Cherry Picking, Black Swans and Falsifiability

Whenever a skeptic points out a new paper or journal article refuting some claim made by the theory of anthropogenic global warming, climate change alarmists often shout “cherry picking!” Evidently, most climate change true believers do not understand how science works or how theories are tested. Scientific theories must make predictions by which they can be tested. Providing evidence that AGW has failed in its predictions is not cherry picking, it is refutation. Unfortunately, when confronted with failed predictions the standard alarmist answer is to disavow the predictions. They will say that those are not predictions at all, they are projections—and that means AGW is not a scientific theory at all.

I recently received a long email from a friend, who is a global warming believer, regarding my earlier post, “Why I Am A Global Warming Skeptic.” This friend is an educated person, a philosopher but not a scientist. In reading his objections and counter arguments to my points I found a number of common misunderstandings that arise when laymen try to jump into a scientific debate. In this report I will address some, but by no means all of my friend's objections.

Having written previously on how to judge global warming as a scientific theory, perhaps it is time to recap some of that discussion. In The Resilient Earth, we wrote about the philosophy of science and how scientific theories are formulated and then validated. Science is both a body of knowledge and an approach to understanding nature by gaining more knowledge. It is based on gathering empirical evidence.

Empirical means simply what belongs to or is the product of experience or observation. If you can touch it, smell it, feel it, see it or measure it, it's empirical. Collecting empirical data through observation or experimentation is how the correctness of theories is established. It is also how theories are found to be invalid.

An important point is that, in order to be testable, a theory must make predictions about how nature behaves. This idea comes from the work of Karl Popper, one of the important philosophers of the 20th century. Popper, who early in life was a communist, came to consider democracy the only form of government in which reason is celebrated. He identified Plato, Marx and Hegel as the greatest enemies of democracy in his 1945 book The Open Society and Its Enemies. As interesting as Popper's philosophy regarding society and politics was, it is his work on the philosophy of science that interests us here.

Popper made the following observations as to what makes a good scientific theory:

  1. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations.

  2. Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory — an event which would have refuted the theory.

  3. Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.

  4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

  5. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.

  6. Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory. (I now speak in such cases of "corroborating evidence.")

  7. Some genuinely testable theories, when found to be false, are still upheld by their admirers — for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status.

Popper made a distinction between what he termed conditional scientific predictions, which have the form “If X takes place, then Y will take place,” and unconditional scientific prophecies, which have the form “Y will take place.” It is the former rather than the latter which are typical of the natural sciences. This means that predictions made by scientific theories are typically conditional and limited in scope—taking the form of a hypothetical assertion stating that certain specified changes will come about if particular preceding events take place. Conversely, if X takes place and Y does not, then the hypothesis must be false.

The Cherry Picking Argument

The first point of contention in this discussion is the time worn claim of “cherry picking.” This charge is often heard when a skeptical article cites papers in support of its position. The complaint as lodged by my friend goes like this:

You are surely here guilty of cherry picking a couple of published articles that go your way (at least when read in a certain way) out of all the thousands of articles in the literature, most of which don't go your way. To form a fair assessment of the state of the science you need to look at all of it, not just take one or two articles out of context.

The problem here is, if you don't cite some recent papers then you have provided no references and will be accused of making unsubstantiated claims (unless, of course, you are presenting experimental observations of your own). If you cite a few representative articles to underline your point you are accused of cherry picking. According to Wikipedia, cherry picking is the act of pointing at individual cases or data that seem to confirm a particular position, while ignoring a significant portion of related cases or data that may contradict that position. While this is certainly a bad thing when dealing with data and collections of repeated experimental results, the definition does not necessarily extend to general scientific argumentation.

The reason for this lies in the concept of falsifiability—a condition that must be met by all valid scientific theories. Popper noted that it is easy to obtain evidence in favor of virtually any theory, and he consequently held that such corroboration should count scientifically only if it is the positive result of a genuinely “risky” prediction. Risky here means that the prediction could conceivably have been false. For Popper, a theory is scientific only if it is refutable by a conceivable event. Every genuine test of a scientific theory, then, is logically an attempt to refute or to falsify it, and one genuine counter-instance falsifies the whole theory.

Basically, a theory must make predictions about how nature behaves so that the validity of the theory can be tested through experimentation and/or observation. For example, say I claim that all swans are white, based on my direct observation of a sample of swan populations. If someone finds a single black swan and is able to document the observation (e.g. by taking a picture or capturing the beast) then the white swan theory is disproved. In this case a single contradicting observation is sufficient to invalidate the theory.

