Extreme Rainfall with Flooding in the U. S. South

Summary.  Two extreme rainfall events with catastrophic flooding occurred in the U. S. recently.  The first was in the Baton Rouge, Louisiana, area in August 2016, and the second is ongoing at this writing in August 2017 in southeastern Texas including Houston.

Attribution of extreme events to global warming has become more reliable as a result of increased capabilities built into the statistical procedures employed in such analyses.  Global warming likely contributed about 20% to the rainfall experienced in the Baton Rouge flooding event of 2016. 

Global warming is now recognized to be due largely to emissions of greenhouse gases by humans.  It is projected to grow worse in coming decades if stringent efforts are not made to reduce these emissions.  In that case it is foreseen that extreme weather events may become more frequent and more severe.

 

Introduction.  The southern United States has suffered two episodes of unprecedented rainfall and flooding in the past year.  In August 2016 Baton Rouge, Louisiana and the surrounding area experienced torrential rain and rapid, extreme flooding beginning August 11 and extending beyond August 16.  Major damage and human dislocations resulted from this catastrophe.

In 2017 Hurricane Harvey left the Gulf of Mexico and made landfall near Corpus Christi, Texas on August 25.  Contrary to the paths of many hurricanes, Harvey degenerated into a tropical depression and stalled over southern Texas for days; as of this writing on August 29 it has drifted slowly to the northeast, hovering over Houston, Texas.  At various locations it has drenched the land with 20-40 inches (50-100 cm) of rain over this time (accessed August 29, 2017), causing extreme flooding, especially in the Houston area.  It is projected to continue northeastward toward Louisiana in the next day or more.

Flooding in Baton Rouge arose as an unusual weather pattern leading to excessive rainy conditions slowed considerably over the region for several days .  In the most severe case rain fell at a rate of 2–3 inches (5.1–7.6 cm) per hour, and produced a total of 24 inches (61 cm) of rainfall, with a maximum recorded as 31.4 inches (79.7 cm) in Watson, Louisiana.  The National Weather Service estimated the likelihood of such an event as 0.1%.  Flooding of eight rivers in the area led to major disruptions and damage, including damage to 146,000 homes, with tens of thousands of people relocated to emergency shelters.  About 265,000 children, or one-third of Louisiana’s school pupils, were prevented from attending school.  The economic impact has been estimated at between $10-$15 billion.

Rainfall and flooding in southern Texas is continuing at the time of this writing, and is expected to migrate east toward Louisiana in the coming days.  The amount of rainfall to date is extremely high; an interactive display of rainfall rates and total accumulated rainfall at various locations is available online (based on the National Weather Service; accessed August 29, 2017).  As of this writing, the total for the Corpus Christi area is 20 inches (50 cm), with a maximum rate of almost 3 inches per hour (7.5 cm per hour) on August 26.  The Houston area is far more seriously affected, according to the interactive map.  One location northeast of Houston shows a total rainfall to date of 52 inches (130 cm) with a maximum rate of about 10 inches per hour (25 cm per hour).  (The normal annual rainfall in Houston  is 49.8 inches (126 cm).  Images and videos of the flooding, its damage and human tragedy can be seen currently on news sources and the internet.  The economic impacts will certainly be extremely high.

Reports such as the Fourth National Climate Assessment draft (NCA) foresee worsening catastrophes such as those described here.   The draft NCA was prepared by climate scientists and related specialists drawn from thirteen U. S. government departments and agencies, as well as a large number of scientists in nongovernmental research facilities. They critically assessed peer-reviewed research and similar public sources, including primary datasets and widely-recognized climate modeling frameworks.  These standards assure that the findings of the report are objectively accurate, avoiding bias toward any unsubstantiated point of view.  By law the NCA cannot make any policy recommendations.

Among its conclusions, the NCA finds it is “extremely likely” that activities by humans have been the “dominant” cause of the warming observed since the middle of the 20^th century.  It states with “very high confidence” that no alternatives, such as cyclical changes in solar energy reaching the Earth or variations in natural planetary factors, can explain the observed climate changes.

The NCA projects with “high confidence” that heavy precipitation events will continue increasing over the 21^st century.  As noted, these trends are attributed to human activity.  They will likely worsen considerably as the climate warms.

Global warming contributes to the severity of extreme weather events.  Of the excess heat retained by the earth, i.e., the land, air and sea, as a result of man-made global warming, 90% enters the waters of the ocean.  The U. S. National Oceanographic and Atmospheric Administration finds that the sea surface temperature of the Gulf of Mexico in the early months of 2017 exceeded the 35-year average for 1981-2016 by about 0.75°C (1.3°F), and about equaled the record for that period.  Since the amount of water vapor that air can hold increases by about 7% per °C (about 4% per °F), the warmer Gulf surface temperature increased the water vapor capacity of the air by about 5% compared to earlier years. 

