Guest Post by Willis Eschenbach
There’s an interesting measure of atmospheric CO2, called the “airborne fraction”. The airborne fraction is the fraction of the CO2 emitted each year which remains in the atmosphere. When humans emit say 9 gigatonnes of carbon, only about half of that remains in the air. The other half of the emitted carbon is absorbed, “sequestered” in some semi-permanent fashion, by various carbon sinks in the land and the ocean.
Dr. James Hansen of NASA, another in the long line of climate alarmists who don’t mind shafting the poor with expensive energy, has come out with a most surprising statement in his latest paper, Climate forcing growth rates: doubling down on our Faustian bargain, hereinafter Hansen 2012. The statement involves Hansen et al.’s explanation for a claimed recent decrease in the airborne fraction. Here’s their graphic showing the changes in the airborne fraction since 1960.
Figure 1. Hansen 2012 Figure 3. I’ve added a vertical line highlighting June 1991.
[ORIGINAL CAPTION] Fossil fuel CO2 emissions (left scale) and airborne fraction, i.e., the ratio of observed atmospheric CO2 increase to fossil fuel CO2 emissions. Final three points are 5-, 3- and 1-year means.
I do wish people would show the underlying data and not just averages, but setting that aside, here are the authors’ claims about the drop in the airborne fraction (blue line) post 2000:
We suggest that the surge of fossil fuel use, mainly coal, since 2000 is a basic cause of the large increase of carbon uptake by the combined terrestrial and ocean carbon sinks. One mechanism by which fossil fuel emissions increase carbon uptake is by fertilizing the biosphere via provision of nutrients essential for tissue building, especially nitrogen, which plays a critical role in controlling net primary productivity and is limited in many ecosystems (Gruber and Galloway 2008). Modeling (e.g., Thornton et al 2009) and field studies (Magnani et al 2007) confirm a major role of nitrogen deposition, working in concert with CO2 fertilization, in causing a large increase in net primary productivity of temperate and boreal forests.
This is an interesting argument, but it has a few moving parts. Let me list them.
1) Increased coal use leads to increased net primary productivity (NPP) .
2) Increased NPP is evidence of increased carbon absorption.
3) Increased carbon absorption leads to increased biologically driven carbon sequestration.
4) Increased biologically driven sequestration explains the post-2000 decrease in airborne fraction.
I’m good with claims number 1 and number 2, but from there they get increasingly unlikely for various reasons. I’ll go get the data and show the actual airborne fraction, but first, let me quote a bit more from Hansen 2012, this time regarding Pinatubo.
Remarkably, and we will argue importantly, the airborne fraction has declined since 2000 (figure 3) during a period without any large volcanic eruptions. The 7-year running mean of the airborne fraction had remained close to 60% up to 2000, except for the period affected by Pinatubo.
and also …
Thus we see the decreased CO2 airborne fraction since 2000 as sharing some of the same causes as the decreased airborne fraction after the Pinatubo eruption (figure 3).
I looked at the chart, and I looked at the dates. Pinatubo was in June of 1991. Here’s what I get from the data:
Figure 2. Annual airborne fraction (red line), along with 7-year average (blue). Green line shows theoretical airborne fraction assuming exponential decay of excess CO2.
So to start with, from both his graph and mine I’m saying absolutely no way to Hansen’s claim that there was a “decreased airborne fraction after the Pinatubo eruption”. Hansen seems obsessed with Pinatubo. He previously has claimed (falsely) that it represented a successful test of his GISS climate model. See here, here , and here for a discussion of how poorly the models actually did with Pinatubo.
He is now claiming (again falsely) that there is some drop in the airborne fraction after Pinatubo. I’m sorry, but that’s a totally false statement. There’s no sign of any unusual drop post-Pinatubo in this record at all, neither in the annual data nor in the average data. The majority of the drop he seems to be pointing to occurred well before Pinatubo occurred …
In passing, let me comment that any reviewer who let any of that Pinatubo nonsense past them should resign their commission. It was the first thing I noticed when I looked at the paper.
There’s a second problem with what Hansen et al. have done. They say regarding their 7-year average (blue line) that: Final three points are 5-, 3- and 1-year means. Sadly, this means that the final point in the 7-year average is forced to be equal to the last point in the raw data … easily the worst choice of ways to handle the final points of any average, almost guaranteed to have the largest error.
