Radiative forcing

Components of radiative forcing of global warming in 2005 related to the reference year 1750 and their net effect on the Earth's heat balance.

The radiative forcing (engl. Radiative forcing ) is a measure of the change in the energy balance of the Earth by changing the effect of radiation from space and is in W / m² measured. The term radiative forcing or climate forcing was introduced by the IPCC to describe the influence of external factors on the radiation balance and the earth's climate system in the context of climate studies . Such factors can be, for example, the changed concentration of greenhouse gases and aerosols , changed incoming (absorbed) solar radiation in W / m² or a changed albedo . With regard to solar radiation, a distinction must be made between the solar constant and the radiation actually reaching the earth's surface, since the atmosphere reflects a part directly and attenuates the non-reflected radiation, see the radiation budget . Imbalances in the radiation balance have the potential to bring about changes in climate parameters and thus a new state of equilibrium in the climate system : an increased radiative forcing leads to a warming of the earth, a reduced radiative forcing to a cooling.

calculation

Causes of global warming (1750–2011) (as of 2018)

The radiative forcing is a so-called forcing in Earth system science jargon . H. a force acting on a system from the outside , which steers this system in a certain direction . For example, solar radiation affects the surface temperature of the earth or the moon and controls it indirectly.

In the context of global warming , the term applies to changes in the radiation balance of the surface tropospheric system that are caused by external factors. It is assumed that there is no change in the dynamics of the stratosphere and that there are no feedback effects in this area; Changes in the amount and distribution of water in the atmosphere resulting from the dynamics of radiative forcing are also not taken into account.

The radiative forcing (RF for radiative forcing , also ) can be linked via a linear relationship with the change in the global equilibrium temperature at the earth's surface ( ): ${\displaystyle \Delta F}$ ${\displaystyle \Delta T_{S}}$

${\displaystyle \Delta T_{S}=\lambda \Delta F}$

With λ = parameter of the climate sensitivity with the unit K / (W / m ² ).

The radiative forcing caused by the increase in CO ₂ concentrations can be calculated approximately as follows:

${\displaystyle \Delta F=5,35{\mathrm {W} \over \mathrm {m} ^{2}}\cdot \ln {C \over C_{0}}}$

With C = CO ₂ concentration of the atmosphere to be considered in ppm , C ₀ = initial concentration of the comparison atmosphere in ppm, = resulting radiative forcing in W / m². ${\displaystyle \Delta F}$

The relationship between the CO ₂ concentration and the instantaneous radiative forcing is logarithmic (for concentrations up to about eight times the current value of 400 ppm).

Of all the climatic factors that have changed since the beginning of industrialization, the increase in CO ₂ concentrations from C ₀ = 278 ppm in 1750 by approx. 40% to C = 391 ppm in 2011 with ≈ 1.82 W / m ² (± 0 , 19 W / m ² ) has the greatest radiative forcing and accordingly has the largest share in global warming. ${\displaystyle \Delta F}$

values

Radiative forcing in the period 1951–2010 according to IPCC, AR5 .

In the Fifth Assessment Report of the IPCC , the total man-made radiative forcing in the period from 1750 to 2011 is calculated net (i.e. after deducting cooling effects such as aerosols) at 2.3 W / m². For comparison: changes in solar radiation caused a radiative forcing of 0.05 W / m² in the same period, which corresponds to about 2 percent; solar activity has even declined since the middle of the 20th century. Gross, all long-lived greenhouse gases emitted caused radiative forcing of 2.83 W / m². The most important greenhouse gas is CO ₂ with 1.82 W / m², followed by methane with 0.48 W / m². Hydrogen halides cause radiation forcing of 0.36 W / m², nitrous oxide 0.17 W / m². Fluorocarbons are also responsible for positive radiative forcing , but their contribution is now decreasing following a massive decline in global production. Of the short-lived greenhouse gases, ozone , the production of which is stimulated by nitrogen oxides, carbon monoxide or hydrocarbons, has the highest radiative forcing at 0.4 W / m². Aerosols cause negative (i.e. cooling) radiative forcing of −0.9 W / m².

See also

• Climatic condition

Individual evidence

1. ↑ ^{a b} IPCC Third Assessment Report, Working Group I: The Scientific Basis, Chapter 6.3.1, Carbon Dioxide, Chapter 6: Radiative Forcing of Climate Change , pp. 356-358, accessed on May 10, 2018.
2. ↑ Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, DW Fahey, J. Haywood, J. Lean, DC Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland: Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, KB Averyt, M. Tignor and HL Miller (eds .)]. Cambridge University Press , Cambridge, United Kingdom and New York, NY, USA. Online (pdf 7.7 MByte)
3. ↑ G. Myhre et al. a .: Anthropogenic and Natural Radiative Forcing . In: TF Stocker (Ed.): Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . 2013, Chapter 8 Supplementary Material - 8.SM.11.3.1 Anthropogenic and Natural Radiative Forcing Metric Values ​​for Carbon Dioxide, p. 8SM-16 ( ipcc.ch ).
4. ↑ Huang, Yi; Bani Shahabadi, Maziar (November 28, 2014). "Why logarithmic?" J. Geophys. Res. Atmospheres. 119 (24): 13, 683-89
5. ↑ G. Myhre et al. a .: Anthropogenic and Natural Radiative Forcing . In: TF Stocker (Ed.): Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . 2013, p. 676-677, 696-698 ( ipcc.ch ).
6. ↑ IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 56: "The best estimate of RF [radiative forcing] from TSI [total solar irradiance] changes over the industrial era is 0.05 [0.00 to 0.10] W m – 2 [W / m²] (medium confidence), which includes greater RF up to around 1980 and then a small downward trend. "
7. ↑ AR5, cit. to: Mojib Latif : Are we getting the climate out of sync? , in: Klaus Wiegandt (Ed.), Courage for Sustainability. 12 ways into the future . Frankfurt am Main 2016, 80–112, pp. 101–104.