Prof Lewandowsky – Where is the overwhelming evidence of climate change?

On Stephan Lewandowsky’s blog (funded by the Australian people) he claims that there is overwhelming evidence of climate change. My question is as follows

You claim that there is “overwhelming scientific evidence on climate change”. Does this apply to:-

  1. The trivial proposition that there is a greenhouse effect, so a rise in GHG levels will cause some rise in temperature?


  2. The non-trivial proposition that the unmitigated increase in GHG levels will lead to significant warming with catastrophic consequences?

The trivial proposition is something for a few academics to ponder. It is only when there is reasonable scientific evidence for the non-trivial proposition that a global policy to mitigate could be seriously contemplated.

Having attended John Cook’s lecture at Bristol University a few days ago, I found out that the vast survey of academic papers found a 97% consensus was about belief in the trivial proposition, and some of the papers were authored by non-scientists. That is, Cook presented weak, secondary, evidence of the trivial proposition.

Cook’s lecture also mentioned the four Hiroshima bombs a second of heat accumulation in the climate system since 1998, the widget for which you have on the left-hand side of this blog. Stated this way, there appears to be a non-trivial amount of warming, that anybody can perceive. It is equivalent to the average temperature of the ocean’s increasing at a rate less than 0.0018oC per annum. That is weak evidence for the trivial proposition.

So where is the overwhelming evidence that can justify policy?

This gives rise to a question that Australian citizen’s may one to raise with their elected representatives.

Should Australian taxpayers be funding a partisan blog that is strongly critical of mainstream political opinion, whose sole current contributor is a non-Australian working outside of Australia?

Kevin Marshall

Notes on John Cook’s presentation at Bristol University

On Friday 19th September John Cook talked on “ Dogma vs. consensus: Letting the evidence speak on climate change” at Bristol University. He was introduced by Stephen Lewandowsky, who is now a professor there. The slides are available at Skepticalscience. Here are some notes on the talk, along with brief comments.

The global warming hypothesis

John Cook started by asking people to see if they can define the greenhouse effect as a way of detecting if people know what they are talking about. However, he did not then apply this criteria in evaluating consensus views.

He stated that there is no single cause of global warming (including solar and volcanic), but that there is a major or principle one. From then on Cook proceeded as if there was a single cause. There was no evidence for relative size of each cause of global warming. Nor was there any consideration of the implications if AGW accounted for half or less of the warming rather than the entirety of it.

He stated that there are multiple lines of evidence for AGW actually operating, no mention of the quality of the evidence, or of contrary evidence that the pattern of warming does not fit the models.

Cook et. al 97% scientific consensus paper

Cook than went on to talk about his 97% consensus paper. He then showed the Barak Obama tweet.

In the Q&A John Cook admitted to two things. First, the paper only dealt with declared belief in the broadest, most banal, form of the global warming hypothesis. That is greenhouse gas levels are increasing and there is some warming as a consequence. Second is that the included papers that were outside the realm of climate science1, and quite possibly written by people without a science degree. The Barak Obama tweet account seems to have got the wrong impression.

This should be seen in the light of a comment about why consensus is important.

Communicating consensus isn’t about proving climate change. It’s addresses a public misconception about expert opinion.

John Cook has spectacularly failed on his own terms.

Fake Experts

Cook pointed to a petition of a few years ago signed by over 31,000 American scientists, opposing the Kyoto Treaty on the basis that it would harm the environment, hinder the advance of science and technology and damage the health and welfare of mankind. They also signed to say that there was no convincing evidence of catastrophic global warming.

He calls these people “fake experts” because these “scientists”, but are not “climate scientists”. But as we have seen neither were all the authors on his climate consensus paper.

If scientists from other areas are “fake experts” on climate science, then this equally applies to those making statements in support of the “climate consensus”. That means all the statements by various scientific bodies outside of the field of “climate” are equally worthless. Even more worthless are proclamations by political activists and politicians.

But most of all neither is John Cook a “climate expert”, as his degree is in physics.

