The greenhouse effect is real. If there were no greenhouse gases in the atmosphere, earth would be a cold place. Compare Mars versus Venus – Mars has minimal greenhouse gas molecules in its’ atmosphere due to low atmospheric pressure, and is cold. By contrast, Venus has a lot of greenhouse gas molecules in its’ atmosphere, and is very hot. Temperature increases as greenhouse gas concentration increases. These are undisputed facts.
outgoing radiation = incoming radiation – changes in oceanic heat content
The image below from AER Research explains the radiative balance.
http://www.aer.com/scienceResearch/rc/rc.html
About 30% of the incoming shortwave radiation (SW) is reflected by clouds and from the earth’s surface. 20% is absorbed by clouds and re-emitted back into space as longwave (LW) radiation. The other 50% reaches the earth’s surface and warms us. All of that 50% eventually makes it back out into space as LW radiation, through intermediate processes of convection, conduction or radiation. As greenhouse gas concentration increases, the total number of collisions with GHG molecules increases. This makes it more difficult for LW radiation to escape. In order to maintain equilibrium, the temperature has to increase. Higher temperatures mean higher energies, which in turn increase the frequency of emission events. Thus the incoming/outgoing balance is maintained.
Click for larger image
http://www.aer.com/scienceResearch/rc/m-proj/lbl_clrt_mls.html
The important greenhouse gases are: H2O, CO2, O3, N2O, CO and CH4. The reason why the desert can get very cold at night is because of a lack of water vapor. The same is true for Antarctica. The extreme cold in Antarctica is due to high albedo and a lack of water vapor and clouds in the atmosphere, which results in almost all of the incoming radiation returning immediately to space.
An earth with no CO2 would be very cold. The first few tens of PPM produce a strong warming effect, and increases after that are incremental. It is widely agreed that a doubling of CO2 will increase atmospheric temperatures by about 1.2C, before feedbacks. So the debate is not about the greenhouse effect, it is about the feedbacks.
Suppose that the amount of reflected SW from clouds increases from 20% to 21%? That would cause a significant cooling effect. Thus the ability of GCM models to model future temperatures is largely dependent on the ability to model future clouds. Cloud modeling is acknowledged to be currently one of the weakest links in the GCMs. Given the sensitivity to clouds, it is perhaps surprising that some high profile climate scientists are willing to claim that 6C+ temperature rises are established science.
So the bottom line is that the greenhouse effect is real. Increasing CO2 will increase temperatures. If you want to make a knowledgeable argument, learn about the feedbacks. That is where the disagreement lies.
Bill Illis says:
The question is not so much one of timeline. The response predicted seems to be highly non-exponential in time, much like the decay in atmospheric concentrations of CO2 is following the release of a slug of it into the atmosphere. Hence the differences in times is at least partly a matter of what sort of time you are talking about…time to get halfway to the equilibrium value, 75% of the way, 90% of the way.
Probably the more relevant way to treat this issue is not to ask about the time…which is not really the useful question anyway for comparing temperature trends between theory and observation. Rather, you would want to make a similar plot to the one that you showed but using an estimate of the transient climate response (TCR) rather than the equilibrium climate sensitivity (ECS).
Table 8.2 of the IPCC AR4 Working Group I report gives a chart of the transient climate response for different climate models and they range from 1.4 C to 2.6 C (although the 2.6 C is a bit of an outlier as the next highest is 2.2 C). The somewhat more conservative conclusion of the IPCC report itself on the TCR is (Section 9.6.2.3)
As a final note, the “transient climate response” technically depends on how fast one is increasing the forcing and the numbers quoted are apparently based on an increase in CO2 in the atmosphere at the rate of 1% / yr. I believe that the actual rate of increase in CO2 is closer to 0.5% / yr, so our current “experiment” lies between the extremes of the ECS and the TCR, but probably still significantly closer to the TCR value I think. (Maybe you can find some studies of how the TCR value obtained depends on rate but I don’t know of any.)
Having said all of this, I should also point out that because of the uncertainties in the aerosol forcing as well as the uncertainties in the level to which natural variability has contributed one way or the other to the temperature trend, it has generally been found that attempts to constrain the climate sensitivity based on the 20th century temperature trend are not very good…I.e., the data is compatible with quite a broad array of climate sensitivity given the uncertainties. Better constraints are obtained from other things (paleoclimate data, the Mt Pinatubo eruption) and, of course, the best are obtained by combining all of this together.
