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

What the science says...

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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

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Comments 51 to 65 out of 65:

  1. June 23, 2018 will be the 30-year anniversary of Hansen's testimony. Seems a good time to raise public awareness of how well the models have fared, despite their imperfections. 

  2. Nov. 13, 2017 - updated the graphic to include data through 2016.

  3. Dear friends of Skeptical Science, are you planning to update the graphic to show the data through 2019? Or can we assume that you only updated the graphic until 2016 because it proved to be a very red and tasty cherry to pick?

    As a separate question, why do you say that Scenario B was closest to reality? I mean, on what basis? I have read the Hansen paper through your link and Hansen was expecting our emissions to grow 1.5% per year in Scenario A, which would have led to a 52% growth by 2016 compared to our emissions in 1988. But our emissions have increased by a whopping 63% since 1988, which is far worse than what scenario A expected. So probably you are referring to something else appart from CO2 emissions to claim that Scenario B is "closest to reality". What is that sentence based on?

    Thanks a lot. 

  4. Nylo @53,

    The graph Fig 1 of the 'basic' OP above without the post-2016 GISS data does indeed suggest a more robust record of warming than would be the case with 2017-19 data added, but I wouldn't go so far as to describe it as being "a very red and tasty cherry". The climate forcing 1988-to-date is a little short of Scenario B and so also is the trend in global temperature. (GISS data relative to 2016, the following years sit 0.09ºC, 0.17ºC, 0.04ºC below 2016 with 2020 potentially topping 2016.)

    Regarding the forcings relative to 1988, Fig 4 of the 'advanced' OP above plots 'actual' relative to the scenarios of Hansen et al. These derive from annual emissions of all anthropogenic forcings as does the 1.5% you quote for Hansen et al for Scenario A. The paper's Appendix B describes in more detail the acceleration in emissions for the various gases in Scenario A and the tailing-off that accelerations in Scenario B. 

    I'm not sure you are describing this change in annual emissions.

    I suspect you are looking at either accumulative CO2 emissions since pre-industrial times (an increase of 69% since 1988) or solely annual FF CO2 emissions (an increase of 67% although that is reduced to 57% if LUC CO2 emissions are included). The numbers I quote are calcuated from Global Carbon Project data.

    The NOAA AGGI gives the annual forcing data from GHG emissions which shows today's annual increase in forcing is slightly reduced relative to 1988 (this the net effect of increasing CO2 emissions balanced by the drop in CFC emissions and the 'hiatus' in CH4 emissions). In more detail, the annual forcing increase dropped from the 1980s into the 1990s but has since been on the rise again. So the forcing accounted in the AGGI are running below the Hansen et al Scenarion B but AGGI does not include any change in negative forcing from aerosols which will have boosted net forcing a bit over the period (as shown in that Fig 4 of the OP).

  5. Nylo@53:

    Skeptical Science is staffed completely by volunteers.   It turns out that few people can find the time to update old posts' graphs to reflect new data.  That is life.

    If you want to find out what the updated graph would look like you might go to the Real Climate Climate model comparison page, which is updated yearly.  Their up to date graph looks like this:

    Data model comparison

    Measuring carefully with my eyecrometer I findl that the data from 2017-2019 makes the model look better.  If the writers were attempting to cherry pick their data they did a poor job and left off data that they should have included.  

    It looks like 2020 is going to be a very hot year.  Perhaps when RealClimate updates their graph next January you can come back here and show us what the new graph looks like.

  6. Thank you very much for the update.

    MA Rodger @54, thanks a lot for the explanation. You say that the increased CO2 emissions compared to scenario B is compensated by the drop in emissions of CFC and CH4. Page 21 of the PDF of James Hansen's article, which is part of Annex B, shows (literally) that in Scenario B he expected a constant increase of 1.9ppmv of CO2 yearly from 2010 onwards. But the average yearly increase of CO2 that we have witnessed since 2010 is 2.4ppmv yr-1. That's a whopping additional 26%. In the same page, James Hansen's article has a graphic showing the relative contribution of the different gases, in which CO2 contributes 4 times the sum of the contributions of CFCs and CH4. Even if we had 100% halted the increase of these gases as soon as 1988 and reduced their influence to zero, the additional 26% of CO2 would put the total influence ABOVE the combined effects of all gases predicted by Hansen. But not only have we not reduced the emissions of those gases to zero, the concentration of both gases is today quite higher than in 1988, which must have a warming effect.

