Editing Svante Arrhenius (section)

==Greenhouse effect==

In developing a theory to explain the [[ice age]]s, Arrhenius, in 1896, was the first to use basic principles of physical chemistry to calculate estimates of the extent to which increases in atmospheric carbon dioxide (CO<sub>2</sub>) will increase Earth's surface temperature through the [[greenhouse effect]].<ref name="Baum"/><ref name=CarbonicAcid>{{cite journal |last1=Arrhenius |first1=Svante |title=On the influence of carbonic acid in the air upon the temperature of the ground |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |date=1896 |volume=41 |issue=251 |pages=237–276 |doi=10.1080/14786449608620846|url=http://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf}}</ref><ref>{{cite journal|last1=Arrhenius |first1=Svante|title=On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground|journal=Publications of the Astronomical Society of the Pacific|year=1897|pages=14|volume=9|issue=54|bibcode = 1897PASP....9...14A |doi = 10.1086/121158 |doi-access=free}}</ref> These calculations led him to conclude that human-caused CO<sub>2</sub> emissions, from fossil-fuel burning and other combustion processes, are large enough to cause global warming. This conclusion has been extensively tested, winning a place at the core of modern climate science.<ref>[https://www.skepticalscience.com/empirical-evidence-for-co2-enhanced-greenhouse-effect.htm "How do we know more CO2 is causing global warming?"], ''Skeptical Science'', founded by John Cook, the Climate Communication Fellow for the Global Change Institute, University of Queensland, Brisbane, Australia</ref><ref>[https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_SPM_FINAL.pdf "Climate Change 2013 – The Physical Science Basis, by the Intergovernmental Panel on Climate Change (IPCC)"], IPCC, 2013: Summary for Policymakers. In: ''Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change'' [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, England and New York, NY.</ref> Arrhenius, in this work, built upon the prior work of other famous scientists, including [[Joseph Fourier]], [[John Tyndall]], and [[Claude Pouillet]]. Arrhenius wanted to determine whether greenhouse gases could contribute to the explanation of the temperature variation between glacial and inter-glacial periods.<ref>Rodhe, Henning, et al. "Svante Arrhenius and the Greenhouse Effect". Ambio, vol. 26, no. 1, 1997, pp. 2–5. {{JSTOR|4314542}}.</ref> Arrhenius used infrared observations of the moon – by [[Frank Washington Very]] and [[Samuel Pierpont Langley]] at the [[Allegheny Observatory]] in [[Pittsburgh]] – to calculate how much of infrared (heat) radiation is captured by CO<sub>2</sub> and water (H<sub>2</sub>O) vapour in Earth's atmosphere. Using 'Stefan's law' (better known as the [[Stefan–Boltzmann law]]), he formulated what he referred to as a 'rule'. 
In its original form, Arrhenius's rule reads as follows:
::''if the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetic progression.''
Here, Arrhenius refers to CO<sub>2</sub> as carbonic acid (which refers only to the aqueous form H<sub>2</sub>CO<sub>3</sub> in modern usage). The following formulation of Arrhenius's rule is still in use today:<ref name=Walter>Martin E. Walter, [http://www.ams.org/notices/201010/rtx101001278p.pdf "Earthquakes and Weatherquakes: Mathematics and Climate Change"], ''Notices of the American Mathematical Society'', Volume 57, Number 10, p. 1278 (November 2010).</ref>

