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Some basic, empirical evidence in favor of AGW

Deuce

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First things first
This post should not be construed in any way, shape, or form to be comprehensive. Climate research spans more than a century and is a product of the work of thousands of scientists in dozens of fields of study. A post on an internet forum cannot possibly address all of it. This post should also not be construed as definitive proof of anything. The purpose is to establish that there is, despite what skeptics tell you, a body of empirical evidence that points to Anthropogenic Global Warming. (AGW) Lastly, it should be made very clear that I, Deuce, am not a climatologist and should not be considered an "expert" on this subject. My qualifications, if you can call them that, are a BS in Aeronautics, an IQ that internet tests claim is somewhat above average, and a lot of personal curiosity about, and interest in, the subject that has lead me to waste an awful lot of time at work reading about this stuff. So, read on if you're interested in some of the science behind the theory. Also, don't tell my boss, ok?

Some basic facts to establish
We need to address some fundamental facts in order to act as a base for this discussion. Although you wouldn't know it from spending time at these forums, agreeing on a base set of reality is important to debate!

  • Mankind has caused an increase in Carbon Dioxide (CO2) levels in the atmosphere.
One would think that this point doesn't need to even be mentioned. After all, we burn rather staggering amounts of various fossil fuels, all of which emit CO2 when burned. Some skeptics, however, dispute that this leads to higher CO2 in the atmosphere, or that it leads to significant change. The usual arguments are that nature emits far more CO2 than we do, or that it absorbs what we put into the atmosphere. (or both) The people who argue this are full of hot air. (drumbeat) Actually, I'll refer to this as a mistake, rather than making the assumption that they are deliberately misleading people.

The reason this mistake is made is a lack of consideration for the other half of nature's carbon cycle. While nature does in fact emit a lot more CO2 than we do, (nearly 800 gigatons per year compared to our ~29) it also absorbs a metric assload every year as well. The net result (800Gt- 1 assload) is that nature actually acts as a net carbon sink. That is, nature pulls more carbon out of the air than it releases into the air.

Thanks, nature! Say, where does all this carbon go? Ahh, plants you say. Every year when plants grow, they do so by absorbing the carbon from carbon dioxide and spitting out the oxygen. Which is also swell for us. Also, the ocean absorbs CO2 as well, there's a tremendous amount of CO2 dissolved into the ocean. (a more pronounced example of this can be found in any soda bottle that hasn't been open for too long. the moral of the story is, don't shake the ocean)



As if the coffin needed an additional nail, we can also detect a difference between naturally-emitted CO2 and CO2 emitted by fossil fuels. While I don't have a great understanding of this research myself, the basics of it is that carbon has different isotopes that have a noticeable difference in ratio when comparing natural CO2 to fossil fuel CO2. C12 vs C13, or something to that effect.

  • Carbon Dioxide absorbs radiation in the long-wave infrared spectrum
This is simple, unassailable physics. We've known this for more than a century, but more recently fine-tuned the wavelengths when the Air Force needed to work on heat-seeking missiles. (apparently, knowing the absorption characteristics of atmospheric gases in the infrared spectrum is useful when you're trying to hit a fighter plan moving five hundred miles per hour by using that same spectrum. who knew.) So why is this all important?

As you can see, the incoming solar radiation is primarily in the shortwave infrared spectrum. (as well as the visible spectrum, which is very convenient seeing as how visible light is... well, how we see) This radiation passes through the atmosphere more or less freely and hits the surface. The earth heats up and emits that radiation back. (think like an electric stove or hot pavement) The outgoing radiation is in the longwave infrared spectrum, and as we see from that chart, this radiation gets absorbed by several atmospheric gases: CO2, O2/O3 (ozone), H2O (water vapor), as well as some not-pictured gases like CFCs and methane. Oh no! The radiation comes in, but not all of it gets out! The greenhouse effect, we're doomed! Actually, for the most part this is a good thing. Without this effect, the earth would be about 33 C colder than it is now. Giant, lifeless ball of ice. Good for snowmen, bad for humans.

Ok, so why is THIS important? The fundamental fact is that CO2 is one of several greenhouse gases. It absorbs radiation that would otherwise have gone to space. This energy gets re-emitted in all directions, causing heating.

Papers on laboratory measurements of CO2 absorption properties « AGW Observer
A whole bunch of papers on the subject.