Since the complete weather system defined as hurricane/depression Harvey is spending a large fraction of its time over the Gulf, it recharges its moisture content continuously, indefinitely.  Over land, much of this added moisture in the system falls as additional amounts of rain, compared to earlier years.  Similar considerations hold for the Baton Rouge extreme event of 2016.  The physical damage and human harm inflicted by such calamities is costly.  Ultimately much of the burden becomes added expenditures imposed as taxes on the population at large.

Conclusion

Attribution of specific events to the general finding that global temperatures are rising has become far more reliable in recent years.  The procedures use advanced statistical measures to assess whether the extent by which the extreme event exceeds historical records has explanations other than global warming.  If not, a proportion of the overall extreme event may be attributed to the excess effect provided by global warming.

Since the Houston extreme rainfall and flooding event is still in progress, it is too early to attempt attribution of its causes.  The Baton Rouge event, however, has been assessed by attribution methods.  Wang and coworkers identified atmospheric weather patterns that promoted the catastrophic rainfall of this episode.  Regional model simulations lead to an estimate that global warming since 1985 likely increased the observed rainfall by 20%.   

Authoritative analyses of the earth’s climate show that the warming experienced to date is primarily due to man-made additions of greenhouse gases to the atmosphere.  This enhances retention of heat within the earth system rather than radiating excess heat to space.  Continued human activity that produces more greenhouse gases in the future is expected to worsen this effect, according to climate models, leading to excessive warming of the planet’s air, land and oceans.  In such a case, one consequence is expected to be more severe, and more frequent, extreme weather events such as the Baton Rouge intense rain and flooding, and hurricane/tropical depression Harvey currently wreaking havoc in Texas and Louisiana. 

Stringent reductions in further emissions of greenhouse gases are called for in order to lessen the impact of future extreme weather events. 

© 2016 Henry Auer

The Earth Continues Warming: The Fourth National Climate Assessment Draft Report

Summary

A draft of the Fourth National Climate Assessment reports that the global average temperature for the 30-year period from 1986 to 2016 rose by 1.2°F (0.7°C). It is extremely likely that activities by humans have been the principal cause of this warming. Extreme temperature and rainfall events have increased over this time, as have forest wildfires.
 

Arctic land-based ice has been lost to melting, and the extent and thickness of sea ice has decreased.  The mean sea level has risen about 7-8 in (about 26-21 cm) since 1900.  Ocean waters have taken up 93% of the excess heat of the Earth system due to global warming since the 1950s.
 

Global greenhouse gas emissions are projected to continue and consequently global temperatures will continue increasing and related trends will continue.  Limits to the intended increase require that humanity reduce annual emissions to zero by 2100. 
 

The draft states “Choices made today will determine the magnitude of climate change risks beyond the next few decades.”

The Fourth National Climate Assessment (NCA) is due in 2018 (See Background at the end of this post).  However the U.S. Global Change Research Program (USGCRP), which oversees preparation of the NCA, has prepared a Final Draft of a Climate Science Special Report (CSSR; see Note 1 at the end of the post) that has become publicly available as a freestanding document on which the actual NCA will be based.
 

This post is based on the CSSR Executive Summary (ES).  Confidence levels and likelihoods given here in italics are taken directly from the ES.  They are carefully defined in the CSSR.  Phrases in quotes are taken verbatim from the CSSR text.

The Historical Record

The global average temperature has risen above the average for the six decades 1901-1960 by 1.2°F (0.7°C) for the recent period from 1986 to 2016 (very high confidence). The map below shows temperature increases gridded across the globe.

Color-coded global map grid of historical changes in the average temperature for the period 1986-2016 relative to the average from the six-decade reference period 1901-1960, in °F. No data are available at the poles, indicated by gray.
Source: CSSR; https://www.nytimes.com/interactive/2017/08/07/climate/document-Draft-of-the-Climate-Science-Special-Report.html.

 

The map shows that since the reference decades the entire surface of the planet, both land and sea, has increased in regional average temperature.  The greatest increase has occurred in Canada (especially in the northern and Arctic regions), Alaska, Siberia, northeastern China and eastern Brazil. Indeed, the Arctic is warming about twice as fast as the global average.

It is extremely likely that activities by humans have been the “dominant” cause of the warming observed since the middle of the 20^th century.  No alternatives, such as the cyclical changes in solar energy reaching the Earth or variations in natural planetary factors, can explain the observed climate changes (very high confidence).

