From their Die kalte Sonne website, Professor Fritz Vahrenholt and Dr. Sebastian Lüning put up this guest Post by Prof. Jan-Erik Solheim (Oslo) on Hansen’s 1988 forecast, and show that Hansen was and is, way off the mark. h/t to Pierre Gosselin of No Tricks Zone and WUWT reader tips.
Figure 1: Temperature forecast Hansen’s group from the year 1988. The various scenarios are 1.5% CO 2 increase (blue), constant increase in CO 2 emissions (green) and stagnant CO 2 emissions (red). In reality, the increase in CO 2 emissions by as much as 2.5%, which would correspond to the scenario above the blue curve. The black curve is the ultimate real-measured temperature (rolling 5-year average). Hansen’s model overestimates the temperature by 1.9 ° C, which is a whopping 150% wrong. Figure supplemented by Hansen et al. (1988) .
One of the most important publications on the “dangerous anthropogenic climate change” is that of James Hansen and colleagues from the year 1988, in the Journal of Geophysical Research published. The title of the work is (in German translation) “Global climate change, according to the prediction of the Goddard Institute for Space Studies.”
In this publication, Hansen and colleagues present the GISS Model II, with which they simulate climate change as a result of concentration changes of atmospheric trace gases and particulate matter (aerosols). The scientists here are three scenarios:
A: increase in CO 2 emissions by 1.5% per year
B: constant increase in CO 2 emissions after 2000
C: No increase in CO 2 emissions after 2000
The CO 2 emissions since 2000 to about 2.5 percent per year has increased, so that we would expect according to the Hansen paper a temperature rise, which should be stronger than in model A. Figure 1 shows the three Hansen scenarios and the real measured global temperature curve are shown. The protruding beyond Scenario A arrow represents the temperature value that the Hansen team would have predicted on the basis of a CO 2 increase of 2.5%. Be increased according to the Hansen’s forecast, the temperature would have compared to the same level in the 1970s by 1.5 ° C. In truth, however, the temperature has increased by only 0.6 ° C.
It is apparent that the next to it by the Hansen group in 1988 modeled temperature prediction by about 150%. It is extremely regrettable that precisely this type of modeling of our politicians is still regarded as a reliable climate prediction.
So:
– The article claims emissions were above the A scenario by considering *only* CO2 emissions, and not all of the emissions actually included in scenarios A, B and C. Once that is considered, scneario B is the closest. So, the article contains a demonstrable error there.
– The article doesn’t make it clear which temperature series is being used, so we are left to guess. Looks like HadCRUT3 to me, which would be a poor choice given that Hansen’s projections were based on GISS. A probable error from the article there when using the same dataset as Hansen would be the obvious thing to do.
– The article claims that Hansen was out by 150% by comparing to a fantasy emissions scenario that bears no relation to any of the actual scnearios, based on the author’s CO2/total GHG’s misunderstanding. He was actually only out by ~25% when compared to scenario B. Another demonstrable error from the article there.
So, what do we take from this? That climate sensitivity to doubling of CO2 is likely in the 2-3C range, rather than Hansen’s ~4C.
Dana1981: “2) Thinking that a ~2 ppm annual CO2 increase is 2.5% of ~390 ppm (arithmetic fail!)”
Well, they are talking about emissions and not the increase in CO2 consentration. Don’t you know the difference and haven’t you heard about the missing sing? Keyword: ocean buffer
Bill Tuttle says:
June 16, 2012 at 1:37 am
…..So, when you guys can’t even decide if CFC is an actual greenhouse gas, let alone how much effect it has (in parts per friggin’ *trillion*, no less), color me less than compelled by the narrative….
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Al Gore said CFCs make the ozone holes bigger. Maybe the “missing heat” slipped out the ozone hole?
There’s a win-win! Stave off CAGW by bringing back freon. Whenever the predicted heat decides to finally show up, build more air conditioners releasing more CFCs making the ozone holes bigger letting out all the nasty heat. We can all stay calm and cool no matter what happens!
(I better add a “sarc” tag or a climate scientist might give this serious consideration.)
Girma says:
June 16, 2012 at 12:32 am
Steven mosher
To evaluate hansens projection we first have to find the scenario that is closest to the projected forcings. That is scenario B, not C and not A.
Steven that is incorrect.