It is possible that a disproved theory can be modified to better fit nature as observed—the white swan theory could be amended to say “most swans are white.” In this case the new theory could not be disproved by a single black swan siting, it would take finding a numerical majority of non-white swans to disprove it. Scientific philosophy would say that the first white swan theory is a stronger theory, the assertion that all swans are white being much more restrictive than the modified “most swans” theory. Simply put, the stronger the theory the simpler it is to disprove, the argument being that an easily disprovable theory which stands the test of time is stronger than a theory, which would take a much larger effort to debunk. It takes a deeper understanding of the assertions made by a theory to know what kind of argument is needed to disprove it.

When it comes to the AGW theory, which states that human generated CO2 is the reason for increasing world temperature, there is some wiggle room for its proponents, but not much. If it can be shown that the sum total of other contributing factors is more influential than CO2 then the theory is proven false. Any valid observation which shows CO2's influence is less important to climate change than other factors diminishes the validity of the theory. Moreover, if many of the predictions made by the theory are shown to be false then the theory is weakened—the death of a thousand cuts scenario.

If a theory claims to explain climate change and new work shows that there are phenomena that the theory does not explain then that theory is incomplete. If nature shows assertions made by the theory to be wrong then the theory is false. The papers I cited showed that there is dispute among scientists, that nature is still serving up big surprises that climate science is at a loss to explain, that the science is not settled. Given this evidence, for any layman to state otherwise is preposterous but as Popper himself said, “irrationalism will use reason too, but without any feeling of obligation.”

Furthermore, scientific arguments are not won by counting the number of papers written either for or against a particular theory. As was demonstrated above, a single counter example can be sufficient to disprove a theory, no matter how many scientists think the theory to be correct. In science there is an ultimate arbiter—nature.

Returning to the charge of cherry picking, the reason I chose the papers I did was because they were both recent, written by known climate scientists who are not fringe denier kooks, and (yes) they help to support my position. The intent is not to provide an argument from authority, another typical logical fallacy, but to show that the arguments presented do originate from trustworthy sources. Even so, that is immaterial to the real argument.

Those papers explicitly stated that mechanisms other than CO2 are noticeably involved in climate regulation. Moreover, the postulated positive feedback mechanism linking CO2 and water vapor does not respond in the expected way. Far from being a minor detail, this directly refutes part of the AGW theory as presented to the public.

If someone purposefully selects data or data sets so a study will give desired, predictable results—which may be misleading or even completely contrary to actuality—then the charge of cherry picking is valid. Michael Mann's use of selected tree ring data sets and then manipulating them statistically to produce the infamous “hockey stick” graph, that was cherry picking. Citing specific evidence that refutes fundamental assertions made by a theory, that is not cherry picking. Under the latter circumstance, the cherry picking retort is weak argumentation and intellectually lazy to boot. Dispute the articles, challenge the assertions, or provide some counter examples of your own but for heavens sake, argue the matter at hand.

Judged and found wanting

Returning to the subject of proving or disproving the theory of anthropogenic global warming, there are only three possibilities here: AGW makes no predictions and hence is not a scientific theory; AGW depends on vague feedback mechanisms that must be constantly reinterpreted, making AGW a very weak theory and scientifically useless; or the predictions made by climate scientists about the effects of AGW are just that, predictions, and if those predictions can be shown to not be true then AGW is a false theory.

It is hard to believe that any pro-AGW climate scientist would agree to the first interpretation, that AGW is simply not a scientific theory, so we can eliminate all that crap about AGW not making any predictions. If it is a theory it must make predictions, it must be falsifiable based on empirical evidence.

In the second scenario, the argument is often made that AGW is correct but not perfect, that it is getting better and its predictions more accurate every day. This fits Popper's final observation about theories, where ad hoc modifications are constantly needed to rescue a theory from falsification. Since such actions rescue a theory from refutation only at the price of destroying or lowering its scientific status—again an outcome that no AGW true believer would accept—we will move on to the final possibility.

The final scenario is that AGW as formulated does indeed qualify as a scientific theory. In this case it must make specific predictions that permit the theory to be falsified. So what are the strongest predictions made by the AGW theory? Let us first identify AGW's primary tenent. That is that human CO2 emissions are causing Earth's temperature to rise. What are the observed facts?

  • Are CO2 levels rising? The evidence seems to indicate that this is true.

  • Is the increase in atmospheric CO2 being caused by human activity? There is some debate over how much is due to nature and how much due to man but let's simply accept this assertion as well.

  • What does AGW theory predict should happen as a result of these conditions? The obvious answer is that global temperature should rise.

