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.
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Steve,
Here is an excerpt from your post on 2/21
“Consider the earth 14,000 years ago. CO2 levels were around 200 ppm and temperatures, at 6C below present values, were rising fast. Now consider 30,000 years ago. CO2 levels were also around 200 ppm and temperatures were also about 6C below current levels, yet at that time the earth was cooling. Exactly the same CO2 and temperature levels as 14,000 years ago, but the opposite direction of temperature change. CO2 was not the driver.
Now consider 120,000 years ago. Temperatures were higher than today and CO2 levels were relatively high at 290 ppm. Atmospheric H20 was high, and albedo was low. According to the theorists, earth should have been warming quickly. But it wasn’t – quite the opposite with temperatures cooling very quickly at that time. CO2 was not the driver.
If CO2 levels and the claimed lockstep feedbacks controlled the climate, the climate would be unstable. We would either move to a permanent ice age or turn into Venus.”
So, if not CO2, maybe its clouds? And what drives the clouds? Is there room for a solar component too? Are the GCM’s even capable of considering these variables or should we start from scratch?
The argument really isn’t about a slight AGW effect (few disagree over that), it’s whether Catastrophic Anthropogenic Global Warming (CAGW) will engender a runaway greenhouse effect that will turn our planet into a mirror of Venus in no time at all, geologically speaking.
For instance: Dr. Hansen says the seas will rise 25M in 91 years, I don’t know why low lying nations are stubbornly insisting on making him a liar.
Thanks, reads like a simple explanation that I could perhaps give it to ten year olds (or is there a better source of information for them?). Was wondering about H2O. I was under the impression that it is the major GHG. Thanks for your patience.
Your use of Mars, Earth and Venus to prove that CO2 putis a major green house gas is totally flawed. You completely neglect their diameters and their distance from the Sun. Venus is 2/3s the distance from the Sun than earth and less than 1/2 that of Mars. Ergo, since the watts/sqm of the Sun’s out decreased with the square of the distance from the Sun, Venus gets over twice the energy that Earth gets and four times the energy Mars gets. Venus is warmer because it has a denser atmosphere and gets twice the energy Earth gets. This would be true if Venus had no CO2 in its atmosphere. Each planet has a different diameter but the difference is insignificant when compared to the impact of their individual orbit radii.
Bill
It seems like there are actually two things you need to know. You need to know the 1st order sensitivity to a doubling of C02 and you need to know the total feedback. So it’s pretty important to know whether the 1.2C number for 1st order sensitivity is right.
What do you think of Miskolczi’s work reassessing this sensitivity? My partial differential equation days are 20 years behind me, but I’ve read his paper and his argument seems superficially coherent.
I don’t feel qualified to fully judge the results though. It would be easy to sneak a specious mathematical argument by my given the current degraded state of my skills. Do you know any serious mathematical physics types that have reviewed his work and formed an opinion? Thanks.
“It has been known for a long time that even a short column of air contains enough CO2 to saturate LW absorption. This has been misinterpreted by some skeptics to mean that adding more CO2 will not increase the temperature. That is simply not true, as higher GHG densities force the temperature up.”
Utterly ridiculuous and contradictory. If CO2 absorption is “saturated”, adding more CO2 cannot have any effect. Period.
Can someone double check this?
It appears the maximum CO2 effect is centered at a wavenumber of 650.
wavenumber = 1/lambda (in cm)
=> @ur momisugly 650cm-1, lambda = 15.38 um
lambda (in um) = 2897/T (in deg K)
=> T = 2897/lambda
= 188K, or -121F (-85C)
The graph also shows that the CO2 absorption is at high altitude. ~10mb.
At 50F (10C) lambda should be about 977 which would be in the H2O absorption region.
Am I missing something? Obviously the heat radiated from the earth’s surface isn’t going to be -85C.
Is this why there should be a CO2 hotspot in the troposphere above 100,000 ft?
Mark N,
Temperatures are very sensitive to H2O levels, particularly at night. Which is why deserts get cold at night. H2O is the most important greenhouse gas.
PolicyGuy,
Good questions. It is clear from the ice core records that there are other cyclical drivers of climate which can vary temperatures by 10C or more. CO2 is higher now than it has been in recent centuries, and Dr. Hansen asserts that the recent rises will overwhelm the natural variation.
Some climate models do consider TSI changes due to solar cycles. Cloud formation is not well understood or modeled. Weather forecasting models often mispredict clouds on the same day.
I have lived many years in desert climates and well remember the temperature drop after sunset. Part of my duties was to note the relative humidity. It drops during the day and increases during the night, so much so that you could get condensation, dew, at dawn. This is what most desert creatures seem to survive on.
This is a personal observation. I would be interested to learn how heating the air would reduce the water content. As I understand, you must cool the air to get the moisture out. Just because deserts are hot and surface dry does not mean there is less moisture in the atmosphere. The air that blows in from cooler climes to replace the rising air over the desert does not lose its moisture. Deserts are dry. Usually.
