Why Greenhouses have nothing to do with the Greenhouse Effect, and more importantly, why CAN'T I microwave toast?
A greenhouse is a glass house sealed to keep air in but made of glass allow sunlight in. This sunlight contributes to the heat in the greenhouse by warming the ground or other material in the greenhouse, and of course the light energy is used by the plants. But the point of a greenhouse is to keep air that is warmed, by the sun and/or heaters that may be required in the greenhouse, from wafting away.
This is not how the so-called "greenhouse" effect works. There is no thing out there keeping warm air from wafting away from the planet. The air just stays there, greenhouse effect or not, moving around and doing the weather thing, and looking blue much of the time.
It is possible to find descriptions of the greenhouse effect (in the atmosphere) that make the analogy very directly, but this is incorrect. A gardener's greenhouse works because it keeps air that has been warmed from leaving the vicinity at the same time it lets in light for plants to use, while the greenhouse effect in the atmosphere is different enough that the gardener's greenhouse analogy is not as useful as it might seem. So let's look at the Earth greenhouse effect, and in so doing, focus on what a "greenhouse gas" is and how it works.1
The sun is very hot. In part, this means that the matter that the sun is made of emits energy of some kind, and since it is VERY hot, this energy tends to be of very high frequency (short wavelength) ... in what we call the "electromagnetic" range of frequency. The relationship between an object's temperature and the frequency/wavelength of energy it emits is a matter of physics beyond our current scope, but you can think of it this way: A slowly moving object (say something vibrating at a few hundred up to several thousand times a second) will "hum" ... it will emit sound. Each movement of the object "back and forth" makes a "wave" of sound, so the faster the movement, the higher pitch the sound.
Electromagnetic radiation ... which sometimes goes by the name of "light" or "radio waves" and so on ... is a kind of energy that can be stored in and sometimes comes out of atoms. It is a phenomenon happening at a much higher frequency than this sound wave analogy, and instead of being a series of sound waves (which involves the repeated compression of, for instance, air molecules) it is a series of waves and/or particles sometimes going by the name of photons. As you probably know already, this kind of phenomenon cannot be described as a stream of "things" (photons) in a way that explains all of its properties, and it cannot be described as a "wave" of energy in a way that explains all of it's properties. If you really need to think about electromagnetic radiation in detail, you have to think of it as both/either/or particle and wave. Fortunately, you don't need to think about it at this level to understand the greenhouse effect. What you do need to know is that this form of energy has a wide range of wavelengths, some of which we see ("light"); the frequency of the the energy determines much of its properties; and hotter things emit higher frequency wavelengths because the atoms in the hotter things are wiggling back and forth faster.
A quick digression on frequency and wavelength: Frequency is the rate at which something vibrates, or changes its state ... like from negative to positive charge, etc. measured in units such as "billion cycles per second." "Wavelength" is measuring the same exact thing, but instead of frequency per second, it is how much distance is traveled by this energy ... typically moving at the speed of light ... before it completes one full cycle from one state to the other. Think of it as the distance between the tips of waves on the sea. If the distance between the wave tips is shorter, there are more waves hitting the shore per minute, but if the distance is greater, fewer waves hit the shore per minute. Higher frequency (many waves) = shorter wave length, lower frequency (few waves) = longer wave length. (The analogy of waves on the sea will only get you so far, however.)
If you knew about a certain wavelength, and discovered an energy of shorter wave length, you might think of calling this "shortwave." If you then discovered even shorter wavelength (higher frequency) energy, you might have to call this "microwave" (because you already used the word "short") etc. Thus we have things we call shortwave radios and microwave ovens. These different machines use energies of different wavelengths.
Light (electromagnetic radiation that our eyes have evolved to convert to neural signals ... i.e., energy we can see) has a range of wavelengths from about 700 to 400 nanometers (nanometers are very small ... there are 1,000,000,000 of them in a meter). Energy that is of higher frequency is called ultra violet, because the highest frequency light we see is what we call "violet" in color, so higher frequency is "ultra" (ultra = extreme). Energy of lower frequency is called "infrared" because the lower end of the frequency range of visible light is called by us humans "red" ... "Infra" means beneath, as in infrastructure (the roads, sewers, etc.) or "inferior."
