Posts Tagged ‘temperature’

Below Zero

January 6, 2014

As I write this, the temperature here in Madison Indiana is -4° Fahrenheit with wind chill down to around -27°. It is cold outside. It is even cooler than I would like inside, even with the heat on. To distract myself from this winter horror, I will try to think warm thoughts and write a little about temperature. What does it mean to say the temperature is 30 degrees or 100 degrees? What exactly are we measuring? Shouldn’t zero degrees be the coldest possible temperature?

People have known that some days are hotter or colder than other days since time immemorial. Before the invention of the thermometer, it was not possible to measure just how much hotter or colder. People could not quantify or measure temperature, except by personal perception, which is subjective.  A person might feel that it is getting warmer, but he could not be sure if the environment was actually getting warmer, or that he was simply feeling warmer, perhaps because he was exerting himself. Also, there was no way of determining just how warmer today was than yesterday. Notice that I am talking about temperature rather than heat. The two concepts are related but are not the same thing. In any substance the atoms and molecules that make up that substance are not standing still but are moving about. In a liquid or a gas, the atoms can move about freely, while in a solid, they are held in place but still vibrate back and forth. In a sense then, the temperature of an object is the average kinetic energy of the atoms in that object. Heat is defined by physicists as the transfer of thermal energy from a warmer body to a colder body. Heat is not measured by degrees but by joules or calories. ( The calories on food labels are actually kilocalories.)

Thermally_Agitated_Molecule

The basic principle on which the thermometer works was actually discovered in ancient times. Hero of Alexandria knew that air expanded or contracted based the temperature and invented a thermometer of sorts by placing a closed tube with its open end in a container of water. The water would move up or down in the tube according to the temperature. Galileo constructed a similar device, as did several other renaissance scientists. None of these devices had a scale, however, so it was still not possible to quantify temperature with them. They were also sensitive to air pressure.

The first thermometer with a scale was invented by either Francesco Sagredo or Santorio Santorio around 1611-1613.

Deutsch: Santorio Santorio. Français : Portrai...

In 1714, Daniel Gabriel Fahrenheit invented a thermometer which used mercury in a glass tube. Once it became possible to

English: Gabriel Daniel Fahrenheit

English: Gabriel Daniel Fahrenheit (Photo credit: Wikipedia)

manufacture thermometers on a standard design, it was also possible to develop a standard scale. Fahrenheit developed such a scale in 1724. He used three points to calibrate his scale. The temperature of a mixture of water, ice, and ammonium chloride was designated as zero. The temperature of water just as ice began to form was set at 32 and human body temperature at exactly 96. Later, it was discovered that there are about 180 of Fahrenheit’s degrees between the melting and boiling points of water so the scale was calibrated to make exactly 180 degrees so that the boiling point of water on the Fahrenheit scale is 212°. The Fahrenheit Scale is the one most used in the United States and is still widely used in Britain and Canada.

In 1742 Anders Celsius developed a scale in which there were one hundred degrees between the melting and boiling points of water. Curiously, he designated the boiling point of water as 0 and the melting point as 100 so the temperature measurement got lower as it got hotter. The Celsius scale was reversed and adopted as part of the metric system. This scale, sometimes called centigrade, is used worldwide, especially by scientists. Conversion between the two scales is easy enough. Because there are 180 degrees Fahrenheit between the melting and boiling points of water, but only 100 degrees Celsius, each degree Fahrenheit is 9/5 of a degree Celsius. Since Fahrenheit has the melting point of water at 32°, to convert from Fahrenheit to Celsius you subtract 32 and then multiply by 9/5. To convert from Celsius to Fahrenheit, multiply by 5/9 and then add 32.

Anders Celsius

Anders Celsius

The coldest possible temperature, at which the atomic motion stops, is called absolute zero. This is -459.67° Fahrenheit or -273.15°. It is not actually possible to reach absolute zero, but scientists have come close. The lowest temperature ever recorded in a laboratory is around .oooooooo1 degrees Celsius. In 1848, the British physicist William Thompson, later to be Lord Kelvin, proposed a temperature scale using degrees Celsius which began at absolute zero. The Kelvin scale is slightly different from other scales in that it does not rely on the physical properties of any materials, being based on absolute zero. Temperatures in the Kelvin scale are measured in “Kelvins” rather than degrees so that you may say that the melting point of water is 273 K. The Kelvin scale is also extensively used by scientists, especially those who work with very low temperatures.

Lord Kelvin

Lord Kelvin

It’s not working. All of this writing about absolute zero is just making me feel colder.

