What does "surface temperature" mean?

In summary: GHE. Is it the air temperature averaged at 1 metre or something like that? If it is not the average air temperature, what is it?
  • #1
Graeme M
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TL;DR Summary
Within the contect of the earth/atmosphere system and the greenhouse effect, what is meant by the term "surface temperature"? In reading about this I find the use of the term confusing as it seems to refer to different quantities at different times.
I have been reading about the "greenhouse effect" of Earth's atmosphere, having been conscious that while I generally understand it I had never really examined it more closely. A problem that bothers me is mention of "surface temperature" which seems to vary according to context.

In some articles I read about how the surface temperature would be -18C without an atmosphere, but is actually 14C with an atmosphere. However, when we talk about 14C, is that the average temperature of the air (atmosphere) as recorded by thermometers, is it an average of air temps AND sea surface temps, or is it a derived value from some measurement by satellites of outgoing radiation?

The reason I am confused by this is that IF the Earth's surface without an atmosphere were -18C, I am assuming we are talking about the actual surface temperature as derived mathematically given incoming insolation and surface emissivity (which I understand for the Earth is close enough to 1). I understand this may be derived using the Stefan-Boltzmann Law, though I have no idea how to do that, mind you.

This seems to be a different quantity from that of measuring an air temperature, so it's not clear to me why we say that the GHE causes the Earth's surface to be 32C warmer than it would be without an atmosphere.

Or is this temperature difference more of a sort of simplified statement for the general public and not necessarily exactly what's going on?
 
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  • #2
If the Earth is a perfect mirror sphere with no atmosphere, all sunshine energy would be reflected and the Earth temperature would be absolute zero.
If the Earth is a perfect container of energy with no release, the Earth temperature would not cease increasing to infinity with constant supply of sunshine energy.
We observe amount of energy got from sunshine and released to the space are equal. Our Earth is somewhere between those two extreme cases and its temperature changes according to change of the Earth structure including amount of GHE gas. For more quantitative discussion some more detailed factors, e.g. heat coming from the center of the Earth by nuclear reaction, friction of sea water current and the Earth by spinning should be considered.
 
  • #3
Thank you mitochan but that isn't my question. I do understand the difference between a surface emissivity of 0 and 1. I also am not particularly concerned about the relative proportions of heating for the atmosphere. What I am not clear on is what "surface temperature" means when people talk of the GHE and its measurable/calculable effect. There is not a 1:1 relationship between the temperature of the air and a given area of land surface for all sorts of reasons (the ground is often much hotter or much colder than the air), but it might be that measuring the air temperature at 1 metre or so is on average near enough to the actual average surface temperature. From what I have read, the average surface temperature normally referred to seems to be a mix of actual sea surface temperatures and near surface air temperatures over land. If it is calculated that the surface temperature without an atmosphere is -18C, then we are talking about an actual surface radiation value. My question might be better framed as whether such a value is directly comparable to the measured temperature of the near-surface atmosphere. I have no particular concern, other than being confused. Is the measured air temperature comparable to the calculated surface temperature? Does it matter that we mix actual sea surface temps with over land air temps?
 
  • #4
I hope I understand your question: The issue is not the temperature of the Green House Gas...it is that it does not allow Infrared wavelengths to escape from the surface into space directly. Because of the relative surface temperature difference the incoming energy from the sun peaks in the visible whereas the outgoing Earth energy peaks in the far Infrared and therefore is much more affected by these gases.
If your question is "does it matter that the temperature of the Earth surface is not absolutely uniform" then the answer is yes...the blackbody result will be slightly different. But the Greenhouse effect will exist either way...although it gets a little bit complicated in the details.
 
  • #6
Mitochan, yes, that's exactly my problem. My question isn't about teasing out what the GHE is, more about the manner in which the magnitude of this effect is described. As that wiki entry says, "surface temperature" is comprised of the temperature of a genuine surface and the temperature of an arbitrary level in the atmosphere.

What I am getting at is the claim that the GHE makes the surface warmer than it would be without an atmosphere. I am not saying there is no greenhouse effect or that scientists are mistaken, I am just confused by the claims about the actual effect of GHGs. So I am quibbling about what a "surface" is in this context.

