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This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.

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Tuesday, August 1, 2017

Foundations of Climate Science: Scientific Endeavor Before the Age of Politics

Summary.  Scientific research is pursued as an unbiased, objective inquiry into the properties of the natural world.  The foundations of climate science were laid over the last two hundred years, establishing that man-made production of carbon dioxide induces an atmospheric greenhouse effect.  Current political influence seeks wrongly to raise doubts about these immutable facts. 

Introduction: The Pursuit of Science.  In the last four posts (Our Life in a Technology-Driven World, Science and Technology in Modern Life, Scientific Underpinnings of Modern Medicine – DNA, Cancer and Immunotherapy, and  Scientific Underpinnings of Modern Medicine – Vaccination) this blog has presented anecdotal selections of ways in which the pursuit of science and the creation of new technologies have vastly improved our lives and helped maintain our good health. 
These advances are all based on a common set of principles that underlie scientific investigation:  the rigorous preservation of independent, unbiased research; pursuit of new scientific knowledge that builds on the results of previous studies; and research that either seeks to find support for new hypotheses by further experimentation or pursues open-ended research in order to gain new, detailed understanding of the natural world.  As the posts exemplify, new knowledge can lead to new technologies that are readily commercialized and broadly benefit the public at large. Regardless of the scientific field, these advances resulted from the universal application of open, unbiased inquiry into the properties of our natural world.
Our understanding of the atmospheric greenhouse effect and the role of excess carbon dioxide produced by humanity’s use of fossil fuels began two centuries ago. The scientists involved were either of nobility or in royal or university research settings.    As with scientific progress generally, the development of climate science was based on the same principles of inquiry detailed above.  The field grew during a time when scientific endeavor was pursued for its own value.  Contrary to the present times extra-scientific factors, such as political influences on science and the results it provided, were largely unknown.
Here five landmarks in the development of what we now call the atmospheric greenhouse effect are summarized and discussed. More complete presentations of each are given in the Details section further below. 
De Saussure’s Heliothermometer.  In the late 18th century Horace-Benedict de Saussure developed an box, blackened on the inside and covered by glass panes, containing a thermometer.  In sunlight the temperature inside this box rose to be much higher than that of the air outside the box.  He called the box a heliothermometer.
Jean-Baptiste Joseph Fourier was a French physicist and mathematician, interested in studying heat flow and thermal equilibrium at a global scale.  In the 1820’s he knew of de Saussure’s box, and analogized its properties to those of the Earth.  He likened the glass panes to the Earth’s gaseous atmosphere.  He distinguished between the visible light of the sun passing through the atmosphere and striking the Earth, and the invisible rays of heat radiation, which he surmised were confined by the atmosphere.  The heat radiation that can not escape to space results in warming of the Earth surface.  As one whose thinking was conceptual, he did not perform any experimental work based on his model.
John Tyndall was a British physicist, who, in the late 1850’s to 1860’s, constructed a novel apparatus that permitted him to measure directly whether a gas absorbed heat radiation.  He showed that carbon dioxide was among several gases he studied that do absorb heat; water vapor also absorbs heat radiation.  Tyndall’s results provided concrete evidence that components in the atmosphere retain heat within the Earth system, instead of radiating the heat into space.
In the 1890’s Svante Arrhenius, a Swedish physical chemist, feared that the excess carbon dioxide entering the atmosphere from burning fossil fuels (coal, oil and natural gas) would warm the Earth.  He performed extensive calculations by pencil and paper supporting his concern, and predicted significant increases in global temperature if fossil fuel use were to continue.
Charles Keeling, an American geochemist, first measured the time dependence of the carbon dioxide level in the air, beginning in 1958.  He showed that the amount was higher than at the time of Arrhenius, and that it increased year by year due to continued use of carbon-based fuels (fossil fuels) by humankind.  His observations certified the fears that Arrhenius expressed.  Others have vindicated the predicted rise in the temperature of the Earth.
The foundation of scientific investigation was laid more than four hundred years ago.  It is based on an unbiased pursuit of new knowledge, gained by factual investigation into the properties of the natural world without preconceived biases on how the results should turn out.  Recent posts here have provided examples of scientific findings and technological advances in the nineteenth and twentieth centuries. 
Development of climate science followed the same principles: unfettered, open inquiry directed only to gaining a better understanding of our climate.  This post highlights five main contributors to this endeavor starting in the late eighteenth century.  Their work has led to an understanding of the atmospheric greenhouse effect, its basis in carbon dioxide and water vapor, and the rapid worsening of global warming as humanity’s use of fossil fuels has continued unabated.  Developments in recent decades, building on the work of these five pioneers, makes clear that the world’s energy economy has to decarbonize as rapidly as possible. 
Yet commercial energy interests have exerted their considerable political influence to maintain the status quo.  They seek to discredit the science of global warming, by questioning that conclusion without supporting scientific data. They could just as readily have embraced the new reality, and committed themselves to new business models, free of fossil fuels, yet which have comparable potential for entrepreneurship and pursuit of profit.


