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.
I have no affiliation with the University of Nebraska, and in fact have never been to Nebraska.
Patronizing lectures from “omniscient” experts illustrate little more than their own hubris.
All, there are a million points which this article does not cover. It is just a first order explanation of the greenhouse effect.
Have at it!
Hank,
There isn’t a lot of LW arriving from the sun. Temperatures on the sun are too hot.
Interview with James Lovelock (he os the bizarre Gaia theory) currently on BBC Radio4: He says there are a thousand climate scientists on the IPCC, and that the seas are rising at twice the level the IPCC predicted. He also says that sea level rise is a barometer on global warming and that if you google sea level rise you’ll see it’s rising.
Hmmm. Is any of that correct, or has this tired man gone off the silly end of the pier completely?
Interview will be available on BBC’s ‘Listen Again’ very soon under ‘Material World’. Listen and weep. Anyone got his address, as I’d like to send him a letter?
Steve Goddard,
Thanks very much for this post. You and I may not agree on that much but I am very pleased to see you clearly spell out those things that there is at least some reasonable scientific uncertainty about (feedbacks) vs those things that are really silly to debate (e.g., whether CO2 is a greenhouse gas that causes a forcing of ~4W/m^2 when its concentration doubles). There are lots of commenters on this website who seem to spend their time talking about things where the science really is so settled that they don’t do themselves any favors by continuing to bring it up.
David Corcoran says:
Do you have a cite for Hansen making such a claim?
Bill Yarber says:
Diameter doesn’t matter. Distance from the sun obviously does. However, compare Venus to Mercury. Mercury, with very little atmosphere has a huge range in temperatures between the side facing the sun and the side facing away but even the side facing the sun is not as hot as Venus, despite being closer.
If the atmosphere heats up, then the oceans will too. This is because the difference in temperature has to remain fixed to maintain equilibrium of heat flow.
I have no agenda for this article, other than the WUWT standard – to find out the truth, and get people talking and thinking. This is the #1 science blog after all.
Question – what is the concentration of CO2 at the various levels in the air collumn? Seems to me that CO2 is heavier the O2 and normal air, it will be concentrated near the ground, not high up. But, according to your graph, CO2 doesn’t even begin to have an effect till you get to around 100 millibars. That translates to over 50,000 feet & I seriously doubt we have anything like even a measurement of CO2 concentration at that altitude and, if we do, I’ll bet it’s very, very low and can be shown to have little to no effect on warming the surface.
Simon sez:
“Have you read through this thread, Matt? It might be a strawman argument if aimed at you, but clearly not so in the case of many others (unless I have imagined all the resistance expressed here to the basics of SG’s article). ”
Yes I have. Can you point me to the posts that flat out deny that CO2 causes any warming? I’m not seeing them. I do not think any of the “regulars” on here believe that.
Chuckle, chuckle. Skepticism on the rampage.
A thing I always wondered about. Since an element of the greenhouse gas explanation involves the sun’s radiation penetrating the atmosphere. How does this play out in the oceans where sunlight penetrates into the ocean and must likewise re-radiate there? Isn’t there anything comparable to greenhouse gases in the ocean? Dissolved CO2 perhaps?
Isn’t it also important to explain that the greenhouse metaphor has a defect since most of the heating in a greenhouse is due to the fact that the heat can’t convect away?
Steve Goddard wrote:
“Heat flow is driven by temperature differences. If the atmosphere is warmer over the ocean, then less heat flows out of the ocean into the atmosphere, and the ocean warms up. And vice-versa.”
This is a juvenile way to look at the phenomenon!
The energy source here in this planet is the ocean and no one can think that air warms the ocean.
All the energy that the ocean gets every day from the Sun has to be re-radiated back to the outer space, after some processes, i.e. convection, meteorology in general and greenhouse effect, all processes that pertain to the atmosphere.
The more the atmosphere is prone to let energy pass through it, the more the ocean loses energy.
So, please, stop saying that the ocean is warmed by air.
The only correct way to express the concept is that a change in those processes pertaining to the atmosphere can change the rate of energy that is lost towards the outer space.
Moreover, since meteorology has a fundamental part in the redistribution of energy from the source to other parts of the planet (and then lost) as well as it influences the planetary albedo, only climate modelists can think that the problem is a linear one!
We are living in “interesting times” really. In the next NH summertime GWrs´will attack again, they will feel reinforced in their beliefs as La Nina produces droughts in the US midwest and west.
Courtesy of George Smith from a recent thread:
“GHG molecules act as individual molecules; they don’t even know there is another like them in the whole universe. At 385 ppm, a CO2 molecule is one of 2597 molecules, and its nearest neighbor CO2 is 14 molecules distant in any direction. The next thing that happens to ANY GHG molecule, either water or CO2, is that it immediately collides with the normal atmospheric gases of Nirogen, Oqygen and Argon, and that energy from the absorbed photon becomes energy of thermal agitation of the ordinary air molecules. Only at extreme altitudes would any GHG molecule have a long enough mean free path to re-emit the photon it absorbed out of the thermal IR or solar spectrum; at lower altitudes the energy becomes thermalized in the normal atmospheric gases.”