Extreme climate-related weather events have increased in number and severity.  Since 1980 the cost of such calamities in the U. S. is over US$1 trillion. Extreme events can impact water quality, agriculture, human health, infrastructure, and lead to disaster events.  In the U. S. the number of high temperature records in the past 20 years is much higher than the number of low temperature records (very high confidence).

Heavy precipitation events in most regions of the U. S. have increased in intensity and frequency since 1901, especially in the northeast. (high confidence). 

The occurrence of large forest wildfires has increased in the U. S. West and Alaska since the early 1980s (high confidence). 

The waters of the oceans have absorbed about 93% of the heat accumulating in the Earth system due to global warming since the 1950s (very high confidence).  This affects climate patterns around the world.

In the Arctic, ice sheets overlaying land have been melting for at least the last three decades; in some locations the rate of loss is accelerating (very high confidence).    The rate of melting of ice sheets over Greenland has accelerated in the last few years (high confidence).  As this ice melts the water flows to the ocean, resulting in a net increase of sea level.

Arctic sea ice has been imaged since satellite flights permitted. The sea ice floats on the Arctic Ocean; its area expands and contracts in freeze-thaw seasonal cycles without any net change to global sea levels.  Rather, the extent responds to changes in air and sea temperatures.  The least extent, i.e., the most melting, occurs typically in September.  Striking images showing the loss of September sea ice from 1984 to 2016, both in thickness (color coded white as having been formed at least four years earlier) and in overall surface area, are shown in the images below:

Satellite images of Arctic sea ice extent and thickness in September, for 1984 (top) and 2016 (bottom).  The color bar shows the local age of the ice in years, a proxy for its thickness, from recent (dark gray) to more than 4 years (white).
Source: Adapted from CSSR; https://www.nytimes.com/interactive/2017/08/07/climate/document-Draft-of-the-Climate-Science-Special-Report.html.

 

Sea ice thickness has decreased by between 4.3 and 7.5 feet.  September sea ice extent has decreased by 10.7% to 15.9% per decade (very high confidence).  These changes reflect warming of the Arctic region over this time frame.  It is virtually certain that human activity has contributed to Arctic surface temperature increases, sea ice loss, glacier mass loss and snow extent decline seen across the Arctic (very high confidence).

The mean sea level has risen about 7-8 in (about 26-21 cm) since 1900 (very high confidence).  This is attributed “substantially” to human-induced climate change (high confidence).  The rate of sea level rise is greater than any found in the last 2,800 years (medium confidence).

Ocean waters are absorbing more than 25% of the carbon dioxide emitted into the atmosphere by burning fossil fuels.  Carbon dioxide is weakly acidic when dissolved in water, increasing its acidity (very high confidence).  This negatively impacts marine ecosystems in many important ways.

Projected Future Climate Trends

 

Extreme climate-related weather events will continue for many decades.

By the end of the 21^st century if the world generates significant reductions in greenhouse gases the global average temperature increase could be limited to 3.6°F (2.0°C) or less. This would require a pathway of annual GHG emissions reaching near zero by then.  In contrast, minimal constraints on the annual emissions rate could result in a rise of 5.8-11.9°F (3.2-6.6°C) (high confidence).

Even if the annual rate of greenhouse gas (GHG) emissions were to fall to zero, the high burden of GHGs already accumulated in the atmosphere would persist for a long time.  The CSSR foresees that even in this event the global average temperature would rise further (high confidence), perhaps by an additional 1.1°F (0.6°C) (medium confidence).

But realistic projections all foresee continued GHG emissions into the future.  U. S. temperatures will continue to rise (very high confidence); new records for high temperatures will be frequent (virtually certain).  Temperatures by the end of this century will be much higher than the present (high confidence).
Heavy precipitation events are projected to continue increasing over the 21^st century (high confidence).  In the western U. S., large reductions in mountain snowpack, and more precipitation falling as rain rather than snow, are projected as the climate warms (high confidence). These trends are attributed to human activity (high confidence).  They will likely worsen considerably as the climate warms (very high confidence).  In the absence of reductions in emission rates long-duration hydrological drought, due to decreased retention of soil moisture, becomes more likely by the end of the century (very high confidence).

Further warming is projected to lead to increases in wildfires (medium confidence).

 

If GHG emission rates continue unconstrained, the average sea surface temperature is projected to increase about 4.9°F (about 2.7°C) by 2100 (very high confidence).

