The News That Matters about the Nuclear Industry

The physics of climate change

Elevator Pitches – Chapter 02 – Radiative Gases Radiative Gases

A Musical Basis for Scattering Heat March 2017 by Rob Honeycutt – This is another excerpt from my book 28 Climate Change Elevator Pitches. I’ll be publishing one chapter here on SkS each month.The scientific basis for understanding climate goes back to the 1820’s when brilliant French mathematician Joseph Fourier first proposed the idea that our planet’s atmosphere had heat-trapping properties. Fourier was trying to calculate what should be the temperature of a planet at our distance from the sun. He derived a figure about 33°C (59°F) colder than the actual average temperature of the Earth. For his figures to be correct, he thought gases in our atmosphere must have “radiative properties” with the capacity to absorb and re-emit heat energy. When visible sunlight passes through our atmosphere it warms the surface of the Earth. The heat that is emitted upward we refer to as infrared radiation, or IR. Infrared radiation is just another wavelength of energy which is invisible to the human eye, but we can feel that energy as heat. It’s this heat energy that is scattered by radiative gases in the atmosphere.

In the 1850’s a British scientist, John Tyndall, devised an apparatus enabling him to measure the heat absorbing properties of various gases. Earth’s atmosphere is composed primarily of nitrogen (78%) and oxygen (21%). The remaining 1 percent of gases are known as “trace gases.” Tyndall discovered that the radiative properties of nitrogen and oxygen are insignificant and transparent to infrared radiation (heat). But, he further discovered that some trace gases do efficiently block heat.

But, how does this work? Why would one gas be transparent to heat and another gas block it?

The most common radiative gases in our atmosphere are water (H2O), carbon dioxide(CO2), and to a lesser extent, methane (CH4), so let’s look at how these molecules are constructed. The first two have a single core atom with two other atoms attached to it. With H2O, there is a central oxygen atom with two hydrogen atoms attached. With CO2, there is a central carbon atom and two oxygen atoms attached. You can picture these being something like soap bubbles joined together, but imagine if you can, that these soap bubbles have an electromagnetic field incorporated into them. This electromagnetic field gently locks the molecule into a specific configuration. That magnetic field also allows the atoms to wobble around a bit as the molecule is floating about in the atmosphere. Methane is somewhat similarly constructed as CO2, but with a central carbon atom surrounded on four sides by hydrogen atoms making it a far more potent radiative gas than the others.

Infrared radiation is a wavelength of light. In a way, it’s analogous to sound waves traveling through the air. If you tap an A note tuning fork on your knee and then hold it against the soundboard of a guitar the A-string of the guitar will vibrate sympathetically. Infrared radiation also has a frequency range, so when visible sunlight (higher frequency energy) comes in and hits the surface of the planet, that energy warms the surface. The surface then emits lower frequency energy as heat (IR) back up through the atmosphere.

The capacity of these molecules to vibrate (the “wobbling”) is “tuned” like the guitar string and when infrared radiation in the right frequency interacts with these gases, the molecule vibrates sympathetically. What they’re doing is absorbing and re-emitting that IR heatenergy. The difference with the dominant molecules, like oxygen (O2) and nitrogen (N2), is they can’t vibrate in this same manner nor at the same frequency ranges, thus they are invisible to IR.

That is the fundamental physics of climate change: the vibrational modes of greenhouse gases acting to absorb and scatter heat energy in the atmosphere. This was a cutting-edge discovery of the mid-19th century but now an indisputable fact of science. Scientists have empirically measured, modeled, and applied these facts in numerous ways for well over a century.


March 27, 2017 - Posted by | 2 WORLD, climate change, Reference

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