Guest post by Bill DiPuccio, Science Teacher
Let’s face it, high school science videos can be boring and ineffective. I like my science with a twist of comic exaggeration. So I decided to produce a video with enough humor to keep the students awake, and enough depth to challenge them intellectually.
This 30 minute video on the Greenhouse Effect is the prototype for a possible new series: “Bill Scientific” (I gave it a personal imprint to infuse some warmth and presence). Unlike introductory videos which attempt to cover a broad field of knowledge in a short time, the goal of this prospective series is to drill down into specific, but pivotal, topics in the physical and earth sciences.
Rather than just spooning out information, each program would be designed around experiments (the simpler the better) that can be used to illuminate and verify crucial scientific principles. Students will see science in action and gain a better grasp of the empirical basis for scientific theories.
Of course, future programs will depend on the response from students, educators, and scientists, as well as securing funding. The “Greenhouse Effect” was shot and produced on amateur equipment and software. Despite these limitations, I believe the final product faithfully conveys the intent of series.
P.S. If you like the video, pass it on!
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
RACookPE1978 says:
May 1, 2012 at 7:37 am
Modern passive solar collectors used evacuated tubes. As a result, conduction and convection have almost no effect on either the daytime high or the night time low temperatures.
And yet, this is a typical winter temperature for the tropopause over Antarctica. Surface temperatures there are typically below -60°C, the record is -89°C.
For exposed surfaces, wind is the only convection that can keep things warm. Lacking wind, isolated surfaces should drop below freezing within an hour of sunset. The fact that they don’t is called the Greenhouse Effect.
I know that the Trenberth radiation diagram confuses a lot of people. What you need to do is to create 2 diagrams – one for day and a separate for night. Assume the day is 4 hours long and multiply the Trenberth solar, convection, and evaporation values by 6. For night, set those values to zero. Then things will make more sense.
ozzieostrich says:
April 28, 2012 at 11:51 pm
I think that if the surface loses 20°C over a long night it would have a higher average temperature than if it lost 50°C over the same time period. Am I missing something?
If the Earth was covered with a perfect long wave insulator but was still able to absorb solar radiation, what would the surface temperature be?
ozzieostrich says:
April 29, 2012 at 5:09 am
That is not correct. Many materials, including Greenhouse Gases, treat long wave and short wave IR radiation differently. As a result, your “Dewar flask” example does not apply here.
No answer to my 2 qustions?
Solar collectors are optimised to use the peak solar spectrum (visible light) but to be a “good” collector, once it has absorbed the visible and converted it to heat then the glass covering should reflect the LWIR back to the collector plate.
LWIR from sunlight and back radiation will be similarly reflected from the glass , but in this case the LWIR will be prevented from entering the collector box.
It would be difficult making a solar collector that utilised LWIR since the glass covering would be required to act differently to LWIR from outside (passes it) to the LWIR from inside (reflects it).
A LWIR collector would lose as much energy that it gained.
Sergei says “It would be difficult making a solar collector that utilised LWIR since the glass covering would be required to act differently to LWIR from outside (passes it) to the LWIR from inside (reflects it). ”
Actually it is even worse than that. The laws of thermodynamics ensure that you cannot focus light so as to warm something above the temperature of the object creating the light (or you would be sending heat from a warm object to an even warmer object). So sunlight (coming from the 5780 K surface of the sun) cannot — even with lenses or mirrors — warm anything above 5780 K. Similarly, if you have radiation from 280 K ground or air or clouds, there is no way to focus that light to warm anything above 280 K.
Think of it this way. The sun is tiny, but can warm things pretty well. With a mirror, I can in effect create a second sun and focus that light onto the collector, doubling the energy heading to the collector. But if are considering thermal IR, it is already coming pretty much every direction. If you put up a mirror to reflect in some IR, the mirror itself will block the same amount IR that would have been coming from that direction.
Anyone who says “if there really were 300 W/m^2 of IR, we should be able to focus it even more effectively than 160 W/m^2 of sunlight” is displaying a fundamental ignorance of thermodynamics.
Robert Clemenzi May 1, 11:51
Sorry. I didn’t notice your comment until now.
To answer your questions in order –
1. Yes. I was talking about an absolute increase in temperature, not a change in rate of cooling. In your ‘think” you lose 20C, or 50C. No warming whatsoever. The amount and/or the rate of cooling is irrelevant. As you have pointed out, there is no warming, as I said.
2. Anything you like. Physically impossible, unless you can adduce experimental evidence to the contrary. If 100 x 0 = 10 x 0, does 100=10? If, if , if . . . . If wishes were fishes, starvation would not exist . . .
3. Energy is energy. If you can point out a filter, or insulator, or some heretofore undiscovered material, that retards the total transmission of energy in an arbitrary direction better than the opposite direction, I will change my thinking. The problem you face is that you can’t. Galling, no doubt, but true.
Until you provide evidence to the contrary (in line with established scientific principals), I see no reason to change my mind.
Over to you.
Live well and prosper.
Mike Flynn.
Tim Folkerts,
Sorry, but I was responding to Robert Clemenzi, and I noticed your comment at 3:00 pm.
If you don’t mind, may I point out that the Sun is not “tiny”, but quite a lot larger than the Earth.
I think I know what you mean, but may I suggest that you make your meaning more precise. There are many people of my level of education (which is to say not much at all) who may take you literally. Maybe I’m wrong. Please let me know if I am.
Live well and prosper.
Mike Flynn.