How do we know anything for certain?

At the start of each semester, I hand my students a short-answer survey called Twenty Questions About the Universe.  Its purpose is to gauge basic knowledge from non-science students about everything from the cosmos to atoms.  It is a wonderful way to collect misconceptions about physics that we can later address in the classroom.  At the end of the survey I ask this question:

How do we know anything for certain? 

I generally get a variety of answers.  Among the more common replies are words and phrases to do with the ‘scientific method’ as students might have learned it, painfully and reluctantly, in grade school.  The poor student is trying to give me the answer he or she thinks I want.  Every once in a while someone will mysteriously write “God,” but rarely will a student say this:

“We don’t.”

(Qualifiers below).

We live in an uncertain world; yet our formal and informal explorations of it reveal that the world is not random.  There seem to be underlying patterns and regularities in the universe – these are what make science possible.  From the rising and setting of the sun to the coursing of blood in our veins – the data suggest that there is some kind of order underlying the dizzying diversity of phenomena in the world.  We can measure, record, experiment, predict, and come up with models of the world that explain how and why things do what they do.

There is a popular misconception about science in general, and in particular physical sciences – that in the ‘exact’ sciences there is only one right answer, and that the search for truth in these disciplines has no attendant ambiguities and uncertainties.

Another popular misconception has to do with exactly the opposite: that scientists don’t know what they’re talking about, that one day they tell you coffee is bad for you, and then they tell you that it’s actually good for you.

And yet, doing science and looking at science more deeply, reveal that neither of these is true.  Their prevalence is an example of the kind of black-and-white thinking that you simply can’t apply to anything as complex as the world around us, and the scientists who study it.  Reality is so much more complicated, and interesting.

I remember how shocked I was when the realization gradually dawned on me that science rests on at least two untested assumptions.  One, that the universe is comprehensible, and two, that physical laws are the same everywhere and through all time.  This was when I was a college student, many, many years ago.  Along the way, during a ten-year absence from academia, and when I returned to it to teach, I realized a few more things.  One, a model is just that, a model.  The truth, whatever it is, can be larger and weirder than we suspect.  The ancient Indian story of the six blind men and the elephant nicely illustrates this point.  Each man has a hold of one part of this infinitely patient elephant, and declares that ‘the elephant is like a wall,” “the elephant is like a rope,” etc.  They are all right and they are all wrong.  So I realized that the success of a model in making accurate numerical predictions does not mean that the model is the only correct way of looking at the phenomenon.  In quantum physics this is particularly apparent, because we actually have no idea what atoms are really like, but our models give us results that match so fantastically with experiment that it is arguably the most successful theory we have. 

The other thing I’ve wondered about, which is somewhat fanciful, is that Occam’s Razor, the supposition that the simplest explanation that fits all the data must be the true one, need not be correct.  There’s no reason to suppose it isn’t, but it is an article of faith, an untested assumption.  But anyway, finally it came to me, after working on my Ph.D. for a while, that the scientific method that students have to memorize (in which dry and desiccated form any intelligent person would get permanently turned off by science) – that scientific method was a lie.   Oh I’m not saying it doesn’t happen that way – hypothesis, prediction, experiment, adjust hypothesis, repeat with related hypotheses until you build the superstructure called a theory.  But that’s not the only way science is done – and, unforgivably, it leaves out creativity and imagination.  It leaves out the fact that ideas can come to you in dreams or nightmares, or that you can observe things and collect data without having a single hypothesis in your head, and sometimes the explanation precedes the data and experiment.

So I came gradually to a sense of the enterprise of science as a much more human, flawed thing than I’d imagined in my early days in the field.  Which also made it so much more interesting.  It also brought home to me why scientists needed to be more honest and more critical of their own work than ordinary people, although, being human, they weren’t always so.  But in what other field is so much time and effort spent in estimating and calculating errors, uncertainties, and the like?  To learn the truth of something, after all, includes learning to what extent it is true, and under what circumstances.