But that method does have one advantage in this case. It greatly exaggerates the amount of the recent drop. Note for example that had the data ended one year earlier, the final point in his average would have had a value 60% … here’s what the 7-year average figured their way would have looked like if the data had ended in 2010.
Figure 3. As in Figure 2, but with the 7-year average ending in 2010 using their method. Note that the final point is forced to equal the 2010 value.
As you can see, their curious treatment of the 7-year average at the end of the data is the only thing that makes the trend look so bad. When changing the data length by one year makes that kind of change in an average, you can assume that your results are far, far from robust.
But neither of those is the main problem with their claim. The main problem is that the general slight decrease in the airborne fraction is an expected result of the exponential decay of the excess atmospheric CO2. As the green line shows, the actual results are in no way different from the value we’d expect to see. The green line shows the result of the exponential decay of the excess CO2 if we assume a half-life of about 46 years. The expected value decreases slightly from 1970 to 2011.
It’s worth noting that if CO2 emissions leveled off entirely, the airborne fraction would gradually decay to zero. This is because if emissions level off, eventually the excess CO2 level will be such that the annual sequestration will equal the annual emission with nothing to remain airborne.
To close, let me return to their claim:
We suggest that the surge of fossil fuel use, mainly coal, since 2000 is a basic cause of the large increase of carbon uptake by the combined terrestrial and ocean carbon sinks.
I must confess that I hadn’t looked at fuel use by type in a while, so I was unaware of a large spike in coal use.
Figure 4. Carbon emissions by fuel type. Note the steady rise of natural gas, which will only increase with the advent of fracking.
So yes, coal use has indeed spiked since 2000, with a jump in coal emissions putting it back out in front of oil. I assume, although I’ve not checked, that this is the result of the huge increase in coal for electricity generation in India and China. And good on them, the folks in that part of the planet desperately need cheap energy.
Returning to the claims in Hansen 2012, it is true that the carbon uptake by the various sinks has constantly increased over time. This increase, however, appears to be much more related to the exponential decay of the CO2, and has less to do with the changes in the biosphere. We know this because the change in the amount sequestered is much larger than the change in the NPP.
Here are the figures. In 1960 the natural sinks were sequestering about 1 gigatonne of excess carbon annually. By 2011, this had risen to 4.5 gigatonnes annually. I agree that CO2 fertilization is real, but clearly this 4.5-fold increase in total tonnage of excess carbon sequestered cannot all be the result of increased NPP from CO2 fertilization.
So while I’m glad to hear that Hansen thinks that coal is good for something, I fear his explanation for the increase in the amount sequestered is not correct. The increases in the amount sequestered have been much, much larger (450% since 1960) than the increase in the amount of sequestration due to greater NPP.
Before I leave, let me remind folks what cheap electricity and energy from coal does for us all, rich and poor alike, every day of the year.
Figure 5. Daily output of coal energy. SOURCE
That huge benefit to the poor and the rich is what Hansen is trying to get rid of … but he and others have very little with which to replace it. So all that happens is that the price of energy goes up, and the poor once again are impoverished the most.
Brilliant plan, that fellow Hansen truly cares about the future … he just doesn’t seem to care if he hurts people in the present.
My best to everyone,
w.
richard verney says:
March 30, 2013 at 2:29 am
That being the case, the warm oceans would have had a lesser capacity to act as a carbon sink. One major issues is how did the planet sequester these high levels of CO2? Precisely what were the sinks?
Have a look at the white cliffs of Dover, UK (and most of South England) and their counterparts in Normandy, France. All carbonates, the remains of countless numbers of tiny coccolithophores:
http://www.soes.soton.ac.uk/staff/tt/eh/
Be aware that the Cretaceous did need some 60 million years to reduce its CO2 levels…
Willis Eschenbach says:
March 29, 2013 at 10:03 pm
AntonyIndia says:
March 29, 2013 at 8:09 pm
……………………..There appears to be a whole folder missing from the Columbia website. The link originally went to a folder on the website of Makiko Sato and James Hansen.
……………………..But the whole folder they reference has vanished, and as far as I can tell none of the documents in the folder is available anywhere on the web.
Go figure …
w.
———————————
I try as they say, to never attribute to malice that which can be attributed to stupidity or ignorance.
But sometimes it gets hard to “Go figure” otherwise when malice is so obvious elsewhere.