On to the empirical evidence
Phew, finally. So, we've got these theories about CO2 causing warming, but can we back that up with evidence? Why yes, we can! These days, it's actually quite easy. Remember that longwave infrared radiation that the earth radiates and CO2 absorbs? We can track that. What we monitor:
1) Outgoing radiation across the spectrum, via satellites.
2) Incoming radiation across the spectrum, via ground stations.
3) Temperature, of course

So, if the theory is that increases in greenhouse gases will cause the atmosphere to absorb more energy that would otherwise escape, causing heating, what can we expect to see?
1) Outgoing radiation in the spectrum absorbed by CO2 to decrease, relative to sun's output.
2) Incoming radiation in the spectrum absorbed by CO2 to increase, as some of this outgoing radiation is reflected back down to earth.
3) The changes in these two to correspond to the increase in CO2 in the atmosphere.
4) A rise in temperature

Hey, what do you know? This is exactly what we see! Outgoing radiation in CO2's absorption spectrum has decreased, the same radiation coming to the surface has increased. Same energy goes in, less energy goes out. Physics 101 tells us that this will cause heating, and we see a warming earth as well!
Papers on changes in OLR due to GHG’s « AGW Observer

Changes in outgoing radiation showing a decrease in the spectrum absorbed by CO2 and other greenhouse gases.


Increases in the radiation at the surface in those same wavelengths.

And, of course, a rise in temperature.
http://img715.imageshack.us/i/heatcontent.png
http://img571.imageshack.us/i/figa2lrg.gif
(this image from NASA GISS temperature data)
(last two images removed because the forums are jerks and I can only use 5 pictures)

Phew! That was a bit of work. I had typed up some more on the common skeptics' counter-arguments, but it got eaten by the computer and I don't feel like retyping it at this particular moment.

Now, I know there are skeptics out there who will just handwave this entire post with "CANT TRUST THE SCIENTISTS," but those people might very well be beyond help. The hope is that there are people out there who are more open-minded while being skeptical, who perhaps just haven't taken the time to learn more about the science behind it all. Maybe they'll read this and go "hmm, maybe there's more to this than I thought. I'll go read more and learn things!"

Hooray for learning.
 
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iangb

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For those who tl;dr, an incredibly brief summary.

1. We've put lots of CO2 into the atmosphere, and it's sitting there accumulating. We know how much there is up there.
2. CO2 is experimentally proven to absorb heat, but let UV light pass through. This means that incoming solar energy (mainly at the UV end of the spectrum) is let in, but outgoing/reflected solar energy (mainly at the IR end of the spectrum) is absorbed and retained. This has a warming effect.
3. The Earth is warming at the rate which the theory (experimentally confirmed: see #2) says it should if CO2 is one of the driving influences.
4. Therefore the CO2 that we have released is causing the warming effect.

QED. See above for all of the experimental links and data.
 
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Deuce

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For those who tl;dr, an incredibly brief summary.

1. We've put lots of CO2 into the atmosphere, and it's sitting there accumulating. We know how much there is up there.
2. CO2 is experimentally proven to absorb heat, but let UV light pass through. This means that incoming solar energy (mainly at the UV end of the spectrum) is let in, but outgoing/reflected solar energy (mainly at the IR end of the spectrum) is absorbed and retained. This has a warming effect.
3. The Earth is warming at the rate which the theory (experimentally confirmed: see #2) says it should if CO2 is one of the driving influences.
4. Therefore the CO2 that we have released is causing the warming effect.

QED. See above for all of the experimental links and data.
Even MORE simplified:
Incoming solar energy compared to outgoing energy shows that more and more energy is being absorbed in exactly the spectrum that CO2 and other man-made greenhouse gases cover, and in direct correlation to the increase in atmospheric concentrations of those gases. High school physics tells us this will warm the planet.
 
