Astronomy - Ch. 9.1: Earth's Atmosphere (25 of 46) What is the Greenhouse Effect?

In this video I will explain what is the greenhouse effect by relating our troposphere to an actual greenhouse, and a person sleeping in a sleeping bag.

Next video in this series can be seen at:

[joneslu]

The greatest lecture I have to follow! Finally, I have got how heat is retained near the surface of Earth, and re-radiated back in space. And definitely the part of the lecture in this video explaining the density of the molecules as the altitude increases and its effect on the direction and speed of heat rediation, has been the key to answering lots of my questions. Again, lectures are the best way for education. Thank you!

[petercamusojr]

You are extremely competent, that is to say a true scientist that knows what you are talking about. You are filling in some wholes in my education.

[brendanward]

Excellent. It's very different from what happens in an actual greenhouse, where the lack of convection is the key factor. Unfortunately, the meteorologists who coined the term "greenhouse effect" were not horticulturists.

[gerryoreilly]

Excellent presentation. So easy to follow for those, like myself, who are challenged in the physics department.

[foxhound]

Another informative video. Question: when the H2O molecule absorbs the radiation from the ground, if this excites one of the vibratory modes of the molecule, and that molecule collides with another molecule, then the energy may go into increasing the kinetic energy of the molecule (increasing temperature). In this case, would the re-radiated energy (from the ground) take even longer to make it back to space?

[petercamusojr]

I find the greenhouse analogy to be a poor explanation that causes most of my associates to dismiss climate change as bad science. Your blanket analogy is the correct simplification for the general public. It is technically correct and relates well to most people's experience.

[grindupBaker]

At 1:25 to 1:33 is incorrect because there is a 2nd way (much smaller quantity than the main way you described) and this 2nd way I assert is EXACTLY the same as the so-called "greenhouse effect" in Earth's troposphere (not the atmosphere, the troposphere).

[SamuliLouko]

@Michel van Biezen
Great stuff! Some questions on the topic though...

If a CO2 molecule absorbs certain wavelength IR photon, does it re-emit an IR photon of exact same energy, or does it change? Or is there certain likelihood(distribution) of wavelengths that it can radiate out?

Does increasing atmospheric CO2(or any other GHG) increase also the height from where the IR can freely radiate back to space(IR chromosphere?) and hence how much does the adiabatic lapse rate play (significant) role on this?
On many occasions, also on your videos, it is referred that some IR band gets "saturated" when amount of certain GHG increases to a certain point, thus can't absorb more IR energy. But doesn't this just mean that the re-emitted IR needs to get higher in the atmosphere before it gets emitted to space eventually?
I've wathced most of your great videos on this series, but those questions above I've not seen addressed on any of the videos int this series. Or if they have been mentioned, could you point which of the episodes such could be found? Or maybe on some of your upcoming videos?
Cheers- S

[grindupBaker]

Thanks, you've reached the definitive statement with this video. Your definitive statement that the tropospheric temperature lapse rate has no effect whatsoever on the so-called "greenhouse effect" is extremely interesting because it directly contradicts the picture that I formed based on just pondering basics without any study in which infrared active gases and liquids manufacture some amount of LWR, not only the solids as you've continuously asserted. This, of course, changes everything about the so-called "greenhouse effect". Your definitive statement that a parcel of CO2 molecules 9, 999 km diameter in interstellar space at 300K being heated by a nuclear fission reactor would emit zero radiation because none is going into the parcel of CO2 molecules for them to re-emit in all directions changes everything. I'll continue my search though just on the off chance that your science there is junk science, not physical reality. There's a simple experiment being done in videos, with highly-varying skill, in which a glass jar with ~100% CO2 warms faster and more than a glass jar with air, both heated by the same infrared lamp. Why does that one jar warm faster and more than the other one ? Your prior video showed 25% latent heat and 5% sensible heat conduction/convection surface to air, how on Earth does that energy ever get out of the air ?

[MairaBay]

Omg, the little sleeping bag guy is so cute!

[EinarBordewich]

According to your explanation the greenhouse effect is also directly dependent on density and thereby of atmospheric weight. Because total atmospheric weight in combination with gravity is what makes the density increase at ground lever. Am I assuming correct?

[natures_guardians]

@michelvanbiezen, I am looking for information about how H2O and CO2 function as GHGs in the stratosphere. Do you have anything on that? The only reference I can find is one paper by Solomon.

[Netsroht]

What i dont understand. In your lower atmosphere in the picture, there are only GH-Gases.

Whats with the non GH-Gases? Is there no interaction?
In you Lecture 9.1(16 of 61) you say, there are many collisions (1 bil/sec). But i think the most of that collisions, due to the very low concentration of GH-Gases, are between GH-Gases and non GH-Gases and non GH-Gases and non GH-Gases?

[markmurphy]

I don't like the blanket anology. A thicker blanket makes a buffer for energy to move through in both directions. Insulation helps a house stay warm in the winter, but also stay cool in the summer. GHG would then seem to promote a more stable temperature the greater their concentration. I think of a beavers dam. The height of the dam sets the maximum depth of the water. Water level being a function of water flowing in vs flowing out, but when in flow slows or stops its also a buffer to outflow. The depth of the water being the temperature. Comparing radiation durring the day vs night for the in/out flow. The concentration of GHG's being the dam and its properties of height and porosity.

[scottjones]

Unfortunately the explanation does not talk about the likelihood that the energy captured by the greenhouse gases is almost totally distributed to O2 and N2 through collisions before it can be re-emitted as radiation. From the earlier presentations there are around 8 billion collisions with other molecules in a second. `
The average time for a CO2 molecule to re-emit radiation is around 1 second.
The likelihood that the energy lost through radiation rather than kinetic collisions is less than

[scottjones]

Within Nanoseconds, the atmospheric gases are in local temperature equilibrium. As a result 99% of the heat in the atmosphere is contained in O2 and N2 molecules and only 0.04% of the heat is contained by CO2 molecules.

[azlktune]

If more H2O and CO2 in atmosphere cause higher thermal insulation, why there is a vacuum in thermos bottle? Isn't better to fill it with GHGes?

[petergrimshaw]

Your Greenhouse Explanations are, overall, excellent.
But the final lynchpin, what causes the greenhouse effect is not accurate, unfortunately, I think?
The 'valve' which traps heat is the emission height I think?

Think of how fast the molecules are travelling at the different heights?
The higher molecules are travelling slower because they are colder, ie, they are less energetic.
Cooler gases emit less energy, less active molecules emit photons/phonons less frequently.

Increasing the density of CO2 raises the average height at which photons can escape directly to outer space.
And, on average, within the Troposphere, photons are emitted less frequently due to the higher molecules being less energetic.
So, on average, less photons escape to outer space from the Troposhere when the CO2 cloud is denser.

It is like a heat escape valve being tightened a bit.
Less efficient cooling = more trapped heat - which means temperatures have to readjust to increase overall heat output to re-estabish the heat in = heat out equilibrium.

I could be wrong Michel, this is a very complicated scenario, and it appears so few people 'get' the emission height idea.
But I think it is the accurate one.

The best science sites to clarify this I have found are Clive Best and the Science of Doom.
Clive has worked at CERN and is furiously clever.
Both sites think there is a Greenhouse effect, but describe it differently to you.

[debt]

What is interesting is, that if all radiation is absorbed within first 100-200m then UAH measurements at Lower Troposphere from satelites are not accurate as they are measurements within range of kilometers?

[arminebner]

will the upper end of the troposphere cool more as a consequence of the green house gasses also? In the example of the blanket. I should feel it much colder touching the blanket than touching the body with the blanket without being there.