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Charlie Martin


June 25, 2013 - 12:45 pm


We know, with great certainty, that the overall average temperature of the Earth has warmed by several degreees in the last 400 years, since the end of the Little Ice Age. Before that was a period called the Medieval Warm Period; before that was another cold period; and back at the time of the Romans there was a long period that was significantly warmer — Southern Britain was a wine-growing region. What we’re a lot less certain about is “why?”

Of course, the “why?” here has been, shall we say, pretty controversial. It’s worth wondering about the controversy and about the social mechanisms through which science is done — I wrote about them during the Climategate controversy as the “social contract of science” — but that’s not what I want to talk about today. Instead, let’s talk about how a scientist thinks about these sorts of questions and arrives at new answers. Back in grad school we called that “doing science,” and it was something everyone liked doing and wished they could be doing instead of whatever they actually were doing, like faculty meetings and refereeing papers.

The process of “doing science” is something you usually learn more or less by osmosis, but there are some good hints around. One of the best is a paper from the 16 October 1964 issue of Science, “Strong Inference” by John R Platt. Let’s say we have some phenomenon of interest, like global warming, or high blood sugar, or that damned yellow patch in my lawn. We want to know why it happens. Platt’s strong inference describes the process we should use when “doing science” as:

  1. We generate a number of alternate explanations, hypotheses, that might explain the phenomenon.
  2. For each hypothesis, we come up with an experiment which will prove the hypothesis wrong. That is, not one that “proves the hypothesis,” but one which, if successful, would disprove or falsify the hypothesis. (Sir Karl Popper argued in his book The Logic of Scientific Discovery that this falsification was the core of scientific knowledge.)
  3. We do the experiments. If an experiment falsifies a hypothesis, we discard it ruthlessly. Then we go back to (1) and try again.

A lot of times, the rub — and the really creative thinking — comes in from finding the right experiment. Richard Feynmann was known for an ability to see right through a problem to a simple and elegant experiment that would disprove a hypothesis. He demonstrated this during the review following the Challenger disaster. You may remember that the launch happened on a very cold morning in January; less than two minutes after launch the Space Shuttle Challenger blew up, killing all seven astronauts.

The question, as always, was “why?”

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From films and debris, it appeared that the solid rocket motors had failed first, sending a blowtorch of hot gas into the external tank, which then exploded. The solid rocket motors were built of a stack of components containing the solid fuel, which were then joined to make the whole rocket motor; it appeared, in fact, that one of the joints had failed.

One proposed explanation was that the cold has made the O-ring seals at the joints stiff. During a public, televised hearing, management people from the solid rocket manufacturers discounted this idea. Feynmann, who was one of the members of the all-star panel doing the investigation, quietly got a salt shaker and a glass of ice. They had a sample of the O-ring material that had been provided as a prop for the hearing. Feynmann put the salt into the ice, making a concentrated salt solution with a temperature much lower than the normal freezing point of water. Feynmann, without making a fuss about it, dropped his sample of O-ring in the water and let it chill.

Here’s the strong-inference part of this. The Thiokol managers’ hypothesis was that the O-ring material remained “sufficiently” flexible at the temperature it would have reached on that unusually cold Florida morning. Feynmann’s experiment simply said “okay, so let’s get a piece of this stuff cold and see what happens.”

The answer, which Feynmann proceeded to demonstrate in a nationally televised hearing, was that the stuff got to be very brittle. Feynmann took what had been a soft, rubbery material at room temperature, and it broke like glass.

So much for the managers’ hypothesis.


As we said, we’re pretty confident that there has been significant warming since the Little Ice Age. The controversy around “climate change” or “global warming” is all about what’s happening; the UN-approved explanation is that humans are releasing gases into the atmosphere that cause less heat to be radiated out into space, and thus causing the average temperature to rise, what’s called the “greenhouse effect.”

Aside: Now, just to try to forestall one of the usual threads of argument, there really is very little question the greenhouse effect actually exists — the natural temperature of a rock in orbit around the Sun at the same distance as the Earth is nearly -40°. So let’s not have the “but there’s no such thing” argument, okay?