Four Hiroshima Bombs and a Zillion Kitten Sneezes

As an encore, Cook had a short presentation on global warming. There were no hockey sticks showing the last thousand years of warming, or even a NASA Gistemp global surface temperature anomaly graph for the last century. The new graph is the earth’s cumulative heat energy accumulation since 1970, broken down into components. It was a bit like the UNIPCC’s graph below from AR5 WG1 Chapter 3. However, I do not remember the uncertainty bands being on Cook’s version.

Seeing that, I whispered to my neighbour “Four Hiroshima Bombs”. Lo and behold the next slide mentioned them. Not a great prediction on my part, as has a little widget. But an alternative variant of this was a zillion kitten sneezes a second, or some such preposterous figure. The next slide was a cute picture of a kitten. Cook seems to be parodying his work.

The Escalator with cherries on top

The last slide was of Cook’s “Escalator” graph, or at least the “Skeptics” view. The special feature for the evening was a pair of cherries in the top left, to emphasise that “skeptics” cherry-pick the evidence.

It was left flickering away for the last 15 minutes.


My thoughts on the presentation

Some of the genuine sceptics who left the room were seething, although they hung around and chatted.

But having reviewed my notes and the slides my view is different. John Cook started the presentation by trying to establish his expert authority on the global warming hypothesis. Then he let slip that he does not believe all global warming is from rising greenhouse gas levels. The centrepiece was the 97.4% scientific consensus paper where he was lead author. But, as Cook himself admitted, the survey looked for support for the most banal form of global warming, and the surveyed papers were not all written by climate scientists. Yet Barak Obama is enacting policy based on the false impression of a scientific consensus of dangerous warming.

Then in dissing an alternative viewpoint from actual scientists, Cook has implicitly undermined years of hard campaigning and entryism by green activists in getting nearly every scientific body in the world to make propaganda statements in support of the catastrophic global warming hypothesis and the necessity of immediate action to save the planet. Cook then parodied his own “four Hiroshima bombs a second” widget, before finishing off with a flickering gross misrepresentation of the sceptics, a number of whom were in the room listening politely.

About the final question was from someone who asked about why nearly all the questions were coming from sceptics, when the vast majority of the people in the room were in support of the “science”. At the end there was polite applause, and the room quickly emptied. I think the answer to the lack of questions was the embarrassment people felt. If John Cook is now the leading edge of climate alarmism, then the game is up.

Kevin Marshall


  1. This was in response to a question from blogger Katabasis pointed out some papers that were clearly not climate science, I believe using Jose Duarte’s list.

Michael Mann’s bias on Hockey Sticks

Two major gripes of mine with the “Climate Consensus” are their making unsubstantiated claims from authority, and a total failure to acknowledge when one of their own makes stupid, alarmist comments that contradict the peer-reviewed consensus.

An example is from Professor Michael Mann commenting on his specialist subject of temperature reconstructions of the past for a Skeptical science “97% Consensus” spin-off campaign.

I will break this statement down.

“There are now dozens of hockey sticks and they all come to the same basic conclusion”

His view is that warming is unprecedented, shown by dozens of hockey sticks that replicate his famous graph in the UNIPCC Third Assessment Report of 2001.

Rather than look at the broader picture warming being unprecedented on any time scale1, I will concentrate on this one thousand year period. If a global reconstruction shows a hockey stick, then (without strong reasoned arguments to the contrary) one would expect the vast majority of temperature reconstructions from actual sites by various methods to also show hockey sticks, in their Medieval Warm Period Project, have catalogued loads of these reconstructions from all over the world. They split them into two categories – quantitative and qualitative differentials in the average temperature estimates between the peak of the medieval warm period and now.

It would seem to me that Mann is contradicted by the evidence of dozens of studies, but corroborated by only a few. Mann’s statement of dozens of hockey sticks reaching the same basic conclusion ignores the considerable evidence to the contrary.

