According to some recent reports (e.g. PlanetArk; The Guardian), the public concern about global warming may be declining. It’s not clear whether this is actually true: a poll conducted by researchers at Stanford suggests otherwise. In any case, the science behind climate change has not changed (also see America’s Climate Choices), but there certainly remains a problem in communicating the science to the public.
This makes me think that perhaps a new simple mental picture of the situation is needed. We can look at climate models, and they tell us what we can expect, but it is also useful to have an idea of why increased greenhouse gas concentrations result in higher surface temperatures. The saying “Everything should be made as simple as possible, but not simpler” has been attributed to Albert Einstein, which also makes me wonder if we – the scientists – need to reiterate the story of climate change in a different way.
Gavin has already discussed this (also see here and here), but it may be necessary to tell story over again, with a slightly different slant. So how can we explain how the greenhouse effect (GHE) work in both simple terms and with a new angle? I also want to explain why the middle atmosphere cools with increasing greenhouse gas concentrations associated with an increased GHE. Here I will try to present a conceptual and comprehensive picture of GHE, explaining both the warming in the lower part of the atmosphere as well as the cooling aloft, and where only the most central features are included. Also, it is important to provide a good background, and we need to start with some very fundamental facts.
Four main physical aspects
Several factors are involved, and hence it may be useful to write a simple recipe for the GHE. This recipe then involves four main ingredients: (i) the relationship between temperature and light, (ii) the planetary energy balance, (iii) the distance light travels before being absorbed, and (iv) the relationship between temperature and altitude.
(i) Temperature and light
Energy can be transmitted in many different ways, involving photons (light or electromangetic radiation), conduction, and motion. Most of these require a medium, such as a gas, fluid, or a solid, but space is basically a void through which photons represent virtually the only form for energy transfer. Hence, planets tend to gain or lose energy to space in the form of photons, and we often refer to the energy loss as ‘radiative heat loss’.
A fundamental law of physics, known as the Planck’s law, says that radiative heat loss from any object depends on its temperature. Planck’s law also explains the colour of the light, or its wavelength, and hence explains why iron gets red hot when heated sufficiently.
Planck’s law predicts that the light from an object with a temperature of 6000K – such as the solar surface – produces light that is visible, whereas objects with a temperature of 288K produce light with a wavelength that our eyes are not able to see (infra red). This is illustrated in Figure 1 showing how the light intensity (y-axis; also referred to as ‘flux density‘) and the colour of the light (wave length) vary for objects with different temperatures (here represented by different curves). The yellow curve in the figure represents the solar surface and the light blue curve the earth.
(ii) The planetary energy balance
The planetary energy balance says that our planet loses heat at the same rate as it receives energy from the sun (otherwise it would heat or cool over time). This is because energy cannot just be created or destroyed (unless it involves nuclear reactions or takes place on quantum physics scales).
The planets’ distance from the sun and the brightness of its surface dictates how much energy it receives from the sun, as the light gets dimmer when it spreads out in space, as described by Gauss’ theorem.
The energy flowing from the sun is intercepted by the earth with energy density described by the ‘solar constant‘ (S0=1366W/m2), and the amount of energy intercepted is the product between this flux density and the earth’s disc (minus the reflected light due to the planet’s albedo: A ~0.3). The average heat loss is given by the product of earth’s surface and its black body radiation:
S0/4 (1-A) = σT4,
where σ=5.67 x 10-8W/(m2 K4) is the Stefan-Boltzman constant. This gives a value of 255K, known as the emission temperature.
Figure 3 shows a comparison between observed surface temperature and calculated emission temperature for the planets in the solar system, based on the balance between energy from the sun and heat loss due to black body emission. In these simple calculations, the greenhouse effect is neglected, and the black body radiation can be derived from Planck’s law. The calculations agree quite well with the observations for most of the objects in our solar system, except for Venus which is known to harbour a strong GHE and has a hotter surface than Mercury despite being about twice as far away from the sun.
(iii) Light absorption
It is also clear that our planet is largely heated at the surface because the light from the sun – which is visible for our eyes – penetrates the atmosphere without much absorption (hence we can see the sun from the ground). However, the atmosphere is a medium of gas and particles that can absorb and scatter light, depending on their wavelength (hence explain why the sky is blue and sunsets orange).
The distance light travels before being absorbed – optical depth – can vary with the light’s wavelength and the medium through which is travels. The optical depth in our atmosphere is different for visible and infra-red light.
Infra-red light is absorbed by molecules, which in turn get more energetic, and the excited molecules will eventually re-emit more infra-red light in any random direction or transfer excess energy to other molecules through collisions. In a optically thick (opaque) atmosphere, there will be a cascade of absorption and re-emission.
Hence, whereas the planet is heated at the surface, it’s main heat loss takes place from a height about 5.5 km above the ground, where most of the radiation is free to escape out to space. The optical depth dictates how deep into the planet’s atmosphere the origin is for most of the planet’s infra-red light (the main planetary heat loss) that can be seen from space. Furthermore, it is the temperature at this level that dictates the magnitude of the heat loss (Planck’s law), and the vertical temperature change (lapse rate) is of course necessary for a GHE. The temperature at this level is the emission temperature, not to be confused by the surface temperature.
We know that the optical depth is affected by CO2 – in fact, this fact is the basis for measuring CO2 concentrations with infra-red gas analysers. Molecules composed of three or more atoms tend to act as greenhouse gases because they can possess energy in terms of rotation and vibrations which can be associated with the energy of photons at the infra-red range. This can be explained by theory and be demonstrated in lab experiments. Other effects are present too, such as pressure and Doppler broadening, however, these are secondary effects in this story.
(iv) The relationship between temperature and altitude
There is a well-known relationship between temperature and height in the troposphere, known as the ‘lapse rate‘ (the temperature decreases with height at a rate -6K/km). The relationship between temperature and altitude can also be seen in the standard atmosphere. The lapse rate can be derived from theory for any atmosphere that is the hydrostatically stable condition with maximum vertical temperature gradient, but it is also well-known within meteorology. Thus, given the height and value of the emission temperature, we can get a simple estimate for the surface temperature: 255K + 5.5km * 6K/km = 288K (=15oC; close to the global mean estimated from observations given by NCDC of ~14oC).
Enhanced greenhouse effect
The term known as the ‘enhanced greenhouse effect’ describes a situation where the atmosphere’s becomes less transparent to infra-red light (reducedincreased optical depth), and that the heat loss must take place at higher levels. Moreover, an observer in space cannot see the infra-red light from as deep levels as before because the atmosphere has become more opaque.
