Sunday, January 23, 2011

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.


  1. I'll be doing this series over January and February. With digressions such as the comments about light as I see fit.

    After the first few entries about antecedent scientific discoveries concerning global warming, I expect my blog to tighten up to the topic, however.

  2. Isaac Newton also studied light extensively. He believed that light was composed of particles (we now know that light has a dual nature of particles (photons) which also have the properties of a wave moving through a medium.

    But there was the Iceland spar [calcite] difficulty. Iceland spar is a mineral which exhibits double refraction, which could not be explained if light was composed of particles. (the reason for this is very technical and convoluted and not one I am going into. If you doubt me, research it yourself ;)

    Newton in his work Opticks struggled with this and had some flashes of insight that light could have a dual nature after all, but basically went with light being particles.

    The lesser minds after Newton had a better solution to the problem of double refraction by Iceland spar.

    They ignored it.

    And still it double refracted:

  3. This comment has been removed by the author.

  4. People didn't know much about light before William Herschel, but they did know a couple things.

    First, some ballpark figures of the speed of light had been determined.

    For those of you who read Longitudem you may remember that one idea before William Harrison's chronometer for determining longitude was to observe the position of Jupiter at the time of eclipses of it's satellites. If you could determine the position of Jupiter in the sky, at the time of a satellite eclipse, it would be possible to determine what longitude you were on!

    Therefore, it was most embarrassing that the time of eclipses varied by several minutes from the predicted times.

    Ole Christensen Rømer began to notice a pattern. The eclipses happened sooner than expected when Jupiter and the Earth were on the same side of the solar system, and later than expected when Jupiter was on the far side of the solar system. He studied this for a few years, making sure the pattern held, and then published his idea in 1676.

    Knowledge of the size of the solar system was just a bit vague in 1676, and most estimates were considerably smaller than we know it now to be.

    Rømer took his best guess, and came up with 138,000 miles a second. This discovery made a small splash, but was not a grand discovery like the Galilean satellites.

    Geovanni Cassini had also made notes about the discrepancy in eclipse times

    This second inequality appears to be due to light taking some time to reach us from the satellite; light seems to take about ten to eleven minutes [to cross] a distance equal to the half-diameter of the terrestrial orbit

    from notes 4 months earlier. Oddly, Cassini then seems to have abandoned the idea.

    Rømer was Cassini's assistant, and he made his presentation to the French Academy of Sciences first.
    Unfortunately, the reporter of the presentation then stamped it as 'incomprehensible', which meant that Rømer's discovery did not get the publicity it deserved.

    Before Rømer and Cassini, most people, if they thought of the speed of light at all, thought it was infinite.

  5. James Bradley was hot on the trail of determining the distance to the stars. All through the 1710s and 1720s he kept trying to measure parallax, using the motion of the earth in its orbit to see if he could determine if a bright nearby star would shift its position against a much dimmer star.

    This didn't work. Stars are not the same brightness, and many bright stars he thought were near were further away than dim stars he was trying to compare them to. He never got his answer. The stars are so far away that it took more than 100 years for instruments accurate enough to measure stellar parallax to be developed.

    While trying to determine the parallax of Gamma Draconis, he noticed that the star was moving relative to its position but not in the circular way parallax would have been, but more a side to side motion.

    Bradley had discovered the aberration of light. You can think of it like this. Imagine standing in rain when the wind is calm. Then get on a bike at 15 mph and see the rain slant. By measuring the angle of the slant, and knowing how fast you are going, you can determine the velocity of the rain as it falls.

    Bradley got a figure of 188,500 miles per second, a figure 1.2% above the real value. Quite good for 1720s technology!

    Plugging this figure into the equations for Romer's eclipse times gave a much more accurate figure for the orbits of Jupiter, and thence the other planets.

    But it was not the distance to the stars, which was what Bradley really wanted. He ended his life disappointed.

  6. William Herschel was a brilliant scientist, but uncommonly poor at naming his discoveries. To flatter the king, and hopefully get support, he named the planet Georgium Sidus, Latin for George's star.

    This name was never very popular in Great Britain, and scorned immediately outside it. Some called it Herschel, and for a while Neptune was popular in Great Britain as well (including variations such as Neptune George III or Great Britain Neptune

    Johann Elert Bode (of Bode's Law fame) suggested that it be named Uranus, since Saturn was the father of Jupiter, Uranus was the father of Saturn. That choice gradually took over. Uranium was also named for this when discovered in 1789 by a supporter of Bode.

    The HM Nautical Almanac Office was the last holdout for Georgium Sidus, finally dropping that name in 1850.

    As for the new heat radiation, William Herschel called his discovery 'calorific rays'. That is not as horrible as Georgium Sidus, but still pretty bad. They of course became known as 'infrared radiation'

  7. Thought you would like this too (I found a link to the whole article): [ ]

    Infrared radiation and planetary temperature

  8. Remember my comment about Icelandic spar (calcite)? It turns out that the double refractive property of calcite can be used to create an invisibility cloak!