The emissivity of CO2 at STP is 9*10^-4 or 1/1000 that of green leaves. The emissivity is directly proportional to the time required for the interaction, the emission of a photon, to occur.
Back-radiation has no practical consequence of heating the surface whatever.
Molon Labe says:
Wrong for two reasons: first there are always the wings of the band where things are not saturated. Second, there is always a height in the atmosphere where the atmosphere is low enough density that this saturation no longer occurs. At the end of the day, what matters is not just if the IR is absorbed but WHERE it is absorbed…Or, more precisely, the last altitude it is absorbed before it escapes the earth because the temperature at this altitude is what will determine the rate of radiative emission int space. (Power radiated ~ T^4).
Jim G says:
If you are talking about the “hotspot” expected in the tropical troposphere then no. It is not a “CO2 hotspot” because it is expected to occur independent of the mechanism causing the warming. (See here for a comparison of the structures of GHG-caused and solar-caused warming: http://www.realclimate.org/index.php/archives/2007/12/tropical-troposphere-trends/ ) It turns out that the structure of the warming in the tropical troposphere is not determined by where the energy is absorbed but rather by moist adiabatic lapse rate theory. I.e., the atmosphere has lots of convection in it, so the temperature structure is determined in large part by this convection.
jae:
I’m sorry, but I’m not really sure what you’re trying to say.
I’m saying both Phoenix and Atlanta have man-made micro-climates and both warm more during the day and cool less at night because of it.
I am also saying I don’t believe your comparison of Atlanta and Phoenix is a good example of what you’re trying to illustrate. The natural climate of those cities is very different and being at the same latitude does not make them comparable.
As to whether high-altitude deserts and low-altitude deserts cool differently at night, I made no comment. If that is really you’re point, Atlanta is not a good example to use as it not in any kind of desert.
If I misinterpreted what you’re saying, I apologize.
Leif,
Your explanation is suspect. If LW emission from a molecule of CO2 had only two possible destinations (space or ground) then the fact that CO2 absorption saturates in the lower two meters would imply that increased CO2 has no effect.
All good questions, Lucy. If science can’t agree on how the greenhouse effect works, then we really don’t know much about the climate, do we?
Follow-up questions: How does increases in atmospheric CO2 affect the climate? Do lab results reflect the real world?
Gary Gulrud,
You wrote: Back-radiation has no practical consequence of heating the surface whatever.
I bicycle year round day and night, and am quite certain that my hands stay warmer on cloudy nights in the winter – due to back radiation from the clouds.
“If the atmosphere heats up, then the oceans will too. This is because the difference in temperature has to remain fixed to maintain equilibrium of heat flow.”
This is manifestly not equivalent to “increases in atmospheric temperature cause the ocean to warm up.”
Now you have need of two clarifications.
tmtisfree (08:44:09) :
george h. (06:22:56) :
“My understanding of the skeptic argument regarding saturation is this: At current CO2 concentrations, all of the available IR in the relevant bands (2.7, 4.3 and 15 µm) is already captured. This is about 8% of the whole IR spectrum, which means that 92% of the IR passes right through without being absorbed by CO2. If the entire atmosphere were composed of nothing but CO2, it would still only be able to absorb 8% of the radiant heat. So if all of the available IR in that spectrum is being captured at current concentrations or lower, then adding more CO2 to the atmosphere won’t matter a bit.”
This is fundamentally correct.
This is apparently a correct description of the ‘skeptic argument’, however as far as the science goes it is fundamentally flawed.
SW radiation cannot penetrate the atmosphere of Venus. The heat from the planet’s centre is conducted through the thin crust and passes by convection and radiation into the atmosphere; there is no greenhouse efect on Venus. A short column (3600m) of air (350ppm CO2) filters out the relevant wavebands from LW radiation. Increasing the CO2 concentration would not absorb more radiation, it would only shorten the absorption distance. The heat energy would mix by convection and the temperature of the atmosphere would not rise. What you have said above is incorrect.
Nebraska is just like Kansas, but without all the glitz.
OT: Bloomberg News story:
“Greenland, Antarctica Glaciers Speeding Faster Toward the Sea”
http://www.bloomberg.com/apps/news?pid=20601124&sid=aTg9EF2NtBCg&refer=home
Sample:
“Altogether, the glaciers in the West Antarctic are losing about 103 billion tons a year of ice in discharge,” he said. “This discharge from west Antarctica would add an additional 10 to 20 centimeters” to the existing UN predictions of sea level rise this century, he said.”
Anthony (and Steve)–Great post, and excellent discussion/contributions. While I’m not a scientist, for ‘climate hobbyist’ like me this is a really enjoyable ’roundtable’ exchange and a great example of what an outstanding forum WUWT is–and why I ping your site several times each day. Thank you!
Anyone happen to know what is the estimated amount of CO2 in the atmosphere and the amount that human activity puts into the atmosphere? It might be helpful to be able to put some perspective on this as it would seem that human activity would be so miniscule as to be dismissable, no?