When you feel heat, you are actually perceiving energy that is down in this infrared range of wavelength. The next level down in frequency from infrared is called "Microwave." The boundaries between these named ranges of wavelength/frequency are not always stark in terms of the effects of the energy. The higher frequency end of microwaves and the lower range of infrared will both cook your food. The higher or middle end of infrared happens to cook your food in a way that facilitates the famous "Maillard reaction" ... a reaction between sugars and amino acids that makes your food taste good. This is why microwaves and "heat" both cook your food but the food comes out differently in taste and texture depending on method.
Yes, this IS related to global warming. The difference between microwaving vs. toasting a piece of bread has to do with the way in which specific, different, molecules react to specific, different, wavelengths of energy. A bunch of water molecules heated in a microwave or on a stove is the same ... hot water. The various molecules in a slice of bread heated in a microwave vs. in a toaster react very differently, producing very different results (something inedible vs. toast).
A gas is a "greenhouse gas" because of the way it (its molecules!) reacts to a particular form of radiation (infrared).
Energy From the Sun
Most of the energy that reaches the surface of the earth is high frequency, including light. Light is only barely affected by the gases that make up our atmosphere. In other words, as the light wave/particles are moving through the atmosphere of the earth, most of them don't get absorbed by the stuff the air is made out of.
(Now, this is not a coincidence. That which we call "light" moves around pretty freely in our planet's atmosphere. We evolved on this planet. Our eyes can detect in fine detail this energy that moves around freely. Our eyes can't detect the energy that is typically trapped by the magnetic field of the earth, because it is never around, so why would natural selection shape our eyes to be able to "see" this? If we evolved on a different kind of planet, physicists, would probably have a somewhat different set of instruments to detect and measure the energies they are so interested in. Perhaps an "optical" telescope would be used for a somewhat different (shifted one way or another, or narrower, or broader) range of "light." OK, that was today's shameless promotion of thinking-of- EVERYTHING -in-terms-of-evolution digression...)
When this high frequency (short wavelength) energy from the sun encounters the relatively solid matter that the earth's surface is made of, including rocks, plants, liquid water, etc., it is absorbed by that matter. Not so much by the MOLECULES that matter is made of, but by the ATOMS that those molecules are made of. At this energy level (light, radiation, and such) the absorption is happening at the atomic level ... this is an important fact.
You can think of it this way: Photons (light "particles") have a very high probability of encountering an atom in, say, a rock. The atom "absorbs" the photon .... this means the photon essentially becomes part of the atom for the time being. An atom with this extra bit (the photon) changes. The way it changes is that one of the electrons (the outermost part of the atom is a cloudy space within which the electrons are flying around) stores this energy, what physicists refer to as "becoming excited." This is probably why physicists do not get a lot of dates.
What has happened here is that high-frequency energy, the kind of energy that is emitted by a very hot object, has found its way to a cool object (earth surface temperatures are cool relative to the sun), and gotten stored there in the atoms that object is made of.
The Earth is a Big Space Heater
Now, this relatively cool matter can release the energy (depending on various laws of physics I won't go into), but since the wavelength (frequency) of the energy released by an object is proportional to the temperature of the object (remember that from several paragraphs back?) this energy is of lower wavelength than sunlight. So, the relatively hard surface of the earth converts high frequency energy into lower frequency energy. This low frequency energy is what we think of as "heat."
In this way, the surface of the earth is a simple machine that converts sunlight into heat. So, as long as the sun is shining on the earth, the surface of the earth is a big heater. Since the atmosphere is sitting right there on top of the surface, this big heater (the earth's surface) heats up the atmosphere. Eventually, this heat ... now in the atmosphere ... makes its way to the outer limits of the atmosphere where it radiates off into space.
Neither rain, nor sleet, nor snow, nor gloom of night ...
On its way towards outer space, this heat energy is absorbed by the molecules of the atmosphere itself, then re-released. Think of a bit of energy as a letter that you put in the mailbox. You know that when you put the letter in the mailbox, it does not simply disappear and rematerialize in the recipient's mailbox. The letter changes hands many times, from the postal worker who picks it up, to other postal workers who sort the mail, move it from one place to the next, to the postal worker who eventually puts it in the recipient's box. Hold this analogy in your mind for a moment...
