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.
EJ,
I believe that the IPCC says ~1.2C for non-feedback CO2 doubling, and that John Christy uses that number as well.
I think everyone could benefit from understanding the greenhouse effect operates at a timescale of hours. It operates at the speed of light and at the speed of quantum physics.
It is just a delay of several hours in the time in takes for the Sun’s energy from the current day and the previous day to escape into space.
Last night, the temperature in my backyard dropped 12C in less than 12 hours – a third of the greenhouse effect. If the Sun stopped for three days, it would be -100C in my backyard. The greenhouse effect is extremely limited in timescale.
There are some other lags in the climate system. The peak of the summer is 30 days after the summer solstice. The atmosphere and land accumulates / loses about 0.5 W / m2 per day as the season’s change. The peak of surface ocean temperatures is 80 days after the solstice. The surface ocean accumulates / loses about 0.2 W / m2 as the season’s change. The deep ocean can accumulate 0.1 W / m2 over long timescales lasting 800 to 1,500 years.
But the greenhouse effect is just a 12 hour delay in how long it takes for a photon of energy received from the Sun to escape into space.
A visible light spectrum photon comes in from the Sun at noon and hits a rock on the beach. The rock warms by one photon.
Overnight, that rock cools off and gives off that photon in the IR spectrum. A new CO2 molecule in the atmosphere produced the day before by a near-by coal-fired power plant now intercepts that photon whereas before that photon would have just gone right through the atmosphere and hit Venus a few minutes later.
An electron in that CO2 molecule then moves to a higher energy state for a picosecond and decides it doesn’t like the new higher energy state and it gives up that photon – one-quarter of the time downward, one-quarter of the time upward and one-half of the time sideways. For the picosecond of time that this CO2 molecule is at a higher energy state, the measured temperature of the atmosphere is now higher – one photon’s worth that is.
That photon then happily skips around from N2 molecule to O2 molecule to another CO2 molecule and so on. The measured temperature is one photon higher but it only spends a few hours in the atmosphere or back on the ground before it is sent flying off to Mars or Jupiter or to the rest of the Milky Way.
This happens on the scale of trillions and trillions of photons in various different wavelengths and through trillions and trillions of molecules in the air and on the ground which intercept photons of light at different wavelengths. But it happens at the speed of light and at the speed of quantum physics.
It is so complicated that only a very detailed climate model can hope to possibly simulate it. Even then, it might be impossible. If it impossible, then we need to rely on empirical data instead which should be able to tell us what really happens (versus just guessing at what really happens). This is my main focus.
What does the empiricial data really say since the entire system is just too complicated to model or to describe in formulae.
gary gulrud says:
Gary, as I noted this statement comes from the website that I linked to, which is by a retired meteorology professor who is sort of a militant in terms of correct pedagogy. He likes the statement because it avoids saying anything technically incorrect. (For example, he doesn’t like saying the atmosphere re-radiates the IR it absorbs because he argues the act of radiating is independent of the act of absorbing. It radiates simply because it has a non-zero temperature.)
I have mixed feelings about his statement myself though because the price that you pay for avoiding saying anything that is at all a shorthand and thus technically incorrect is that the statement does not give a very holistic view. (E.g., it begs the question of where the energy came from in the first place that raised the atmosphere up to a finite temperature.)
At any rate, these are all really pedagogical issues. I have no disagreements with him on the actual physics of what is involved.
maksimovich (12:22:58) :
Many thanks for that maksimovich!
Richard says:
Well, I count a few things. First of all, your numbers are confused. The fractional amount of CO2 in atmosphere by volume is ~0.000385, which is 0.0385%. Since it was ~0.0280% in pre-industrial times, we have raised the level by ~0.010%.
Now, that may not sound like much to you, but your intuition on this is bad for a couple of reasons: One is that 99% of the atmosphere consists of diatomic molecules (N2 and O2) that are transparent to infrared radiation. So, the remaining 1% play a disproportionate role in the climate. A second is that over a large range of concentrations, the radiative effect of CO2 is logarithmic in concentration, which again means that small amounts can play a disproportionate role.
Joel Shore,
At the beginning of my comments, I gave what I believe to be the correct definition of positive feedback, namely an internal amplification factor greater than 1. If you plug this number into any equation describing a feedback system, it will give you a runaway system. You say that my definition is not correct, but you fail to give an alternative definition and use a hand waiving argument about the positive feedback being “weak” or ” strong”. I am willing to listen to your argument, but only if you give me an objective and consistent definition of positive feedback, which will give you an enhanced response without runaway. I do not think that such system exists, in the climate, or anywhere else.
foinavon opines that “…the Lindzen data uses asumptions that we know are incorrect.”
Well now. Who are we to believe? foinavon? Or the head of M.I.T.’s Atmospheric Sciences department?
And Bill Illis, thanks for that explanation, which shows that there is simply a short delay when a CO2 molecule absorbs and re-emits a photon, rather than a runaway buildup of global heat.
Yes, you are.
