Guest post by David Archibald
The greenhouse gasses keep the Earth 30° C warmer than it would otherwise be without them in the atmosphere, so instead of the average surface temperature being -15° C, it is 15° C. Carbon dioxide contributes 10% of the effect so that is 3° C. The pre-industrial level of carbon dioxide in the atmosphere was 280 ppm. So roughly, if the heating effect was a linear relationship, each 100 ppm contributes 1° C. With the atmospheric concentration rising by 2 ppm annually, it would go up by 100 ppm every 50 years and we would all fry as per the IPCC predictions.
But the relationship isn’t linear, it is logarithmic. In 2006, Willis Eschenbach posted this graph on Climate Audit showing the logarithmic heating effect of carbon dioxide relative to atmospheric concentration:
And this graphic of his shows carbon dioxide’s contribution to the whole greenhouse effect:
I recast Willis’ first graph as a bar chart to make the concept easier to understand to the layman:
Lo and behold, the first 20 ppm accounts for over half of the heating effect to the pre-industrial level of 280 ppm, by which time carbon dioxide is tuckered out as a greenhouse gas. One thing to bear in mind is that the atmospheric concentration of CO2 got down to 180 ppm during the glacial periods of the ice age the Earth is currently in (the Holocene is an interglacial in the ice age that started three million years ago).
Plant growth shuts down at 150 ppm, so the Earth was within 30 ppm of disaster. Terrestrial life came close to being wiped out by a lack of CO2 in the atmosphere. If plants were doing climate science instead of us humans, they would have a different opinion about what is a dangerous carbon dioxide level.
Some of the IPCC climate models predict that temperature will rise up to 6° C as a consequence of the doubling of the pre-industrial level of 280 ppm. So let’s add that to the graph above and see what it looks like:
The IPCC models water vapour-driven positive feedback as starting from the pre-industrial level. Somehow the carbon dioxide below the pre-industrial level does not cause this water vapour-driven positive feedback. If their water vapour feedback is a linear relationship with carbon dioxide, then we should have seen over 2° C of warming by now. We are told that the Earth warmed by 0.7° C over the 20th Century. Where I live – Perth, Western Australia – missed out on a lot of that warming.
Nothing happened up to the Great Pacific Climate Shift of 1976, which gave us a 0.4° warming, and it has been flat for the last four decades.
Let’s see what the IPCC model warming looks like when it is plotted as a cumulative bar graph:
The natural heating effect of carbon dioxide is the blue bars and the IPCC projected anthropogenic effect is the red bars. Each 20 ppm increment above 280 ppm provides about 0.03° C of naturally occurring warming and 0.43° C of anthropogenic warming. That is a multiplier effect of over thirteen times. This is the leap of faith required to believe in global warming.
The whole AGW belief system is based upon positive water vapour feedback starting from the pre-industrial level of 280 ppm and not before. To paraphrase George Orwell, anthropogenic carbon dioxide molecules are more equal than the naturally occurring ones. Much, much more equal.
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@ur momisugly Glenn Tamblyn (00:02:14) :
Glenn, I remember seeing a NASA satellite study that showed CO2 was not evenly distributed in the atmosphere but rather it was concentrated in a few long bands that circled the earth. Do we know what the implications of this non-uniform distribution are? It would seem to me that a climate model assumption of uniform CO2 distribution might inject significant errors in the calculations.
““The assumptions are mind boggling. Surface emitted LWIR is uniform and constant all over the earth, and CO2 distribution is the same all over the earth, and nothing else has any say in what the Temperature of the atmosphere is, and somehow the Temperature of the atmosphere sets the surface temperature of the earth. Meanwhile the most common molecule on the planet, just sits by and lets all that happen””
“”” Glenn Tamblyn (00:02:14) :
…..
George E Smith (19:25:01)
“I would aprpeciate a citation”
Try this discussion over at RealClimate by RayPierre Humbert:
http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/
“The assumptions are mind boggling. Surface emitted LWIR is uniform and constant all over the earth, and CO2 distribution is the same all over the earth, and nothing else has any say in what the Temperature of the atmosphere is, and somehow the Temperature of the atmosphere sets the surface temperature of the earth. Meanwhile the most common molecule on the planet, just sits by and lets all that happen”
And exactly how do you know what the assumptions used in climate models actually are? Simple question. Are you critising something based on how you THINK it is done, rather than ACTUAL KNOWLEDGE of how it is really done. And if you have actual knowledge of how they do it, care to share your sources. “””
Glen, I don’t recall saying anything about “climate models”; certainly not those of the type you referenced at real climate. If somehow I left that impression; that was an error, on my part.
My comment, which you referenced above, derives from the NOAA global energy budget cartoon depiction; which apparently is attributed to Dr Trenberth.