If the atmosphere was made of a gas that is lousy at absorbing heat energy, the heat would radiate more or less directly into outer space, the total time required being a function of the total thickness of the atmosphere (and some other things). But if the atmosphere contains a certain number of molecules that are good at absorbing heat energy, that is like having a lot of extra postal workers ... a certain unit of heat energy leaving the surface of the earth will be absorbed by a molecule, held for a while, then released, again and again. The greater the relative number of these heat-absorbing molecules in the atmosphere, the more this will happen, and the total amount of time this energy hangs around in the atmosphere will be greatly increased.
So the difference is ... a postal worker picks up the letter directly from you and drives it directly to the recipient, vs. there is a system of many postal workers mucking around with your letter.
Imagine that a bit of gas absorbs a unit of heat. It then releases the heat. It will release the heat in all directions around itself. So a unit of heat that may have been moving "up" towards the outer edge of the atmosphere gets stopped and then released, and some of it continues on it's way to the edge of the atmosphere, but some of it is released back towards the surface of the earth. So it isn't just the number of postal workers (greenhouse gas molecules) that slows down the delivery (of your postcard, or of the heat to outer space) because there are more "handlers." Imagine every postal worker has a 50-50 chance of sending your post card on in the right direction towards it's destination, and a 50-50 chance of sending it back in the direction of the sender. That's what the gas does. It randomizes the heat's flow.
So a million letters mailed each day in an efficient postal system all move through the system quickly, so at any moment there is just over a million or so letters in the various bins and boxes in the postal system. But if we add just a few postal workers and program their behavior to be random, the letters will build up, and the bins, boxes, trucks, and mailbags will on average have more letters on a given day than otherwise.
Greenhouse gases are molecules that absorb and release heat passing through the system in random directions. The more greenhouse gases, the more the heat is passed around in random directions in the atmosphere, and the more the atmosphere "swells" with this heat.
Recap
Hot object (sun) irradiates cold object (the earth) with high frequency energy, cold object (earth's surface) converts high frequency energy into low frequency energy (heat) which radiates away. Greenhouse gas molecules interfere with this process by randomizing the direction in which the heat goes.
But ... what are greenhouse gases, already?
So why do some molecules absorb (and release) this heat while others don't so much? It's a matter of how the atoms that make up the molecule are bound together. The atoms in a molecule are held together by electromagnetic forces. The nature of this binding between atoms varies in different kinds of molecules. A molecule made of two identical atoms (which is how atmospheric nitrogen or oxygen usually occurs, two molecules each) are bound together with a kind of tightness and symmetry that they essentially act like they were a single atom, when it comes to low frequency radiation (like heat). Heat moves across a collection of gas molecules of this type a bit like waves in water ... the molecules all sit there but the movement of the molecules (heat) passes across this matrix of molecules: Heat "arrives" by pushing on some molecules, then the molecules just push the next ones in line ... and thus the heat passes along. (sort of) But if the molecule is made of different atoms, put together a certain way, then the relationship among the atoms in the molecule is in a sense flexible, so this heat energy (motion) can go from a wave of movement across a matrix to a bunch of movement WITHIN the molecule itself. Thus the energy is trapped for a while inside that molecule.
When the molecule then releases this energy, there is no "memory" of the direction in which it was moving ... the energy now simply moves outward from the molecule. There may be a directionality to that ... frankly I don't know ... there must be in some cases ... but the direction of emission of this energy from a given molecule which is floating around in the air is not related to the direction from which the heat originally came, and there are a lot of molecules, so the effect is omni directional. The non-greenhouse gas molecules are like the hallways in the post office ... they have nothing to do with stopping or redirecting the energy (letters). The greenhouse molecules are the perfect random postal workers. They stop the energy (letter), hold on for a while, and then send the energy (letters) off in a random direction.