Hansen is not stupid, Gleick is not a moron, Mann is not a dunce and Jones is not ignorant (Excel excluded). They have to know what they are doing to the poor of the world so about the only thing I have left is malice or greed on their part. It seems everything they know will bring harm.
They lie, cheat, steal, whitewash, stop fuel development, hide declines, destroy data, delete communications, control peer review, withhold information etc, all for the Cause. And who knows what we haven’t caught them doing, as yet?
These are the people in leadership and this is their Scientific Method.
Thanks
cn
And to help the guy here because it appears he does not know….there is NO fossil fuel. Hdrocarbons are everywhere, even oceans of it on Titan and Saturn etc etc…..
A-biotic oil? Oil is here on this planet forever and Mother Earth generates oil all the time…
How does mankind control the prices of diamants? The same they do with Crude.
Ferdinand Engelbeen:
I do not intend to engage in another of our interminable debates which get nowhere, but your comment at March 30, 2013 at 3:32 am is so wrong that I write to correct it.
You say
The sequestration of the biosphere is not “relative easy to know” because the bulk of the world’s biota is in the oceans. Oceanic microorganisms sequester CO2 and lose CO2 (e.g. by decomposition of dead organisms). Each year, orders of magnitude more CO2 are pumped in and out of the oceans than the anthropogenic CO2 emission of any year.
Furthermore, the anthropogenic emission is mostly from burning fossil fuels which – being derived from biota – have similar isotope composition to biological CO2.
The observed change to the carbon isotope ratio is consistent with it being caused by the anthropogenic emission. But there is a 50:50 chance that it would be in the right direction. Importantly, the magnitude of the isotope change is WRONG by a factor of 3 if the increase to atmospheric CO2 has a purely anthropogenic cause from accumulation of emitted CO2 from anthropogenic sources.
Simply, the magnitude of the isotope change indicates the opposite of what you claim. Most of the change is observed to NOT be anthropogenic so it cannot be known if any of it is anthropogenic.
I repeat, I don’t know if the cause of the recent rise in atmospheric CO2 is entirely anthropogenic, or entirely natural, or partly anthropogenic and partly anthropogenic. Nobody can know because there is no available data capable of resolving the matter. Some people think they know but that is belief and not science.
Richard
Nature had it worked out so that CO2 was in balance before humans started burning fossil fuels. Or at least that is what we are told.
If nature is able to balance 100% of total CO2 emissions in 1850, it seems most illogical to assume that nature will not be able to balance 104% in 2013. (human CO2 emissions are 4% of natural emissions)
What apparently escaped Hansen and others is the lag in Nature’s response. CO2 levels must increase first before Nature can respond and balance them once again.
The truly faulty logic by Hansen and others was to assume that plant life could not increase in response to more CO2. That “sinks” were already saturated. That is completely illogical because it was already well known that plants grow faster when CO2 is raised above 1850 levels and continue to grow faster even when CO2 levels are increased above the levels predicted if we were to burn all known fossil fuel reserves on the planet in a single day.
From the graphs one could just as well argue that the change in CO2 rates coincides with the leveling of global average temperature and what we are seeing is the result of a change in the rate of out-gassing of CO2 from the oceans and noting to do with humans or plants.
WIllis, thanks for your (as usual) interesting and eminently readable analysis. When I have one of my (frequent) discussions with my AGW believer friends, they always say that CO2 is resident in the air for 50 – 100 years. Now that sounds like a BS argument to me but what have actual studies shown the free CO2 residency to be and what do GCM’s assume it to be?
An open discussion of climate issues was why I came to WUWT, after experiencing the censorship and intolerance of Real Climate to alternative and competing theories. I am disappointed to see this intolerance raise its ugly head on WUWT.
If I could para-phrase James Delingpole substituting Hansen for Beddington:”what I actually be doing is retiring to my study with a bottle of whiskey and my trusty service pistol, there doing the only proper thing a chap should do when he has brought shame on himself and brought untold suffering to millions.”
richardscourtney says:
March 30, 2013 at 2:37 am
===========
Richard, I agree with you 100%….and I call bullocks on the whole thing
First, 390 ppm is not high…….it’s low enough it would be considered limiting to plant growth….
….when some greenhouse of pot grower jacks their CO2 levels up into the thousands ppm…only to have it drop back to limiting within one light period…and they have to constantly keep adding CO2 just to keep levels up to where they can even grow plants
If that few plants can drop CO2 levels that far…….