The Heliothermometer.   In 1779 Horace-Benedict de Saussure, a meteorologist and geologist of noble origins, published a set of experiments based on a thermally insulated box he devised.  It was lined on the bottom with blackened cork and topped by a set of three glass panes separated from one another by air gaps.  (Jean-Louis Dufresne: Jean-Baptiste Joseph Fourier et la découverte de l’éffet de serre. La Méterologie, Méteo et Climat, 2006, 53, pp. 42-46) The box contained a thermometer.  He found that when the sun shone on this apparatus the temperature inside was much higher than that of the outside air.  De Saussure, however, did not try to understand the basis for his finding.
Jean-Baptiste Joseph Fourier was a French physicist and mathematician of the early nineteenth century.  His interests lay in understanding the physics of heat, and in deducing the sources of heat that led to the ambient temperature of the Earth and its atmosphere.  He was granted a faculty position at the École Polytechnique, and was elected to the Académie des Sciences.
Fourier concerned himself with heat fluxes of the entire Earth system (even though direct measurements had to wait until satellites became available about 150 years later; Jerome Whitington, 2016,  The Terrestrial Envelope: Joseph Fourier’s Geological Speculation). 
He considered that de Saussure’s heliothermometer provided an analogy for the Earth.  As described by Dufresne (cited above), Fourier first noted that the heat accumulated within the box is not dissipated by circulation to its exterior, and second, that the heat arriving from the sun as (visible) light differs from what he calls “hidden (i.e. invisible) light”.  Rays from the sun penetrate the glass covers of the box and reach its bottom.  They heat the air and walls that contain it.  These rays are no longer “luminous” (i.e. are not visible) and preserve only properties of “dark” (or invisible) heat rays.  Heat rays do not freely pass through the glass covers of the box, or through its walls.  Rather, heat accumulates within it.  The temperature in the box increases until a point of thermal balance is reached such that the heat added from the sun is balanced by the poor dissipation of heat through the walls.

Heat radiation had been discovered earlier during Fourier’s lifetime and he probably was familiar with this phenomenon.  Today we identify heat as infrared radiation, and de Saussure’s heliothermometer as a fine example of a greenhouse.  Indeed any car standing closed in the sun becomes a greenhouse.  When we get in it we are immediately immersed in a very hot atmosphere.
According to Dufresne, Fourier drew the analogy between the glass covers of de Saussure’s heliothermometer and the Earth’s atmosphere.  He understood that the atmosphere is transparent to the visible light of the sun, which then reaches the surface of the Earth.  The surface is heated by the sunlight and emits its energy as “dark”, or heat, radiation.  Fourier wrote (Dufresne; this writer’s translation): “Thus the temperature is raised by the barrier presented by the atmosphere, because the heat easily penetrates the atmosphere in the form of visible light, but cannot pass through the air [i.e., back into space] when converted into dark [i.e. invisible] light.”  This is the phenomenon which we now call the greenhouse effect exerted by the atmosphere.

John Tyndall showed that carbon dioxide absorbs heat radiation.  Tyndall was a British physicist whose research centered around radiation and energy.  He became a fellow of the Royal Society in 1852, and became a professor at the Royal Institution of Great Britain. 
He studied whether the gaseous components of air absorb radiant heat.  He devised an apparatus, shown in the image below, that compares the absorption of heat by a gas to that of a reference:

Tyndall’s differential spectrometer for measuring radiant heat absorption by a gas.  The gas was introduced into the long tube in the upper center.  Loss due to absorption of radiant heat by the gas was compared to a reference heat signal produced at the left.  The losses were compared in the double-conical thermopile at left center, and the resulting electrical signal was measured by the galvanometer (a sensitive measuring device) at the lower center.
Source: James Rodger Fleming, “Historical Perspectives on Climate Change”, Oxford University Press, 2005; attributed in turn to John Tyndall, “Contributions to Molecular Physics in the Domain of Radiant Heat” (London, 1872).