If surface is the atmosphere, then where in that atmosphere are we measuring? Close to the ground, it is claimed that the average is 14C, though it appears this isn't strictly true because we are averaging a true surface (sea surface) and an arbitrary height in the atmosphere (about 1 metre over the land). At much higher altitudes, the temperature is much colder until we get to the thermosphere. If we used the temperature at 20,000 metres we would record around -50C.

I am assuming that if we calculated the surface temperature of a spherical blackbody in the location of the earth, we are deriving the actual surface radiative temperature. In effect, how hot that surface is, on average.

But measuring the Earth's atmosphere at some arbitrary point is not the same thing at all, or so it appears to me. If we are really interested in an apples and apples comparison, aren't we really interested in the surface radiative temperature of the Earth with an atmosphere. In which case, wouldn't it be cooler than the average struck without an atmosphere? As about 30% on incoming insolation is reflected back to space, we have significantly less energy to heat the surface, so the average surface temp would be cooler (though I do not know what average temperature the surface is supposed to be with the effects of "back radiation" added into the mix.

Is it accepted that measuring the air temp at one metre, adding in the sea surface temps (and not the air at one metre over the sea) and then striking an average is sufficiently close to the true surface value? Has anyone ever calculated or measured the true surface value? Is the very idea invalid?

Put another way, on my naive take on things, the Earth's actual surface without an atmosphere is calculated to be -18C on average, with an atmosphere I'd expect it to be calculated to be colder on average due to albedo effects of cloud etc, but that the atmospheric layers, being matter, are warmer than this and vary with altitude and composition. The atmosphere isn't warming the surface, it is cooling the true surface, though the atmosphere itself varies in temperature.

And in even simpler terms, what I am asking is whether the state of the system in terms of surface temperature really reduces to the difference between a spherical blackbody at the Earth's location receiving 341w/m2 at the surface versus one receiving 239w/m2. What am I missing? Is it the backradiation adding to the total irradiation at the surface?
 
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  • #7
Keeling curve https://en.wikipedia.org/wiki/Keeling_Curve observes a paced increase of CO2 concentration of the Earth air in 60 years. Theoretical physicists with simple planet models and with condition that other factors are kept same, can say that internal energy and "temperatures" of the Earth would increase in general anyway.

I must confess that I do not know the way what "temperatures" Earth scientists are working with, e.g. of what, where, when, momentous or time average, how much and why so chosen.
 
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  • #8
Graeme M said:
So I am quibbling about what a "surface" is in this context.
It's the average global annual temperature - a combination of temperature measurements of sea surface, air above sea surface, and air over land, averaged over long term and over the planet. The methods are described in this paper (section 6):
https://www.st-andrews.ac.uk/~rjsw/papers/Jones-etal-1999.pdf

My understanding is that when averaged over long term, near-surface air can be taken to be in thermal equilibrium with the ground. So it's a good proxy for the temperature of the emitting surface.

Graeme M said:
Put another way, on my naive take on things, the Earth's actual surface without an atmosphere is calculated to be -18C on average, with an atmosphere I'd expect it to be calculated to be colder on average due to albedo effects of cloud etc, but that the atmospheric layers, being matter, are warmer than this and vary with altitude and composition. The atmosphere isn't warming the surface, it is cooling the true surface, though the atmosphere itself varies in temperature.
The -18C result for a black body thermal equilibrium already takes into account average planetary albedo, which includes clouds.
The simplified model assumes the atmosphere to be reflective (contributing to albedo, expressed as a single coefficient), but otherwise fully transparent to radiation. In that model, the same methods used to obtain the GST would nett you -18 C (keeping in mind that the model is very simplified). So in this way the two temperatures are directly comparable.

Graeme M said:
And in even simpler terms, what I am asking is whether the state of the system in terms of surface temperature really reduces to the difference between a spherical blackbody at the Earth's location receiving 341w/m2 at the surface versus one receiving 239w/m2. What am I missing? Is it the backradiation adding to the total irradiation at the surface?
The first number you quote is what you get if you divide the solar constant (1361 W/m2) by 4 (the ratio of the surface of a sphere to its cross-section), and the second is the first reduced by albedo. I.e., what you describe is the state with or without albedo, not with or without the GHE.

