Monday, January 31, 2011

The study of Global Warming Part 5: Joseph Adhemar and James Croll

Joseph Adhemar (1797-1862) was the first person to develop an astronomical theory for the ice ages and interglacials. Aggasiz's publication of Etudes sur les glaciers stimulated a great interest in the causes of climate change, now that it was shown to have occurred.

Joseph Adhemar was the first to propose an astronomical cause for the ice ages. Adhemar's theory was wrong, but it did point later scientists in a useful direction.

Adhemar knew about the precession of the equinoxes (which made such a splash a few weeks ago when it was revealed that astrological signs are no longer correct). The Earth's orbit is elliptical, and as a result the earth moves more slowly when it is further away from the sun. Now, the Earth is closest to the sun during the first week of January, and furthest during the first week of July. As a result, the polar night is 178.8 days at the North Pole and 186.5 days at the South Pole.

As a result, Adhemar believed that ice ages alternated by hemisphere, with the Southern Hemisphere currently in an ice age, and the Northern Hemisphere in an interglacial. He published his ideas in Revolutions of the Sea (1842). He believed the length of the polar night was the determining factor. This was wrong, he didn't take into account that when the polar night is longer, the sun is closer to the Earth during the summer, and actually delivers more heat. And of course it turned out that ice ages are global, not alternating by northern and southern hemisphere.

And yet, Adhemar did stimulate new investigations into astronomical influences on climate change.

James Croll (1821-1890) was the first scientist to develop a good astronomical mechanism for causing the ice ages. His ideas were valid--although his calculations contained many errors and his timing was way off. However, these errors were not his fault.

Croll was not from a wealthy background and was not formally educated. Many bright people in the 19th century never were able to obtain a high school, let alone university education. He was apprenticed as a wheelwright when he was 16, but being very bright was not happy with his lot in life. He read when he could and self-taught himself physics and astronomy, and became a tea merchant, then a manager of a hotel, and then an insurance agent. In 1859 he became caretaker to the museum of the Andersonian college (presently the University of Strathclyde), so as to have access to the college library, where he could get information on his pet project---solving the mystery of the ice ages!

Croll worked for over a decade, working out how variations in the eccentricity of the orbit of the Earth, the procession of the equinoxes, changes in the tilt of the Earth's axis and variations in sunlight received at the poles that these variations caused could cause the ice ages.

An objection to astronomical influences on climate had been that the changes in sunlight in the polar regions were so small and subtle. Croll realized that these variations could be more than 10% and therefore significant. Croll also had a key insight. The albedo variations caused by changes in snow cover could amplify the changes in climate--a positive feedback! This new idea when combined with orbital and axial variations enabled them together to account for all the temperature change needed to plunge the Earth into an ice age, and bring it out!

Unfortunately, information was not available to calculate accurately how the gravitational attraction of other planets changed the eccentricity of the Earth's orbit. The distances of the planets from each other and the Earth were known to a relative degree, but the absolute distances were still not known to within a few percent. The masses of the planets were also not known very well. Jupiter and Venus influence the orbit of the Earth more than other planets (although all the planets from Saturn inwards have measurable effects). In particular, while the mass of Jupiter could be determined with some accuracy due to the orbital motions of the Galilean satellites---Venus has no satellites, and therefore there was no way to determine its mass. The same thing with Mercury.

Another factor was that relativity had not been discovered. In relativity, mass and energy are equivalent, and the energy of gravitation has its own mass---which changes the orbit of Mercury enough so that its orbit had motions not accounted for in Newtonian mechanics. In fact, there was a widespread belief that there had to be a planet closer to the sun than Mercury to account for its orbital behavior, and astronomers were on the hunt for the planet Vulcan, believed to be between one-third and half the distance from the sun that Mercury is.

The result of all this is that while Croll calculated accruately with the best available information he had, his solutions to the equations for determining variations in the orbit of the Earth were wrong. Way wrong.

Croll thought the last ice age had ended 80,000 years ago. Before carbon dating emerged after World War II, it was impossible to date material accurately. But there were two clues that indicated 80,000 years was far too long.

First, Niagara Falls. By the late 19th century, Niagara Falls had been observed for more than 200 years, and its rate of erosion back along the Niagara River was well known. Timing back from when the falls first started on the Niagara Escarpment yielded estimates of around 10,000-12,000 years for the age of the falls when the ice sheet receded. Of course the river flow and the condition of the rocks could be different in the past, and the extreme outlier estimates were as young as 6,000 years and a few estimates were beyond 20,000 years---30,000 at the very extreme. But there was no way, geologically, that Niagara Falls was 80,000 years old.