Here is from the original paper
Scenario A => Annual greenhouse growth rate of 1.5% of the 1980s emission
Scenario B => Annual greenhouse growth rate constant at the 1980s level
Scenario C => Annual greenhouse growth rate decreases after the 1980s such that it ceases to increase after 2000
Steven, CO2 emission has not been “constant at the 1980s level”, so Scenario B does not match observation. It is Scenario A that matches observation.
Reading comprehension problems again!
Hansen in the 88 paper explicitly states a rate of increase of 1.9ppm/yr for Scenario B from 2010 onwards, last decade it averaged 2.07ppm/yr. http://co2now.org/
Why don’t you guys who want to criticize Hansen read the paper and get the facts straight, starting with the dog’s breakfast that the original author of this post made. To get the facts so consistently wrong just makes the critic look stupid.
Gunga Din says:
June 16, 2012 at 6:27 am
(I better add a “sarc” tag or a climate scientist might give this serious consideration.)
You’ll need to clarify that “sarc” isn’t an acronym for “scientifically arrived-at reasearchiness conclusion”…
AUSphysicist says:
June 15, 2012 at 10:50 pm
KR mentions,
“Forcings, as observed, as driven by economics, are around Scenario B, the most likely outcome according to Hansen 1988.”
What is most amusing in your desperate defense KR is that,
1) You know very well that CO2 is the primary claimed driver of global warming in that paper. This is obvious since its growth is the main factor that shapes those scenario curves in the paper.
No unlike you he’s read the paper and has his facts straight! I suggest you look at Fig 2 which quite clearly shows that you are wrong!
2) You try to blame reductions in CFCs as the reason why the temperatures have not gone according to predictions. Yet, CFC have very little contribution to climate change and furthermore their abundance in the atmosphere has changed little since 1988.
Again read the paper! The point is not that they’ve gone down since 1988 (which of course they have), rather that they stopped increasing at the former rate which is what Scenario A was based on.
At the end of the day, the observed CO2 emissions growth has been well ABOVE scenario A and yet the temperature is below scenario C. You really can’t get it any more wrong that this paper.
Again you’re wrong, Scenario B had CO2 increasing by 1.9ppm/yr after 2010 compared with the last decade’s average of 2.07ppm/yr
When one reads a hundred or so comments by informed people arguing about whether something with an indeterminant greenhouse gas effect measured in parts per trillion that didn’t change much validates the assumptions that underly a prediction of rising temperatures that didn’t rise, one tends to think they are locked in a loop arguing about how the tail ( specified greenhouse gases) really did wag the dog.
Bottom line as some have less bluntly put it: The only way you can say Hansen’s assumptions involving a group of gases might still be somewhat close – despite the fact that the main prediction of temperature is way off of all implied scenarios – is to admit that his main assumption, that C02 is the primary driver – isn’t important at all. — Even within the narrow range of greehouse factors to whcih he limited himself. It’s more than a little analagous to restricting one’s arguments to whether the St. Louis Cardinals won the 1964 World Series because I first became a fan that year.
What this Hansen justification loop strongly indicates is that CO2 is the gnat on the elephant’s — and that greenhouse gases as a whole don’t hold most of the answers to even the small climatic temperature changes we have experienced in our climatically short lifetimes.
scarletmacaw says:
June 15, 2012 at 8:45 pm
Phil. says:
June 15, 2012 at 7:22 pm
It didn’t go into effect until 1989, the scenario A assumed the continuation of the existing growth rate, scenario B assumed a reduction in emissions with elimination of CFC emission by 2010, scenario C assumed an earlier elimination by 2000.
Reagan signed the Montreal Protocol in 1987. There were no major CFC producing countries opposing it. By 1988 there was no reason to expect CFC production to continue as usual. Like I said, Hansen was clearly not the sharpest tack in the shed. Either that or he purposely mislead the public by displaying a scenario he knew was not going to happen.
The people who are misleading the public are those like the original poster who presents such an incorrect summary of Hansen’s paper. Hansen presented three scenarios, what would happen if we continued doing what we had been for the previous decade, what would happen if emissions were reduced somewhat (which he called the most plausible), and what would happen with more drastic restrictions. No misleading of the public by him, rather by those like Pat Michaels and Solheim.