Thus Dr. Naomi Oreskes’ brilliant lectures this week on “The Scientific Consensus on Climate Change – How Do We Know We’re Not Wrong?” took up pretty much where my informal musings over the years had left off.  Here are some highlights of what I learned, along with my own thoughts and opinions.

Firstly, there isn’t any such thing as a scientific method – there are scientific methods.  There are also standards by which the scientific community evaluates claims.  There are five broad classifications of these:

  • Methodological, being either deductive (the classic ‘scientific method’ as taught in grade school) or inductive (think Darwin); Note from Karl Popper – scientific hypotheses must be falsifiable
  • Evidential standards, including tests of reliability (replication, witnessing, peer review) and Consilience of evidence (different studies on different aspects come to the same conclusion, i.e. amalgamate different lines of evidence)
  • Performance Standards and Pragmatism (the test of the truth of something is whether it holds up in action – so you can send a spaceship to the moon based on Newton’s laws, ergo Newton’s laws must be true)
  • Inference to the Best Explanation – take different aspects of a body of knowledge: experiments, observations, evidence, etc., and infer the best explanation that encompasses them all (somewhat like induction but at a larger scale)
  • Consensus of experts – each of the above methods has a logical flaw. Thus none can be relied upon separately.  While science is often said to be objective, scientists must make judgments that have a subjective element to them.  In the context of climate, the statement that the current rate of global warming is caused by humans is supported by ALL of the above four standards.  Taken together, they make a compelling case in support of Anthropogenic climate change.  This is what consensus among scientists means.

Doubt and skepticism are important in science.  History reminds us of so many times people believed in the wrong ideas, and their suppositions were overturned with more data, data that challenged their earlier worldview.  So for instance Galileo’s observations with the telescope challenged the Ptolemaic view upheld by the Catholic church of the day.  Ultimately people were persuaded that the geocentric theory simply did not work – there was too much evidence, too much support for the heliocentric view.  Sometimes contrarians claim the position of the lone, noble resister, but the point is that the resister has to have evidence on his/her side, as Galileo did.  There was a famous scientist who did not believe in the idea of plate tectonics even when there was overwhelming evidence in its favor.  That scientist is the truer analog of the contrarians today.

So it is not impossible that there are things climate scientists simply don’t know yet which might explain the current temperature increase better than anthropogenic CO2.  But one must have evidence, after all, of an alternative, better explanation.  So far all the typical ‘alternative explanations,’  from the behavior of the sun to the complete denial that global warming is even happening have been debunked so long ago and so thoroughly that one can only yawn when one is subjected to them repeatedly.

An oft-mouthed misconception among the public is that there is considerable disagreement about climate change among scientists.  This is a clever ploy by climate deniers funded by the fossil fuel industry (in a manner reminiscent of the tobacco industry casting doubts on the evidence that cigarette smoking causes cancer).  The Union of Concerned Scientists’ expose of Exxon-Mobil’s funding of denial groups, and the more recent Scientific American report of how that funding has now gone underground all point to powerful interests attempting to hijack public understanding of the issue.

The two readings that formed part of my weekly assignment studied abstracts in which climate change was mentioned, in order to gauge the level of consensus in the climate science community.  One paper (Quantifying the consensus on anthropogenic global warming in the scientific literature, John Cook, et al. in Environmental Research Letters) came to the conclusion that 97% of the abstracts from 1991 to 2011 that took a position on anthropogenic global warming (AGW) endorsed it.  The other, (The Scientific Consensus on Climate Change by Naomi Oreskes) concluded that of nearly a 1000 papers (1993 to 2003) in the area, not a single one disagreed with the idea of AGW.  However nearly 60% of the American public believes that AGW is the subject of much scientific debate.  This is completely appalling, and on can see why the American government hasn’t acted on climate change.  You can’t have meaningful action without public pressure, and you can’t have public pressure of the sort that would lead to meaningful action without the public having a clear idea of what climate scientists are thinking.

