Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


What do we learn from James Hansen's 1988 prediction?

What the science says...

Select a level... Basic Intermediate Advanced

Hansen's 1988 results are evidence that the actual climate sensitivity is about 3°C for a doubling of atmospheric CO2.

Climate Myth...

Hansen's 1988 prediction was wrong

'On June 23, 1988, NASA scientist James Hansen testified before the House of Representatives that there was a strong "cause and effect relationship" between observed temperatures and human emissions into the atmosphere. At that time, Hansen also produced a model of the future behavior of the globe’s temperature, which he had turned into a video movie that was heavily shopped in Congress. That model predicted that global temperature between 1988 and 1997 would rise by 0.45°C (Figure 1). Ground-based temperatures from the IPCC show a rise of 0.11°C, or more than four times less than Hansen predicted. The forecast made in 1988 was an astounding failure, and IPCC’s 1990 statement about the realistic nature of these projections was simply wrong.' (Pat Michaels)

In 1988, James Hansen projected future warming trends. He used 3 different scenarios, identified as A, B, and C. Each represented different levels of greenhouse gas emissions.  Scenario A assumed greenhouse gas emissions would continue to accelerate.  Scenario B assumed a slowing and eventually constant rate of growth. Scenario C assumed a rapid decline in greenhouse gas emissions around the year 2000.  The actual greenhouse gas emissions since 1988 have been closest to Scenario B. As shown below, the actual warming has been less than Scenario B.

Hansen through 2016 
Figure 1: Global surface temperature computed for scenarios A, B, and C, compared with observational data

As climate scientist John Christy noted, "this demonstrates that the old NASA [global climate model] was considerably more sensitive to GHGs than is the real atmosphere."  However, Dr. Christy did not investigate why the climate model was too sensitive.  There are two main reasons for Hansen's overestimate:

  1. Scenario B, which was the closest to reality, slightly overestimated how much the atmospheric greenhouse gases would increase. This isn't just carbon dioxide. It also includes methane and chlorofluorocarbons (CFCs).
  2. Hansen's climate model had a rather high climate sensitivity parameter.  Climate sensitivity describes how sensitive the global climate is to a change in the amount of energy reaching the Earth's surface and lower atmosphere.

If we take into account the lower atmospheric greenhouse gas increases, we can compare the observed versus projected global temperature warming rates, as shown in the Advanced version of this rebuttal. To accurately predict the global warming of the past 22 years, Hansen's climate model would have needed a climate sensitivity of about 3.4°C for a doubling of atmospheric CO2.  This is within the likely range of climate sensitivity values listed as 2-4.5°C by the IPCC for a doubling of CO2. It is even a bit higher than the most likely value currently widely accepted as 3°C.

In short, the main reason Hansen's 1988 warming projections were too high is that he used a climate model with a high climate sensitivity. His results are actually evidence that the true climate sensitivity parameter is within the range accepted by the IPCC.

Basic rebuttal written by John Cook

Nov. 13, 2017 - updated graphic with data through 2016 (BaerbelW)

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 14 November 2017 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.


Prev  1  2  3  Next

Comments 26 to 50 out of 65:

  1. Stephen — Of course emissions are central to his testimony.  Without the assignment of emissions scenarios, A B and C are just random points on a graph, chosen for no particular reason, with no relevance to policy.

    "Hansen could not know that methane would show it's odd pattern over time"

    Exactly my point, thank you.  Hansen made predictions about things he could not know. 

    "You're argument for your fixation on old models doesn't ring true. More sophisticated GCMS produced later have plenty of new data they can be compared against."

    I don't think you quite understand the problem.  Models may produce any arbitrary amount of data, but reality produces one year of results to compare their predictions against per year, and that only after the prediction.  

  2. TallDave - You appear to have rather completely misunderstood my comment and the graph therein (not putting the graph in this comment, as it's right up there in @22). Concentrations of GHGs are well below what would result from Hansen Scenario A, and in fact below Scenario C, and the concentrations listed in that graph for the scenarios is what results after emissions and after accounting for the carbon cycle in the model. 

