Global cooling

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World map showing the change in mean temperature 1965–1975 compared to 1937–1946

As global cooling is generally referred to a reduction in the global average temperature. In particular, however, this refers to the observed cooling of the near-Earth atmosphere and the oceans between 1940 and 1975, the likely cause of which was largely the anthropogenic emission of aerosols . The further cooling predicted by some scientists in the event of increasing aerosol emissions was spread by the media in the 1970s in particular and was often dramatized in the process.

The cooling and its causes

The development of the average temperature and the proportion of the various physical drives, especially sulfate aerosols, counteracted the warming

From 1940 to 1975 a global cooling trend was noted; between 1958 and 1965 the world average temperature fell by 0.3 ° C. This cooling, known as “global”, occurred particularly in the northern hemisphere.

As early as 1967 McCormick and Ludwig had come to the conclusion that the anthropogenic aerosol emissions increased the albedo and thereby caused the cooling. Aerosols are connected to a carrier gas, liquid or solid suspended particles, mostly industrial or volcanic emissions in the form of hygroscopic particles as condensation nuclei in the formation of clouds are involved. Depending on their concentration, chemical composition and atmospheric distribution, they mainly contribute to cooling.

According to the fourth assessment report of the IPCC (2007), human aerosol emissions were an important source of uncertainty when researching the causes of climate changes in the 20th century using climate models . However, the IPCC noted that, especially for the 1950s and 1960s the rapidly increasing aerosol concentrations cooled the earth. In fact, global sulfur emissions have increased enormously since 1950, only to decrease again since the 1980s. The development since the 1980s has been regionally inconsistent: emissions fell in Europe and North America, while they rose in South and East Asia. In addition to industrial emissions, volcanic emissions also played a role during the period: an eruption of the Agung in 1963 temporarily triggered additional cooling. In general, volcanic eruptions of magnitude 5 or 6 on the volcanic explosivity index have the potential to cause aerosol-related global cooling (around -0.3 to -0.5 ° C) over a number of years, as is the case for the Outbreak of the Pinatubo (1991) was detected.

The results were largely confirmed by review articles in the 2010s. Of all climate-affecting factors, aerosols caused the greatest negative radiative forcing in the period 1950–1980 and thus clearly counteracted global warming.

Scientific opinion in the 1970s on further climate development

1965–1979 published specialist articles on the long-term development of global temperature: forecast warming (red), cooling (blue), neutral (orange).

In the 1970s, scientists disputed predictions of a further cooling for the following decades. While in the early seventies warming and cooling prognoses were almost balanced, from the middle of the seventies the realization took hold that the cooling effect of the aerosols would be superimposed by the warming effect of the CO 2 emissions, according to a study by Peterson et al. a. from the year 2008. There was never a consensus among scientists about an impending global cooling.

For example, in 1971, if global aerosol emissions were to quadruple, Rasool and Schneider predicted a decrease in global average temperature of up to 3.5 ° C and warned that this could trigger a cold period . But they also pointed out that their model did not take into account the dynamic effects of increasing CO 2 and aerosol concentrations. At the time, they did not consider it possible to make a statement as to which of the opposite effects would outweigh. In 1975, Schneider came to the conclusion in a review that included newer climate models that a doubling of the CO 2 concentration could trigger a temperature increase between 1.5 ° C and 3.0 ° C. This would mean a serious risk.

Parallel to the discussion about the short-term trend of emissions continued in the course of the 1970s and 1980s, the recognition that the cold periods of recent history by fluctuations in the Earth's orbit around the Sun ( Milankovitch cycles ) with a corresponding slowdown or hemispheric shift of sunlight caused and were amplified by the associated reduction in atmospheric carbon dioxide concentration. On this basis, long-term predictions could be made about a gradual cooling and the end of the current interglacial , the Holocene . It is currently assumed that the next cold period in the course of natural climate change will only begin in around 30,000 to 50,000 years, as the periodic change in the earth's orbit (from slightly elliptical to almost circular) gradually approaches a new eccentricity minimum. According to current assumptions, however, this time sequence could fundamentally shift due to anthropogenic influences.

A group of experts from the World Meteorological Organization in 1976 summarized the state of knowledge as follows:

“It must be recognized that these predictions [of transition to a colder, Ice Age climatic form] will be invalid if - what is now believed to be probable - the introduction of carbon dioxide into the atmosphere and other effects of human activity over the next 200 years become one general warming of the earth. "

- WMO Executive Committee on Climate Change

Media coverage

The media around the world took up the cooling and ice age scenarios. The Time magazine reported in 1974 under the title Another Ice Age? about droughts and starvation in Africa, record floods in the USA, Pakistan and Japan and crop failures in Canada's grain belt. The unusually cold winters would herald a new ice age, according to a growing number of scientists. The New York Times headlined in 1975 that "Major Cooling Widely Considered to Be Inevitable" is generally considered to be inevitable. An article in Newsweek , one of the most cited articles in the news magazine, warned in 1975 of drought and the resulting crop failures and epidemics, as well as possible climate refugees from the affected areas. The author later admitted that the article was only looking at part of the science and that he was partly too passionate about it. Even then, there were indications of global warming, which is largely scientifically accepted today, due to increasing CO 2 concentrations. There were similar articles at the same time in German media, including in Spiegel .