There were also annual deposits of silt in lakes that left thin layers---and these could be investigated. None of these lake deposits went back more than 20,000 years. And during the oldest lake deposits, investigations of pollen in lake bed sediments revealed that the vegetation was from colder adapted plants more than 10,000 years ago, and no lakes in areas were ice sheets occurred seemed to be older than 19,000 years.

Croll's ideas about the influence of orbital variations, axial tilt and procession of the equinoxes were much discussed, and regarded as interesting. But they just didn't fit the direct evidence of erosional rates of Niagara Falls and other falls, and the lake deposits. And as more and more lake deposits were studied, the evidence against such an ancient end to the last ice age became untenable.

It was not until Milutan Milankovitch did his work well into the 20th century, with accurate figures for the mass and orbit of the planets that a workable astronomical theory of the ice ages was developed.

Croll was just ahead of his time--he had the right ideas, but didn't have the right information to make his theory stand up.

Despite this, Croll was well respected among scientists. He had regular correspondences with Charles Lyell from 1864 on, and Charles Darwin. Croll published his work Climate and Time, in Their Geological Relations in 1875, and reviews from other scientists were very positive. (it took over a decade for him to make all the astronomical calculations!) In 1876, despite never having completed a middle school education, Croll was elected as a fellow of the Royal Society, and granted an honorary degree from St. Andrew's university. It may have helped that Croll was friendly, funny, and well liked. Croll retired in 1880 due to ill health but at least he got to the pinnacle of scientific respect. Quite an achievement for a wheelwright with a 6th grade education!

If you interviewed a geologist or physicist from 100 years ago they would probably tell you that Croll was a brilliant man who had an interesting idea about the ice ages, researched it well, and was just plain wrong.

No he wasn't wrong--he just had inaccurate information to work with. Croll was ahead of his time.

Wednesday, January 26, 2011

The Study of Global Warming Part 4: John Tyndall

John Tyndall (1820-1893) was a distinguished physicist with many interests.  Although his first papers were about magnetism, explaining magnetic polarity, his papers ranged across almost every branch of physics. He also invented many scientific instruments, such as the nephelometer and turbidimeter. He was the first to create germ free air. He discovered thermophorisis. He discovered that ozone is a form of oxygen. He developed the first method of sterilization that was effective against bacterial spores that were not killed by boiling water. Among his more practical inventions were the firemen's respirator and an effective foghorn.

Of more relevance to the atmosphere and climate, he discovered the Tyndall Effect, a form of radiation scattering by colloidial suspensions.

His interest in climate began when he visited Switzerland in the summer of 1856 and became fascinated with glaciers. For the rest of his life he spent almost every summer in Switzerland, and became an accomplished mountaineer, becoming the first person to climb the Weisshorn in 1861.

Tyndall was enthralled by glaciers---how they flowed, how they changed. How they eroded landscapes and modulated river flow. Glaciers were much talked about after Louis Agassiz had published his Ice Ages hypothesis--the first indication that climate can change!

In the 1850s, it was believed that the atmosphere was transparent to infrared radiation. After all, how else would the Earth get warm? Fourier's insight that light could penetrate the atmosphere and reach the earth, which then absorbed some of it and re-radiated it as infrared radiation had been largely forgotten or discarded. (Even though Fourier didn't think the atmospheric greenhouse effect was real, he was the first to seriously discuss the idea)

Tyndall thought this was nonsense. If the atmosphere was transparent to infrared radiation, then how could Earth stay warm? Fourier had thought that outer space was not that cold. But observations of asteroids that looked like they were composed of ice contradicted that idea. If they could survive as ice bodies that close to the sun, he calculated that interstellar space had to be close to absolute zero.

So how to test this his hypothesis that the atmosphere could trap infrared radiation? In 1859 he built this apparatus:

He tested oxygen and nitrogen. Both were transparent to infrared radiation. So he then tried coal gas (mostly methane, with some carbon dioxide, carbon monoxide and water vapor). Eureka! Coal gas blocked infrared radiation as much as an inch of wood!

He also tested carbon dioxide and found that it also absorbed part of the infrared rays.

And then tested water vapor which was also avidly absorbed infrared radiation. And measured the temperature of these gases--the absorbed infrared radiation indeed warmed the gas!

This was a very important discovery. Gases could trap radiation and warm the earth!