Werner Brozek says:
June 15, 2012 at 8:29 pm
Ric Werme says:
June 15, 2012 at 4:44 pm
No, he’s 60% wrong – see my 10:55 am comment. 60% of 1.5 ° C is 0.9 ° C, and his projection was 0.9 ° C too high.
However below the diagram, we read:
In reality, the increase in CO 2 emissions by as much as 2.5%, which would correspond to the scenario above the blue curve. The black curve is the ultimate real-measured temperature (rolling 5-year average). Hansen’s model overestimates the temperature by 1.9 ° C, which is a whopping 150% wrong.
I must admit this part is very unclear, but it seems that since scenario A is for a 1.5% increase, then another line should have been drawn higher up to show what should have happened according to Hansen if the increase was 2.5%. Had that been done, we may have seen the 1.9 C at 2011. Or am I missing something?
You’re missing the fact that the original poster, Solheim, is wrong about just about everything he said about the 88 paper
Gunga Din says:
June 15, 2012 at 7:24 pm
dana1981 says:
June 15, 2012 at 6:16 pm
For the record, despite Solheim’s poor analysis, it is true that observed temps have been closest to Scenario C, while emissions have been closest to Scenario B. What this tells you is indeed that Hansen’s model was “wrong” – meaning its sensitivity was too high.
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ME: The Wizard of COz was rubbing his crystal ball based on CO2 emissions, not all emissions. He and his model was, and continues to be, just plain wrong. (That little dot at the end of the sentence is a PERIOD!)
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Nope, another one who can’t read! It was based on all emissions as has been pointed out several times in this thread.
So much misinformation (from both sides) I feel like my head is going to explode….
From the original AGU publication: “We make a 100-year control run and perform experiments for three scenarios of atmospheric composition. These experiments begin in 1958 and include measured or estimated changes in atmospheric CO2, CH4, N20, chlorofluorocarbons (CFCs) and stratospheric aerosols for the period from 1958 to the present. Scenario A assumes continued trace gas growth, scenario B assumes reduced linear growth of trace gases, and scenario C assumes a rapid curtailment of trace gas emissions such that the net climate forcing ceases to increase after the year 2000.” http://pubs.giss.nasa.gov/docs/1988/1988_Hansen_etal.pdf
Basically the 3 steps in the Hansen (1988) model experiment are as follows:
For assumed GHG emission scenario » Δ atmospheric composition » Δ forcing » Δ temperature
Step 1: Assume future GHG emissions path (3 scenarios)
Step 2: Project GHG concentrations in atmosphere for each scenario
Step 3: Calculate forcing for resulting atmospheric composition
Step 4: Project regional and global temperature changes for change in forcing.
In evaluating how well Hansen’s projections have stacked up against the 24 subsequent years of observed reality, I see both sides making serious mistakes (that unsurprisingly favour their own arguments about whether the model projections were good or bad).
First, I’ll challenge the skeptics (since I consider myself to be one).
1. Everyone here is automatically comparing observed warming to Hansen’s Scenario A. This is more than a bit too convenient as it yields the greatest possible difference. Keep in mind… Hansen wrote in his paper “Scenario A, since it is exponential, must eventually be on the high side of reality in view of finite resource constraints and environmental concerns, even though growth of emissions in scenario A (~1.5%/yr) is less than the rate typical of the past century (~4%/yr)… Scenario B is perhaps the most plausible of the three cases” The question to ask is: “How did actual emissions during the last 24 years compare against the 3 scenarios?”
2. Justifications for using Scenario A as a reference have focused narrowly on CO2 emissions increases (observed 2.5%/yr vs. assumed 1.5%/yr). To be fair, it would be necessary to focus on ALL GHG emissions, not just CO2. I see some of this above (references to methane and CFC’s, but not a comprehensive inventory of all emissions).
Now, for the warmists (dana1981, Phil, KR etc.)
1. SkS presents a very detailed dissection of the Hansen scenarios by GHG, calculates the actual GHG forcings, and concludes that forcings were closest to Scenario B. However, this analysis ignores changes in EMISSIONS and jump straight to FORCINGS. Yes, forcings ended up different from the various scenarios in the model projections… however, nobody bothers to ask: A) why CO2 forcing is in line with projections despite even higher emissions, B) why methane forcing is so far below projections.