The effect of heightened level of heat loss on the surface temperature is illustrated in Figure 4, where the emission temperature and lapse rate are given if we assume an energy balance and a hydrostatically stable atmosphere on average (a generally hydrostatically unstable atmosphere would be bad news).
Hence, a reducedincreased optical depth explains why atmospheres are not easily ‘saturated‘ and why planets such as Venus have surface temperatures that are substantially higher than the emission temperature. Planets with a thin atmosphere and insignificant greenhouse effect, on the other hand, have a surface temperature that is close theto the estimates from the planetary energy balance model (Figure 3).
Feedback processes
The way the atmosphere reacts to changes in the optical depth is more complicated, due to a number of different feedback mechanisms taking place. But to get a simple overview, it is useful to keep in mind that the optical depth is sensitive to how much water vapour (humidity) there is in the air, and that the lapse rate is sensitive to the composition of the atmosphere (i.e. humidity). Furthermore, the albedo A is affected by clouds, snow, ice, and vegetation, all of which affect the way the earth receives energy from the sun.
In our simple picture, feedback processes affect changes in the height of the level where most heat loss takes place, the slope of the lapse rate, and heating at the surface (and hence the emission temperature).
So why is the upper atmosphere cooled then?
The upper atmosphere, comprising the stratosphere and mesosphere, is expected to cool during an AGW, as shown by the GCMs. So what is happening there? This is when the picture becomes more complicated.
Since CO2 mostly absorbs/re-emits infra-red light at around 14 microns, an increased concentration in the troposphere will reduce the upward infra-red radiation at this band. The total energy is roughly constant, but it is made up from increased emissions at other bands because it’s warmer. There is less absorption by CO2 of upwelling infra-red light above the troposphere, but increased emission as a function of increased concentrations. Thus there is a cooling.
Controversy?
Can this picture be falsified, e.g. if other factors were to play a role too? For instance, can this situation be altered by changes in the sun?
Changes in the sun can of course affect the amount of energy received by the earth through changes in its output, variations in the intensity of UV-light, or perhaps even clouds through galactic cosmic rays. But it’s hard to see any systematic long-term trend in the level of solar activity over the last 50 years, and it is difficult to see how solar activity may have an effect while other factors, such as GHGs, don’t. Gavin and I recently published a study on the response to both solar activity and GHGs, and found similar magnitude for both forcings in both observations and the GISS GCM.
There have been claims of negative feedbacks, such as the “iris effect“. One would expect negative feedbacks in general to dampen the response to most forcings, unless they involve a particular process that is active for a particular forcing. In other word, why would a negative feedback act for GHGs but not for solar forcing? Many feedbacks, such as changes in atmospheric moisture, cloudiness, and atmospheric circulation should be similar for most forcings.
Another question is why we do see a global warming trend if the negative feedbacks were most important (Figure 5). Negative feedbacks usually imply quiet conditions in a complex system, whereas positive feedbacks tend to lead to instabilities, often manifested as internal and spontaneous oscillations (see Figure 5). It is reasonable to expect the feedback processes to affect natural variations as well as forced changes such as an enhanced GHE, orbital changes, volcanoes, or changes in the sun.
The point about negative feedback also brings up another interesting issue: Negative feedbacks usually act to restore a system to a particular zero-level state. What would the zero-state be for our climate? No greenhouse effect or some preferred level of greenhouse warming? There is already a natural GHE that, together with other atmospheric effects, can account for about 32oC higher global mean surface temperature. What makes this state so special, and can we explain the present natural GHE in the presence of negative feedbacks (consider starting from a state with no GHE)?
Hence, claims of negative feedback is controversial because all these tough questions then need to be addressed. We can write down a simple recipe for the GHE, but it is indeed challenging to reconcile a presence of a negative feedback with our observations, or explain the current observed global warming in any other terms.
Patrick027,
Uh, I think you are wasting your time on Mr. Dodds. He is either a brilliant satirist or a loon. His name links to a paper purporting to show that gravity is responsible for climate change.
John Pearson, Lynn…
It is worth keeping in mind that radiative transfer encompasses a variety of different “regimes” for which different impacts are important. For instance, scattering by particles is negligible in the limit of small particle sizes and large wavelengths, but not so in various other scenarios. With regard to “logarithmic” arguments for GHG absorption, many of the popular talking points concerning how the greenhouse effect works is quite Earth-centric and may not apply in the same way to different atmospheric regimes.
For instance, the notion that diatomic molecules like H2 or N2 do not behave like greenhouse gases is not at all the case in general, despite being true enough for Earth. That scattering of infrared radiation is very small on Earth may not be the case on early Mars where you could get condensation by CO2 and CO2 clouds. Similarly, the logarithmic nature of the radiative forcing does have a theoretical basis, but strictly speaking, is only a good approximation that is valid for a relatively narrow range of CO2 concentrations (although the range is broad enough to encompass what you’d expect to see for our present day climate change). In the limit of very low CO2 concentration as well as in very high amounts (~0.2 bars of CO2 for instance when many weaker absorption features that are unimportant now start to become vital) the log curve is no longer valid. CO2 also becomes a more effective greenhouse gas at higher atmospheric pressures (even if super-imposed upon several more bars of a non-greenhouse gas like N2 would generate a much stronger GHE by increasing absorption away from line centers). Line-by-line type radiative transfer calculations used to find a forcing for a certain fractional change in CO2 (e.g., the Myhre et al 1998 paper) cannot be applied to conditions like Venus or ancient Earth. Various parametrizations for line and continuum absorption by CO2 yield similar results in present-like atmospheres, but differ substantially in CO2-rich atmospheres in the past, and at the present day it is not possible to obtain quantitatively confident answers with the usage using current models to examine such climates (e.g., Halevy et al., 2009, JGR).
Please forgive if I’m repeating something someone else said.
I’m getting the impression that the general public is 10-20 years behind the basic understanding of the researchers. I say that because I like to think I’m pretty sharp, and it has taken me some years to get to the point where I think I have a pretty good understanding. Another reason I say that is because I’m answering a lot of yes-but challenges, with, true-but-that-is-already-factored-in answers.
Q:”It’s the sun.”
A:”The sun isn’t changing and, if you look, it’s the outbound flow of energy that originally came from the sun that we’re talking about. Yeah, we know the sun warms the earth.”
Q:”More clouds.”
A:”Well maybe, but also more water vapor. Else, what are the more clouds made from?”