In 1859, among other gases, Tyndall studied oxygen, nitrogen (the major components of air), water vapor and carbon dioxide.  He found that oxygen and nitrogen had minimal absorption of heat radiation, and that water vapor was a strong absorber.   His experiments placed water vapor and carbon dioxide as main contributors to the role of the atmosphere in retaining heat radiation.  He stated “if…the chief influence be exercised by the aqueous vapor [i.e., water], every variation…must produce a change of climate.  Similar remarks would apply to the carbonic acid [i.e., carbon dioxide] diffused through the air…” (cited by Crawford, “Arrhenius’ 1896 Model of the Greenhouse Effect in Context”, Ambio, Vol. 26, pp 6-11, 1997).  Tyndall’s specific findings extended the theory that Fourier had set out in more general terms (see above) more than three decades earlier (Rudy M. Baum, Sr., “Future Calculations; The First Climate Change Believer”, in Distillation, 2016). 

[Climate scientists are not concerned about a danger to our planet from warming due to water vapor.  The amount of water vapor in the air at any temperature has an upper limit: what we call 100% relative humidity.   When that limit is reached water vapor in the air returns to Earth as liquid (rain) or solid (snow, hail) precipitation.  The water vapor content of the atmosphere can never exceed this upper bound.  This limit is slightly higher with increased global temperature.  In contrast, the atmospheric content of carbon dioxide has no upper bound.  That is why scientists urge us to decarbonize our energy economy.]

Svante Arrhenius was a Swedish physical chemist working around the turn of the 20th century.  He had wide-ranging interests in various aspects of chemistry, including the effects of carbon dioxide on the temperature of the Earth.  He won the Nobel Prize in Chemistry in 1903, and became the Director of the Nobel Institute in 1905.  He was motivated by the desire to understand the origins of past ice ages. Knowing of Tyndall’s work on carbon dioxide, he raised the possibility that humanity’s use of coal and other fossil fuels would lead to excess warming. 

Arrhenius estimated the intensity of heat absorption by water vapor and carbon dioxide in the atmosphere from data gathered by an American astronomer, Samuel Langley (described by Crawford).  He hypothetically changed the absorption intensities of the gases due to changes in their quantities.  This is important in today’s context because the increase in the quantity of carbon dioxide is the principal cause for warming today.  [As we recall that his mode of calculation was pushing pencil on paper, it is estimated that he formidably carried out between 10,000 and 100,000 individual calculations.] 

Importantly, Arrhenius identified human use of fossil fuels as a significant contributor to increased amounts of atmospheric carbon dioxide. He predicted that if the gas amounts increased by 50% the temperature would rise by 3°C (5.4°F); for a doubling of carbon dioxide in the atmosphere he predicted an increase in global temperature of 5° to 6°C (9.0 to 10.8°F ; J. Uppenbrink, Science, 272, p. 1122).

His projection was met with skepticism at the time because the actual amounts of the gas added to the atmosphere then was thought to be inconsequential, and because some assumed that much the gas would be absorbed by the oceans.

Charles Keeling was the first to show atmospheric carbon dioxide is increasing with time.  He was an atmospheric scientist working at the Scripps Institution of Oceanography in the U. S., beginning in 1956. (Scripps was the nucleus for the University of California campus at San Diego.) A few years earlier he developed an instrument that measures atmospheric carbon dioxide content in real time.  Keeling began monitoring carbondioxide on the summit of the volcano Mauna Loa, in Hawaii, 3000 m (ca 2 mi) above sea level.  Because of its remote location and high altitude this site was thought to be largely unaffected by short term changes arising from human activities.
Keeling earlier had determined that the carbon dioxide level was higher than in the 19th century.  After three years he showed clearly that the level was increasing with time.  He, and the Mauna Loa laboratory more recently, has tracked the gas level in the atmosphere; the results (now called the “Keeling Curve”) to 2016 are shown here:
Atmospheric carbon dioxide level reported monthly at the Mauna Loa observatory from 1958 to 2016, in molecules of carbon dioxide per million molecules of all components of air.  The vertical axis scale markers are 330, 360 and 390.   Source:


A principal motivation for Keeling’s interest in the carbon dioxide content of air came from Arrhenius’s prediction 60 years earlier that addition of carbon dioxide to the air from burning fossil fuels could increase global temperature.  In contrast to doubts about warming raised in Arrhenius’s time, Keeling’s measurements show unequivocally that the carbon dioxide level is rising rapidly (see the graphic above). 

Keeling also devised the measurement of the ratios of the isotopes of carbon in atmospheric carbon dioxide.  This permitted others to show clearly that the excess carbon dioxide in the atmosphere can only arise from plant matter, i.e., from the industrial scale burning of coal, oil and natural gas by humanity.  Keeling’s work was the basis for a report from the U. S. National Science Foundation in 1963, and of the U. S. President’s Science Advisory Committee in 1965, warning of dangers of excess, and increasing levels of, heat-trapping gases (such as carbon dioxide) in the atmosphere.

© 2017 Henry Auer

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