“The recent warming does appear to be unprecedented as far back as we can go”

Maybe, as Mann and his fellow “scientists” like to claim, that the people behind this website are in “denial” of the science. Maybe they have just cherry-picked a few studies from a much greater number of reconstructions. So let us look at the evidence the SkS team provide. After all, it is they who are running the show. Under their article on the medieval warm period, there is the following graph of more recent climate reconstructions.

It would seem the “Mann EIV” reconstruction in green does not show a hockey stick, but flat (or gently rising) temperatures from 500-1000 AD; falling temperatures to around 1800; then an uptick starting decades before the major rise in CO2 levels post 1945. The twentieth century rise in temperatures appears to be about half the 0.7oC recorded by the thermometers, leading one to suspect that reconstructions understate past fluctuations in temperature as well. The later Ljungqvist reconstructions shows a more pronounced medieval warm period and a much earlier start of the current warming phase, in around 1700. This is in agreement with the Moberg and Hegerl reconstructions. Further the Moberg reconstruction has a small decline in temperatures post 1950.

Even worse, the graphic was from the Pages2K site. On temperature reconstructions of the last two millennia Pages2K state:-

Despite significant progress over the last few decades, we still do not sufficiently understand the precise sequence of changes related to regional climate forcings, internal variability, system feedbacks, and the responses of surface climate, land-cover, and bio- and hydro-sphere.

Furthermore, at the decadal-to-centennial timescale we do not understand how sensitive the climate is to changes in solar activity, frequency of volcanic eruptions, greenhouse gas and aerosol concentration, and land cover.

So Michael Mann’s statement if warming being unprecedented is contradicted by peer-reviewed science. Skeptical Science published this statement when it was falsified by Mann’s own published research and that of others.

“But even if we didn’t have that evidence, we would still know that humans are warming the planet, changing the climate and that represent a threat if we don’t do something about it”

There is no corroborating evidence to the climate models from temperature reconstructions. In fact, empirical data shows that the models may be claiming as human-caused temperature increases that are naturally-caused, but for reasons not fully understood. So the “knowing” must be assumed to be from belief, just as the threat and the ability of the seven billion “us” to counter that threat are beliefs as well.

Kevin Marshall



  1. The emergence from the Younger Dryas cooling period 11,500 years ago was at least 10 times the warming of the past 100 years, and was maybe in a period of less than 300 years. See WUWT article here, or the emerging story on the causes here.

Climatologists and gambling addicts

At Jo Nova’s unthreaded Carbon500 asks

How can the opposing points of view be effectively communicated without using too much temperature data?

There are no easy answers. Start quoting one set of figures and an “expert scientist” will counter with some other figures, call you a denier and say you know nothing.

An alternative approach is to compare climate “experts” with experts in other fields. Hundreds of expert scientists, over nearly three decades, should have gained a track record in predictions through their understanding of the climate system, and learnt from their mistakes. The public relations aspect should now be in emphasising their scientific achievements in predictions and the increasing quality of their work. The PR should not be in banal statements, saying how much they all agree, and denigrating the opposition.

Let me give an analogy. Suppose someone claims, after years of study, to have a developed a scientific system for predicting the winners of horse races. How would you distinguish between that person being a true expert or just a gambling addict, whose system is just a sophisticated way of denying their problem?

Using the climate consensus approach, the true expert would be somebody who has published on the subject in the peer-reviewed literature, and has a lot of similar experts reaching similar conclusions. The gambling addict would be marked out by the one who goes it alone, rejecting the opinion of other “experts”.

My approach would be to evaluate on whether the betting system actually works.

  1. As the purpose of placing a bet is to win, one would expect a minimum requirement is to make money. That is not that you get a winner ever time, but over a series of bets to more than break even.
  2. From a human point of view, a way to identify the expert to see observe they cope with losses. The true expert would learn from the mistakes and use this to improve the predictive ability of the system. Over time, the profit margin would get greater. The gambling addict would come up with a plethora of excuses why their system did not work, then proclaim that a winning streak is just around the corner.
  3. A true expert would know the limits if their system, whilst the addicted gambler would make totally exaggerated claims about the precision and accuracy of their unimpeachable system.