The above is a good explanation. However, I would not assume the public does a good job of keeping things in perspective, or even that they understand what K means. It would be good to explain that the energy coming in from the sun and re-emitted by the earth is orders of magnitude larger than any other energy exchange the earth is involved in. It should not be so hard to accept that doubling the concentration of a gas that interacts with earth’s radiative output (which is orders of magnitude larger than any other energy loss), over time and with feedbacks included, can change change the surface temperature by about 1%. Not a lot of the general public understand just how little change, on an absolute scale, is being predicted. (Or how that little change can affect them in large ways for that matter, but first work on getting them to accept that it will get warmer. (And more acidic, but that is another battle.)) That might not be terribly precise, but it’s in the right ballpark and it keeps things simple.
Minor grammar error at the end:
“claims of negative feedback is controversial”
should be
“claims … are controversial”
Re my 246 Re 238 John E. Pearson (and/re Lynn Vincentnathan)
You will occasionally hear people claim that Beer’s law is somehow responsible for the logarithmic dependence but this is nonsense.
So true. At any particular frequency (wavelength), Beer’s law does allow and call for eventual saturation in some conditions, which would not be logarithmic but rather asymptotic, and would occur when, at the point considered, photons reaching that point are being emitted from places all at the same temperature as at the point considered.
Swap ‘Beer’s law’ for ‘Schwarzchild’s equation’.
Beers law: transmission of a beam of radiation decays exponentially over optical thickness (A flux distributed over solid angle decays as a sum of exponentials; if there is scattering it can get complicated).
Including emission along a path (Schwarzchild’s equation), a flux will approach saturation as the optical thickness becomes large over scales where the temperature variation is small; at smaller optical thicknesses, the temperature distribution may vary and larger temperature variations make the nonlinearity of the Planck function important, but over short distances, the temperature variation can be approximated as linear and the associated Planck function values can be approximated as linearly proportional to distance for small temperature changes, so the flux will approach an asymptotic value as a hyperbolic function (the difference between the flux and the saturation value of the flux will be proportional to 1/optical thickness per unit distance (assuming isotropic optical properties (or even somewhat anisotropic properties), it will have that proportionality for all directions and thus for the whole flux across an area).
The net flux goes to zero when both fluxes in opposite directions saturate, except where the net flux is across a temperature discontinuity; the top of the atmosphere can have such a discontinuity in effect.
Re 253 Chris G – sounds right to me.
Re 244 Iskandar – as stated several times in several different ways, the gist is this: Yes, space is not a complete vacuum and mass can flow in or out of the atmosphere, carrying energy. But the process is just not big enough to matter, except to long-term chemical evolution (very slow H escape) and things like aurora; the energy is too small to make a significant difference to climate. (PS I’m not sure about proportionalities on this point but at least some portion of what enters the atmosphere is matter that left the same atmosphere and vice versa – aside from gravity, charged particles can be trapped by the magnetosphere, which has a tendency to deflect charged particles coming from space; the particles within the magnetosphere can gain energy from electromagnetic interactions, but see previous statement.)
172
Patrick 027 says:
6 July 2010 at 11:35 PM
“Note that it is possible, hypothetically, to introduce so much optical thickness that the tropopause level or any level besides the very top of the atmosphere becomes saturated (zero net LW flux); ”
Is it? Optical thickness depends on density; does it not? The density of an atmosphere is roughly a negative exponential; it declines very rapidly with altitude at first, but as the altitude increases, the rate of decline decreases. The rate of decline decreases so much that it is a bit of a judgment call where the atmosphere ends and space begins.
Even if you had a pure CO2 atmosphere that had liquid CO2 at the bottom, there would still be a large region below what you would consider space that was not saturated optically. You would definitely have some greenhouse effect. If you doubled the mass of the atmosphere, the region below what you called space and above what you called optical saturation would get wider, and you’d have more greenhouse effect.
OK, we aren’t doubling the atmosphere. However, we are converting carbon in a liquid or solid state to CO2 in a gas state and dumping that into the air. (Effectively trading O2 for CO2.) The number of moles (mass) of CO2 in the atmosphere is increasing and the CO2 molecules will interact with the IR photons regardless of what else is going on in the atmosphere.
Uh, bad example, if you had enough mass above to liquify CO2 at the bottom, probably the added CO2 would just be more liquid on the bottom. So, let’s run it the other way. Start with just enough to get liquid at the bottom and half it. The region between space and saturation will be less, and you’ll have less GHE.
I’m not doing a good job here. What I’m trying to get around to is that a lot of people treat the top of the atmosphere as a constant. It isn’t; in particular, it is not in terms of partial pressure (and hence density) of CO2.
Rasmus in #166,
I thought it must be something like that. Thanks again especially for fig. 4. That is a nice way to present the idea.
[Response: My mistake, and since I’m away on holiday, it took a while to correct – my Internet connections are not as frequent as when I’m working. Anyway, thanks a lot! -rasmus]
Re 228 Jacob –
Let T’ be the temperature departure from a reference equilibrium and For’ be an imposed forcing departure from a reference equilibrium, and let F’ be the feedback** (** including the Planck response) in terms of an increase in net outgoing radiation (from a reference equilibrium), where F’ = G*T’, so that G is positive if the feedback (including the Planck response) is negative (which is what we expect). Let C be the heat capacity (per unit area).
The heating rate = the radiative imbalance = For’-F’
C*dT’/dt = For’-F’ = For’-G*T’
dT’/dt = (For’-G*T’)/C
At equilibrium, T’ is constant and equal to Teq’, so G*Teq’ = For’, thus Teq’ = For’/G, so that equilibrium climate sensitivity = 1/G (perhaps G could be called the climate ‘insensitivity’).
dT’/dt = -G*(T’-Teq’)/C
C is not constant for the dT’/dt equation to apply because heat penetrates through different parts of the climate system (different depths of the ocean in particular) over different time scales (also, if T’ is supposed to be at some reference location or the global average at some vertical level, T’ at other locations will vary; C will have to be an effective C value, the heat per unit change in the T’ at the location(s) where T’ occurs)
But if we held C constant, then
————
for a fixed Teq’:
dT’/dt = d(T’-Teq’)/dt = -G*(T’-Teq’)/C
T’-Teq’ = (T’0-Teq’0)*exp(-G/C), where T’0 and Teq’0 are values at time 0.
Thus the time scale for equilibration is proportional to the climate sensitivity * heat capacity.