The “model” which that diagram clearly espouses, is of a planet that is uniformly irradiated over 4 pi steradians, continuously 24 hours a day; 365 days a year, never changing and uniform everywhere. That is the only way, that a real TSI of about 1366 W/m^2, that is scanned by a 24 hour axial rotation about a tilted axis, and a 365 day elliptical orbit journey about a near point source (0.5 degree angular diameter) radiation source, can end up as a 342 W/m^2 total insolation over the entire surface. And the 390 W/m^2 total surface radiation, again emitted 24/365 from each and every square meter of the surface, corresponding to an isothermal radiator at a BB Temperature of 288 K; to be contrasted, with an actual real planet, which at any one instant of time, could have surface temperatures ranging over an extreme temperature range of 150 deg C, from a low of about -90C to a high of +60 C or even more, so the actual surface radiation available to interract with CO2 or any other GHG including water vapor, varies by more than an order of magnitude in total Radiant emittance.
If Trenberth’s depiction, is in fact not that of a static isothermal uniformly irradiated object, I would appreciate somebody pointing out where on that diagram should one look to find evidence that that is not the case.
Doug S (08:54:34) :
@ur momisugly Glenn Tamblyn (00:02:14) :
Glenn, I remember seeing a NASA satellite study that showed CO2 was not evenly distributed in the atmosphere but rather it was concentrated in a few long bands that circled the earth. Do we know what the implications of this non-uniform distribution are? It would seem to me that a climate model assumption of uniform CO2 distribution might inject significant errors in the calculations.
Yes, the implications are zero, an ~2% fluctuation is of no consequence!
phil,
How long on average does CO2 slow down OLW energy from escaping to space? Is it on the order of minutes, hours, days, months, or years? What is the corresponding time for H2O to slow down LW from radiating to space?
When sunlight penetrates the ocean as light, for how long, on average, is that energy stored in the ocean before it is radiated as LW?
How effective is a cloud at turning sunlight into LW radiation?
Isn’t the critical factor in measuring global warming the ohc? How effective are ghg at heating the ocean? If sunlight is much more effective at heating the ocean than ghg, then wouldn’t anything that converts sunlight to LW tend to have a long term cooling effect on the ocean?
I understand that clouds can result from increased heat. I don’t really get clouds increasing the ohc. What % of sunlight that hits a cloud is immediately reflected back to space?
Back in 2005 Hansen predicted that ohc was going increase every year for several years by a significant amount (IIRC, it was something like 10^22 joules/year). That prediction did not happen as OHC leveled off and even declined in recent years. Where did Hansen go wrong? Has that shaken your confidence in modeling global climate?
Re: Phil. (Mar 11 20:56),
The path length problem was that I left the VMR (volume mixing ratio) at the default setting of 0.1. Duh (Or, *smacks forehead* D’oh)! I always thought there should have been a concentration setting somewhere, but never really looked until today. I must have assumed that VMR was some sort of instrument function. 100,000 cm path length with a VMR of 0.000375 looks exactly like your spectrum. So for Mars the VMR would be ~1. Learn something new every day. Spectracalc charges more than I want to spend for a subscription to do their more interesting stuff.
DeWitt Payne (13:57:17) :
Re: Phil. (Mar 11 20:56),
The path length problem was that I left the VMR (volume mixing ratio) at the default setting of 0.1. Duh (Or, *smacks forehead* D’oh)! I always thought there should have been a concentration setting somewhere, but never really looked until today. I must have assumed that VMR was some sort of instrument function. 100,000 cm path length with a VMR of 0.000375 looks exactly like your spectrum.
Good, I wondered if it was something like that, I used 0.000385.
So for Mars the VMR would be ~1.
Yeah, I used 0.95, again no biggie.
Learn something new every day. Spectracalc charges more than I want to spend for a subscription to do their more interesting stuff.
Right, If I need to do some of the fancy stuff I just save everything up and subscribe for a month.
George E. Smith (10:32:17) : “If Trenberth’s depiction, is in fact not that of a static isothermal uniformly irradiated object, I would appreciate somebody pointing out where on that diagram should one look to find evidence that that is not the case.”
We are on the same wavelength . It is in fact logically impossible to explain a variations in a radiantly heated object’s due to spectrum with a 1 dimensional sum because that’s computationally equivalent to a point surrounded by a sphere of uniform temperature . By the 0th law of thermodynamics , the point must come to the temperature of the sphere . Spectrum makes no difference . As I have repeated , it is the integral over the correlations between the spectra of a sphere in various directions and the spectra of the heat sources and sinks in those directions which determines the sphere’s mean temperature . My few lines of array code accept any partition of a radiated sphere and its surrounding distribution of temperatures . Its answers match those of the one dimensional simplification in those cases the cruder model can handle . But , I think makes the physics much more understandable by correctly implementing the actual 3 dimensional reality .
It is good to see that a number of people here understand how fraudulent the “cold earth” 255k assertion for a naked earth is .
If you want to see a real world extreme example in real-time, the OLR anomaly at about 160W to 160E, the Nino 4 region, has been as high as -50 watts/metre2 over the past few months.
