Contrary To Contrarian Claims, IPCC Temperature Projections Have Been Exceptionally Accurate

Rajendra Pachauri, chairman of the IPCC

by Dana Nuccitelli, via Skeptical Science

There is a new myth circulating in the climate contrarian blogosphere and mainstream media that a figure presented in the “leaked” draft Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report shows that the planet has warmed less than previous IPCC report climate model simulations predicted. 

Tamino at the Open Mind blog and Skeptical Science’s own Alex C have done a nice job refuting this myth.  We prefer not to post material from the draft unpublished IPCC report, so refer to those links if you would like to see the figure in question.

In this post we will evaluate this contrarian claim by comparing the global surface temperature projections from each of the first four IPCC reports to the subsequent observed temperature changes.  We will see what the peer-reviewed scientific literature has to say on the subject, and show that not only have the IPCC surface temperature projections been remarkably accurate, but they have also performed much better than predictions made by climate contrarians (Figure 1).

Predictions Comparison

Figure 1: IPCC temperature projections (red, pink, orange, green) and contrarian projections (blue and purple) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; black and red) for 1990 through 2012.


The IPCC  First Assessment Report (FAR) was published in 1990.  The FAR used simple global climate models to estimate changes in the global mean surface air temperature under various CO2 emissions scenarios.  Details about the climate models used by the IPCC are provided in Chapter 6.6 of the report.

The IPCC FAR ran simulations using various emissions scenarios and climate models. The emissions scenarios included business as usual (BAU) and three other scenarios (B, C, D) in which global human greenhouse gas emissions began slowing in the year 2000.  The FAR’s projected BAU greenhouse gas (GHG) radiative forcing (global heat imbalance) in 2010 was approximately 3.5 Watts per square meter (W/m2).  In the B, C, D scenarios, the  projected 2011 forcing was nearly 3 W/m2.  The actual GHG radiative forcing in 2011 was approximately 2.8 W/m2, so to this point, we’re actually closer to the IPCC FAR’s lower emissions scenarios.

As shown in Figure 2, the IPCC FAR ran simulations using models with climate sensitivities (the total amount of global surface warming in response to a doubling of atmospheric CO2, including amplifying and dampening feedbacks) corresponding to 1.5°C (low), 2.5°C (best), and 4.5°C (high).  However, because climate scientists at the time believed a doubling of atmospheric CO2 would cause a larger global heat imbalance than today’s estimates, the actual climate sensitivities were approximately 18% lower (for example, the ‘Best’ model sensitivity was actually closer to 2.1°C for doubled CO2).

FAR temp projections

Figure 2: IPCC FAR projected global warming in the BAU emissions scenario using climate models with equilibrium climate sensitivities of 1.3°C (low), 2.1°C (best), and 3.8°C (high) for doubled atmospheric CO2

Figure 3 accounts for the lower observed GHG emissions than in the IPCC BAU projection, and compares its ‘Best’ adjusted projection with the observed global surface warming since 1990.

FAR vs Obs

Figure 3: IPCC FAR BAU global surface temperature projection adjusted to reflect observed GHG radiative forcings 1990-2011 (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 1990 through 2012.

FAR Scorecard

The IPCC FAR ‘Best’ BAU projected rate of warming from 1990 to 2012 was 0.25°C per decade.  However, that was based on a scenario with higher emissions than actually occurred.  When accounting for actual GHG emissions, the IPCC average ‘Best’ model projection of 0.2°C per decade is within the uncertainty range of the observed rate of warming (0.15 ± 0.08°C) per decade since 1990, though a bit higher than the central estimate.


The IPCC Second Assessment Report (SAR) was published in 1995, and improved on the FAR by including an estimate of the cooling effects of aerosols — particulates which block sunlight and thus have a net cooling effect on global temperatures.  The SAR included various human emissions scenarios; so far its scenarios IS92a and b have been closest to actual emissions.

The SAR also maintained the “best estimate” equilibrium climate sensitivity used in the FAR of 2.5°C for a doubling of atmospheric CO2.  However, as in the FAR, because climate scientists at the time believed a doubling of atmospheric CO2 would cause a larger global heat imbalance than current estimates, the actual  “best estimate” model sensitivity was closer to 2.1°C for doubled CO2.

