This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
Objection:
Taking into account the logarithmic effect of CO2 on temperature, the 35% increase we have already seen in concentrations represents about 3/4 of the total forcing to be expected from a CO2 doubling. Since we have warmed about .7oC so far, we should only expect about .3oC more for a doubling from pre-industrial levels, so about 1oC not 3oC as the scientists predict. Clearly the climate model sensitivity to CO2 is much too high.
Answer:
Even without addressing the numbers in this argument, there is a fundamental flaw in its reasoning. We don't yet know exactly how much the climate will warm from the CO2 already in the air, there is a delay of several decades between forcing and final response. Until an equilibrium temperature is reached, present day observations will not tell us the exact value of the climate's sensitivity to CO2. The reason for this is primarily the very large heat capacity of the oceans. The enhanced greenhouse effect from higher CO2 levels is indeed trapping energy in the climate system according to expectations, but the enormous quantity of water on Earth is absorbing most of the resulting heat. Due to water's very high heat capacity, this absorbed energy shows up as only a very modest ocean warming, which in turn dampens the temperature change on land and lowers the global average trend.
This is commonly referred to as the climate system's thermal inertia. According to model experiments and consistent with data from past climate changes, this inertia results in a lag of several decades between the imposition of a radiative forcing and a final equilibrium temperature.
Now let's look at a couple of further details. CO2 is not the only factor effecting the global temperature and in fact there is a phenomenon often called Global Dimming which is counteracting greenhouse gas warming. Global dimming refers to the blocking of incoming sunlight by particulate pollution in the troposphere and airplane contrails in the stratosphere. It is not a well quantified effect but it may well be masking a great deal more warming, definitely it is masking some.
This is just one example, clearly an important one, of why we can not look at the temperature trends and pretend we can attribute everything to only CO2. This same mistaken argument is made when looking at the mid-century cooling trend.
I believe it is Richard Lindzen who originated this argument, but it seems there is another problem as well, the numbers he is using don't add up. 35% increase in CO2 should correspond to 43% of the forcing from 2x CO2 (ln(1.35)/ln(2) = 43%) which is not 3/4.
This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
"Observations Show Climate Sensitivity Is Not Very High" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.
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Coby claims: "Taking into account the logarithmic effect of CO2 on temperature, ..."
What formula is he using? As the temperature increases, the amount of heat radiated by a black body increases by the 4th power of the temperature. This is not a logarithmic relationship.
As the CO2 in the oceans increases, the water becomes more acidic. This make the water less able to absorb CO2. How does he take into account this effect?
As the water warms, it can hold less CO2. Where are the terms in his formula to take into account this effect?
As the oceans absorb CO2, the CO2 is locked up by Ca cations to form carbonates. There are a finite number of Ca cations and when they are gone, the rate at which the oceans can absorb CO2 will precipitously decrease. Where is this effect modeled in his formula?
Why is anyone taking this hand waving argument seriously? Does anyone think that the carbon cycles in the oceans and atmosphere can be modeled with a simplistic logarithmic relationship?
I do not. I think the effects and relationships are FAR more complex than Cody asserts. I would be very interested to see this formula. Why does he not back up his wild claim with THE mathematical model that would make climate science easy. Until he does so, I consider this claim to be so much spam.
Warm regards, Rick.
Posted by: Rick | July 31, 2008 4:42 PM
"Taking into account the logarithmic effect of CO2 on temperature"
This is about the only valid bit of his argument. The log law was first put forward by Arrhenius in 1895 and is sometimes called the law of global warming.
Realclimate argues that it is the worst way to determine the climate sensitivity by starting from twentieth century temperatures. As Coby points out the problem lies with the uncertainty involved with the aerosols (dimming). But it should have been at the top and not classified as a "further detail". It sinks the methodology because that way you can easily obtain any sensitivity whatsoever including an infinite one. Lindzen is perfectly aware of all of this and also of the inertia as can be seen from his writing. What he has done is to choose his data to get the result he wants (just what he claims is done by the modellers).
What if you reject Realclimate's position and follow Lindzen in trying to work backwards from the observed temperatures? You must allow for all the possible sensitivities and allocate them probabilities. One example is in Natalia G. Andronova and Michael E. Schlesinger,2001. J.Geophys.Res, VOL. 106, NO. D19, PAGES 22,605�22,611. They end up with a 90% probability that the sensitivity will lie between 1C and 9.3 C and a 54% probability that it will lie outside the IPCC TAR range (mainly on the high side). A corrected version of Lindzen would just consist of one point which might just get on to the the bottom of the range.
Of course Lindzen would argue that Andranova and Schlesinger must be rejected because it is based on a climate model. That leaves the way open for him to substitute his own back of the envelope model without any justification.