::<math>\Delta F = \alpha \ln(C/C_0)</math>

where <math>C_0</math> is the concentration of CO<sub>2</sub> at the beginning (time-zero) of the period being studied (if the same concentration unit is used for both <math>C</math> and <math>C_0</math>, then it doesn't matter which concentration unit is used); <math>C</math> is the CO<sub>2</sub> concentration at end of the period being studied; ''ln'' is the natural logarithm (= log base e ({{nowrap|log<sub>''e''</sub>}})); and <math>\Delta F</math> is the augmentation of the temperature, in other words the change in the rate of heating Earth's surface ([[radiative forcing]]), which is measured in [[Watt]]s per square [[meter]].<ref name=Walter /> Derivations from atmospheric radiative transfer models have found that <math>\alpha </math> (alpha) for CO<sub>2</sub> is 5.35 (± 10%) W/m<sup>2</sup> for Earth's atmosphere.<ref>[http://www.esrl.noaa.gov/gmd/aggi/aggi.html "NOAA Annual Greenhouse Gas Index, Spring 2016"], NOAA Annual Greenhouse Gas Index, NOAA Earth System Research Laboratory, Boulder, CO, James H Butler and Stephen A Montzka</ref>
[[File:Solvay conference, 1922.jpg|thumb|Arrhenius at the first [[Solvay conference]] on chemistry in 1922 in [[Brussels]]]]

Based on information from his colleague [[Arvid Högbom]],<ref>{{Cite book |last=Weart |first=Spencer R. |url=https://books.google.com/books?id=5zrjngEACAAJ |title=The Discovery of Global Warming |date=2008 |publisher=Harvard University Press |isbn=978-0-674-03189-0 |pages=6 |language=en}}</ref> Arrhenius was the first person to predict that emissions of carbon dioxide from the burning of fossil fuels and other combustion processes were large enough to cause global warming. In his calculation Arrhenius included the feedback from changes in water vapor as well as latitudinal effects, but he omitted clouds, convection of heat upward in the atmosphere, and other essential factors. His work is currently seen less as an accurate quantification of global warming than as the first demonstration that increases in atmospheric CO<sub>2</sub> will cause global warming, everything else being equal.
[[File:Svante Arrhenius 01.jpg|thumb|upright|Arrhenius in 1909]]
Arrhenius's absorption values for CO<sub>2</sub> and his conclusions met criticism by [[Knut Ångström]] in 1900, who published the first modern infrared absorption spectrum of CO<sub>2</sub> with two absorption bands, and published experimental results that seemed to show that absorption of infrared radiation by the gas in the atmosphere was already "saturated" so that adding more could make no difference. Arrhenius replied strongly in 1901 (''Annalen der Physik''), dismissing the critique altogether. He touched on the subject briefly in a technical book titled ''Lehrbuch der kosmischen Physik'' (1903). He later wrote ''Världarnas utveckling'' (1906) (German: ''Das Werden der Welten'' [1907], English: [https://archive.org/details/worldsinmakinge01arrhgoog ''Worlds in the Making''] [1908]) directed at a general audience, where he suggested that the human emission of CO<sub>2</sub> would be strong enough to prevent the world from entering a new ice age, and that a warmer earth would be needed to feed the rapidly increasing population:

:: "To a certain extent the temperature of the earth's surface, as we shall presently see, is conditioned by the properties of the atmosphere surrounding it, and particularly by the permeability of the latter for the rays of heat." (p. 46)

:: "That the atmospheric envelopes limit the heat losses from the planets had been suggested about 1800 by the great French physicist Fourier. His ideas were further developed afterwards by Pouillet and Tyndall. Their theory has been styled the hot-house theory, because they thought that the atmosphere acted after the manner of the glass panes of hot-houses." (p. 51)

:: "If the quantity of carbonic acid [ CO<sub>2</sub> + H<sub>2</sub>O '''→''' H<sub>2</sub>CO<sub>3</sub> (carbonic acid) ] in the air should sink to one-half its present percentage, the temperature would fall by about 4°; a diminution to one-quarter would reduce the temperature by 8°. On the other hand, any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4°; and if the carbon dioxide were increased fourfold, the temperature would rise by 8°." (p. 53)

:: "Although the sea, by absorbing carbonic acid, acts as a regulator of huge capacity, which takes up about five-sixths of the produced carbonic acid, we yet recognize that the slight percentage of carbonic acid in the atmosphere may by the advances of industry be changed to a noticeable degree in the course of a few centuries." (p. 54)