Using global climate models and the various IS92 emissions scenarios, the SAR projected the future average global surface temperature change to 2100 (Figure 4).

IPCC SAR Projections

Figure 4: Projected global mean surface temperature changes from 1990 to 2100 for the full set of IS92 emission scenarios. A climate sensitivity of 2.12°C is assumed.

Figure 5 compares the IPCC SAR global surface warming projection for the most accurate emissions scenario (IS92a) to the observed surface warming from 1990 to 2012.

SAR vs obs

Figure 5: IPCC SAR Scenario IS92a global surface temperature projection (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 1990 through 2012.

SAR Scorecard

The IPCC SAR IS92a projected rate of warming from 1990 to 2012 was 0.14°C per decade.  This is within the uncertainty range of the observed rate of warming (0.15 ± 0.08°C) per decade since 1990, and very close to the central estimate.


The IPCC Third Assessment Report (TAR) was published in 2001, and included more complex global climate models and more overall model simulations than in the previous IPCC reports.  The IS92 emissions scenarios used in the SAR were replaced by the IPCC Special Report on Emission Scenarios (SRES), which considered various possible future human development storylines.

The IPCC model projections of future warming based on the various SRES and human emissions only (both GHG warming and aerosol cooling, but no natural influences) are shown in Figure 6.

IPCC TAR projections

Figure 6: Historical human-caused global mean temperature change and future changes for the six illustrative SRES scenarios using a simple climate model. Also for comparison, following the same method, results are shown for IS92a. The dark blue shading represents the envelope of the full set of 35 SRES scenarios using the simple model ensemble mean results. The bars show the range of simple model results in 2100.

Thus far we are on track with the SRES A2 emissions path.  Figure 7 compares the IPCC TAR projections under Scenario A2 with the observed global surface temperature change from 1990 through 2012.

TAR vs. obs

Figure 7: IPCC TAR model projection for emissions Scenario A2 (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 1990 through 2012.

TAR Scorecard

The IPCC TAR Scenario A2 projected rate of warming from 1990 to 2012 was 0.16°C per decade.  This is within the uncertainty range of the observed rate of warming (0.15 ± 0.08°C) per decade since 1990, and very close to the central estimate.

2007 IPCC AR4

In 2007, the IPCC published its Fourth Assessment Report (AR4).  In the Working Group I (the physical basis) report, Chapter 8 was devoted to climate models and their evaluation.  Section 8.2 discusses the advances in modeling between the TAR and AR4.  Essentially, the models became more complex and incorporated more climate influences.

As in the TAR, AR4 used the SRES to project future warming under various possible GHG emissions scenarios.  Figure 8 shows the projected change in global average surface temperature for the various SRES.

AR4 projections

Figure 8: Solid lines are multi-model global averages of surface warming (relative to 1980–1999) for the SRES scenarios A2, A1B, and B1, shown as continuations of the 20th century simulations. Shading denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The grey bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios.

We can therefore again compare the Scenario A2 multi-model global surface warming projections to the observed warming, in this case since 2000, when the AR4 model simulations began (Figure 9).

AR4 vs. obs

Figure 9: IPCC AR4 multi-model projection for emissions Scenario A2 (blue) vs. observed surface temperature changes (average of NASA GISS, NOAA NCDC, and HadCRUT4; red) for 2000 through 2012.

AR4 Scorecard

The IPCC AR4 Scenario A2 projected rate of warming from 2000 to 2012 was 0.18°C per decade.  This is within the uncertainty range of the observed rate of warming (0.06 ± 0.16°C) per decade since 2000, though the observed warming has likely been lower than the AR4 projection.

As we will show below, this is due to the preponderance of natural temperature influences being in the cooling direction since 2000, while the AR4 projection is consistent with the underlying human-caused warming trend.

IPCC Projections vs. Observed Warming Rates

Tamino at the Open Mind blog has also compared the rates of warming projected by the FAR, SAR, and TAR (estimated by linear regression) to the observed rate of warming in each global surface temperature dataset.  The results are shown in Figure 10.

tamino IPCC vs obs

Figure 10: IPCC FAR (yellow) SAR (blue), and TAR (red) projected rates of warming vs. observations (black) from 1990 through 2012.

