Arguments
Empirical evidence that humans are causing global warming
Posted on 9 July 2013 by gpwayne
This post is a new 'basic' level rebuttal of the myth: "There is no actual empirical evidence that carbon dioxide emissions are causing global warming."
What the Science Says: Less energy is escaping to space. Carbon dioxide (CO2) acts like a blanket; adding more CO2 makes the 'blanket' thicker
It is the Earth’s atmosphere that makes most life possible. To understand this, we can look at the moon. On the surface, the moon’s temperature during daytime can reach 100°C (212°F). At night, it can plunge to minus 173°C, or -279.4°F. In comparison, the coldest temperature on Earth was recorded in Antarctica: −89.2°C (−128.6°F). According to the WMO, the hottest was 56.7°C (134°F), measured on 10 July 1913 at Greenland Ranch (Death Valley).
Man could not survive in the temperatures on the moon, even if there was air to breathe. Humans, plants and animals can’t tolerate the extremes of temperature on Earth unless they evolve special ways to deal with the heat or the cold. Nearly all life on Earth lives in areas that are more hospitable, where temperatures are far less extreme.
Yet the Earth and the moon are virtually the same distance from the sun, so why do we experience much less heat and cold than the moon? The answer is because of our atmosphere. The moon doesn’t have one, so it is exposed to the full strength of energy coming from the sun. At night, temperatures plunge because there is no atmosphere to keep the heat in, as there is on Earth.
The Earth is wrapped in an invisible blanket
The laws of physics tell us that without the atmosphere, the Earth would be approximately 33°C (59.4°F) cooler than it actually is.
This would make most of the surface uninhabitable for humans. Agriculture as we know it would be more or less impossible if the average temperature was −18 °C. In other words, it would be freezing cold even at the height of summer.
The reason that the Earth is warm enough to sustain life is because of greenhouse gases in the atmosphere. These gases act like a blanket, keeping the Earth warm by preventing some of the sun’s energy being re-radiated into space. The effect is exactly the same as wrapping yourself in a blanket – it reduces heat loss from your body and keeps you warm.
If we add more greenhouse gases to the atmosphere, the effect is like wrapping yourself in a thicker blanket: even less heat is lost. So how can we tell what effect CO2 is having on temperatures, and if the increase in atmospheric CO2 is really making the planet warmer?
One way of measuring the effect of CO2 is by using satellites to compare how much energy is arriving from the sun, and how much is leaving the Earth. What scientists have seen over the last few decades is a gradual decrease in the amount of energy being re-radiated back into space. In the same period, the amount of energy arriving from the sun has not changed very much at all. This is the first piece of evidence: more energy is remaining in the atmosphere.
Total Earth Heat Content from Church et al. (2011)
What can keep the energy in the atmosphere? The answer is greenhouse gases. Science has known about the effect of certain gases for over a century. They ‘capture’ energy, and then emit it in random directions. The primary greenhouse gases – carbon dioxide (CO2), methane (CH4), water vapour, nitrous oxide and ozone – comprise around 1% of the air.
This tiny amount has a very powerful effect, keeping the planet 33°C (59.4°F) warmer than it would be without them. (The main components of the atmosphere – nitrogen and oxygen – are not greenhouse gases, because they are virtually unaffected by long-wave, or infrared, radiation). This is the second piece of evidence: a provable mechanism by which energy can be trapped in the atmosphere.
For our next piece of evidence, we must look at the amount of CO2 in the air. We know from bubbles of air trapped in ice cores that before the industrial revolution, the amount of CO2 in the air was approximately 280 parts per million (ppm). In June 2013, the NOAA Earth System Research Laboratory in Hawaii announced that, for the first time in thousands of years, the amount of CO2 in the air had gone up to 400ppm. That information gives us the next piece of evidence; CO2 has increased by nearly 43% in the last 150 years.
Atmospheric CO2 levels (Green is Law Dome ice core, Blue is Mauna Loa, Hawaii) and Cumulative CO2 emissions (CDIAC). While atmospheric CO2 levels are usually expressed in parts per million, here they are displayed as the amount of CO2 residing in the atmosphere in gigatonnes. CO2 emissions includes fossil fuel emissions, cement production and emissions from gas flaring.
The Smoking Gun
The final piece of evidence is ‘the smoking gun’, the proof that CO2 is causing the increases in temperature. CO2 traps energy at very specific wavelengths, while other greenhouse gases trap different wavelengths. In physics, these wavelengths can be measured using a technique called spectroscopy. Here’s an example:
Spectrum of the greenhouse radiation measured at the surface. Greenhouse effect from water vapor is filtered out, showing the contributions of other greenhouse gases (Evans 2006).