P

Pappadaver

JUST A COUPLE SIMPLE QUESTIONS. WE LIVE ON A PLANET 4.6 BILLION YEARS OLD AND WE HAVE STUDIED WEATHER AT BEST FOR 150 YEARS; CAN YOU HONESTLY CLAIM TO UNDERSTAND ALL THE CYCLES AND SCIENCE OF WEATHER? GLOBAL WARMING ENDED THE ICE AGES NOT ONCE BUT SEVERAL TIMES; MAN WAS NOT EVEN PRESENT FOR MOST OF THESE CYCLES, WHO DUNNIT? WE WOULD NOT BE HERE AS A SPECIES WITHOUT THE GLOBAL WARMING OF THE PAST. THE ATMOSPHERE IS TWENTY MILES THICK, A VAST OCEAN OF GASES; HOW CAN WE MAKE THESE DIRE CLAIMS BY MEASURING ONLY THE RISE IN SURFACE TEMPERATURES, I.E. tHE BOTTOM OF THE OCEAN? PAPPADAVE.
 

Deuce

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JUST A COUPLE SIMPLE QUESTIONS. WE LIVE ON A PLANET 4.6 BILLION YEARS OLD AND WE HAVE STUDIED WEATHER AT BEST FOR 150 YEARS; CAN YOU HONESTLY CLAIM TO UNDERSTAND ALL THE CYCLES AND SCIENCE OF WEATHER? GLOBAL WARMING ENDED THE ICE AGES NOT ONCE BUT SEVERAL TIMES; MAN WAS NOT EVEN PRESENT FOR MOST OF THESE CYCLES, WHO DUNNIT? WE WOULD NOT BE HERE AS A SPECIES WITHOUT THE GLOBAL WARMING OF THE PAST. THE ATMOSPHERE IS TWENTY MILES THICK, A VAST OCEAN OF GASES; HOW CAN WE MAKE THESE DIRE CLAIMS BY MEASURING ONLY THE RISE IN SURFACE TEMPERATURES, I.E. tHE BOTTOM OF THE OCEAN? PAPPADAVE.
Typing in all caps is considered poor etiquette when it comes to internet posting.

You're making the very common and very fundamental error of assuming that an effect can only have a single cause. Temperature changed on earth without the presence of man, but that does not necessarily mean man is incapable of changing temperature. People got lung cancer before cigarrettes existed, does that mean cigarrettes are safe? There are multiple primary drivers of global average temperatures. We can observe and measure them. Some of the main drivers: The greenhouse effect, continental configuration, solar output, volcanic activity, and milkanovich cycles (regular "wobbles' in the earth's orbital mechanics). Over a mere 150 years, continents and orbital mechanics don't change enough to cause a temperature spike of this magnitude. The sun we can measure directly, we've been observing sunspot activity for more than a century and for the last 40 years we've been directly measuring solar output

A couple things to point out:
1) This thread is not comprehensive, there's a lot more evidence than what I just showed you.
2) We measure temperature not just at the surface, but at various altitudes via weather ballons and also using satellites.
3) The energy being absorbed by CO2 has to go somewhere, it's simple physics. If you want more proof that CO2 is a greenhouse gas, check out Venus. Despite being closer to the sun, Mercury is not as warm as Venus.
 

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Did you email Algore for talking points again hun?
 

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Thanks Deuce for another informative post. I enjoy reading your logically-consistent deductions about global warming.
 

Renae

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Thanks Deuce for another informative post. I enjoy reading your logically-consistent deductions about global warming.
It's talking points, it's kool-aide for true believers.

Do you know why no one posts counters anymore? It's NOT WORTH THE EFFORT! But we do read, and laugh. It's like a comedic relief moment.

AGW is a political movement, not a scientific one.
 

Renae

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Hey, about that CO2, increase, what's the yearly PPM increase again?
 

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Most of the OP I've already seen many times. What I didn't see was repudiation of the fact that, since CO2 makes up such a tiny portion of greenhouse gasses overall (95% of which is water vapor), humans activity accounts for less than half of 1% of greenhouse gasses in the atmosphere. Maybe there's a case to be made that this is all it takes, but I have yet to see that case be made.

I don't doubt that human activity is causing the globe to get warmer... by somewhere between .001 and 1.5 degrees C. The question is how much within that scale.
 

majora$$hole

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it's not just the co2 we burn but the co2 eating trees we cut down every year and the oil we release into the system ect...
 

Deuce

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It's talking points, it's kool-aide for true believers.

Do you know why no one posts counters anymore? It's NOT WORTH THE EFFORT! But we do read, and laugh. It's like a comedic relief moment.

