Showing posts with label greenhouse. Show all posts
Showing posts with label greenhouse. Show all posts

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There is no greenhouse effect

Quote-miners will love that subject line, and it isn't a statement of my belief.  But it's been recurring some that there are people denying that anybody believes that there is no greenhouse effect.  Yet, typically on the same day as that claim, I keep seeing people deny that there is a greenhouse effect.  It's also common enough that Fred Singer, who probably would label me as a 'warmist', has made his own complaints about people denying that there is a greenhouse effect.

Nevertheless, it's always a good idea to check in more systematically to what is really out there.  The search here will limit itself to Google searches which show up for the exact phrase "there is no greenhouse effect" and are within the past year.  Alas (I keep giving away the surprise ending) it turns out that there really is no difficulty at all in finding sites which claim that there is no greenhouse effect.  And, of course, are wrong in doing so.  If someone were to demonstrate it and be correct, I'd have to be nominating them for major scientific medals.  No such concern with these.
The arguments claiming to 'disprove' the greenhouse effect's existence seem to fall mainly in to 3 groups.  I add the usual 'other' category since a philosopher friend has noted that all classification schemes wind up with one.

The first group, the 'linguistic argument' is the silliest.  The problem with it is to mistake the words used to describe something with the thing itself.  And then consider that if you can find a problem with the words, that there's nothing being described.  Poof, it's gone.  In this case, that if greenhouses don't operate by the 'greenhouse effect', that there is no greenhouse effect in the earth's atmosphere.  I discuss it at more length in Greenhouse misnomer.  The thing is, the words we use don't change the reality we're trying to deal with.  The earth's atmosphere, due to water vapor, carbon dioxide, and some other rare gases, is fairly transparent to solar radiation and absorbs the earth's radiation pretty well.  It's been suggested that we call it 'atmosphere effect' or 'Callendar effect' instead.  They might be better names, but, regardless, whatever words you use, the fact of selective absorption of energy by the atmosphere remains.

The second argument also relies on giving words supremacy over the reality they're working to describe.  One of the may verbal descriptions of the second law of thermodynamics is that 'heat doesn't spontaneously flow from a colder source to a warmer one'.  But that's only a partial description -- as usual, the statement requires that you make some assumptions.  Those assumptions aren't all true when considering the flow of energy by radiation in the atmosphere. In order to apply the second law properly, you have to sit down with the mathematics.  If you don't want to, or can't apply the mathematics, at least remember that the first law of thermodynamics regards the conservation of energy, not 'heat'.  Radiation carries energy, as does the motion of particles, the elevation of those particles (such as make up the atmosphere above ground), and other things.  'heat' refers only to temperature.  The conservation of energy applies to all, and means that if radiation goes from here to there, there gets hotter (has more energy).

Venus supplies the third argument, which strikes me as bizarre, but, then, so does denying that there is a greenhouse effect.  If you look at Venus, particularly at the surface, it is exceptionally hot.  Far hotter than its blackbody temperature (about 224 K, colder than the earth's 255 K !) would suggest, and far hotter than Mercury -- which is closer to the sun and you'd expect to be hotter than Venus.  The reason for that exceptional warmth is the extreme greenhouse Venus has due to its extremely heavy greenhouse atmosphere.  It has about 90 times the surface pressure of the earth, and almost all of that is due to carbon dioxide, versus the Earth's about 0.04%  Ok, that makes it apparent why someone who would want to deny that there's a greenhouse effect (or at least that CO2 isn't a greenhouse gas) would go to Venus.

The argument, however, is absurd.  I haven't gone in to detail about this yet, but there's a concept called 'potential temperature'.  This is the temperature that a blob of gas potentially has -- if you moved it in a plastic bag that perfectly insulated it against heat conduction or radiation but was fine with shrinking to fit your blob as you moved it from where it was to the surface.  There is an old saying that 'hot air rises', which runs in to a bit of a problem with the fact that at 10 km elevation (the tropopause in mid-latitudes) the local temperature is far colder than the surface is.  If hot air rises, why is that much higher air so cold?  Because the potential temperature is so high for that air.  If you lowered that blob to the surface, it would be much warmer than the surface air.  Take a tropopause temperatures of, say, 225 K, versus surface temperature of 300 K.  By the time you brought that blob down to the surface it would be 325 K -- it really is the hotter air.