In fact, back in 1988, NASA’s in house climate alarmist James Hansen presented a prediction of steadily rising temperatures to Congress. Has this prediction been substantiated, proving that AGW is a valid theory? It should be obvious from the graph below that Hansen got it wrong.

Not only was Hansen wrong back in 1988, all the models used by all the AGW proponents managed to miss the leveling off and slight downturn in temperature rise that started in 1995. In an email to Michael Mann, Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research (NCAR), asked “where the heck is global warming?” He went on to explain:

The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t. The CERES data published in the August BAMS 09 supplement on 2008 shows there should be even more warming: but the data are surely wrong. Our observing system is inadequate.

Trenberth was a lead author of the 1995, 2001, and 2007 IPCC Scientific Assessment of Climate Change. If he had any sense of shame he would give back that Nobel Prize he shares (as a member of the IPCC) with Al Gore.

Furthermore, Dr. Phil Jones from the UK's Climate Research Unit (CRU), has recently conceded the possibility that the world was warmer in medieval times than now–suggesting global warming may not be a man-made phenomenon. He is quoted as saying that for the past 15 years there has been no “statistically significant” warming. Yet the yearly averaged atmospheric CO2 level has continued to steadily rise. What we have here, as Popper showed, is a false theory.

When contradicting evidence is found you must reevaluate the theory that made the discredited assertions. Based on direct measurement, AGW's fundamental prediction that an increase in CO2 levels causes an increase in temperature is false, therefore AGW is a false theory. The correct answer might not be known but the wrong answer is still wrong. In the mean time, climate scientists must stop making unsubstantiated claims or accept that their theory has been proven false by the very predictions they use to argue their case.

Be safe, enjoy the interglacial and stay skeptical.

Post Script: This is the second of two articles that centered on the philosophy of Karl Popper. The first article was “More Fictitious Hurricane Predictions.”

Addendum: There has been quite a flurry of comments regarding the “Hansen vs reality” graph I used in the article above. This graph has been criticised for presenting only the “A” scenario while Hansen actually presented three scenarios back in 1988 in his famous presentation to Congress. The prediction scenarios, labeled A, B and C, were based on a paper by Hansen et al. that had recently been published. Here is an updated graph showing all three scenarios plus NASA RSS satellite data and GISS surface temperature data.

Each of the three scenario described forcing projections for CO2, CH4, N2O, CFC11, CFC12 and the other Montreal Protocol traces gases as a group. Hansen is on record as saying that scenario B was the “most plausible,” and that it was his preferred scenario. As can be seen, there was substantial divergence between Scenario B in 2007 and both the RSS satellite temperature and the GISS temperature surface temperature series.

According to Steve McIntyre, “Hansen's statement that Scenario B was "used" in his 1988 testimony is very misleading: Hansen's oral testimony called Scenario A the "Business as Usual" scenario and mentioned Scenario B only in maps purportedly showing extraordinary projected warming in the SE USA.” Scenario C assumed that atmospheric CO2 levels were stabilized at 368 ppm in 2000 but that level has already been surpassed, rendering that prediction moot. If anything scenario C's curve should be below observed temperatures, but this is obviously not the case.

So there you have it: the graph I used in the article above does compare measured temps only with scenario A and I am guilty of not presenting the other scenarios. However, the assumptions on which C was based have not come to pass so it is now superfluous. And since Hansen chose to put the worst case scenario A forward, obviously trying to alarm members of Congress and the public, I feel absolutely no shame in using it in the comparison above. Scenario A was an exaggeration of Hansen's own creation and if you choose to persuade by exaggeration you should expect your case to die by exaggeration.

The graph and the background data presented here are taken from an article by Steve McIntyre at There is a lot of additional information at that link which is well worth reading. Thanks to the anonymous reader who posted this link and several others below.

"prediction" is not prediction

In the topmost figure, Hansen's "prediction" is not a prediction. It is easy to see that this is so as the relation from the predictions that are made by a model and the elements of a statistical population is one-to-one. One statistically tests a model by comparison of the predicted to the observed relative frequencies of the various possible outcomes of the events in the associated population in a sample of observed events that is drawn from this population but Hansen's "prediction" generates no relative frequencies and references no population. It follows that Hansen's claim is non-falsifiable thus lying outside science.

Thanks for a great article!

You might find my article on climate useful. I worked with the raw temperature data for the current interglacial period and it was easy to show there is no global warming problem:
"Climate science: observations vs. models"

richard moore

A Skeptical Look at Karl Popper

Readers may in interested in the essay “A Skeptical Look at Karl Popper” by Martin Gardner, published in the Skeptical Inquirer back in 2001.