    "Emissions (especially of CO2) rose like Scenario A" - False. Look. At. That. Graph

    CO2 has been reasonably close to the Hansen scenarios, in fact to all of them, because there is little difference (at this early date) between A, B, C, and observed CO2. But there have been far fewer emissions of CFCs, CH4, NO2, and hence lower total GHG concentrations remaining than in any of the Hansen scenarios. To a large extent the 1987 Montreal Protocol limiting CFCs is responsible for that difference, rather than cuts in fossil fuels. 

    "Hansen made predictions about things he could not know" Bzzzzt!!! You are attacking something other than the subject of Hansens climate model. Hansen made projections of climate response, not predictions of economic development, demonstrating the modeled climate responding to various GHG changes. The scenarios were presented to map the response space. He wasn't, and isn't, speaking in the business of economics, but rather in the science of climate. If the relationship between observed emissions and climate change match that of his model, then it's skillful. 

    Attacking a climate model because economic development and the ensuing emissions didn't exactly match the economic scenarios posed to map the input/output of those climate models is just absurd. That criteria would only be applicable to economic models, to economists, not climate science. 

    The best test is to run the model against observed emissions and see whether it matches observed temperature response, and [with the more correct CO2 direct forcing incorporated from Myhre 1998] Hansens model does that quite well. 

  3. "Stephen — Of course emissions are central to his testimony. Without the assignment of emissions scenarios, A B and C are just random points on a graph, chosen for no particular reason, with no relevance to policy."

    Not if his main point, As Tom C points out, was establishing the role of humans in climate change to that point, and not on the future projections. TC has deliberated on the testimony itself. You should address his points, not simply make an assumption based on your impression of the role the graph must have played based on what is in it. I'm not saying that his presentation was not intended to get congress to act on emissions, mind you, just that his testimony focused on whether the observed temp change was human caused, and not on those scenarios.

    "Exactly my point, thank you. Hansen made predictions about things he could not know."

    As KR points out,  he used what-if scenarios precisely because he could not predict future GHG development. That is the whole point of scenarios, and lack of certainty about the future is implicit in their use. Tell me, what would you do in this situation? Assume no change? That would be highly unlikely. scenario he didn't have involved a management decision (the Montreal protocol) that he himself would have approved of because of his model results. Does that mean he didn't think it was a good idea, or he didn't believe that such an action would have no effect on GHG forcing? Of course not.   That would be akin to saying that because the model was right the model was wrong.  Scenarios can't be thought of in that way.

  4. TallDave @24:


    "Emissions (especially of CO2) rose like Scenario A."

    Not according to Gavin Schmidt at Real Climate:

    Or  Tamino at Open Mind:

    Or Dana at Skeptical Science:

    Or Steve McIntyre at Climate Audit:

    What distinguishes all four from TallDave is that they have actually consulted the concentration data for the three scenarios, and done the calculations and compared them to observed changes in radiative forcing.  All show actual forcings due to greenhouse gases slightly less than that for Scenario B, with the exception of Tamino who compares to all forcings (except volcanic) and finds the result slightly less than scenario C.  (Note: he is not in disagreement with the others, he merely makes a different comparison.)

    As can be seen from Steve McIntyre's graph, and in the following graph from Dana, while growth in CO2 (and NO2) was close to that predicted in Scenario A, growth in other greenhouse gases was way below that predicted for scenario A so that the total forcing was significantly less than that in Scenario A.


    (Note with respect to Dana's graph:  Hansen 1988 included the value of a host of minor greenhouse gases by the expedient of doubling the concentration of CFC 11 and CFC 12.  Because Dana compares to the actual values of CFC 11 and 12, he leaves out these other minor gases.  The actual growth in GHG radiative forcing is slightly greater than shown in Dana's graph.)