As this figure shows, even without accounting for the actual GHG emissions since 1990, the warming projections are consistent with the observations, within the margin of uncertainty.

Rahmstorf et al. (2012) Verify TAR and AR4 Accuracy

A paper published in Environmental Research Letters by Rahmstorf, Foster, and Cazenave (2012) applied the methodology of Foster and Rahmstorf (2011), using the statistical technique of multiple regression to filter out the influences of the El Niño Southern Oscillation (ENSO) and solar and volcanic activity from the global surface temperature data to evaluate the underlying long-term primarily human-caused trend.  Figure 11 compares their results with and without the short-term noise from natural temperature influences (pink and red, respectively) to the IPCC TAR (blue) and AR4 (green) projections.

RFC12 Fig 1

Figure 11: Observed annual global temperature, unadjusted (pink) and adjusted for short-term variations due to solar variability, volcanoes, and ENSO (red) as in Foster and Rahmstorf (2011).  12-month running averages are shown as well as linear trend lines, and compared to the scenarios of the IPCC (blue range and lines from the 2001 report, green from the 2007 report).  Projections are aligned in the graph so that they start (in 1990 and 2000, respectively) on the linear trend line of the (adjusted) observational data.

TAR Scorecard

From 1990 through 2011, the Rahmstorf et al. unadjusted and adjusted trends in the observational data are 0.16 and 0.18°C per decade, respectively.  Both are consistent with the IPCC TAR Scenario A2 projected rate of warming of approximately 0.16°C per decade.

AR4 Scorecard

From 2000 through 2011, the Rahmstorf et al. unadjusted and adjusted trends in the observational data are 0.06 and 0.16°C per decade, respectively.  While the unadjusted trend is rather low as noted above, the adjusted, underlying human-caused global warming trend is consistent with the IPCC AR4 Scenario A2 projected rate of warming of approximately 0.18°C per decade.

Frame and Stone (2012) Verify FAR Accuracy

A paper published in Nature Climate Change, Frame and Stone (2012), sought to evaluate the FAR temperature projection accuracy by using a simple climate model to simulate the warming from 1990 through 2010 based on observed GHG and other global heat imbalance changes.  Figure 12 shows their results.  Since the FAR only projected temperature changes as a result of GHG changes, the light blue line (model-simulated warming in response to GHGs only) is the most applicable result.

FS12 Fig 1

Figure 12: Observed changes in global mean surface temperature over the 1990–2010 period from HadCRUT3 and GISTEMP (red) vs. FAR BAU best estimate (dark blue), vs. projections using a one-dimensional energy balance model (EBM) with the measured GHG radiative forcing since 1990 (light blue) and with the overall radiative forcing since 1990 (green). Natural variability from the ensemble of 587 21-year-long segments of control simulations (with constant external forcings) from 24 Coupled Model Intercomparison Project phase 3 (CMIP3) climate models is shown in black and gray.  From Frame and Stone (2012).

FAR Scorecard

Not surprisingly, the Frame and Stone result is very similar to our evaluation of the FAR projections, finding that they accurately simulated the global surface temperature response to the increased greenhouse effect since 1990.  The study also shows that the warming since 1990 cannot be explained by the Earth’s natural temperature variability alone, because the warming (red) is outside of the range of natural variability (black and gray).

IPCC Trounces Contrarian Predictions

As shown above, the IPCC has thus far done remarkably well at predicting future global surface warming.  The same cannot be said for the climate contrarians who criticize the IPCC and mainstream climate science predictions.

Richard Lindzen

One year before the FAR was published, Richard Lindzen gave a talk at MIT in 1989 which we can use to reconstruct what his global temperature prediction might have looked like.  In that speech, Lindzen remarked

“I would say, and I don’t think I’m going out on a very big limb,  that the data as we have it does not support a warming…I personally feel that the likelihood over the next century of greenhouse warming reaching magnitudes comparable to natural variability seems small”

The first statement in this quote referred to past temperatures — Lindzen did not believe the surface temperature record was accurate, and did not believe that the planet had warmed from 1880 to 1989 (in reality, global surface temperatures warmed approximately 0.5°C over that timeframe).  The latter statement suggests that the planet’s surface would not warm more than 0.2°C over the following century, which is approximately the range of natural variability.  In reality, as Frame and Stone showed, the surface warming already exceeded natural variability two decades after Lindzen’s MIT comments.

