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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.

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How the IPCC is more likely to underestimate the climate response

What the science says...

Select a level... Basic Intermediate

Numerous papers have documented how IPCC predictions are more likely to underestimate the climate response.

Climate Myth...

IPCC is alarmist

"Unquestionably, the U.N. Intergovernmental Panel on Climate Change (IPCC) was formed to build the scientific case for humanity being the primary cause of global warming. Such a goal is fundamentally unscientific, as it is hostile to alternative hypotheses for the causes of climate change." (Roy Spencer)

"Unquestionably, the U.N. Intergovernmental Panel on Climate Change (IPCC) was formed to build the scientific case for humanity being the primary cause of global warming. Such a goal is fundamentally unscientific, as it is hostile to alternative hypotheses for the causes of climate change."

Climate scientist Roy Spencer made this statement. He starts by suggesting something highly questionable isn’t open to being questioned. What he seeks to do is suggest, by inference, that the IPCC has an agenda, and this distorts the reports they produce. In other words, Spencer (and others) suggest that the IPCC exaggerates what the science says in favour of anthropogenic global warming. It is perfectly legitimate to question this assertion, since Spencer and others offer no evidence to support it.

Some critics go further, suggesting that the IPCC actively suppresses science that doesn’t support the theory that climate change is being caused by human activities. It is notable this ‘other science’ is rarely produced to support the accusation.

Does the IPCC accurately report the findings of science?

The IPCC was formed to report on a broad range of scientific enquiries into the climate, and our effects on it, and to summarise the science for laypeople. The science they summarise is published so it is simple to compare the primary science with the IPCC reports, and compare both to what actually took place.

There are numerous instances where the IPCC reports, which are summaries of published climate change science, have understated the case - hardly suggesting exaggeration in pursuit of an agenda. Here are some examples:

  • CO2 output from fossil fuels: observed emissions are close to the worst-case projections made by the IPCC, despite them offering a range of potential emission scenarios. (In fact, atmospheric CO2 is increasing ten times faster than any rate detected in ice core data over the last 22,000 years).
  • Sea-level rise is accelerating faster than the IPCC predicted. Actual sea-level rise is 80% higher than the median IPCC projection. By 2100 sea-level rise was predicted by the IPCC to be in the range of 18-59 cm. It is now believed that figure may be far too low, because estimates of contributions from Greenland and Antarctic ice-caps were excluded from AR4 because the data was not considered reliable. (This omission hardly supports the notion that the IPCC seeks to exaggerate global warming trends).
  • Each Arctic summer, sea-ice is melting faster than average predictions in the last IPCC report. The Arctic is experiencing a long-term loss of multi-year ice which is also accelerating.
  • The body of scientific literature has consistently shown that human greenhouse gas emissions are responsible for more global surface warming than has been observed over the past half century, whereas the IPCC only says that greenhouse gases are responsible for "most" observed warming over this timeframe.

In many similar cases, the evidence suggests that changes in climate are occurring faster, and with more intensity, than the IPCC have predicted. It is not credible to suggest the reports were biased in favour of the theory of anthropogenic global warming when the evidence demonstrates the IPCC were, in fact, so cautious.

In fact, there is evidence however to suggest that the exact opposite is actually the case, both in terms of the scientific evidence itself (see below) and the way the work of the IPCC is reported. A recent study (Freudenburg 2010) investigated what it calls 'the Asymmetry of Scientific Challenge', the phenomenon in which reports on science fail to evaluate all outcomes, favoring certain probabilities while ignoring others. They found that " scientific findings were more than twenty times as likely to support the ASC perspective [that disruption through AGW may be far worse than the IPCC has suggested] than the usual framing of the issue in the U.S. mass media".

Claims that the IPCC is alarmist are not supported by evidence, and there are clear indications that the opposite may be the case.

Basic rebuttal written by GPWayne

Update July 2015:

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 5 July 2015 by skeptickev. View Archives

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Comments 126 to 138 out of 138:

  1. andrewii

    This article discusses the findings by Lee Kump and colleagues wrt the rate of inctrease of CO2 during the Paleocene/Eocene Thermal Maximum, around 55 million years ago.