The analogy does break down after this. Catastrophic global warming is a belief system, mainly deriving from extreme left-environmentalist political perspectives. CAGW is a collective belief system, not an isolated individual. The consequences of the climate alarmists to recognize their failure in understanding go far beyond that of someone with a gambling problem.

Theconsensusproject – unskeptical misinformation on Global Warming


Following the publication of a survey finding a 97% consensus on global warming in the peer-reviewed literature the team at “” launched website. Here I evaluate the claims using two of website owner John Cook’s own terms. First, that “genuine skeptics consider all the evidence in their search for the truth”. Second is that misinformation is highly damaging to democratic societies, and reducing its effects a difficult and complex challenge.

Applying these standards, I find that

  • The 97% consensus paper is very weak evidence to back global warming. Stronger evidence, such as predictive skill and increasing refinement of the human-caused warming hypothesis, are entirely lacking.
  • The claim that “warming is human caused” has been contradicted at the Sks website. Statements about catastrophic consequences are unsupported.
  • The prediction of 8oF of warming this century without policy is contradicted by the UNIPCC reference.
  • The prediction of 4oF of warming with policy fails to state this is contingent on successful implementation by all countires.
  • The costs of unmitigated warming and the costs of policy and residual warming are from cherry-picking from two 2005 sources. Neither source makes the total claim. The claims of the Stern Review, and its critics, are ignored.

Overall, by his own standards, John Cook’s Consensus Project website is a source of extreme unskeptical misinformation.



Last year, following the successful publication of their study on “Quantifying the consensus on anthropogenic global warming in the scientific literature“, the team at (Sks) created the spinoff website

I could set some standards of evaluation of my own. But the best way to evaluate this website is by Sks owner and leader, John Cook’s, own standards.

First, he has a rather odd definition of what skeptic. In an opinion piece in 2011 Cook stated:-

Genuine skeptics consider all the evidence in their search for the truth. Deniers, on the other hand, refuse to accept any evidence that conflicts with their pre-determined views.

This definition might be totally at odds with the world’s greatest dictionary in any language, but it is the standard Cook sets.

Also Cook co-wrote a short opinion pamphlet with Stephan Lewandowsky called The Debunking Handbook. It begins

It’s self-evident that democratic societies should base their decisions on accurate information. On many issues, however, misinformation can become entrenched in parts of the community, particularly when vested interests are involved. Reducing the influence of misinformation is a difficult and complex challenge.

Cook fully believes that accuracy is hugely important. Therefore we should see evidence great care in ensuring the accuracy of anything that he or his followers promote.


The Scientific Consensus

The first page is based on the paper

Cooks definition of a skeptic considering “all the evidence” is technically not breached. With over abstracts 12,000 papers evaluated it is a lot of evidence. The problem is nicely explained by Andrew Montford in the GWPF note “FRAUD, BIAS AND PUBLIC RELATIONS – The 97% ‘consensus’ and its critics“.

The formulation ‘that humans are causing global warming’ could have two different meanings. A ‘deep’ consensus reading would take it as all or most of the warming is caused by humans. A ‘shallow’ consensus reading would imply only that some unspecified proportion of the warming observed is attributable to mankind.

It is the shallow consensus that the paper followed, as found by a leaked email from John Cook that Montford quotes.

Okay, so we’ve ruled out a definition of AGW being ‘any amount of human influence’ or ‘more than 50% human influence’. We’re basically going with Ari’s porno approach (I probably should stop calling it that) which is AGW= ‘humans are causing global warming’. e.g. – no specific quantification which is the only way we can do it considering the breadth of papers we’re surveying.

There is another aspect. A similar methodology applied to social science papers produced in the USSR would probably produce an overwhelming consensus supporting the statement “communism is superior to capitalism”. Most papers would now be considered worthless.

There is another aspect is the quality of that evidence. Surveying the abstracts of peer-reviewed papers is a very roundabout way of taking an opinion poll. It is basically some people’s opinions of others implied opinions from short statements on tangentially related issues. In legal terms it is an extreme form of hearsay.