The argument relies on a ... well, I don't know what to call it, but it isn't honest or accurate.  The argument relies on taking the (observed) temperature at some large height and then bringing it down to the surface and saying that this potential temperature explains why the surface is hot.  It's a falsehood, though, because it doesn't explain why that temperature isn't reached until the great (observed) elevation.  If there were fewer greenhouse gases in the atmosphere, that elevation would be lower is the truth that is being ignored.  It is the balance between incoming energy, albedo (reflection), and greenhouse effect which determines the temperature through the depth of the atmosphere.


Linguistic argument
Second Law Argument
Venus is warm because of surface pressure / lapse rate, not a greenhouse effect

Other / Multiple

The links show some overlap, citing each other or the same, somewhat older, sources.  This takes us past the 20 links standard. Peruse them yourself, of course. That's rather the point. That, and the reference for future use that there are indeed people (and sites to publish them) who deny that there is such a thing as a greenhouse effect.

We also see that some of the same names are showing up.  We've previously seen icecap and 'climaterealists' on the blog here as unreliable sources.  More of the same.  And several others up there, I've seen in my other looking around -- such as the oft-reprinted + rewritten John O'Sullivan.  There's a certain persistence involved.

In doing this look-around, I also noticed the 'there is no greenhouse effect' argument getting unfriendly response from WUWT and Jo Nova's.  Notice also that I'm quoting Fred Singer above, and Roy Spencer for one of the physics descriptions.

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A heuristic for stratospheric cooling

I mentioned in the climate fingerprinting post that if you have more greenhouse gases in the atmosphere, we expect the stratosphere -- the upper atmosphere -- to get colder.  That, naturally, brought on the question 'why'.

I'm far from the first person to make the comment, or to attempt to write up a description of how it works on a blog.  Recently the Stoat took a swipe, or rather referenced a prior attempt and one by Realclimate, and the Rabett has also had a go.  Plus, I'm sure, there are a raft of other efforts in existence.  Yet the questioner is still asking.  That being the case, and having seen prior efforts make the attempt to describe the full situation that you have, I'll aim for a simpler version.

This will be a heuristic description.  It will be capable of being made rigorous, in the sense that you can take the heuristic and put solid math behind it.  But it will be incorrect in many of its details.  The merit of such heuristics is that even though they are incorrect in details, they lead your intuition in the right directions, such that you can then work with and understand the version of the argument that is completely correct in its details.

The simplest heuristic for surface warming in the face of an increase in greenhouse gases is our starting point.  For this, start with the surface at some temperature in balance with the atmosphere at its temperature, and with the incoming solar energy.  Now wave your hand and magically add some greenhouse gas to the atmosphere.  We will say, heuristically, that if more photons come back to the surface than used to, that the surface warms.  The surface emits some photons, same as usual.  But, thanks to the extra greenhouse gas in the atmosphere, some more get absorbed by the atmosphere.  Some of them get tossed out of the atmosphere (where they'd have gone before), but some get thrown back to the surface -- which then warms up.  The real analysis is much more involved than this, but this does give you a correct starting intuition.  It also points to the importance, yet again, of the first law of thermodynamics -- conservation of energy.

For looking at what happens in the atmosphere, let's again track photons.  (Remember those are the packets of energy carried by light).  Again, we'll start with an atmosphere and surface which are in energy balance with solar input.  Add a little bit of greenhouse gas in every layer of the atmosphere.  These cause more photons to be emitted from that layer -- half go towards space, and half towards the ground.  We'll take the heuristic approach that if most of the photons wind up in space, the layer cools.  If most wind up at the surface, the layer warms.  The heuristic also suggests that if almost all photons go to space (eventually), then the layer cools 'a lot' (it doesn't tell us how much, just a relative sense), and if half go to space and half to the surface, then it stays the same temperature.

We need to think a bit about those 'layers'.  They're being caused by energy emission from greenhouse gases.  But greenhouse gases don't emit all photon energies (or wavelengths -- short wavelengths, like blue, are higher energy than longer wavelengths, like red) equally well.  In a band (a small range of energies or wavelengths) that the gas is a strong emitter, it can easily be 1000 times better an emitter than at a wavelength a little bit different.  There is a converse to this.  By Kirchoff's law, any wavelength that the gas emits well, it also absorbs well.  So consider a strong band (15 microns, for instance, for CO2).  That strength means that a photon emitted here will very likely be absorbed before travelling very far.  That 'not very far' means that through the depth of the atmosphere, the photon will be absorbed many times.  So we can turn around and let the number of layers represent how strongly the wavelength is absorbed.  If the gas is a very strong absorber at a wavelength, then we have, say, 1000 layers.  If it's a poor absorber, it might only be one or two.

