Climate Change Attribution – The Rapid Evolution of Uncertainty to Near Certainty in Consecutive IPCC Reports (Part I)



This subject has undoubtedly been covered before by other people over the years but I think now is a very apt time to revisit the question of just how and why establishment climate science went so rapidly from not knowing if climate change was natural or not to claiming it was virtually all man-made.

The First Assessment Report released in 1990 said all of it could be natural; the Fifth Assessment Report stated it was “extremely likely” that most or all of the warming since 1950 was anthropogenic. A huge leap of confidence in just 23 years, but the really remarkable thing is that just three years after claiming that the unequivocal detection of the enhanced greenhouse effect would not be detected for a decade or more and that the signal of human caused climate change could not be disentangled from that of natural variability, scientists suddenly declared that a human influence on climate was discernible and that the rise in global mean temperature since the late 19th century was unlikely to have been all natural. Five years after that (in 2001), the IPCC stated that most of the observed warming over the last 50 years was “likely” due to anthropogenic GHGs. Was this change of heart due to a sudden and huge leap in understanding of the climate system – or was it due to political pressure?

I think that there is not enough evidence of original, definitive, robust scientific research published around that time which would justify the adoption of a scientific consensus that climate change was largely man-made, not natural. I think that enormous pressure was put on the IPCC to conform to the policy aspirations of the UNFCC, the United Nations Framework Convention on Climate Change. The UNFCC, from the word go, actually defined ‘climate change’ as being man-made. This organisation came into being specifically to enable countries to adopt GHG emission reductions in order to tackle a ‘problem’ which had not even been unequivocally demonstrated to be occurring. I quote:

On 11 December 1990, the UN General Assembly establishes the Intergovernmental Negotiating Committee (INC) for a Framework Convention on Climate Change. The INC held five sessions where more than 150 states discussed binding commitments, targets and timetables for emissions reductions, financial mechanisms, technology transfer, and ‘common but differentiated’ responsibilities of developed and developing countries.

This was less than a month after the IPCC FAR was released, so they might have been a bit dismayed that scientists were not fully on board with their AGW political bandwagon. But such a minor issue was not going to stop the UNFCC from plowing full steam ahead with their de-industrialisation/fossil fuel reduction agenda. In May 1992, the text of the United Nations Framework Convention on Climate Change was adopted at the UN Headquarters in New York, which was later formally opened for signatures at the Rio Earth Summit in June 1992. The UN Agenda 21 ‘sustainable development’ political project went global and eventually led to the Kyoto Protocol and the Paris Agreement, the latter of which was just recently used by Greens to shut down the development of the third runway at Heathrow. So it’s working, obviously – growth is being curtailed to suit green ideology, an ideology born even before the term ‘climate change’ was in popular usage, a political ideology which adopted very successfully the threat of supposed man-made climate change in order to foist its agenda upon developed Western nations in particular. It adapted ‘climate change’ to its cause, as we have seen, even before ‘climate change’ became supposedly scientifically demonstrable. But ‘science’ caught up – quickly.

So let’s look at what scientists had to say about climate change in 1990 when the first assessment report was released:

Our judgement is that: Global mean surface air temperature has increased by 0.3°C to 0.6°C over the last 100 years, with the five global average warmest years being in the 1980s. Over the same period global sea level has increased by 10-20 cm. These increases have not been smooth with time, nor uniform over the globe. The size of this warming is broadly consistent with predictions of climate models, but it is also of the same magnitude as natural climate variability. Thus the observed increase could be largely due to this natural variability; alternatively this variability and other human factors could have offset a still larger human-induced greenhouse warming. The unequivocal detection of the enhanced greenhouse effect from observations is not likely for a decade or more. There is no firm evidence that climate has become more variable over the last few decades. However, with an increase in the mean temperature, episodes of high temperatures will most likely become more frequent in the future, and cold episodes less frequent.

On extreme weather:

Changes in the variability of weather and the frequency of extremes will generally have more impact than changes in the mean climate at a particular location. With the possible exception of an increase in the number ot intense showers there is no clear evidence that weather variability will change in the future. In the case of temperatures, assuming no change in variability, but with a modest increase in the mean, the number ot days with temperatures above a given value at the high end of the distribution will increase substantially. On the same assumptions, there will be a decrease in days with temperatures at the low end ot the distribution.

This is just saying that they expect the mean of hot days to increase with generalised surface warming, but not the variance. The increase in the intensity of showers is the Clausius-Clapeyron relation – simple thermodynamics. In order to affect the variance, you have to affect atmospheric dynamics:

If the large-scale weather regimes, for instance depression tracks or anticyclones, shift their position this would effect the vai lability and extremes of weather at a particular location, and could have a major effect. However, we do not know if, or in what way, this will happen.

