Global Warming In A Box
The Debate Rages
Have heard different views on this which I will coarsely summarize. To do so I will use the rough analogy of a green house. In fact a glass box.
Imagine if you will a glass box in your back yard on a cloudless day. Inside the box we place a candle and two devices to measure temperature and CO2 levels. We won’t light the candle yet. Outside the box we will place an environmental scientist and a physicist.
So we leave it for a while and notice that the temperature in the box rises initially and then comes into thermal equilibrium. The temperature inside the box is certainly higher than outside, but it is no longer changing.
If we light the candle we notice the temperature inside the box rises and the CO2 level rises.
The environmental scientist tells us that the byproducts of the candle are modifying the inside of the box. In a rough sense the CO2 is adding to the properties of the glass so that less energy is transmitted from the box due to the CO2 layer.
The physicist says “that may be so” but the increase in temperature is the same as the thermal energy released by the candle and corresponds to the CO2 produced by the candle so I must conclude that it is the candle heating up the box.
The environmental scientist says nonsense. The heat from the candle is insignificant compared to the total heat coming into the box from the sun. The additional heat from the candle is simply being mixed with the sunlight and being radiated away. Of course less of it is being radiated away because of the extra insulation, but it’s contribution will be proportional to its ratio to the total input energy.
The physicist asks the environmental scientist; “The fact that the temperature rise matches the heat given off by the candle?”
“Coincidence” is the response.
So who is correct?
The physicist is, but why?
The intuitive answer is to wait for night time and notice that most of the candles heat is still inside the box. Apart from the removal of the external source, nothing has changed. If you ran the whole thing at night, the temperature in the box would rise, hit equilibrium and then remain constant.
The environmental guy is correct that there is a lot more energy coming into the box from the sun than the candle produces. But to correctly compare the solar energy entering the box with the energy released by the candle we would have to “replace” the candle with the equivalent solar source required to raise the temperature by the amount of heat released by the candle. The big question mark is that the energy from the sun is not coming in as kinetic energy, whereas the candle is pumping heat directly into the box.
In one dimension we can imagine light coming into one face of the box and out the other side leaving a residual amount of energy behind that balances the cooling of the gas in the box so that we maintain a reasonable 14 degrees C average temperature. Now the energy in and the energy out over time have to be equal, but it doesn’t mean it can’t change form. So if you imagine a photon, hitting an atom, releasing an electron and another photon. The input and output spectra would be different. The output spectra would have a spike at lower frequency than the input spectra, with the difference being the residual kinetic energy of the electron that is still bouncing around the box.
In this case the “heat” in the box is in effect the residual kinetic energy left behind after incoming photons interact with the atmosphere. The atmosphere also loses energy over time so for a single photon entering the box, it would take a while for all the residual kinetic energy to be burned off. In effect we would have to integrate the output spectra over time to match the power of a single input pulse.
Anyway to work out how the candle was effecting the system compared to sunlight, we would need to replace the candle with an equivalent solar source to create the same residual kinetic energy.
Alternatively we could replace the sunlight with an equivalent number of candles to create the same kinetic energy as the sun created.
But I think it is improper to compare apples to oranges.
Making bold claims about the huge wattage of solar energy entering the box compared to the source energy is dangerous. Particularly as not all that solar flux is converted to kinetic energy of the atmosphere. Even more complicated is that there are lots of layers in the atmosphere where all the real action takes place. When you do see figures about the solar flux interacting the atmosphere you really need to ask and how much of that was the troposphere (the warm wet and cuddly bit we live in) and how much energy was lost in the various more exotic layers above us compared to how much of the residual flux was lost in our warm wet layer.
The fact that the atmosphere we live within is not glowing to a large extent suggests to me that not a lot of photons are being released by energetic electrons so I would suspect that absorption is not high and most of the heat is from the ground and oceans rather than direct absorption.
The more I look at this the, less trivial it becomes.
If we wanted our box to match reality we would need to wrap the box in various layers of material, each of different material properties and place our candle in the middle. It could be reasonably modeled using a time domain analysis such as that used in electromagnetism.
And I still have not had an answer of what the process is that has flattened temperature variation through the Holocene. Something has dampened temperature variation and I don’t know what it is. Arrrgh!
December 07 2009 09:22 pm | Climate