———-
If Teq’ = Teqamp*cos(w*t)
then
T’ = Tamp*cos(w*t-phaselag) = a*cos(w*t) + b*sin(w*t)
where
Tamp = (a^2+b^2)^(1/2)
tan(phaselag) = b/a
dT’/dt = -w*a*sin(w*t) + w*b*cos(w*t)
= -G*(T’-Teq’)/C
= -G*[a*cos(w*t) + b*sin(w*t) – Teqamp*cos(w*t)]/C
therefore
w*a = b*G/C and w*b = (Teqamp-a)*G/C
b = (Teqamp-a)*G/C
b/a = w*C/G
(Teqamp/a – 1)*G/C = w*C/G
Teqamp/a = w*(C/G)^2 + 1
a = Teqamp/[w*(C/G)^2 + 1]
and
b = a*w*C/G
tan(phaselag) = w*C/G
Tamp
= (a^2+b^2)^1/2
= Teqamp/[w*(C/G)^2 + 1] * [1 + (w*C/G)^2]^(1/2)
Tamp/Teqamp = [1 + (w*C/G)^2]^(1/2) / [1 + w*(C/G)^2]
I thought I could simplify that farther but I forgot what I did the last time…hopefully the algebra is correct.
Correction: solution for constant Teq’ and C:
T’-Teq’ = (T’0-Teq’0)*exp(-G/C * t)
#253
The public is more like 30-60 years behind I’d say. With hindsight and as far as the big picture is concerned, the consensual stuff published the 80s was already pretty good.
#264,
I think your estimate is better than my first one.
The point is that the researchers have already been through something like
A) What effect will more CO2 have?
Ah, warming.
B) How much warming are we seeing now?
Whatever the increase is, about 0.7 K.
C) How much warming can we expect from BAU?
Likely in the range of 2 – 4.5 K per doubling.
D) What effects will, say 3.5 K, have?
Uh, Houston, we have a problem.
E) How would we prevent this?
Stop producing CO2 (and other GHGs).
So, a lot of times, the focus of the argument is around points D and E, because for them, A-C are old news, while a lot of the public is still stuck at A. If you are stuck at A, arguments concerning B-E don’t mean anything to you.
Incidentally, I get the impression that many people consider the answer to E to be a policy decision and take offense at scientists suggesting policy. It’s not policy; it’s a physical answer to a physical problem. Policy is how to go about reducing the use of fossil fuels which are producing the extra CO2. Personally, I like the idea of taxing fuels at their source. It was my favorite idea even before I read Jim Hansen’s book, but I’m not expecting that to happen.
Rasmus,
I think you’d achieve a greater comprehension from your audience if you used the inverse-square law instead of Gauss’ theorem. Even architects are familiar with the law in terms of inverse-square (for lighting). Gauss might be more precise, but I think it is a foreign concept to more people than inverse-square.
Also, if you have a section for ‘(iv) The relationship between temperature and altitude’, IMHO, you should also have a section for the relationship between density and altitude, because you are previously talking about optical absorption, which, the rate of which I believe is more related to the density of the gas than to its temperature.
Re Chris G – I often picture the situation in mass coordinates – how much mass is above a given level. The top of the atmosphere (TOA) would be at 0 to a first approximation…
(and TOA would actually fill the space surrounding the Earth – though given the spherical geometry, W/m2 would have to be expressed as m2 at a reference radius or else W/m2 will drop as the inverse square; most of the mass of the atmosphere is within such a narrow range of radii that we can approximate the global area as constant with height (and ignore the apparent upward curvature of straight lines) (PS increasing index of refraction going downward would tend to counteract both effects by bending rays downward and increasing blackbody intensities and magnification of lower levels as they appear from above – and to a first approximation we can ignore that as well. etc… Relativistic effects, etc.) – so we can approximate TOA as extending downward to the same narrow range of radii and then just consider the fluxes at the base of TOA (refering to TOA specifically as the base of that region of zero mass) to get around the spherical geometry)
About increasing optical thickness per unit mass path (via changes in composition or imposed conditions) –
About hypothetically doing that until all levels are saturated except at TOA:
Of course, there are realistic limits for realistic materials for how much optical thickness could be packed into a given mass path; I am refering the a limit wherein this approaches infinity – recognizing the nonzero mass at TOA, optical thickness would be held at finite or zero values at/above TOA.
Approaching that limit, the net flux goes to zero except at TOA (and above). There always has to be a net flux at TOA (for nonzero temperature and assuming optical thickness is not entirely from scattering/reflection), so the process concentrates the emission to space into an ever thinner region next to TOA. Upward concentration of that source of flux to space would, in isolation, have a cooling effect within the upper portion of that region and a warming effect just below that.
Re my 245 The only way such kinetic energy of these objects is converted to heat within or at the surface of such an object – I forgot to include the raising of tides (in a process that is not completely elastic/inviscid/adiabatic) – the relative smallness of that for most familiar objects of course having already been covered…
It is all very well to argue the science, but what you have here is a question of leadership. Most of the people who even bother to look at your “simple” explanation of the Greenhouse Effect (instead of getting it third or fourth hand, from some pundit) will not have the background to vett your science. So, you are asking them listen to you based on the simple fact that you are “scientists,” and to take action on the basis of what you believe will happen (because, despite your best efforts, you are not yet gods, and cannot actually know the future). And you aren’t just asking them to change the brand of shampoo they’re using. You’re asking them to make serious changes in the way they do practically everything. Would it be surprising if they were to ask you what you are doing to reduce your carbon footprint?
You are asking people to be lead by what you have to say. But, you don’t get to be a leader just because you say “follow me.” You don’t get to be a leader just because you are right. You get to be a leader by leading, by going first. If you want people to believe what you say, show them that you have the courage of your convictions by taking action, the kind of action you are asking them to take.
Gordon says, “because, despite your best efforts, you are not yet gods, and cannot actually know the future”
OK. I’m sorry, but this statement betrays an ignorance so profound that I can only conclude the poster has missed not just the 21st century, but the 20th and 19th centuries as well. It requires nothing godlike to predict the future when it comes to physical systems. It requires understanding the science sufficiently and playing the fricking odds. This is not divination. This is science that has largely been known for over a century!
And I’m sorry you are going to have to change your life, but your life is going to change one way or another. Oil is running out and we don’t yet have anything to replace it. That is a reality quite independent of climate change. All climate change does is make it more imperative to develop a sustainable energy economy sooner rather than later. It means we don’t have the added luxury of burning up all the coal as well as all the oil.
So, Gordon, get in your time machine, set it 200 years ahead and join us in the 21st century.
Patrick,
I’m not sure I’m following what your definition of the TOA is. It sounds like you are saying that TOA is where most of the mass is and that it is at a fixed height.