    Scenario C also shows that the biggest influence for the dramatic drop in expected temperatures compared to Scenario B is CO2, because it is CO2 that experiences a huge change compared to Scenario B whereas CFCs and CH4, while smaller, do not show such an abrupt difference. So clearly Hansen attributes to CO2 a much bigger effect on temperatures than the other 2 gases. And he expected a waaaaaay smaller increase of CO2 in his scenario B compared to what we have witnessed, which is more according to Scenario A. It may not be fair to expect temperatures to evolve like in Scenario A as the CFCs and CH4 increases are smaller, but we should expect something between the 2 scenarios. And what we get is in temperatures is below scenario B. We are approximately 0.3ºC cooler than what would have been be expected by Hansen's models, back in 1988, with the known GHGs evolution as input.

  7. Nylo @56,

    I'm with you part the way on your first point. (And your second point, the comparison with Scenario C; that seems a step too far.)

    On the first part of the first point, the value given for Scenario B CO2 increase post-2010 in Hansen et al (1988) (PDF p21) is 1.9ppm/y, the MLO-measured CO2 ran at 2.4ppm/y and that does translate into being 26% above Scenatio B.

    From here, I initially assumed you are looking at Fig b1 which gives a value for CO2 at 1.2 and a combined value for CFCs & CH4 of 0.46 or 38% of the value given for CO2, or 2.6x the given CO2 value. So, firstly, I am not sure where you get the "4 times the sum" and , secondly, I'm not sure why you woud be taking numbers from Fig b1. Indeed, I'm not exactly sure what Fig b1 is meant to be demonstrating. The values are described as "arbitrary" but, in the case of CO2 give a value of non-feedback warming for a doubling of CO2 (315ppm→630ppm). The CFC11&12 is for 0→2ppb each and the CH4 also for doubling although there are complications with such a stand-alone value for CH4.

    I think you should be examining Fig b2 which provides the values for the decadal increments of forcing - for the 1980s CO2 0.08, CH4 0.03 & CFC11&12 0.2. Thus, back-of-fag-packet, the 2010s CO2-above-ScenarioB of +0.5ppm/y equates to a third of the 1980s annual increase or 0.027 of the 0.8 from figb2. If you venture to examine the NOAA AGGI numbers, you'll find CFC11&12 today remain at 1990 values and the CH4 increase post-2010 is a third the 1980s increase suggesting forcing below ScenarioB of -0.2 & -⅔ of 0.3 = -0.4. So by that reckoning, the additional 26% CO2 forcing would sit below the lost CFC & CH4 forcing, not "ABOVE".

    Or a simpler analysis using just AGGI, the missing CO2 forcing 2010-on would be 20.6% of the additional CO2 forcing = +0.065Wm^-2, or perhaps double that for all three of the three post-1990 decades combined. The CH4/CFC11&12 forcing through the 1980s was +0.126Wm^-2 which would continue at or above that value for the following 3 decades in Scenario3, so totaling +0.378Wm^-2. But the actual forcing is given over this period 1990-2019 as +0.056Wm^-2 so relative to ScenarioB forcing that is -0.322Wm^-2 from CH4/CFC11&12 and with the extra CO2 forcing included yielding (-0.322 + 2x0.065 = ) -0.192Wm^-2. It works out again with less forcing, not "ABOVE".

  8. MA Rodger @57 I think you are making a mistake but I cannot blame you. I was taking for granted some of the things claimed in the main article but I have done some calculations and it happens that they were not true!

    This is how Hansen describes the evolution of the CH4 increases in Scenario A, the one with the most emissions, I copy literally:

    "CH4, based on estimates given by Lacis et Al. [1981], increases from 1.4ppbv in 1958 at a rate of 0.6% yr-1 until 1970, 1% yr-1 in the 1970s, and 1.5% yr-1 thereafter".

