Tuesday, January 05, 2010

Bunny's got a new puzzler

At Rabett Run Lodge where all the Rabetts went for the holidays, the girls wouldn't let the guys watch football, so Eli spent New Years on the couch looking at this. No accounting for nerds. According to the Beeb

Scientist Dr Maggie Aderin-Pocock from EADS Astrium visits the Royal Institution’s new Young Scientist Centre to carry out a simple experiment that shows how CO2 traps heat. -BBC

Watch the video (opens in new window)

Skeptical Rabett says, technically true, but it's not a demonstration of the Greenhouse Effect, only part of it. Since the annonomice are batting the New Years Puzzler about pretty well, let's see how they do on this one

Clue on the flip side:

Alexander Graham Bell would have figured this out.


Mark said...

She generated CO2 using a reaction between vinegar (aqueous solution of acetic acid) and sodium bicarbonate. That means some water vapor will enter the bottle along with the CO2.

They also have the lamps set up close to the bottles, so there will be some convective heat transfer from the lamp to the bottles. The control bottle essentially provides the baseline for that.

I love her British accent!

When I clicked on the video and she started talking, it wasn't loud enough, so I clicked on the volume control. The volume goes to 11! Love it!!!!

carrot eater said...

I watched that video some time ago, and was annoyed by how it was portrayed. My thought was that she was simply showing that CO2 absorbs differently than nitrogen and oxygen. That, in itself, will not explain to you why the earth's surface would then be warmer; as you say, it's only part of the story.

Beyond that, the lamp she's using will be producing rather shorter wavelengths than the earth's emission. At least, so I would think. So I'd guess she'd be hitting a different absorption band.

Setting up a bench top (or kitchen-countertop) apparatus that showed all the relevant features of radiative transfer and lapse rate would be pretty difficult.

Then again, I don't get the clue with Bell, so maybe I'm off.

carrot eater said...

teach me a lesson to assume I know what a video is, without watching it.

I had seen this one


but the experiment looks to be the same, so my criticism is the same. Simply showing that CO2 absorbs IR does not explain the entire effect.

does Eli care to weigh in on the earthquake puzzler?

Hank Roberts said...

Harlan Ellison, audio.
Definitely not safe for work.
Turn the audio down, now.
Then listen.

From http://www.deepshag.com/artists/ellison.html

Via http://harlanellison.com/heboard/unca.htm

Which has cute bunnies.

Arthur said...

Incomplete, but I thought it was quite nicely done. My only real criticism would be that she says the lamps are acting like the sun, but it's the parts of them acting like the Earth (emitting infrared radiation) that matter for CO2 absorption.

In essence, proof of absorption (which this is) is all the underlying basic science you need to conclude you will have a Greenhouse effect - the rest is, as Wittgenstein might say, tautology (mathematically forced by the properties of the physical system). Nevertheless, sometimes even tautologies need to be demonstrated to the dimwitted, so it would be nice to have a more direct table-top demo of the whole effect.

But this one isn't bad at all. Much better than I was expecting.

Anonymous said...

Its a common school level demonstration to show that some gases absorb radiation. It does what it does.

Fuller description here designed for students up to sixteen.


Atmoz threatens to investigate, controls water vapour, gets in a bit of product placement and fails to deliver:)


Arthur you might like this one. Its an altogether more elegant attempt to demonstrate the different considerations in the greenhouse effect



Arthur said...

I don't think the practicalchemistry experiment is a good idea at all, at least if I understand it - but maybe I don't fully understand it because I don't get the point of the "lead flags" either. In any case, it's not coming close to the temperature differential that you have in the real atmospheric case, which as we discussed last time is an essential element to getting warming of the surface.

Anonymous said...


:) I think I am well below your radar. It was part 2 of the demo which caught my eye particularly after your comment 'parts of them acting like the Earth etc.' but on consideration I don't think anything actually different is happening there.

EliRabett said...

IEHO, there are two things here.
1. The CO2 is absorbing IR light from the lamp. The lamps go out far enough. WHICH absorption is another question. At best it is the asymmetric stretch @ 2565 cm-1, although it might be some combination of overtones/harmonics. (basically combinations of stretches and bends). A lot of polymers used in water bottles have good IR transmission, although not as far out as the bending modes of CO2 @ 526 cm-1.

2. The absorbed IR is being degraded to heat by collional energy transfer from vibration to translation.

What is not being captured is the IR emission by the thermally excited CO2 and, of course, how the temperature differential at the top of the atmosphere acts as a limitation on emission in the CO2 i

So it captures two parts of the greenhouse effect, but

carrot eater said...

woohoo. i award myself one carrot for wondering about which absorption band was involved.

EliRabett said...

On the hint: Alexander Graham Bell discovered the photoacoustic effect, turning it into, what else, a telephone.

Anonymous said...

Iain Stewart demonstrates infrared radiation absorption by CO2

Cymraeg llygoden

Anonymous said...

OK, this anonymouse (AKA Marco) is getting majorly confused now. The Rabett points to the bending and (asymmetric) stretching vibrations of CO2, but those are at much different wavenumbers than this mouse has ever seen them. 2565 cm-1? 526 cm-1? I see them around 2350 and 670 or so (haven't checked the exact numbers). Did I just correct the bunny, or am I to hang my head in ultimate shame?

EliRabett said...

Just picked them off a web site with modes of motion. I'll check. The 670 looks right

Anonymous said...

Turns out that there is another reason that this experiment may not have been picking up radiation effects at all, but rather convective/conductive differences between pure CO2 and air: an argon control should become a requirement for any tabletop CO2 experiemnt...