So, some further thoughts.  Suppose you were a member of the public, a lay person, a non-scientist.  You wanted to be informed about climate science in a reliable way.  In my opinion it is not enough to be told that the experts are saying this, so this must be so.  Sometimes people use the analogy that, let’s say, 97% of heart surgeons believe in a particular procedure.  If you had to have heart surgery, would you go to them, or to the 3% who take the contrarian view?  It is certainly sensible to go with the 97% but I don’t think the intelligent lay person should stop there.  I strongly dislike the notion of believing an expert just because they are experts (and dislike it even more when the expert is from a professions under the control of large corporations, such as the medical industry).  The intelligent layperson, I believe, is fully capable of understanding the basics of any field of inquiry or endeavour, with some help and guidance.  Thus such a person must also know why the experts say what they say.  To summarize:

What does the intelligent layperson need to reliably understand anthropogenic climate change?  Based on what I’ve learned so far, I suggest tentatively that such a person should:

  • Know what the experts think
  • Know how and why the experts think that way
  • Have some idea of the basic science, including time factors (more on this in another post)
  • Have some idea of the evidence and impacts, including what is considered almost certain, and what is still in doubt.

So much to think about on this topic and in this course!  I leave you with a really powerful video from Stanford University climate scientist Steve Schneider, now deceased, speaking with passion and clarity on climate science and media distortion.  One of the most chilling scenes is a clip of an old tobacco industry ad, which gave me quite a creeped out sense of déjà vu.

Note Added on Jan. 18: Apparently some denialists tried a low trick with a new science journal — check it out here.  

This entry was posted in climate change pedagody, UCSD Climate Change Course and tagged . Bookmark the permalink.

5 Responses to How do we know anything for certain?

  1. Very nice and thought provoking post. I particularly hope the statistics on the number of papers on quantifying the scientific consensus, 1991 to 2011, that is a TEN year span of research on climate change, global warming, and CO2,; a 97% specialist endorsement on global warming, makes a clear statement for the public. As a friend, very happy for you, Vandana!