    By this description, if you do the calculations, the yearly increase by 1970 would be 1.5ppbv, then 1.66ppbv by 1980... etc (continue to multiply by 1.015 each year) until 3.01ppbv per year today, in 2020. This is, I repeat, the evolution of CH4 concentrations in Scenario A. The reality, what the data shows, is that today's CH4 concentrations are increasing by more than 5ppbv per year, every year in the last decade, and some years almost 10ppbv, averaging +8ppbv per year. My data comes from here, if you have different data feel free to share:

    Now, I don't know what is the starting methane concentration that Hansen is using. I highly doubt that he is using the concentration in 1958 because we already knew by 1988 that the progression in the methane levels of the model would have been completely wrong. But no matter what his starting concentration is, he would get a total increase of +70ppbv in the 30 years following 1988. And what we have witnessed is more than twice that ammount. More than twice the methane increase of Scenario A. Therefore not only do we have a worse increase in CO2 than Scenario A, we also have a twice as bad increase of Methane than Scenario A. And they are the main contributors according to Fig b2. The only one that is lower than expected by Hansen is CFCs.

    As you say, the effect of the extra 0.5ppm per year of CO2 would be quantified by Hansen as having a 0.027 additional forcing. With a similar calculation, the twice-as-big-as-1980 increase that Hansen expected to have by now in Scenario A (3ppbv/year vs a starting 1.5ppbv/year) would have had a +0.06ºC forcing per decade, and given that the real, measured, increase in concentration has been twice as big as what Hansen expected, we are getting another +0.06 forcing compared to Hansen expectations in our last decade. So we are already at a +0.087ºC/decade forcing compared to Hansen's scenario A, if we add together the extra CO2 and the extra CH4.

    Now, Hansen expected a lower forcing from CFCs than from methane, like you have said. This means that if the real forcing of Methane has doubled, then it would not matter even if the CFCs had stopped increasing in 1988, reducing their impact to zero. The effect of Methane alone, would still be larger than what Hansen predicted for the two. And again, we are talking about scenario A, not B!

    Emissions of the largest contributor by Hansen's expectations are 26% bigger than scenario A. Emissios of the second largest contributor by Hansen's expectations have been twice as big (+100%) as scenario A. Are we saying that the reduction of CFCs, the third largest contributor, have the power to counter all of that? Even if it had such a power, we would still be at scenario A's expected increase of temperatures, not B's!

    I beg you to tell me where is it that I did wrong the calculations. Because I cannot find it.

  9. I think I understand what is going on here, why the original article claims that the CH4 emissions have been lower than scenario B (and therefore also A) despite they have been twice as big as scenario A. The article was written in 2010, judging by the dates of the first comments. And in 2010 we had witnessed an almost complete stop in the increase of CH4 concentrations that had lasted roughly a decade. I guess it was predicted to continue to stop. It hasn't, so if we are going to continue to compare what Hansen predicted to today's temperatures, we also need to update the emissions scenario that we are closest to. And this is scenario A.

  10. MA Rodgers @57 please allow me a small correction to what I wrote in @58, as I made a small mistake. Our CO2 emissions are higher than what was expected in Scenario B, but they are not higher than expected in Scenario A, I mixed up things. Our CO2 emissions are exactly equal to the ones expected in Scenario A, which would have provided +2.6ppmv increase per year by 2020 and an average for the last 10 years of 2.44ppmv which is almost exactly the same that has been observed. Therefore:

    * The observed CO2 concentration evolution is almost exactly what Scenario A contemplated,

    * The observed Methane concentration increase is twice as big as what Scenario A predicted,

    * The observed CFCs evolution is way smaller than what Scenario A expected, although not enough to compensate for the doubling of the emissions of CH4.

    For all of this, I think that the correct scenario to which we should compare the evolution of temperatures is Scenario A.

  11. Nylo @58/59/60,

    I don't see that I can agree with any of that.

    Note the primary source of CH4 levels is NOAA ESRL and these provide global data from 1983 although this record was not established as such until the 1990s. Thus you will note that Hansen et al (1988) references Lacis et al (1981) for its CH4 data. And this reference should give a bit of a warning that something is amiss with the passage from Hansen et al  Appendix B that you quote.

    Lacis et al describe the rise in CH4 1970-80 as being 150ppb, from 1.5ppm to 1.65ppm.

    And there is evidently an error in Appendix B of Hansen et al. We have two alternative errors, one a simple typo (although an error nonetheless) and the other one a careless omission with massively significant implications. (i) Either the error was that the "1.4ppbv" should have read "1.4ppmv" = 1,400ppbv.  (ii) Or the value "1.4ppbv" for 1958 which CH4 "increases from" is meant to be the start value of a rate-of-increase rising by a set percentage per year. If this were the case, it should have read "1.4ppbv per year in 1958".