This was 30 years ago. Scientists know little more now, even though ‘extreme weather attribution’ has become all the rage. They still cannot demonstrate that man-made global warming has had any significant effect upon weather extremes, though they pretend they can. They cannot demonstrate any effect at all upon atmospheric dynamics, least of all a mysterious decrease in headwinds at Greek airports. More controversially, they still cannot demonstrate robustly that the increase in global mean surface temperature observed since 1950 (or 1850) is due almost entirely to GHGs. They claim huge advances in ‘detection and attribution’ of global and regional climate change, but when you examine this supposed advancement in knowledge, what you find is that it still suffers from the same large structural uncertainties outlined in the first assessment report 30 years ago. The same range of uncertainty for climate sensitivity exists as was first presented in the Charney report going as far back as 1979. All that’s happened is that scientists claim to be a lot more confident that the modern rise in global temperatures is due entirely to GHGs. In the interim, mainstream climate science has made little or no progress in understanding and quantifying natural variability. Pierre Darriulat, former director of CERN and an award-winning physicist, sums up nicely the IPCC’s increasingly confident stance re. attribution and the need to act on climate change:

The AR5/WG1 IPCC report, and particularly the Summary for Policy Makers (SPM), conveys an alarmist evaluation of the influence on the climate of anthropogenic C02 emissions that does not properly reflect current scientific knowledge. This results in part from the ambiguity inherent with asking scientists to express themselves consensually on what they think is the best message. There is a need to produce a scientific summary addressed to scientists and giving an objective picture of our knowledge and ignorance in climate science, with emphasis on the issues that are less well understood and what it implies to clarify them. Such a summary should pay particular attention to a number of contentious issues that have been identified by a number of climate scientists who do not share the alarmist interpretation of the science. In the short term, the IPCC report weakens the case for taking urgent action.

When writing the SPM, the authors are facing a dilemma: either they speak as scientists and must therefore recognize that there are too many unknowns to make reliable predictions, both in the mechanisms at play and in the available data; or they try to convey what they “consensually” think is the right message but at the price of giving up scientific rigour. They deliberately chose the latter option. The result is they have distorted the scientific message into an alarmist message asking for urgent reaction, which is quite contrary to what the scientific message conveys.

It is sensible to ask for a scientific summary of the IPCC work, not addressing policy makers but as objective as possible a summary of the present status of our knowledge and ignorance about climate science. Such a report must refrain from ignoring basic scientific practices, as the SPM authors blatantly do when claiming to be able to quantify with high precision their confidence in the impact of anthropogenic C02 emissions on global warming. Statistical uncertainties, inasmuch as they are normally distributed, can be quantified with precision and it can make sense to distinguish between a 90% and a 95% probability, for example in calculating the probability of getting more than ten aces when throwing a die more than 10 times. In most physical problems, however, and particularly in climate science, statistical uncertainties are largely irrelevant. What matters are systematic uncertainties that result in a large part from our lack of understanding of the mechanisms at play, and also in part from the lack of relevant data. In quantifying such ignorance the way they have done it, the SPM authors have lost credibility with many scientists. Such behaviour is unacceptable. A proper scientific summary must rephrase the main SPM conclusions in a way that describes properly the factors that contribute to the uncertainties attached to such conclusions.

Needless to say, that hasn’t happened. IPCC SR15 went full alarmist in its take home message to policymakers and ever since, activists and scientists (if you can spot the difference) have been ramping up the alarmism to fever pitch, such that the science is now largely irrelevant and even what the IPCC says about the science is ignored when it does not fit the catastrophe narrative. But the science is relevant and was relevant back in the day when scientists still preferred to do science, not politics. However, politics quickly intruded and by the time of the Second Assessment Report in 1995, politics (and funding) was beginning to become dominant. Of the global warming since 1900, FAR says:

Much of the warming since 1900 has been concentrated in two penods, the first between about 1910 and 1940 and the other since 1975 the five warmest years on record have all been in the 1980s. The Northern Hemisphere cooled between the 1940s and the early 1970s when Southern Hemisphere temperatures stayed nearly constant. The pattern of global warming since 1975 has been uneven (with some regions mainly in the northern hemisphere continuing to cool until recently). This regional diversity indicates that future regional temperature changes are likely to differ considerably from a global average.

The size of the warming over the last century is broadly consistent with the predictions of climate models but is also of the same magnitude as natural climate variability. If the sole cause of the observed warming were the human made greenhouse effect, then the implied climate sensitivity would be near the lower end of the range inferred from the models. The observed increase could be largely due to natural variability, alternatively this variability and other man-made factors could have offset a still larger man-made greenhouse warming.