Ferdinand Engelbeen says:
March 30, 2013 at 4:12 am
Error? The current concentration of CO2 in the atmosphere is just over 395 ppmv. 9% of that is just over 35 ppmv. Where did you get double the calculated amount for your 70 ppmv? Are you saying all human-contributed CO2 (because half has been sequestered) historically comes to 70 ppmv?
Nice analysis Willis, as we’ve come to expect from you. I’d make a couple of small modifications that don’t effect your analysis much. 1) Re Pinatubo, there is an inflection downwards at 1991 to a sharp (annual mean) minimum and then a rebound – perhaps a small concession to Hansen. Certainly, the trend was down already before Pinatubo but it does have a modest signature. 2) although global temps have flattened over the past 15 years or so (assuming the same for the ocean itself), they are sitting at a plateaued high for the present rather than rising and increasing amounts of CO2 to the atmosphere. The temperature record does seem to be reflected with little lag unless the 1998 high El Nino coincidentally coincides with the large spike in “airborne” CO2. What happens over the next few years may reinforce this apparent rapid response to change in CO2 airborne. The overall ocean temperature is, of course, not changing quickly, so this should be seen as high SST “blocking” rate of solution of CO2 into the ocean.
richardscourtney says:
March 30, 2013 at 2:37 am
It is extremely unlikely that the 97% natural CO2 emission is mostly back and forth cycling which can be assumed to be constantly in balance.
Dear Richard,
As we have discussed before, it was near constantly in balance before humans started to emit huge quantities of fossil fuels. The ice cores show a quite constant ratio between temperature and CO2 levels of about 8 ppmv/°C over the past 800 kyrs, with a high correlation and a lag of CO2. Even today, one can see a change of about 4-5 ppmv/°C around the trend over the seasons and the year by year variations, again with a lag of CO2. Of course, the ice cores are smoothing the past variability, but the current CO2 records are not.
The quite small variability of CO2 levels around the trend, despite huge hemispheric temperature changes over the seasons maybe caused by the counteracting fluxes between atmosphere and oceans at one side and atmosphere and vegetation on the other side. Anyway, over the past 50+ years, natural variability was not more than 1 ppmv around the 2 ppmv/yr trend, while humans emitted 4 ppmv/yr.
Increased undersea volcanism would release additional sulphur ions which travel with the thermohaline circulation until they reach ocean surface layer centuries later.
As said before, all alternative explanations for the increase in CO2 violate one or more observations:
In the case of acidification of the oceans by SOx from undersea volcanoes (or more acidic discharge from rivers), the amount of total dissolved inorganic carbon (DIC, CO2 + bicarbonate + carbonate) would decrease over time, as acidification releases CO2 at the cost of bicarbonates and carbonates. But we measure an INcrease of DIC in all oceans over time as well as in a few long term series as with regular ship surveys… That is only possible if CO2 enters the oceans from the atmosphere and is the cause of the pH reduction, not the reverse.
Further, something else in nature should then increase its sink capacity, according to the mass balance:
If the oceans over time increased from a net sink to a net source of CO2, of let us say actually 6 ppmv/year into the atmosphere and humans are a net source of 4 ppmv/year, the total increase would be 10 ppmv/year. But we measure only a 2 ppmv/year increase. Thus some non-ocean natural sink increased its capacity with 8 ppmv/year and the total natural cycle still removes a net 2 ppmv/year out of the atmosphere. The only difference is that the natural turnover increased with about 6 ppmv or 12 GtC/year and still humans are responsible for almost all of the increase…
Its funny how common sense is so rare, one commentator asked why the increase in biomass was not instant? how long does he think it takes to green a desert? and at the same time there was wholesale loss of rain-forest hell man look at the whole picture! Then people say ethanol is a good fuel and give as an example the power some engines have made on it well they need to look at the size of the jets in the carburettors needed to run the rubbish, the jets are several times the size needed for gasoline imagine the fuel consumption! it seems no one on the “green” side ever thinks of side effects do they? The warmist crowd are looking increasingly desperate do we need to be cautious near cornered rats? I would think so, common sense again!
richardscourtney says: March 30, 2013 at 2:37 am
[…..] It is extremely unlikely that the {97% of CO2 emission which is natural} is mostly back and forth cycling which can be assumed to be constantly in balance. This improbable balance may exist, but nothing else in nature is observed to be so in balance and constant.