The graph shows different wavelengths of energy, measured at the Earth’s surface. Among the spikes you can see energy being radiated back to Earth by ozone (O3), methane (CH4), and nitrous oxide (N20). But the spike for CO2 on the left dwarfs all the other greenhouse gases, and tells us something very important: most of the energy being trapped in the atmosphere corresponds exactly to the wavelength of energy captured by CO2.
Summing Up
Like a detective story, first you need a victim, in this case the planet Earth: more energy is remaining in the atmosphere.
Then you need a method, and ask how the energy could be made to remain. For that, you need a provable mechanism by which energy can be trapped in the atmosphere, and greenhouse gases provide that mechanism.
Next, you need a ‘motive’. Why has this happened? Because CO2 has increased by nearly 50% in the last 150 years.
And finally, the smoking gun, the evidence that proves ‘whodunit’: energy being trapped in the atmosphere corresponds exactly to the wavelengths of energy captured by CO2
The last point is what places CO2 at the scene of the crime. The investigation by science builds up empirical evidence that proves, step by step, that man-made carbon dioxide is causing the Earth to warm up.
Proofreading note: the second paragraph after "The Earth is wrapped in an invisible blanket" has a repeated sentence and sentence fragment. Please feel free to delete this comment.
[GPW] Good call Sir. I decline to remove the comment, since it would also remove my thanks. Thanks too to Michael (next post).
In the first paragraph after the first graph the chemical formula for methane is wrong.
Also, I don't think the Smoking Gun argument comes across as convincing. I know what you are saying, but to state CO2 traps specific wavelengths but then say it radiates at the same wavelengths could be confusing for the target audience. I feel few more sentences of explanation may be useful.
Well, only a tiny amount less. The energy balance at the top of the atmosphere is still pretty close to zero, isn't it? The simplicity of "less energy is escaping to space" is appealing, but it will take hours to explain whay you mean by that, and along the way you come up with a misleading concept that looking at the planet from outer space, you would see less energy coming out.
Paul S, it is true that "looking at the planet from outer space, you would see less energy coming out," as long as there is an energy in/out imbalance. That "tiny amount" is sufficient to cause enough warming to cause serious problems.
And understanding that tiny imbalance is critical to a good understanding of the process. It represents the system's delayed response, and it represents the idea of an ongoing process. Whenever I talk with people about the TOA situation, they assume a static system and expect a large imbalance. No - it's ongoing: the system is progressively storing energy and radiating at a higher temperature at the same time. That there is a measurable delay in response highlights the difficulty in using the TOA imbalance to say anything more than "GW continues." The systemic delay is not uniform. That's a jump off point for explaining transient climate response and the way that energy moves through the system. TOA imbalance is also one step away from the physical mechanism of the greenhouse effect.
So while it might be confusing simply to mention the imbalance, it's also an excellent starting point to work from while explaining the whole shebang.
The WMO has decided that the 1922 Libya temperature record was a result of observational error, rather than the hottest temperature on record. You may want to use the Death Valley record as the hottest temperature on record.
[GPW] Thanks for that - now updated accordingly
I'll add that I like the detective slant. You could add a tab to the "it's not us" myth that extends the metaphor. It wouldn't take much to re-write Tom's Climate Change Cluedo to fit this crime scene narrative (it's already 3/4s of the way there). Of course, the outcome is obvious and we have no alibi. The question is the crime and intent: assault and battery, murder, manslaughter, harm through negligence, torture, kidnapping, or something else.
"Part of me loved her. Part of me wanted to force her to my will. Part of me wanted her to take care of the daily routine so I could be the superstar the public wanted me to be. What I did to her, though, was an accident. It was an accident. It had to be an accident. No matter what her kids say. Our kids. She'd better be there for me. Her friends say she's going away. Filthy liars! She loves me. She'll be back. It's not my fault!"
GPWAYNE,
Why is the greenhouse effect from water vapor filtered out? I tried to follow the link to Evans, 2006, but is does not work.
[GPW] Sorry about the link: fixed now.
And thanks to DSL for answering the question.
Terranova, this may be what you're looking for.
[RH] Tweaked URL for page formatting.
From the paper: "The contribution of water vapour to the increase in greenhouse radiation has not been included since it is a part of the natural climate feedback. There is some argument to suggest that tropospheric water vapour has already increased by several percent; hence, the corresponding flux contribution may need to be included, but this effect is beyond the scope of current models."
