013, Chapter 8: Anthropogenic and Natural Radiative Forcing, pp. Table 8.1.A, pages 8–88 to 8–99 ( climatechange2013.org [PDF; 2.9 MB ; accessed on October 13, 2013] Final Draft Underlying Scientific-Technical Assessment).
  2. ↑ Global Warming Potentials . In: United Nation Framework Convention on Climate Change . 2013. Retrieved May 26, 2013.
  3. ↑ Ray F. Weiss et al .: Nitrogen trifluoride in the global atmosphere . In: Geophys. Res. Lett. , 35, L20821, doi: 10.1029 / 2008GL035913 .
  4. ^ Vassileios C. Papadimitriou, RW Portmann, David W. Fahey, Jens Mühle, Ray F. Weiss, James B. Burkholder: Experimental and Theoretical Study of the Atmospheric Chemistry and Global Warming Potential of SO 2 F 2 . In: The journal of physical chemistry A . 112, No. 49, August, pp. 12657-12666. doi : 10.1021 / jp806368u .
  5. ↑ Port: Climate-damaging gas is used en masse. NDR 90.3, January 13, 2020, accessed on January 21, 2020 .
  6. ↑ Lecture Atmospheric Chemistry WS 2005/2006, last slide (PDF; 1.8 MB)
  7. ^ Spencer Weart: The Discovery of Global Warming , Center of History at the American Institute of Physics , 2003, aip.org
  8. ↑ IPCC Third Assessment Report, Chapter 6.3.5, Radiative Forcing of Climate Change, Simplified expressions grida.no ( Memento from January 3, 2016 in the Internet Archive )
  9. ↑ The greenhouse gases . Federal Environment Agency
  10. ↑ NOAA's Annual Greenhouse Gas Index of 2015
  11. ↑ AR Ravishankara et al: Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century. In: Science . 2009, PMID 19713491 .