Soren wrote on Nov 14^th, 2009 at 1:29pm:


OK. As I understand it, you accept that atmospheric CO2 has been rising recently, largely as a result of human activities, and you are asking me to prove the link between that progressively increasing level of CO2 and global warming.  I think that's what you are saying here. Please confirm that I'm not misrepresenting you.

If that is where you stand, then there is not much point dwelling too much on the former point any further than this post. I'll summarise the key points for that conclusion in this post. If you accept that the dramatic increase in CO2 is not largely due to volcanoes or some other factor, then it saves a great deal of work on my part to convince you otherwise.

It's quite easy to get to that point from a simple consideration of inputs and outputs. Any factory, refinery or industrial plant that exists anywhere in the world has records of how much fuel was burnt and the type of fuel. The main three sources of carbon dioxide emissions are:

Coal and other solid fuels: 35%
Oil and other liquid fuels: 36%
Natural gas and other gaseous fuels: 20%
Cement production: 3%

We can determine how much carbon is being emitted to the atmosphere, and we can break this down quite accurately in terms of country, in terms of industry sector and many other classifications.  

We know that certain greenhouse gases are emitted by specific processes, for example nitrous oxide is emitted primarily in fertiliser and explosives  manufacture.

If you look at the emissions of various gases, atmospheric methane  has levelled off around  1750ppb. Although it has a higher greenhouse gas potential than CO2, you can see than its concentration in the atmosphere is about 200 times less that of CO2 (by volume), its Greenhouse Gas potential is 72 (CO2=1) over a period of 20 years and it has an atmospheric lifetime of about 12 years.

CO2 concentration is climbing at a rate of approximately 2ppm per year, up from approximately 0.7ppm per year in the 1950's and 60's. It's quite obvious that CO2 levels are rising in line with anthopogenic emissions. While volcanoes emit CO2, a cursory examination of the statistics show that the level of emissions is less than 1/100 of that due to human activities.

Methane emissions have levelled off as a result of improved practices in gas flaring. Most methane is emitted from oil and gas production, agricultural byproducts and  waste disposal and treatment.

Let me know if you have a problem with any of that, and we'll move on to the causal links and evidence connecting greenhouse gases and global warming.

Now we come to the crux. This will take several posts, so you'll have to bear with me.

I don't think anybody will dispute that CO2, methane and N2O are greenhouse gases. The degree to which they each absorb infrared radiation can easily be demonstrated using an infrared spectrometer.

What we say about CO2 applies to other greenhouse gases in terms of warming effects, but of course methane and N2O do not lead to ocean acidification.

The crux of the matter lies in the fact that we have an enormous reservoir of the most significant greenhouse gas (water) in contact with the atmosphere and the trend of increasing atmospheric water vapour concentration is directly related to warming trends. (I'll talk about where CO2 comes in later)  

When a warming trend results in effects that induce further warming, the process is referred to as a "positive feedback"; this amplifies the original warming. When the warming trend results in effects that induce cooling, the process is referred to as a "negative feedback"; this reduces the original warming. Because water vapor is a greenhouse gas and because warm air can hold more water vapor than cooler air, the primary positive feedback involves water vapor.

This positive feedback does not result in runaway global warming because it is offset by other processes that induce negative feedbacks, which stabilise average global temperatures. The primary negative feedback is the effect of temperature on emission of infrared radiation: as the temperature of a body increases, the emitted radiation increases with the fourth power of its absolute temperature.

OK, I'll take an anti-divorce break and get back into this tomorrow morning.

Soren wrote on Nov 14^th, 2009 at 4:44pm:


You can use percentage or ppmv, it doesn't matter. It still accounts for about 25% of the total greenhouse effect on Earth (directly).

These levels are much higher than at any time during the last 850,000 years, using ice cores data. We also have indirect geological evidence (proxy data) that indicates that CO2 values this high were last seen about 20 million years ago.

The radiative forcing equation for CO2 is:

ΔF = αln(C/Co), where α = 5.35

I won't go into the maths in any detail, unless you want me to.

Regardless of the fact that the CO2 concentration is 'only' 0.0387% volume, the actual radiative forcing is a fundamental mathematical relationship and is generally accepted as non controversial.  

This equation is based on fundamental physics which has been established for many years. It is a derivative of the Stefan Boltzmann equation.  (black body radiation)

As I said previously, the warming effect for a doubling of CO2 is around 0.7 degrees due to CO2. The amplified effect due to water vapour is around 2.3 degrees in addition to that.

The water feedback has been the aspect with the greatest error in past years. A great deal of work has been done on this in recent years, and the 3 +/- 1.5 will be plus or minus a lot less in the latest report.  The Mount Pinatubo eruption was a good test of our knowledge, and I'll expand on that later.