AGW is a political movement, not a scientific one.
The amusing part is how you read the OP (you did read it right?) and maintain that this is not a scientific argument. Really? Physical properties of greenhouse gasses and satellite measurements of incoming and outgoing radiation are "talking points?" All those papers discussing the subject are political writings?

Hey, about that CO2, increase, what's the yearly PPM increase again?
I suppose gigatons is a bit of an abstract.




1958: 315
Current: 390
CO2 Now | CO2 Home <--- Wow there's a whole websie devoted to this?
An increase of about 23-24% since 1958, or about 1.5ppm/year. More on this in a moment!

Most of the OP I've already seen many times. What I didn't see was repudiation of the fact that, since CO2 makes up such a tiny portion of greenhouse gasses overall (95% of which is water vapor), humans activity accounts for less than half of 1% of greenhouse gasses in the atmosphere. Maybe there's a case to be made that this is all it takes, but I have yet to see that case be made.

I don't doubt that human activity is causing the globe to get warmer... by somewhere between .001 and 1.5 degrees C. The question is how much within that scale.
The confusion on this point usually stems from the difference between the total greenhouse effect and the net change in the greenhouse effect. Water vapor is indeed responsible for about two-thirds of the greenhouse effect.
From Kiehl 2007,
The authors find that for the clear sky case the contribution due to water vapor to the total longwave radiative forcing is 75 W m-2, while for carbon dioxide
it is 32 W m-2.
http://sites.google.com/site/coelhomota/RadiationBudget.pdf?attredirects=0

However, there's a few things to keep in mind:
1) Water vapor is confined primarily to the extreme lower parts of the atmosphere, while CO2 spreads throughout the atmosphere.
2) You can't really add water vapor to the atmosphere. The air has a saturation point, if you put in water vapor beyond this point, it will simply fall back down as rain. Even if not saturated, water vapor does not stay in the atmosphere for very long.
3) Mankind is emitting a lot more CO2 than water vapor

For reason 2, water vapor is known as a climate feedback rather than a climate forcing. To add more water to the atmosphere you must first increase the temperature. Water vapor can't start a temperature trend on its own. Instead, water vapor amplifies already existing temperature trends in either direction. Warm the world, more water vapor enters the atmosphere, which amplifies the warming. Cool the world, less water in the atmosphere, amplifies the cooling.

Water vapor is contributing to the warming caused by CO2, but would not be causing warming by itself because it is physically incapable of doing so.

CO2 can be both a feedback and a forcing. As the world warms, ice melts and releases trapped CO2, and the ocean releases CO2 as well. (gases mixed into liquids will come out due to temperature increases. If you've ever made coffee, tea, or pasta, you've observed this effect!) We've observed this numerous times in the planets history, which unfortunately leads to another skeptical talking point. Historic temperature changes have had temperature change and THEN CO2 change. First the planet warmed, and then the CO2 levels rose, and the reverse on the downside of the temperature cycle. "CO2 lags temperature changes, therefore it cannot cause temperature changes!" the skeptics will cry, conveniently ignoring that this is not the case today, when CO2 is rising in direct correlation. Today, CO2 is acting as a forcing because there is an artificial injection of CO2 to the atmosphere that is causing warming.

As for your statement that less than .5% of GHGs in the atmosphere, the important issue is the change in GHGs. After all, we're trying to measure and predict a change in temperature, not total temperature. Water vapor has not appreciably changed in the last century, (only 2-3%) but CO2 has increased nearly 40%. It may not seem like much, after all it is only ~400ppm these days, but remember that about 99% of the atmosphere has no impact on the greenhouse effect because nitrogen and oxygen do not absorb the proper spectrum of radiation. (Makes me wonder about potential life on other planets. A different-sized star might give off radiation in a slightly different spectrum distribution, making different gases have a greenhouse effect or not have one. space is awesome, but I digress..)


it's not just the co2 we burn but the co2 eating trees we cut down every year and the oil we release into the system ect...
This is indeed contributing to the issue. Nature is a net carbon sink, every year when plants grow. However, cutting down large swaths of forests reduces nature's ability to absorb carbon. Most deforestation, however, is done to create farmland, where we still grow plants, so it's not a total loss.

EDIT: Not the most exciting voiceover guy, but this video starts to give an inkling of all the different lines of research that is done.
 
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Renae

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65PPM over 46 years = 1.413 MORE CO2 molecules per year.

OH GNOES IT'S THE END OF THE WORLD MAN!!!!