Bill Illis (09:12:30) :
No, that’s incorrect. And it’s not a “transient equilibrium response”. There is an equilibrium response (that incorporates several time constants) which is the full response to forcing once all of the elements of the Earth system have come to equilibrium….and there is the transient response (which is the real time evolution of temperature in response to a change in forcing).
At no time was the Earth’s equiibrium temperature response to a change in forcing considered to be instantaneous. Yet that’s the implicit assumption in your plots. That’s clearly incorrect, and it’s pointless to make an analysis based on knowingly incorrect assumptions.
Hansen hasn’t redefined “it” to take 1500 years. Why not simply read Hansen’s papers if you’re going to comment on them? They’re all freely downloadable. Hansen assesses the fast feedback (direct greenhouse warming, water vapour and sea ice albedo feedbacks) to give a climate sensitivity near 3 oC with ocean thermal inertia, much in line with a large amount of other analyses. The time constants are of the order of several decades. They’re of interest to events occuring during the coming decades/century
This climate sensitivity corresponds (according to Hansen) to the situation where there are negligible changes in polar ice sheets and albedo effects from major vegetation changes. When the latter are included over long time scales (centennial to millenial timescale) the climate sensitivity becomes (according to Hansen) closer to 6 oC.
No one considers that the time constants are sufficently well defined that we can establish the short term climate sensitivity precisely by analysis of contemporary temperature evolution (e.g. last 100 years). The uncertainties in climate response times and aerosolic contributions means that the problem is under-determined. Thus most analyses of climate sensitivities make use of analyses involving paleotemperature evolution under conditions where the Earth might be expected to come near equilbrium with forcings, or analyse transient responses (to the solar cycle or vlocanic effects).
Despite all of this you’ve chosen to assume that every response element to enhanced forcing occurs instantaneously. You’ve plotted data corresponding to the transient response against a model corresponding to the equilibrium response. Whatever our uncertainties about the respective time constants, we certainly know that they’re not all zero!
EM Smith: “The issue isn’t honor. It’s accuracy…They do not “deny”, they question.”
If the issue is simply accuracy, then ‘denier’ should be acceptable, since it is arguably even more accurate than ‘sceptic’ — many AGW sceptics are selective questioners, subjecting AGW claims to scrutiny while giving as free pass to sceptic claims.
“The AGW hypothesis supporters have unfortunately earned the term alarmist.”
Many AGW sceptics also paint alarming scenarios of mass misery and death from measures for mitigating AGW, so from the point of view of accuracy they could also earn the term ‘alarmist’. Some of these anti-AGW alarmists can also be accurately described as ‘paranoids’, with their fantasies of eco-terrorist plots to rule the world.
“And I’d be happy to be called an “Anti-AGW alarmist” raising the alarm about all the harm it will do to our economy. By anyone. I’d wear it as a badge of honour…”
So the issue isn’t just accuracy, but also honour? Do you regard ‘AGW alarmist’ as a badge of honour?
Reply: NO NO NO! The word “denier” is a specific attempt to draw skeptics with the same brush as holocaust deniers and for that reason and that reason alone is prohibited as a pejorative on this site. End of story. It’s Anthony’s blog. It’s his rules. ~ charles the moderator
If not for the Holocaust association, “denier” would be an acceptable term. It’s connotation would be of people “in denial” about the ill-effects of their short-sighted, ego-centric behavior. (Drunkenness, abusiveness, etc.) IMO, that is what 90% of the users of the term intend to convey. I wouldn’t mind the label.
Believer and Disbeliever would be a pair of matched terms, but they lack the necessary zing. And Believer carries the disparaging hint of True Believer.
What’s needed is a set of terms that are only mild “zingers.” (Two that I like for the Believers are Warmmongers and Hotheads.) Alarmist qualifies, but there needs to be a countervailing term for their side to use. (Cold fish? Snoozer? Scoffer? Slug-a-bed?) Is there some well-known character from film or fiction who ignored a warning with disastrous consequences? I bet there is, but I can’t call it to mind.
Oops: Second line, change to “Its connotation.”
Edward (06:39:24) :
tmtis free 00:39:45
You stated earlier: “As an analogy, if you use a blind over a window on a sunny day, adding more blinds will not make the room any darker”
I like your analogy, however I partially disagree and suggest an improvement . Think of the gases in the atmosphere as if the “shade” was cut into narrow strips. Pulling these strips down individually would block particular segments of the incoming light. The more strips you brought down the darker the room would become. Some strips would overlap while others would still allow light into the room through gaps between each other. To completely block light from coming into the room you would need to add multiple layers of shading to eliminate all of these “gaps”.
Sorry for the late response.