See also

literature

Media releases

  • Betty Friedan: The Coming Ice Age. In: Harper's. September 1958, pp. 39-45. Harper's Archives
  • James D. Hays: The Ice Age Cometh. In: Saturday Review of the Sciences. March 24, 1973, pp. 29-32.
  • Another Ice Age? In: Time Magazine. June 26, 1974, p. 86.
  • Peter Gwynne: The Cooling World . In: Newsweek . April 28, 1975, p. 64 ( org.uk [PDF]). , today's assessment of the author ( html )
  • Walter Sullivan: Scientists Ask Why World Climate Is Changing; Major Cooling May Be Ahead. In: New York Times. May 21, 1975. Abstract
  • Samuel W. Matthews: What's Happening to Our Climate? In: National Geographic. Volume 150, 1976, pp. 581-82.
  • Richard Wolkomir: Is a New Ice Age Coming? In: Saturday Evening Post. March 1976, pp. 50-51, 78.
  • Even US Farms May Be Hit by Cooling Trend. In: US News & World Report. May 31, 1976, p. 56.

Individual evidence

  1. ^ GJ Kukla et al.: New data on climatic trends. In: Nature. 270, 1977, 573-580. doi: 10.1038 / 270573a0
  2. ↑ JK Angell, Korshover: Estimate of the Global Change in mb Temperature, Surface to 100, Between 1958 and 1975. In: Monthly Weather Review. Volume 105 (4), 1977, pp. 375-385. doi : 10.1175 / 1520-0493 (1977) 105 <0375: EOTGCI> 2.0.CO; 2
  3. ^ Paul E. Damon, Steven M. Kunen: Global Cooling? In: Science Volume 193, 1976, pp. 447-453. doi: 10.1126 / science.193.4252.447
  4. ^ Robert A. McCormick, John H. Ludwig: Climate Modification by Atmospheric Aerosols. In: Science. 156 (3780), 1967, pp. 1358-1359. doi: 10.1126 / science.156.3780.1358
  5. ↑ a b Frequently Asked Question 9.2. Can the Warming of the 20th Century be Explained by Natural Variability? In: Assessment Report 4th IPCC, 2007, accessed August 15, 2014 .
  6. ↑ David I. Stern: Global sulfur emissions from 1850 to 2000. In: Chemosphere, Vol. 58, 2005, pp. 163-175, doi: 10.1016 / j.chemosphere.2004.08.022
  7. ↑ a b Gabriele C Hegerl, Stefan Brönnimann, Tim Cowan, Andrew R Friedman, Ed Hawkins, Carley Iles, Wolfgang Müller, Andrew Schurer. Sabine Undorf: Causes of climate change over the historical record . In: Environmental Research Letters . tape 14 , no. December 12 , 2019, doi : 10.1088 / 1748-9326 / ab4557 (Topical Review, open access).
  8. ^ Brian J. Soden, Richard T. Wetherald, Georgiy L. Stenchikov, Alan Robock: Global Cooling After the Eruption of Mount Pinatubo: A Test of Climate Feedback by Water Vapor . (PDF) In: Science . 296, April 2002, pp. 727-730. doi : 10.1126 / science.296.5568.727 .
  9. ↑ G. Myhre, D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura, H. Zhang: 2013: Anthropogenic and Natural Radiative Forcing . In: TF Stocker, D. Qin, G.-K. Plattner, M. Tignor, SK Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and PM Midgley (eds.): Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . 8.5.2 Time Evolution of Historical Forcing.
  10. ↑ a b c Thomas C. Peterson et al .: The myth of the 1970s global cooling scientific consensus (PDF; 698 kB). American Meteorological Society, 2008.
  11. ^ Wallace S. Broecker : Climatic Change: Are We on the Brink of a Pronounced Global Warming? In: Science. Volume 189 (4201), 1975, pp. 460-463. doi: 10.1126 / science.189.4201.460
  12. ^ SI Rasool, SH Schneider: Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate. In: Science. Volume 173 (3992), 1971, pp. 138-141. doi: 10.1126 / science.173.3992.138
  13. ↑ Stephen H. Schneider: Are We Winning the War Against Pollution? (JPEG) In: New York Times. September 9, 1971, accessed August 15, 2014 (publication date September 16, 1971).
  14. ^ SI Rasool, SH Schneider: Aerosol Concentrations: Effects on Planetary Temperature . In: Science . tape 175 , 1972, pp. 95–96 , doi : 10.1126 / science.175.4017.95-a ( PDF ).
  15. ↑ Stephen H. Schneider: On the Carbon Dioxide-Climate Confusion . In: Journal of the Atmospheric Sciences . tape 32 , no. November 11 , 1975, abstract and 4th Conclusion, doi : 10.1175 / 1520-0469 (1975) 032 <2060: OTCDC> 2.0.CO; 2 .
  16. ^ A. Berger, MF Loutre: An Exceptionally Long Interglacial Ahead? In: Science. Vol. 297, (2002), pp. 1287-1288. doi: 10.1126 / science.1076120
  17. ^ Richard E. Zeebe: Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions . In: PNAS . 110, No. 34, August 2013, pp. 13739-13744. doi : 10.1073 / pnas.1222843110 .
  18. ^ A. Ganopolski, R. Winkelmann, HJ Schellnhuber: Critical insolation - CO 2 relation for diagnosing past and future glacial inception . In: Nature . 529, No. 7585, January 2016, pp. 200-203. doi : 10.1038 / nature16494 .
  19. ↑ Technical report of the expert group of the WMO Executive Committee on climate change . In: WMO Executive Committee on climate change (ed.): Promet . No. 4 , 1977, pp. 25 .
  20. ↑ Another Ice Age? In: Time Magazine. June 24, 1974.
  21. ^ A b Peter Gwynne: My 1975 'Cooling World' Story Doesn't Make Today's Climate Scientists Wrong. In: Inside Science. May 21, 2014, accessed May 27, 2014 .
  22. ↑ Disaster in installments . In: Der Spiegel . No. 33 , 1974 ( online ).
  23. ↑ The stones blown away . In: Der Spiegel . No. 3 , 1977 ( online ).