If you had no albedo and no GHE, then the 341 W/m2 would result in equilibrium temperature of approx. 5 C.

The states being compared, the -18 C and +14 C equilibria, in terms of average energy balance at Earth surface are approx. 239 W/m2 vs 390 W/m2.

In other words, the 390 number is what the surface emits (and receives from the sun and back radiation, since we're talking equilibrium), while 239 is what leaves the upper atmosphere (since it's also what enters the system). The difference is trapped in the greenhouse.
 
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  • #9
What are these numbers?

Graeme M said:
And in even simpler terms, what I am asking is whether the state of the system in terms of surface temperature really reduces to the difference between a spherical blackbody at the Earth's location receiving 341w/m2 at the surface versus one receiving 239w/m2. What am I missing? Is it the backradiation adding to the total irradiation at the surface?
The surface of a black body is, well, black (or at least gray). This means opaque...a transparent sphere is not a good blackbody. Because the atmosphere is transparent to many wavelengths but absorptive (because of particular gases) at others the question of "where is the surface" depends upon wavelength. Globally this is a small effect because the atmosphere absurdly thin (~10 miles out of 4000). For specific questions (like "doesn't the existing amount of CO2 already absorb all of the IR? Why worry?") this turns out to be crucially important but for the general energy balance not so much.
But I'm afraid I still do not understand your specific question. What exactly are the two two energy fluxes you quote above? (maybe I am missing something...)

OOPs I missed the latest response let me read
 
  • #10
Graeme M said:
There is not a 1:1 relationship between the temperature of the air and a given area of land surface for all sorts of reasons (the ground is often much hotter or much colder than the air), but it might be that measuring the air temperature at 1 metre or so is on average near enough to the actual average surface temperature.
The part in parentheses is wrong and contradicts the part at the end: it's an average, so it does indeed take into account times when the ground is hotter and colder than the air. That's the entire point of taking an average.
My question might be better framed as whether such a value is directly comparable to the measured temperature of the near-surface atmosphere. I have no particular concern, other than being confused. Is the measured air temperature comparable to the calculated surface temperature?
Yes, it is.
Does it matter that we mix actual sea surface temps with over land air temps?
No.
Graeme M said:
This seems to be a different quantity from that of measuring an air temperature, so it's not clear to me why we say that the GHE causes the Earth's surface to be 32C warmer than it would be without an atmosphere.
Are you asking why its warmer at all? Because that's a different question than being unclear on how the averages are measured/calculated.
 
  • #11
Ah, this helps greatly. I see that I had misunderstood the approximations being used. So now I understand that the case being made is that if the Earth did NOT have an atmosphere, it's surface temperature would be on average 5C. With an atmosphere, it is 14C. In the case of an atmosphere and no GHE, clouds would add to albedo thereby reducing energy reaching the surface and the surface temperature would be -18C. Mind you, this seems a strange case given there'd be no clouds without a GHE. In terms of an atmosphere, the effect of our atmosphere on surface temperature is a warming of 9C (including effects of cloudiness and GHE).

While I was not certain how an air temp is comparable to an actual surface temp, Bandersnatch notes that over the longer term, the near surface air can be considered to be in equilibrium with the surface.

Russ_watters, my question about the measurement of air rather than surface is this. When I think about this, it seems to me that the ocean drives the warming of the atmosphere. There is far more of it and it's surface temp is likely to be within a far smaller range (eg 0C to what, 30C?). It is also more stable (ie little variation over short time scales). The land however varies far more with extremes from far below zero to perhaps as high as 75C (here I am talking actual surface temps, eg sand and frozen tundra, though I do not really know how hot or cold these can be). This also means that air temps over land are affected far more than over the ocean, with local and regional extremes driven by local conditions. The sea is far less likely (I'd have thought) to exhibit those extremes.

When we average air temps by using local thermometers, we will be including both local extremes as well as the effects of land cover change. For example, ongoing vegetation clearing will add to the heating of the surface thereby heating the air locally. I think here in Australia this is noticeable at significant scale, for example research suggests reforesting lands degraded by agriculture could reduce summer extremes by as much as 2C. That suggests to me that average air temperatures are strongly influenced by factors other than simply the GHE.