This is all good except that the number of strips is so high that adding some more will not allow the light to pass through any further because the light already does not pass through.
I suggest you to calculate (it is easy) the number of CO² molecules (only) present in a, say, 10km high square meter column of atmosphere. You can use then the simple Beer’s law to approximate the heigh of the atmosphere required all to absorb the LW radiated photons. Then you can reduce the estimated height by plotting the power absorbed by increased level of CO² (x2, x3, X4). Finally the calculation of this height by using the absorption cross section of CO² at 15µm (see HITRAN for that) will show you that the height is minimal. This means that there are many many strips (10km in fact) above the height at which LW radiations are absorbed by CO².
Bye,
TMTisFree
Steven Goddard (11:59:22) :
Phil,
Ahh… earlier you were arguing that IR excited tropospheric CO2 immediately loses it’s energy through collisions with N2 and O2 molecules. But now you are saying that those processes also work in reverse.
Of course that’s the point.
Previously you said –
Leif, the bolded statement is only true high in the atmosphere, ~stratosphere, near the surface any energy is exchanged via collisions with neighboring molecules almost immediately (timescale less than a nanosecond).”
and then you said-
Sorry N2 and O2 are homonuclear diatomics and dont radiate.
You described it initially as a one-way phenomenon, when actually it is more of an equilibrium. The N2 and O2 can also pass energy back to CO2, which does radiate.
It’s one-way as far as the excited state is concerned. Yes over a large number of molecules it’s equilibrated but the lifetime of an individual excited state is very limited by those collisions, it doesn’t stay excited long enough to significantly radiate at low altitude. At high altitude the lifetime is longer because of reduced collision frequency and there is a bigger contribution from emission.
tmtisfree (15:34:11) :
Edward (06:39:24) :
tmtis free 00:39:45
You stated earlier: “As an analogy, if you use a blind over a window on a sunny day, adding more blinds will not make the room any darker”
I like your analogy, however I partially disagree and suggest an improvement . Think of the gases in the atmosphere as if the “shade” was cut into narrow strips. Pulling these strips down individually would block particular segments of the incoming light. The more strips you brought down the darker the room would become. Some strips would overlap while others would still allow light into the room through gaps between each other. To completely block light from coming into the room you would need to add multiple layers of shading to eliminate all of these “gaps”.
A better analogy would be a set of strips hanging vertically which can be rotated to block more light. As they’re rotated it’s the equivalent of increasing the concentration of the absorber.
Roger Knights –
Good post. Personally I don’t think of myself as denier, as you point out it links in to being in denial. It’s not like I’m not looking for answers. They just have to be believable answers. I get nowhere hearing that we know global warming is real because Jim Hansen say it’s real. Just call me a skeptic, a doubter and a disbeliever.
“Reply: NO NO NO! The word “denier” is a specific attempt to draw skeptics with the same brush as holocaust deniers and for that reason and that reason alone is prohibited as a pejorative on this site. End of story. It’s Anthony’s blog. It’s his rules. ~ charles the moderator”
The issue here is EM Smith’s claim that he regards “alarmist” as an accurate description, so therefore it is “devoid of pejorative nature”. My contention was that if the only criterion is accuracy, “denier” is no more pejorative than “alarmist”.
However, it’s clear that the connotation of the term “denier” can be more pejorative than the connotation of the term “alarmist”, although a pejorative phrase such “in denial” has no connection to the holocaust as far as I can see. But that’s not the point at issue.
So my original question (2) stands: “Would you say that “alarmist” is an honourable term?”
Personally, I use the term AGW proponents, but given Anthony’s treatment by some of them, and some of their pronouncements, I understand his willingness to use the term alarmist. I think it’s too much of a harsh generalization myself.
Phil,
Then it sounds like we are in agreement.
The more GHG in the atmosphere, the greater the number of collisions between photons/molecules and molecules/molecules, and the higher the temperature required to maintain equilibrium.
Steve,
I had the impression that the CO2 infra-red absorption bands were saturated at sea-level; rather the variation in CO2 caused changes in the amount of energy transmitted from the upper troposphere to outer space. Does this not mean that any increases in surface temperature would theoretically be caused by higher surface temperatures being necessary to force convective heat transfer, rather than direct radiative effects at the surface?
If so, would not the role of extra water vapor be to induce negative feedback, by decreasing lapse rates, rather than further plugging already saturated energy bands?
I don’t understand now CO2 in the atmosphere can change the temperature of the planet. Please help out a novice.
