Cutting to the heart of the public policy debate about climate change

Summary:  After a quarter-century of the climate wars, the chaff thrown up by political activists on both sides has largely obscured the key questions which we must answer in order to deal with this, perhaps the most important of the many shockwaves facing us. Today we look at the most important question of logic in the decision-making process.

“This impatience with ambiguity can be criticized in the phase: the absence of evidence is not the evidence of absence.”
— Carl Sagan in The Demon-haunted World – Science as a Candle in the Dark (1995), using the phrase attributed to British astrophysicist Martin Rees

Globe Aflame



  1. The very heart of the climate debate
  2. Absence of evidence is not evidence of absence
  3. Isn’t the climate signal from humanity obvious?
  4. For More Information


(1)  The very heart of the climate debate

Judith Curry (Prof Atmospheric Science, GA Inst Tech) carved to the heart of the climate wars — the debate over the public policy response to climate change (running on a different track than the policy debate in the pubic arena) comes down to questions of epistemology and logic. How do we leap from a body of evidence to knowing enough to rely on theories? Especially when the theories are compelling, but there is as yet minimal evidence to validate or prove them.

Curry starts with the basics of scientific reasoning, with two methodologies — both equally legitimate. Which to use depends on one’s professional judgement.

Recall the dueling papers on Climate Null Hypotheses by myself and Kevin Trenberth.   Depending on which null hypothesis you select as a default position when conducting research you approach the problem in a different way.

  1. Humans have no influence on extreme weather events
  2. Humans are influencing extreme weather events

For #1, the null would be rejected if you find evidence of a human influence. In the absence of such evidence, #1 is not rejected. This is what Roger Pielke Jr argued.

For #2, the null would be rejected if there is evidence of no influence. RealClimate and Kerry Emanuel  {Prof Meteorology, MIT} essentially conclude that the data is insufficient, so they argue from ‘physics’ and state that there is no evidence of absence.

To me, the ‘no evidence of absence’ argument is rather fatuous given that simple thermodynamical reasoning is not really useful in elucidating the impacts of AGW on extreme weather events.

This grounds the debate in science and logic, not a matter of certainty as implied by activists.  For those of us who are not scientists, let’s look at this logical tool: “Absence of evidence is not evidence of absence.” What does it mean?

(2)  Absence of evidence is not evidence of absence

Its first known use is by the British astrophysicist Martin Rees, discussing the search for extraterrestrial intelligence (SETI):


Spock & logic

“Some brains may package reality in a fashion that we can’t conceive. Others could be uncommunicative: living contemplative lives, perhaps deep under some planetary ocean, doing nothing to reveal their presence. There may be a lot more life out there than we could ever detect. Absence of evidence is not evidence of absence.”

— Our Cosmic Habitat, Martin Rees (2001). The phase was attributed to him long before this book. See his Wikipedia entry.

It’s a powerful by limited tool, as Rees explains in an interview of Martin Rees by Errol Morris in “The Certainty of Donald Rumsfeld“, New York Times, 28 March 2014 — Excerpt:

MORRIS: The absence of evidence is not evidence of absence — every time I’ve tried to track down its origins, it leads back to you.

REES: I’ve used it, but I’m sure I wasn’t the first to use it. …

MORRIS: Even if you didn’t originate it, I was hoping you would explain to me what you meant by it. … it appeared initially in the context of, “Is there life elsewhere in the universe?” And it’s not just an absence of evidence, because we have all kinds of statistical evidence that would suggest that there is.

REES: No, we don’t. We don’t have any evidence.

MORRIS: Yes and no. We have statistical evidence. We have evidence of how many planets that might be like ours. For example, the Drake equation [the equation that estimates the likelihood of life elsewhere in the universe] …

REES: Yes. But we don’t know if life started in these places.

Let’s look at use of this in a different context than climate science.  As in this interview of Errol Morris by Calum Marsh, “On Donald Rumsfeld’s Inability to Separate Fact from Fantasy“, Esquire, 3 April 2014

EM:  He {Rumsfeld} wrote this to the president of the United States: “The absence of evidence isn’t the evidence of absence.” What’s he doing? He’s taking a phrase that was popularized by Martin Rees, the British Astronomer Royal and former president of the Royal Society, and Carl Sagan. They’re the ones who used this expression, but they used it in a very specific context. They used it in the context of searching for extraterrestrial life and extraterrestrial intelligence, saying that the universe is a very big place, and that just because we haven’t had evidence of life doesn’t mean it isn’t there. Then all of a sudden the ballistic missile commission picks it up, and Rumsfeld runs with it, and it’s trucked out during the run-up to the Iraq war.

ESQ: Not exactly the same situation.

EM: But no one seems to notice that the context is different. This is not the universe at large, this is Iraq, and a very specific site in Iraq where it was suspected that a WMD could be found. A UN weapons inspector goes to Iraq and can’t find any evidence of a WMD — that’s not absence of evidence, that’s direct evidence that the suspected WMDs are simply not there. The way I describe it is that it’s like someone tells you there’s an elephant in the room. You open the door and you look in the room, you open the closets, you look under the bed, you go through the bureau drawers, and you don’t find an elephant. Is that absence of evidence or evidence of absence? I would submit it’s the latter.