Dry "atmosphere" is made of Nitrogen (78%), Oxygen (21%) and Argon (1%), and a tiny amount of other gases. The atmosphere can then include varying amounts of water vapor. Less than one percent of dry air is carbon dioxide and other greenhouse gases not counting water. At "100% humidity" something like 7% (depending on temperature) of the air is water vapor, and there can be as little as almost zero locally. Water vapor is a greenhouse gas.
Water vapor is both fairly fixed and highly variable. The total amount of free water on the earth does not really change, and how much is in the atmosphere at one point in time in a given spot varies a lot. The other atmospheric gases don't change back and forth between gas and liquid (or solid) like water does, so they are more or less a constant (on a day to day basis) but since water converts back and forth between liquid or solid and gas form at typical Earth atmospheric temperatures (through evaporation and precipitation), it varies all the time. This, mainly, is what we know of as weather (along with a few details such as if the non-gas water is liquid or ice/snow!). The point is that humans do not directly change the water vapor system in any way that alters the greenhouse effect, but by adding (or removing) the other greenhouse gases, we can have large effect.
So how long it takes for your letter to get delivered on a given day may have to do with how many other people send mail that day (seasonally varying perhaps) and things like traffic, delays at airports, etc. but that all evens out over time so there is an average delivery rate. But if you go and hire twice as many inefficient postal workers, you slow down all delivery, on average, and over the long term.
Carbon Dioxide is the main greenhouse gas that humans add to the atmosphere. Prior to human effects it is estimated that the level of this gas in the atmosphere was about 260 - 280 parts per million for the previous thousands of years. The current level, elevated primarily because of human activities, is about 380 parts per million. That's a lot of postal workers.
1In an earlier version of his post, a few commenters insisted that the analogy is the same because glass transmits light but not heat, so a gardener's greenhouse is like the atmosphere. However, glass transmits heat pretty nicely. The reason a gardener's greenhouse works is not because the glass does not transmit heat, but rather, because glass does not let the warmed air to escape. One can add to this, and this has been done only recently in actual greenhouses, double layer glass, which has air trapped between two layers of glass. The air does not transmit heat very well, so the greenhouse is reasonably well insulated.
- Log in to post comments
More like this
Glass is a pretty fair conductor of heat. It's transmissivity in the far infrared (300 K emissions spectrum) is not impressive. Partly because of reflectance.
When we want to do far-IR spectroscopy or imaging we don't use glass.
I understand conduction to be a subset of transmission. (radiation and convection being two other modes)
As far as heat goes, glass conducts heat about 20 times better than air does.
Greg, thank you for that.
Layman me had no idea that the heat we're talking about is a far later byproduct of the sunlight that hits the earth. I was wondering where you were going with the mailman analogy, but when I got to the end of the article, it made a hell of a lot of sense.
I have a much better grasp of what's going on now. Thank you for that!
But, even in the real world, doesn't your mail have a 50/50 chance of getting where you want it to go anyway....?
{rimshot}
Not a bad layman's level discussion of the "greenhouse" effect.
Now you just need to discuss the fact that the effect of adding more CO2 is logarithmic not linear, and that for each additional CO2 molecule (or postal worker in your analogy) there is a diminishing amount of warming. A doubling of CO2 is agreed by most scientists to, by itself, add only about one degree Celsius to the average global temperature.
The real issue is feedback. If, like most physical systems, that feedback is negative then there is little reason to be concerned about anthropogenic CO2. If the feedback is positive then we need to know the magnitude of that feedback to asses the possible warming.
Clouds are the biggest feedback issue and current global climate models do a very poor job of accounting for their effect.
Think of the mechanisms involved:
* Convection involves the bulk movement of hotter/colder material to a different location.
* Conduction involves what amounts to acoustic transmission of energy via molecule-molecule mechanical forces (or hot electrons in metals)
* Radiation involves photons emitted or absorbed by the material (in this case, the surface of the Earth or the leaves of plants in the greenhouse.)
Glass is fairly low density and has a great modulus of elasticity -- it's a very good conductor of acoustic forces. Thus it conducts heat well. As a solid (or supercooled liquid, it's sorta strange) it's a rather crappy convector.