If we plan another game of strong inference, what we want is an explanation for the rise in temperature, and particularly for the amount the temperature has gone up. There are a whole lot of different things that might explain it:

  • Human-generated greenhouse gases might be doing it.
  • Human changes in land use — like lots of asphalt highways, which are pretty black — might be causing the Earth to absorb more heat.
  • There might be measurement error — we have to estimate the temperature based on thermometers around the world. Some of these thermometers themselves have had some pretty significant changes in their environments, like having a parking lot built around them, that would make the temperature higher locally. This would increase the measured average temperature, which would make it harder to find a natural explanation.
  • There might be variations in the Sun’s output that cause the changes.
  • There could be other factors than greenhouse gases that cause the Earth to retain more heat. (One interesting possibility that’s being explored is that more cosmic radiation might be causing cloud cover to change.)

Performing a good experiment to test each of these hypotheses is difficult: we can’t just make a spare Earth with no people, no roads, and a different influx of cosmic rays along with a different Sun maintaining standard conditions. So we have to use other methods.


Into this comes modeling. One way of looking at any hypothesis is that it’s a model of the way you think the phenomenon is behaving: “If I’m right, then this will happen.” Medical experiments share a lot of characteristics with these climate experiments, and in particular, you can’t take a lot of human patients, use them as lab rats, and mess with them just to see what happens.

What’s more, both patients and planets have the troublesome characteristic that they tend not to be very predictable — no one really exppected snow in Boulder in the middle of May like happened this year, even though it certainly had happened before. If there is a lot of variation happening with a lot of different causes, we have to use statistics to try to tell the different causes apart.

So let’s imagine we’re testing a new hay fever drug, an early summer topic near and dear to my nose. I take the new drug, and my hay fever gets better. Cool.

But what if I would have gotten better anyway, just because the cottonwood trees have stopped emitting cottonwood fluff or something?

We want to know what would have happened if we did nothing. We call this treatment of no treatment the null hypothesis. Statistically, we want to know if we can tell if what we did had an effect.

Notice this isn’t the same as saying “tell if it had an effect or not.” The new hay fever drug might have worked, but I might have at the same time caught a cold — so the hay fever drug might have been working, but my nose could still be stopped up and my eyes itching.

(Or half the freaking state of Colorado could be on fire and it’s the smoke that’s bothering me. But the Colorado fires are another column.)

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So now let’s talk about climate. (You thought I’d never get there, didn’t you?) We know there’s warming; there is a hypothesis that this is caused by an increase in the amount of greenhouse gases, and particularly in carbon dioxide, in the air as a result of human action. The core of this hypothesis is a model, a picture of how we think things work, that computes what the average temperature should be based on the increase in CO2. These models all center around a value — either assumed in, or computed in some way — of how the temperature responds to changes in CO2 concentration. This is called sensitivity.

The models that have been proposed by the “mainstream” climate science community all have substantial sensitivity to CO2 concentration — which is as it should be. That’s the hypothesis. But since this is a statistical property we’re measuring, they also have a range of values that are plausible predictions. This is stated as a confidence interval, which just means “we’re willing to bet you 20-1 that the temperature will stay in this range based on the assumption that human-released CO2 is causing the warming.”

These models are now running into a problem, though — the warming appears to have, well, stopped. For 17 years. Even though the amount of CO2 in the atmosphere has gone up.

In global warming, the null hypothesis would be that the “treatment” has no effect, or in other words that the human-caused increase in CO2 is overwhelmed by other effects. And again, note that this isn’t the same as saying “it has no effect,” just that we can’t tell if there has been an effect.

At which point, we can bring in this lovely little chart, stolen from The Economist magazine.


The dark line is the actual measured temperature; the light blue band is the “95 percent confidence interval,” which is to say, that band of 20 to 1 odds. The hypothesis from the models lays down a bet of about 20 to 1 that the temperature will stay inside that light blue band.

The real temperature, however, says otherwise. It’s either already out of that confidence interval or it’s very close to the edge.

Why? We don’t know. Time for some new hypotheses.


images courtesy shutterstock / Samot / Kingan /  sextoacto /

Charlie Martin writes on science, health, culture and technology for PJ Media. Follow his 13 week diet and exercise experiment on Facebook and at PJ Lifestyle

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What you are getting at is known as the Null Hypothesis. We have records of prior inter-glacial periods in the ice cores, varves, oceanic sediment, and various forms of terrestrial sediment to help show past climates for the planet. Prior inter-glacial periods have a definite pattern to them and singular events, like volcanic eruptions or boloid impacts, can be seen in the record by the changes they produce. Our record can be compared to those similar periods and the proposition put forth that our inter-glacial period is in no way different from prior ones. By putting high/low bars on climate and mapping our current set of records against past records, the onus is on those who wish to prove any difference between our current climate and past similar ones.