Submit away

1) There are a large number of models that have been used to make predictions. Often the output of a number of different models are combined to form an “ensemble.” The primary IPCC model, however, is the one developed and maintained by NASA GISS. The source code for it is constantly updated and can be found online (Google is your friend).

2) Please do send me your paper. We will certainly consider publishing it as a guest article on our site, after a little peer review :-)

Cherry Pickin' Science

Cherry Pickin’ Science

Critical reflection starts the dialectic,
Driving the zealot as well as the skeptic.

But one must check the hypothesized notions,
With measures of nature, it’s states and its motions.

If you’ve tried, in earnest, to prove yourself wrong,
Failure to do so may support a new song.

For Science advances, according to Popper,
By kicking hypotheses out of the hopper.

“Cherry pickin’ the literature for hypothesis support,
In Science is seen as attempt to distort.

Rather, pick cherries for hypothesis refutation,
That should mark true, one’s scientific reputation.

“Honesty with self” is by far the best move;
Seek to refute, never to prove.

-- Anonymous, 2009

That is very funny

Thanks for posting it. So few people seem to see the humorous side of science.

CO2 feedback

One of the debates I see from time-to-time on ClimateGate and elsewhere involves CO2 (and maybe NH4) "feedback". It appears to be the next fallback since there is no evidence that CO2 has any direct influence on temperature.

The feedback theory seems to be unsettled. Some scientists claim that greenhouse physics is not even applicable.

Then there seems to be empirical evidence that CO2 has been much higher during ice ages and going into at least one ice age, so whatever feedback was evidently not adequate to create warming.

Any comments on that?

We are in partial agreement

Your statement is pretty much inline with what I have been saying in some of my articles, except that CO2 does have a direct influence on temperature—it's just a diminishingly small one. Certainly the link to water vapor is not as previously thought. The greenhouse effect is real and it does affect Earth's climate, but there are many other, evidently stronger, influences as well.

Popper, Kuhn, Feyerabend as well as Feynman


Your post was terrific, and timely. This morning, I was wishing I had the time to write a post like yours, and examine not just Popper but also Kuhn, and Feyerabend's theory of science, and see what they have to say about how our current AGW warmists have behaved.

Like the blind guys describing the elephant, I think Popper, Kuhn, and Feyerbend all can be used to accurately describe and shed light on how what the climate scientists are doing is wrong, and in some ways typical and representative of other scientific fads in the past.

However, I really don't understand much of those guys -- I switched out of philosophy for a good reason. But I do understand Feynman, and what he wrote in Cargo Cult Science. I read Cargo Cult Science, and I look at the AGW crowd, and I read Cargo Cult Science, and I look at the AGW crowd, and I wonder: have the considered best practices of science really changed and perverted so much across all sciences, or just in climate research?

Feynman is on the way

We quoted Kuhn in The Resilient Earth but Feyerabend is too much an anarchist for my taste. I have, however, an upcoming post that centers on Richard Feynman. He was worried about bad practices across all the sciences more than 35 years ago.

Falsification of a theory

I enjoy this blog and have learned from the clarity of your discussion. Being an amateur with a good scientific background, the question occurs to me whether it's completely appropriate to subject the AGW theory to an up or down vote - could they be right in some sense, but wrong in toto - for example, correct that increasing concentrations of CO2 tend to increase global temperature, but wrong (by a large factor, if Lord Monckton and others are correct) about the level - and even the sign - of positive feedbacks crucial to this prediction. The arrogance of proclamations such as "the science is settled" really invites refutation - and as presented, the evidence for the kind of future that Hansen et al. are predicting seems increasingly scanty - but that may be a matter of degree: is that the same as refutation? AGW has been compared to Lysenkoism - the concept that became dominant in the Soviet Union that acquired characteristics can be inherited: to my knowledge,except in cases of specific genetic damage, that theory is totally false - not accurate in any sense. AGW is perhaps different in that some of the basic ideas may be correct, but they have been stretched out of all proportion for political reasons - so the while the specific prediction is entirely false, parts of the theory may be true. Obviously, if you make several incorrect predictions, confidence in the underlying theory would have to be weak at best - but in a case with so many moving parts is proving a prediction wrong the same as invalidating a theory?