Don Easterbrook

Climate contrarian geologist Don Easterbook has been predicting impending global cooling since 2000, based on expected changes in various oceanic cycles (including ENSO) and solar activity. Easterbrook made two specific temperature projections based on two possible scenarios.  As shown in Figure 1, neither has fared well.

Syun-Ichi Akasofu

In 2009, Syun-Ichi Akasofu (geophysicist and director of the International Arctic Research Center at the University of Alaska-Fairbanks) released a paper which argued that the recent global warming is due to two factors: natural recovery from the Little Ice Age (LIA), and “the multi-decadal oscillation” (oceanic cycles).  Based on this hypothesis, Akasofu predicted that global surface temperatures would cool between 2000 and 2035.  Akasofu’s prediction is the least wrong of the contrarian predictions examined here, but with a 0.02°C per decade cooling prediction between 2000 and 2012, has not matched the 0.06°C per decade warming trend, despite the fact that according to Foster and Rahmstorf, natural climate influences have had an approximately 0.1°C cooling effect since 2000.

John McLean

John McLean is a data analyst and member of the climate contrarian group Australian Climate Science Coalition.  He was lead author on McLean et al. (2009), which grossly overstates the influence of the El Niño Southern Oscillation (ENSO) on global temperatures.  Based on the results of that paper, McLean predicted:

“it is likely that 2011 will be the coolest year since 1956 or even earlier”

In 1956, the average global surface temperature anomaly in the three datasets (NASA GISS, NOAA NCDC, and HadCRUT4) was -0.21°C.  In 2010, the anomaly was 0.61°C.  Therefore, McLean was predicting a greater than 0.8°C global surface cooling between 2010 and 2011.  The largest year-to-year average global temperature change on record is less than 0.3°C, so this was a rather remarkable prediction, and not surprisingly turned out to be very wrong.

IPCC vs. Contrarians Scorecard

Figure 1 at the top of this post compares the four IPCC projections and the four contrarian predictions to the observed global surface temperature changes.  We have given Lindzen the benefit of the doubt and not penalized him for denying the accuracy of the global surface temperature record in 1989.  Our reconstruction of his prediction takes the natural variability of ENSO, the sun, and volcanic eruptions from Foster and Rahmstorf (2011) (with a 12-month running average) and adds a 0.02°C per decade linear warming trend.  Note that this was not a specific prediciton made by Lindzen, but rather is our reconstruction based on his 1989 comments.  All other predictions are as discussed above.

Not only has the IPCC done remarkably well in projecting future global surface temperature changes thus far, but it has also performed far better than the few climate contrarians who have put their money where their mouth is with their own predictions.

Conservative IPCC Errs on the Side of Least Drama

Although the IPCC climate models have performed remarkably well in projecting average global surface temperature warming thus far, Rahmstorf et al. (2012) found that the IPCC underestimated global average sea level rise since 1993 by 60%.  Brysse et al. (2012) also found that the IPCC has tended to underestimate or failed to account for CO2 emissions, increased rainfall in already rainy areas, continental ice sheet melting, Arctic sea ice decline, and permafrost melting.  Brysse et al. concludes that the on the whole the IPCC has been too conservative in its projections, “erring on the side of least drama” — in effect preferring to be wrong on the conservative side in order to avoid criticism.

Dana Nuccitelli is an environmental scientist at a private environmental consulting firm in the Sacramento, California area. This piece was originally published at Skeptical Science and was reprinted with permission.

21 Responses to Contrary To Contrarian Claims, IPCC Temperature Projections Have Been Exceptionally Accurate

  1. Superman1 says:

    Our choices today are between very bad and worse. I’m all for a positive outlook, but there has to be some basis for optimism. Otherwise, it becomes wishful thinking or delusion. I have seen no credible Strategic Plan or Roadmap that will allow us to ameliorate climate change given the restrictions we have on adding further CO2 to the atmosphere in the process.