For instance, you wrote, “Of course, there are realistic limits for realistic materials for how much optical thickness could be packed into a given mass path;”.
Yes, but the upper part of the atmosphere will remain thin by virtue of the fact that if you add more gas, the TOA goes to a higher altitude.
What I’m saying is that TOA, as far as radiative energy is concerned, for CO2 or other IR absorbing gas, is effectively the altitude where the chance that a photon will be absorbed, and emitted back in a direction that will lead it to being absorbed again by a molecule in the atmosphere, becomes negligible.
The two heights are related, but they are not the same. Most importantly, the altitude of the TOA from a radiative energy standpoint is concerned, is not constant.
It goes back to #1.
The tropopause is where the energy being absorbed from the sun is approximately equal to the energy being absorbed from the earth. It is not fixed or constant either and varies with latitude and season.
#269,
We’ve entered into the commons problem. For instance, it would be better for the planet if I took my family off the grid. But it would put my children at a distinct disadvantage because my employment requires that I be on the grid, and my children’s college prospects depend a lot on me being employed.
It’ll take legislation to give people the feeling that the sacrifices are being made fairly and across the board, but no one wants to go first – least of all the fossil fuel industry.
Gordon,
The RC Team has taken action by spending countless hours writing and moderating this world-class blog so that people like you and me can become better educated. The hope is that you and I can then carry this message to the masses. The Team is very busy with their own research and unfortunately, defending themselves against ridiculous accusations, and yet they persist. The Team are our “heroes” and we cannot ask them to be superhuman.
Having said that, I agree 100% that scientists need to model Dr. James Hansen and others like him and begin to marry science and politics. Science alone had not been able to convince policymakers in the US, Canada, Auistralia, and others to take immediate, drastic action to curb and then reduce emissions.
The latest Climate Interactive Scoreboard shows us that 4C is likely even in the unlikely event that countries actually do what they propose. 4C is catastrophic and yet there is still political hemming and hawing.
Scientists need to start forcing themselves into the media limelight. People still respect scientists and if, as a large coordinated group, they keep showing what is likely to happen in a 3 – 5C warmer world, people would take notice and demand action.
Stepping down now….
Scott A. Mandia, Professor of Physical Sciences
Selden, NY
Global Warming: Man or Myth?
My Global Warming Blog
Twitter: AGW_Prof
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Chris G, and the optical depth discussion…
The “TOA” is, strictly speaking, at pressure = 0, and of course above the tropopause. Radiative forcing at the tropopause and TOA are only similar in that regions above the tropopause are typically optically thin enough to not matter much for the net radiative budget (minus the strong UV depletion in the stratosphere). It’s not really the top of the whole atmosphere that shifts to higher altitudes, but the region of bulk emission to space which we can locate at one unit optical depth below the optical depth of the whole atmosphere (looking down from space). The definition of optical depth TAU is the integral from z1 to z2 of k*rho*dz where k is an absorption co-efficient with dimensions of area per unit mass, and rho is the density of the absorber. Thus one can make the optical depth smaller by moving two fixed altitude levels ever more close together until z1=z2.
Looking down from space, a sensor will see emission coming from all levels of the atmosphere depending upon the opacity in that wavelength region. Regions around 10-12 um in the atmosphere window can originate from the surface and low atmosphere and make its way to space, while in the 15 um band even the stratosphere is opaque. The bulk of emission comes from the TAU=1 level which itself is the “radiating level” that balances the absorbed incoming solar radiation. Consequently, the transmission to space is the product of the transmissivity of all present absorbers and falls off with increasing atmospheric optical depth like t= exp(-TAU). Regions below TAU=1 tend to have radiation absorbed before its exit to space where the opacity is high, and regions above are thin enough to let radiation escape to space. The physical altitude of TAU=1 is what shifts to higher altitudes when you increase CO2, but the temperature here (say, T_rad) must stay such as to balance So*(1-albedo)/4 allowing one to define the surface temperature T(s) at the atmospheric pressure p_s to be T(s) = (T_rad)*(p_rad/p_s)^(-.286) (assuming the adiabat of a dry atmosphere). Thus, the ratio p_rad/p_s is close to unity in the optically thin limit and very small with a strong greenhouse effect.
Well, Ray, you said it yourself, “playing the odds.” That means, your best estimate of what is likely to happen…not will happen. God (if he/she/it exists) gets to know what will happen. Us mere mortals have to “play the odds.” And, the thing about odds is, each of us, individually, gets to decide just how favorable (or unfavorable) the odds are before we bet. You want folks to reduce their carbon footprint because you say the odds are 99% that if they don’t we’re screwed. But, Bob figures he won’t really have to do anything until the odds are 99.9%. So…
And, Scott… So, if I understand you, what you want everybody else to do is to spend countless hours moderating world class blogs so people can be better educated. You don’t want them to drive their cars less, or turn down the air conditioning in the summer and keep their houses cooler in the winter. You don’t want them to get their food locally, so it isn’t costing thousands of pounds of CO2 per ton-mile to have it shipped across the country. In fact, you don’t want them to do anything that would actually, in this moment, reduce the rate at which CO2 is being pumped into the atmosphere, you just want them to do some good blogging. That and forcing themselves into the media limelight. Well, shoot, that is what I call leadership.
I have to apologize. It is not my intention to get into a pissing match. My point was, and is, about the effectiveness of the efforts of the people behind this blog, and about the nature of leadership. I still hold that it is not about being right (Ray), nor about media attention (Scott). I believe that to be effective with the larger society, it is not enough to be right nor to be seen on television. You have to show that you, personally, individually and collectively, are willing to do, now, the things you are telling everyone else they will have to do tomorrow. Sure, people will call you nuts, until their back yard is eaten away by the rising sea, or their favorite foods become too expensive, or someone they know dies in a heat wave.
Gordon, we should all be energy conservative and we should all practice and preach it. However, doing so is a dent in the problem if we do not as nations greatly reduce our emissions. My point is that the best way to get people and nations on board is to be the squeaky wheel politically.
Re 269 Gordon You’re asking them to make serious changes in the way they do practically everything. Would it be surprising if they were to ask you what you are doing to reduce your carbon footprint?
Generally speaking, ‘we’ aren’t asking ‘you’ to do anything that we won’t also have to do (a policy like a tax on fossil C emissions wouldn’t somehow miss the scientists and environmentalists).
You don’t get to be a leader just because you are right. You get to be a leader by leading, by going first.