[…..]
An imbalance of less than 2% p.a. between the natural emission and sequestration would account for all of the observed rise in atmospheric CO2. And there are several possible reasons why such an imbalance may have occurred.
The myth that natural emissions and sequestrations of CO2 are known to be in a constant balance needs to be dispelled if we are to determine the true causes of the recent rise in atmospheric CO2 concentration and, thus, to avoid distortion of energy and economic policies.
Richard
That is a helluva good post by Richard…. very important points, very educational (to me, at least), and very well explained.
RockyRoad says:
March 30, 2013 at 7:05 am
Error? The current concentration of CO2 in the atmosphere is just over 395 ppmv. 9% of that is just over 35 ppmv.
You are completely right: I had calculated the 9% from the ~800 GtC in the atmosphere, but forgot to devide by the C/CO2 GtC/ppmv factor of 2.1 GtC/ppmv… Thanks for the correction!
Excellent piece. It’s always interesting to see other people’s take on the various papers. As I browsed the comments, I see that most have missed what I consider the most important part to rebutting the paper.
Hansen’s entire premise is based upon the idea that increasedhuman SO2 emissions are the cause for the warming hiatus. Well, is that true? Hansen focuses on China and India’s coal consumption. But, that assumes quite a bit. Is coal use up? Yep. But, worldwide, the burning of coal has changed. There’s a lot less SO2 being emitted from coal use today vs 30 years ago. Further, coal isn’t the only source for SO2, so while coal use may be increasing other behaviors are decreasing.
So, we’re back to the basis of Hansen’s premise. Are human global SO2 emissions increasing? Well, no. They’re not. From the most comprehensive and up to date information we have, SO2 emissions have generally declined since the 1990s. There was a bump circa 2003-2005, but has since declined because China employed newer technologies to decrease smog. SO2 emissions in 2011 were less than the emissions in 2000. The worse part of this is that even if one ends the emissions at 2006, as Hansen did, it is still less than what was being emitted in 1990.
http://iopscience.iop.org/1748-9326/8/1/014003/article
As Willis and others rightly point out, there’s plenty else wrong with Hansen’s paper, but, I think this information utterly destroys his premise, rendering his paper nothing but babbling nonsense.
I’ll be charitable and say Jimmy just wasn’t aware of this information. But, then, isn’t it science to endeavor to find such before they spew their idiocy? It would be really nice if our “scientists” actually started engaging in, …… well, science.
“Hansen is not stupid, Gleick is not a moron, Mann is not a dunce and Jones is not ignorant .”
Permit me to strongly disagree with these opinions.
M Courtney says:
March 30, 2013 at 5:18 am
Ferdinand Engelbeen, please could you clarify what you mean by “net”?
If a flux into the atmosphere increases but the other fluxes are unchanged then surely the “net” CO2 in the atmosphere will change?
How do you dissociate the “net gain or loss per year” from the movements of CO2 into and out of CO2 reservoirs?
Any unknown in an equation can be calculated if the other terms in the equation are known.
The unknown in this case is the net gain or loss of all natural fluxes together in/out the atmosphere. What is known are the human emissions with reasonable accuracy and the increase in the atmosphere with high accuracy. The net result is:
increase in the atmosphere = human emissions + natural releases – natural sinks
including the knowns for average recent years:
4 GtC = 8 GtC natural releases – natural sinks
or
natural releases – natural sinks = -4 GtC
Thus whatever the real height of natural fluxes in and out, individual or in total, the net change in atmospheric carbon from all natural fluxes together is a loss of about 4 GtC (or 2 ppmv) per year in recent years with the natural temperature caused variability of +/- 2 GtC (or 1 ppmv) per year. In the early years the sink rate was a lot less, but still over the past 50+ years in every year there was more natural sink than source:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/dco2_em.jpg
****
TonyfromOz says:
March 29, 2013 at 8:53 pm
The Chinese are using USC (UltraSuperCritical) technology for their new plants, enabling them to run higher Power generators, in fact single units capable of generating 1000MW, previously only the province of large scale Nuclear Power Plants.
****
B&W was building 1300 MW super-critical-pressure coal-fired boilers back in the late ’70s. I’ve seen ’em. Later, the increased capital costs of new plants (caused mostly by new regulations) caused a reduction in the sizes built.