I recall a thought experiment from college physics. Takt an insulated box with two spheres inside and everything in thermal and radiative equilibrium. Make it a big box so the spheres have gravity and atomspheres. Both spheres start at the same temperature.
Now change the color of one sphere. Maybe add CO2 to the atmosphere, maybe add water vapor. Maybe paint it pink.
The assertion is that the change in color will affect both radiation absorption and emission in the same way so that the temperature of the two spheres will remain the same. If the don’t then you can hook a heat engine between the two spheres and extact heat from a system in thermal equilibrium in fine disregard for the second law of thermodynamics. You can also make a perpetual motion machine.
So in what sense can CO2 in the atmosphere change the temperature of a planet? Or has the second law been falsified while I wan’t looking?
++PLS
I seem to recall the IPCC reports saying that the stratospheric cooling was largely from ozone depletion and then later that the true AGW signature was the combined tropospheric warming and stratospheric cooling. Nevertheless can someone tell me if it’s possible to get a feedback factor from just from the the non-ozone stratospheric cooling? If that is meant to be the gold standard signature of GHG warming then why don’t we treat it as such and ignore all the other guesstimations for sensitivity. I’m perplexed though because I’d have thought that if the strong postulated water vapour feedback wasn’t in the tropical troposphere then it wouldn’t be anywhere. Does water vapour feedback extend to the stratosphere?
As far as I can bear to read Hansens papers, he seems to get his main feedback calculations from Vostok – as if what happened there could be applied across the entire planet. His gross assumptions for those sensitivity calcs have been mocked even by AGW stalwarts like Annan and Connelley.
On alarmist, can we agree that the scientists and pundits who go beyond the findings of the IPCC reports are by definition alarmist? There are lots and lots of those types. One enviro journalist (M. Lynas I believe) actually replied once on R. Pielke Jr’s blog and confirmed he was an alarmist and proud of it. Schneider and Gore have said much the same thing in interviews, though in different words. But if alarmist offends then what’s the best way to describe someone who believes the gross media distortions that routinely go way beyond the IPCC reports and all other scientific consensus statements?
PLS,
Forget about second law. This is about radiation, not heat.
View CO2 as a semitransparent mirror, more CO2 give more reflection.
JamesG,
Ozone depletion is cooling the lower stratosphere, more CO2 is cooling higher up. I would also like to know whether more H2O in the stratosphere will give extra cooling and whether this has any impact on surface temperature.
pls,
You are neglecting the sun, which has a temperature of 10000 degrees K at its surface, sends high energy photons to the surface of the earth, which has to heat up at its surface to about 290K to export its energy so that it has an apparent temperature of 250 degrees K at mid-upper troposphere. So I think all the laws of thermodynamics are being obeyed.
So if one of the balls in your experiment is 10000K, I think you will find the other ball will probably be quite warm.
“View CO2 as a semitransparent mirror, more CO2 give more reflection.”
Idiocy.
“the lifetime of an individual excited state is very limited by those collisions, it doesn’t stay excited long enough to significantly radiate at low altitude.”
And this has been given congruent explanations in complete agreement above by George Smith and myself.
Brendan H.:
Can’t agree with that, my friend.
As stated here repeatedly, the term ‘denier’ has an unsavory connotation with holocaust denier. That is exactly why it is used.
The term ‘alarmist’, on the other hand, is absolutely accurate. Here’s why:
Alarmism is the only reason that $Billions [so far] have been shoveled into global warming research and grants. More $Billions are in the pipeline. Why? Because AGW proponents use unsavory scare tactics to extract money from taxpayers.
If the truth were being told based on the Scientific Method, AGW proponents would be forced to acknowledge that the only basis for their scary scenarios comes from always-inaccurate computer models.
Solid, empirical [real world] evidence showing that CO2 causes global warming is non-existent. Therefore, if the truth were being told by the proponents of the AGW/CO2-global warming-tipping point hypothesis, they would be forced to admit that they are only putting forth a conjecture, based on speculation, which would normally merit only a footnote or two in a few minor scientific journals.
But minor journal footnotes do not result in $Billions in grant money to study a non-frightening problem. Thus, those working the system resort to alarmism over a harmless, beneficial rise in a very minor but essential trace gas.
Alarmism over CO2 showers the alarmists with money and status. Without alarming the public, the status would be missing and the money would go to much more deserving scientific research [which is currently being starved of funds because global warming alarmism sucks up most of the available money].
Scientists and journal editors are as human as the rest of the population, and they are just as susceptible to temptation. So some of them resort to alarmism to get what they crave.