There is something to that, I guess. It’s not really fair, though – it’s not that I’m complaining, but I hope you realize that it’s not fair; you are asking ‘us’ to be the heroes, to make greater sacrifices. But politically, that may be how it has to be. So… what have Bill Nye and Ed Begley Jr, and some number of other famous people and a number I’ve wouldn’t have heard of … what have they been up to lately? Aside from which, there are things that a small number of pioneering individuals can’t (with some exceptions) do very well, such as speed up the development of affordable alternatives via their own buying decisions. There are some things that are easier for individuals to do when the whole of society shifts, such as buying an energy efficient home, which should become easier when more of those are being built, which will be more likely if more people want to buy them. To a great extent, we can’t go first, at least in an efficient way, with everything that we want to do because it requires the economy to move. Even assuming otherwise ideal market behavior, the economy now has a glitch – there is this big externality, and it requires public policy to correct it.
If you want people to believe what you say, show them that you have the courage of your convictions by taking action, the kind of action you are asking them to take.
Okay, but then ‘we’ run the risk of getting labelled as activists who are already invested in the idea and thus can’t be trusted. Better that than be labelled as hypocrites, though, because at least ‘we’d’ be doing something. But again, it isn’t truly hypocritical to demand public policy changes while not doing anything as an individual, because in that case you’re not asking anything of others that you aren’t asking of yourself (unless you’re planning to break the law and be lucky enough to get away with it).
PS A week or two (?) ago I saw Hannity (ick) talking to someone with environmentalist credentials/reputation, and the issue of flying on a private jet came up. Hannity ridiculed the idea of emissions offsets as something like cheating on your spouse and making up for it with some expensive gift. This betrays an ignorance of the concept. What matters to climate is net emissions. A carbon offset would be like having the opportunity to cheat and then deciding not to do it. It isn’t like an indulgence at all. Of course there is the possibility that an offset might be measured incorrectly or perhaps fraudulent, but that doesn’t undermine the concept.
Gordon, Let us review the options open to us. First, what is NOT on the menu: Business as usual. The days of the petroleum-based economy are scarce. Reliance on petroleum will take us down a path of increasing energy insecurity where we seek oil in ever more difficult and risky locations (e.g. sucking it through a mile-long straw in the ocean) until we can no longer meet demand not just for oil but also for food. Not a good option.
Now what we can do is
1)develop a sustainable energy economy
2)a)burn all the coal and other fossil fuels, buying us, if we make optimistic assumptions, perhaps a century of ever more elaborate schemes to meet energy needs with less and less suitable sources
b)THEN in a severely degraded environment
And this is not even taking into account the effect on climate. Option 2 raises CO2 above 1000 ppmv and results in catastrophic climate change.
This is NOT divination. This is science, and the choice science gives us is simple. Either follow what the science tells us, which we’re 95% confident is the right path, or go against the science 180 degrees and bet the future of humanity on a 20:1 longshot. Feel lucky?
@29 re Hawking – I agree with the earlier comments saying that the post, good as it it, is way too technical for Joe Public.
The success of Hawking’s book does not disprove that view. For one thing, Hawking listened when his publisher told him that ‘each equation you include will halve the sales of the book’ (OWTTE) and included only the one (unavoidable) equation in his whole book. It probably helped that Hawking, by his own account (in ‘Black Holes and Baby Universes’) thinks in pictures, not in equations.
And sales of 9 million copies, worldwide, over a couple of decades, still represent quite a small minority readership – on the order of 0.5% of the Western world – even assuming that every buyer finished the book. Just to give a personal slant on all that: most of my friends are tertiary-educated non-scientists, as I am, and I think only one of us who started the book actually finished it.
I’m sorry, rasmus, but an explanation which will be meaningful to the people who still don’t understand the science needs to aim a lot lower. Visualising yourself telling it to truckies in a roadhouse over a pie and chips may be a useful mental exercise ;->
Re 271 Chris G
my response in addition to 275 Chris Colose’s response:
It sounds like you are saying that TOA is where most of the mass is and that it is at a fixed height.
No. TOA is not at a fixed height in geometric height (z) or geopotential height (Z), or geopotential (Φ); it is approximately at a fixed pressure (p) at p = 0; it is also approximately at a fixed sigma level at σ = 0. If optical thickness τ is measured downward as a coordinate, TOA would be approximately at τ = 0.
That wasn’t all really necessary but I wanted to highlight the fact that there are several different coordinate systems, and the physics of the atmosphere (radiative, mechanical, etc.) are sometimes more conveniently expressed and evaluated in one or another coordinate system.
dΦ = g*dz
Z = Φ/g0, where g0 = 9.80665 m/s2 (Holton, “An Introduction to Dynamic Meteorology”, 1992, p.20)
dp = -ρ*g*dz
σ = p/psurf, where psurf is the pressure at the underlying surface at a particular time (the thickness of the whole atmosphere in σ is always 1 everywhere at all times)
mass path, as measured downward from TOA (approx.), would be equal to p/g if g were constant (good approximation for most of the mass of the atmosphere)
d(mass path) = -ρ*dz = dp/g
on the other hand, one could use a mass coordinate that refers to how much mass lies above a certain level over the whole globe; that would be proportional to mass path except for the increase in global area with increasing radius (a minor issue for most of the mass of the atmosphere).
θ = potential temperature, which is conserved for dry adiabatic processes and is a useful vertical coordinate for examining various fluid mechanical processes (like Rossby waves) when the atmospheric lapse rate is stable (for dry convection) (which is generally true on a large scale away from the boundary layer).
measuring τ downward along a vertical path from TOA (approx.), τ would be proportional to mass path for a single frequency and constant mixing ratios (of radiatively important matter), except for the varying effects of p and T on line broadenning and line strength.
———
The tropopause is where the energy being absorbed from the sun is approximately equal to the energy being absorbed from the earth. It is not fixed or constant either and varies with latitude and season.
In the approximation of zero non-radiative vertical heat fluxes above the tropopause, net upward LW flux = net downward SW flux (equal to all solar heating below) at each vertical level (in the global time average for an equilibrium climate state) at and above the tropopause (for global averaging, the ‘vertical levels’ can just be closed surfaces around the globe that everywhere lie above or at the tropopause; the flux would then be through those surfaces, which wouldn’t be precisely horizontal but generally approximately horizontal).
Ray, as it happens, I agree with you about our options. And, in fact, I don’t feel lucky at all. The way it looks to me, the most likly scenario is catastrophy…the lessons of history teach that many, many people have to suffer horrendously before serious change is implemented…and that change as often by fiat as by careful consideration. So, I’d like to see the goals of this blog succeed.
