How much more warming will additional atmospheric CO2 cause?

Mike,

By and large all your ‘for’ and ‘against’ arguments are correct, or at least have a good degree of truth about them.

CLIMATE SENSITIVITY: This is an area we still haven’t fully got to grips, with and as we learn more about this exceptionally complex issue it appears that early projections were probably on the high side. For many years the range into which ECS falls has been narrowing as it tended toward a value of 3.0°C but there were always uncertainties. As we learn more and eliminate or quantify variables we’re in a better than ever position to say with a reasonable level of confidence (1SL) that the value is around 2.4°C to 2.5°C. This falls somewhere in the middle between the early high IPCC values and the low skeptic values.

TEMP/CO2 CORRELATION: The correlation is actually excellent, where there appears to be divergences this is the result of other factors. For example, CO2 rose throughout the 20th century but during the middle of the century temperatures levelled out whilst CO2 rose. This coincided with the period of worst pollution when huge amounts of sulphates and black particulate matter were being released into the atmosphere. Both these cool the climate. So it’s not that the warming went away or the link between temp and CO2 was broken, simply that significant cooling influences were also involved. We’re seeing exactly the same thing happening now as the emerging Asian economies once again emit vast amounts of these cooling materials into the atmosphere.

RECENT WARMING: The warming is unprecedented. It’s often cited that the Earth has warmed and cooled of it’s own accord in the past, and whilst this is correct it’s very rare that any attempt is made to put this into context. Historic warming has occurred over very long periods of time, often over thousands or even millions of years. The rate of warming in recent decades is 26 times faster than anything that has ever before been known to happen as a result of any natural cycle. To put it into context, if an ice-age (natural cycle) occasioned the same magnitude of warming as has happened recently then the planet would boil itself to extinction every 95,000 years.

IPCC MODELS: As with ECS, these are constantly being refined and the range of projected temperature change over any given time is narrowing. The earliest projections were for a temperature rise of anywhere between 1°C and 7°C by the end of the century, back then there were so many unknowns that such a wide range had to be attributed to future change. As more and more is learned the range is narrowing and it’s now likely that the rise in temps by 2100 will be in the order of 3°C to 4°C.

WATER VAPOUR FEEDBACK: The big unknown is more concerned with the role water vapour has in affecting the potentials of other greenhouse gases in contributing to warming. Again, it’s an area that is constantly being revised and the range is slowly narrowing. Early work suggested that anywhere between 9% and 36% of additional warming could have been down to water vapour, today we can say with high confidence (1.5SL) that it’s in the 20’s. It still means that, even attributing the maximum warming possible to H20, two-thirds to three-quarters of warming is down to enhanced GHG emissions.

AEROSOLS: As before, we’re learning more all the time but still have a way to go. Also as before, the range is narrowing and is tending toward the upper end of the range. This won’t be good news for the skeptics as it means that the cooling element is stronger than might have been considered previously and therefore a greater degree of warming is required to compensate for this. In short, take away the aerosol effect and the level of warming jumps sharply. It was back in 1991 following the Pinatubo eruption that models could be tested in a real world environment. Leading this was Jim Hansen (the skeptics favourite) and his projections for the aerosol effect were met with some incredulity from all quarters. Over the following two to three years the climate behaves precisely as he predicted and we had to accept that aerosols played a more significant role than had perhaps been thought.

LAWS OF PHYSICS: Increasing levels of CO2 and other GHG’s has to result in a greater retention of heat, this is governed by the laws of thermodynamics and quantum mechanics, like it or not there’s no escaping it. But this doesn’t mean that temperatures have to rise proportionately. If, using simplified and made up numbers, 1 unit of GHG = 1 unit of heat retained, and 1000 units of GHG are released then there will be 1000 units of heating. At the same time if some other factor introduces 2000 units of cooling then the net effect will be a cooling one. No laws of science have been broken, the global warming theory has not been invalidated in any way and the warming still exists, just that the cooling is more powerful so it’s being masked.