There's another feature we need in our layers, for the heuristic explanation.  Consider layer 28 (out of, say, 100).  Like all our layers, half the photons it emits go up (towards space) and half go down (towards the ground).  But ... the layers are so thick that photons will be absorbed in the next layer.  So the photons from layer 28 get absorbed in 27 or 29, rather than going to the surface or space immediately.  Now that some are in 27, we can again ask where they go -- and the answer is half go to 26 and half to 28.

I certainly wouldn't try this by hand for 1000 layers, but give yourself 3 layers.  Start with 1024 photons in the top layer (which I'm calling layer 3), send half upwards (space) and half down (layer 2, now has 512 photons).  Send half the photons up and half down, again.  Keep repeating this until all the photons are either in the bucket for space, or for the surface.  Then count up the totals in each bucket.  Repeat the process, starting with photons in layer 2, and then starting with layer 1, and compare your tallies.  You could carry this out with a stack of chips, or coins, whatever.  Or just do it on paper and copy the numbers across (it takes very good writing to carry this out, I discovered).  Or, of course, my solution of writing a short program.

It's a good idea to draw yourself a diagram here, or [Update] take a look at jg's graphic.

The outcome is, when you have several layers, the photons from the top layer mostly wind up in space.  Photons from the bottom layer mostly wind up in the ground.  The more layers (try the program, or write your own), the more this is the case.  With 100 layers, over 99% of the photons go to space from the top layer (or to the ground from the bottom layer).

So there's our heuristic answer -- the top of the atmosphere cools with an increase in greenhouse gas levels because most photons from the upper atmosphere go to space.  At the same time, the lower atmosphere warms as most photons from the lower atmosphere get caught by the surface.


That said, here's one of the limits to our heuristic description: Most of the photons don't get absorbed and re-emitted immediately, even though that's what our heuristic model says.  Most of the time, a CO2 molecule (or any other greenhouse gas) collides with an oxygen or nitrogen molecule, and hands off the energy to those molecules instead of radiating it away.  This is why nitrogen and oxygen have the same temperature as CO2.  But it also means our heuristic model is incomplete.  In addition to radiation, we should be considering what happens to the temperatures of the layers.  What saves the heuristic model is that after we let the energy slosh around, the now-warm oxygen and nitrogen molecules sometimes crash in to a CO2 molecule.  And sometimes, even if it's rare it does happen, that CO2 molecule emits a photon before it collides with another oxygen or nitrogen molecule.

There are a ton of elaborations that can be made to this heuristic.  One direction of change is to start doing Monte Carlo modeling of radiation.  This is particularly common in dealing with earth radiation in clouds.  The second is the more obvious one of tracking the full conservation of energy.  This, as you get more rigorous, becomes Radiative-Convective Modeling.

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The Biggest Control Knob

I've mentioned Richard Alley before, with good reason.  You can get a flavor of the reason by looking at his Bjerkenes lecture The Biggest Control Knob: Carbon Dioxide in Earth's Climate History.

It's about 50 minutes, and you can skip the introduction to save a little time.  One thing not to miss from the introduction, so I'll mention it here, is the title of Richard's popular book The Two Mile Time Machine.  In it, he discusses how we (he) figures out what climate was like from examining ice cores.  First hand discussion.

Digressing to the personal a second, I do know him personally.  I was a guest lecturer in the 1991 edition of the class he mentions.  My thing at the time being deep ocean circulation, with some concern about how that affected atmospheric CO2 levels.



Back to his talk; he says a few things that I think are particularly useful for thinking about how science is actually done.  At one point, he notes that good scientists doing good work come to one conclusion -- one which makes for a conflict between two sorts of data.  And there are other good scientists also doing good work, but differently, who come to an answer that shows no conflict between the two types.  Now, who's right?  We need to do more work.  It isn't that one group is bad people, or doing bad science.  There's a conflict in the results, so we need to learn more, which means do more work to understand how the conflict comes about.  Probably (my opinion) it means that there's a loophole in one of the sorts of analyzing the geologic record, so that it doesn't only record what the method expects.  Finding that loophole is the challenge.

You'll see, also, something about what scientists are like inside.  Most of us aren't as demonstrative about liking our subjects.  But nobody can watch Richard for more than a few minutes and not realize that he loves his subject.  The rest of us do, too, just not so obviously.

This all actually relates well to the post I promised in my last note.  It turns on looking at ice cores and CO2, and Richard will fill you in on parts of the story that surround the two.
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