But it was also limited. Water vapor is the greatest contributor to our present temperature deviation from equilibrium--but what of methane and carbon dioxide?

The problem was that both gases are rare. Methane is less than 2 parts per million in the atmosphere, and CO2 was less than 1/3000th of the atmosphere. In 1859 there was no way to accurately measure the concentration of such gases in the atmosphere. In fact, methane levels were too low to be detected. It was obvious that carbon dioxide must be part of the atmosphere--after all every animal exhales it. Tyndall was able to determine that carbon dioxide was present between 100 ppm and 600 ppm by pumping controlled amounts of air through a weak alkaline solution and see how much was converted to its salt, reacting with the carbon dioxide. But that margin of error told him nothing. He had no way to accurately measure carbon dioxide changing its concentration from night to day, season to season, year to year.

In 1862 Tyndall wrote this: "As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial [infrared] rays, produces a local heightening of the temperature of the Earth's surface." from Further Researches on the Absorption and Radiation of Heat by Gaseous Matter

By 1863, frustrated by his inability to measure what effect methane and carbon dioxide had on trapping infrared radiation, and recognizing that water vapor was the most important greenhouse gas (which it is) he wrote that water vapor "is a blanket more necessary to the vegetable life of England than clothing is to man. Remove for a single summer-night the aqueous vapor from the air....and the sun would rise upon an island held fast in the iron grip of frost." from "On Radiation through the Earth's Atmosphere", Philosophical Magazine pp. 204-205.

The Study of Global Warming Part 3: Louis Agassiz and the discovery that climate can change!

Louis Agassiz (1807-1873)was a zoologist, paleontologist, geologist who discovered that the Earth had been subject to global ice ages in the past. Yes, he got the timing and sequences wrong, but he was the first to recognize that glacial advance and retreat could be a global phenomenon and the first to realize that the whole Earth's climate could change.

The idea that glaciers had expanded and contracted in the past was not an entirely new idea. Few things are. Jean de Charpentier (1786-1855) observed the breakout of an glacially dammed lake in the Val de Bagnes and subsequent flood destroying Martigny, killing many on June 16, 1818. Amazingly, he was an eyewitness to the breakup and flood, which showed him how suddenly glaciers and the natural environment could change. Fascinated by this, and seeing the landforms left underneath the glacier when it disintigrated, he recognized erratic boulders and moraines all over Switzerland! He did not try to explain how glaciers had expanded and retreated---he freely admitted he had no ideal But Charpentier was convinced that all of Switzerland had been covered by glaciers in the distant past.

The ice age theory was expanded a little more by Ignaz Venetz, the chief engineer who had been attempting to drain the ice lake before it catastrophically failed. He read reports of similar glacial landforms across much of northern Europe and Britain, and concluded by 1821 that there had been an ice age over much of Europe in the distant past. He traveled and researched, and in 1833 he published Mémoire sur les Variations de la température dans les Alpes de la Suisse which concluded that there had been times in the past when glaciers had covered all of Switzerland and northern Europe, and that these had happened at the same time.

Another contributor was Karl Friedrich Schimper. In fact he may have been the originator of the theory of global ice ages. It is known that his private papers are filled with the idea of a global ice age cooling, based on new reports from New England, the Midwest, and Canada. They worked together, along with Charpentier for 3 years in the Swiss Alps in the 1830s. Schimper never published anything, although he complained bitterly that Agassiz had taken his ideas and never gave him any credit. It is as if Wallace and Darwin had corresponded about evolution, and Wallace published and gave Darwin no credit. How much Agassiz got his ideas from Schimper is unknown--there is often symbiosis in creating a new idea when bright minds exchange information. But it is certain that at the least, Schimper contributed a lot of ideas and data for a global ice age, and Agassiz never acknowledged his contribution. Not one word. Agassiz did acknowledge some contributions by Charpentier (whose private papers show much less insight into the topic)

The moral of this is 'publish or lose'

Agassiz made his big splash in 1840 with his monumental two-volume work Etudes sur les glaciers (Study of glaciers) that described Switzerland as having been another Greenland in the past, that glaciers had covered much of North America, and that the climate across the entire Earth had been much colder.

Agassiz was just a bit vague about what drove the ice age and how Earth got out of it. He didn't know about greenhouse gases, he didn't know about orbital and axial shifts. He didn't attach himself to a specific idea, although he thought the sun was probably responsible. He wondered if the fall of a large comet or planet into the sun had caused it to brighten and melt the earth out of the ice age.

