I Misunderstood the Greenhouse Effect. Here's How It Works.

How does the greenhouse effect work? Greenhouse gases, such as carbon dioxide and methane, prevent infrared radiation from escaping to outer space. This warms the surface of earth. More greenhouse gas means more warming. Simple enough! Alas, if you look at the numbers, it turns out that most infrared radiation is absorbed almost immediately above the ground already at pre-industrial greenhouse gas levels. So how does it really work? In this video, I try to sort it out.

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00:00 Intro
00:40 The Greenhouse Effect: Middle School Version
03:17 The Greenhouse Effect: High School Version
9:48 The Greenhouse Effect: PhD Version
13:45 Stratospheric Cooling
15:39 Summary
17:29 Protect Your Privacy With NordVPN

#science #climate

[Biga]

When I first went to college I wanted to educate myself on climate change. I took a course on environmental science hoping to get a better understanding. Unfortunately I didn't realize the course was a sociology course, so we didn't actually learn anything about climate change or the environment. Instead it was about people's perception of the topics. An environmental economics course I took a couple years later was actually very good and useful, but still never really got a good understanding of the principles behind climate change. It is amazing how for such an important topic most of the conversation about it seems to not actually revolve around what it is.

[renatanovato]

I usually understand things easily when Sabine explains. Not this time, though. I will have to watch it once more.

[paulbloom]

I'm a PhD Physicist who teaches general education climate science (when I don't have to teach the physics curriculum). This is an outstanding and clear presentation of how the greenhouse effect actually works (which I didn't fully appreciate for the first too many years I taught the class). The way you propose to modify the energy flow diagrams is spot on. Definitely some of your best work. Brava, and thank you for doing this. Heck, gonna show it in my class...

[Patrick-kqfy]

Having been involved in radio technology for most my life, I understood the "wiggling" a different way. I think of a molecule as a kind of antenna tuned to a specific frequency and associated harmonics.
So... Basically a molecule like H2O or CO2 is like an antenna that is tuned to certain frequencies that, when excited, resonates (vibrates, wiggles)... or you can think of it like a tuning fork.
Just as a tuning fork emits a specific sound regardless of what causes it to vibrate, a CO2 molecule resonates at specific frequencies of the EM spectrum.

So... that's my understanding.

[sentinel]

Sadly it's even more complicated than that. The greenhouse effect causes less than 50% of the warming effect predicted from increasing CO2, with the remainder being caused by climate feedback effects: There are a huge number of climate feedbacks, but a simple example of a "positive feedback" is that white snow reflects sunlight, but once it's melted by a warming environment, then more sunlight will be absorbed by the ground, and so the temperature will increase further (so causing even more snow to be melted, etc). An example of a "negative feedback" is that as temperature increases, there is more evaporation from the ocean, which causes more clouds to form in the lower atmosphere, reflecting more sunlight into outer space, so reducing temperature. Unfortunately these feedback effects are often not understood very well (as they are often hard to measure), hence the large variation in predictions made by different climate models (and so why the IPCC prefers to average over a large number of models). In the distant past there was probably a period known as the Snowball Earth where most(*) of the surface was covered in ice (reflecting sunlight into space) from a massive ice age, and without volcanism producing CO2 the Earth might still have been like that today. (* I have simplified to avoid writing too much.)

[alexanderkohler]

I really liked this episode, however, I think the explanation at 6:45 - 7:15 of why the roundness of earth and the inverse square law for gravitiy were relevant and why the pressure decreased with the height above the earth is totally incorrect. The pressure doesn't decrease due to the decreasing gravitational pull. In fact, the latter almost stays constant in that area. What changes, is the remaining amount of air above you that has a weight and thus exerts pressure on you. The same principle applies in water. You observe a higher water pressure at the ground of a swimming pool than at its surface. Again, that is not due to a higher gravitational pull, but due to a higher amount of water above you.

[aDifferentJT]

Air pressure doesn’t decrease with altitude because the gravitational force decreases, in a uniform gravitational field the air pressure would also decrease, and the gravitational force in LEO is pretty similar to that on the surface. It decreases because the mass of air above that point is lower.

[KruczLorand]

the pressure of the atmosphere doesn't decrease with height due to the inverse square law of gravity being weaker. The difference in gravitational acceleration is negligable from the surface to 100km high which is where space begins. The pressure decreases because is given by the weight of the column of air above and as you move towards space that columns is less and less massive.

[delveling]

I didn't realize that this subject is so complicated, i almost took a break and went back to watching quantum mechanic videos to clear my mind a little, thank you for the enlightening explanation.

[AlanTheBeast]

@07:00 the falling gravity with altitude has negligible effect on the pressure gradient. The pressure gradient is mostly due the weight of the air column - densest at the bottom due to all the weight piled on it from above. About 50% of the atmosphere (by mass) is in the first 5000 metres or so. Earth's gravity potential at 100, 000 metres is 0.97g. Has pretty much no effect on the change of air pressure (density) with altitude.

As to GH effect: I had the same issue up until this video:

[glennbabic]

Gravity is BARELY less at the cruising altitude of an airliner, not even as high as the ISS, the air pressure is less because there is less atmosphere pushing down from above you.

[guenthermichaels]

Stratospheric Cooling. That is the net proof that I didn't know before.

[prydin]

Sabine! A good science communicator is one who’s not afraid to say “this is more complicated than you think”. Thank you again for the great content you put out!

[Elloziano]

Very necessary video, my favorite channel never fails to deliver!

[gabrielapetrie]

This is going to prove so useful for a lot of people for a long(-ish?) time!

[blinkingmanchannel]

Again, fantastic explainer!

I watched it again after trying to integrate these ideas into my reading of other sources... The revisit is way more valuable to my little brain. I'm always surprised how good it is to go back over my earlier steps, despite the fact that I "know" about this effect. Anyway, very well done!

[Sean-llcm]

Everything's always so much more complicated than it seems 😭

[himbeertoni]

Wow, that just blew my mind!

I've a phD in physics and still had exactly the same misunderstanding. I think, it's not just the arrows in the diagram, but most sources of information trying to make the complex topic understandable. Kind of similar to the various atomic models out there in schools and the web, which are scientifically all oversimplified, thus wrong when it comes to explaining chemistry (Schrödinger and Dirac are nodding).

[alterego-bggs]

I have a PhD in AMO physics and you just blew my mind. Thank you for this video! I feel when it comes to global warming there is a coverage gap between super-simplified explanations and full-blown climate models. I really appreciate your video explaining it layer by layer.

[trevorcrowley]

"It Is Difficult to Get a Man to Understand Something When His Salary Depends Upon His Not Understanding It"