Molon,
What you are not considering is that LW is absorbed and emitted many times on it’s tortuous path out of the atmosphere. The more GHG, the more times it is absorbed.
Your argument is analagous to saying that one stop light has the same effect on your commute time as does 100 stop lights.
Holy Cow! Your first diagram doesn’t show any longwave radiation in the Solar spectrum which is +/-50% depending on your choice of the wave length for the boundary. Seems that might at least be mentioned.
“There is no dispute about this in the scientific community.”
“It is widely agreed that a doubling of CO2 will increase
atmospheric temperatures by about 1.2C before feedbacks.”
Neither of these is true.
David Archibald claims an increase to 620 ppm, projected by 2150, will raise the temperature by only 0.2 degrees C. (May 2007) in “The Past and Future Climate.”
“An earth with no CO2 would be very cold.”
Proof? Why should this be as H2O and the other gases you mention don’t rely on CO2 to work as GHGs.
Also, AGW is “widely” questioned and even if it is “widely agreed” that doesn’t make it true. The references to Mars and Venus don’t help. The situations are so different you set me thinking about other topics.
Is the phrase “before feedbacks” meant to imply positive feedbacks?
How do you explain the cooling after 1940 to 1977 while CO2 was increasing and with no change in that trend a warming began in 1977?
Now for the past ten years temps have not continued there rise, even decreased some, and CO2 has not stopped going up?
Most reading this will be aware of or can easily find on WUWT material questioning the straightforward and undisputed facts you present so I haven’t bothered to add sources here. If anyone needs these, say so.
Your short primer appears not just to be short in length but short in its explanatory power. Give it another try. There are many of these short explanations on the WEB so I think this one is a set-up of some kind. I can’t figure out, though, just what the purpose is.
I feel lost…
Isn’t the enthalpy and specific heat capacity somehow missing?
The potential heat content of the entire atmosphere above 10mb is less than 1/100 (because of lack of water vapours high heat capacity) of the potential heat content below 10 mb.
And it is above 10 mb the big CO2 effect comes is as I read the chart…
Richard111,
Relative humidity means just that – relative to the temperature. You can change the relative humidity without changing the absolute humidity, by heating or cooling the air. The Utah desert can have swings of 60 degrees between day and night with no changes in the very low absolute humidity. As soon as water starts condensing due to cold, it releases heat and limits further temperature drops.
Thanks for the post. I’ve long been frustrated by friends claiming “there is no greenhouse effect” or “man is not responsible for the extra CO2”.
I would point at that the disagreement lies in three places. The first is that computer climate “feeback” models are bogus.
The second is that the data are inadequate, such as the UHI, the “How Not To” series posted here, fertilized tree rings, etc.
The third is obvious scientific malfeasance, such as the “Hockey Stick” affair, GISS “normalized” temperatures, and so on.
Kudos
It is useful to have clarifications on this theme, and I will store this for later revisits.
Just a minor quiggle in a hurry.
When stating your fundamental desciption of the earth as a thermodynamic unit, you do (correctly) include heat content (or eventually changes in ocean heat content).
But my old and battered brain vaguely remembers that borehole reconstructions of temperature was fairly prominent a number of years ago.
I assume borhole reconstruction of temperature is based on models wehre rock also have thermal heat content?
Bur regardless borehole reconstructions: Does not earth (rocks + soil) have heat content (with thermal inertia ) as well?
I assume it should be closer to the properties of water than atosphere.
Cassanders
In Cod we trust
@Richard111
Heating the air doesn’t reduce the water content, it just reduces the relative humidity, which is a measure of moisture content compared to the dewpoint of the air at that temperature. That also explains why rising air forms clouds; as air with a certain moisture content rises, it cools to its dewpoint, and water condenses into droplets. See an article in Wikipedia for a graph showing the relationship between the dewpoint and temperature.
Oops, clarification: relative humidity is a measure of actual moisture content compared to the amount of moisture that can be contained at the dewpoint.
Note that CO2 doesn’t heat but rather act as a ”radiation blanket” . Nils Bohr showed that gas molecules that absorb light are exited to a energy level and can only give off this energy with light at the same wavelength. This light can go in any direction. Some will again hit earth and create heat. Before Bohr it was believed that gas was heated by absorbed radiation.
This effect is called “greenhouse effect” in the debate. A greenhouse is however heated because the glass stops air convection. A greenhouse build with glass transparent to all wavelength would be as good as one built with window glass. This was also shown early last century (by a physicists named Wood).
I very much doubt that increases in atmospheric temperature cause the oceans to warm up to any significant extent, given the vastly greater thermal mass of water compared to air. Since about 72% of the Earth’s surface is water, which shows as black on IR photographs and is therefore absorbing everthing, it is fairly obvious that the oceans warm the atmosphere. We in the UK know this very well, as the North Atlantic Drift stops us having the climate of Newfoundland.