I wondered if this was relevant in considering the average warming values posited for the GHE. In other words, is the average over land actually comparable to the true average of the surface temperature. Over the ocean, I can see that it would be. But over land, the wide extremes of actual surface temperature seem to swing far outside the ranges of temperatures exhibited by the air. But I can see that over long time scales, we *could* consider the air to be in equilibrium with the ground.

I think my worry about over-land air temps remains though. When talking about the GHE, we are using highly simplified models operating over long time scales. When talking about measured over-land air temps, local effects seem to dominate over the short time scales we care about. Temperature extremes caused by things such as land clearing for agriculture will affect local averages, more so than the GHE I'd have thought.
 
  • #12
Graeme M said:
So now I understand that the case being made is that if the Earth did NOT have an atmosphere, it's surface temperature would be on average 5C. With an atmosphere, it is 14C. In the case of an atmosphere and no GHE, clouds would add to albedo thereby reducing energy reaching the surface and the surface temperature would be -18C. Mind you, this seems a strange case given there'd be no clouds without a GHE. In terms of an atmosphere, the effect of our atmosphere on surface temperature is a warming of 9C (including effects of cloudiness and GHE).
No, that would be the case if all albedo was due to atmospheric reflection. Most of it comes from surface reflectivity.

Graeme M said:
Over the ocean, I can see that it would be. But over land, the wide extremes of actual surface temperature seem to swing far outside the ranges of temperatures exhibited by the air.
That's why you use averages.
 
  • #13
I understood atmospheric albedo to be in the order of 20-30% of incoming insolation. Energy budget diagrams show 79W/m2 being reflected versus 23W/m2 from the surface? Also, on the matter of averages, if the sea surface temp is on average 16C, doesn't this mean that the average land surface temp must be very much below zero?
 
  • #14
If one wishes to talk about the effect of large patches at different temperatures on total blackbody emission one would use the average (over the surface) of T4 not the average of T. So the variability itself will slightly increase the emission for the same average T . If the rms variability in T is 10% this might be as much as 6% energy if it is variable all over the planet...with the steady oceans it will be less of course.
 
  • #15
Graeme M said:
I understood atmospheric albedo to be in the order of 20-30% of incoming insolation. Energy budget diagrams show 79W/m2 being reflected versus 23W/m2 from the surface?
You're right, I should have checked instead of relying on fickle memory. Atmosphere reflects more (although not 79/23 times more, since 23 W/m2 is what is reflected from the part of solar radiation that reaches the surface).

Graeme M said:
Also, on the matter of averages, if the sea surface temp is on average 16C, doesn't this mean that the average land surface temp must be very much below zero?
Why? Using the numbers 14 C average and 16 C sea (but see below), with approx. 70.8% surface covered by oceans, we get 0.708*16+0.292*X=14, so the land temperature in this case would be 9.15 C.

However, always check your temperature sources, so that you don't compare apples with oranges (like 1990 temperature of land with 2010 of sea). E.g. this source
https://www.ncdc.noaa.gov/sotc/global/201908
has 15.6 C for global 20th century average temp, and 16.4 for sea. So then land temp comes out appropriately higher - I'm getting 13.7 C vs 13.8 the same source reported, probably due to rounding errors.
 
  • #16
Yes, you are right. Though this is a bit circular - the global average is derived by mixing measured land averages and sst averages, so working back just gets us the original averages. I was more thinking of fictional Earth without GHE. In that case if average surface temp is -18C without GHE but with clouds, and SST average is 16.4C, then isn't land surface average about -100C? I am so easily confused...
 
  • #17
Graeme M said:
I am so easily confused...
You're overthinking it. This type of problem is addressed by math models and calculations, not logic and reasoning. Your ambition to understand just by thinking about it is not realistic.
 
  • #18
Yes, I do realize that now. Still, some of the uncertainties I had have been cleared up. I guess it is that the simplistic model to illustrate the GHE just is that - a simplistic model.
 
