The Greenhouse Analogy

The Greenhouse Analogy

When I discovered that thermal conduction was underestimated as an impact of CO2 I was not particularly surprised. Having worked in Heating and Air Conditioning for many years, I am used to looking for system inefficiencies and ways to take advantage of natural heat sources and sinks. What was surprising is how much the atmosphere does behave as a Greenhouse.

The radiant effect is of course the main concept that rules the greenhouse roost as far as climate science is concerned. Builders of real greenhouses know that ground source energy, reduced convective loss and insulation are just as important as the radiant effect in trapping heat.

Dr. Roy Spencer, is one of many that has built and experiment to measure the impact of Down Welling Long wave Radiation. In his experiment, Ambient temperature and dewpoint remained more stable than the radiant temperature he was measuring. The relatively steady conduction of surface temperature to the surface air, stabilized the local ambient conditions. This would indicate that surface/air conductivity is not negligable with respect to DWLR since in effect, DWLR is dependent on the surface emission of thernal flux.

Convection in the atmosphere is somewhat limited by water vapor and clouds. That sounds counter intuitive, since clouds and rain are the most obvious convective events. Warm moist air rises from the surface as it is heated, most often by solar energy at the surface. What is not so obvious is that sunlight absorbed by the water vapor and clouds in the atmosphere tends to stabilize the air above the latent shift layer of the atmosphere. http://en.wikipedia.org/wiki/Planetary_boundary_layer This layer is known as the Atmospheric Boundary Layer (ABL) or Planetary Boundary Layer (PBL).
While the atmosphere below the ABL is subject to considerable turbulence from local thermals, the drag of the surface reduces wind speeds. The area below the ABL is a quasi-laminar flow region in many cases. In other words, there is less convection than there would be without the latent shift of energy from the surface to the APL.

The latent shift also regulates the radiant impact of solar energy by shifting the ratio of solar absorbed at the surface versus in the atmosphere. Water in the form of liquid and ice above the APL has a more open radiant window to cool than it would below where the outgoing radiation would interact with water and water vapor above.

As in a greenhouse, the surface to air boundary is responsible for most of the energy that can be retained when solar absorption is not optimum. Since water vapor has a limited half-life in the atmosphere, more water vapor implies more precipitation which enhances the thermal transfer from the surface both via latent and conductive processes.

Apparently, Carbon Dioxide also improves the surface/air thermal conduction both as CO2 in the air and as Carbonic Acid in the oceans, ice and in moisture laden air. The small conductive impact is completely over looked, yet has the potential to greatly impact surface cooling with improved thermal transfer.

Because the conductive impact is at the surface and the true radiant impacts well above the surface, conductive change has 30 to 40 percent more impact per unit change than radiant impacts which have to compete with water vapor in order to transfer energy to the surface.

The Greenhouse Analogy is much better than I would have ever thought.

A Greenhouse Effect?

http://redneckphysics.blogspot.com/2011/11/greenhouse-analogy.html

I will probably delete this post in favor of the one linked above. For now, I will leave things as they are.


A Greenhouse Effect

Quite a few people have and intend to experiment with how the Greenhouse effect works, in simulated greenhouses. Woods did his experiment. A Vaughan Pratt did his experiment. Myth Busters did their experiment. I think even Al Gore commissioned an experiment. What do all these experiments have in common? None of them were actual Green Houses.

While a greenhouse gets its warmth from the sun it is the retention of that warmth that makes a greenhouse useful. The warmth it retains is from the surface or ground. In addition to proper greenhouses, there are also cold frames and a variety of other methods used to retain surface heat. Plants need sunlight to survive, so a greenhouse can’t use highly efficient insulation to retain heat, it has to use less efficient transparent materials. In very cold climates, these transparent materials need to include double glazing and if one can accord, triple glazing, to prevent excess heat loss to the environment.
Greenhouse are also equipped with ventilation systems to prevent over heating in the day, which damages the plants watering and misting systems to maintain humidity and in some cases, CO2 injection to improve plant growth rate.
So if someone wants to study a greenhouse, why not use a greenhouse?

Simple experiment number 1. Build two greenhouses of identical construction. In the first, till the soil and plant directly in the ground. In the second, insulate the ground and provide a moisture barrier. Then plant in pots or use hydroponics. Since the solar input is roughly the same, why is the second so much less efficient? There ya go, the surface is the source of the heat we are trying to retain.