    The growth in CO2 concentration is close, but not the same as that in Hansen's scenario A.  Specifically, throughout the 1990s growth in CO2 was less than projected in scenario C.  Since then, the growth rate has exceeded that in Scenario A so that concentrations have recently risen to about the scenario A level (and will soon exeed it if it has not already) - a pattern that can be seen in the EPA graph.  The lower initial growth results in a lower initial radiative forcing, and hence a lower initial temperature growth that will not be eliminated for several years due to the thermal inertia of the ocean.

    This is one of many topics in climate science where the common pseudo-skeptical opinion (as presented by Dave) cannot be honestly sustained except by the expedient of not checking the data.  Comments such as Dave's are therefore always either insincere, or misinformed.  Given the copious sources of information to the contrary, if misinformed by somebody who maintains some knowledge on the topic (as TallDave clearly does), then they are negligently misinformed.

    2)  TallDave quotes a small portion of the congressional testimony from a section of which I have already quoted at length.  It comes just before the section I bolded, a section which makes quite clear that the the purpose in mentioning the scenarios was simply to explain the features of the graph, not to draw any conclusions from it.  In other words, in response to my extensive quotation, TallDave's only response is a small out of context quotation that fails to address any of the points I raised.  Therefore it requires no further refutation.

    His rhetorical question regarding Scenaro C is shown to be less than candid by the fact that the common opinion of those who have analysed the data is that the observed GHG forcings most closely match scenario B.


    "Obviously because they're the only ones that can be tested on any meaningful time scale. Contra this site, the ability of a model to hindcast a highly complex phenemonen gives little confidence in its forecast (something painfully well-known in other fields)."

    Contrary to TallDave's missinformed epistemology, there is no logical difference between forecasting and hindcasting.  The only additional epistemic support to be obtained from successfull forecasting is forecasting is by its nature immune to overfitting the data.  With GCMs, the number of parameters is very small relative to the number of predicted variables.  That is not the case if you only pay attention to GMST, which is why pseudo-skeptics only consider GMST (plus a few other cherry picked data) for comparison to models, whereas climate scientists validate models against a large range of observed data.  That is also, by the way why there is an approximately 15% mismatch between hindcast GMST model and observed trends over the last thirty years.  The models are not fitted to obtain that result (for if they were, they could get a better match), but obtain that near match anyway.


    [PS] To all commentators on this thread. Please note the comments policy:

    "No profanity or inflammatory toneAgain, constructive discussion is difficult when overheated rhetoric or profanity is flying around."

    The tone in this thread is getting heated. Please step back, concentrate on the science and avoid throwing accusations around. This will ensure noone oversteps the mark.

  5. The EPA is not lying.

    Concentrations are not emissions.  If Hansen's explicitly described emissions scenarios didn't result in the concentrations he expected them to, that's a failure of his model.  Pretending otherwise is the just the kind of three card monte that is causing the public to justifiably lose faith in climate science as an objective enterprise.

    "Contrary to TallDave's missinformed epistemology, there is no logical difference between forecasting and hindcasting."

    I'm just going leave that there to speak for itself.


    [Rob P] - Sloganeering struck through.

  6. TallDave:

    It is incumbent upon you to translate the EPA emissions data (shown as Tg of CO2 emitted over time) into radiative forcing over time. Otherwise, you have no ground on which to claim that the EPA data supports you.

    When even the work of a self-styled "climate skeptic" refutes your claim, IMO you should probably look at your own position for error instead of repeating it ad nauseum without any modification - a behaviour which, by the way, is prohibited by the Skeptical Science comments policy.

    I might add that characterising the work of tens of thousands of researchers across the world as a common con game is, at best, dancing on the line of an enormous accusation of deception.

    The fact of the matter is that climate science is based first and foremost on rather basic thermodynamics (net radiative energy in vs. net radiative energy out), the radiative properties of the greenhouse gases, and the thermal properties of the atmosphere and ocean. Speaking bluntly, you're setting yourself up for a hopeless task if you think that your attempt at refuting Hansen's 1988 work will unravel the physics establishing the reality of global warming.

    Also speaking bluntly, arguing against climate science in 2014 by reference to Hansen's work in the 1980s is equivalent to, say, arguing against oncology in 2014 by reference to where the knowledge base of that discipline stood in the 1980s. Such a line of argument says little to nothing about the science but much about the person who resorts to it.