  • #19
Graeme M said:
Ah, this helps greatly. I see that I had misunderstood the approximations being used. So now I understand that the case being made is that if the Earth did NOT have an atmosphere, it's surface temperature would be on average 5C. With an atmosphere, it is 14C. In the case of an atmosphere and no GHE, clouds would add to albedo thereby reducing energy reaching the surface and the surface temperature would be -18C. Mind you, this seems a strange case given there'd be no clouds without a GHE. In terms of an atmosphere, the effect of our atmosphere on surface temperature is a warming of 9C (including effects of cloudiness and GHE).

This comparison to assess the contribution from the greenhouse effect is actually not totally correct. You have a first case without atmosphere and a second case with atmosphere but in both you took in account only the thermal radiation emitted by the surface in average. Actually, in the second case there is the thermal radiation emitted by the atmosphere itself and the thermal conduction from the ground to the air. In reality, the contribution from the greenhouse effect is much greater than simply comparing -18°C with 14°C. Because a planet with an atmosphere totally transparent to thermal radiation from its ground would be much colder than a planet without atmosphere. From Manabe & Strickler (1964)* figures, it seems that without surface evaporation and convective heat loss, the surface would be about 70°C warmer, rather than 33°C warmer, far more than simple solar absorption by the surface would suggest.

*Manabe, S., & Strickler, R. F. (1964). Thermal equilibrium of the atmosphere with a convective adjustment. Journal of the Atmospheric Sciences, 21(4), 361-385.

Edit: by the way, about this simplistic comparison, it is explained on the website of the American Chemical Society
https://www.acs.org/content/acs/en/climatescience/energybalance/energyfromsun.html
 
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Hight from surface varies from place to place, and that might be confusing for some. Because we often combine several measurements for an average, in certain areas. It depends on weather stations etc. combined with satellite measurements. Its not that many years ago they found out that sea temperature is measured incorrectly for example, because of heat transitions. This is before they started to use buoys. Global average surface temperature does not seem to be correct at all.
 
  • #21
Genava, let me see if I have you right (I haven't read the referenced paper). The existing Earth - with an atmosphere (and a GHE), oceans and land surfaces - has an average surface temperature of about 14-15C. The same system but with IR transparent atmospheric gasses would be about -18C.

However, IR emission isn't the only energy transfer system as conductive heat loss and convection play a greater role overall. The Earth with land, ocean, atmosphere and GHE but without conductive/convective processes would in fact have an average surface temperature of 52C.

So you are saying that at equilibrium, the IR contribution is actually to warm surface temperatures from -18C to +52C. Other processes act to increase energy loss to space reducing the average surface temperature to ~+15C.

Strictly speaking, you are saying that the GHE adds about +70C to the surface temperure which is offset by conductive and convestive processes to cool it to the observed 14-15C.
 
  • #22
Graeme M said:
Genava, let me see if I have you right (I haven't read the referenced paper). The existing Earth - with an atmosphere (and a GHE), oceans and land surfaces - has an average surface temperature of about 14-15C. The same system but with IR transparent atmospheric gasses would be about -18C.

No. -18°C is the temperature of the Earth according to a balance between IR radiation from the ground and solar radiation from the Sun, without atmosphere (but taking in consideration the average albedo, see ACS webpage). If you add an atmosphere totally transparent to IR, there will be a loss of IR from the ground in addition with a loss of IR from the whole atmosphere. Moreover, the ground (or air temperature at the surface) will loss heat from thermal conduction to the upper layer. The ground temperature of an Earth with atmosphere but without GHE should be colder than -18°C. Because an atmosphere without GHE would decrease the temperature. I don't have a value because I don't know if someone did a model of this situation.

Graeme M said:
However, IR emission isn't the only energy transfer system as conductive heat loss and convection play a greater role overall. The Earth with land, ocean, atmosphere and GHE but without conductive/convective processes would in fact have an average surface temperature of 52C.

So you are saying that at equilibrium, the IR contribution is actually to warm surface temperatures from -18C to +52C. Other processes act to increase energy loss to space reducing the average surface temperature to ~+15C.

Strictly speaking, you are saying that the GHE adds about +70C to the surface temperure which is offset by conductive and convestive processes to cool it to the observed 14-15C.