Proof one: Laboratory measurements show that carbon dioxide saturates (absorbs to extinction) at its main peak in 10 meters under atmospheric conditions.* This means there is no radiation left at the peak frequencies after 10 meters. If then there is a doubling of CO2 in the atmosphere, the distance of absorption reduces to half, or 5m. A reduction in distance is not an increase in temperature. Convectional currents stir the heat around removing any relevance for distance.

Scientists who promote the global warming hype try to work around this fact by claiming something different happens higher in the atmosphere, which they claim involves unsaturation on the shoulders of the absorption peaks. (See Disputed Zone.) The difference due to height is that the absorption peaks get smaller and sharper, so they separate from each other. Near the earth's surface, the absorption peaks for water vapor partially overlap the absorption peaks for CO2, while there is less water vapor high in the atmosphere. Supposedly, separating the peaks creates global warming. There is no credibility to that claim. It is nothing but an attempt to salvage global warming propaganda through fake rationalizing of complexities.

What it means is that climatologists admit there is no mechanism at lower levels of the atmosphere, and their rationalization for higher up is phony.

It's important to realize that radiation from the sun does not greatly heat the atmosphere, because the sun must give off high frequency radiation in the area of visible light, which goes through the atmosphere. Something as hot as the sun cannot give off low frequency radiation. Temperature determines frequency. This means that most of the sun's radiation heats the surface of the earth, and then the heat moves from the earth's surface into the atmosphere through conduction, convection, evaporation and infrared radiation. The infrared radiation can be absorbed by so-called greenhouse gasses.
CO2 Absorption Spectrum Explained.
 

Deuce

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65PPM over 46 years = 1.413 MORE CO2 molecules per year.

OH GNOES IT'S THE END OF THE WORLD MAN!!!!


CO2 Absorption Spectrum Explained.
Parts per million per year. Not molecules per year. Also, on what basis do you make the suggestion that this isn't significant? It is possible for small amounts of a substance to have a powerful effect, and remember that we're not talking about small amounts here anyway. A few parts per million over the mass of our entire atmosphere is actually a large amount. Remember the graph in the OP that measured this in gigatons?

I've seen this link you posted before. There's a problem with that article's premise, though:
If CO2's effect were already saturated, we would see very little or no change in outgoing radiation in the spectrum that CO2 absorbs, as well as no change in the downward radiation in that same spectrum. However, that isn't the case. As CO2 levels increase to this very day, we still see a decrease in the outgoing radiation and an increase in the downward radiation. The experiment referenced in this article proposes a theory that directly contradicts what we're seeing in reality. The article is not supported by the facts.

Edit: Also, if CO2 at our present levels was saturated at 10 meters, the temperature on Venus becomes rather difficult to explain.
Edit2: And if an increase in the greenhouse effect is not a cause of the current warming trend, what is? Keep in mind that it is provably NOT the sun, and that "it's natural" isn't an answer any more than "it's magic" is. There has to be a mechanism for the change.
 
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Renae

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Parts per million per year. Not molecules per year. Also, on what basis do you make the suggestion that this isn't significant? It is possible for small amounts of a substance to have a powerful effect, and remember that we're not talking about small amounts here anyway. A few parts per million over the mass of our entire atmosphere is actually a large amount. Remember the graph in the OP that measured this in gigatons?

I've seen this link you posted before. There's a problem with that article's premise, though:
If CO2's effect were already saturated, we would see very little or no change in outgoing radiation in the spectrum that CO2 absorbs, as well as no change in the downward radiation in that same spectrum. However, that isn't the case. As CO2 levels increase to this very day, we still see a decrease in the outgoing radiation and an increase in the downward radiation. The experiment referenced in this article proposes a theory that directly contradicts what we're seeing in reality. The article is not supported by the facts.

Edit: Also, if CO2 at our present levels was saturated at 10 meters, the temperature on Venus becomes rather difficult to explain.
Edit2: And if an increase in the greenhouse effect is not a cause of the current warming trend, what is? Keep in mind that it is provably NOT the sun, and that "it's natural" isn't an answer any more than "it's magic" is. There has to be a mechanism for the change.
Venus is about the CO2. L2Science.
 

iangb

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Venus is about the CO2. L2Science.
Uh, Venus is an excellent example of the effects of CO2. It's surface temperature averages at about 462C (864F), almost purely from CO2 effects - this temperature does not noticably fall at night. Compare this to Mercury, which averages at 121C (251F) because, while the sun heats it up during the day to temperatures comparable to Venus, it falls to immense coldness at night.

