Iain Stewart demonstrates infrared radiation absorption by CO2

[bstills32]

Interesting. I'm trying to investigate the truth of global warming. The light does not reach the sensor but how can you infer that it is CO2 infrared absorption. Could it not also just be reflecting it? Also, you are increasing the density of the mass inside the tube. Would another gas, liquid, or material have the same effect. Meaning, increasing the density means blocking more light.

[undeadpresident]

Why is it so hard for so many of you morons to see that what is happening is that the CO2 is absorbing the infrared wavelengths?

Now, does anyone know how to quantify infrared absorption?

[m1der1]

@undeadpresident If, instead of a candle, you have a source of infrared radiation with known wavelength(s) and intensity of output (say an infrared LED), you can use an infrared camera to determine how much and what wavelengths of radiation have been absorbed by the CO2 between its output and reaching the camera.

[campgalley]

 What is been demonstrated here is the low thermal conductivity of CO2 - relative to air. If it showed absorbsion of IR (heat) the monitor would glow yellow orange.

IR cameras don't (easily) show CO2. I've asked the manufacturors of FLIR cameras, they do most other gases - not CO2.

Bad science BBC.

[tyburczj]

@campgalley This is NOT a demonstration of thermal conductivity. There is no way you'd get a cleanly resolved image like that across a large gas-filled space based on conductivity. Such an image could ONLY be the result of TRANSMISSION of infrared wavelengths.

[janama77]

cool - now try it where the CO2 is .039% of the atmosphere an not in tanks next to you.

[nigelelsass]

@janama77: Well there is a reason why NASA used a high altitude airplane as "Stratospheric Observatory for Infrared Astronomy"...

Although the concentration in the atmosphere is low, its length is not just 1...2 meters so that the probability for a photon at IR wavelength to encounter a CO2 molecule is high.... just like in your short tube with almost 100% CO2 concentration.

[JuanVoyce]

complete rubbish....CO2 absorbs infrared radiation, not visible radiation

[robhoneycutt]

@JuanVoyce That's why they were using an infrared camera.

[JuanVoyce]

@robhoneycutt And that explains why the yellow light from the candle is absorbed by the CO2? Think about it.

[robhoneycutt]

@JuanVoyce Yes, let's think about this for a moment....

A candle puts of visible light and what else? Heat. What is the infrared camera seeing? Heat. What is the yellow color for the flame you see in the monitor? Is it visible light? No. Infrared cameras see heat. The yellow you see is the hottest part of the flame. Not the visible light. If you were to put your eye next to the camera lens you'd still see the yellow flame through the CO2.

[robhoneycutt]

@robhoneycutt That's supposed to be "puts out" not puts of.

[JuanVoyce]

@robhoneycutt I get it now! Thanks

[ScientificSolutions]

Nice demonstration!! I am trying to do the same experiment but with emphasis on viewing the CO2 flow patterns. If you could do the same experiment with a wide light source (as opposed to the candle point source) you may be able to see the CO2 motion and flow properties. Did you need to use any specialized bandpass filters on the camera? Maybe the Camera sensor has specific response in the CO2 absorption band(s)? Sure would like to chat about this more. Thanks again for the demo!

[m1der1]

Hi, your welcome, but unfortunately this isn't my own experiment - it's from a BBC documentary. Sorry! Good luck with your experiment.

[C2shiningC]

Interesting experimental set-up

The light absorbed from the candle is in the visible spectrum? I notice that the light blue halo is not attenuated as much by the introduction of CO2. Is that the long wave IR? Rather than a candle, try a long wave IR source or filter out-of-band radiation. Then use an appropriate detector to see if you get the same results?

[m1der1]

Hi, sorry for the delay in replying. I'm afraid this is not my own experiment so I don't know the details - it was demonstrated on a BBC documentary. I can tell you though that the light absorbed was definitely infrared, not visible. I'm not sure why the blue halo wasn't attenuated - perhaps the radiation from that part of the flame is outside the CO2 absorption spectrum? I'm not a physicist though, so not sure!