WRT radiation, the primary question is whether a photon interacts with the material at all. All materials have absorption spectra: the amount absorbed varies by wavelength. Glass is pretty transparent in the visible range -- but have you ever noticed that really thick glass such as conference tables looks greenish? Different absorption depending on wavelength.
BTW, you're quite right about the nondirectionality of reradiated photons. Photon->molecule results in molecule at higher energy state with a bit of momentum change in the direction of the photon's initial direction. Molecule->photon is the same in reverse, with the direction being random. If the reradiated photon is back in the direction that the first came from, you get 2x the momentum transfer.
As long as I'm quibbling, there are a couple of other minor effects. Well, "minor" in the sense that they aren't necessary for reading most of the news, but "major" in terms of nuts-and-bolts effect on the Earth.
Carbon dioxide, as a gas, has a rather sharp absorption spectrum. Even a 100% CO2 atmosphere will transmit heat at some wavelengths, and it doesn't take 100% to block almost all of the radiation in the CO2 wavelengths. After "saturation" more CO2 doesn't make that much difference.
Unfortunately, other greenhouse gasses have different absorption spectra. Such as methane. Not a lot of it in the atmosphere right now, although it seems that since the beginning of agriculture there's been more than in previous interglacial periods. If we warm up the Earth enough to defrost Arctic tundra or warm up the oceans enough to release deep-water clathrates, a lot more will be released. Methane spectra are different from CO2 spectra and pretty much add to the heat retention. That's one of the "tipping points" that climatologists sweat over.
Lance, you speak as though the climate has not already warmed. We have already managed about a 0.6 degree C warming, which is not a small amount. Unfortunately, it is not at all likely that feedback effects are going to work in our favor. Most effects are likely to be positive feedback (more Co2 -> warming -> more forcing (one way or another) of warming.
"Lance, you speak as though the climate has not already warmed."
How so? As you point out the average global temperature has gone up about 0.6 - 0.7C. The question, among many others, is whether this is a "bad" thing and how much of it is anthropogenic and how much is due to natural variation.
If the evidence for the Medieval Warm Period is correct then this level of warming may be nothing out of the ordinary and may be, on net, beneficial.
"Unfortunately, it is not at all likely that feedback effects are going to work in our favor. Most effects are likely to be positive feedback (more Co2 -> warming -> more forcing (one way or another) of warming."
Well, that's an issue of some debate among climate scientists. Even the scientists that agree that the climate's sensitivity to CO2 is enhanced by positive feedbacks disagree on the magnitude of that enhancement.
Hence the wide disparity of estimates of the actual effect of doubling CO2, with estimates ranging from 2.0 - 10.0 C often quoted, depending on the source.
Lance, sorry, but you are hoplessly out of date and incorrect. That will be enough of that.
@D.C.: Many of the infrared CO2 bands are saturated - at least around the middle of the bands - yet the wings still absorb quite a bit and in a linear fashion. There guys have some infrared spectrometers pointing at the sun:
http://www.ndsc.ncep.noaa.gov/
Maybe it's possible to get some spectra from them to show the effect of CO2 absorption - see if there is a measurement taken with the sun high in the sky and again with the sun ~20 or 30 degrees above the horizon. It will take some effort to point out the CO2 regions though. :)
@Lance: No one has come up with any negative feedback mechanism which withstood even the slightest scrutiny; the only suggested feedback mechanisms which have data to support them are the positive feedbacks. It would be quite a gamble hoping for a significant negative feedback which no one thought of - possible in theory, but science works with what it knows and tries to explore the unknown - we don't say "hey that sounds possible" and then bet on it without evidence.
"Lance, sorry, but you are hoplessly (sic) out of date and incorrect."
Out of date, incorrect, where?
"That will be enough of that."
Oh, I see. So much for an open scientific discussion of the evidence huh?
Sorry, I mistook you for an actual scientist.
"The question, among many others, is whether this is a "bad" thing and how much of it is anthropogenic and how much is due to natural variation."
Considering that analysis of atmospheric carbon isotopes has revealed that it is essentially all ours, that isn't a realistic question any more.
"If the evidence for the Medieval Warm Period is correct then this level of warming may be nothing out of the ordinary and may be, on net, beneficial."