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That is incorrect. If you think it is correct, then tell me what you think the radiative forcing contribution of nitrogen, oxygen and argon should be, and on what basis.

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Slow solar variation and orbital factors. edit - (Actually CO2 content of the atmosphere has never been irrelevant. There is a clear correlation between CO2 and temperature through time. )


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- because we can measure solar irradiance very accurately thanks to satellite technology, and we know that it has actually shown a slight reduction if anything. (I think I have covered that before) I think I can give you a better answer than that. I'll try again tomorrow morning.

You're right in saying that the recent trends are correlation and not causation.  The causation is more fundamental, and relates to the structure of the CO2 molecule, and for that, I'm going to have to think about how to word the explanation to make it easily understood.

The historical trends can serve as confirmation of the causal relationship. They are not the fundamental proof.

Now for the Infrared spectrum of the atmosphere. This shows the absorption bands associated with different Greenhouse gases.

I think from what I have said so far, you will appreciate that carbon dioxide is a greenhouse gas. The efficiency of CO2 as a greenhouse gas is related to basic physical properties of the gas that can be demonstrated in any laboratory equipped with an infrared spectrophotometer. The Greenhouse Gas Potential of any gas can be measured quite accurately. While water vapour is a less efficient greenhouse gas, it is present in much larger quantities in most of the atmosphere. That last point may be important later on. Unlike CO2, water vapour is not uniformly distributed geographically or in terms of altitude.

All greenhouse gases heat the atmosphere by absorbing infrared radiation from the sun and re-emitting that infrared at all angles, thus trapping a greater proportion of the heat from the sun.

We can easily establish that when the global atmospheric temperature increases, for whatever reason (eg solar variations, CO2 forcing), the water vapour concentration of the atmosphere increases. Since water vapour is a greenhouse gas, we can establish that there is a feedback which will amplify the initial warming.

I have not yet adequately demonstrated that last point.

The 1991 eruption of Mount Pinatubo was a good test of water vapour feedbacks, because the volcanic ash cloud that enveloped the world effectively turned down the sun and consequently reduced the global temperature.

One of the parameters measured by the Mauna Loa Observatory is Solar radiation transmitted through the atmosphere. You can see the dips corresponding to the major stratospheric volcanoes that have erupted during the past 50 years.

Fascinating reading, muso, thanks for putting those posts up.

Do you have links to websites or books etc for further reading?

Darwin wrote on Nov 15^th, 2009 at 8:02am:


Darwin, When I have adequately addressed the issue and answered all of Soren's questions, I'll post a bibliography on the sticky section.  Here's an interesting summary:

CLIMATE SCIENCE: Warming Vapors

Water vapor is the atmospheric gas that collectively has the greatest greenhouse effect on climate, although it does not directly instigate warming or cooling trends, because the amount of water vapor in the atmosphere varies only in response to temperature change. Instead, water vapor only amplifies temperature trends being caused by other factors such as atmospheric CO2 concentration or Earth's albedo. The extent to which humidity changes in response to temperature variation is therefore a key parameter in global climate models, because that quantity determines the strength of the associated warming or cooling.

Dessler et al. present satellite data from 2003 to 2008 which show that models have gotten that relationship correct, and that relative humidity is effectively constant at any given temperature. Thus, the temperature increases predicted by global models are virtually guaranteed to be several degrees Celsius by the year 2100. Knowing the water vapor content of a warmer atmosphere is also important for predicting rainfall and storminess.

[Summary by Science editor H. Jesse Smith]

Geophys. Res. Lett. 35, L20704 (2008).

Unfortunately I don't have access to Geophysical Research Letters so I can't read the full paper.

muso wrote on Nov 14^th, 2009 at 5:47pm:




It may well be a mathematically non-controversial relationship. But we are not talking about mathematics. The climate is not a mathematical formula that we have fathomed yet.

I have seen a graph and learned exposition on how there is a case of diminishing returns when it comes to increasecd CO2 in the atmosphere and warming effect (radiative forcing): after a certain amount ofCO2 in the atmosphere, its radiative forcing effect diminishes rapidly.

There is clear evidence that whatever the occasional correlation (not causation) may be between CO2 and temperature, there is certainly no mathematical or any other correspondence between temperatuire and CO2.

The point is - there are other things at play. What they are, we do not seem to know. To pin it all on man made CO2 is unsupportable. Climate science is like brain science - we are making great and fascinating advances but to pretend that we understand how they work, or that we can identify single causalities (that we the proceed to complicate to death) is preposterous. For mine, this is a massive, hubristic over-reach. akin to phrenology or astrology.