Since some labs have limited space, how would you simulate a greenhouse accurately on a small scale?
Tip one, not by shine heat lamps on poor unsuspecting items, but by simulating a surface source with a upper sink and measuring how conduction, convection and radiant heat flow are all impacted. The percentage of each is the greenhouse effect, just as it is in our atmosphere.
Since our atmosphere has layers, why not include layers in your greenhouse effect experiment.

Comments are misbehaving again, either spammers or Foxfire issues:

Lisaray,

True, the question is what are the limits? A true greenhouse seem to be just a more applicable model for determining those limits. A nursery would allow more ventilation if it became too warm. The atmosphere seems to have the same option. The tropics for example.

If there is not enough sunlight, the greenhouse doesn't work, the Antarctic for example.

Things have to be tuned for best performance, the Northern hemisphere for example.

So other than opening a window, what else can be done to control temperature in a Northern hemisphere greenhouse? More plants? More water? Less water? A nurseryman on a budget may grow more tomatoes and fewer impatients. In other words, land use may have a much greater impact than estimated.

Mulling Over Latent

With another high quality graphic I am taking another look at the DWLR situation with respect to the latent shift.

The black numbers are from the NASA budget and the red numbers are what should be leaving the surface if there were no DWLR. The red 390 minus the black 174 is the estimate of the DWLR intensity, 216Wm-2. If you add the red thermal flux, 54 to the red radiant flux 161 you get the same 216Wm-2 allowing for rounding. The red latent, 177Wm-2 is the value buggering up the simple budget issue. At first blush, I would say that latent is not contributing to the DWLR felt at the surface. That makes some sense as the water below the latent heat release would tend to block its return to the surface and enhance the convection of the clouds. In effect the energy released by condensation increase convection generating more condensation once things get rolling, thunder heads. Perhaps a bit simplistic, but not too far from the realm of possibility. Clouds are the caveat after all.

These are average values of course, so in the tropics, the numbers would be more than twice the values, but the ratios may be close to the same. At the poles, the numbers would be totally different.

Since the poles are much colder, the would benefit from the latent energy added to the atmosphere by the tropics.

The North pole, since it summer temperature can be above freezing, receive energy from the atmosphere and radiant interaction with the water vapor would help retain more of the heat gained both by solar and atnmospheric transit. In other words, the north pole shows what the expected greehouse effect should show. Looking at the satellite temperature trends from UAH, the north pole mid-troposphere is warming by 0.25C per decade and the northern pole stratosphere is cooling by -23C per decade. Just as advertised.

The Southern pole, since its temperature never gets above freezing, is not benefiting from the water vapor portion of the greenhouse effect and is lossing more heat than it gains from the atmospheric transit of tropical energy. By the UAH data, south pole mid-troposphere is cooling by -0.15 C per decade and the stratopshere is cooling by -0.55C per decade. That is a huge difference, data quality aside.

The ozone hole has been blamed for this difference, but the northern pole has a hole of its own forming. Chemicals, fluorcarbons mainly are blamed for ozone depleation and I have no doubt contribute to some degree. Something though is missing from the standard explanations. Possibly, low energy photons are not heathy medicine for ozone molecules. Possibly, some form of carbon dioxide at low temperatures in a stream of low energy photons is the issue. That is beyond my pay grade at the moment, but something is just not right.

In the southern polar atmosphere, the latent portion is near zero. Sometime earlier I had guestimate roughly 5 to 10Wm-2, but that is difficult to confirm.

If I ratio the radiant and thermal flux values down for the low average temperature of -50 C or 238K, using the S-B relationship I would get 182Wm-2 from the surface on average. That is 34 Wm-2 less than the average value of DWLR I had caluculated, so on average the southern pole should benefit by that amount from the atmospheric effect. That should maintain the average surface temperature. If the surface maintained, the mid-troposphere temperature should not be decreasing.

My theory of improved conduction/convection due to CO2 may be causing the reduced greenhouse impact, doesn't fully explain the degree of reduction of mid-troposphere temperature AND the stratospheric cooling. Not without some help from either ozone being impacted by some combination of increase low energy photons and/or chemical interaction with CO2 or carbonic acid in frozen ice crystals.

The frozen carbonic acid is something new I have been trying to look into without my luck so far. At the surface, it does appear to enhance surface conductivity which would be part of the Antarctic conductive feedback I believe is happening. Determining the degree of enhancement is not all that simple.

I am going to leave this open for more mulling. I need to get an idea of the at least one of the factors before I can even guess at the other or others, natural variability is always a potential factor.