    It is evident from Lacis et al that the corrected version is "1.4ppmv". Using percentage increases set out in Hansen et al, the "1.4ppmv" start-point in yields a 1970-80 CH4 level running from 1504ppb to 1670ppb.

    The alternative appears a tiny bit ridiculous as, if Hansen et al did work with CH4 based on "1.4ppbv per year in 1958" it would require both a profoundly mistaken reading of Lacis et al and an egregious miscalculation of the forcing resulting from the vastly reduced rise in CH4 levels. That is, CH4 rise would total 20ppb 1980-90 rather than the 270ppb using the "1.4ppm". (Modern estimates/measurements yield 220ppb 1980-90.)  If you examine Figb1, an increase of 1.6ppm CH4 yields 0.16ΔTo(ºC) which pro rata would yield from Figb2's 0.0295ΔTo(ºC) a 1980's decadal CH4 rise of 295ppb, a finding which is wholly incompatible with the adoption of a 20ppb decadal increase.


    Concerning the CH4 'hiatus' of the early 2000s, the deceleration in the atmospheric CH4 rise was spotted by the early 1990s and its cause (a reduction in anthropogenic emissions) was understood before 2010 (although which anthropogenic source wasn't clear), as was the obvious signs if it ending.

  12. MA Rodger @61 I think that what you say is good. The description by Hansen of what the evolution of methane is in his scenario A must contain an errata. Lacis claimed a 150ppbv increase in 1970-1980 instead of 1.5ppbv per year which would hardly achieve 15ppbv.

    Admitting that you are probably correct and reworking my calculations accordingly, Hansen would have expected a rise of 282ppbv for the period of 2010-2020, and we have experienced only 80ppbv. So we are indeed below Scenario A emissions in terms of methane, by 200ppbv in the last decade, which would lead to around 1/8 of 0.16ºC less (by figure B1, as 200ppbv=0.2ppmv is 1/8 of 1.6ppmv), or 0.02ºC less in this latest 10 years period for which Scenario A forecast half of a degree increase (by latest Real Climate diagram shown above in @55). So based on methane and CO2 alone, we should change that 0.45ºC increase in 2010-2020 to 0.43ºC. The observed increase has been 0.26ºC so the remaining extra 0.17ºC that we have not experienced in the last 10 years must all be due to differences in CFC emissions compared to Scenario A expectations.

    For CFCs (F11, F12) the forcing in the 1980s was, according to figure B2, roughly 0.02ºC. As Scenario A expected a 3% increase in emissions per year, doing the calculations the forcing in 2010-2020 for CFCs would be 2.57 times bigger than the forcing in the 80's, or about 0.055ºC. Assuming that, instead, we have experienced none, that would reduce the expected temperature increase in that scenario for this decade if we use actual instead of modelled emissions by 0.055ºC. The +0.43ºC warming that the model would have predicted by replacing methane projections with actual values, goes down to +0.375ºC if we do the same with CFCs. And again, we have witnessed +0.26ºC. Hansen projections seem to be off by approximately 44% (44% more warming in his models than in real world).

    Am I ignoring something else perhaps? Feedbacks to radiative forcings? Would those change the 0.075ºC of combined radiative forcings of the differences in methane and CFCs between model and reality, to the needed +0.28ºC difference between Scenario A predictions and observations? That would require a feedback level of more than 3.5 to the forcings.

  13. Nylo @62,

    It is good to see we make progress, but it is not giant strides.

    While you do rush past many aspects of this matter that do require consideration and perhaps have dropped a few beads off the abacus before reaching your assessment that the Hansen et al Scenario A results "seem to be off by approximately 44%", I perhaps would flag up the point that climatologists do use complex climate models for a reason.

    On the CH4, I don't find the -200ppb value you arrive at for the 2010-20 difference between Scenario A and 'actual'. And I'm not aure that is a useful measure even if it were correct.

    The Scenario A increase from1400ppb at 0.6%, 1% then 1.5% yields roughly the 1500ppb and 1650ppb 1970-80 seen in Lacis et al Table 1. Running forward, that gives 2984ppb for 2019, and an increase over the decade from 2009 of 413ppb. The measured CH4 levels (from ESRL) are 1794ppb and 1867ppb, a 2009-19 rise of 73ppb. Thus 'Actual' - Scenario A = 340ppb. But do also note that the 'actual' CH4 increase 1988-2019 is also similarly less that the Scenario A projection for the two preceeding decades.