  7. "Concentrations are not emissions. If Hansen's explicitly described emissions scenarios didn't result in the concentrations he expected them to, that's a failure of his model. Pretending otherwise is the just the kind of three card monte that is causing the public to justifiably lose faith in climate science as an objective enterprise." (my emphasis)

    And "scenarios" are not "models," as has been described ad nauseum. This is the kind of double speak that makes people use the word phrase "climate denier" instead of "climate skeptic."

    People run scenarios all the time, with finances, with their shopping, with personal life choices. They choose among scenarios using "models" that can allow them to determine which scenario produces the most favorable or viable outcome.

    If I choose to save more money and my bank account increases as a result, it does not invalidate the same accounting model that has me go broke if I spent way above my income. The scenario (what I chose to do with my money) is different from the accounting model that turns that choice into a result. The same is true of Hansens study — he tried to capture a range of possible scenarios so people could understand the consequences of different actions.

  8. Talldave would have us accept Lindzen's model that the temperature would stay the same, rather than Hansen's model that temperature would rise.  He ignores that record high temperatures have been set every five years since 1988, including 2014.  2014 will be the highest ever recorded and the hottest the Earth has been in thousands of years. 

    Talldave wants to wish away the temperature data and claim that the temperature is not rising.  If Hansen cannot predict in advance when people would reduce pollution than the temperatures canot be rising.

  9. This is a bit off topic, but TallDave's assault on 'cutting edge 1980s science' helps illuminate a pattern I've seen before. Essentially, there seems to be a mindset amongst many deniers which reasons that belief in scientific principles derives from faith in individuals... so the goal becomes an effort to discredit individuals they see as the 'preachers' (?) of science rather than the actual facts.

    For example, even if Hansen got some things wrong in the 80s (and he did, ironically just not the things TallDave is harping on) that would do nothing to invalidate modern global warming science. Over the past 30 years we've accumulated vastly more confirmation than Hansen had in the 80s... yet the mindset remains that if you can bring down someone viewed as the 'original actor' then all the facts just go away.

    We saw the same thing with Beck's assault on Callendar's atmospheric CO2 level analysis... decades after Callendar had died and Keeling had proven him correct. Ditto the endless assaults on Michael Mann despite dozens of subsequent studies having confirmed the findings of the 'hockey stick'. Similarly, whenever I've discussed evolution with creationists they have been endlessly fixated on supposed errors by/flaws of Darwin... as if there hadn't been two hundred years of additional confirmation since then.

    I don't know what this pattern of fixation on individuals / 'originators' means, but it shows up reliably enough that I suspect there must be some underlying reason. Does any of the 'psychology of denial' type research shed any light?

  10. CBDunkerson: You may find the answer to your question in:

    The 7 psychological reasons that are stopping us from acting on climate change by Chris Mooney, The Wonkblog, The Washington Post, Dec 11, 2014

  11. The moderation policy at SkS and the overall tone is far better than most other internet forums on the subject. I have read through this thread and I could not find an ad hominem argument against you TallDave. Can you quote or link the specific post that contained that particular logical fallacy?


    [JH] Phillipe, TallDave's most recent post constituted argumentative sloganeering and was therefore deleted. He/she seems bent on relinquishing his/her privelege of posting on SkS.

  12. Sorry folks, but you guys discredit yourselves by acting like a bunch of radicals defending your prophet.  TallDave is absolutely right.  You guys need to be clear about Emissions and Concentrations... Emissions are what are emitted.  The EPA and the IPCC both conclude emissions have increased more than the 1.5% That Hansen classified as business as usual. 

    Now, if concentrations are lower than Hansen expected based on those emission scenarios... than you should clearly state that and admit, yes, the ocean (most probably) absorbed much more CO2 than Hansen expected and therefore CO2 concentrations are more in line with Scenario blah blah blah. ... 

    That is a calm, coherent argument. But claiming Hansen wasn't wrong... Hansen can't be wrong...  that's just irrational and makes you look anything but scientific.  