    PETM CO2

    This period is considered a reasonable analogue for today. The world was originally warmer than today by perhaps 4-6 DegC, then it experienced a doubling or more of CO2 very quickly (in geological time scales). Temps climbed another 4-6  DegC, a small Extinction event occurred and an Anoxic event occcurred in the ocean.

    Kump et al found that CO2 levels today are climbing 10 times faster than during the PETM.

  2. Thanks DSL, gws and Glenn Tamblyn!

  3. I'd like to suggest a subject for a future post:

    IPCC figures are virtually all limited to 2100. And all IPCC scenarios assume some emmission curbing at some point (ranging from slow to fast). That's unrealistally optimistic at this point, since there are no signs of leaving carbon reserves unexplored and buried undergound. They're even exploring new possibilities in hydrocarbons (like methane clathrate), and looking for new oil reserves (like in the Arctic).

    If we burn every reserve we know, this paper below projects a 16 ºC warming eventually, making "much of the planet uninhabitable by humans".

    "Climate sensitivity, sea level and atmospheric carbon dioxide"

    Hansen et al. 2013

  4. The reason the IPCC projections are necessarily conservative is that all participating countries have to agree on the information included!

  5. Hope this thread is appropriate.

    Over the years I've used the SKS escaltor in my blog posts from time to time.  Recently I recieved a reply "it is a great example of cherry picking noisy high/low points along a period when first the PDO and then the AMO moved into their positive phases. If you remove the noise then the escalator magically disappears. What's left is two step rises. The first from 1976-1980 was the PDO going positive. The 2nd from 1993-1995 was due to the AMO going positive.


    [PS] Try here. Cherry picking by the way is making an argument by selecting only the part of the dataset that supports your argument. Real statistician have removed noise rigourously. See here. Sks escalator is that only deniers believe in step changes. The science shows that when internal variability is removed, then temperatures steadily rise with the increase in CO2.

  6. I've downloaded the 2018 IPCC report 

    Changes in Climate Extremes and their Impacts on the Natural Physical Environment


    I've perused the References section and I can find no research that takes place later than 2011. I guess there's a possibility  the report is for 2013 but the link indicates that it's 2018 (No explicit mention of the date of the report in the text. Why?)

    If in fact it's 2018, why the delay in examining research?

  7. Cozumelito:

     From the title page of the report you cite:

    "This chapter should be cited as:
    Seneviratne, S.I., N. Nicholls, D. Easterling, C.M. Goodess, S. Kanae, J. Kossin, Y. Luo, J. Marengo, K. McInnes, M. Rahimi,
    M. Reichstein, A. Sorteberg, C. Vera, and X. Zhang, 2012:" my emphasis

  8. Take note that these are very large reports that take years to compile, write, and publish. Thus, the latest research will be several years prior to the published date of the final report.

  9. I believe the IPCC reports are probably the most used information to help set climate policy around the globe. However after reading this,

    and part of their summary :

    " Climate policymaking and the public narrative are significantly informed by the important work of the IPCC. However, IPCC reports also tend toward reticence and caution, erring on the side of “least drama”, and downplaying the more extreme and more damaging outcomes. Whilst this has been understandable historically, given the pressure exerted upon the IPCC by political and vested interests, it is now becoming dangerously misleading with the acceleration of climate impacts globally. What were lower-probability, higher-impact events are now becoming more likely. This is a particular concern with potential climatic tipping points — passing critical thresholds which result in step changes in the climate system — such as the polar ice sheets (and hence sea levels), and permafrost and other carbon stores, where the impacts of global warming are non-linear and difficult to model with current scientific knowledge.However the extreme risks to humanity, which these tipping points represent, justify strong precautionary management. Under-reporting on these issues is irresponsible, contributing to the failure of imagination that is occurring today in our understanding of, and response to, climate change. If climate policymaking is to be soundly based, a reframing of scientific research within an existential risk-management framework is now urgently required. This must be taken up not just in the work of the IPCC, but also in the UNFCCC negotiations if we are to address the real climate challenge. Current processes will not deliver either the speed or the scale of change required."


    So, i was wondering just how correct is this need to modify the scope of the IPCC reports. 

    " What Lies Beneath" put into words my feelings on our current  Aussie state - pretend we care but open more coal mines and do nothing..

    This video was also enlightening , a new documentary series , pt 1.!

