But HOW Does Carbon Dioxide Trap Heat?

Check out NOVA's video on cloud seeding and the PBS Earth Month Playlist:

We all know about the greenhouse effect, but how many of us actually understand it? Turns out, CO2 is not a “blanket,” and saying it “absorbs” heat is barely half the story. In today’s episode we figure out what’s so special about this one molecule that allows 0.04% of it to change our entire planet.

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Credits:
Executive Producer:
Matthew Radcliff

Producers:
Elaine Seward
Andrew Sobey
Darren Weaver

Writer/Host:
George Zaidan

Scientific Consultants:
W. Paige Hall, Ph.D.
Leila Duman, Ph.D.
Brianne Raccor, Ph.D.

Executive in Charge for PBS: Maribel Lopez
Director of Programming for PBS: Gabrielle Ewing
Assistant Director of Programming for PBS: John Campbell

Reactions is a production of the American Chemical Society.
© 2023 American Chemical Society. All rights reserved.

Sources:

[djmit]

Let me just add one more comment praising the quality of your videos. This video made an important, and frankly complex, topic very accessible and intelligible. And you did it with great charisma and editing to pull us all in.

[thawineethongprajiad]

Dude what a great video. I could see the amount of work and effort put into every single detail and the cut was seamless. I needed this video.

[krystleyoung]

Thank you! I've been trying to wrap my head around this concept to teach others and this video just made it a whole lot easier for me to understand. I love the metaphor too, will definitely be using it when explaining to others.

[hoon_sol]

I don't think it's inaccurate to say that it acts as a blanket even when you account for all of this, because it's essentially trapping thermal energy that would otherwise radiate outwards; but it's certainly a great and thorough explanation regardless.

[gglez]

Wow, for years I've tried to understand the greenhouse effect and global warming. I heard about it in primary school all the way to college, yet, I never understood as I understand it now after watching your video. So, thank you. And you know, that last example with the nuclear bomb was just jaw dropping, and perfectly reflects how crucial action on carbon emissions is.

[WForrestFrantz]

Well done!

"uses the energy from photons to make nearby molecules move faster". . Energy states (the O-C-O relationship) in CO2 are quantum. They only change in quantum amounts. That is why CO2 has only a few narrow bandwidth of photons it can absorb. In fact, each bandwith would be a thin line (not a tiny normal distribution of frequencies around that thin line) if it wasn't for the Doppler effect (molecules are moving at about the speed of sound). A crash between two molecules isn't quantum (think about the infinite number of ways that N2 can approach CO2 as the Oxygen molecules vibrate towards and away from the incoming N2). So, no energy is transferred because a higher CO2 state can't collaspe to its stable state. It's all or nothing. The change in energy (potential to photonic) has to be exact (quantum). That is why a crash results in nothing or it results in the only quantum action available--creation of nearly the same photonic energy that was absorbed. So at about a billion times a second (how often crashes occur), the energy from a photon is converted to potential energy inside a CO2 molecule and then back to photonic energy.

So what causes the air to warm if not from Kinetic transfer? IR ends up taking a tortured path to space (it takes a few weeks). Pinballing between H2O and CO2 molecules until, a few weeks later, the energy finally escapes to space. But in the meantime, incoming irradiation doesn't stop, waiting for the IR to reach space. So IR accumulates for a while causing temperatures rise until a new balance is achieved (higher temperatures support higher levels of IR).

Notes: (a) Air molecules can crash all they want but the net Kinetic Energy is conserved (doesn't change). (b) There are also momentum transfers between a photon and CO2 molecule but those are net zero (adding as often as subtracting). (c) A quantum collapse of a higher unstable state (resulting in a photon and stable state) doesn't require a crash. Decay can be spontaneous.

[hunter__]

This is amazing content. Just shows how Physical Chemistry applies to our day-to-day life, like meteorology.

[balahmay]

Finally I can feel like I really understand this. Thanks for the excellent explanation.

[critiqueofthegothgf]

this was the best educational video ive ever seen. you managed to entertain me but also provide an extremely simple to understand explanation as someone who struggles with math. thank you

[Jedermeister]

I am going to show my class this video. Fantastic.

[singingway]

This is exactly what I've been trying to understand. Thanks!

[grindupBaker]

This is a good Part 1 because it includes 9:37 to 9:56 instead of the usual annoying irrelevance "absorbs and then re-emits 50% back down to the surface". This is Part 1 which is only ABSORPTION in the air. There's a required Part 2 that is absent from this video. Part 2 is MANUFACTURE in the air. Hint: Presenter never states the phrase "tropospheric temperature lapse rate", but it's ESSENTIAL because, guess what, cooler parcels of matter radiate less than warmer parcels of matter (the stratospheric "greenhouse effect" is backwards).

[The_Daliban]

Keeping my attention with constant match cuts definitely worked. Thanks for the phenomenal video

[anon_q]

This video is so well produced. Absolutely amazing video

[johnmckeon]

For explanation 10/10. For good natured humour 10/10. Thank you. 🙂

[jaymayhoi]

damn! studied BSc physics and have been watching sci edu content for many years but have only understood this now. Such a clear fun video - thanks!

[DANGJOS]

Very nice! I just want to point out one thing. Vibrations of a molecule on their own can't raise the temperature. They have to transfer to the translational motion of the gas molecules in order to raise their temperature, probably through collisions.

[ronkirk]

I guess methane has more vibration modes to cause the dipole effect so it absorbs more IR energy? Is this what causes it to be a more intense greenhouse gas? I think some of us would like a short video on how these other greenhouse gases such a methane, CFC and HFCS differ from CO2. Thanks for your great chemistry videos. Very informative.

[joelweiner]

Regarding your description of CO2 increasing in KE (around 10:15) and transferring that increase to O2 and N2 via conduction, thus increasing atmospheric temperature: This is a misconception and entirely incorrect. Warming occurs via a disruption to the earth's energy equilibrium. Yes, the absorbed IR will increase GHG KE, which has two results, either a release of IR, which brings the GHG KE back to pre-absorption KE, or a transfer of KE to surrounding molecules. The latter can result in a momentary localized warming. Momentary due to eventually (and quickly) tranferring, via conduction, that energy back to a GHG, which will then emit it as IR. All localized increases in KE eventually end up at a GHG that will emit IR. Of course the GHG can start a new cycle of conduction, but it always comes back to a GHG, which at some point releases the energy as IR, which is eventually either lost to space or lost to the earth via IR absorption at the surface. There is no net change in KE in the atmosphere. The consequences of increasing CO2 and other GHGs in the atmosphere is to disrupt any established energy equilibrium between incoming solar energy and outgoing IR energy. The increase in atmospheric temperature that we call global warming comes from the earth retaining more solar energy to increase IR output in an "effort" to reestablish the equilibrium that has been lost through increasing atmospheric GHGs. As the earth retains more solar energy, much of that is transferred as heat to the atmosphere via conduction, and so the atmosphere increases in temperature. CO2 and other GHGs do not trap heat in the way you describe. They trap IR energy, which does not translate to higher KE beyond a short moment as described. Global warming is a phenomenon of disrupted energy equilibrium, not a phenomenon of simple energy collection. The warming occurring in a bottle with more CO2 in it is due to the localized increase in KE being trapped, via conduction, by the material of the bottle itself, whether glass or plastic, and conducting KE back into the bottle (as well as out).

[JWentu]

This explanation was absolutely amazing, thanks!