WV is filtered out probably to isolate the effects of the long-residence, well-mixed, and/or human-increased GHGs (WV is none of the above).
I'm missing the link to humans in this article. The rise in the last 150 years is only a correlation and is not necessarily caused by humans.
stbloomfield
Did you miss the second figure in the post?
stbloomfield:
You'll have to forgive my asperity, however saying humans are behind the recent global warming is a bit like saying the ocean is full of water.
Bluntly put, in order for humans to not be responsible for global warming, an enormous body of atmospheric and radiative physics, atmospheric chemistry, and empirical measurements would have to be completely upended.
True, stbloomfield, but then again you have no empirical evidence that the food you eat each day provides you with energy. Sure, theoretically it's possible and highly probable, yet you can't directly observe the process. Eating and energy availability are only strongly correlated. So why eat? It's really expensive.
Am I being silly? Sure, but every day you intuit and act on correlations that are much, much weaker than the connection between human emitted CO2 and the rise in atmospheric CO2. If you choose to deny the connection, I'm curious as to how you erase human-sourced CO2 from the physical equation.
stbloomfield:
There are no known natural cycles which explain the following changes in the Earth's climate system.
-The disappearing Arctic sea ice
-The melting Greenland ice sheet
-Melting alpine glaciers
-The warming and expanding troposphere
-The warming global ocean system
-The cooling and shrinking stratosphere
-The melting permafrost in Canada, Alaska, and
Siberia
-Rising sea levels
The above listed observed and measured changes are all being caused by the enhanced greenhouse effect caused by mankind's continuing release of greenhouse gases into the Earth's atmosphere.
stbloomfield @11, I am not clear which correlation you are referring to, and hence which link between human activity and global warming you are calling into question.
Do you call into question the link between anthropogenic emissions of CO2 and the rise in CO2 concentrations? In that case you need to examine the ten lines of evidence that conjointly make it certain that humans are in fact the cause of the recent rise in CO2 concentration. The evidentiary support of those lines of evidence for various alternative hypotheses is summarized in the chart below. Curiously, I have never seen a "skeptical" scientist discuss all ten lines of evidence, or indeed more than one or two, and then not the relevant ones compared to the hypothesis they prefer. (The one, honourable exception is Ferdinand Engelbeen who has always been quite clear on the overwhelming nature of the evidence that humans are responsible for the CO2 increase, and actively corrects people making these errors on major "skeptical" blogs.)
Or is it something else you are questioning?
John at 15
Are you saying that none of those have happened before? That is untrue and weakens your position.
Terranova @ 17
Yes, they have happened before but always because the global climate was forced to change.
What is your reason for it changing this time? Please check out the myth section of SkS before replying.
Science says there is a new forcing agent on the block – human activity and specifically the burning of fossil fuels.
DSL @ 5
I concur - the TOA energy imbalance is the root of the matter. If it is there, AGW. If not, it is all bunkum.
It is clear that a change in the concentration of greenhouse gases in the atmosphere will cause a change in the spectrum as seen from space, but that does not necessarily mean that there is an overall energy imbalance. Throw in a process with hysteresis and all bets are off.
Terranova:
Problem is that when those events occurred in the past, they gnerally occurred over a geological time scale.
guinganbresil, I'd say that the system has a form of hysteresis. There is a systemic lag between input and output, and the mechanisms that cause that lag are themselves integrated in a complex way. I should perhaps rather have said, "That there is a measurable delay in response highlights the difficulty in using the TOA imbalance trend to say anything more than 'GW continues.'" Of course, the theory of the greenhouse effect is not dependent on the TOA energy imbalance. It's physics. TOA imbalance provides corroborating evidence, but the difficulty in making a meaningful reading of TOA imbalance and quantitatively connecting it with the enhanced GHE (with feedbacks), with natural forcings (and their feedbacks) separated, is difficult (as Trenberth and climate modelers would undoubtedly point out).
Another version of Brian: all of those things have happened at the same time in the past, and there was a physical mechanism in place that explains their occurrence. All of those things are happening now, and no natural mechanism is available to explain them. An extremely fit explanation is the theory of the enhanced greenhouse effect. Are we responsible for the enhancement? Weigh the evidence, Terranova. Or ignore it, but the ignorance is then your own, personal, conscious responsibility.