More important still is whether as a true “skeptic” all the evidence (or at least the most important parts) has been considered. Where is the actual evidence that humans cause significant warming? That is beyond the weak correlation between rising greenhouse gas levels and rising average temperatures. Where is the evidence that the huge numbers of climate scientists have understanding of their subject, demonstrated by track record of successful short predictions and increasing refinement of the human-caused warming hypothesis? Where is the evidence that they are true scientists following in the traditions of Newton, Einstein, Curie and Feynman, and not the followers of Comte, Marx and Freud? If John Cook is a true “skeptic”, and is presenting the most substantial evidence, then climate catastrophism is finished. But if Cook leaves out much better evidence then his survey is misinformation, undermining the case for necessary action.


Causes of global warming

The next page is headed.

There is no exclusion of other causes of the global warming since around 1800. But, with respect to the early twentieth century warming Dana Nuccitelli said

CO2 and the Sun played the largest roles in the early century warming, but other factors played a part as well.

However, there is no clear way of sorting out the contribution of the relative components. The statement “the causes of global warming are clear” is false.

On the same page there is this.

This is a series of truth statements about the full-blown catastrophic anthropogenic global warming hypothesis. Regardless of the strength of the evidence in support it is still a hypothesis. One could treat some scientific hypotheses as being essentially truth statements, such as that “smoking causes lung cancer” and “HIV causes AIDS”, as they are so very strongly-supported by the multiple lines of evidence1. There is no scientific evidence provided to substantiate the claim that global warming is harmful, just the shallow 97% consensus belief that humans cause some warming.

This core “global warming is harmful” statement is clear misinformation. It is extremely unskeptical, as it is arrived at by not considering any evidence.


Predictions and Policy

The final page is in three parts – warming prediction without policy; warming prediction with policy; and the benefits and costs of policy.

Warming prediction without policy

The source info for the prediction of 8oF (4.4oC) warming by 2100 without policy is from the 2007 UNIPCC AR4 report. It is now seven years out of date. The relevant table linked to is this:-

There are a whole range of estimates here, all with uncertainty bands. The highest has a best estimate of 4.0oC or 7.2oF. They seem to have taken the highest best estimate and rounded up. But this scenario is strictly for the temperature change at 2090-2099 relative to 1980-1999. This is for a 105 year period, against an 87 year period on the graph. Pro-rata the best estimate for A1F1 scenario is 3.3oC or 6oF.

But a genuine “skeptic” considers all the evidence, not cherry-picks the evidence which suit their arguments. If there is a best estimate to be chosen, which one of the various models should it be? In other areas of science, when faced with a number of models to use for future predictions the one chosen is the one that performs best. Leading climatologist, Dr Roy Spencer, has provided us with such a comparison. Last year he ran 73 of the latest climate CIMP5 models. Compared to actual data every single one was running too hot.

A best estimate on the basis of all the evidence would be somewhere between zero and 1.1oC, the lowest figure available from any of the climate models. To claim a higher figure than the best estimate of the most extreme of the models is not only dismissing reality, but denying the scientific consensus.

But maybe this hiatus in warming of the last 16-26 years is just an anomaly? There are at possibly 52 explanations of this hiatus, with more coming along all the time. However, given that they allow for natural factors and/or undermine the case for climate models accurately describing climate, the case for a single extreme prediction of warming to 2100 is further undermined. To maintain that 8oF of warming is – by Cook’s own definition – an extreme case of climate denial.

Warming prediction with policy

If the 8oF of predicted human-caused warming is extreme, then a policy that successfully halves that potential warming is not 4oF, but half of whatever the accurate prediction would be. But there are further problems. To be successful, that policy involves every major Government of developed countries reducing emissions by 80% (least including USA, Russia, EU, and Japan) by around 2050, and every other major country (at least including Russia, China, India, Brazil, South Africa, Indonesia and Ukraine) constraining emissions at current levels for ever. To get all countries to sign-up to such a policy combatting global warming over all other commitments is near impossible. Then take a look at the world map in 1925-1930 and see if you could reasonably have expected those Governments to have signed commitments binding on the Governments of 1945, let alone today. To omit policy considerations is an act of gross naivety, and clear misinformation.