Of course, the fact that the MWP disappears when you look at a Global - rather than Northern Hemisphere - scale shows that your assertion is meaningless. (The "little ice age" also changes at the Global scale. It doesn't entirely disappear, but it becomes much less pronounced.)
"Well, that's an issue of some debate among climate scientists. Even the scientists that agree that the climate's sensitivity to CO2 is enhanced by positive feedbacks disagree on the magnitude of that enhancement."
There is some healthy discussion about the extent of the feedback, but the skeptics that attack this virtually always focus on one: clouds (they also typically understate the forcing portion of CO2, but that's another issue). The problem is that while low-lying clouds are likely negative feedbacks (research cuts both ways on this question), the myriad of other feedbacks skeptics ignore (loss of albedo effect, thawing of CO2 and methane sequestering permafrost, increased desertification of tropic and near-tropic zones, etc.) are positive to the extent that we know the overall feedback effect is positive. In the end, that's the thing that matters most. The forcing (which is not part of the "sensitivity" - get your terminology right) and the feedbacks all contribute to a warmer pale blue dot than before.
These kinds of "I know just enough to get myself into trouble" comments that Lance is writing perfectly emphasizes the need for clear communication about what science says is happening and what it means for us. Unfortunately, ignorance more often breeds arrogance than it does humility. While the Earth will survive anything we can do to it, we ignore at our peril that every major climate shift coincides with a known mass-extinction. Accelerating the time needed to make that shift means more danger, not less.
Me: "The forcing (which is not part of the "sensitivity" - get your terminology right) and the feedbacks all contribute to a warmer pale blue dot than before."
To clarify, I wrote this about your statement of "...the climate's sensitivity to CO2 is enhanced by positive feedbacks..." which made it sound at first glance like there is more to the sensitivity than the feedbacks. Since the only factors in play are forcings and feedbacks, I assumed that meaning. The totality of the feedbacks to a given forcing are by definition the sensitivity to that forcing. As I reread the comment, though, I realize your statement is not against the definition but merely a little ambiguous. I'll give you the benefit of the doubt. Sorry for the selective reading.
Mystyk,
"Considering that analysis of atmospheric carbon isotopes has revealed that it is essentially all ours, that isn't a realistic question any more."
I was referring to the 0.6 - 0.7C increase in average global temps not the CO2. Which is clear if you read the sentence right before the one you are critiquing.
"Of course, the fact that the MWP disappears when you look at a Global - rather than Northern Hemisphere - scale shows that your assertion is meaningless. (The "little ice age" also changes at the Global scale. It doesn't entirely disappear, but it becomes much less pronounced.)"
These assertions are highly contested in the literature. One need only read the recently leaked (stolen?) emails of certain CRU scientists to see that some of them even disagree with your assertion.
You then make some further unfounded assumptions, and insults, that you retract and partially apologize for in your next post.
I acknowledge that this is a highly contentious and politicized topic. I appreciate the tone of your second reply if not the first.
I am a trained physicist and currently I am employed as a university math instructor. This is to head off the inevitable, not to mention spurious, arguments of qualifications.
I can certainly understand any of the primary literature which is not to say that I cannot be educated as to the scope and nuance of the research in the field.
I voted for Obama and have never been a Republican or worked for any oil or coal related industry. My issues with AGW are based solely on my interpretation of the scientific evidence.
My cards are on the table. What about you Mystyk?
I'd love to hear more on this topic. Having been employed by the EPA to produce global warming gas blends for CO2 related emissions testing, I'm always interested in discussion on the topic, even if it always seems one of extreme angst. It's nice to find a place for discussion where we haven't all been reduced to name calling from the get go.
Being in the chemical industry, specifically an industry which deals in a high amount of Methane gas, I always wonder why there isn't a greater discussion of the Methane effects on global warming. Especially with the recent increase in Methane growth after a rather stable period of decline.
@James: At the moment all non-water non-co2 greenhouse gases combined have an effect far less than that of the increasing CO2. So if we can push methane up from the atmospheric concentration of ~1.8ppm to, say, 20ppm then methane becomes an issue. The thing with that is methane has a much shorter residence time in the atmosphere, so you have to pump out incredible amounts to drive up the methane in the atmosphere and you have to sustain that release (much of the methane will be converted to CO2 over time). Humans are increasing the methane in the atmosphere, but the increase is simply dwarfed by the increase in CO2 and the same goes for its heat retention effect.