"@Trevor: " Increasing levels of CO2 and other GHG’s has to result in a greater retention of heat, this is governed by the laws of thermodynamics and quantum mechanics, like it or not there’s no escaping it."

This statement is true in isolation with CO2 the only variable changing like in lab conditions. However, in the climate system there are feedbacks (both positive and negative) since there are many variables and processes interacting. In nature there are plenty of examples where the positive addition of a variable results in negative feedbacks being more powerful. I'm not saying this is the case with CO2 in the atmosphere I'm just saying it's not impossible and it would not break any laws of physics."

Charitably, your "rebuttal" to Trevor is flawed. You can't have a feedback of any kind overpowering a nonexistent effect. Some feedback might be possibly overpower increased heat retention from CO2, but that does not negate the fact that CO2 increase MUST increase heat retention. You appear to be doing your best to muddy up scientific thinking. If enough people point out that your reasoning is flawed, we may get increased scientific understanding - but it doesn't erase your original attempt, just the negative effects.

The response of the various earth systems to increased CO2 and warmer temperatures is not completely known. At issue is how many positive feedback systems there are and how many negative ones. It takes a lot of research to measure these quantitatively.

So are the biggest possible negative feedback -- something that would response to diminish warming after CO2 increases -- doesn't look too likely. That's is humankind would respond by reducing the amount of CO2 emissions.

A big positive possible feedback is if the increased warming melts places where methane, a powerful greenhouse gas, is stored. Scientists measure methane emissions from melting Siberian peat bogs. Also from clathrates, 'ice' frozen undersea in the Arctic containing methane. Nobody knows how much stored methane will be let loose, how soon. Some people are scared the melting clathrates will destroy the earth's life.

If there were no feedbacks, positive or negative, increasing CO2 would still warm the air. If there were no CO2 in the air, earth would freeze everywhere except a narrow equatiorial belt in 50 years. (Oct 2010 article in Science). Some CO2 is a good thing, too much more will be uncomfortable for humans and many other species -- or extinct them

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OK, I'm a little confused. Everything beginning with and below this paragraph --

>>Another common argument that increased CO2 MUST cause increased warming is due to the laws of thermodynamics. In other words, for CO2 to increase and global temperatures not to increase would break some laws of physics. No, it wouldn't break any laws of physics it would invalidate the CO2 positive feedback hypothesis which is not a law.<<

-- is a jumbled mess of common Denier claims that either misstate or intentionally misrepresent climate science and statements made by climate scientists. It therefore is properly a continuation of the AGAINST list. However, the wording suggests that the statements and faulty logic originated with climate scientists. It's as if you are staking out the high road of multivariate complex nonlinear systems and accusing scientists of making simpleminded linear assumptions and claims.

If that's the case, I defer to >>John's<< answer, which is basically what I would say.

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Gunny T --

>>First you gotta get the math and physics right, Climate temperature increase causes a natural increase in Co2, not the other way around.<<

That is false - You have the physics and the math wrong. You haven't be doing your homework, huh?

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edit --

I also defer to Trevor's answer which is far more detailed than I would have given.

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Other things being equal, no feedbacks at all would still mean some warming. To try to calculate what sort of feedback would mean no warming, you would get a proportional band of zero. Such strong negative feedback would not stabilize climate, buy would act as a square wave generator. Since weather is not a square wave, we do not have a negative feedback with a proportional band of zero.

And other than in the case of short term weather, your hypothetical case of no warming is simply not happening. However, short term periods where one year is not warmer than the previous is due to such factors as ENSO and sunspots. But neither shows a trend which could explaining the warming.

Mike, your entire post looks like a copy and paste from an Anthony Watts article. What IS your source for this "information"?

"How much more warming will additional atmospheric CO2 cause?" - This is what the TRUE skeptics are still debating. What they do not debate is that the planet is warming and that human activity is the primary cause of the additional warming we are observing.