If methane forcings were less than projections, and CO2 forcings were inline with projections despite higher emissions that implies at least one of three things… A) methane emissions fell far below assumptions all by themselves, despite no coordinated effort to reduce emissions, B) methane and CO2 emissions don’t reside in the atmosphere for as long as assumed so a given level of emissions results in a lower than projected atmospheric concentration, or C) feedbacks (such as the release of additional methane or CO2 which further increases concentrations beyond what’s caused by primary emissions) just aren’t happening as modeled. If it was A) then Hansen can only be accused of making lousy assumptions, but if it was B) or C) that would indicate serious weaknesses in the model.
2. The warmists start their argument with forcing values closer to Scenario B and then conclude the projections weren’t so bad if you just use a lower climate sensitivity value (3.0 vs. 4.2 degC /doubling). The problem I have with this argument is that climate models don’t just plug in a desired value for sensitivity. They attempt to model physical processes and feedback mechanisms and the equilibrium climate sensitivity value is a derived output. So, it’s pretty lazy to just say… “well if you assume a lower sensitivity the projections would have been decent” without addressing the deficiencies in the model that led to the overstated climate sensitivity. It’s basically saying… “if the model projections weren’t so bad, they’d be pretty good”.
old engineer says:
June 15, 2012 at 10:13 pm
So the question is: which scenario best matches the actual rate of change of the increase in the atmospheric concentration of CO2 over the past 30 years?
Somewhat lower than Scenario B.
http://co2now.org/
Russ R. says:
June 16, 2012 at 8:02 am
2. Justifications for using Scenario A as a reference have focused narrowly on CO2 emissions increases (observed 2.5%/yr vs. assumed 1.5%/yr). To be fair, it would be necessary to focus on ALL GHG emissions, not just CO2. I see some of this above (references to methane and CFC’s, but not a comprehensive inventory of all emissions).
Which is what I have been asking for here, continuing to focus on CO2 only in this thread amounts to lying since ample references have been provided to show that this is not true. In fact the claim that the CO2 levels are higher than Hansen predicted is also wrong, Scenario B expected a decline in CO2 growth to 1.9ppm/yr by 2010 whereas the last two decades have shown an average growth rate of 1.6ppm/yr and 2.07 ppm/yr. The 2.5% issue raised by Solheim is to be charitable a misunderstanding by him.
2. The warmists start their argument with forcing values closer to Scenario B and then conclude the projections weren’t so bad if you just use a lower climate sensitivity value (3.0 vs. 4.2 degC /doubling). The problem I have with this argument is that climate models don’t just plug in a desired value for sensitivity.
Well we’re discussing Hansen’s paper not ‘climate models’ and he explicitly uses a model that has an equilibrium climate sensitivity of 4.2ºC/doubling of CO2. So the problem you mention is moot. Hansen’s summary concluded that there was a need for improvements “in our understanding of the climate system and our ability to predict climate change”. It is a popular ‘sceptic’ meme to try to portray this paper as ‘the last word’ in their criticism (and to misrepresent it) and use any deviation of the predictions from the observations (real or imagined) as a critique, whereas it is quite clear that this was not Hansen’s intent! The original post in this thread is just another in a long line starting with Michaels to adopt this approach (and a rather poor one at that).
Russ R. – Thank you for a rather balanced post. Scenario B is the closest to actual emissions, and hence the only reasonable starting point.
Some things I would point out, however:
“…this analysis ignores changes in EMISSIONS and jump straight to FORCINGS”. Forcings are, after all, the most important thing to discuss. At any one point in time the forcings are what affect the climate, regardless of the emissions that make up those forcings.
“A) methane emissions fell far below assumptions all by themselves” You might look at the literature, such as Dlugokencky 1994 (http://www.agu.org/pubs/crossref/1994/93GL03070.shtml), which notes that “…a sharp decrease in the growth rate in the Northern Hemisphere during 1992…the most likely explanation is a change in an anthropogenic source such as fossil fuel exploitation, which can be rapidly and easily affected by man’s activities.” Fossil fuel production is a major source of anthropogenic CH4, and between more economic recapture of waste gas and some increased regulations on releases, that factor has decreased significantly. We’ve reduced CFC’s with regulation, and CH4 with what is most likely a combination of economics and regulation.
“B) methane and CO2 emissions don’t reside in the atmosphere for as long as assumed…” Actually, they do. CO2 has a residence time of 75/100 years to a 1/e decrease, while methane has an atmospheric lifetime of 12 +/- 3 years or so, before breaking down into more CO2 with a lower forcing.