  13. planet8788 - See this comment above. If you include all emissions, including in particular differences in CFC emissions due to the Montreal Protocols and in methane levels, the actual forcings are far closer to Hansen Scenario C than A or B.

    Actual versus scenario forcings

    Note that Hansen did use a larger than currently estimated direct CO2 forcing (largely due to early radiative mis-estimates of that direct CO2 forcing, corrected by ongoing research in 1998), but when you account for that issue his model was indeed quite good. 

    Your claim that "The EPA and the IPCC both conclude emissions have increased more than the 1.5% That than Hansen classified as business as usual" [i.e. Scenario A?] is only close for CO2, not all emissions of GHGs that were incorporated into his model. And is hence quite incorrect. 

  14. planet8788 @37, Hansen describes Scenario A in Appendix B of his paper, saying with regard to CO2:

    "CO2 increases as observed by Keeling [at Mauna Loa] for the interval 1958-1981, and subsequently with 1.5% yr-1 growth of the annual increment."

    For somebody lecturing us on needing to " clear about Emissions and Concentrations", it is astonishing that you have not noticed that the scenario is specified with respect to the concentrations as measured at Mauna Loa, not according to emissions data.  You may think it was specified according to emissions because Hansen wrote in the main body of the paper:

    "Scenario A assumes that growth rates of trace gas emissions typical of the 1970s and 1980s will continue indefinitely; the assumed annual growth averages about 1.5% of current emissions, so the net greenhouse forcing increases exponentially."

    That statement, however, gives the average growth across all greenhouse gases specified - not just of CO2.  Therefore it cannot be interpreted as specifying the growth rate of CO2 uniquely.  Further, it only gives an approximate value (about), and is no basis for claiming any growth rate more exact than somewhere between 1.25 and 1.75%.  In any event, the detailed statement above takes precedence.

    Based on the detailed statement in appendix B, it is trivial to get the Mauna Loa data from 1958-1981 (actually 1959 forward for annual averages), and project from 1981 forward.  It is not clear if the increment is expressed as an absolute value, or as a percentage.  Taking the former possibility, Hansen's specified CO2 growth compared to actual values is as follows:

    The final value in the Hansen projection represents 410 ppmv in 2015 (compared to an actual 401 ppmv).  Incrementing on the absolute value gives a lower increase of 407 ppmv in 207.  In either case, Hansen's projected CO2 increase for scenario A is comfortably larger than the actual increase.

    This is far more the case for CH4 and chlorofluoro carbons. 

  15. For what it is worth, the tabular concentration data for the three scenarios and all included greenhouse gases as used in Hansen 88, and supplied by Gavin Schmidt shows a CO2 concentration for 2015 of 403 ppmv.  Again, this is more than has actually occurred.

    This denier talking point is based entirely on:

    Ignoring four of the five greenhouse gases;

    Ignoring Hansens explicit specification of the scenarios in Appendix B;

    Ignoring the tabular data as supplied by Gavin Schmidt;

    Ignoring that 1982 (not 1989) is the first year of projection; and

    Loudly bewailing the fact that annual emissions have grown 1.62% per annum for CO2 when Hansen only specified emissions growth averaged across all GHGs of "about" 1.5%.

    If they shut their eyes any tighter against the facts of the case they would go permanently blind.

  16. Okay, So, we've increased CO2 emissions and we're still at Scenario C.  So we have little to worry about. Becauses CFC emissions aren't going to go back up. CO2 emissions will probably peak by 2030... 


    The only wildcard is methane. And that is evolving much much slower than expected. 

  17. In fact, CFC concentrations are still going down and it looks like they have a long way to go. So that is still going to continue offsetting warming by CO2. 

    The ocean is absorbing more CO2 than expected. We probably don't have much to worry about. The main wildcard is methane. 

