Life Sciences > The Environment

Why do we blame carbon dioxide for global warming?

<< < (12/21) > >>

Karsten:
I tried something rather simple. I went to Google and typed in "CO2 Absorb Infrared". I found an interesting article in the image search (http://www.creative-science.org.uk/hollywood15.html). This guy shows experimentally that CO2 absorbs infrared.

Absorption is the OPPOSITE of reflection, just to clarify. At this point I really don't know what the issue is. And in this case I prefer to err on the safe side anyways.

Ophiolite:

--- Quote from: Henry Pool on 30/04/2009 14:35:58 ---Ben,I am old man. ..   

--- End quote ---
I am an old man too. Frankly you are the kind of old man who gives old people a bad name. Your willfull ignorance and blatant refusal to accept simple facts placed in front of you are a distasteful embarassment. You would do yourself a favour by reading just a few of the many references you have been provided with, then returning with some intelligent questions rather than your foolish observations.

Henry Pool:
I am sorry you feel that way of me. I have resigned from the forum. In defence I just wanted to say that I realize now (from a glimpse of one of the links) that I did not catch the hints you guys were giving because I cannot open the links(files) you are giving. They are too big. This is Africa here.My computer is too slow to download this and I don't have that many megs. So the truth is, I still don't know the nature of that relationship between elevated Co2 and  heat retention. There was a formula for this?

Karsten:
This is the text in the link I provided:

"
The Climate Wars
CO2 is a greenhouse gas
Note: these articles have been published in InfoChem, the supliment to Education in Chemistry produced by The Royal Society of Chemistry.
Many are based on the two BBC OU TV series - Hollywood Science

In The Climate Wars [1] (BBC1) the presenter, Iain Stewart, demonstrated that CO2 absorbs Infrared (IR) energy and so showed how it can trap heat in the Earths atmosphere contributing to the so called 'green house effect' [2]. The apparatus was simple enough; there was a 1m long, 20cm diameter tube which was filled with CO2 from a cylinder. A lighted candle was held at one end of the tube while a thermal imaging IR camera viewed it from the other end. The bright false colour image of the hot candle on the camera screen slowly disappears as CO2 was introduced into the tube showing that the gas absorbs in the IR. I built the apparatus for the program so let me share what I learnt about this experiment.

Due to the vibrations of the atoms in the molecule CO2 has a number of absorption's in the IR, the main bands being at 4.3 Ám (2350 cm-1), 7.5 Ám (1388 cm-1) and 15 Ám (667 cm-1) [3]. The latter band lies very close to the maximum of the Earth's IR black body emission making CO2 a very important greenhouse gas.

The thermal imaging camera we used was sensitive from ca. 1 to 5 Ám, quite a large part of the IR spectrum. A lit candle or match produces lots of energy through the IR to the visible. Consequently a candle looks very bright (colourful) on the false colour IR camera image.

In order to be able to seal and look through the tube the ends were covered in plastic cling film. Now plastics absorb strongly in the IR so it's hardly as transparent as it looks to the eye but the film was so thin these simple 'windows' actually worked quite well in practice. The CO2 was flowed in to one end of the tube and vented out the other so that it was well flushed with gas at about atmospheric pressure. In the process the thin film windows bulged a little.

You would think from what I said above that when you view the candle through the tube using the camera, and you introduce CO2 the bright flame would 'disappear' due to the IR absorption. However, when you try this it doesn't work, the candle doesn't disappear!

The reason is that the CO2 absorptions observable by the IR camera are quite weak and are only in a relatively small part of the spectrum. The only way to get the demonstration to work is to have a 'CO2 filter' on the camera. This only lets through IR at around 4 Ám, close to one of the CO2 absorption's (which are broadened a bit at atmospheric pressure). The filter blocks out much of the IR energy so that the CO2 absorption is not so swamped anymore and this allows us to now observe our vanishing candle effect.

In the Thomas Crown Affair we talked about how IR cameras usually have an Automatic Gain control (AGC) to make the camera responce as versatile as possible. In this case the AGC will stop the candle from disaperaing as it will re-adjust the gain to try and make it farly constant as the signal drops. So to get this demonstration to work the Camera AGC needs to be turned off.

We used a large diameter tube so that we had the option of seeing the presentors face through the apparatus (see last paragraph below). In the end we used it to observe a candle so we could have had a smaller diameter tube. The 1m path length seemed to work well when the tube was filled with CO2 at atmospheric pressure. If you just wanted to measure an IR absorption and were not worried about getting a recognisable image (of say a candle) then a much smaller length tube could be used if multiple passes were arranged using mirrors.

In the Earths atmosphere the CO2 also absorbs in bands but of course there is a much greater amount of gas and also other greenhouse gases present. We also think that global feedback systems in the ocean for example, increase the amount of CO2 available as things heat up multiplying the amount of warming greenhouse gases still further.

An alternative USA series on climate change [4] recently did the same experiment using a military state-of-the-art IR camera and CO2 filter (unfortunately not available for us to use in the UK). It was so sensitive that they used the heat from the presenters face rather than a candle to demonstrate the effect.

References:
[1] The Climate Wars, BBC1 Sept. 2008, see: web site
[2] A real glass greenhouse actually works by preventing convection not by IR absorption! See the Wikipedia section on 'Greenhouse' effect :
greenhouse effect on Wikipedia
[3] Greenhouse Gas Absorption spectrum in the Earths atmosphere
[4] Global Warming: what's up with the weather, Nova, DVD. ISBN 978 1 59375 729 8
....................... "

I am surprised that you can get to the NakedScientist site but not to those that were provided.

Ophiolite:

--- Quote from: Henry Pool on 01/05/2009 10:55:11 ---I am sorry you feel that way of me. I have resigned from the forum.
--- End quote ---
I am sorry you have decided to retreat from an opportunity to learn something. You say you did not understand the hints that were being offered. Henry, these were much more than hints. Specific information was provided by several posters. You chose either to ignore this completely, or state that it was irrelevant, or declare it was wrong.
I regret that my comments may have offended you, but your responses were indefensible. I hope you will reconsider your departure, but then listen to the sound information that is being presented to you by other posters, rather than promoting your own viewpoint, which is currently based on ignorance.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version