The El Nino is now dumping its heat into the atmosphere and this area has been nearly continuously covered in tropical convection storms for the past 3 months. As a result, the long-wave radiation is not escaping from the atmosphere – it is being held in. This is a fairly typical response for the end and immediate period after an El Nino, while the opposite happens with a La Nina.
http://cawcr.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/ts.r4.l.gif
http://cawcr.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/map.lastmonth.gif
A drop from the normal OLR of 230 W/m2 to 170 W/m2 at the end of January is a big number. Temperatures in this region should increase by 5C as a short-term immediate (speed-of-light) response from this alone (average -30 W/m2 over the past few months). On the other hand, the reduction in sunlight from all the tropical convection storms (if 50% higher which looks reasonable) could reduce temperatures by about 3C.
What are temperatures in the region doing? The closest I could find was Truk in the Caroline Islands (a little north and west of the centre of the region but close enough) which is about 1C to 2C above average over the last 90 days.
http://www.cpc.ncep.noaa.gov/products/global_monitoring/temperature/tn91334_90.gif
So, my estimates above constructed using the Stefan Boltzmann equations are not far off. Clouds and water vapour (with impacts as high as 20 to 30 W/m2 on both sides) have much more impact that a minor GHG with 3.7 W/m2 impact upon doubling.
This does provide a little example of how an El Nino can affect global temperatures as well (the warming in this large region will filter off to the rest of the planet now and the OLR anomalies appear with a lag of a month or two compared to the peak of the El Nino).
RE: Phil. (20:56:40) :
Thanks Phil, my original suggestion was for a presentation graphic that could be used by those who might wish to show the real effect that added-CO2 has on the atmosphere. This could serve as an introduction to explain why added CO2 has a logarithmic effect. I believe that Bill Nye’s simplistic linear darkening model is *the* concept generally accepted by the public and that this is much of the motivation behind those who support the fierce return to ‘350’ movement.
I suspect an expanded and perhaps simplified view of the “Radiation Transmitted by the Atmosphere” chart (copied from another WUWT article) might be best suited to that purpose. A similar shaded graphic zoomed to cover the important 5 to 20 micron (or 15 to 60 THz linear frequency) IR range might be very telling. I include this link once more for quick reference.
http://www.globalwarmingart.com/images/7/7c/Atmospheric_Transmission.png
DeWitt,
greetings and thank you for the input, I initially missed seeing them as I think we might have beenposting at the same time and my time this week has been extremely limited. As I was traveling all day yesterday I’ve got a bit of catch up to do still.
Henry Pool wrote: “Sorry Frank, you lost me here. How do you people always seem to know absolutely for sure that CO2 is a greenhouise gas?”
If you google “Absorption Spectrum of Carbon Dioxide” you will see many similar figures, some of which have the emission spectrum for the sun and earth superimposed. For example, see: http://chriscolose.wordpress.com/2008/03/09/physics-of-the-greenhouse-effect-pt-1/ The absorption of sunlight by carbon dioxide is negligible because it occurs where the emission from the sun is very weak and the carbon dioxide absorption overlaps with water vapor. On the other hand, the absorption spectrum of carbon dioxide has very strong absorptions at wavelengths where the earth emits.
Phil wrote (09:48:55) :
6) Although cold water does hold more CO2 than warm, CO2 won’t get low enough to endanger plants because plants are the main consumers of CO2 not cold water.
Not true, the ocean is a larger sink for CO2 than plants.
Perhaps you are right. The difference between the last LGM (180 ppm) and pre-industrial (280 ppm) is believed to be due to the extra carbon dioxide the colder ocean. It is an interesting question to consider how much colder would the ocean have to be in order to drive carbon dioxide concentration below 100 ppm. According to the “snowball earth” hypothesis, the oceans have gotten cold enough to freeze over in the distant past when the sun was cooler, but I’m not aware that CO2 ever approach 100 ppm during those times. Those periods were supposedly ended when volcanos emitted enough GHG’s.
Frank wrote
“The absorption of sunlight by carbon dioxide is negligible because it occurs where the emission from the sun is very weak and the carbon dioxide absorption overlaps with water vapor. On the other hand, the absorption spectrum of carbon dioxide has very strong absorptions at wavelengths where the earth emits”
Henry@frank
1) you are probably only referring to the absorption between 4 and 5um, not the others (see argument below).
2) You cannot say that without actual results from an actual experiment. I had this argument with Phil. before.
here it comes again:
Here is the famous paper that confirms to me that CO2 is cooling the atmosphere by re-radiating sunshine (12 hours per day).
http://www.iop.org/EJ/article/0004-637X/644/1/551/64090.web.pdf?request-id=76e1a830-4451-4c80-aa58-4728c1d646ec
Note that they measured this radiation as it bounced back to earth from the moon. Follow the green line in fig. 6, bottom . Note that it already starts at 1.2 um, then one peak at 1.4 um, then various peaks at 1.6 um and 3 big peaks at 2 um.