The greenhouse effect on Earth is a massive contribution of heat in the troposphere and has a huge impact on the different layers of the atmosphere, with strong thermal gradients resulting of it. Technically, the case of an atmosphere with GHE and without convection is not really possible because the GHE is an important driver of the convection. Radiation is the primary way that air is heated. Convection currents move that heated air around the earth, and the difference between warm and cold air provide the energy needed to create weather. So convection is a way how the atmospheric system dissipate this excess of heat in the ground higher in the atmosphere and higher in latitude. This estimation of +70°C instead of +33°C for the contribution of the greenhouse effect is what we should see on the ground if the heat wasn't dissipate more homogeneously by the convection (in addition with conduction and evaporation). Like you said, this is a kind of offset or short-circuit from the convective and hydrological cycle which reduces the temperature on the ground in average. It is a feedback reducing the effect (on the ground).

Solomei said:
Hight from surface varies from place to place, and that might be confusing for some. Because we often combine several measurements for an average, in certain areas. It depends on weather stations etc. combined with satellite measurements. Its not that many years ago they found out that sea temperature is measured incorrectly for example, because of heat transitions. This is before they started to use buoys. Global average surface temperature does not seem to be correct at all.

You are not getting correctly the issue. It is impossible to know with an absolute certainty the surface temperature, this is always a matter of estimation and of estimation of the uncertainties. The measurement issue was reported as a new source of uncertainty in the old data but actually the uncertainty is not that big and it is still manageable to use the data. If you are interested to the measures of the global temperature, the Berkeley Earth initiative leaded by Richard Muller gives you a figure with the uncertainty ranges.
http://berkeleyearth.org/2019-temperatures/

hutchphd said:
For specific questions (like "doesn't the existing amount of CO2 already absorb all of the IR? Why worry?") this turns out to be crucially important but for the general energy balance not so much.

Actually, the saturation doesn't have that much an effect. This is something known the "saturation fallacy", see Ray Pierrehumbert article "Infrared radiation and planetary temperature".
 
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  • #23
Hmmm... unless I am misunderstanding what's been said, Genava and Bandersnatch are at odds with each other.

Bandersnatch says that an Earth with an atmosphere transparent to IR and with an albedo of about 30% would have a surface temperature about the same as if it were a blackbody with the same albedo, that is, -18C.

Genava says that in the former case, the Earth's surface would be colder than -18C because an atmosphere without GHE would decrease the temperature.

Certainly, every article I read uses the -18C value (as well as the 33C value) so I guess now I am not sure what the claimed -18C really refers to.
 
  • #24
That's because I didn't take into account the atmosphere carrying heat away through evaporation, conduction, and convection (and then radiating it away) while Genava did.

In the black body exercise, the only effect the atmosphere has is its contribution to albedo. So all of its physical properties other than that are ignored. It's a very constructed scenario, that asks you to forget about the atmosphere but keep the albedo as-is, even though in reality the latter wouldn't stay the same without the former.

If you start adding effects that were previously ignored, then you'll get a more complex model. But that would be going outside the bounds of the exercise.

Maybe rephrase the exercise in your mind, so that instead of Earth with a wonky unphysical atmosphere that doesn't do most of the things an atmosphere does, imagine it talks about a barren rocky airless planet that is in the same spot as Earth, but its surface happens to have the same albedo.
The equilibrium temperature you get from the exercise is what this rock would have.
 
  • #25
Graeme M said:
Certainly, every article I read uses the -18C value (as well as the 33C value) so I guess now I am not sure what the claimed -18C really refers to.

I can help you: https://www.acs.org/content/acs/en/climatescience.html

With an average of 342 W/m2 reaching the ground from solar radiation.
With an average albedo of 30%.
With an emissivity of 1 (blackbody).
The predicted temperature can be solved with this:
342(1 – 0.3) = σT4 [W/m2]

This is simply an equilibrium between the energy reaching the ground from the Sun (342*0.7) and the energy emitted by the ground from the Stefan-Boltzmann law for a blackbody (σT4).
 