The number of parts does not matter

The number of "parts" involved in the system doesn't really matter. The theory predicts gross behavior. The gas law predicts the behavior of an arbitrary number of parts, atoms or molecules in a gas, yet its predictions are close enough to reality to be considered true (or at least useful). AGW theory says it is CO2 that matters, the underlying mechanisms are not specified and are unimportant when it comes to falsifying the theory. If CO2 goes up and temperatures do not over a sufficiently long period of time AGW is not correct. Remember, it was the AGW extremists who hung the whole theory on human CO2 emissions. How long is "sufficient" remains an item for debate.

Cherry Picking, Black Swans and Falsifiability


Your summary of Popper's criteria are fairly accurate, but also reveal the weakness at the heart of his "falsifiability" argument.

In ALL sciences, 'facts' are only provisional. That is, it's through the accumulation of a statistically significant amount of data, that we slowly ONLY approach 'truth' or 'falsehood'. So no alleged example – or small set of examples – can either prove OR falsify a theory. And even LARGE sets of data can, at best, only increase confidence – but not PROVE – any 'fact'.

So much for "Falsifiability".

That's exactly wrong

Your reasoning is false. If you propose a theory that says lighter objects fall slower than heavy objects in a vacuum the prediction can be tested. One verifiable example proves the theory wrong. Not statistically wrong, not a little bit wrong but absolutely WRONG. Falsifiability is not only possible, it works. As Popper noted, it is proving things that is hard and usually relies on confidence built over time—your statistical approach. But it is possible to build confidence in a theory's correctness more rapidly than relying on a statistical sampling of events.

This is tied to the riskiness of a prediction. When Einstein predicted that the gravitational field of a star would bend light passing by it, that was a bold prediction. A number of researchers around the world scrambled to prove Einstein wrong by direct observation. They failed, light was observed to be deflected by strong gravitational fields. Because the assertion was contrary to the conventional wisdom of the time, the “consensus” view, its confirmation greatly strengthened Einstein's theory. It was not proof but, in Popper's terms, corroboration. If the prediction had proven false, however, Einstein's theory would have been shown to be false. Not kind of false, not probably false, the theory as it stood would have been disproven.

Moreover, it can certainly be proven that some chemical compounds will explode under the right conditions, or that enough ionizing radiation will damage living cells. How about the fact that oxygen is necessary for humans to live? Do you accept that as proven fact or do you just feel “really confident” about the assertion? Your belief that we can neither prove nor disprove anything is the same kind of muzzy headed thinking that lies at the root of cultural relativism and other politically correct foolishness. Such specious thinking and vacuous intellectual twaddle may work in the social “sciences” but in real science it does not. The weakness does not lie at the heart of falsifiability but with your illogical world view.



I won't list references that, since David Hume's classic 1730's to 1777 treatises, agree that inductive reasoning can NEVER lead to absolute truth or falsehood.

The bending of starlight by the mass of the sun, observed in 1916 by Eddington, made it quite likely that Einstein's General Relativity was a 'good theory'. But the 'proof' that it wasn't definitive is the need physicists had to keep testing it. If Eddington's measurements had been negative, other scientists would nonetheless also have continued to test it.

Observations that are severely perturbed by 'noise' require a great deal of replication to provide trends in mean values that are statistically significant (e.g., as in climatology). When noise is very low, a few measurements can quickly provide high LEVELS of confidence of 'proof' or 'falsity'. The latter kind are 'more easily' accepted as 'facts'.

But both are subject to Hume's lessons: matters of observation and therefore, inductive reasoning (empirical, factual, therefore scientific) can never be proved or disproved with the logical certainty of deductive reasoning (e.g, of logic and of a great deal of mathematics)!


No theory can ever be proven under Popper's rules. It can only fail to be refuted. The more intensive, competent, and prolonged the attempts are, the more scientists will tend to rely one it, and the less inclined they will be to mount trivial or carelessly designed and thought-out challenges or tests. After a while, it may be taken as a "given", unless there are holes and areas it doesn't cover.

In physics the Standard Model has so far passed all tests, but it doesn't include some significant areas, like gravity. So true physicists dearly hope someone will come up with a test the SM will fail, so they can maybe get at some better idea or hypothesis that will fill in the holes.

AGW hasn't dared to hang its hat on any of its "projections". Doug, above, mis-states the question: "Has this prediction been substantiated, proving that AGW is a valid theory?" If the prediction had been correct, it would mean only that it had failed to be refuted, so still remained in the group of hypotheses that predicted such a warming. If there were very few such hypotheses, making the prediction "risky", then that counts for more. It is also possible that a wrong or irrelevant theory could be right in a particular case just by luck, so more such tests would be needed to strengthen its reputation. Detailed sub-tests of the mechanisms it proposes would also have to be done over time. (A theory can be apparently right, but for the wrong reasons, like Ptolomaen epicycles.)