Note that not only do they say that warming could be all natural but that even if it was all due to GHG emissions, the implied sensitivity would still be near the lower end of the modeled range (i.e. nearer to 1.5C that 4.5C). By 1992, when the IPCC issued a supplement to FAR, they still maintained that observed changes could be natural:

The conclusion of IPCC (1990) remains unchanged: “the size of this warming is broadly consistent with predic-tions of climate models, hut it is also of the same magnitude as natural climate variability. Thus the observed increase could he largely due to this natural variability; alternative-ly this variability and other human factors could have offset a still larger human-induced greenhouse warming”.

Three years later, in the Second Assessment Report, the ‘denier talking point’ that climate change is largely a natural cycle, suddenly became less popular with mainstream IPCC climate science which shifted gear from claiming that natural variability might explain most or all of the observed post-industrial warming to claiming that there was a discernible human influence and that the rise in temperature was unlikely to be all natural. I will look at this sea-change (and the possible reasons for it) in Part II.




  1. Great summary..and the bullshit gravy train and scare tactics…carries on anyway.
    What has always irked me more the most is having this shite pushed down my throat by people that own cars and are connected to the grid and use planes all the time.
    And if you pattern interrupt them with questions..they just repeat cool memes..with a slight glazed look on their faces..its almost like they are in a light trance repeating stuff they have never spent a milli second thinking about..

    Liked by 1 person

  2. If you accept the no-feedback climate sensitivity of 1.2C per doubling of atmospheric CO2, can you then construct a non-paradoxical scenario under which more than half of the observed warming is non-anthropogenic?


  3. When are you getting off the grid and not jumping on planes anymore Ken…?….because..Greta… 🙂


  4. Ken, if you don’t accept that mid 20th century cooling was caused by or significantly caused by anthropogenic aerosols, can you construct a non-paradoxical scenario where all of the warming since 1950 is anthropogenic, best estimate 110%?


  5. Yes. we are first told that events under 30 years is just weather. Now 3 years IS Climate Change !?
    I am 71 and have seen a lot of weather. My guess is present warming is natural & caused by the
    present Solar minimum generating more cloud due to the increase in cosmic rays.


  6. Jaime,
    Sure, that’s pretty straightforward. In fact, if climate sensitivity is high, then internal variability can also have a reasonable impact on decadal timescales. Hence, a scenario where slightly more than all the warming since 1950 was anthropogenic can be entirely consistent with a reasonably short period of cooling during the mid 20th century. You still haven’t really answered my question, though.


  7. KR: to paraphrase Darriulat the question is not whether you can construct non-paradoxical scenarios about human contributions, but whether you wish to speak as scientists and recognize that there are too many unknowns to make reliable predictions or try to convey what you think is the right message at the price of giving up scientific rigour.

    Liked by 1 person

  8. Ken, climate models cannot reproduce mid 20th century cooling without invoking the effects of anthropogenic aerosols which are theorised to have had a significant effect post WW2, but not during the later 70s to 2000. With high climate sensitivity, the need for aerosol forcing in order for models to match the historic record becomes even greater. Climate models do not simulate mutlidecadal climate variability. The IPCC attribution statement relies solely upon a simple summing of radiative external forcings on the assumption that over the short period from 1950-2010, multidecadal variability effectively sums to zero. There is little or no justification for this assumption. If one assumes that sulfate aerosols were not the main reason for mid 20th century cooling, that the primary cause was internal variability, then it follows logically that multidecadal variability must also have contributed significantly to subsequent warming, which rather messes up the IPCC’s neat sums.

    Liked by 1 person

  9. Why would there not have been a recovery from the desperately cold period of the LIA. The 60’s and 70’s cooling period lasted 34 years, that’s climate in anyone’s book….isn’t it?

    Since, by decree of James Hansen, there were no reliable thermometers prior to 1880, we have a pretty short record in the overall scheme of things. However the UK Central England Temperature record goes back to 1659, when the “non-existent” Little Ice Age was producing extremely low temperatures, with winter averages barely above zero deg C.

    A Press Release from 1698 could have said for example:
    1698 – “Eight of the coldest years have occurred in the last 15 years.”

    An enterprising environmental journalist of the time could then have totally forgotten that period, and produced this headline, as temperatures recovered:

    1733- “The UK has heated by a massive 3.2 degrees over the last 4 decades.” (that’s 8 times more than the “safe” figure of 0.1C per decade often quoted)

    The 95% likelihood was determined by “expert opinion”. Guess who the experts were?

    Liked by 1 person

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