To date no changes in climate for this inter-glacial period are going significantly outside those error bars. Even worse is that a typical high point is reached and then climates trend colder to the next ice age, and our climate is mapping to just such a high point and start of a fall-off. Until there is evidence to demonstrate, clearly and over a few centuries, that our climate is going outside those error bars, the Null Hypothesis stands.
1 year ago
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On 'warming', you raise an interesting point. My online dictionary defines it as "having or giving out a moderate degree of heat" or "conserving or maintaining warmth or heat", but it's true the common use of the word makes one think in terms of temperature. Perhaps we should say 'global heating' if that's what we mean.

Re the relative contribution of man-made contribution to the GHG effect, every textbook I have has a huge amount of experimental data on this, all suggesting that the man-made contribution is very significant relative to natural processes. I see no reason to doubt the experts, I guess that comes down to your level of trust in scientists.

One final point; just supposing a hitherto unsuspected natural cause of natural warming became evident (seems unlikely after all this study), surely the last thing we want to do is add to it? We already know how the GHG effect works, and we know we have signicantly increased the GHG conc. So it seems to me that doing nothing would be a bit like a doctor saying "Keep on smoking because we don't know for sure that your lung cancer is not caused by something else"....
1 year ago
1 year ago Link To Comment
Yeah, the temperature vs heat thing used to confuse me too -- I had to finally figure it out back when I was writing about the Fukushima accident and trying to explain radiation exposure by analogy.

But you're correct with your point about the heat content in any case -- if GHGs are causing the net heat balance to change significantly, it has to go *someplace*; if the GAST isn't rising then it must be something else.

As to my level of trust in scientists, well, my PhD work was in Computer Science, but I was working with big ugly nonlinear systems then; I like to think of myself as kinda-sorta a scientist, notwithstanding the old jokes about "if it has science in the name it's not one." As someone who *has* actually "done science", as well as someone who started as a philosophy major interested in, among other things, philosophy of science, I can tell you how much any real scientist trusts scientists -- it's right up to the point at which a result can't be verified, a hypothesis is falsified, a flaw in the methodology is identified, or statistical examination makes it appear the null hypothesis can't be excluded.

But that's a topic for another column. No matter what the energy balance is, the predictions that said the increase in retained energy would cause an increase in GAST now disagree with the observations, outside those predictions' 95 percent confidence interval. Which means we need new models and new hypotheses. Which, if you read through the article, is all I said.
1 year ago
1 year ago Link To Comment
Charlie, re "And strictly you can't have *warming* per se without the temperature going up":
I'm afraid you certainly can, this is one of the big worries. In physics, latent heat is the name given to the heat taken in during a phase change. Typically, quite a large amount of heat absorption occurs withut any temp change at all, even in a lab. Thus, the loss of land-ice we have already measured at the poles represents a great deal of heat absorbed, and there may be much more we haven't yet been able to measure.

I agree with you on simple demonstrations. I usually demonstrate the latent heat effect to students by starting the lecture with a very large glass full of ice at zero degrees Celcius. Before the end of the class, we note that most of the ice has melted to liquid, while its temperature hasn't changed a jot. the point is that significant heating has ocurred that cannot be measured as a temp rise.....nasty
1 year ago
1 year ago Link To Comment
nd strictly you can't have *warming* per se without the temperature going up": I'm afraid you certainly can, this is one of the big worries.

Well, no, actually you can't. "To warm" is to increase the temperature. Yes, you *can* increase the heat content without warming; the most obvious case is, as you note, during a phase change, eg, ice to liquid water, and water to steam. But what's distinctive in those cases is that it's *not* warming. In fact, you sort of give it away -- by definition, latent heat is heat that is absorbed without temperature change.

But it's a bit of a red herring anyway, since I explicitly pointed to the models that predict an actual rise in GAST as the ones that are failing. Part of the problem here is that you're defending a proposition I haven't attacked -- in fact I started out by saying that there was no realistic question that there has been actual warming, and no question that GHGs cause heat to be retained.