Both Hansen’s high 4.2C/doubling sensitivity (the state of the science in 1988, mind you) and an actual forcing somewhat below Scenario B make his 1988 model overestimate temperatures somewhat. So yes, the 1988 model is far from perfect, as he himself stated multiple times in the paper itself. But certainly not by the strawman 150% presented here. Or the strawman “science is settled”, which Hansen clearly did not claim in this paper.
Furthermore, taking that very same model, using actual emissions, Hansen’s model’s best fit to observations is found when run with a climate sensitivity of ~3.2C/doubling. With regional temperature anomaly patterns very much in line with observations (see Plate 2 of his paper). Which is just one more piece (of a great many) of evidence supporting the 2-4.5C range, most likely 3C per doubling, climate sensitivity that is the current estimate.
It is hard for me to believe that commenters that I have always considered knowledgeable are commenting on Hansen’s paper without reading Appendix B of his paper.
I know that in the text he says “Scenario A assumes that growth rates of trace gas emissions typical of the 1970s and 1980s will continue indefinitely: the assumed annual growth rate averages about 1.5% of current emissions…” That what he says, but that is not what he means. In Appendix B he clearly indicates that he is talking about a the ppmv increase from year to year increasing by 1.5% each year.
If you take the 1986 atmospheric CO2 level as 347.39 ppmv, and use the average yearly increase from 1970 to 1986 as 1.34 ppmv, then increase the 1.34 ppmv by 1.5% per year until 2011, you will get a value of 388.3 ppmv for the atmospheric CO2 . The measured CO2 concentration for 2011 is 391.6 ppmv.
So yes, Scenario A actually under estimates the measure atmospheric CO2 concentration, but is the closest to the actual. Therefore, considering only CO2 , Scenario A is the one that should be used for comparison
A suggestion for Hansen and his supporters.
It is time for Hansen of NASA to take his million+ dollars of compensation & awards that he received from alarmist science institutes & NGOs which he earned by being an obedient policy influenced scientific alarmist and use it to buy billboard space globally. He could finally achieve some integrity if he put on the billboards the message “I WAS WRONG ABOUT AGW CLIMATE ALARMISM, James Hansen NASA”. It would be what a person who is concerned about trust in science would do.
John
My apologies – in my previous post I erred on one of the numbers: Hansen’s model fits the data best with a sensitivity in the 3.4-3.6C/doubling range, not 3.2C/doubling (as shown at http://www.skepticalscience.com/Hansen-1988-prediction-advanced.htm), as opposed to the 1988 sensitivity figure of 4.2C.
Again, a piece of evidence (one of many) for sensitivities somewhere in the 2-4.5C/doubling range, most likely around 3C.
old engineer @ur momisugly 9:07am,
1. You’re measuring concentrations, not emissions. Apples & Applesauce. You need to look at what annual emissions were in 1986, and apply the 1.5% growth rate to that figure.
2, You’re only looking at CO2. You need to include methane, NO2 and CFCs.
old engineer says:
June 16, 2012 at 9:07 am
So yes, Scenario A actually under estimates the measure atmospheric CO2 concentration, but is the closest to the actual. Therefore, considering only CO2 , Scenario A is the one that should be used for comparison
Since you have read Appendix B you will be aware that Scenario A should not be used for comparison because it includes some more speculative effects which were excluded from B and C. As far as CO2 alone is concerned there was a minimal difference in the expected level between A and B by the present (see fig 2).
Bottom line, Phil:
Did Hansen get it right with Scenario A? No. Did he get it right with Scenario B? No. Did he get it right with Scenario C? No.
What you’ve essentially been saying is that, if Hansen had some bread, he could make a ham sandwich with mustard, if he had some ham and a jar of mustard.
Alcheson says:
June 15, 2012 at 12:53 pm
Because Hansen did not include CFCs in his model calculations to produce this infamous graph,he CANNOT now subtract them out to get a better fit with his CO2 graph.
More lies Alcheson, now you’re really looking stupid.
Bill Tuttle says:
June 16, 2012 at 9:42 am
Bottom line, Phil:
Did Hansen get it right with Scenario A? No. Did he get it right with Scenario B? No. Did he get it right with Scenario C? No.
Did he do what he intended i.e. to bracket the future conditions, yes. Try not to make such a fool of yourself.