But certainty of correctness is unobtainable. It is always conceivable that someone will come up with a more exact and or inclusive explanation for what the theory addresses. Certainty of incorrectness, however, follows from a single, clear, failed prediction that followed as a necessary consequence of the theory.

I should have said corroborated

You are correct, if the IPCC/GISS model's had predicted the future temperature trend exactly it still would not have proven AGW's validity. It would have corroborated the theory and strengthened the theory's claim to correctness. Popper himself said that all theories are false, but some are less false than others. To him, scientific progress is a process of testing and discarding false theories, moving toward better, less false ones. And as we stated in The Resilient Earth, no theory is ever beyond doubt and further testing.

Hume is irrelevant

You are referring to David Hume, the 18th century Scottish philosopher and historian? While Hume was hot stuff in the 1700s, hanging around with d'Alembert, Voltaire and Adam Smith, he was philosophizing at a time when science was still in an embryonic stage. He does address matters scientific in Enquiry Concerning Human Understanding but his arguments seem silly and contrived in the face of modern science.

Hume argued that it is natural instinct, not reason, that explains our ability to make inductive inferences. Causes and effects are discovered, not by reason but through experience, when we find that particular objects are constantly conjoined with one another. When “repetition of any particular act or operation produces a propensity to renew the same act or operation…we always say, that this propensity is the effect of Custom.” Belief is “a peculiar sentiment, or lively conception produced by habit” that results from the manner in which ideas are conceived, and “in their feeling to the mind.” It is “nothing but a more vivid, lively, forcible, firm, steady conception of an object, than what the imagination alone is ever able to attain.”

At the heart of his complaints about science is what he called the Problem of Induction, which calls the power of human reason into doubt. Hume's argument is that we cannot rationally justify the claim that nature will continue to be uniform, and as a consequence nature is unpredictable. He went so far as to claim we can not depend on the Sun rising tomorrow. He argued that science is wrong to draw inferences from observation, that causation, while it does exist, is not knowable using rational inferences based on instances of perception. He stated that “there are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion.”

The course of modern science in the two centuries after his death certainly discredits the foundation of Hume's predictions for the future of human knowledge. An example of Hume's arguments falling flat is his statement: “Our senses inform us of the colour, weight, and consistence of bread; but neither sense nor reason can ever inform us of those qualities which fit it for the nourishment and support of a human body.” Science can, indeed inform us of those qualities today. Quoting from an article on

That proteins, vitamins, carbohydrates, minerals, etc. explain the basis of human nutrition, and that electromagnetism and atomic, nuclear, and particle physics explain much of the fundamental behavior of matter, are not just things that escaped Hume's imagination -- they escaped everyone's imagination until the discovery of them was effected -- but they are things that occupy a cognitive space whose very existence Hume explicitly denied: They do not correspond to "impressions" any more than God or the soul do. By Hume's criterion they are "without any meaning or idea."

Hume's “sceptical doubts about the operations of the understanding,” about causation and induction do not fare well in light of modern science. Science is the search for underlying mechanisms, the discovery of causation. And though Popper could be said to agree with Hume regarding the weakness of inductive reasoning, Popper never said anything as silly as Hume's assertion that “in all reasonings from experience, there is a step taken by the mind which is not supported by any argument or process of the understanding.” Popper's great insight was that, although proving a causal relationship is generally very hard, disproving causation is not only possible but the single best tool to separate good theories from false ones.

Hume was a clever man who took great pleasure in his own wit, a philosopher not a scientists, who's comments on science are as outdated as the belief that Earth is only 85,000 years old (proposed by Hume's contemporary Buffon, to the great consternation of the Church), or that flies and maggots are spontaneously created on dead meat. Modern science has rendered Hume's ruminations about understanding nature null and void. While they are great fun for philosophy students to argue, they have no utility in the modern world, science or on this web site.

Confidence intervals

His criticism of induction is valid in terms of not being able to prove an hypothesis true. Confidence intervals and error bars are the legacy of modern statistical techniques and the realization that all measurements are at some level inexact. Read Hume's original papers, putting error bounds on measurements has nothing to do with Hume's philosophy. Hume would not have recognized a confidence interval if it bit him on the arse.

Dueling Philosophers

Repeating yourself and SHOUTING about it does not make your points any more valid or any more believable. Readers are invited to follow the links regarding Popper and Hume and draw their own conclusions. This thread has drifted off into the philosophical weeds and become overly argumentative—it is now closed.