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  • #26
Hi Genava, yes, I know we can derive the temperature for a given set of parameters. I am more trying to get my head around the model being proposed. I get that this is a gross simplification and completely unphysical, but as I say, those numbers (-18C, 15C, 33C) are everywhere so they must refer to something.

My understanding is that the simplified, unphysical case being presented is just this:

A spherical blackbody with emissivity of 1 and albedo of .3 receiving an average of 342 W/m2 at the surface will radiate at an average surface temperature of -18C at equilibrium. The Earth with an IR transparent atmosphere but containing clouds would be at approximately the same temperature (emissivity is assumed to be close enough to 1). The Earth with an IR opaque atmosphere is actually 15C. Therefore the GHE adds 33C to average surface temperatures.

You are disagreeing with this case, saying that this rough approximation is wrong because it does not account for thermal conduction and convection. In a true atmosphere that happens to be IR transparent but retains conductive and convestive processes, the surface temperature would be colder than -18C. Similarly, you are saying that in a true atmosphere that lacks conductive and convective processes but is IR opaque, the surface temperature would be closer to 52C. Bandersnatch says that in a true atmosphere that is both IR transparent and lacks conductivity and convection but has no albedo, the surface temperature would be around 5C (this last case must be roughly equivalent to the earlier blackbody case with no albedo).

Is that it, in a nutshell?
 
  • #27
Graeme M said:
Genava says that in the former case, the Earth's surface would be colder than -18C because an atmosphere without GHE would decrease the temperature.

How would it do that?
 
  • #28
I guess that the bottom line is that trying to assign values to arbitrary non-physical models is somewhat of an approximation. The bottom line just is that a blackbody stand-in for Earth with the same emissivity/albedo would be -18C. The real Earth with a complete atmosphere and variable land surface is about +15C. I'm still not clear though whether the larger influence is CO2 concentrations or convective processes?

My original question was answered by learning that the averaged air temp is good enough over land as land and air are broadly at equilibrium (or rapidly reach equilibrium). I take that to mean that air temps warm and cool quickly in response to surface radiation over short time scales (eg days/weeks) while the ocean does not. I also assume that if the Earth were all water, variations in surface temperature over time would be small and similarly, the air would be relatively closer to the average Earth temperature most of the time.

One thing this leads me to ask is how much surface variation plays in local/regional temperatures. Consider the Arctic. If maybe one million km^2 is no longer covered in sea ice in winter, I'd take that to mean that surface temps there must have changed considerably. If average surface temps over ice there are what, maybe -30C in winter, they'd now be no less than perhaps -2C (because there is now unfrozen water there, though I guess I don't know how much actual ice remains over the surface that is declared ice-free). Or consider an area covered in vegetation and now cleared back to stubble or bare earth. I'd assume that the latter case would be significantly hotter on average in summer, assuming greenhouse gas concentrations remain stable?
 
  • #29
Graeme M said:
I'm still not clear though whether the larger influence is CO2 concentrations or convective processes?

Without greenhouse gases there would be no significant temperature change by atmospheric convenction. Convective processes just reduce the GHE by limitation of the atmospheric temperature gradient to the adiabatic laps rate.
 

1. What is the definition of "surface temperature"?

Surface temperature refers to the measurement of the temperature of the Earth's surface, including land and water. It is typically measured in degrees Celsius or Fahrenheit.

2. How is surface temperature different from air temperature?

Surface temperature refers to the temperature of the Earth's surface, while air temperature refers to the temperature of the air in the atmosphere. Surface temperature can be significantly different from air temperature due to factors such as land cover and wind speed.

3. What factors affect surface temperature?

Surface temperature can be affected by a variety of factors, including solar radiation, cloud cover, land cover, and human activities. These factors can influence the amount of heat absorbed or reflected by the Earth's surface, which in turn affects surface temperature.

4. How is surface temperature measured?

Surface temperature is typically measured using instruments such as thermometers, infrared cameras, and satellites. These instruments can provide accurate measurements of the temperature of the Earth's surface at different locations and times.

5. Why is surface temperature an important metric to study?

Surface temperature is an important metric to study because it can provide insight into the Earth's climate and how it is changing over time. Changes in surface temperature can impact weather patterns, ecosystems, and human activities, making it a crucial factor to monitor and understand.

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