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| Subject: Re: Climate Change - A quick rebuttal to Augie Auer's opinion ... | |
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Author: The Hunter |
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Date Posted: 17:24:45 05/21/07 Mon In reply to: Duncan7 's message, "Re: "It's become a witch-hunt"" on 08:28:25 05/21/07 Mon In the first week of May 2006, former NZ MetService chief meteorologist Augie Auer said global warming was a myth. He blamed journalists and bad science. In a nutshell, his main argument against anthropogenic (human made) climate change, and an argument made by many other climate sceptics is, that water vapour in the atmosphere is a much more potent 'greenhouse' gas than Co2 and that due to the vast abundance of water vapour the relatively small (380 parts per billion) Co2 content in the atmosphere would not contribute much to global warming, let alone the small contribution that humans were making to that Co2 content. And as most water vapour is naturally generated due to evaporation of the oceans, there was nothing that humanity would be able to do about it. Let us look at the situation a bit more carefully: It is true that by comparison of quantity there is a hell of a lot more water vapour in the atmosphere than Co2. Water vapour is a perfect absorber of infrared radiation and thus the main contributor to the so called 'greenhouse' effect. So far Augie is right. And he is also right, that the Earth would be covered in ice, if it was not for the warming blanket of that water vapour. However Augie omits to say this: Water vapour is not absorbing (shielding against radiation heat loss) in the entire infrared spectrum. In fact there are, thankfully, a few relatively clear 'open windows' in the absorption spectrum of water vapour because of the physical properties of the water molecule. If it was not for these 'windows' in the absorption spectrum of water vapour, our earth would find it very difficult indeed to radiate heat away at all. And radiating in the infrared spectrum, a bit like the glow from your hot potbelly stove in winter, is the only way that Earth can loose thermal energy to space! If these remaining open windows in the infrared spectrum between the various bands in which water vapour absorbs were not there, then Earth would be a boiling quagmire, and not very conducive to the current forms of life. Water is so abundant in the atmosphere that in those areas where it absorbs heat radiation, the atmosphere is practically impermeable or 'black'. In other words in these areas the absorption spectrum is completely saturated. And no matter how much more water vapour there would be, it can't get 'blacker than black'. It’s a bit like putting a black tarp over your window at home. After the first one it dose not matter how many more you add, it won't get any darker - at least through that window! But here is the catch: Co2 and also Methane have absorption areas of infrared radiation in some of the few remaining 'windows' in which the earth can 'shine out' so to speak and loose heat, because these windows in the spectrum are not already closed by water vapour's thick blanket. And it does not take much of a Co2 concentration at all, to lead to a strong absorption in these areas. In fact Co2 is so good at absorbing heat radiation in its bands that even at the natural background concentration of 280 parts per billion of Co2, the atmosphere is practically already almost 'black' in the centre of the Co2 absorption band! The anthropogenic additions of Co2 - in fact we will be practically doubling it by the mid of the century - will have a very measurable effect to the ability of Earth to radiate out of this 'window' precisely because the natural Co2 concentration is so low (compared to water) and the absorption is not yet saturated in these frequency bands so that any additional Co2 we bring to release is directly contributing to the darkening around the Co2 window in the absorption spectrum. Thus Augies argument of the low concentration of Co2 relative to Water is actually coming home to roost! Absorption spectra of Water (H2O) - blue, Carbon Dioxide (CO2) - green, Oxygen and Ozone (O2 and O3) - red and the total (added) absorption spectrum - top. The black line marked 5780K is the incoming solar spectrum, the 255K is the spectrum of the earth radiating out. It is clear that the green Co2 absorption lines are blocking an important part of the 'water window' (blue line) in which the Earth can radiate in the infra red out of the atmosphere. To come back to the example of the house: Imagine that you have 6 windows through which you can see out. 4 are covered by a mile high stack of thick black blankets (water vapour). Now somebody darkens one of the last two open windows with a thin sheet of dark fabric. How would that affect your house? Augie says: How come you argue about one little thin sheet of fabric when I can see that stack of thick blankets…. Well, it all matters where you put it as it seems…. And so it goes that these few hundred parts per billion of Co2 will have a very dramatic effect on life on Earth. All this is not to say, that there is nothing left to discover about the mechanisms of climate change and the regulatory system of our Earth atmosphere, far from it. And water plays a vital role in transporting heat around the Earth, especially in though processes of evaporation and condensation and the fact that these two processes happen often in different places. But the basic science behind the effects of Co2 and Methane on the ability of Earth to radiate heat away to space is pretty sound. And once you calculate this, then it is obvious that Earth must warm measurably in response to our human made doubling of Co2. Everything else is almost an afterthought, i.e. what happens to the trapped heat, where will it go and how will it affect us. [ Next Thread | Previous Thread | Next Message | Previous Message ] |