The biggest concern with methane is that permafrost regions may be storing huge amounts of methane and also have the capability to generate incredible amounts of methane if only they'd warm up. So the thinking is, warm up the tundras, release a lot of methane in a short time, push the temperature way up and take a few hundred thousand years to recover.
We have warmed the temperature 0.6-07 degrees centigrade. Already the polar ice is melting, mountain ice is melting, many regions are seeing early springs and later winters.
I wonder what 4 degrees will be like?
The biggest potential feedback is water vapor. NASA recently published a summary of observations from the AIRS satellite that confirms that water vapor feedbacks appear to be tracking model predictions quite nicely.
One more reason to have more confidence in the models than the well-known and hand-waving claims of denialists like Lance.
Quantify "very poor" in terms of degrees C per doubling of CO2, pleease.
Climate modelers state that uncertainties in cloud feedbacks are the major reason why climate sensitivity to a doubling of CO2 lies within the 2-4.5C range with a most likely value being close to 3C. Better understanding of cloud feedbacks will narrow that range.
Whether the mainstream quantification of "very poor" is large enough to warrant ignoring what climate science is telling us is something each of us must decide for ourselves. I don't find the fact that there's a small chance sensitivity might be 2C per doubling particularly comforting.
The stolen e-mails are not part of the literature (with your BS in physics you should know this). "Highly contested in the literature" is an exaggeration. There's evidence for a variety of warming events over a several hundred year period which aren't synchronized globally. This evidence is not "high contested". What's highly contested is the very limited evidence for any synchronized global event.
Mann recently published a paper on this, summarizing results from analyzing 1000+ proxy records from around the globe.
The problem with Lance is that while science marches on, he repeats his claims unchanged.
I just noticed that Lance claims that science claims a range for the sensitivity to a doubling of CO2 2C-10C. 10C is far, far higher than any value coming from any credible mainstream effort to quantify sensitivity. I'd like a credible published reference for that figure. I know that Hansen believes the figure is higher than that given by current models but I also know that few within the climate science community agree.
OK, a little googling yields references of the sort, "a higher sensitivity such as 6C or even 10C can't be ruled out", but this isn't the same as stating a range of 2C-10C. However it does underscore the fact that the generally accepted 2.0-4.5C range with 3C being most likely, isn't normally distributed around 3C. The probability distribution is skewed towards the >3C range.
Ah yes, I wondered if dhogaza would slither in with his usual snide combination of misinformation and personal attack.
You hit all your usual low points I see.
"Mann recently published a paper on this, summarizing results from analyzing 1000+ proxy records from around the globe."
Nothing like citing a guy whose work has been proven time and time again to be biased, sloppy, and inaccurate.
Here is a recent peer reviewed study that questions the idea that the MWP was more heterogeneous than the current era.
Esper, J. and Frank, D. 2009. The IPCC on a heterogeneous Medieval Warm Period. Climatic Change 94: 267-273.
"Climate modelers state that uncertainties in cloud feedbacks are the major reason why climate sensitivity to a doubling of CO2 lies within the 2-4.5C range with a most likely value being close to 3C. Better understanding of cloud feedbacks will narrow that range."
It suddenly got breezy in here. It must be all the hand waving you're doing. It is quite possible that cloud feedbacks may have been assigned the wrong sign in the models that even include them.
So a sensitivity of >3C is possible because you like that number?
Oh, and there is the very inconvenient fact that global temps have been statistically flat over the last decade while CO2 has increased, but don't let reality get in the way of your vituperative ranting.
Thanks so much for this post. This is one of the aspects of global warming that I did not understand, now I have a better understanding. The terms "greenhouse gas" and "heat trapping" were always misleading, even though they might be somewhat technically correct.
Mann's still top gun in his field. Potshots from the likes of Lance, McIntyre, etc haven't hurt his scientific reputation one bit. You can rant about it all you want, no one in climate science gives a flying f***.