This paper here shows that there is absorption of CO2 at between 0.21 and 0.19 um (close to 202 nm) (UV):
http://www.nat.vu.nl/en/sec/atom/Publications/pdf/DUV-CO2.pdf
There are other papers that I can look for again that will show that there are also absorptions of CO2 at between 0.18 and 0.135 um and between 0.125 and 0.12 um.
We already know from normal IR that CO2 has big absorption between 4 and 5 um.
So, to sum it up, we know that CO2 has absorption in the 14-15 um range causing some warming (by re-radiating earthshine, 24 hours per day) but as shown and proved above it also has a number of absorptions in the 0-5 um range causing cooling (by re-radiating sunshine). This cooling happens at all levels where the sunshine hits on the carbon dioxide same as the earthshine. The way from the bottom to the top is the same as from top to the bottom. So, my question is: how much cooling and how much warming is caused by the CO2? How was the experiment done to determine this and where are the test results? If it has not been done, why don’t we just sue the oil companies to do this research? (I am afraid that simple heat retention testing will not work here, we have to use real sunshine and real earthshine to determine the effect in W/m3 [0.04%]CO2/m2/24hours)
I am going to state it here quite categorically again that if no one has got these results then how do we know for sure that CO2 is a greenhouse gas?
RE: Henry Pool (07:41:38) : “So, to sum it up, we know that CO2 has absorption in the 14-15 um range causing some warming (by re-radiating earthshine, 24 hours per day) but as shown and proved above it also has a number of absorptions in the 0-5 um range causing cooling (by re-radiating sunshine).”
I believe that most solar radiation is in the 0.2 to 1.5 micron range (1500 to 200 THz, respectively, one micron is nominally 300 THz.) So, other than Rayleigh scattering, there should be no significant CO2 absorption bands in the optical range. I believe the best argument against the hypothetical CO2 crisis is that you cannot kill a horse more than once and most of that horse is already dead.
I suggest looking at the graphics in the WUWT article titled “A Window on Water Vapor and Planetary Temperature, Part 2.”
http://wattsupwiththat.com/2008/06/21/a-window-on-water-vapor-and-planetary-temperature-part-2/
I ran across an article at RealClimate based on data from the HITRAN spectroscopic archive which seems to indicate that a nominal CO2 concentration designated 1xCO2 (280 ppm, I believe) would yield a CO2 saturated absorption band of 13.5 to 17 microns and increasing the CO2 concentration to 4xCO2 (1120 ppm) only appears to make this range 13 to 17.5 microns. (Ref: “Part II: What Ångström didn’t know.”)
Spector said:
“I believe that most solar radiation is in the 0.2 to 1.5 micron range ”
Henry@Spector
the sun radiates from 0 to 5 um. The energy associated with infra red coming from the sun is 46 or 47%, which I think is still considerable.
You can feel this here in Africa. You cannot stay in the sun for too long, the physical heat is sometimes too much even for 10 minutes exposure. Unless during the day the humidity goes up, then you can feel the heat becoming less. So I would not underestimate the total cooling caused by CO2, from all the absorptions in the 0 – 5 um range, taking together……
I agree that the debate is somewhat moot, to me as well, as I believe that global warming as such is not possible. Earth has its own (water) cooling plant with built-in thermostat. Fluctuations are (most probably) caused by the mechamism that causes cloud formations. (Svensmark theory). But there are an awful lot of people still out there who believe CO2 is a problem. A person is not dead until some doctor declares him dead. So we have to test it.
I am afraid that simple heat retention testing will not work here, we have to use real sunshine and real earthshine to determine the effect in W/m3 [0.04%]CO2/m2/24hours). We know Svante’s Arrhenius formula was wrong. It appears no one did the correct research to get the correct formula.
Again, I say that if no one has got these results then how do we know for sure that CO2 is a greenhouse gas?
Come on folks, if you’re truly skeptical then where’s your skepticism? Why are you skeptical of climate scientists and not David Archibald? Well, what’s there to be skeptical about?
To begin with, how did Mr. Archibald convert from a radiative forcing (in watts per square meter) to an actual temperature increase? A good skeptic should be curious about that and should look into it. In order to produce his figures, Mr. Archibald has simply assumed that for each 1 W/m2 increase in radiative forcing there is a corresponding temperature increase of 0.1°C. This is what he is calling “Natural Warming”. Time for some skeptical alarm bells to go off!
A climate sensitivity of 0.1°C per W/m2 is an absurdly low value that cannot be taken seriously. Even the prominent climate skeptic Richard Lindzen agrees that without feedbacks in the climate system this value should be about 0.3°C per W/m2 (3 times as high). This is relatively straight-forward physics. However, of course there ARE feedbacks in the system and this number is likely quite a bit higher.