The question is the magnitude of the net change, and of that, the net change that can be attributed to anthropogenic forcings, and of that the net gain that can be attributed to human release of GHGs, and of *that* the magnitude of the net change caused by carbon emissions in particular.

The models for net warming based on the assumption that human carbon emissions are by far the dominant cause of net warming are the specific models that also show some degree of positive feedback, leading to the nice more or less exponential curve in the predictions. That curve is not matching observation.

The question, as I said, is why?

One of those possibilities is that the energy is going into melting ice -- but it takes some real Tennessee windage to make those numbers come out. Another is that its adding heat to the oceans, but as Willis Eschenbach notes here [], the numbers for actual heat content added are so small they are within measurement error and show no significant trend.

Again, I'm not saying there is no anthropogenic effect. I'm asking "can we distinguish an anthropogenic effect in the measurements from the null hypothesis?"
1 year ago
1 year ago Link To Comment
Hi Charlie, I was just reading through your piece again and it struck me that is is very clearly written and I like the idea of invoking the null hypothesis. However, it seems to me that one flaw in the argument might be that you apply the null hypothesis to one observable only, average global surface temperature. This follows logically from your statement '"the core of this hypothesis is a model... that computes what the average temperature should be based on the increase in CO2."
I think most climate scientists would say that temperature rise is *not* core - according to every textbook I have it is only one symptom of warming among many (such as a gradual melting of land-ice, a gradual rise in sea level, a reduction in infra-red radiation emitted to space etc - all observables that change very slowly). If you frame your null hypothesis in terms of all or most of the main expected symptoms, I suspect you would get a very different answer - perhaps a good topic for a future post?

P.S. On temp, I'm sympathetic to your comment "you can argue that these temperature measurements are themselves flawed, but then you can't use them as evidence for the warming since 1900 or 1930". I doubt if they are flawed, I think the point is that temperature is a useful, but incomplete measurement of heat - when temp rises, we assume heating, yet when it stays flat (or more accurately, rises very little), it does not necessarily mean that no warming is happening, because of processes such as the huge latent heat absorbed by melting of land ice and because of the absorption of heat by the deep oceans (water has a very high specific heat capacity). It's possible that many environmentalists and science journalists have put too much emphasis on temperature rise, but none of the main textbooks on climate do. Indeed, some climate scientists suggest that during 'phase II warming', temperature rise will be less and less obvious for several decades as the deep oceans and polar ice absorb heat. Silent but deadly. Regards, Cormac
1 year ago
1 year ago Link To Comment
when temp rises, we assume heating, yet when it stays flat (or more accurately, rises very little), it does not necessarily mean that no warming is happening,

Hm. Okay, I sort of understand what you're saying, but the model to which I was referring is GAST, and GAST is what is most commonly invoked. See, the the GAST project in Berkeley. Of course, Mann et al have based the dendroclimatology stuff on an inferred GAST measurement as well. And strictly you can't have *warming* per se without the temperature going up.

I'm aware of the arguments about heat content etc, but last I looked they're too small to account for the supposed difference too.
1 year ago
1 year ago Link To Comment
Love the allergy reference. Cottonwood fluff doesn't cause allergy symptoms. Its the grass pollen that peaks at the same time the cottonwood is scattering seeds with fluff. You see the fluff but you don't see the pollen. At least that's what my scientific observations tell me. Analogy to CO2 and climate?
1 year ago
1 year ago Link To Comment
Well, consider I was born in Alamosa Colorado. SOMETHING sure has hell goes nuts about that time.
1 year ago
1 year ago Link To Comment
Have you seen the robot 'hands' made with balloons and coffee? When I first saw them I was struck by a statement that they had the idea (a phase transition they called jamming), and thinking about the phase transition led them to predict ground coffee as a substance they could change from 'loose' to solid
I'm not claiming it's true, but if things like that do happen wouldn't that be an experiment that 'proved' coffee as a jamming phase transition?
Also I understood that experiments followed the '?pattern?'predicted by Einsteins theories?
1 year ago
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1 year ago
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Re falsification of GHGs as a cause, another nice experiment is to test atmospheric warming as a function of height (layers). For exterrnal sources such as solar cycles or perturbations in the earth's orbit, one would expect the greatest warming at the highest levels. In fact, measurements show evidence of a cooling of the stratosphere over the last 30 years, while the lower layers heat up. This is highly suggestive of a cause close to home - in fact, my understanding is that it's quite hard to construct a model that predicts stratospheric cooling and tropospheric warming without invoking a strong greenhouse effect(known as the Venus syndrome)
1 year ago
1 year ago Link To Comment
Many thanks for reply Charlie, and an interesting discussion. Re temperature predictions and observable warming, I think three things to remember are that surface temps do not tell the whole story, that about 90% of warming is thought to be occuring in the oceans, and that temperature rise is not always a good measure of heating. This is why symptoms such as rising sea levels and ice melt are also of great importance.
I have a newspaper article on this you might enjoy at