    I find it interesting that the climate science community is willing to generate environmental variable time series from thousands or millions of years ago, and extrapolate to the present and future. However, when it comes to generating time series of actions to reverse climate change, a polar opposite approach is used. Consider the past thirty years, since Hansen elevated the climate change alarm to a new level. We have a time series of thirty annual points of ZERO action taken to address climate change, yet we extrapolate super-exponentials into the future that will reverse climate change. The voluntary, democratic, free market approach to limiting emissions and other ameliorating practices has not worked, is not working, and, as far as I can see, will not work. There is zero evidence to the contrary!

    Where are we now? According to Anderson (and others) there is sufficient man-made CO2 that has been added to the atmosphere to place us in the Extremely Dangerous regime. Not only will we be seeing a dramatic increase in what were once considered Extreme Events, both in frequency and magnitude, but there is increasing probability that some degree of runaway temperature will occur. That translates into the extinction of civilization before the end of this century.

    We need to minimize the temperature increase in the near term. Practically, this requires eliminating CO2 emissions ASAP, and removing as much CO2 from the atmosphere ASAP. It probably also means some form of geo-engineering for the short term to minimize the temperature increase and ‘quench’ the self-sustaining positive feedback mechanisms that we are observing already.

    So, what are our options today? Thirty years ago, had we had the awareness of today relative to climate change, we could have made a transition to renewables with modest discomfort. We had some CO2 concentration ‘slack’ in the atmosphere. Today, that no longer exists. So, if the voluntary approach I outlined above is not working, there are two generic choices. One is business as usual, which results in the loss of seven billion people by century’s end. The other is some form of involuntary approach. In another post, I mentioned takeover by those who control the physical levers of power because that’s the only group who has the ability to enforce the required level of changes. There is nothing the President or Congress could, or would, do to enable these draconian changes. They could not impose the type of rationing we had during WWII, or even more extreme, or double or triple the price of fuel. The electorate would not stand for it.

    So, the only thing I see that gives us any chance is this assumption of power by those with the physical forces to impose it, and then imposition of the most draconian measures. As some posters have pointed out, this could result in the premature deaths of hundreds of millions of people. Well, in 1941, when the Germans invaded the USSR, it appeared they would reach Moscow in a month or two, and the game would be over. Stalin ordered troops to fight a series of delaying battles to forestall the advance. Even the troops knew they were being sacrificed, as later letters showed. Stalin was willing to sacrifice hundreds of thousands so that millions, or tens of millions, would survive. It worked. That’s the position we are in today with respect to climate change. This is not something I am ‘promoting’; this is the only lifeline I see at this point in time. If anyone sees a better option, please outline.

  2. Paul Klinkman says:

    If a political candidate claims that his opponent sleeps with pigs, the opponent must take the time to prove that he does not, in fact, sleep with pigs.

  3. Will Fox says:

    Our likely future…

    (anyone here seen this documentary?)

  4. Superman1 says:


    Along those lines, if Guy McPherson claims we are on the read to irreversible extinction due to unstoppable feedbacks, perhaps within a generation or two, must those with more optimistic views prove he is wrong?

  5. Sasparilla says:

    I see what you’re saying Superman1, but I also think the likelihood of individuals (or groups of individuals) who could essentially take over the control of (governments?) acting in a rational and responsible manner with all that power and control at their fingertips (as opposed to using it to their own ends) is – well I think the likelihood of that (based on my own observation of human behavior) is extremely….unlikely.

    I’d rather take my chances with a corrupted democracy (like we have here in the U.S.) and hope we can turn the ship on climate change in the next decade or so as stronger climate effects possibly enable action over the interests of fossil fuel players at the federal and world level. JMHO…

  6. Susan C. Harris says:

    In the middle of the 20th century, the global climate cooled over the short term. Carbon dioxide pollution is warming our planet over the long term.