What does a sensitivity of 0.1°C per W/m2 imply? Well, the ice ages don’t make sense any more (at all). The 8°C rise coming out of the last ice age would take an astronomical 80 W/m2 of radiative forcing! Also, the 20th century rise in surface temperatures of about 0.7°C would require a radiative forcing of 7 W/m2. Well, for those of you still clinging to the “it’s the sun” theory, this doesn’t jive very well with an upper-bound increase in solar radiative forcing during the 20th century of about 0.3 W/m2 (then again, changes in solar activity don’t jive with any accounting of 20th century warming). Okay, so Mr. Archibald’s “Natural Warming” seems to violate fundamental physics and is completely incapable of explaining ANY climatic changes, natural or anthropogenic. Hmmm…
But what does he compare this to? Well, Mr. Archibald suggests that “some of the IPCC climate models predict that temperature will rise up to 6° C as a consequence of the doubling of the pre-industrial level of 280 ppm.” Really? The upper bound of 6°C is associated with the “A1FI” future emissions scenario which is far more than doubling of CO2: achieving a concentration of nearly 1000 ppm (more than a tripling!) by 2100. And does Mr. Archibald think that CO2 is the only climate driving factor? The rise in CO2 only accounts for about half of the total anthropogenic greenhouse gas forcing over the twentieth century.
So Mr. Archibald’s “Natural Warming” uses an impossibly low climate sensitivity and he then compares it to “Anthropogenic Warming”, for which he uses the absolute upper bound of climate model sensitivities (which is actually for 1000 ppm CO2 not 560 ppm – whoops, a minor oversight that happens to produce an even more “shocking” figure).
Moral of the story? If you multiply something by a small number, you get a smaller value than if you multiply it by a large number. Tada! Mr. Archibald has just demonstrated multiplication! Wait, I thought he was trying to say something about climate…
ATTENTION SKEPTICS! Live up to your title and apply the same level of skepticism to all claims. Why believe Mr. Archibald and not the thousands of trained, competent, and honest independent scientists who are dedicated to understanding our climate system? Mr. Archibald just spoon-fed you nonsense. You should read the label before you swallow.
p.s. Mr. Archibald: where on earth did you get the idea that “plant growth shuts down at 150 ppm” CO2?! That is completely bogus. I should know – it’s what I study. SOME plants have trouble “breaking even” at 150 ppm, but not even close to all. Just for my own satisfaction, tomorrow I will expose a leaf to 150 ppm of CO2 and watch it photosynthesize.
RE Henry Pool (21:02:01) : “how do we know for sure that CO2 is a greenhouse gas?”
I believe you are assuming the term ‘greenhouse gas’ is more restrictive that it actually is. All it means, I think, is that the gas in question has electro-magnetic radiation absorption bands in the far infra red range typical of ‘earthshine’ and is transparent to radiation in the optical range typical of sunshine. I do not think this term requires that an increase of the fraction of these gases in the atmosphere must necessarily produce a corresponding increase in the terrestrial greenhouse effect.
From the data I have seen, increasing the CO2 in the atmosphere to a whopping 1120 ppm will only reduce the width of the window open to earthshine by about a half micron from that of pre-industrial times. In the WUWT article, “A Window on Water Vapor and Planetary Temperature,” it says that water vapor is generally assumed responsible for 70 to 90 percent of the greenhouse effect on earth.
http://wattsupwiththat.com/2008/06/18/a-window-on-water-vapor-and-planetary-temperature/
At the Earth, the flux of solar radiation, otherwise known as ‘The Solar Constant’ is about 1368 watts per square meter. According to the Stefan Boltzmann formula, that is enough to cause any flat surface directly facing the sun with no other means of heat dissipation or reflection to reach a temperature of 394 degrees K (121 degrees C.) I believe this is why you can sometimes cook eggs on the hood of a car. The peak heating power from the sun appears to be coming in at wavelengths around 0.5 microns.
Luckily, the Earth reflects an average of about 30 percent of incoming energy and the Earth also has four times as much surface area as it has area facing the sun so it only needs to radiate an average energy of about 239 watts per square meter to expel the energy received from the sun. This reduced average energy flux corresponds to a temperature of 255 degrees K (-18 degrees C.)
Greenhouse gases restrict the window available for ‘earthshine,’ so, according to Dr. Miskolczi, the average Earth surface temperature needs to be about 33 degrees C higher than -18 degrees C to force all the received (and internally generated) energy back out.
ABG (11:38:03 , 14th March 2010) wrote:
“A climate sensitivity of 0.1°C per W/m2 is an absurdly low value that cannot be taken seriously. ”
It depends on what boundary one is talking about. At the lower boundary (the Surface) the sensitivity at 15DegC is between 0.095DegC/W/m^2 (Clausius Clapeyron increase of evaporation of 6.5% per degC) and 0.15DegC/W/m^2 (lowest guess increase in evaporation of 2.5% per DegC).