It is just this…I believe that what we are dealing with, at its root, is a deeply pshchological issue, a matter of the most basic elements of human motivations. Freud said we are all, at the root, motivated by sex. Otto Rank (at one time a protege of Freud), broke with his master and posited that we are, rather, motivated by the undeniable conflict between our sense of ourselves as “immortal souls,” and our realization that we exist by virtue of our all-too-mortal bodies, that we are desperate to believe that we will, somehow, live beyond our bodies, and that, in order to do so, we pursue “immortality projects,” that we invest in our activities the promise of eternal life. To tell people that this project we have been pursuing, this dream of “ever increasing quality of life/endlessly increasing consumption” is, instead, going to lead to our destruction is to tell them that the whole idea they have based their lives on is false.
So, Patric, yes, it is not fair. And, yes, I am saying you…somebody…many somebodies…are going to have to be heroes. That is what it takes to be a leader (as opposed to what it takes to get elected): a willingness to go first, to do what you know needs to be done, regardless of how stupid you look, regardless of how you will be labeled, regardless of how unfair it is. Is the preservation of our species worth it?
Rasmus in #261,
Yes, I recall edits getting made more quickly but that was a case when an RC contributer was not an author. Better to have the contributers control their own content in this case.
When explaining how this works, I usually try to get people to remember that they have experienced the lapse rate when they have climbed a hill and get them to understand that the lapse rate is suspended from a particular altitude. Then I point out that raising that altitude is like lifting the temperature profile over Death Valley and setting it at the valley edge. This seems to have helped some people.
If you’re talking about being right, it seems to me that scientists have a pretty good track record. That matters. Otherwise, I doubt that most people give a flying duck whether scientists go off the grid or not: It’s just not interesting theater– anymore than trying to understand the issues at a basic level (even though it only requires exercising enough attention to realize that scientists will go the extra mile to explain the complicated problems while deniers only exercise rhetorical tricks).
It is a problem in part, it seems to me, of reversing a spiral of lowered expectations. Turn on your TV and try to guess who is being targeted. Either the audience is swamped by the lowest common denominator, or programming is actively designed to dumb people down. Not good either way. While I agree that scientists have to expand their bag of tricks in order to reach people and grab their interest, nobody is well served by treating people like a compacted mass of dumbass sheep.
Gordon, I have a lot more faith in the predictive power of physics than I do in that of psychology. As such, I think it is in our interest to push as hard as we can toward a solution in the hopes that enough our our fellow homo sapiens wake up in time.
In actuality, the problem of denialism is mainly localized in a few nations–e.g. the US, USSR, Czech republic–where the blinkers of ideology get in the way of the citizens seeing the truth. That does not mean we are in the clear by any means, but it does belie the contention that human nature is the only problem. There are also a lot of people out there who get paid to make us believe comforting lies.
Former USSR?
Not sure I buy Gordon’s “concern” anyway. Sounds to me like a repackaged denialist talking point. I do not buy the assumption that scientists don’t practice what they preach or the implication that they are somehow hypocrites or that it even matters. I don’t even buy the notion that this is an efficacious talking point (except maybe among the very immature) or that the best way to offset it is for scientists to dance around to the tune of a bunch of wingnut noise in order to prove worthiness.
“Many feedbacks, such as changes in atmospheric moisture, cloudiness, and atmospheric circulation should be similar for most forcings.”
Why should they be?
Increased cloud cover will raise albedo and cause cooling at the surface through diminished insolation. Sure it also increases back radiation, but this doesn’t penetrate the ocean, 7/10’s of Earth’s surface.
This is the main reason for the re-convergance of the surface and tropospheric datasets since 1997.
Polite discussion please at
http://tallbloke.wordpress.com/2010/07/11/divergence-and-reconvergence-of-uah-and-hadcru/
Gordon, I have enough science background to trust the mainstream to be good enough vs. the denial side, which is close enough to every other denial campaign that I’ve followed that I am pretty sure there’s no substance to their case. You don’t have to be a climate scientist (physicist, or any of the other specialities) to figure this out. A competent journalist could figure this out. The pattern of the denial campaign is an absolutely classic Gish Gallop. You can even find the same suspects as in other campaigns like tobacco.
The big failure is not one of science, it’s one of journalism.
What can we do in practical terms? Write in to news media whenever they get the story wrong. Point out to them how naive they are being and hope you hit a nerve. Get it right on your own blog. Go into politics on a green ticket. That’s just a short list. But blaming the good people at RealClimate is a tad unfair. There’s just so much they can do.
Ray,
I agree but I still find that even those that trust the scientists about the human cause of climate change cannot get their heads around the potentially catastrophic consequences that await their grandchildren.
I think it is critical that we keep showing the public about the likely dangers ahead and we cannot pull any punches for fear of being wrong or too strong.
I am currently researching the impacts of climate change on various ecosystems and it is quite disturbing.
Scott A. Mandia, Professor of Physical Sciences
Selden, NY
Global Warming: Man or Myth?
My Global Warming Blog
Twitter: AGW_Prof
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Ray, I don’t claim that human nature is the only problem, rather that it is a LARGE problem that is not being addressed. And, Radge, I don’t deny the realities of global warming, I don’t assume that scientists (as a body) don’t practice what they preach, nor do I intend to imply that they are hypocrites. What I am saying is that real, useful, competent action on reducing greenhouse gas emmissions will require an intellectual and emotional movement of great proportions, and my observation is that such movements do not arrise without leaders and heroes.
Rog Tallbloke,
What it comes down to is that a Watt is a Watt is a Watt. It may make some difference WHERE said Watt is supplied, but since the climate system is pretty efficient at spreading energy, this is likely a second order effect. Don’t forget the skin effect for the oceans. It is a pretty efficient warming mechanism.
Gordon, the realities are changing. I heard recently that a Prius was now considered more of a chick magnet on campuses than a Porsche. Younger people seem to be more reality based than the old farts running things now. I only hope that we leave them enough options to save civilization.
Really, what is going on is not complicated. If an organism is incapable of perceiving reality as it is, that organism will not survive. If a species is composed overwhelmingly of such individuals, the species will decline and eventually become extinct. As I’ve said before, we may be working out the answer to the Fermi Paradox empirically.