KR,
“Forcings are, after all, the most important thing to discuss. At any one point in time the forcings are what affect the climate, regardless of the emissions that make up those forcings.”
You seem to forget that people can only take action on emissions… which is why Hansen framed his scenarios on whether or not the world is able to either slow or reduce emissions.
But back to evaluating the projections in Hansen (1988). I agree with you that calling it “150% wrong” is ridiculous and probably embarrassing.
But, it’s also insufficient to confirm the validity of Hansen’s projections (given an assumed level of emissions) by only comparing differences in modeled vs. observed forcings, as you’re doing.
Remember Hansen’s 4 steps: Assume emissions growth rate scenarios >> project atmospheric composition >> calculate change in forcing >> project regional and global temperature variance.
You’re giving Hansen a free pass on step 2, which I’d argue is a pretty important part of modeling climate. If you can’t accurately project atmospheric composition from a given amount of emissions, you’re not going to be very convincing. It gets to important questions about how much of emitted GHGs are absorbed by sinks, how quickly they decompose, how long they persist, and how much additional GHGs are released due to feedbacks, etc.
So, the right thing to do would be to calculate 1986 (or 1988) total emissions in CO2-equivalent terms, and apply Hansen’s three assumed emissions growth paths to that starting point. Then compare this to the cumulative emissions that actually occurred since then to see which of the three scenarios is most relevant for comparison. Only then can you compare projected forcings for that emissions scenario to observed forcings.
Now, on explaining the lower than projected forcing, you cited a 1994 paper that measures a decrease in methane concentrations. This is insufficient to make your case as it only speculates on an anthropogenic cause. I didn’t see any actual data on a change in man-made emissions, nor any accounting for the variance in CH4 forcing at present vs. what was projected.
But you haven’t at all addressed the CO2 problem at all. How could CO2 emissions have increased at a greater rate than assumed, but forcings remain in line with what was projected?
Look, I’m not yet arguing that Hansen’s projections were good or bad compared to what’s been observed since 1988. I’m saying that I haven’t yet seen anyone here present an honest, fair analysis in order to come to an objective conclusion.
As to the estimation of climate sensitivity, I’m becoming increasingly skeptical that there’s a single CS value that describes the climate system under all conditions. I’d argue that the sensitivity value is materially different under different climactic conditions (ice age vs. interglacial vs. transition period) because the climate system is being driven by a completely different assortment of forcing and feedback mechanisms, but that’s a discussion for a different thread.
Russ R. says:
June 16, 2012 at 9:20 am
“old engineer @ur momisugly 9:07am,
1. You’re measuring concentrations, not emissions. Apples & Applesauce. You need to look at what annual emissions were in 1986, and apply the 1.5% growth rate to that figure.”
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Okay Russ R, I took my own advice and reread Hansen’s Appendix B. Here’s what Hansen says about Scenario A.:
“Specifically in scenario A, CO2 increases as observed by Keeling for the interval 1958-1981 [Keeling, et al., 1982] and subsequently with a 1.5% per year growth of the annual increment.”
The Keeling reference in his paper is titled “Measurements of the concentration of carbon dioxide at Mauna Loa observatory, Hawaii. “
Yes indeed, there is a difference in atmospheric concentrations and emissions, and Hansen clearly used atmospheric concentrations from Mauna Loa. Note also he used a 1.5% growth of the annual increment each year.
I did make an error in my calculations. I assumed that when Hansen said in the text that he used
growth rates typical of the 1970s and 1980s that is what he meant. As can be seen in the quote above he used the measured increase from 1958 to 1981, and the increase in the yearly increment of 1.5% for the remaining years of the study..
My calculations are therefore:
If you take the 1981 atmospheric CO2 level as 340.10 ppmv, and use the average yearly increase from 1958 to 1981 in atmospheric CO2 as 1.05 ppmv, then increase the 1.05 ppmv by 1.5% per year until 2011, you will get a value of 379.0 ppmv for the atmospheric CO2 . The measured CO2 concentration for 2011 is 391.6 ppmv.
Thus Hansen underestimated the atmospheric concentration of CO2 by 12.6 ppm, or about 3%.
Since I haven’t looked at the actual trends of the other trace gases he considered, I can’t comment on how well he estimated those.
Old engineer, you’re right, I stand corrected.