At the upper boundary, say the Tropopause, where the air is cold and there is only radiation to consider, the sensitivity is around 0.4DegC/W/m^2, ie much higher than the surface.
The Climate Crew bang on a bit about the “Radiative Forcing” (ie the energy imbalance) at the Tropopause for an increase in CO2, and take it as read that any increase in Tropospheric temperature is necessarily translated into the SAME temperature increase at the surface. I’m not so sure about that. I would like to see somewhere, the SURFACE BALANCE accounted for – what is the level of cloud influence on insolation and reflection, what is the change in albedo, what is the level of back-radiation, and where does it come from? It would be nice to see a version of the Kiehl-Trenberth diagram at 18DegC for example. Is there some problem? Do the surface fluxes now balance? Or not?
For an Ice Age to be sustained, there would need to be a large increase in the effective albedo of the planet – by about an additional 60%. We know that lots of ice over the land will increase the surface albedo. It seemsthat the average day in an Ice Age would be cloudy but with very little rain/snowfall (around 40% of today’s values).
That seems to work well, but of course if one assumes a positive cloud/water vapour feedback you could get anything.
I don’t see a low sensitivity as implying that an Ice Age cannot occur, only that it would be a low precipitation, very cloudy, not much weather happening sort of planet. Under those conditions, which seem to be borne out by the guesses of what happened in the last Ice Age, the surface will sustain a non-heating ice box.
The big Ice Age question is what causes the switch from this apparently stable state to and from the present rather more salubrious condition. I like Hoyle’s theory best…
ABG wrote:
“A climate sensitivity of 0.1°C per W/m2 is an absurdly low value that cannot be taken seriously. Even the prominent climate skeptic Richard Lindzen agrees that without feedbacks in the climate system this value should be about 0.3°C per W/m2 (3 times as high).”
ABG is assuming that any feedback must be positive. He starts from the “without feedback” case and seems to assume that there must be at least some positive feedback. A stable system, or one in equilibrium, must have negative feedbacks. Examples of negative feedback would be:
Higher temperatures give more evaporation. The water vapour rises and carries heat to the upwards. When the water condenses, the heat can escape to space without radiating from the surface. The increased heat loss opposes the increase in temperature.
Higher temperatures give more evaporation. The water vapour rises and creates more cloud cover, reflecting sunlight into space.
There can be negative feedbacks and positive feedbacks. If the net effect was positive, the earth’s temperature would be unstable. For example, a volcanic eruption such as Krakatoa would cause an ice-age.
So Lindzen can agree with 0.3°C per W/m2, but then negative feedback can take that to 0.1°C per W/m2.
Spector said
“I believe you are assuming the term ‘greenhouse gas’ is more restrictive then it actually is. All it means, I think, is that the gas in question has electro-magnetic radiation absorption bands in the far infra red range typical of ‘earthshine’ and is transparent to radiation in the optical range typical of sunshine”.
Henry@Spector
Ok, I think they have to come clear on the definition of a greenhouse gas.
I was assuming that the term “greenhouse” refers to a substance in the atmosphere where the net effect of the cooling and warming properties is warming, rather than cooling. It is true, they also call ozone a greenhouse gas (because it has absorption at around 13) but it has strong absorption in the UV region, thereby blocking a lot of UV from the sun. I assume the net effect of ozone is cooling, rather than warming, but again I could not find the relevant test results on this. As I said and proved before, CO2 is not transparent to sunshine, it has quite a number of absorptions in the 0-5 range, so I donot understand why you keep on re-stating that it is (which also seems to be the common line that is taught at tertiaire institutions).
then you say:” Luckily, the Earth reflects an average of about 30 percent of incoming energy”
Yes, and if you look carefully at the two graphs showing the incoming and outgoing radiation (that you referred to earlier – there are better ones that also show the clear gaps caused by CO2 on the incoming solar radiation -) then you will have noticed that this 30% is due to the combined effect of water, oxygen/ozone & carbondioxide.
You see what I am getting at? I honestly donot know what the point is talking about GHG’s if you donot know for sure that the net effect of the substance in the atmosphere is warming rather than cooling. You first have to test this! Don’t come to me with an IR spectrum of a substance that has some absorption in the earthshine region and then call it a GHG. Even if it is methane. I think that is stupid. You first have to determine how much cooling it causes (by blocking/re-radiating sunshine) and then you have to determine the warming (by trapping/re-radiating earthshine) and then compare those two…
So where are those results? That is what I was looking for. .. I put is to you it does not exist. Everybody thought that somebody would do it, in the end nobody did it.
Carl Chapman wrote:
“There can be negative feedbacks and positive feedbacks. If the net effect was positive, the earth’s temperature would be unstable. For example, a volcanic eruption such as Krakatoa would cause an ice-age.”
Well first off, your example is not a good one. Aerosols leave the atmosphere in a few years and they don’t nearly have enough of a sustained effect to allow for strong feedbacks to happen.