Agassiz then relocated to the United States, where he became a scientific star. He had some serious foibles late in life. In 1865 he traveled to Brazil, where he was convinced he saw glacial landforms (there have never been large glaciers in Brazil during any of the recent ice ages)

Agassiz also fought against Darwin's theory of evolution for the rest of his life after he published On the Origin of Species Upon encountering African-Americans, Agassiz became convinced that different races had different origins and that the white race from temperate climates was superior to all other races, and was one of the architects of the scientific racism school of thought in the 19th century.

The key thing about the discovery of past ice ages is that for the first time, scientists realized that climate could change, and change dramatically. Which raised an obvious question. How did the global climate change? For the first time, scientists began to investigate how climate change can happen.

Sunday, January 23, 2011

The beginning of the discovery

Charles Fourier was a scientist and mathematician, who was fascinated by the flow of heat and determining how heat flow occurs.

His main paper was Théorie analytique de la chaleur (The Analytic Theory of Heat) in 1822. He claimed that any function or variable, continuous or discontinuous, could be expanded in a series of sines of multiples of the variable. This is not quite correct, but some discontinuous functions are the sum of a series, and that was a breakthrough.
Fourier's idea was that the flow of heat between two molecules is proportional to the extremely small difference in temperature between adjacent molecules.

His interest in heat lead him to this inquiry---why doesn't the sun just heat the Earth up until the Earth's temperature match the surface of the sun?

The answer was that heat radiates away from the Earth, preventing the Earth from heating up catastrophically. However there was a serious problem.

There had been some attempts to determine what the equilibrium temperature of the surface of the Earth should be, notably by Georges-Louis Leclerc Comte de Buffon and his attemps, and others, indicated that the Earth should be colder than it really is.

When Charles Fourier used his new equations, he came up with temperatures between 0F and 5F. Most of the world would be frozen! (This actually understates the degree of cold considerably. If the world was really that coldm the ice covered oceans and snows to the equator would increase the albedo of the Earth sufficiently to cool the Earth down to ~-50C on average.

Something else was clearly going on, but he was not sure what. The heat equations he was sure were right (and they largely were). What was going on?

One idea (the right one) was that the atmosphere was partly opaque to Herschel's newly discovered infrared rays. This would require most of the energy of the sun to arrive as visible light or other ways and warm the Earth. At the same time some of the IR radiation emitted by the warm earth would be trapped in the atmosphere and warm the earth enough for it to reach its current equilibrium temperature.

Fourier didn't know if this was a general property or the result of minor gases in the atmosphere.

But Fourier was led astray by another idea.

Olber's Paradox (why isn't the sky bright as the sun, and why isn't the whole universe at the same temperature as the suns) made a big splash in 1823. Heinrich Wilhelm Olbers considered if the universe was infinitely big, every line of sight would end up on the surface of a star. So why isn't the entire sky as bright as the surface of the sun?

Nebulas wouldn't help. They would be heated from all directions till they were as hot as the surface of suns as well.

Olber's paradox contains some hidden assumptions. The universe is infinitely big. The universe is not expanding. The speed of light is infinite. Or if the speed of light is finite, the universe is infinitely old.

The speed of light was known to be finite by 1823. Which meant that the universe could not be both infinitely old and infinitely big. Olber's paradox is the first scientific inquiry that showed there had to be limits on either the size or the age of the universe. Which implied that either the size of the universe or its age, or both, were bound by limits--and a limited figure could be determined.

Heinrich Wilhelm Olbers was not the first to come up with this paradox. There were even some before him who made superior mathematical treatments of it.

However, for some reason or another, his publication of this idea made a big splash.

Olbers also discovered the asteroid Pallas, the second asteroid found (1802) and Vesta, the brightest asteroid and the fourth discovered.

Olber's paradox mislead Fourier. Fourier believed the warmth of the earth could be explained if space were not close to absolute zero, but if the interstellar voids were warm. Instead of temperatures dropping asymptotically towards absolute zero (or 2.7K) as one gets further from the sun, what if the temperature dropped asymptotically to 100K? or 150K? Then the warmth of the earth would fit. Interstellar radiation could be responsible for the warm Earth! (Yes I know there was no Kelvin scale yet in the 1820s, but you get the idea)

Charles Fourier's main papers on the subject of the temperature of the earth were Remarques Générales Sur Les Températures Du Globe Terrestre Et Des Espaces Planétaires (General Remarks on the temperatures of the terrestrial globe and planetary spaces) [1824] and Mémoire Sur Les Températures Du Globe Terrestre Et Des Espaces Planétaires (Disseratation on the Temperatures of the Terrestrial Globe and interplanetary spaces) [1827]

While Charles Fourier discussed the idea of the atmosphere warming the earth by selectively trapping infrared radiation, he was strongly influenced by Olber's paradox and believed the warm baseline temperature of interstellar space to be responsible. A pity.