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Winter Has Come

December 21, 2012

We’ve had our first snowfall of the season here in Madison, Indiana and temperatures have dropped below freezing so I think it would be safe to say that winter has finally arrived after an unusually mild autumn. I was hoping that it would continue to be mild all winter but that is too much to hope for. This reminds me of a recent poll which showed that larger number of Americans were believing in the reality of climate change and that temperatures are rising worldwide. These results are not too surprising considering that the poll was taken during a warm autumn. I suspect that if January turns out to be unusually cold and snowy many of these same people will be convinced that a new ice age is upon us.

Thinking about my own recollections of past seasons, I seem to recall, as a child we never got any snow before the new year. But, then the worst snow we have ever had was in 1977 or 1978 when school was closed for a whole month. The teachers started to send us our homework so that we wouldn’t get too far behind. I do not think we have had so much snow since.

I could be wrong, but it seems to me that temperatures have been more even in the past few years. Perhaps I have a difference sort of tolerances for heat and cold. I don’t think we have had many days in which the temperature has risen above 100 degrees Fahrenheit in the past few summers. I remember whole weeks in which the temperature stayed in the upper nineties and hundreds. Somehow summer used to be more miserable than it is now. I also remember more winter days in which the temperature dropped below zero degrees Fahrenheit when I was growing up. I do not believe there were more than one or two such days in the last few years, nor do snowfalls seem to be quite as bad. As for extreme weather events,the worst that happened in my lifetime, in the local area, was the super cluster of tornadoes that devastated much of the Midwest back in 1974. We have had tornadoes since then, including several bad ones but none that did quite so much damage. We also had a bad wind storm back in 2005 which was the last remnant of Hurricane Katrina.

None of this means anything, of course. These are just the personal recollections of one man with a fallible memory. I hope this turns out to be a mild winter with little or no snow.

The World Was Warmer

July 12, 2012
Dendrochronology

Dendrochronology (Photo credit: fdecomite)

I have been criticizing the Global Warming advocates of making exaggerated claims beyond what the data might warrant, but now I suppose I ought to take on the other side. I am referring to the article I read in the Daily Mail titled Tree-ring study Proves that Climate was Warmer. In fact, from what I read, the study does no such thing. You cannot, in fact, prove what the temperatures were a thousand years ago unless someone invents a time machine and takes thermometers into the past to measure them.

How did the Romans grow grapes in northern England? Perhaps because it was warmer than we thought.

A study suggests the Britain of 2,000 years ago experienced a lengthy period of hotter summers than today.

German researchers used data from tree rings – a key indicator of past climate – to claim the world has been on a ‘long-term cooling trend’ for two millennia until the global warming of the twentieth century.

This cooling was punctuated by a couple of warm spells.

These are the Medieval Warm Period, which is well known, but also a period during the toga-wearing Roman times when temperatures were apparently 1 deg C warmer than now.

They say the very warm period during the years 21 to 50AD has been underestimated by climate scientists.

Lead author Professor Dr Jan Esper of Johannes Gutenberg University in Mainz said: ‘We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low.

‘This figure we calculated may not seem particularly significant, however it is not negligible when compared to global warming, which up to now has been less than 1 deg C.’

In general the scientists found a slow cooling of 0.6C over 2,000 years, which they attributed to changes in the Earth’s orbit which took it further away from the Sun.

The study is published in Nature Climate Change.

It is based on measurements stretching back to 138BC.

The finding may force scientists to rethink current theories of the impact of global warming

Professor Esper’s group at the Institute of Geography at JGU used tree-ring density measurements from sub-fossil pine trees originating from Finnish Lapland to produce a reconstruction reaching back to 138 BC.

In so doing, the researchers have been able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling.

I suppose that I should take into consideration that this is an article intended for a popular audience on a newspaper’s website and I am sure the authors of this study were more nuanced in the papers they wrote. Still, a more accurate headline might read “Study based on assumptions on the relation of tree-rings to temperature and climate infers that Europe, and possible the entire world was warmer in the past”. But, maybe they would have trouble fitting all that in.

The study seems to be a very extensive one and considering that there are other lines of evidence that show a warmer Earth at these times, the Romans growing grapes in Britain and the Vikings being able to colonize Greenland and Vinland, I really don’t have any doubt that their conclusions are accurate. I would like to emphasize, however, how tentative any such studies actually are.

By the way, if the Earth really is in a long term trend toward cooler weather, should we be worried about a new ice age? As I have said before, I would be a lot more worried about global cooling than I would about global warming. After all, the glaciers weren’t that far north of where I am sitting during the last ice age.

 


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