Science and decision-making

Dear Doug,

I have been considering the problems of scientific vs legal proof for a number of years and I think that what you are discussing here is another example of this trend.

In a legal argument, there are two sides and each one presents evidence in support of its position. This - in and of itself - is cherry-picking, but is made even worse by the whole process of casting doubt on both the other side's evidence as well as the motives of the source of that evidence.

You have nicely summarized the scientific method so I wont repeat that, but the whole approach taken to most issues in the modern world is a legal one - develop a case by picking evidence, disparage the source of conflicting evidence and appeal to some form of inherent moral value that the jury should uphold.

This is not science.

In no way can it be compared with science.

In no way should it be construed as being science.

Of course the world is not and can not be run as a scientific experiment - decision-making is the art of determining a course of action in the absence of proof and leaders nearly always make decisions following this legal/debate approach. But by trying to justify their decisions by invoking scientific proof they are hiding behind the scientists (looking for someone else to blame if it turns out they have made the wrong decision) and as a consequence they are degrading science as an approach to understanding the natural world. Even worse, a number of scientists have forgotten their role in this and begun to act as direct advocates - lawyers, by another name - thus debasing their work and removing their claim to be treated as scientists.

In the fight for free speech, it is often quoted that "I abhor what you say, but I will defend your right to say it". Right now, we need a defense of free science, that says "I disagree with your findings, but I will attempt to disprove them, not prevent them being published or impuning your motives".

If the climate debate can do one good thing for science it would be to remind people of the proper role for science and scientists - to inform decision-makers not to take responsibility away from them.

Thanks for your article and I hope you feel my comment has added to the debate.

For the record, as a scientist, I do not believe in AGW. But then again, I try to believe in very little. That is the point. As a human being, I trust in our ability to adapt as a species and to cope with any issues that a changing climate may throw up. Reducing our ability to adapt has to be the worst possible response to these circumstances.

Langmuir's Laws

Doug, you might want to consider writing something about Irving Langmuir's Laws of bad science:

1.The maximum effect that is observed is produced by a causative agent of barely detectable intensity, and the magnitude of the effect is substantially independent of the intensity of the cause.

2. The effect is of a magnitude that remains close to the limit of detectability, or many measurements are necessary because of the low level of significance of the results.

3. There are claims of great accuracy.

4. Fantastic theories contrary to experience are suggested.

5. Criticisms are met by ad hoc excuses thought up on the spur of the moment.

6. The ratio of supporters to critics rises to somewhere near 50% and then falls gradually to zero.

Thanks for these two articles on Popper, well-written as usual. It seems to me that there is also a logic rule that says it's a logical fallacy to "confirm the consequent" of a theory and present that as proof of it.

A Body of Knowledge

A big part of what science is is the accumulated knowledge of scientists past and present. That body of knowledge is essential for science to work, otherwise each new theory would have to be judged without the benefit of previous discoveries and observation. Scientific theories don't just stand on their own, they must be in agreement with other accepted theories or they must offer alternate explanations for what those theories describe. This is why Marcello Truzzi made the statement “In science, the burden of proof falls upon the claimant; and the more extraordinary a claim, the heavier is the burden of proof demanded.” This is often shortened to “extraordinary claims require extraordinary proof.”

This is the rock that many believers in pseudoscience founder on. The claims of Young Earthers not only must account for the things explained by evolution, they must also provide convincing alternate explanations for facts from geology, astronomy, paleontology, chemistry, physics biology, genetics, and protein science. Evolution not only provides plausible explanations for the development and diversity of life, it also fits in with the observed age of Earth and the Universe, Earth's planetary strata and the fossil record that it contains, the functioning of the carbon and nitrogen cycles, etc. No scientific theory is judged in a vacuum, it is always tested against the body of knowledge that is as much “science” as the scientific method used to gather and validate that knowledge.

Global Warming

You have shown a chart that disproves the predictions of James Hansen.

Here is a chart that disproves IPCC projections.

No More Cherries Please!

Dr. Hoffman,

I too enjoy your blog and I am indeed enjoying the current interglacial, and staying sceptical (of ALL sides). I was with you on this article right up until your use of the graph of Hansen's Predictions vs actual temperatures. Didn't James Hansen predict 3 scenario's in 1988? One under current emissions (A), one under current emissions with a few volcanic eruptions (B), and one with reduced emissions (C)? Am I correct in interpreting that your graph only shows scenario A? Surely it is cherry-picking to only show the prediction that is furtherest from the actual, when others have been put forward with different qualifiers. I admit I don't actually know how close the other scenarios are to the actual, and I have seen this version of the graph (with just scenario A) elsewhere - so maybe it was just a quick copy-and-paste, but I fear you do yourself a disservice sir.