The benefits and costs of policy

The benefits and costs of policy is the realm of economics, not of climatology. Here Cook’s definition of skeptic does not apply. There is no consensus in economics. However, there are general principles that are applied, or at least were applied when I studied the subject in the 1980s.

  • Modelled projections are contingent on assumptions, and are adjusted for new data.
  • Any competent student must be aware of the latest developments in the field.
  • Evaluation of competing theories is by comparing and contrasting.
  • If you are referencing a paper in support of your arguments, at least check that it does just that.

The graphic claims that the “total costs by 2100” of action are $10 trillion, as against $20 trillion of inaction. The costs of action are made up of more limited damages costs. There are two sources for this claim, both from 2005. The first is from “The Impacts and Costs of Climate Change”, a report commissioned by the EU. In the Executive Summary is stated:-

Given that €1.00 ≈ $1.20, the costs of inaction are $89 trillion and of reducing to 550ppm CO2 equivalent (the often quoted crucial level of 2-3 degrees of warming from a doubling of CO2 levels above pre-industrial levels) $38 trillion, the costs do not add up. However, the average of 43 and 32 is 37.5, or about half of 74. This gives the halving of total costs.

The second is from the German Institute for Economic Research. They state:-

If climate policy measures are not introduced, global climate change damages amounting to up to 20 trillion US dollars can be expected in the year 2100.

This gives the $20 trillion.

The costs of an active climate protection policy implemented today would reach globally around 430 billion US dollars in 2050 and around 3 trillion US dollars in 2100.

This gives the low policy costs of combatting global warming.

It is only by this arbitrary sampling of figures from the two papers that the websites figures can be established. But there is a problem in reconciling the two papers. The first paper has cumulative figures up to 2100. The shorthand for this is “total costs by 2100“. The $20 trillion figure is an estimate for the year 2100. The statement about the policy costs confirms this. This confusion leads the policy costs to be less than 0.1% of global output, instead of around 1% or more.

Further the figures are contradicted by the Stern Review of 2006, which was widely quoted in the UNIPCC AR4. In the summary of conclusions, Stern stated.

Using the results from formal economic models, the Review estimates that if we don’t act, the overall costs and risks of climate change will be equivalent to losing at least 5% of global GDP each year, now and forever. If a wider range of risks and impacts is taken into account, the estimates of damage could rise to 20% of GDP or more.

In contrast, the costs of action – reducing greenhouse gas emissions to avoid the worst impacts of climate change – can be limited to around 1% of global GDP each year.

The benefit/cost ratio is dramatically different. Tol and Yohe provided a criticism of Stern, showing he used the most extreme estimates available. A much fuller criticism is provided by Peter Lilley in 2012. The upshot is that even with a single prediction of the amount and effects of warming, there is a huge range of cost impacts. Cook is truly out of his depth when stating single outcomes. What is worse is that the costs and effectiveness of policy to greenhouse emissions is far greater than benefit-cost analyses allow.



To take all the evidence into account and to present the conclusions in a way that clearly presents the information available, are extremely high standards to adhere to. But does not just fail to get close to these benchmarks, it does the opposite. It totally fails to consider all the evidence. Even the sources it cites are grossly misinterpreted. The conclusion that I draw is that the benchmarks that Cook and the team have set are just weapons to shut down opponents, leaving the field clear for their shallow, dogmatic and unsubstantiated beliefs.

Kevin Marshall



  1. The evidence for “smoking causes lung cancer” I discuss here. The evidence for “HIV causes AIDS” is very ably considered by the AIDS charity AVERT at this page. AVERT is an international HIV and AIDS charity, based in the UK, working to avert HIV and AIDS worldwide, through education, treatment and care. – See more here.
  2. Jose Duarte has examples here.