DSL, I disagree that TOA energy imbalance is merely hard to measure corroborating evidence - it is critical to the whole theory. A change in the shape of the OLR spectrum does not by itself cause a change in temperature - the total emission needs to be out of balance with the incoming energy...
stbloomfield That the rise in atmospheric CO2 is anthropogenic is quite unequivocally established by the fact that atmospheric CO2 is rising more slowly than anthropogenic emissions, which means that (unless conservation of mass is violated) the natural environment is a net carbon sink and removes more CO2 from the atmosphere each year than it puts in.
It is obviously more than just a correlation as we have direct observations of the causal mechanism, we know we are putting CO2 into the atmosphere by burning fossil fuels!
guinganbresil,
Ignoring the fact that the total emission is out of balance with the incoming energy, it's not true to say that if there were not an energy imbalance at TOA then AGW would be "all bunkum". AGW predicts that if the forcing were to stop increasing then the energy imbalance would shrink until the climate reached a new equilibrium. All the energy imbalance tells us is that the climate is not yet in equilibrium with the current change in forcing.
I always thought it was too difficult to measure this accurately enough. Could you provide a reference to this?
Bouke -- as I understand it, the measurements are indirect. I don't know of any actual measurement of radiation being re-radiated into space. What there is rather is measurement of heat energy being absorbed -- which is itself a really difficult measurement since it involves measurement ocean temperatures around the world and down the watere column. (This is the dominant contribution). If the ocean is heating more rapidly, then (on the assumption of roughly constant or even very slightly falling solar input) it is fair conclusion that there's less energy being radiated.
A reference here would help, I agree! One possible reference is this NASA science brief: http://www.giss.nasa.gov/research/briefs/hansen_16/ which is a recent measurement. But even that is a tad problematic since the text of this post is refering to an observed gradual decrease -- which would need a continuous measurement of some kind, and I don't think we have that yet. The measurements is sufficiently difficult and dependent on quite recent data sources that my take is we are still working on getting good measurements. (BTW: this problem with measurement and with having the instruments to make measurements is the guts of "Trenberth's Travesty".)
I think that phrase you have quoted from the blog post would be improved by replacing "seen" with "inferred". Perhaps this could be taken up in an "intermediate level" response which would be the place for being a little bit more precise.
Thanks for some of your replies. The title of the article is "Empirical evidence that humans are causing global warming" but to me it simply shows that CO2 causes warming and we have more CO2 in the atmosphere. The second figure doesn't show how we know it is human created CO2. Isn't there something like a particular carbon isotope that links it? I think it would help if there was more shown than inference. Perhaps that's not possible with a basic level article like this, I don't know. As it's written now, I think the title should be changed to "Empirical evidence that CO2 has increased" because I don't think it does a good job pinning it on humans.
guinganbresil - Since the starting point for the emission spectra at TOA is constrained by blackbody emission, and since the changes in spectra have all been in the direction of reduced effective emissivity (less energy emitted at any particular temperature than before):
The predicted and observed change in emission spectra is negative ->is a reduction in outgoing energy -> hence leads to a TOA radiative imbalance -> and therefore a change in temperature. It really is that simple.
A reduced emission spectra to space requires (as per the Stefan-Boltzmann relationship) a higher average climate temperature to make outgoing energy equal to incoming energy - that spectral change is and of itself sufficient evidence of an enhanced greenhouse effect.
stbloomfield @28, while I will grant you the article glosses over the connection between human emissions and the rise in CO2 concentration, it nevertheless contains evidence of that connection in the second figure. If you look carefully, you will see that the CO2 in the atmosphere has increased by less than 1000 gigatonnes (in fact by about 800 gigatonnes). Meanwhile humans have emitted more than 1000 gigatonnes into the atmosphere (around 1200 gigatonnes according to the graph). It follows that because human emissions exceed the CO2 increase in the atmosphere, net natural sources and sinks removed more CO2 than they emitted. Ergo, absent human emissions, CO2 concentration would have fallen, or at best, stayed constant.
Of course, much more evidence to this point is available elsewhere on this site as pointed out above. However, the article contains sufficient evidence of that point, even if it could be spelt out a bit clearer.
stbloomfield, yah I'd agree with that. Gpwayne probably didn't address it because for people who have been around the science for a while, the anthro element is bat-upside-the-head obvious. Also, SkS regulars sometimes forget that not everyone looks through the whole (or even 1/100th of) site before commenting. It's now huge.