“As Dr. Hansen has correctly argued, increases in atmospheric temperature cause the ocean to warm up”
I suppose I should throw out all the oceanographic courses, knowledge and the limited experience I have. With this statement, everything I’ve observed has been wrong….
I just don’t ever recall the water column, to any significant depth, to be affected in the way Dr Hansen portrays.
Larry – nice link. Dr Stevenson was a giant in the field. The ocean systems and mitigation effects on the the underpinnings of the theory of AGW have been vastly underestimated. The effects of the atmosphere, and by CO2 in particular, on the ocean sysytems has been vastly overestimated.
James Griffiths
“Sure, but without an atmosphere, the surface temperature would be much higher during the day, right?
Anyway, clearly a high intensity of radiation form the sun does outweigh a small radiation from the whole sky, because the vast majority of the sky is only radiating because it has been heated by processes resulting from the heating of the surface by the sun. Am I correct?”
In a word, no. The earth’s mean temperature without an atmosphere would be -18C. The sky radiates because it has been heated by both the sun and the earth’s surface.
Great article. Small quibble: in your list of important green house gases you list N2O. Should this be NO2?
And that’s how this whole thing got started…
Phil. (16:58:21) :
Any CO2 molecule which absorbs an IR photon will be rotationally/vibrationally excited, the radiation lifetime of that excited state is order microseconds or greater whereas the average time between collisions is less than 1 nanosec.
Even going along with that and that the N2 and O2 take up the heat, they in turn must re-radiate that heat [because they are now warmer], half up and half down [which then eventually heats the surface. Nothing changes with that, you still get a greenhouse effect.
Simon Evans, I agree with what you say. However, to put it in context, the whole history of life on earth is constant change. The whole history of mankind is conflict and adaptation to change. Plus ça change, plus c’est la meme chose.
DR says:
Well, his quote is not incorrect but it is subject to misinterpretation. It is indeed a robust feature of climate model simulations. However, it is true that such warming is a robust feature of those simulations whether the warming is driven by increases in greenhouse gases or something else.
Indeed, if you actually read that whole paper rather than just quoting a single sentence, you would learn that one of their major points is that the amplification applies not only to the long-term temperature trends due to rising greenhouse gases but even to shorter-term temperature FLUCTUATIONS (such as those that occur due to ENSO). And, they point out in that paper, that this amplification of the fluctuations is seen observationally in all the data sets, which tends to confirm that the models are handling the basic features that produce this (convection) at least approximately correctly. It is only when one looks at the multidecadal trends that one sees significant discrepancy between the models and (many of) the observational data sets. Since these trend measurements are very sensitive to artifacts that are known to exist in the data, this is why they suspect that the problem is most likely to lie with the data.
To summarize it more succintly: The models and observations agree over the timescales for which the data is reliable but the observations disagree both amongst themselves and (in many cases) with the models over the timescales for which the data is known to have serious issues.
Roger Knights (14:05:43) :
OT: Bloomberg story: “Obama Plan Has $79 Billion From Cap-and-Trade in 2010″
(Moderator: Snip if too off.) One reason for this dialog is to avoid a REAL catastrophe from fear-based labeling of CO2 as a “pollutant.” With piles upon piles of evidence that the biosphere has survived and excelled in higher CO2 environs and FACE studies showing unarguable evidence for CO2 fertilization – taxing this trace gas that enhances plant growth is tantamount to calling a dyslexic the spawn of the devil.
Joel Shore,
You did not reply to my post on Gavin Schmidt et al 2005 quoted thusly:
“Tropospheric warming is a robust feature of climate model simulations driven
by historical increases in greenhouse gases (1–3). Maximum warming is predicted
to occur in the middle and upper tropical troposphere.”
http://www.osti.gov/energycitations/servlets/purl/881407-xk2Sdg/881407.PDF
Your statement, and those being bandied about the various pro-AGW blogs are now back pedaling. With that, you are saying GCM predictions are mistaken.
If your version is correct, why then have Schmidt, Santer and the usual suspects been attempting to a) discredit satellite data and b) attempt to show models in agreement with observations? Surely you are aware of the serious “problems” with Santer et al 2008?
You can’t have it both ways. Are GCM predictions, which are driven by increases in GHG emissions, correct or not?
Assuming that the AGW hypothesis is correct, should not Mars (atmosphere 90% CO2) be a tropical paradise?
Re: Steven Goddard (05:51:38) :
“Ric,
I did a canoe trip down the Green River in Utah about 25 years ago in July. It was too hot to sleep when you went to bed, and too cold to sleep when you woke up!”
Sorry to go a bit OT Steven, but your account of this just fascinated me. I spent 6 months in a camp on the banks of Mahat River in Central Sumatra ten years ago: in a mosquito-infested jungle just north of the equator, 100 Km inland and only 150m above sea level. It was almost too hot and humid to survive by day, and almost impossible to sleep at night, but then every morning at about 2.00am a freezing wind came though the camp and we shivered until sunrise. After about a week, I finally realised what was happening at night: a river of freezing cold air was flowing down the topography from the 6,000ft mountains to the west of us, eventually converging into the main valley that we were camped on and eventually hitting us like a flash flood about eight hours after sunset. Obviously the same thing happens on the Green River in Utah, and from considerably colder highlands at its source.