The term “alarmist”, when applied to those promoting the AGW/CO2 climate catastrophe hypothesis, is entirely accurate. They are deliberately alarming the public, akin to crying “Wolf!!” when there is no wolf. They have no shame. But the concept of shame in the new millennium is as old fashioned as the concept of honor. Now, money and status trumps all, and alarmism is just another tool used by alarmists to achieve their desired ends.
PLS:
When the two spheres in the box are at the same temperature, then they are in thermal equilibrium and Kirchoff’s law applies, meaning that they will remain at the same temperature regardless of differences in color.
However, if one of the spheres has an internal energy source (such as the sun) then Kirchoff’s law no longer applies and the temperature of the spheres will depend on color. Adding the first whiff of CO2 to a transparent atmosphere changes its color, resulting in warming, although we can’t see the color change because it is in the infrared wavelengths. Adding more and more CO2 is akin to adding more and more coats of paint to your house. At some point the next coat of paint doesn’t matter.
PLS: Just to add to what others have said, your thought experiment is in fact used to prove that the emissivity and absorptivity of a body must be equal to each other AT EACH WAVELENGTH. (Because, as you say, if this were not the case then if you have two bodies at the same temperature but different emissivity / absorptivity characteristics at some wavelengths, one would warm the other.)
However, with the sun – earth system, you have two bodies at very different temperatures. So, the radiation that the earth receives from the sun is primarily in the visible (and near-ultraviolet and near-infrared) whereas the radiation it emits is well into the infrared. By changing the emissivity and absorption in the infrared but not the visible, you can therefore raise the temperature.
JamesG says:
I think you are mixing a couple things together. I think the argument has been that the statospheric cooling while the troposphere warms is a signature of GHGs being the cause. However, I don’t think the argument has been that you can determine the feedbacks from the stratospheric cooling. Feedbacks are estimated in different ways.
That is not so. In estimating the equilibrium climate sensitivity (ECS) Hansen uses an estimate for the global temperature rise that is about 1/2 the rise seen at Vostok and I think most people agree that this is a pretty good estimate.
I don’t think that Annan and Connelley have mocked the 3 C part of the ECS calculation, what Hansen calls the “Charney sensitivity”. I think that they have strongly doubted that there is enough ice left to be melted to raise the long-term sensitivity to 6 C. (They may also be somewhat skeptical of Hansen’s claims that what ice disintegration does occur is really likely to occur as fast as Hansen thinks it might.)
Well, in that case, we would need to have a similarly-pejorative term to describe those who make predictions that disagree with the IPCC findings in the other direction too. There is a finite probably that the IPCC might be wrong on various things…but that probability extends in both directions.
Joel
“However, I don’t think the argument has been that you can determine the feedbacks from the stratospheric cooling.”
I know that’s not the argument, it was something I thought about on the spur of the moment and thought I’d ask. And I meant total sensitivity including all feedbacks. It just seems to me if that is the one unique attributable effect to an increase in GHG’s then we should try to use it to pin down the actual effect of the GHG increase and reduce the guesswork. Can we not determine anything from the stratospheric cooling numbers? eg. Joules retained in the system.
“we would need to have a similarly-pejorative term to describe those who make predictions that disagree with the IPCC findings in the other direction too”
You could use contrarian, since that seems to be the new preference at RC, perhaps used pejoratively. And while it is probably pejorative to say alarmist, it’s merited by a lot of people wouldn’t you say?
“Alarmist – a person who tends to raise alarms, esp. without sufficient reason, as by exaggerating dangers or prophesying calamities”.
Clearly that is a very good description of many of the actors in this drama, certainly most of the journalists and politicians, and a great deal of the scientists who court the press. I’ll be fair though and say I believe that the contrarians are often ridiculously alarmist about the costs involved in moving away from dirty to clean fuels. By dirty I mean of course all the other gunk that comes out of the tailpipe and chimneys, not the CO2 🙂
Steve Goddard,
To suggest that because convective heat transfer is a feedback because it only comes into play after absorption would be the same as suggesting that emission is a feedback. It is a primary heat transfer mechanism just like radiative emission and should be included in all clear sky simulations as it is the dominant effect.
Alex B
All emission except the Sun’s are indeed feedbacks. The sun is the only driver (excluding seismic effects, the odd meteor strike and cosmic rays). Even carbon-based fuels were created by the sun. Forcings are just artificialities to make climate models a lot simpler. It’s also routine in heat transfer models to have convective heat transfer as a feedback (or a secondary effect) from a radiative source eg a reactor – even when it dominates the heat transfer mechanism.