History of the science edit
In Greco-Roman geography, climate was thought to be simply set by klima, the angle of the midday sun defining bands of latitude which suited different peoples. Theophrastus thought agriculture caused local climate changes. Colonists expected North America weather to match latitudes, but found winters unexpectedly harsh. Du Bos in 1719, followed by Montesquieu and Hume, said millennia of farming had given Europe the temperate climate needed for civilisation, and cultivation could bring rapid climate improvements to America. Colonists including Thomas Jefferson began research to confirm this warming.[1] Savants thought the earth had incandescent origins; in 1778 Buffon proposed climatic Epochs of diminishing warmth, shown by fossils of tropical animals found in subarctic zones.[2]
Edme Mariotte had noted in 1681 that glass let through the warmth of sunlight but obstructed radiant heat.[3] In 1774 de Saussure measured heat from the sun using his "heliothermometer"; an insulated box capped with three layers of glass (separated by airspaces), pointed at the sun for an hour. The temperature inside the box was then taken: it reached 190 °F (88 °C) at the top of Crammont in the Graian Alps, and a slightly lower temperature in the valley below, though air temperatures were warmer in the valley than on the mountaintop.[4][full citation needed]
Joseph Fourier researched heat transfer including invisible infrared radiation (discovered by William Herschel in 1800) and in an innovative 1824 memoir assessed what sources heat the globe, and the balancing emission of infrared radiation. He proposed, using an analogy with de Saussure's device, a simple formulation of what was later called the greenhouse effect; transparent atmosphere lets through visible light, which warms the surface. The warmed surface emits infrared radiation, but the atmosphere is relatively opaque to infrared and slows the emission of energy, warming the planet.[5][full citation needed] He also calculated that earth's cooling from a molten state had slowed over time.[6]
Adolphe Brongniart found fossils of luxuriant tropical vegetation in coal seams, and in 1828 suggested there had been widespread warmth and higher levels of carbon dioxide during the Carboniferous.[7] Eunice Foote's 1856 experiments used glass cylinders filled with different gases heated by sunlight (which could not distinguish the infrared greenhouse effect). Moist air warmed more than dry air; CO2 warmed most, so she concluded higher levels of this in the past would have increased temperatures.[8]
In the 1830s Melloni combined Seebeck's thermopile with a galvanometer to measure radiant heat transmission through air. In 1839 he noticed variations which he thought might be due to changing proportions of water vapour amounts, but did not experiment on this.[9]
In detailed research starting in 1859,[10] John Tyndall established that nitrogen and oxygen (99% of dry air) are transparent to infrared, but water vapour and traces of complex molecules (significantly methane and carbon dioxide) absorb infrared, and when warmed emit infrared radiation. He found that this increased with concentration of these gases up to a point when the effect became saturated. His 1861 paper proposed changing concentrations of these gases could have caused "all the mutations of climate which the researches of geologists reveal" and explain ice age changes. Water vapour appeared to be the main factor, his subsequent thermal research focussed on molecular physics and meteorology.[11] By then, as Humboldt noted in 1850, decades of climate measurements showed stability in North America rather than the expected improvement. Popular belief that rain follows the plow was dismissed by Cleveland Abbe in 1889.[12]
Svante Arrhenius sought a mechanism causing ice ages, starting with the understanding that water vapour in air continuously varied, but carbon dioxide came from long term geological processes. Warming from increased CO2 would increase the amount of water vapour, amplifying its effect in a feedback process. In 1896, after laborious calculations, he published the first climate model of its kind, showing that halving of CO2 could have produced the ice age drop in temperature. His source for geology, Arvid Högbom, had estimated industrial carbon output. From this, Arrhenius calculated the temperature increase from doubling CO2. Other scientists highlighted flaws; Ångström said that saturation of the greenhouse effect meant adding more CO2 made no difference. Experts expected climate would be self-regulating.[13][14] From 1938 Guy Stewart Callendar published evidence that climate was warming and CO2 levels increasing,[15] but his calculations met the same objections.[13]
In the 1950s military research provided new data, showing less saturation of the greenhouse effect at high altitudes. Earlier calculations had treated the atmosphere as a single layer, Gilbert Plass used digital computers to model the different layers and found added CO2 would cause warming. Hans Suess found evidence CO2 levels had been rising, Roger Revelle showed the oceans would not absorb the increase, and together they helped Charles Keeling to begin a record of continued increase, the Keeling Curve.[13] Revelle, Plass and other scientists alerted media to press for government attention,[16] the dangers of global warming came to the fore at James Hansen's 1988 Congressional testimony.[17] Scientific research on climate change expanded, and the Intergovernmental Panel on Climate Change, set up in 1988 to provide formal advice to the world's governments, has spurred unprecedented levels of exchange between different scientific disciplines.[18]
References edit
- Tyndall, John (1861). "On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connection of Radiation, Absorption, and Conduction". Philosophical Magazine. 4. 22: 169–194, 273–285. Archived from the original on 26 March 2016. – newer link
- ^ Fleming 1998, pp. 11–16, 58, 21–22; Calel 2014.
- ^ Rudwick 2005, pp. 142–144.
- ^ Calel 2014; Fleming 2008, Fourier.
- ^ Archer & Pierrehumbert 2013, pp. 5, 12–13.
- ^ Archer & Pierrehumbert 2013, pp. 10–14
- ^ Rudwick 2010, pp. 124–125.
- ^ Rudwick 2010, p. 169, 171.
- ^ Huddleston 2019.
- ^ Fleming 1998, p. 70.
- ^ Tyndall 1861.
- ^ Archer & Pierrehumbert 2013, pp. 39–42; Fleming 2008, Tyndall.
- ^ Fleming 1998, pp. 49–53.
- ^ a b c Weart 2008, "The Carbon Dioxide Greenhouse Effect".
- ^ Fleming 2008, Arrhenius.
- ^ Callendar 1938; Fleming 2007.
- ^ Weart 2014a, Suspicions of a Human-Caused Greenhouse (1956–1969). See also footnote 27.
- ^ Weart 2014b, "News reporters gave only a little attention....".
- ^ Weart 2013, p. 3567.