[GPW]. I think the issues raised merit further consideration, but can I also point out that we're reading this rebuttal out of context - as a stand-alone post. Its primary use is as part of the multi-level rebuttal here:
http://www.skepticalscience.com/empirical-evidence-for-global-warming-intermediate.htm
It strikes me that the discussion has been of an intermediate level, while the rebuttal is rather more basic. In context, the issues raised may be addressed in the intermediate version, which in context is only a tab away.
Writing the basic level rebuttals always involves some compromise. They are circulated to many working scientists and science professionals for comment and approval prior to publication, and many who review the work want something added, some clarification, some elaboration. Of course, if we accomodated all the suggestions, the rebuttal would no longer be basic.
It seems that writing about science for the general public requires some compromises that will always be a little unsatisfactory. But thanks for all the constructive criticism. I'll have a think about them and see if I can improve the text.
guinganbresil - In anticipation of possible comments (having Googled SkS for previous discussions on the subject and your comments), I will note that cloud changes would be a feedback to temperatures, not a forcing, and that despite attempts to show negative cloud feedback by Lindzen and Choi 2011, or Spencer and Braswell 2011, the evidence indicates that any such cloud feedback would be small and likely positive (as per Dessler 2011).
Spectral reductions in effective emissivity are indeed direct evidence for an enhanced greenhouse effect.
Just one straw man more, any skeptic would agree with the title of this post. What most skeptics thinks is that:
- There are no empirical evidence that humans are the main factor caused the global warming of the second half of pass century.
- There are no empirical evidence of that this small anthropic component global warming might become catastrophic, rather the opposite.
And there isn't.
Too much CO2 in the atmosphere? Come on, we are closest to the minimum needed for life existence (150 ppm?) that of where we are now from the real value of worries about extinctions (1000 ppm?). Try this.
If the avg temp of the moon is -36 C ((100 + -173)/2), why doesn't physics tell us that without an atmosphere the earth's temp wouldn't also be -36 C? Something is missing from the presentation.
Eclectikus, no comprehensive counterargument that accounts for physics and observations has been offered by anyone. No matter what other forcing is discovered, the enhanced GHE must be accounted for. It's power is well-demonstrated to be within a range that would make it the dominant forcing of the last fifty years. Solar variation (orbital + output) is the only other comparable forcing, and it has been flat or falling for fifty years.
As far as "catastrophic" is concerned, you're going to have to provide a definition. Everyone who uses the word seems to have a different definition. Some people even like to define it differently for different rhetorical objectives. Also, you are under a basic misconception: the absolute ppm for CO2 is not the issue re extinction. The issue is the rate of increase and the resulting rate of increase in global energy storage.
DSL #35
But that is not the point of this entry. To say that there is "empirical evidence that humans are causing global warming", is meaningless. Of course that human CO2 contributes to Global Warming, we know this from Arrhenius times. The discussion arise when we try to quantify the warming, and in that direction we have advanced little over the last thirty years, in terms of empirical evidence.
Well, I mean "catastrophic" in the sense of need to scare people. And there is no need without empirical evidence.
There is no basic misconception, CO2 concentrations are important for life not only in the terms you are pointing at, but also in absolute value. Both sides should be taken into account. And 400 ppm is only round number, nothing else.
Eclectikus, "we" know it, but I talk with people every day who confidently claim that human CO2 does not contribute to global warming, and in fact that it's all a hoax. This website is aimed partially at those people and partially at the people who are lying to to the claimers.
I disagree on the no progress in thrity years claim. Articulating the strength of the various forcings has come a very long way in thirty years. You're going to have a hard time arguing that the last thirty years' worth of sensitivity, feedback, and modeling work has all been redundant and pointless.
"catastrophic" as you define it is no definition. All you're saying is "well, catastrophic as other people use and define it." What does "catastrophic global warming" mean to you?
Sure, CO2 concentrations are important for life at both ends of the ppm range. Yet pushing the extremes of that range is not what the current problem is all about. Within the context of rapid climate change via anthropogenic global warming, discussing the extreme ends of the range is irrelevant--basically a red herring made of straw. Discussing the effect of the likely range of change on plant life is relevant.
The "classic" reference would be:
Philipona, R., B. Dürr, C. Marty, A. Ohmura, and M. Wild (2004)
Radiative forcing - measured at Earth's surface - corroborate the increasing greenhouse effect
Geophys. Res. Lett., 31, L03202, doi:10.1029/2003GL018765.