"Another common argument that increased CO2 MUST cause increased warming is due to the laws of thermodynamics." - This is true only to the point until CO2 is not able to trap any further heat. There is a point of no further effect. The closer we get to this point the less effective CO2 is as a greenhouse gas. A blanket can only retain so much heat, Mike. We will never see this point of no further effect because all life on Earth would have long become extinct before it reaches that point.

"In other words, for CO2 to increase and global temperatures not to increase would break some laws of physics." - This is a blatantly false statement. There are variations, called noise, that will allow for short term temperature drops even as the CO2 levels rise. Eventually the noise will fade and the temperatures will again rise at a faster pace in the absence of the noise.

"No, it wouldn't break any laws of physics it would invalidate the CO2 positive feedback hypothesis which is not a law." - First, you need to learn the scientific distinctions between "hypothesis", "theory" and "law". - http://chemistry.about.com/od/chemistry101/a/lawth... - The AGWT is a scientific THEORY based on the Laws of Physics, The Laws of Thermodynamics and The Laws of Chemistry. NO ONE, NO GROUP and NO set of observations have ever even come close to invalidating the Anthropogenic Global Warming THEORY! I most certainly do wish that someone could! The denial industry, with all of its efforts, have not been able to do so. Why? Simply because it focuses on misdirection, misinformation, attacking the messengers, distractions, introducing confusion and through the telling of blatant lies! These qualifications place you firmly as a member of the denial industry and you give true skeptics a bad image whenever you try to pass yourself off as only a skeptic.

Added********

"You've already forgotten yesterday's question. There certainly is debate if CO2 is the PRIMARY cause of the warming. That's a direct corollary to this question and that's what we are debating." - Nicely worded, Mike, if your intent is for more misdirections. "....PRIMARY cause of the warming....". Nope! You are blatantly wrong again, Mike. There is no debate among the climatologist that the PRIMARY warming is due to the Sun. There is also no debate among the climatologist that CO2 will trap some of this heat from our sun and keep it from returning to space. There is also no debate among climatologist that human activity is adding significantly meaningful amounts of CO2 into our atmosphere. Do you dispute any of this, Mike? So, your entire debate point is not even a debate point among the climatologist. Everything you have posted here that follows the "for" and "against" comments are worthless in a scientific discussion.

Added - Part 2********

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I can't quite read your question. Let me get out of my greenhouse and turn down the CO2 manipulator. The windows have condensation on them and my computer does too. (sarc)

Now I can read it! Great question Mike! But reasoning with these people is like arguing with a monkey that just got pooped on by an elephant and thinks he can solve the problem with a cork.

If 300pm is the proper balance of the atmosphere (as antarcticice would suggest) then the current increase of CO2 would have already had a drastic impact on the planet. A 30% increase is very significant yet recent temperatures do not reflect such a massive change. The IP CC and its modelling have always been troubled in their predictions.

When the new fresh water freezes in the Arctic Ocean things will change back to a cooler Northern Hemisphere.

Proxi data and recent actual atmospheric data both show that CO2 lags behind temperatures. I think we should pay attention to what has happened in the Arctic and read the clues as to why the northern hemisphere is so warm lately. The fresh water renewal is above North America. I would bet that once the Arctic Ocean freezes again (this may take a few years to actually freeze to the extent it was) that the northern hemisphere will be much cooler than in recent decades.

http://www.jpl.nasa.gov/news/news.php?release=2012...

http://www.nasa.gov/topics/earth/features/earth201...

Trevor seems to have the Alarmist's view down very solid, but he doesn't site NASA's inquiry as to what is going on in the Arctic. The melting was (and still is) extreme. The replenishing of fresh water in the Arctic does have reasonable merit as to why the northern hemisphere warmed so much. As to the cause, it is still unknown. Theory says that the Arctic is replenishing its fresh water to control oceanic and global temperatures. Fresh water freezes faster and is more solid when it comes to a natural barrier/proponent against/for other salt-water flows. This has a lot to do with our oceanic river flow.

It seems that natural causes of any warming in any part of the world are thrown out by the Warmons (as Pheonix Quill would address them). Shallow thinking as always.