Posted by: Geoff Wexler | September 6, 2008 9:03 AM
Reply to Rick.
The log law relates radiative forcing to concentration of greenhouse gas. Your comment diverts attention from this to all sorts of other non-linear effects which might be important at large warmings but which might be ignored to start with. The fourth power law due to Stefan Boltzmann is not one of them because it is essentially a linear relationship for the 'small' warmings we are discussing. Small here means relative to the absolute temperature of about 300K; it does not mean harmless.
As for the log law I suggest that you try Ray Pierrehumbert's theoretical book which is partly on line. I only have a bit of it at hand which includes a relevant remark :
"The logarithmic effect of water vapor is somewhat more difficult to cleanly quantify than is the case for well mixed greenhouse gases like CO2, but if one adopts a base-case vertical distribution and changes water vapor by multiplying this specific humidity profile by an altitudeindependent factor, one finds that each doubling of water vapor reduces OLR by about 6W/m2 (Pierrehumbert 1999)."
Posted by: Geoff Wexler | September 6, 2008 3:56 PM
I would be somewhat more persuaded by this argument if, at the same time, an obvious consequence of this was considered. That is, the possibility that some or all of the current warming being due to the heat that was stored in the oceans due to the solar irradiance related warming in the early part of this century.
But this or any alternatives weren't even ruled out - apparently the ocean only releases heat ahead from now, it rather conveniently isn't releasing any at the moment from past warmings. Hmmm.
Don't get me wrong, I'm not saying it definitely was - I certainly don't know - but that isn't the point. The argument above is not science, it is a sales pitch.
Posted by: frank | September 12, 2008 2:53 AM
Hi frank,
Don't forget that there are 60+ arguments in this guide they each have a very narrow focus by design so don't expect every aspect of the situation covered in every article!
You are quite right that we would expect a similar lag time from any forcing, including solar. Solar irradiance has not varied with any significance since around 1950, so I think is is quite reasonable to rule it out copletely as a contributor to the post 1980warming trend.
But this or any alternatives weren't even ruled out
Well, not by me in this article, but please refer to the extensive work cited in the IPCC chapter's on attribution.
(Chapter 9 from this page
Posted by: coby | September 12, 2008 9:17 AM
I think it "quite reasonable" to rule out CO2 as the primary driver of temperatures, but I'm sure we can both agree that this is not an argument.
And anyway, really? I've heard of longer timescales than that being stored as heat in oceans (no reference for that unfortunately).
Solar irradiance has not varied since 1950? Hmm, not according to the IPCC report where fig 2.17 on page 190 shows a rise from around the turn of the century to 1950, then a dip about 1970, and then a rise to levels clearly (if not massively) higher than the pre-1970 levels. Let me think, I'm sure there's some other measurement relevant here that did something like that....let me get back to you.
Posted by: frank | September 13, 2008 12:39 AM
That graph does not show what you describe, but it is not very suitable to your purpose anyway, it is on a very large timescale and does not have the 11 year solar cycle removed from it makeing it very hard to discern any trend. Why don't you check the sources cited at this article.
Another argument against solar dominance of the warming is the fact that the warming signal is greater at night than the day, consistent with an enhanced greenhouse effect but not with increased irradiance.
Posted by: coby | September 13, 2008 8:42 AM
The graph I mentioned can be seen in here -
http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch02.pdf
It is titled “Total Solar Irradiance” and the first line of the caption reads “Reconstructions of the total solar irradiance time series starting as early as 1600”, and so covers 400 years.
There are 9 cycles after 1900, covering the whole century. Looking at the newer Wang reconstruction, the peak of each of these cycles has the following values, each of these being the amount above 1365 W/msq.
0.7, 1.2, 1.0, 1.1, 1.4, 1.4, 1.2, 1.6, 1.7
The values of the nadirs of the cycles are closer together but follow the same trend broadly. The 1.2 is the dip I mentioned around 1970. The trend I described that you claim is hard to see is to me rather obvious.
Maybe you could explain you assertion that this graph “does not show what [I] describe” and is “not very suitable to [my] purpose”.
I examined the links on the page you suggested. The graph here
http://www.mps.mpg.de/images/projekte/sun-climate/climate.gif
seems to be showing an increase in temperature of more than 0.8 degrees from 1900 to now. I’ve never seen such a claim anywhere else.
And another of the links is to, erm, Wikipedia. So I was redirected from the IPCC report to Wikipedia.
People reading this can draw their own conclusions about the fact that the answer to so many questions on this site is to refer to the IPCC reports, yet you glibly suggested I go elsewhere when the IPCC data did not support your argument.
Posted by: frank | September 14, 2008 7:45 AM