NASA GISS Model E is the only one I've looked at. It includes a module that models clouds through a convection model and quite nicely generates realistic results, including anvil heads that punch through the stratosphere. Cloud feedbacks using modeling of this sort isn't "assigned" a sign or value but rather is generated by the model.
When someone doesn't even know this, it's hard to take their claims seriously.
No, a sensitivity of greater (or less, as I pointed out when I stated the accepted 2.0-4.5C range) than 3C is possible due to uncertainties in the physics, mostly pertaining to clouds. Major models like Model E have been used very successfully to model paleoclimate which adds to the evidence that they're quite solid. As I mentioned, AIRS data shows that modeling of water vapor feedback - crucial because it's by far the largest positive feedback - matches observations very closely, which is another piece of evidence that they're quite solid.
As I said, science marches on, Lance continues to sing his unchanged tune.
Yawn. Exactly the kind of variability we've seen in the historical record. Exactly the kind of variability that models demonstrate in individual (not averaged ensemble) runs. Exactly the kind of variability that statisticians understand are expected when you have a lot of noise imposed on a relatively weak signal.
As someone with a BS in physics, you should know this.
For those interested in what a professional statistician who specializes in time-series analysis thinks, read this.
The paper also questions the idea that the MWP was as homogeneous as the current era.
From the abstract:
and later ...
Hit post too soon ...
In other words, the paper Lance cites doesn't support either view, that the MWP was synchronous and homogeneous as is warming today, as claimed by the denialsphere, or that it was heterogeneous and unsynchronized as most researchers in the field believe.
Also, Greg, i have a longer, previous post held up in moderation ...
And, Lance, this statement is a curiousity:
You didn't point out a single bit of supposed misinformation I "slithered in with".
If my pointing out that your training in physics amounts to no more than a BS is a "personal attack", maybe you shouldn't lean so hard on being a "trained physicist" when you try to buffalo people about climate science...
Ugh one last point ...
Lance mischaracterizes the paper. It doesn't question the idea that the MWP was more heterogeneous than today. It simply states that they don't think there's sufficient data to reach any conclusion about the MWP. It's critical of the analysis presented in IPCC AR4 in support of that idea, but is neutral on the idea itself.
That distinction may seem subtle, but it's important.
dhogaza,
I use my real name and never exaggerate my qualifications. I am continuing to pursue my graduate work, if slowly, and a bachelors degree in physics from Purdue University is nothing to be ashamed of.
What exactly are your qualifications? Or your real name for that matter.
You selectively dance around the papers main point, that AR4 wrongly assumes the MWP to be a localized phenomenon.
Christ the name of the paper is "The IPCC on a heterogeneous Medieval Warm Period." which it disputes. I brought this paper up in response to your assertion that the MWP was not "globally synchronized".
I notice you didn't quote this "...quantification of proxy data coherence suggests that it was erroneous [for the IPCC] to conclude that the records displayed in AR4 are indicative of a heterogeneous climate during the MWP."
This means that there is no reason to think that the "smattering" of data from many different sites over hundreds of years that show warming greater than or equal to the present day was not global.
While they do say that not enough data exist to say it was a worldwide phenomenon they also say that doesn't make it regional as you claimed it to be.
Also your confidence in cloud modeling is charmingly naive, why I could almost see lightening bolts coming out of those "anvil heads".
If the GCM's are so amazingly good at replicating the current and future states of the climate why is the IPCC's nominal projection, from AR4, of 0.2C/Decade outside of the 95% confidence interval when compared with any of the four main global temperature data sets when using the year 2001 as a starting point and out of the 95% confidence interval of all data sets, except for GISStemp for which it barely stays in bounds, when using a start date of 2000?
Oh, don't tell me those amazingly accurate models can't account for "...the kind of variability that statisticians understand are expected when you have a lot of noise imposed on a relatively weak signal."
Noise huh? What could that "noise" be? The buzzing noise in your head perhaps?
Hey, maybe it's that pesky "natural variability"? The same natural variability that warmed the planet without any medieval or Roman era Escalades inflating Co2 levels? The same natural variability which at the moment is making a monkey out of your favorite computer models?
Greg, are you gonna do part 3? This was great.