1 year ago
1 year ago Link To Comment
More generally, physicists who study global warming say that instead of looking at a symptom (rise in global surface temperature etc) and casting around for the most likely cause, a better and simpler approach is to work from basic principles of physics. If we understand how the greenhouse effect works, and if we have established that the concentration of long-lived greenhouse gases in the atmosphere has increased by about 40% since pre-industrial levels, is there any good reason to suppose this has *not* affected global climate? That’s the basic question. Quantitatively speaking, every detailed climate model predicts that such an increase in GHG would indeed have a significant forcing effect on climate. Once you know this, it is no great surprise to measure symptoms such as a slight rise in surface temperature, a rise in deep ocean temperature, a rise in sea level and a rise in ice-melt. This does not rule out the possibilty that some warming could also be part of a natural cycle, but most of the alternatives you mention such as solar cycles and cosmic rays are a very poor match in terms of the cycle lifetimes...
1 year ago
1 year ago Link To Comment
The problem is that when a hypothesis has been falsified, the fact that others don't do well either doesn't make the hypothesis true. In the case of CO2 being the major, dominant, sole important forcing, the actual temperature measurements of the last 20 years show that temperature is about flat, even though CO2 continues to rise. You can argue that these temperature measurements are themselves flawed, but then you can't use them as evidence for the warming since 1900 or 1930.
1 year ago
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Re falsification, a very interesting way of testing the greenhouse gas hypothesis, and the size of the effect, is to measure the heat emerging from our atmosphere into space as a function of wavelength. If no reduction is observeable in heat emitted at wavelengths associated with absorption by GHGs, this would be strong evidence that the theory is falsified. Since the 1970s, satellites have been measuring this. In fact, a pronounced dip in energy escaping from the atmosphere occurs at just the wavelengths associated with the major long-lived greenhouse gases. Not only that,this dip that has been growing steadily in tandem with the rise in atmospheric GHG concentration…direct empirical evidence of the effect of GHGs. There is a good summary of these experiments at
for a good summary.Another stron test is the observed cooling of the stratosphere; this presents strong evidence that the source of the warming is external to the planet.
1 year ago
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And no one questions that the GHGs do affect that -- although see also Dick Lindzen's work. But none the less, the temperature predictions aren't working out. If there's no observable warming, there's no observable warming from anthropogenic GHGs.
1 year ago
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Thank you. That was very clear, simple and helpful. It's easy to understand now.

This is all extremely confusing and troublesome for an ordinary, non-scientifically-minded person -- trying to pick out the science from "leanings" and politics is very difficult.

It's a pity that this scientific subject can't be discussed without acrimony. But then, I often feel it too -- although it does come mostly from the Left -- it is their "way" more than the rest of us.

While the scientific opinions of many are driven by their political leanings, I do believe that most scientists on either side of this question are doing their best to be honest.

Of course, leanings do affect what is emphasized.

While drastic warming (or cooling) cd affect different parts of the world in different ways -- perhaps some good, some bad -- if there's a rise in sea levels back to Viking days in Greenland, it wd be very good if we cd predict it and prepare -- no matter what the cause. But I don't believe at this point that anyone can predict so well. Perhaps soon if we're lucky.

Sometimes I read something from a "warmest" science report, that clearly defeats or explains away an argument I'd read in a "skeptic" report. So far, vice versa has happened more often, though.

Of course, this current plateau in warming will end -- climate ... changes -- and none of us know which way it will go. Both sides of this issue are just guessing.

The trend in temp may go down. That will cause an upheaval in thinking. If it goes up, we're still left with the question of how much is caused by human behavior. I tend to think that it's less than is believed by warmists, but am not sure. I don't think anyone is sure -- yet.

1 year ago
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