All the theorising is fine, but before going public with the results of models you have to show that the undoubtedly correct theoretical basis for some individual parts of an immensely complex real system extends to all parts of that system. In particular, if you want me to believe your predictions you must be able to show, reliably, that any model run will always reflect accurately the state of the climate at any time over known history. You are a very long way from even approaching that.
As Dr. Hansen has correctly argued, increases in atmospheric temperature cause the ocean to warm up.
really!
I have seen no proof of this, the average ocean temperature is about 4-5 deg c
90 % of the ocean is below the thermocline with a temperature of about 3 deg c
hardly a heat sink more like a cold sink, the surface temperature varies from -5 to + 30 deg c but its effect on the average ocean temperature is small.
The climate sensativity to co2 doubling is the issue, no one disputes the absorption effect at 650 wave no, but there is dispute about the effect in the upper atmosphere.
If there was no co2 in the atmosphere what would be the temperature using the IPCC models?
an ice age ? it wouldn’t happen : The models are flawed. The average temperature might drop 2 degrees ?
Isn’t water vapor responsible for 95% of absorption, thus maintaining the planets temperature in a +- 5degree range, from ice age to ice age !
“It has been known for a long time that even a short column of air contains enough CO2 to saturate LW absorption. This has been misinterpreted by some skeptics to mean that adding more CO2 will not increase the temperature. That is simply not true, as higher GHG densities force the temperature up.”
The 2 last sentences contradict physical laws. Reasoning only with CO²:
1/ As you said, all LW radiations are exciting a small and finite number of CO² molecules within the first meters (<10m) above the surface. That means adding more CO² molecules will not increase this finite number of excited molecules. Thus the number of excited molecules depends exclusively on the solar irradiation.
2/ Calculation and comparison of the frequencies (which can be interpreted as probabilities of occurrence) of
a) decay rate (natural broadening),
b) relative molecular movement (Doppler broadening) and of
c) molecular collision (collisionnal broadening)
show that the frequency of molecular collision is at least 4 orders of magnitude higher than the frequency of decay rate. That means that through molecular collisions and de-excitation as kinetic energy (heat measured with a thermometer), system reaches rapidly to a pseudo thermal equilibrium.
3/ The calculation of the velocity distribution in such system shows that only a very tiny part of the CO² molecules will keep enough energy to re-emit a photon with an energy corresponding to a 2.10^13 Hz frequency (or a 15 µm wavelength) to re-excite an other (CO²/H²O) molecule. The tiny part which re-radiates does so 50% upwards and 50% downwards, but as the number of non excited CO² molecules is far more higher (ie molecular system is far from being saturated), the downwards re-radiation is rapidly trapped again by CO² (or H²O) and re-thermalized by molecular collision as kinetic energy. Thus re-radiation in this frequency range plays only a very small part in the energy “trapping” process. Adding more CO² molecules just increases the probability that radiations from the surface excite CO² molecules at a lower height of the atmospheric column.
4/ Consequently, any radiation outside this frequency range will be (except for macroscopic aerosols which will absorb and re-radiate as a blackbody) transparently returned in part to earth (slightly warming it) and in part to the upper atmosphere (and thus slightly cooling it). This is this tiny re-radiation that is thought to be the GH effect accounted for the GW. Quantitatively, the total number of these low frequency photons depends only on the total number of the photons radiated by the surface, and thus only on the solar irradiation. Thus adding more CO² molecules will not change the total number of low frequency re-radiated photon towards surface, that is to say the slight warming which results of will not be modified when doubling (or more) the number of CO² molecules. As the atmosphere is transparent for these downwards photons, their number will also be independent of the height at which CO² molecules have been excited.
5/ So, what do an increase of CO² level?
As the number of CO² molecules increases, the probability that a finite number of CO² molecules is excited tends also to increase at the same height. But as almost the totality of the radiation from the surface is “trapped” within the first meters above the surface, it will not modify the total number of exited CO² molecules and have thus no effect on the total number of low frequency re-radiations towards the surface (GH effect). And because atmosphere is transparent to them, the height at which this process occurs will have no effect on the total number of this re-radiation returned to the surface.
The slight warming is therefore independent of
a) the number of CO² molecules (at the current level),
b) the height at which CO² molecules have been excited.
and is dependent only of
c) the solar irradiation.
I hope the above, which is not true for very low level of CO² (or any GH gases), makes sense.
Bye,
TMTisFree
As an analogy, if you use a blind over a window on a sunny day, adding more blinds will not make the room any darker.
Bye,
TMTisFree
Is all of this CO2 at ground level? Thermodynamics aside, how does CO2 force heat back to the surface of the earth? Include thermodynamics, how can there be an energy budget or a heat budget for the earth? I am neither pro or con AGW, more interested in the science…
I forgot the main conclusion.
As the slight warming is already accounted for when temperature is measured, consequently, and given the above, the current temperature can not increase with an increase of CO² level.
Bye,
TMTisFree
“Its’ amosphere” indeed. Your Nobel is cancelled!