  18. planet8788 @41, based on Gavin Schmidt's calculation, the Hansen 88 GHG concentration trajectories would have resulted in a net forcing increase relative to 1983 of 3.35 W/m^2 for Scenario A, 2.33 W/m^2 for Scenario B, and 1.41 W/m^2 for Scenario C.  The actual increase was 2.2 W/m^2, or just below Scenario B and 56% greater than scenario C.  More importantly, Scenario C has a slightly declining forcing from 2000, while anthropogenic forcings have continued to rise at an approximately linear rate:

    Therefore it is seriously misleading to say "we're still at Scenario C".

    Further, and importantly, we are in our present position of a forcing increase slightly below Scenario C in part because of a significant, and ongoing effort to reduce GHG emissions.  The correct conclusion, therefore, is not that everything will be fine, but that we need to continue, and indeed strengthen substantially those efforts.  In the medium term (30 to 50 odd years), we need to bring net emissions to effectively zero.  BAU will not do that.  Even a continuation of current mitigation efforts will not do that.

    Finally, even if we do that we will reach a mean global temperature close to 2 C above the preindustrial average.  Likely even that increase will be significantly harmful, and certainly it will be catastrophic for some.  It is just a much better scenario than genuine BAU which, if pursued in the long term would see the tropics become seasonally uninhabitable for large mammals (ie, humans, sheep, cattle, and dogs would die of heat prostation within a few days of unairconditioned exposure to 'normal' heatwaves under that scenario for more than a day or so).

    That we are doing very slightly better than what Hansen considered the most likely scenario in 1988 is hardly a great comfort.

  19. planet8788: Accoding to Meinhausen et al, the Montreal gas forcing (CFCs etc) peaked at about 0.32 W/m2 and is projected to drop to about 0.2 W/m2 by 2050. Do you disagree with those figures?

  20. I had thought I was about to disagree with the post but I might only be disagreeing with the myth. Anyway, I disagree with any premise that a computer simulation such as these can have "climate sensitivity" as an input, because it's an output, a result. I've written a computer simulation program. It's more problematic to have a pre-determined output from a computer simulation than it is to compute a trapdoor function in reverse. I think it's impossible. The only way would be iterative simulations, still not an input. You run a few simulations with diverse settings for parameters such as forcings, cloud effects and many others. Then compare the "climate sensitivity" results and there's a technique I've forgotten that I programmed in 1970 (ironically, oil exploration) where the one with least preferred result is discarded and the results are projected from worst to best to yield a set of preferred inputs. And so on iteratively until the desired result is produced, then those inputs are the ones to use. That's the only way that a simulation can produce an output such as "climate sensitivity" as a pre-determined result.

  21. Sorry, I have two eyes, and the data clearly shows me it's closer to Scenario C, not Scenario B. 


    [PS] It is not clear to me that you have read the article that carefully. Read the comment policy- you are risking sloganeering .Scenario B is about an emission scenario. Hansen considered what would happen for 3 different emission scenarios. What we actually emitted is closer to Scenario B, so should compare his prediction for scenario B to actual temperatures for B. His prediction is too high for reasons the articles discusses.

  22. The Hanson 1988 paper link is dead. I think it is:

    Hope this is right!


    [PS] Link activated. Thanks for that.

  23. bobbyj on another thread asked how last year's temps (GISS) fit with The Hansen model.

    As 2016 annual anomaly came in at 1C, this puts last year's anomaly very close to the B scenario line for 2016. (Slightly above, actually, but that's random variation)

  24. Ah, maybe someone can clear this up. What's the mean? the baseline?

    59 degrees F or 15 degrees Celsius, right?  The glaring omission in my mind coloring the issue of whether predictions were right or how wrong they were, etc, simply the fact none of the past 30 years exceeded this baseline. 

    Obviously then, the baseline of the mean from 1950-1980 was changed. Can someone show me the peer-review papers discussing that change and who and why it was done?

  25. Randman @49 , for multiple reasons I have given you a reply on the other thread where you made a contemporary similar type of question [ i.e. the "Temp Record Is Unreliable" thread ] .

Prev  1  2  3  Next

Post a Comment

Political, off-topic or ad hominem comments will be deleted. Comments Policy...

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

Link to this page

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us