  7. Merrelyn Emery says:

    Social change is not the sort of phenomemom that is easily measured by linear means. It tends to remain relative invisible until it burst through when there is a critical mass. Glimpses of it from things like opinion polls and the data Joe has posted above on the decline of denier sites are indications of it. You will get a critical mass of demand for action over there, ME

  8. Merrelyn Emery says:

    This will demand some extreme ‘creativity’ from Mr Watts but I’m sure he is up to the task, ME

  9. Hah, Watts’ response (via Twitter) is that this post is a “Major fail” because it doesn’t show the IPCC AR5 graphic referenced at the top of the post. The graphic that I explained I wasn’t going to show because it’s part of an in-process draft document, but linked to two sites where people can see it if they’d like.

    Talk about a major fail, but that’s pretty standard fare for Watts.

  10. Mulga Mumblebrain says:

    Unfortunately, as Superman so cogently argues, when and if it (popular awareness) arises (mass sentiment can also be diverted by the cunning into dead-ends like fascism, which is rearing its head again in austerity-ravaged Europe)it will almost certainly be too late. I’m all for optimism, as pessimism never achieved anything, but, as Superman says, when it becomes self-delusion then it turns toxic. Indeed those with the preponderance of the means of violence are going to take power sometime in any case, as societies crumble,so it could be construed as optimistic to hope that they might prove more enlightened than the current generation of political and business rulers who are, have been, and, I believe, will remain utterly useless.

  11. Mulga Mumblebrain says:

    I’d expect the pigs to vigorously deny it, also. They have their reputations to protect.

  12. Merrelyn Emery says:

    Yep, he is not bright but that gives an insight into that fascinating little cult, ME

  13. Merrelyn Emery says:

    Fascism and related are always a danger particularly when people have been sensitized to inequality and ‘them and us’. They see a possibility of themselves becoming the new bosses. However, there are increasing numbers of well educated people who know it is the system that must be changed – how it plays out will probably vary by culture, ME

  14. Mulga Mumblebrain says:

    A waste of carbon.

  15. Mulga Mumblebrain says:

    Whenever I contemplate The Dunning-Kruger mob, and their congruence with the political Right, I always recall the eejit at High School who was of the Right because he imagined that the term denominated correctness, as in right and wrong, not having grasped the concept of ‘Left’ in any way. We were all ‘Communists’ in any case.

  16. Esop says:

    Excellent post.
    2013 could well be the warmest on record. UAH lower troposphere temperatures have been so high lately that they had to rewrite the software and launch a 5.5 version that showed less warming. As they always do when temps get into record territory.

  17. Superman1 says:

    “hope we can turn the ship on climate change in the next decade or so”. Hope has never, is not, and will never be a substitute for a credible Roadmap and Strategic Plan. How many data points do you need before you can conclude that this ‘imperfect’ voluntary democracy is not up to the job of addressing climate change, and never will be?

  18. Doug Proctor says:

    Observations appear in the lower quadrants of IPCC narrative. Okay. By 2015, if observations don’t rise above 2012, then the IPCC narrative most closely followed is the lower one.

    Is there a catastrophic end when the rise is at the lower end? Should not the upper end scenarios not be retired, and the forcings of CO2 be “settled” at the lower end of the ranges to-date?

    2015 will be 27 years. Should be long enough if we really have a good handle on the science and observational techniques. So then we will really know what future we will face. So far it does not look like 6C and 6m of sea-rise, so our financial danger will be better than worse.

  19. dave says:

    Thanks for your highly thoughful, informative and, of course, disturbing post. But yes, it seems to sum up our most basic situation at present. I’ve accepted your challenge of coming up with some better solution, but for now all I can do is ponder.

    But like you I’d rather go down with my eyes open and accepting whatever the truth might reveal, than in delusion and denial.

  20. dave says:

    Ridicule if you must, but I think we should look into closer contact with whomever is creating the crop circles…(and I conclude aliens, especially as two circles seemed to come in direct response to the Challenger’s 1974 message, and I have seen no other even remotely plausible explanation for cc’s).

    Perhaps some measure of technological assistance might be available…(though whether truly intelligent aliens would actually help such a dangerous and intransigent sort of species as the enemy that is us is another matter entirely…)

  21. john atcheson says:

    Great post. Fact filled and informative.

    It might be useful to observe that while the IPCC has been accurate with regard to temperature increases, they have consistently underestimated the consequences of those increases on sea level rise, draughts, fire, storm intensity etc,