Charles Fourier referred to an experiment by Horace-Bénédict de Saussure in his papers. He was also interested in heat, and may have developed the first solar oven. Saussure performed an experiment with a box of black cork, with three pane of glass 1 1/2" apart, and measured the temperature between each pane. The temperature increased the more interior one checked in the box. This box with panes of glass was like a greenhouse in some ways, and lead to references of the "greenhouse effect"

So for all you who think the "greenhouse effect" is some insidious French plot---let the conspiracy yarns start!

Fourier also was ignorant of some important properties of the atmosphere. He thought that eddies and convection would immediately carry heat away from the surface of the Earth--that these eddies went all the way to the top of the atmosphere. Today we know that the stratosphere is very stable, with temperatures rising with altitude, the opposite of the troposphere we live in. This also lead him to look on the atmospheric 'greenhouse effect' with disfavor.

The Study of Global Warming

1800 was not so long ago, 7 generations or so. Yet it was a different world, one most of us would only dimly recognize and most of us would have great difficulty living in. Something less than a billion people lived on the globe. Almost all of those people lived short lives of great misery and toil, not much changed from centuries past. Lives were not much different from 1700 or 1600. Technological advances were speeding up, but were not affecting most people's lives.

England had far more green fields than satanic mills, and the 5 million in the USA lived mostly east of the Appalachian mountains, and much land even in the east was still wilderness.

True, there were signs of change. The Enlightenment had been gathering force for the previous two centuries, powered by science. Which in turn was powered by empiricism---observations, experiments, hypotheses and deductions. Science was (and is) a powerful way of discovering new knowledge. Even so, the Enlightenment in 1800 was more seeing the light at the end of the tunnel versus breaking out into the sun.

In 1800 people were ignorant about how the world worked. We had no idea how old the earth was (although some clever people realized that the world had to be over 6,000 years old) We had no knowledge of evolution, of plate tectonics. We didn't know about ice ages, or even if the climate had been different in the past. Most people, even scientists, didn't realize the climate could change, much less how it could do so.

And yet humanity may a factor in the climate even then. For thousands of years, wet rice paddy cultivation had released methane into the atmosphere, which may have prevented the earth from beginning to slide into a new ice age. I think that is likely, although it is not proven yet.
China had greatly increased the use of coal during the Song dynasty, but even so the impact of rice paddy agriculture and Chinese coal consumption was much smaller than what we do today.

In 1800 freedom and capitalism scarcely existed. Aside from Roger Bacon (who in the 1200s predicted television, telescopes, microscopes, spectacles, and airplanes) and Leonardo da Vinci, hardly anyone predicted much technological advancement. Far-seeing people perceived that the Americas would be much more developed but no one predicted the level of population and economic growth that the spread of capitalism and freedom over the next two centuries would bring around the world.

Our world today would simply be inconceivable to all those from 1800.

And yet this seems as good a time as any to begin, because a relevant scientific discovery was made in 1800.

William Herschel was the most famous astronomer of his time. In 1781 he had discovered the planet Uranus, doubling the diameter of the solar system. The fame from this enabled him to establish his own astronomical observatory, with the unsung help of his devoted sister, Caroline (a noted astronomer herself, who lived 2 months short of her 98th birthday and never had much of a life of her own)

The discovery that sunlight was a mixture of colors had been made by Isaac Newton, but for a century not much more was known about radiation---light was all that there was, as far as anyone knew.

Until February 11, 1800.

On that day, William Herschel was testing colored filters to observe the sun, looking for sunspots. He noticed that the light coming through the red filter was warmer than the other colors. William Hershel then took a large prism, and put thermometers into the different colors to see which thermometers grew warmest. An extra one was laying outside the spectrum of visible light, but on the red side.

To his surprise that thermometer got warmer than any of the others!

In addition to the planet Uranus, William Herschel had discovered infrared radiation! William Herschel investigated this new radiation and discovered that most of the heat energy came from beyond the red.

In a stroke, the known electromagnetic spectrum doubled, just like the solar system.

And the notion that this new form of radiation could have a role to play in our climate would soon be explored.

But I'll talk about that in the next entry.