And of course there can be negative feedbacks – I’ll get to that in a second. With or without feedbacks, IF the ultimate climate sensitivity to a radiative forcing is 0.1°C per W/m2, the climate system makes no sense. It should be so insensitive that temperatures will barely respond unless forcings are HUGE. Given our best estimates of the changes in forcings and temperature over the last century, a reasonable estimate for climate sensitivity with feedbacks is around 0.7°C per W/m2. This implies that positive feedbacks dominate over negative feedbacks.
But again, the main point is that if you compare a small number to a high number, you’re going to see a big difference that will make a shocking(!) graph. Archibald uses an implausibly low number that nobody considers close to reality and compares it to the UPPER BOUND of climate models (and in doing so he mistakenly suggests that this corresponds to a 560 ppm scenario instead of a 1000 ppm scenario AND that all of the warming is due to CO2 alone – wrong). The result – a shocking(!) graph.
Carl Chapman wrote:
“If the net effect was positive, the earth’s temperature would be unstable.”
Not true. If you’re a good skeptic then you should be curious. If you’re curious then look this up and see what people have to say about it. Do you think that nobody’s ever thought about this??
In a system with positive feedbacks, the total gain of the effect (the multiplier of the initial temperature change) is G = 1/(1-f) where f is the feedback factor (in degrees of warming per degree of warming). The feedback responds to the initial warming, but much of the additional warming is due to the feedback upon feedback upon feedback, etc., but with diminishing returns. Unless f > 1, this additional warming dampens and G is a real number, i.e. there is no runaway effect.
With a doubling of CO2, the direct temperature increase without feedbacks would be about 1.2°C (using 0.3°C per W/m2). A feedback factor (f) of 0.4 would produce a total temp increase of 2°C. If f = 0.7 then the total temp increase would be 4°C. Note that all of the climate model forecasts imply that f < 1 (by quite a bit). If f = 0.95 we would see the temperature increase by 24°C, but still there would be no runaway! The runaway greenhouse claim is a red herring. It has been well studied and it is exceedingly unlikely. In no way do positive feedbacks imply a runaway effect – only EXTREMELY strong positive feedbacks.
“ABG is assuming that any feedback must be positive.”
No I am not. I study plants – they are a negative feedback. What I am suggesting is that a climate system where the NET feedback is negative doesn’t fit with reality. We cannot explain observed changes in climate with a net negative feedback. All of the evidence points towards a predominance of positive feedbacks over negative feedbacks.
Please be a good skeptic and investigate your claims before spouting them. Look it up and think it through: Does a sensitivity of 0.1°C per W/m2 make sense? Do positive feedbacks really lead to an unstable climate? No and No.
Skeptics shouldn’t have an agenda, they should have a curious mind that seeks the best answers. In general, scientists are about as skeptical as it gets. We can’t wait to be the one to show that the other is wrong! Then why is there such a broad consensus on the main principles of climate change? Because it’s the best answer – far and away. There’s no agenda.
ABG (13:22:01)
Well, before getting that far, ask your self “does the idea of a single unchanging climate sensitivity make sense?” I say that climate sensitivity is temperature dependent. This is because, like any heat engine, as the temperature rises, the parasitic losses increase. And with the earth, the throttle also shuts down.
Consider a day in the tropics. When it is cool in the morning, there are no clouds. Temperature rises quickly as the sun’s energy increases, so climate sensitivity is high.
By about 10:30, however, clouds start to form. And although the energy from the sun continues to rise, the temperature rise doesn’t keep up. So the corresponding climate sensitivity (warming per additional unit of solar energy) is lower.
As an example from another field, consider an old, non-aerodynamic car. Give it some gas, and it will go a certain speed. Double the amount of gas, however, and the speed doesn’t double. Why not? Because the aerodynamic drag from the air increases roughly by the square of the speed. So what is the “speed sensitivity” of the car to an increasing input of energy? Well, it depend on the starting speed, just as the climate sensitivity of the planet depends on the starting temperature.
The same is true for the planet as a whole. For example, radiation losses rise as temperature to the fourth power, so as the surface warms, radiation increases faster than temperature. Evaporation (a parasitic loss) also increases faster than temperature. So each additional degree of warming takes more and more energy to achieve.
This is why, for example, that the oceans never get much over 30°C. A combination of evaporation, cloud cover, and thunderstorms makes the climate sensitivity over the warmest oceans effectively zero …
As a result, I say that climate sensitivity is a function of temperature, and the idea of a single unvarying “climate sensitivity” for the planet is an incorrect understanding of a dynamic system.
I despise statements like this, they are so vague as to be meaningless. There is a broad consensus, for example, that the earth has been warming over the last few centuries. On the other hand, there is no consensus on the net effect of aerosols, even the IPCC says we have a low level of understanding of their complete effects. Any time anyone starts talking about “consensus” I tune them out, because I know that they are not talking science any more. See here for more information on the dangers of consensus.