Venus supports Deuce's point. That's probably why he mentioned it in the first place.
 

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I like this thread. It is rare when a proponent of GW is tall on data and abstains from hype and doom. I think MrVicchio jumped the gun with post #13. I haven't seen any hysteria here.

I oppose the "Gore contingent" of the issue, but I'm all for cleaning up our act in a efficient manner.
 

Deuce

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I like this thread. It is rare when a proponent of GW is tall on data and abstains from hype and doom. I think MrVicchio jumped the gun with post #13. I haven't seen any hysteria here.

I oppose the "Gore contingent" of the issue, but I'm all for cleaning up our act in a efficient manner.
Al Gore is not a scientist and global warming research started well before he was even born. Al Gore is the biggest straw man in the history of this issue. Skeptics and denialists attack him constantly, because they are unable to attack the science. They also grossly inflate what Al Gore says. I don't recall him ever saying we were going to go extinct, but if you ask a skeptic that's what they'll tell you he is saying. I've even heard people claim "Al Gore said polar bears were extinct." Seriously, if that's true, show me where he said that. I don't believe he ever said anything of the sort. I could be wrong, though, because I don't really ever listen to him and haven't even watched "An Inconvenient Truth."

That said, I have to ask, what is the "Gore contigent" and why do you oppose it?
 

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The confusion on this point usually stems from the difference between the total greenhouse effect and the net change in the greenhouse effect. Water vapor is indeed responsible for about two-thirds of the greenhouse effect.
From Kiehl 2007,

http://sites.google.com/site/coelhomota/RadiationBudget.pdf?attredirects=0

However, there's a few things to keep in mind:
1) Water vapor is confined primarily to the extreme lower parts of the atmosphere, while CO2 spreads throughout the atmosphere.
2) You can't really add water vapor to the atmosphere. The air has a saturation point, if you put in water vapor beyond this point, it will simply fall back down as rain. Even if not saturated, water vapor does not stay in the atmosphere for very long.
3) Mankind is emitting a lot more CO2 than water vapor

For reason 2, water vapor is known as a climate feedback rather than a climate forcing. To add more water to the atmosphere you must first increase the temperature. Water vapor can't start a temperature trend on its own. Instead, water vapor amplifies already existing temperature trends in either direction. Warm the world, more water vapor enters the atmosphere, which amplifies the warming. Cool the world, less water in the atmosphere, amplifies the cooling.

Water vapor is contributing to the warming caused by CO2, but would not be causing warming by itself because it is physically incapable of doing so.

CO2 can be both a feedback and a forcing. As the world warms, ice melts and releases trapped CO2, and the ocean releases CO2 as well. (gases mixed into liquids will come out due to temperature increases. If you've ever made coffee, tea, or pasta, you've observed this effect!) We've observed this numerous times in the planets history, which unfortunately leads to another skeptical talking point. Historic temperature changes have had temperature change and THEN CO2 change. First the planet warmed, and then the CO2 levels rose, and the reverse on the downside of the temperature cycle. "CO2 lags temperature changes, therefore it cannot cause temperature changes!" the skeptics will cry, conveniently ignoring that this is not the case today, when CO2 is rising in direct correlation. Today, CO2 is acting as a forcing because there is an artificial injection of CO2 to the atmosphere that is causing warming.

As for your statement that less than .5% of GHGs in the atmosphere, the important issue is the change in GHGs. After all, we're trying to measure and predict a change in temperature, not total temperature. Water vapor has not appreciably changed in the last century, (only 2-3%) but CO2 has increased nearly 40%. It may not seem like much, after all it is only ~400ppm these days, but remember that about 99% of the atmosphere has no impact on the greenhouse effect because nitrogen and oxygen do not absorb the proper spectrum of radiation. (Makes me wonder about potential life on other planets. A different-sized star might give off radiation in a slightly different spectrum distribution, making different gases have a greenhouse effect or not have one. space is awesome, but I digress..)
I'm not entirely sure what you're trying to say here... that even though it's a tiny portion that humans are contributing, because it's CO2 and because there is a feedback loop, it's enough to make a difference? I can get that, though it's more of an assertion than it is proof of an assertion.
The most confusing part is where you insist that skeptics ignore that even though CO2 levels only followed temperatures in the past, that's not what's happening now, therefore causation isn't disproven. Correlation doesn't prove causation, but lack of correlation automatically disproves causation. And even if there's correlation now, the fact is that there hasn't been in the past:



Note that pretty much every little blip in the CO2 level represents more of a change than what has happened recently.
Granted, there are other factors at work when it comes to temperature than greenhouse gasses. But why should we assume that this is not the case now? How come when through all of history rising CO2 was not correlated with rising temperatures (in a manner implying causation, at least), there were other factors at work, but the one time that the correlation is right, there aren't?
And really, the correlation isn't right. Here's something else I found while I was at it:



Now, that's just for fossil fuel consumption, but the fact remains that, for example, the period between 1940 and 1970 does not have a correlation between temperature and change in CO2. Obviously there were other forces at work during that peroid - but why only during that period? Why does CO2 have to invariably be the culprit every time it is followed by rising temperatures, even if this has only happened once in known history, intermittently in the past 150 years, which is an extremely short length of time to begin with?
 
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For reason 2, water vapor is known as a climate feedback rather than a climate forcing. To add more water to the atmosphere you must first increase the temperature. Water vapor can't start a temperature trend on its own. Instead, water vapor amplifies already existing temperature trends in either direction. Warm the world, more water vapor enters the atmosphere, which amplifies the warming. Cool the world, less water in the atmosphere, amplifies the cooling.

Water vapor is contributing to the warming caused by CO2, but would not be causing warming by itself because it is physically incapable of doing so.
The assumption that water vapor acts as a positive feedback is unfounded.

Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data

Abstract

The National Centers for Environmental Prediction (NCEP) reanalysis data on tropospheric humidity are examined for the period 1973 to 2007. It is accepted that radiosonde-derived humidity data must be treated with great caution, particularly at altitudes above the 500 hPa pressure level. With that caveat, the face-value 35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes. It is significantly positive below 850 hPa in all three zones, as might be expected in a mixed layer with rising temperatures over a moist surface. The results are qualitatively consistent with trends in NCEP atmospheric temperatures (which must also be treated with great caution) that show an increase in the stability of the convective boundary layer as the global temperature has risen over the period. The upper-level negative trends in q are inconsistent with climate-model calculations and are largely (but not completely) inconsistent with satellite data. Water vapor feedback in climate models is positive mainly because of their roughly constant relative humidity (i.e., increasing q) in the mid-to-upper troposphere as the planet warms. Negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2. In this context, it is important to establish what (if any) aspects of the observed trends survive detailed examination of the impact of past changes of radiosonde instrumentation and protocol within the various international networks.

SpringerLink -
 

Deuce

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I'm not entirely sure what you're trying to say here... that even though it's a tiny portion that humans are contributing, because it's CO2 and because there is a feedback loop, it's enough to make a difference? I can get that, though it's more of an assertion than it is proof of an assertion.
The most confusing part is where you insist that skeptics ignore that even though CO2 levels only followed temperatures in the past, that's not what's happening now, therefore causation isn't disproven. Correlation doesn't prove causation, but lack of correlation automatically disproves causation. And even if there's correlation now, the fact is that there hasn't been in the past:



Note that pretty much every little blip in the CO2 level represents more of a change than what has happened recently.
Granted, there are other factors at work when it comes to temperature than greenhouse gasses. But why should we assume that this is not the case now? How come when through all of history rising CO2 was not correlated with rising temperatures (in a manner implying causation, at least), there were other factors at work, but the one time that the correlation is right, there aren't?
And really, the correlation isn't right. Here's something else I found while I was at it:



Now, that's just for fossil fuel consumption, but the fact remains that, for example, the period between 1940 and 1970 does not have a correlation between temperature and change in CO2. Obviously there were other forces at work during that peroid - but why only during that period? Why does CO2 have to invariably be the culprit every time it is followed by rising temperatures, even if this has only happened once in known history, intermittently in the past 150 years, which is an extremely short length of time to begin with?
You kinda touched on the answer yourself. There are other factors that affect temperature. If you ONLY look at CO2 and temperature, you're going to miss some things and might come to the conclusion that there is no correlation in that period. Adjust for solar activity and your chart is going to look different. Also, note how your temperature scale is pretty narrow. This makes small changes in temperature appear drastic, and appear to diverge from the CO2 line.
 