  2. Bill Everett says:

    Regarding an apparent use of a peer-reviewed journal for publishing AGW denial can be found in the following sequence:
    1. 19 Nov 2012, Editorial: “Climate—A New Open Access Journal Covering the Complex, Multi-Disciplinary Climate Research Challenge.” Abstract: “Climate has changed over the Earth’s past, is changing continuously and will do so in the future due to external and internal drivers. Some external drivers, such as the astronomic constellation of the Earth-sun system and continental shifts, have led to slow changes over long time scales. While others, for instance volcanic eruptions, may lead to fast, quasi-abrupt changes with impacts on climate over a limited time. Internal drivers like albedo, or the greenhouse effect are parts and processes of the climate system itself that may again change the climate at comparatively shorter time scales than most external drivers.”
    2. 3 May 2013, Article: “On the Present Halting of Global Warming,” Abstract: “The rise in global average temperature over the last century has halted since roughly the year 2000, despite the fact that the release of CO2 into the atmosphere is still increasing. It is suggested here that this interruption has been caused by the suspension of the near linear (+ 0.5 °C/100 years or 0.05 °C/10 years) temperature increase over the last two centuries, due to recovery from the Little Ice Age, by a superposed multi-decadal oscillation of a 0.2 °C amplitude and a 50~60 year period, which reached its positive peak in about the year 2000—a halting similar to those that occurred around 1880 and 1940. Because both the near linear change and the multi-decadal oscillation are likely to be natural changes (the recovery from the Little Ice Age (LIA) and an oscillation related to the Pacific Decadal Oscillation (PDO), respectively), they must be carefully subtracted from temperature data before estimating the effects of CO2.”
    3. 12 Sep 2013, Editorial: “Invitation for Discussion of a Paper Published in Climate: Akasofu, S.-I. On the Present Halting of Global Warming. Climate 2013, 1, 4–11,” Abstract: “It has recently been brought to our attention by members of the scientific community that a paper published in Climate (ISSN 2225-1154, has raised some controversy regarding its originality, overall quality, and the scientific validity of the data presented. Moreover, two members have resigned from the Editorial Board, stating they are not willing to be associated with a journal where such articles are published. The paper they referred to was “Akasofu, S.-I. On the Present Halting of Global Warming. Climate 2013, 1, 4–11”, published in the first issue of Climate in May 2013 [1], available online at:”
    4. 19 Sep 2013, Comment: “Comment on: Akasofu, S.-I. On the Present Halting of Global Warming. Climate 2013, 1, 4–11,” Abstract: “A recent article which has set forth new interpretations of Earth’s recent climate history has included some questions of authentic scientific inquiry, particularly related to the impact of ocean oscillations on atmospheric temperatures. In fact, this very issue is currently being investigated by multiple research groups. On the other hand, the claim that a two-century linear temperature increase is a recovery from a recent cool period is not supported by the data. Furthermore, this thermal recovery hypothesis is not connected to any physical phenomenon; rather it is a result of a simplistic and incorrect curve-fitting operation. Other errors in the article are: the claim that the heating of the Earth has halted, misunderstanding of the relationship between carbon dioxide concentration and the resultant radiative forcing, and a failure to account for forcings other than carbon dioxide (such as other greenhouse gases, atmospheric aerosols, land use changes, etc.). Each of these errors brings serious question to the conclusions drawn in the referenced article. The simultaneous occurrence of all of these errors in a single study guarantees that its conclusions cannot be supported and, in fact, are demonstrably incorrect.”
    5. 3 Dec 2013, Editorial: “Research on Climate Change and Its Impacts Needs Freedom of Research,” Abstract: “Climate change captured my interest as a teenager when, at the dining table, my dad talked about potential anthropogenic climate changes. He brought up subjects such as “climate could change if the Siberian Rivers were to be deviated to the South for irrigation of the (semi) arid areas of the former Soviet Union”. Other subjects were afforestation in the Sahel to enhance precipitation recycling, deforestation in the Tropics that could have worldwide impacts on climate, the local climate impacts of the Merowe High Dam in its vicinity and downstream, Atlantropa, a new ice age, and the increase in days with sunshine after the introduction of the high-chimney policy in the Rhein-Ruhr area, just to mention a few.”

    • vsinghsblog says:

      Thanks, Bill, this is very interesting. The author of the controversial paper appears to be the founder (now emeritus) of the International Arctic Research Center at the University of Alaska, Fairbanks, which is not a hotbed of contrarian views, as far as I know. (I’ve been following the work of Natalia Shakhova, also at the center, who has been studying methane outgassing in the East Siberian sea.) It seems reasonable to ask, as he does, that the effects of natural cycles be subtracted to isolate the effect of CO2, but that is standard practice in any case, isn’t it? The failure to account for other effects, particularly ocean absorption of thermal energy, is problematic. I wonder if he is a contrarian loner, or whether he didn’t think the whole thing through. I found the editorial written in a peculiar style, but I do agree that one should always consider serious scientific challenges to the prevailing view — that’s how science is done. This particular paper doesn’t seem to qualify at all.

      • Bill Everett says:

        Not just appears to be but is the founder. But climate science is not his field. There has been a suggestion that the appearance of his paper as the first paper in a brand-new peer-reviewed journal was an attempt to get his previously published work a “new hearing.” See, for example, and

        Personally, I think it is a little sad. He was a very good scientist and made significant contributions. I think he earned his honors. (Similarly, over the past decade, I have read several papers by Logunov and his colleagues proving that black holes cannot exist. And I know sadder stories of good dogs barking up the wrong tree.)

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