In addition to the ASRB network [MeteoSwiss] reference @38 it may be useful to mention a very short and recently published overview [free access!] on the current status of measurements of radiation profiles by Philipona:
Philipona, R., A. Kräuchi, and E. Brocard (2012)
Solar and thermal radiation profiles and radiative forcing measured through the atmosphere
Geophys. Res. Lett., 39, L13806, doi:10.1029/2012GL052087
@Eclectikus - The style of presentation of this website is to address specific myths about global warming. You're bringing up questions that this article doesn't claim to address and then comaplining whenever they aren't answered in it. A bit like throwing a fit at your local mechanic's shop because they don't stock croquet sets.
If you're interested, there are other articles on this site that address the questions you're asking:
DSL #37
I understand that there is people with no background in Science, and that they form their opinion on the debate based on their political bias, but I did not know that this site was dedicated to those people, in fact, I'm pretty sure that that kind of people do not read these entries, and in the rare event that they stumble upon them, they will understand nothing. So if it comes to send a message, I think is better that the message be correct, and in someway to imply that skeptics discusses the anthropogenic CO2 causes some warming is fallacious. The dispute comes in how much warming, not in ellemental physics.
Of course there has been a lot of improvement over the last years, in Climatology, and in all... but still we are in the first stadiums in terms of empiric verification, probably (surely) is not a scientists fault, is by the very nature of this Science. So a minimum of caution on predictions should be compulsory.
If there were evidence of catastrophic character of the case, there would be no discussion, no one can be interested in destroying a planet or its inhabitants / customers. And use weather events of the present and the recent past does not seem very tight to the scientific method.
Thanks for the link, I leave it as homework for tonight.
Thanks heb0 #40. I'm an old reader of this blog, and just wanted to point out what I pointed out. In this case it's more like to tell my mechanic that the spark plug that he put to my car was secondhand. Question of nuances.
Eclectikus, there are "skeptics" who claim that there is no such thing as the greenhouse effect, for example "Atmospheric "greenhouse forcing" does not warm the planet, never has and never will. In fact, the very idea that there is a greenhouse effect in our atmosphere is absurd.". So while skeptics are generally letting go of climate myths such as "there is no empirical evidence" one by one, there is still a need to deal with these myths for the sake of those who have heard them from the misguided and want to hear the other side of the story.
Please do not further disrupt the discussion of the science by trying to hold an off-topic meta discussion about what the site should be for. SkS has been around for a while, and a fair bit of thought has gone into who the intended audience actually is, and which arguments ought to be addressed.
#43 Amen.
The statement: " But the spike for CO2 on the left dwarfs all the other greenhouse gases, and tells us something very important: most of the energy being trapped in the atmosphere corresponds exactly to the wavelength of energy captured by CO2." is wrong because the primary greenhouse gas in our atmosphere was not included.
eklectikus @33, from 1900, total forcings have increased by approximately 1.56 W/m^2. The current TOA energy imbalance is approximately 0.63 W/m^2 meaning there has been an increase in outgoing radiation of 1.2 W/m^2 due to increased temperatures of about 0.7 C over the twentieth century. Therefore, each degree C of increased temperature results in about 1.32. That means it would take a 2.8 C increase in temperature to compensate for a doubling of CO2. It would also take a 1.35 degree increase to compensate for the increase in CO2 forcing since 1970.
It is not that there is no empirical evidence. It is that some people are eclectic about the evidence they will look at.
William @45... Being that WV (which you're referring to) is not a long lived gas, it responds to the forcing from these other gases. So, your point is moot. Including WV doesn't change the accuracy of the statement.
Rob at 47
TC at 46
William at 45 made a point that is valid, and not moot. You cannot dismiss the contribution of water vapor.
Mind you, I do not disagree that human actions have contributed to increased CO2 in the atmosphere, and the increased CO2 has led to some increase in temperature.
And, JH at 20: prove that statment. No models, but proof.
Terranova,
You cannot dismiss the contribution of water vapor.
I wouldn't dream of it, water vapour is a significant feedback that approximately doubles the warming effect that increased CO2 would have on its own.
But pointing it out in this context is like a driver complaining to the cop who just pulled him over for speeding that it's the turbo's fault that he was going so fast and not the position of his foot on the accelerator.
Terranova @48, from forcings alone, we expect 3.7 Wm-2K-1. That is, for each one degree C increase in temperature, we expect a 3.7 W/m^2 increase in outgoing radiation. The observed ratio is 0.75 Wm-2K-1, the difference being the net effect of all fast feedbacks, including the water vapour feedback, so my calculation already includes water vapour. It does not include slow feedbacks such as glacial melt so the final equilibrium response will be greater than that indicated by the calculation, although it will take centuries and possibly millenium to reach that equilibrium response.