The mean sea level will continue increasing, to varying extents depending on future emission rates, by at least 1 ft (30 cm; very high confidence) and as much as 4 ft (130 cm; low confidence) by 2100.  If the Antarctic ice shelf is lost due to high emission rates the upper bound could be as high as 8 ft (260 cm).  It is extremely likely that sea level will continue rising beyond 2100 (high confidence) as ice continues melting.

Further loss in Arctic sea ice will continue throughout the 21^st century, very likely resulting in a virtually ice-free ocean by the 2040s (very high confidence).

Conclusions of the CSSR

 

Limiting the total global average temperature increase to 3.6°F (2.0°C), or less, from a 19^th century baseline will require significant constraints on future GHG emission rates. Even though annual emission rates decreased slightly in 2014 and 2015, they are still too high to meet commitments that nations made upon entering the 2015 Paris Agreement (high confidence).  Indeed, present and projected emission rates would bring the atmospheric level of GHGs to levels so high that they have not occurred for at least the last 50 million years (medium confidence).

New carbon dioxide released “today” is long-lived, persisting in the atmosphere for decades to thousands of years. Therefore it’s important to note that the relationship between total atmospheric CO₂ concentration and the increase in global temperature is a linear one. 

The ES states “Choices made today will determine the magnitude of climate change risks beyond the next few decades.  Stabilizing global mean temperature below 3.6°F (2°C) or lower relative to preindustrial levels requires significant reductions in …CO₂ emissions…before 2040 and likely requires net emissions to become zero….”  If humanity continues emitting GHGs at rates higher than called for here we would reach the 3.6°F limit only two decades from now, with further temperature increases later.

Finally, changes that are unanticipated or difficult or impossible to manage, may arise during the next century.  Examples are complex (or simultaneously occurring) phenomena, and self-reinforcing changes (positive feedbacks).  Such occurrences would accelerate the world’s changes to points beyond the accepted CO₂ temperature limits.

Analysis

Issuance of this NCA is mandated by an act of Congress.  It is important that this Final Draft, the CSSR, continue on its bureaucratic trajectory and be issued on schedule in 2018.  Yet some of the scientists contributing to the Draft hold positions in departments or agencies whose heads have expressed disdain or opposition to the phenomenon of global warming, the Paris Climate Agreement, have acted to reverse federal policies that limit extraction and use of fossil fuels, or have deleted pages concerning global warming from their agency’s websites.  They all work in an administration whose head has declared global warming to be a hoax. These situations potentially place the contributing scientists in conflicting positions.  Their work is commendable and should be supported.  The NCA should be issued without being altered, nor should it be suppressed.

[Update August 17, 2017: The science journal Nature has published a news article that discusses the CSSR and the political considerations facing the U. S. administration as it weighs issuing the Fourth NCA. Climate scientists are concerned about the fate of the Report. Nature notes that the Heartland Institute, a conservative think tank that promotes skepticism about global warming, is consulting with the Environmental Protection Agency on this issue.]
 

This NCA is only the latest in a long series of reports detailing the reality of warming and specifying the harms that global warming and climate change cause to our planet.  In particular, it attributes the cause to human activity, including the burning of fossil fuels. 

We must all undertake to reduce emissions of GHGs in our personal lives, and support policies promoting reductions at the state, national and international levels.
 

Background

The U. S. Global Change Research Act of 1990 mandates preparation of assessments of global change every four years to “assist the nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change”.  It assesses the current state of scientific understanding of global change on the natural and human environments. Its tasks, however, do not include formulation of policies to address global warming.

Climate scientists and related specialists drawn from thirteen U. S. government departments and agencies (see Note 2 at the end of this post), as well as a large number of scientists in nongovernmental research facilities, prepared the CSSR and the NCA. They critically assessed peer-reviewed research and similar public sources, including primary datasets and recognized climate modeling frameworks.

 Notes

1.    USGCRP, 2017: Climate Science Special Report: A Sustained Assessment Activity of the U.S. Global Change Research Program [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 669 pp.

 

2.    The federal scientists involved in preparing the NCA and the CSSR are drawn from the:  

Department of Agriculture,

Department of Commerce (National Oceanic and Atmospheric Administration),

Department of Defense,

Department of Energy,

Department of Health and Human Services,

Department of the Interior,

Department of State,

Department of Transportation,

Environmental Protection Agency,

National Aeronautics and Space Administration,

National Science Foundation,

Smithsonian Institution, and

U.S. Agency for International Development.      

© 2017 Henry Auer

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 18^th 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.

Conclusion

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.

Details

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 20^th 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 19^th 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: https://en.wikipedia.org/wiki/Charles_David_Keeling#/media/File:Mauna_Loa_CO2_monthly_mean_concentration.svg

  

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