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You kinda touched on the answer yourself. There are other factors that affect temperature. If you ONLY look at CO2 and temperature, you're going to miss some things and might come to the conclusion that there is no correlation in that period. Adjust for solar activity and your chart is going to look different. Also, note how your temperature scale is pretty narrow. This makes small changes in temperature appear drastic, and appear to diverge from the CO2 line.
Yep, you have to seperate the temperature with CO2 from the termperature without CO2, so that the only difference between the two is CO2. This is why GW has been such a hard thing to prove, because there are so many variables to take into account. Its hard to get a controlled experiment.
 

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The most confusing part is where you insist that skeptics ignore that even though CO2 levels only followed temperatures in the past, that's not what's happening now, therefore causation isn't disproven. Correlation doesn't prove causation, but lack of correlation automatically disproves causation. And even if there's correlation now, the fact is that there hasn't been in the past:
I don't think lack of correlation is really an issue here, however, lack of correlation does not disprove causation.

If something is independent, then it is uncorrelated. It is not necessarily true the other way around.
 

Deuce

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Yep, you have to seperate the temperature with CO2 from the termperature without CO2, so that the only difference between the two is CO2. This is why GW has been such a hard thing to prove, because there are so many variables to take into account. Its hard to get a controlled experiment.
And we only have a sample size of one!

It is tough, but that's why climate research spans so many fields and so many different types of data. At this point, it's pretty definitive that CO2 causes warming. That's just basic physics, the question then becomes how much extra energy is being absorbed and how that will affect things. There's mountains of evidence pointing towards the general premise of "warmers:" Mankind's CO2 output is noticeably and significantly affecting the earth's temperature, and when temperature changes too quickly (in either direction), it has a strong negative impact on animal and plant life. Seeing as how we eat animals and plants, this will be an issue.

Dav said:
I'm not entirely sure what you're trying to say here... that even though it's a tiny portion that humans are contributing, because it's CO2 and because there is a feedback loop, it's enough to make a difference? I can get that, though it's more of an assertion than it is proof of an assertion.
The most confusing part is where you insist that skeptics ignore that even though CO2 levels only followed temperatures in the past, that's not what's happening now, therefore causation isn't disproven. Correlation doesn't prove causation, but lack of correlation automatically disproves causation. And even if there's correlation now, the fact is that there hasn't been in the past:
Your correlation/causation logic is incorrect. There's no particular reason that CO2 can't be both a result of and cause of temperature changes. CO2 has a greenhouse effect, that's been explained already. CO2 is also stored in large quantities in ice caps/glaciers and the ocean. Warming the planet will release more CO2, cooling the planet will trap more. Hence CO2 being described as both a forcing and a feedback for temperature. The reason CO2 "lagged" temperature changes in the past is exactly that: CO2 doesn't get released from ice spontaneously, something else needs to start the warming process. That's how previous glaciation cycles worked.

Here's the catch, though. Milankovitch cycles (the regular variations in the earth's orbit and axial tilt) take thousands of years. We've seen significant (geologically speaking) temperature change in a century. The current warming trend cannot be explained by that natural cycle nor by solar activity.
 

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Since Venus was brought up I think we should all understand the exact nature of the Venutian atmosphere. It is almost entirely composed of carbon dioxide and is 93 times as massive as the atmosphere of Earth. We are thus talking about nearly 2000 times as much carbon dioxide and yet the temperature is only about nine times that of Earth. Now I'm sure you'll come up with some reason for why that is, but let's be honest here: How much of an effect can it really have on Earth given this fact?

Compared to the amount of carbon dioxide that has been emitted by humans from all effects we are talking about an essentially irrelevant amount when considered with regards to Venus.

There are countless reasons why outgoing radiation would be lower than incoming radiation that do not involve carbon dioxide. Our climate is incredibly complex and can be affected by dozens of occurrences. When the scientific community is so quick to claim carbon emissions as the cause of all our ills I get skeptical. Certainly pointing to fossil fuels as the main culprit is purely political in nature. Unfortunately, some people actually believe in the integrity of the scientific establishment.
 
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