  10. prove we are smart @134,

    With one exception, I have only read the summary of the paper Spratt & Dunlop (2018) 'What Lies Beneath: The understanding of existential climate risk' which you refer to. In short, the need for action on AGW was demonstrated by the science over a quarter of a century ago yet globally our emissions increased as though no such science existed. There is now, policy-wise, an agreement that radical action is needed to prevent a +1.5ºC increase in global temperature, radical as such a goal requires global CO2 emissions in future years to be restricted to something like 120Gt(C). The general message from the science is that such a goal will prevent the very bad AGW effects from happening. Yet in terms of policy, there is still little urgency. The enthusiasm for declaring a Climate Emergency has not yet resulted in any useful policy but let us hope that it will, soon. Spratt & Dunlop (2018) suggest the 120Gt(C) is flawed but it seems to me that its argument would need to be far better presented to be a useful contribution.

    Their main criticism is that the science includes those "fat tails" which may make a +1.5ºC world a bit too hot to handle. There has been quite a bit of criticism of the IPCC for failing to make such potential outcomes better known. Most recently, Oppenheimer et al (2019) 'Discerning Experts: The Practices of Scientific Assessment for Environmental Policy' has described well instances of the IPCC's failings (three of the authors have an account of the book HERE). But while there are systemic problems within the IPCC assessments, they do not systematically underestimate AGW. There is perhaps need for the failings of the IPCC assessments to be better understood and in addressing that, I have no criticism of Spratt & Dunlop (2018).

    But Spratt & Dunlop (2018) goes further than this. There is a feel of this in their assessment of the impacts of AGW. Their Summary begins:-

    "Human-induced climate change is an existential risk to human civilisation: an adverse outcome that will either annihilate intelligent life or permanently and drastically curtail its potential, unless carbon emissions are rapidly reduced."

    The word "existential" is usually, in my view, very poorly wielded in regard to AGW. Here, the use "an existential risk to human civilisation" is refreshing to see. But then it is followed by "annihilate intelligent life" which is something I find very difficult to envision.

    So this got me delving into one further section of Spratt & Dunlop (2018). The section Carbon Budgets makes a number of points (♣ Not working other GHGs into the budget, ♣ Not evaluating "fat tails" which would reduce carbon budgets to zero, ♣ Relying on models that potentially run cool, ♣ Not defining pre-industrial temperature adequately, ♣ Ignoring actual peak temperatures) but I only see one of these issues that is germane to setting carbon budgets (the cool models). So for me, Spratt & Dunlop (2018) seems to be 'firing from the hip' a bit too much and needs to tighten up its message if they want to make a serious contribution.

  11. M A Rodger @ 135, i think shooting from the hip is exactly what the IPCC should be doing. With CO2 levels still increasing from the last three decades, taking slow aim and firing is just missing the target. Just how unprepared / misinformed are we in Australia? Look at this,

  12. Why has the IPCC and other international bodies attempting to address the problem stopped talking about the cumulative nature of CO2 and who has historically contributed more to the problem?

    AFter all, those of us old enough to remember the Kyoto Protocol recognize this:

    "The Kyoto Protocol is based on the principle of common but differentiated responsibilities: it acknowledges that individual countries have different capabilities in combating climate change, owing to economic development, and therefore puts the obligation to reduce current emissions on developed countries on the basis that they are historically responsible for the current levels of greenhouse gases in the atmosphere."

    This was almost universally recognized before, ignored today.  Does the IPCC have a poltical agenda?  I know political topics are not allowed, but here there is talk about IPCC as if it is just a scientific body, when it clearly has taken political positions throughout its history.  

  13. Gzzm @137 ,

    your language is rather vague wrt  "address the problem".

    The various IPCC reports, over the years, are intended to summarize the overall climate science.  The IPCC also produces a condensed version for Policymakers i.e. politicians.

    Gzzm, best if you clarify what you mean by politics  and political positions.   The term politics  covers a vast range of meaning.

    As example, is it politics  to say about a wildfire: "Quick, send in the fire-fighters"  or on the other hand to say:  "Nah just let it burn, come what may" ?   Are such decisions practical decisions, or are they political decisions?

    Can be hard to say what, if any, is politics.   Probably best if we simply use common sense wrt  "the problem".

    Gzzm, please clarify any points you wish to make.

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