Ray Ladbury,
Thanks for the response. I ran some calculations from the satellite altimetry to calculate the additional Watts/m^2 the ocean must have been recieving over the 92-03 period to account for the steric component of sea level rise. This came out at around 4W/m^2. If some of this was greenhouse forcing then a bit more must have been additional insolation due to diminished cloud cover. The tricky bit is working out the proportions. The ISCCP data, although imperfect, gives at least some numbers to play with. I have asked a few oceanologists about skin effect and downward mixing of energy from short and long wave radiation, but there seem to be as many opinions as there are oceanologists.
One thing I am pretty sure about is that the tendency for el nino to occur near solar minimum and la nina to occur near solar maximum, and the capability of the ocean to store solar radiation on decadal timescales has led to an underestimation of the solar forcing. Watts are watts but where they come from is as an important consideration as where they go.
Ray, I hope you are right. I’m an old fart myself, and don’t expect to live to see what could be the living-out of a worst case (or even bad case) scenario.
I have spent some time trying to find the simple truths hidden within the IPCC reports. (Perhaps there aren’t any simple truths there.) If I understand them, a reduction of 50-85% of CO2 emissions will be required to stabilize at year 2000 levels, which may be expected to produce a global average temperature rise of around 2C. And will this mean that methane will not be released from deep ocean methane hydrates? Will it mean that CO2 sequestered in permafrost will not be released? And what other unknowns are lurking?
The IPCC says that such reduction will require a reduction in global GDP. Are the citizens of the developing nations going to happily consent to the citizens of the US continuing to use ten times as much energy as, say, the Chinese? Or is the world going to demand that the citizens of the US step up and take responsibility for their past by reducing the US GDP by ten times more than everyone else? And are we going to be willing to do it?
You say “If an organizm is incapable of perceiving reality as it is…” And I have to quibble with you a bit here. Most organisms (all but one, I believe) do perceive reality “as it is.” Their inhereted response systems may be incapable of adjusting to new environmental realities, but they aren’t having any trouble with perception. It is only the human animal, with all his psychology, that is capable of perceiving reality falsely, that is capable of so thoroughly filtering the evidence of his senses.
How many Priuses will the US need in order to reduce our CO2 emissions by 85%?
Re 288,294 Rog Tallbloke
Relative to the entire depth, oceans are essentially both cooled and warmed from above, but within the upper layer of the ocean, it is often the case that the oceans are warmed from below and cooled from above. This is because solar radiation penetrates deeper into the ocean than LW radiation. (Evaporative cooling also takes place at the surface, and produces denser water via increased salinity, which can sink down. Addition of fresh water at the surface has the opposite effect. Winds (and tides and planckton) stir and mix the ocean and can force convection of heat downward.
Reducing the net LW cooling at the surface reduces the upward flow of heat to the surface, thus heating the ocean over the depth of the upper layer.
4 W/m2 seems way too high; the ocean heat content hasn’t been increasing that much (or am I getting my timescales mixed up?).
The change in solar insolation can be measured. A change in clouds (which must generally be in response to something) will change solar heating but that isn’t considered solar forcing.
Hey Dr. Benestad,
This article is a great start. As you suggested the Models tell us what may happen; but, not necessarily how it may happen. I would that we had more of the former then the later in the literature over the last 12 years; however, a start now is better then no start at all.
I said all of this to only request the team to consider addressing more “cause and effect” articles in relation to climate change. If as you note the GHE without anthropogenic inputs would be approximately 32 Deg C.; Given the amount of CO2 by natural process would be approximately 280ppm would suggest roughly 9 ppm of GHG would increase temperatures approximately 1 Deg. C.
The end result would suggest an increase of 105ppm of CO2 should cause an increase in temperature of roughly 12 Deg. C. Going further to add in other contributors such as more water vapor as a secondary effect of the increase in CO2 the temperature as a result of GHG should be even Higher. Given there could be hysteresis in the atmospheric and oceanic systems it would appear that the march towards inclement temperatures should be ever onward and dramatically higher each year.
The problem is we do not appear to be measuring an change in any of the documented contributors to Climate Change; that seems to demonstrate the a rate of change similar to the rise in CO2. The expectation is that there should be a proportional change in the contributing factors.
Also at issue is the relative balance between anthropogenic emissions and the ability of the Earth’s natural systems to absorb most of the annual emitted fossil fueled CO2 up through the 1950’s.
Were that the case then the true difference of temperature change between the natural level of say 240 ppm and the 330ppm of the 1950’s would likely have to of been sourced somewhere other then fossil fuel emissions.
Hence, a little clarification on the total processes would be very welcome. Then to go a bit further it would be even more useful if we could examine how the GHG warming was eliciting the warming of the surface temperature. It is clear that it is unlikely due to direct radiation. By the same token we do not seem to have sufficient insights into how the warming is manifest. I was hoping that the team would consider expanding on your initial article here to offer the laymen among us more insight into the current knowledge base.
My Thanx!
Dave Cooke
Re Gordon @295: “How many Priuses will the US need in order to reduce our CO2 emissions by 85%?”
Enough to tide us over until plug-ins and full electrics arrive in the market in force.
Think of the Prius not as a solution, but as a highly visible paver of the way. A necessary real-world test bed of electric drive systems, and a rolling billboard that we have to try something else.
Hi Patrick,
thanks for the insight on salinity and cooling from above. The ocean is a complicated body of water for sure. I too was surprised at my 4W/m^2 figure, but if the good folk at Colorado have done the job correctly (and I see no reason to think they haven’t) then that’s how the sums work out if the IPCC estimate of the percentage due to thermal expansion is correct. There may be some kind of issue with the splice between XBT and ARGO data to consider as well. I did some checking, and it seems to be more in line with the figures which were in Levitus et al 2000 (after correction for his maths error). The more recent figures in Levitus et al 2007 and after seem to have been revised downwards, and I’m not sure why. Perhaps he could tell us, though he didn’t answer my emails.
Whether or not clouds changing the level of insolation at the surface is regarded as a solar forcing or not probably depends on your assumptions about what is changing cloud albedo levels.
I think there are two ways round to see changes in cloud albedo levels. Either as a response to internal change (feedback to greenhouse radiative forcing) or as a response to external change (solar activity/GCR level feedback). In the second case it is a forcing as far as the internal climate system is concerned as I see it.
Either way it would seem that quite small changes in cloud cover percentage have quite large effects on the amount of energy entering the ocean.
Hi Rasmus,
If I was to turn this article into an animated cartoon would you be happy to provide input.
If so. I will work out a storyboard with pen and paper, annotate it, then scan and send it to you, where you can comment.
I will then make corrections until we are both happy, before I put it into Adobe Flash and turn it into a movie.
Cheers
Phil