ABG (13:22:01 16Mar10) wrote:
” IF the ultimate climate sensitivity to a radiative forcing is 0.1°C per W/m2, the climate system makes no sense”
I previously posted that:
1. The Surface sensitivity, at equilibrium, is between 0.095 and 0.15 DegC/W/m^2.
2. This is quite different to the upper atmosphere where the sensistivity is about 0.3 (I said 0.4, but had not allowed for the emissivity, which for the atmosphere is much less than 1).
The Surface sensitivity is derived directly from the First law of Thermodynamics which gives the surface balance equation:
Forcings = Response to Forcings
or, Absorbed Solar Radiation + Back IR Radiation from the Atmosphere = IR Radiation from the Surface + Evaporated water + Direct Conduction into the Atmosphere.
Differentiating, I get:
d(Forcings) = d (IR Radiation from the Surface) + d (Evaporated water), assuming that conduction does not change, which seems most reasonable – equivalent to assuming the same sort of relationship between the boundary layer and the surface at the slightly elevated temperature, at equilibrium.
d(IR Radiation from the surface) is evaluated from Stephan’s law as 4sT^3dT, where s is 5.67×10^-8. d(evaporated water) is 78xdT where x is the percentage change in Evaporation per degree.
Putting reasonable numbers for x in , you get 0.095 to 0.15.
If one accepts the hypothesis that the thin, thermally feeble upper atmosphere drives the solid, thermally huge Surface, then you can probably get away with claiming a sensitivity of 0.3. On the other hand, given the uncertainty in evaporation, given the poor state of knowledge of the clouds, convection and water vapour, is it reasonable to use an upper atmosphere number for the Surface temperature sensitivity?
Surely, the boundary layer is driven by the surface. The upper atmosphere cannot drive this layer, as it is not invited to the thermodynamic party by the Second Law.
What drives the surface is the Forcings at the surface – and there are only two at equilibrium:
Absorbed Solar Radiation
Back IR Radiation
We know that if the temperature increases, Evaporation increases (there are arguments about how much – the climate science consensus seems to be “as little as we can get away with and still keep our huge positive feedback”, but this area of the “science” is very far from settled.), so cloud cover should increase, resulting in a REDUCTION of incident Solar radiation, ie a reduction in forcing.
We also know by doing the numbers, that to maintain a Surface temperature 3 Degrees higher than at present, the forcing from Back IR Radiation has to increase by a large amount – by between 22 and 32 W/m^2, weven without the additional forcing required to offset the increased cloud.
So according to the We’re-all-about-to-fry-because-of-the-warm-sky brigade:
1. A doubling of CO2 causes a radiative imbalance of 4W/m^2 at the Tropopause. This “radiative forcing” translates to a SURFACE temperature change of about 1DegC, increased by positive feedback to 3DegC.
2. At the surface then, the initial 1 DegC change is forced by a change in surface forcing of between 7 and 11W/m^2 (Where does it come from?) and results in 2 to 7% more evaporation.
3. But that’s not all (you forgot the Steak knives). By the time the system has settled down into an equilibrium state, the 4W/m^2 tropopausal imbalance has been translated by magic to a 22 to 32W/m^2 surface imbalance, this being the change required to maintain the surface at its new elevated temperature.
Please account for this forcing.
ABG (13:22:01)
Well … no. You are assuming that the temperature is set by the change in forcings. However, we have no evidence that this is the case.
For an example from another discipline, consider the temperature of the human body. It is very insensitive to the environmental temperature. When the forcing from the environment goes up or down, the human body temperature barely responds.
But when we get a fever, our temperature can spike radically. All the human body’s lack of sensitivity to forcing shows is that human temperature is not set by the forcing … but that doesn’t mean it can’t change as you claim.
See my post here for a different explanation of what sets the temperature of the earth.
w.
Willis Eschenbach wrote: “You are assuming that the temperature is set by the change in forcings. However, we have no evidence that this is the case.”
We have NO evidence? In which scientific world do you live? You could lean towards the vast body of research linking forcings and temperature OR you could lean toward a single unsupported (by the evidence) hypothesis that the earth will maintain its temperature. It’s certainly possible that tropical clouds could play an important role, but it is not well supported by the data. If it were supported by the data, I would certainly give it consideration – it is an interesting and plausible hypothesis. However, alternative explanations (i.e. forcings change temperature) are supported by the data.
Also, you are very liberal with your use of the word “stable”. Using “bi-stable” doesn’t cut it either as the last several hundred thousand years don’t really show much stability in any way. Huge temperature increases in 5000 years followed by long-term cooling over 50,000-100,000 years with lots of noise in between. If your “thermostat” allows for this much variability, I’m not at all convinced in its ability to dampen future warming.
Putting forth hypotheses is good. Accepting them and promoting them without solid empirical evidence is not.