A very real problem is sorting out the biological and chemical components of the ocean “sink”. Carbon dioxide has a nearly magical affinity for water and distilled water equilibrates with ambient CO2 at astonishing speed. As Richard Courtney points out this sink is strongly modulated by pH and by no means is ocean pH all carbonic. The chemical sink is transparent to isotopes.
The ocean biological sink filters strongly for 12C, but it also produces vast amounts of 12CO2 in what I call the nano carbon cycle. I’m not yet prepared to calculate it nor conjecture about the proportions that remain entirely aqueous and involve the atmosphere, but the nano cycle is enormous.
It is tempting to draw an analogy to the enormous energy cycle (roughly 110% of SI) that takes place between the ocean surface and the atmosphere.
http://geosciencebigpicture.com/2013/02/13/the-nano-carbon-cycle/
richardscourtney says:
March 30, 2013 at 6:13 am
The sequestration of the biosphere is not “relative easy to know” because the bulk of the world’s biota is in the oceans.
It makes no difference for the calculations. The oxygen balance and the d13C balance are (near) equally changed by land or ocean biota: both land and sea plants discriminate similarly against 13CO2 and both produce O2 while sequestering CO2. Thus the O2 balance includes the growth and decay of organics both in the oceans and on land, including soil bacteria, insects, animals and humans. For the d13C balance, that needs more calculation, as the higher d13C of the oceans and the back and forth isotopic discrimination at the sea-air boundary need to be taken into account. But both calculations show similar results.
Furthermore, the anthropogenic emission is mostly from burning fossil fuels which – being derived from biota – have similar isotope composition to biological CO2.
Yes, you are right. But the oxygen balance shows that in current times (since about 1990) the total biosphere is a net sink for CO2. The measured O2 decline (compared to oxygen use for fossil fuels burning) means more CO2 sequestering than CO2 release from the biosphere and preferentially more 12CO2, leaving a higher ratio of 13C/12C in the atmosphere. But we see a constant DEcrease of the 13C/12C ratio, thus not caused by the biosphere. Neither by the oceans, as the oceans 13C/12C ratio also is higher than of the atmosphere, even including the water/air border isotopic discrimination.
Importantly, the magnitude of the isotope change is WRONG by a factor of 3 if the increase to atmospheric CO2 has a purely anthropogenic cause
You forget that each year 20% of all CO2 in the atmosphere is exchanged by CO2 from other reservoirs. That makes little difference for the 13C/12C ratio if the exchange is with the ocean surface or the biosphere, as most of the exchange is bidirectional in short time (seasonal to a few years). What makes a difference is the longer term sequestering in the biospere (humus, peat, roots) and the deep oceans. The latter absorbs the current 13C/12C ratio into the deep, but releases the 13C/12C ratio of many hundreds of years ago. That can be used to estimate the deep ocean – atmosphere exchanges:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/deep_ocean_air_zero.jpg
The mismatch in the early years is interpretated as more CO2 release from the biosphere than sequestering.
Thus based on the 13C/12C changes and the oxygen balance, neither the oceans, nor the biosphere are the cause of the increase in CO2 and all other known sources (rock weathering, volcanic vents,…) have 13C/12C ratios above the current atmospheric ratio…
Hansen’s confusing some things. Fertilization is from NOx, which tends to come more from internal combustion than power plants. The cars are causing the trees to eat the CO2 from the power plants.
martha durham says:
March 29, 2013 at 6:17 pm
Martha, I agree. A true environmentalist knows that the way to save the Amazon rain forests is to industrialize Brazil( for example). Moving people into urban areas.
This has worked in North America.
This CAGW nonsense could be the death of true environmentalism.
Greg Goodman says:
March 30, 2013 at 5:58 am
Bill Illis says: The equilibrium level is about 270 ppm to 280 ppm.
Equilibrium for what? There is no equilibrium in such a dynamic system.
Why do you think that is a suitable “equilibrium” figure for today or in 150 years?
———-
280 – 285 ppm given it is perhaps a little warmer today.
CO2 back to 1 AD. The data is from the Law Dome ice cores which have a resolution ranging from 1 year to about 40 years in some periods and fit with a 20 year Cubic Spline fit.
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/antarctica/law/law2006.txt
http://s7.postimg.org/893ubewnf/CO2_1_AD_2012_Law_Dome_Global.png
CO2 last 40 million years – all reliable estimates.
http://s13.postimage.org/pvmtijcw7/CO2_Last_40_Mys.png