:: "Since, now, warm ages have alternated with glacial periods, even after man appeared on the earth, we have to ask ourselves: Is it probable that we shall in the coming geological ages be visited by a new ice period that will drive us from our temperate countries into the hotter climates of Africa? There does not appear to be much ground for such an apprehension. The enormous combustion of coal by our industrial establishments suffices to increase the percentage of carbon dioxide in the air to a perceptible degree." (p. 61)

:: "We often hear lamentations that the coal stored up in the earth is wasted by the present generation without any thought of the future, and we are terrified by the awful destruction of life and property which has followed the volcanic eruptions of our days. We may find a kind of consolation in the consideration that here, as in every other case, there is good mixed with the evil. By the influence of the increasing percentage of carbonic acid in the atmosphere, we may hope to enjoy ages with more equable and better climates, especially as regards the colder regions of the earth, ages when the earth will bring forth much more abundant crops than at present, for the benefit of rapidly propagating mankind." (p. 63)
[[File:1922 Svante Arrhenius.jpg|thumb|[[Autochrome Lumière|Autochrome]] portrait by [[The Archives of the Planet|Auguste Léon]], 1922]]
At this time, the accepted consensus explanation is that, historically, [[orbital forcing]] has set the timing for ice ages, with CO<sub>2</sub> acting as an essential [[positive feedback|amplifying feedback]].<ref>{{Cite web|url=https://scripps.ucsd.edu/programs/keelingcurve/2014/06/20/how-do-co2-levels-relate-to-ice-ages-and-sea-level/|title=How do CO2 levels relate to ice ages and sea-level?|last=Monroe|first=Rob|date=2014-06-20|website=The Keeling Curve|language=en-US|access-date=2019-12-19}}</ref><ref>{{cite journal |last1=Ganopolski |first1=A. |last2=Calov |first2=R. |title=The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles |journal=Climate of the Past |date=2011 |volume=7 |issue=4 |pages=1415–1425 |doi=10.5194/cp-7-1415-2011|bibcode=2011CliPa...7.1415G |url=http://www.clim-past.net/7/1415/2011/cp-7-1415-2011.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.clim-past.net/7/1415/2011/cp-7-1415-2011.pdf |archive-date=2022-10-09 |url-status=live|doi-access=free }}</ref> However, CO<sub>2</sub> releases since the industrial revolution have increased CO<sub>2</sub> to a level not found since 10 to 15 million years ago, when the global average surface temperature was up to {{convert|6|C-change|0}} warmer than now and almost all ice had melted, raising world sea-levels to about 100 feet (30 m.) higher than today's.<ref>{{Cite web|url=https://www.climatecentral.org/news/the-last-time-co2-was-this-high-humans-didnt-exist-15938|title=The Last Time CO2 Was This High, Humans Didn't Exist|last=Andrew Freedman|website=www.climatecentral.org|language=en|access-date=2019-12-19}}</ref>

Arrhenius estimated based on the CO<sub>2</sub> levels at his time, that reducing levels by 0.62–0.55 would decrease temperatures by 4–5&nbsp;°C (Celsius) and an increase of 2.5 to 3 times of CO<sub>2</sub> would cause a temperature rise of 8–9&nbsp;°C in the Arctic.<ref name=CarbonicAcid /><ref>{{cite web |last1=Graham |first1=Steve |title=Svante Arrhenius : Arrhenius' Carbon Dioxide Research |url=https://earthobservatory.nasa.gov/features/Arrhenius/arrhenius_2.php |publisher=Nasa Earth Observatory |language=en |date=18 January 2000}}</ref> In his book ''Worlds in the Making'' he described the "hot-house" theory of the atmosphere.<ref>{{cite web |last1=Graham |first1=Steve |title=Svante Arrhenius : Hot House Theory |url=https://earthobservatory.nasa.gov/features/Arrhenius/arrhenius_3.php |publisher=Nasa Earth Observatory |language=en |date=18 January 2000}}</ref>