    And while you might imagine we could put that CO2 assessment to bed as the concentrations projected by Scenario A and 'actual' are entirely similar, the assessment of the resulting forcing from such a CO2 increase has been revised in the years since 1988. As per Fig b1, the 1988 assessment was a non-feedback equilibrium temperature increase for 2xCO2 of +1.2ºC. Yet today that is put at +1.0ºC, a significant difference in the underlying forcing.

    To complete this analysis will require an item by item assessment. A quick back-of-fag-packet calculation suggests to me that adding all the forcings from the different GHGs shows the 1988-2019 projections of Scenario A to be 200% of 'actual'. I'm not surprised to see that is roughly what is shown in Fig 4 of the Advanced OP above.  So, without considering negative forcings, we should expect Scenario A to be showing a lot more warming than 'actual'.

    If you wish, we could work through this assessment. But that does lead to the need to calculate the resulting warming. Climatologists turn to their models at that point. Maybe we can dodge that with a short cut. Yet reaching that objective is, on our past performance, not a quick exercise to see through to a conclusion.

  14. MA Rodger @63

    You are right again, the errata by Hansen could be writting 1.4ppbv instead of 1.4ppmv. Given the very low number I though he had missed the per year part, but he actually probably meant total concentration and just gave it in parts per million instead of per billion and that would lead to your numbers. So while for every other gas he is talking about the progression of the concentration change (the delta), here he was talking about the progression of the concentration itself.

    Isn't it fantastic that, despite ZERO efforts to reduce our methane emissions and despite the alleged existance of a methane bomb in the arctic that is releasing more and more methane each day, the actual increase in the atmosphere in the last decade is 5 times smaller than predicted? And this is after accelerating, because the previous decade saw almost no increase at all.

    You write:

    A quick back-of-fag-packet calculation suggests to me that adding all the forcings from the different GHGs shows the 1988-2019 projections of Scenario A to be 200% of 'actual'.

    I think that what you have just written there means that Hansen expected the forcings from Methane and CFCs together to be bigger than the forcing of CO2 in that scenario. Because if they are smaller but not zero today, and CO2 is like scenario A, but we are getting half the warming that he expected, then the missing part of CH4+CFCs must be not-having an impact as big as the current CO2+CH4+CFCs. Interestingly though, the focus to avoid a climate catastrophe due to warming has always been the CO2 emissions, never the other 2. The reasons for the CFCs reduction have always been the ozone hole, and to my knowledge no effort has been made to reduce CH4 emissions. Lots of talking but zero measures. There is no reason to believe that we are emitting less methane than in the 80s, despite it is increasing at about half the rate that Lacis said that it was increasing in the 80s (8ppbv/year instead of 15ppbv/year). The reduction must come fundamentally from natural sources, or else, it is disappearing now faster from the atmosphere than it was then.

    I think I will leave the discussion here.



  15. @ Nylo

    You said, " to my knowledge no effort has been made to reduce CH4 emissions. Lots of talking but zero measures. There is no reason to believe that we are emitting less methane than in the 80s, despite it is increasing at about half the rate that Lacis said that it was increasing in the 80s (8ppbv/year instead of 15ppbv/year)."

    This is not true at all. There have been significant changes in agricultural practises that have partially restore methane absorption and metabolism by methanotrophs in the soil over vast acreages.

    Namely the widespread use of no-til combined with multispecies cover crops.

    “No-Till” Farming Is a Growing Practice

    And also there is significant acreage that has been converted from set stock acreage to holistic managed acreage, even though there is huge active resistance campaigns to prevent this. That reduces atmospheric methane even more.

    I have written about that here before, but was asked to consolidate that information and use it like a reference. So I wrote about it here:

    What reaction can you do to remove methane?


    There is actually more though. Several major gas pipeline leaks have been documented and repaired too. Those apparently were a major source of the increased methane. Some say the major source.

    preindustrial CH4 indicates greater anthropogenic fossil CH4 emissions.


    There are multiple reasons and the issue is at least as complex as the CO2 cycle. So while there is certainly a huge degree of uncertainty, claiming there is nothing being done is just wrong.

    A lot is being done, we are just not entirely sure how efficacious it is yet.

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