Close but no cigar

You are right and wrong. It would appear that the graph does indeed only show scenario A from the Hansen paper, that is the only one that needs to be shown. Scenario A was "business as usual", Scenario B was actually under reducing emissions so that the forcing stayed level and C was with severely reduced emissions.

Since the emissions since 1988 have neither levelled off or declined, the temperature predictions for either B or C are irrelevent.

Hansen 1988 predicted strong temerature rise under a "business as usual" scenario. The graph accurately compares what the model said would happen with the reality. The model is wrong.

Some (like realclimate) like to point out that the prediction for B is quite close to reality. While this is true, as the underlying assumptions that led to the prediction bear no relation to reality. This makes the argument invalid.


I'm a novice in all this and am not familiar with the details of Hansen's three scenarios. The question I have is what exactly was 'business as usual' defined as? I'd presume that the key would be what levels of future carbon emissions Hansen was assuming in the A vs B vs C projections, and which of the three different assumptions most closely matches subsequent actual emissions. that would presumably tell us which of the three predictions is the one to compare with the subsequent observed temperature data. If B's assumed levels of carbon emissions most closely track actual emissions then presumably it's the one we should be looking at. Likewise for scenario A. I have seen elsewhere claims that scenario B actually overestimated/assumed future carbon emission (even though it is labelled reducing emissions). I assume you would dispute this. It sure makes it hard for a 'novice' to know what to think!

All scenarios

I don't have the full set handy, but the actual data falls below the entire group, including C. There is zero overlap.
Hansen gets an unfudgeable and unqualified FAIL.

And ONLY long-term predictions with locked-in modelling and data count. The minute you touch either, the clock starts over and you must wait out the duration of the predictions. 'Retro-casting' (which the IPCC models also fail at) is merely suggestive, exploratory guessing prior to making a real prediction.


Here is an older but worth reading article from WUWT. This demonstrates perfectly the difference between 'warmism' (saying "The temperature's likely to go up a bit") and 'alarmism' (screaming "It's going to kill us all!")

No More Cherries Please!

Thanks to you both for the info. I've been forced to look closer at this (which means I'm in danger of learning something ;-). This actually seems to be a bit of a football, back-and-forth, with both sides claiming victory. Hence I am now more confused than ever.
From Lucia's Blackboard (
"Scenario A: Continued growth rate in emissions at 1.5% / year.
Scenario B: Emissions frozen at 1988 rates.
Scenario C: Drastic reductions in emissions in 1990."

From Grist ( -
"Line A was a temperature trend prediction based on rapid emissions growth and no large volcanic event [...]
Line B was based on modest emissions growth and one large volcanic eruption in the mid 1990s.
Line C [...] included the same volcanic eruption, but showed reductions in the growth of CO2 emission by the turn of the century -- the result of hypothetical government controls"

So I went to the original 1988 paper itself (
From the abstract -
"Scenario A assumes continued exponential trace gas growth, scenario B assumes a reduced linear growth of trace gases, and scenario C assumes a rapid curtailment of trace gas emissions [..]"
From Section 4.1 -
"Scenario A assumes that growth rates of trace gas emissions typical of the 1970s and 1980s will continue indefinitely; the assumed annual growth averages about 1.5% of current emissions, so the net greenhouse forcing increases exponentially. Scenario B has decreasing trace gas growth rates, such that the annual increase of the greenhouse climate forcing remains approximately at the present level. Scenario C drastically reduces trace gas growth between 1990 and 2000 such that the greenhouse climate forcing ceases to increase after 2000."
From Section 4.2 -
"In scenarios B and C, additional large volcanoes are inserted in the year 1995 [...], in the year 2015 [...], and in the year 2025 [...], while in scenario A no additional volcanic aerosols are included [...]."

Comparing Scenario B descriptions, 'Frozen emissions' is not the same as 'modest emissions growth' which is not the same as 'decreasing trace gas growth rates'.
I believe there may be confusion over the difference between reducing emissions, and reducing the GROWTH of emissions.
Yet again, it appears there is nothing in climate science that is simple, straightforward, or anywhere near 'settled'.

There is further discussion (and links) here: (

Hansen's own take on how he did (in 2006) is available here: ( I haven't read this yet - it'll have to wait until at least the weekend.

Steve McIntyre's take on it is here :(

Personally I prefer to see the graph as like Lucia's or McIntyre's(with ALL scenarios vs. several major temperature datasets), but I willingly recant my accusation of cherry-picking against our gracious host :)