Do people usually take these topographic effects into account when discussing night-time temperatures? If they don’t, they should.
Joel Shore (15:08:14) :
“The global climate models are programmed with the best understanding of the actual physical processes involved. ”
Since much of AGW theory is promulgated via these GC models – do we have independent analysis of the programming procedures and details? I understand that many of these details are unpublished or redacted under claim of proprietary interest. Considering that much climate science is conducted under grants of public funds – the code and algorithms utilized should be transparent to scrutiny by third parties.
Paddy (17:45:06) :
Assuming that the AGW hypothesis is correct, should not Mars (atmosphere 90% CO2) be a tropical paradise?
No. The atmosphere on Mars is too thin for any significant “greenhouse effect”.
Steve Goddard, an interesting explanation. However, you go a bridge too far when you say:
Absolutely not. There is agreement in the scientific community that increasing GHGs will increase the net downwelling radiation. However, whether and how this will affect the temperature is an open question.
An example I have used before is this: suppose we take a 75kg block of say copper, and stick one end into hot water. After a while, the heat is transferred to the other end of the copper block. I propose a theory that if you stick one end of something into a block of hot water, the other end will heat up at a certain rate. Simple physics, no problem. I try a block of wood. I notice that it works just the same, except it heats up more slowly. I try a steel block, same thing, it heats up, just takes a different time.
Finally, having proven my theory, I decide to test it on myself. I put my feet into the hot water, and I wait for my head to heat up … and wait … and wait.
The moral is, complex systems don’t obey simple physics.
The same is true about the climate. Everyone agrees that more GHGs will lead to more downwelling radiation, just as putting something in hot water leads to increased heat transfer to the object.
But as my example shows, this may have a) a larger effect than predicted, or b) a smaller effect than predicted, or c) no effect at all.
Nor is this a simple matter of getting the feedback right. In my opinion, the earth has an active system to keep it from getting too hot or too cold (thunderstorms, for those interested). This is why as far as we know, for the last half billion years or so, the earth’s temperature has only changed about ±2% …
As a result, changing the CO2 might lead to no change at all, not because of feedback, but for the same reason that putting my feet in hot water doesn’t heat up my head. It may not change because in both cases there is an active system which works to keep the temperature stable.
So in fact there is little scientific agreement on whether, and by how much, a change in CO2 will change the temperature of the earth, even in the absence of feedbacks.
w.
Simon Evans (16:02:27) :
Scientists were considering positive feedbacks as an explanation in advance of discovering the relationship between temperature and CO2. When the Vostok cores were pulled up, by 1985, the correlation was evident..
Care to explain a little more? I still don’t see how this explains the lag between temperature change and CO2 change. Is CO2 the driver or the follower?
Steve and Anthony
I am enjoying Steve’s post as well as the comments I’ve been able to read so far. I apologize if the question I’m about to ask has already been posed and discussed. The question is:
Why is there NOT a bona-fide greenhouse effect in the Earth’s atmosphere?
The main functions of a real greenhouse are to ensure that the air inside gets warmed by the sun and then kept warm by preventing its escape or mixing with outside air. I believe that the non-greenhouse gases in Earth’s atmosphere perform these functions as well. They are warmed by coming in contact with the materials at the Earth’s surface (independently of radiation), participate in convection (independently of radiation), and tend to stay warm because they cannot cool via radiation. Atmospheric air does not escape or mix with alien air. Gravity plays the role of glass panes.
I have tried to estimate the internal energy contained in atmospheric nitrogen, oxygen, and argon (actually argon is lost in round-off errors). Assuming an atmosphere at 0 degrees C, and using the relation U = 1.5 nRT, where U is internal energy, n is the number of moles, R is the universal gas constant, and T is temperature in Kelvin, then the atmosphere contains about 1.7E+17 kW hrs of internal energy.
That figure could be wrong, but if it’s close then it’s roughly the same as:
1) The amount of energy that would be consumed by the human race in 1250 years, using the 2006 worldwide energy consumption rate given by the EIA at http://www.eia.doe.gov/pub/international/iealf/tablee1.xls, or
2) The amount of solar energy intercepted (and not reflected) by the Earth in about two months.
So here we are back to my question: How can it be that all that energy does NOT participate in keeping us warm at least a little bit via a good old-fashioned greenhouse effect like Grandma used to use?
Larry Kirk,
Interesting memories of Sumatra. Normally downslope winds are quite warm, due to adiabatic heating, so there must have been something else going on.
In the case of Canyonlands, the air was very still and most of the heat loss was due to heat stored in the rock radiating rapidly out into the dry night air. Of course it was colder at the bottom of the canyon because cold air sinks, but even up 20 or 30 meters it was still quite cold at night, and over 100F during the day.