Yes, that's true too. From what I read, the scattering of green light in air at 1atm. is 10-5m-1, and blue light about double that. From that I calculate that about 4% of green light and 8% of blue light would never make it through. Taking the mean power loss as 6%, that would knock 1.5% off the surface temperature, or 4o K.Hi haruspex:
I very much like your Insight article. I have a question though.
The article says:
If we treat the Earth as emitting and absorbing radiation as a “black body”, ignoring the atmosphere, and treating incoming light as spread evenly over the whole Earth’s surface all the time, we can calculate the equilibrium temperature as -18C. At that temperature, black body radiation would balance insolation.I understood that N2 scatters blue light, and this is what makes the sky look blue. Wouldn't the scattering of blue photons by N2 then reduce the number of blue photons that hit the earth, since about half the scattered photons return to space? Wouldn't this reduce the equilibrium average temperature of the surface compared with no atmosphere?
Adding a non-greenhouse atmosphere, e.g. pure nitrogen, doesn’t change this.
They are errors I have come across in posts (not just in these forums), and, just occasionally, errors I have made myself.What conclusions can be drawn from such 'frequent errors". Who do you think is making such errors and what are the effects? Thanks.
You are wandering off the topic of what errors are commonly made and what the correct versions are. If you wish to engage in a discussion on the politicisation of science; on the relationship between scepticism, consensus, scientific progress and public policy; or on the use of models of complex systems, let's do that as a private dialogue.Oh, the horror!! Yet, one must secure government grants or perish.
In most scientific models, a single false prediction invalidates the model.
Climate models seem immune from such scrutiny.
Thanks D H, I was not aware that was wrong. But I like the image, much clearer than most, so I've just added a note. (Is the curve wrong, or just the number? The peak seems to be in about the same place as in other images I found.)Minor comment: Please replace that image that depicts a 5250 °C blackbody curve with something else. The Sun's effective blackbody temperature is not 5250 °C, or 5523 kelvins. It is 5777 or 5778 kelvins, depending on who you read. Siting that image has become a "frequently made error in climate science." This is a good example of why wikipedia is not a good source.
Otherwise, this is a very nice insight article.
I included some examples. I made no claim it was exhaustive. There are several more I could have listed (positive and negative). My purpose was to illustrate what is meant by a feedback.Regardless of the current uncertainty on the subject, why no inclusion of the possibility of clouds in Negative Feedbacks? The CFMIP modeled feedback is "approximately zero", but this is not the same as saying there is none.
IPCC AR5 22.214.171.124: "The key physics is in any case not adequately represented in climate models. Thus this particular feedback mechanism is highly uncertain"
Negative feedback is more complicated than you imply. It can cause dynamic instability. It depends on the dynamics of the system, which is very complicated in this case.I included some examples. I made no claim it was exhaustive. There are several more I could have listed (positive and negative). My purpose was to illustrate what is meant by a feedback.
The Insights post concerns aspects of climate science that are well settled and uncontentious yet often misunderstood or misrepresented. I have no plan to get into the more debatable areas. That would be beyond my expertise.
Last I checked, the general view was that whether clouds act mainly as negative or positive feedbacks depended on altitude, but I don't recall which way it worked or whether there was consensus on which dominates.
To address your earlier comment I already added a clause on time delayed feedbacks. If you feel it is necessary to mention instability specifically I'm happy to add that.Negative feedback is more complicated than you imply. It can cause dynamic instability. It depends on the dynamics of the system, which is very complicated in this case.
No. I like your insight post. Thanks for the addition. I think what you have is as good as it can reasonable be. Negative feedback such a can of worms that it's not realistically possible to do much better.To address your earlier comment I already added a clause on time delayed feedbacks. If you feel it is necessary to mention instability specifically I'm happy to add that.
I think that is miss leading. Even if the atmosphere were argon, the sky would still be blue. On the scale of longer wave lengths, say red light wave length, there is nearly a constant number of atoms (or molecules) in a cube with edge of length equal to red wave lengths. But in a cube with half that edge length (1/8 as many molecules inside) the statistical fluctuation as a percentage in number of molecules inside the cube are more significant. The scattering is due to the greater varying index of refraction that small volumes have. Nothing to due with air being mostly N2.… I understood that N2 scatters blue light, and this is what makes the sky look blue. ... Buzz
You're right, I missed a chunk. But I believe the fraction reradiated is more like 80% (Kiehl and Trenberth, 1997). Most of that is radiated back down again, so convection is (just) the major escape route through the troposphere.2) More than 90% of the heat transmitted from the surface to the atmosphere comes in the form of terrestrial infrared radiation. Again, mostly radiation from water molecules. Conduction and enthalpic cycling (condensation, not evaporation) play only very minor roles.
Hi BillyT:I think that is miss leading. Even if the atmosphere were argon, the sky would still be blue.
Read the last paragraph of right column, page 269 here:Hi BillyT: Thanks for your post. I am always interested in learning something new. Can you recommend a reference that explains more about this phenomenon? Regards, Buzz
Hi @BillyT:That gives the Einstein / Smoluchowski theory which does not even require discrete molecules - only density fluxuation, that cause refractive index spatial variation.
Note I said:Hi @BillyT:
Thanks very much for the reference. I am a bit confused by your quote relative to what I read in the reference.
The quote above seems to be saying that the Einstein / Smoluchowski theory about fluxuations explains the blue sky. The following is a quote from the reference.
Einstein stated that "it is remarkable that our theory does not make direct use of the assumption of the discrete distribution of matter" . . .This seems to contradict your quote's suggestion that molecules are not responsible for the blue sky. Your quote seems to support the Einstein / Smoluchowski theory, and the references seems to say it's wrong. Or have I misinterpreted what you said? Or what the article says?
There is no dispute, then, about what really causes the sky to be blue? Is it "really" scattering by molecules? Or, if you want to be more precise, scattering by electrons. Even more precise, scattering by bound electrons: free electrons would not give us a blue sky. The preposition "by" indicates an agent, and molecular scattering is the agent responsible for the sky's blueness.
Now that I have read the whole article, I get that any molecule of sufficiently small size, e.g. argon, would also make the sky blue, provided such molecules have no specific energy levels in its spectrum that would absorb blue light. So the reason that NO2 makes the sky blue is that NO2 makes up most (~80%) of the atmosphere. Since O2 makes up most of the remainder, I am curious. Does O2 also scatter light with smaller wavelengths like blue and violet? Regards, Buzz