So is the present state of climate science like looking for data in a room and not seeing it? Or looking for data in the vastness of space and not seeing it (yet)? The answer to this question determines how you see the debate.

(3)  Why the debate? Isn’t the climate signal from humanity obvious?

Finding a signal of anthropogenic climate change is far more difficult than activists imply. The strongest consensus among climate scientists is, in the words of the new IPCC AR5 (Working Group I):

“It is extremely likely (95 – 100% certain) that human activities caused more than half of the observed increase in global mean surface temperature from 1951 to 2010.”

While a well-established finding, even that is not obvious in the data, as seen in this graph from the UK Met Office report “The recent pause in global warming: What do observations of the climate system tell us?“, July 2013.

UK Met Report, July 2013
“The recent pause in global warming: What do observations of the climate system tell us?”, UK Met Office, July 2013

The anthropogenic climate signal is far more difficult to see in other forms of weather, and immensely more difficult to detect in the relatively rare instances of extreme weather since 1950. Hence the IPCC’s tentative statements about the likelihood of anthropogenic factors increasing extreme weather.

Other than temperature and (to a lesser degree, precipitation) the IPCC — reflecting the climate science literature — sees more absence of evidence than evidence. Hence many people’s reluctance to take large-scale measures to prepare for future extreme weather.

Yet consensus climate science theory (seen in the IPCC’s reports) tells us to expect severe increases in extreme weather during the rest of this century. Hence the perfectly legitimate warning that the absence of evidence is not evidence of absence.

Eventually the climate will answer all our questions, but unfortunately probably too late for us to prepare if the answer is bad news. So we need to make decisions now. We have the logical tools and experience to make sound decisions, but are hindered by chaff thrown into the air by both sides. But, in my opinion, mostly by the climate activists on the Left. The smears and exaggerations make rational debate difficult or impossible, so we do almost nothing.

This is not the way a great nation conducts its business, or provides leadership to the world. We can do better.

(4) For More Information

(a) Posts about epistemology and the progress of science:

  1. Magical theories of science, and how they influence us, 14 February 2014
  2. A key to understanding the climate wars (about one of our big weaknesses), 15 March 2014

Truth Will Make You Free

(b)  Reference Pages about climate on the FM sites:

  1. My posts
  2. Studies & reports, by subject
  3. The history of climate fears

(c)  A few important things to remember about global warming

Please read this before commenting about my views about global warming and climate change. It also has links to the key posts on the FM website on this topic.

(d)  Posts asking if we’re prepared for past weather:

  1. Have we prepared for normal climate change and non-extreme weather?, 11 February 2014
  2. Droughts are coming. Are we ready for the past to repeat?, 12 March 2014

(e)  Posts about extreme weather:

  1. Ignorance and propaganda about extreme climate change, 10 July 2012
  2. A look behind the curtain at the news of extreme climate events in the US, 22 August 2012
  3. Hurricane Sandy asks when did weather become exceptional? (plus important info about US hurricanes), 28 October 2012
  4. Has global warming increased the frequency & virulence of extreme weather events?, 10 February 2013
  5. The Oklahoma tornadoes can teach us about our climate, and ourselves, 22 May 2013
  6. The IPCC gives us straight talk about Extreme Weather, 4 October 2013
  7. The IPCC rebukes the climate doomsters. Will we listen?, 15 October 2013
  8. A summary of the state of climate change and extreme weather, 12 December 2013




18 thoughts on “Cutting to the heart of the public policy debate about climate change”

  1. Climate is not weather. You have set up a strawman and proceed to knock it down. A more practical hypothesis is: “human activity influence climate.” IF you answer yes, then the issue becomes one of why (“due to GHG emissions”), how much, and what are the pros and cons.

    There are ways to test the model predictions in a prospective manner. Make a prediction a year out. Wait a year. See how well it tracks. Pick best models and repeat for 30 years.

    The climate models made by IPCC have made a number of predictions (the models themselves, not the reports, since the IPCC used a range of models). Since the point of modelling is to make things better over time, you start actually by going back 30 years and making predictions for 30 years out and take the best performing models/parametres and run them out for another year. Wait one year. Take the best performing models/parametres and run another year out. And so on. Every year you keep updating the models/parametres from the previous year’s performance. After 30 years, every single prediction would be a *true* blind prediction. Now see how well they are doing.

    This sort of a thing has been done for predictions made from 1990 models and it turns out the models perform surprisingly well:

    1. About your cherry-pick from of one paper from the large literature on the accuracy of model predictions, that doesn’t tell us much. The accuracy of climate models is an active focus of research by climate scientists.

      (1) As always, I believe we should start with the latest IPCC report, as a guide to the consensus of climate scientists. See AR5, WGI, Chapter 9: “Evaluation of Climate Models” for a long detailed analysis. The bottom line, from the Executive Summary:

      Most simulations of the historical period do not reproduce the observed reduction in global mean surface warming trend over the last 10 to 15 years. There is medium confidence that the trend difference between models and observations during 1998–2012 is to a substantial degree caused by internal variability, with possible contributions from forcing error and some models overestimating the response to increasing greenhouse gas (GHG) forcing. Most, though not all, models overestimate the observed warming trend in the tropical troposphere over the last 30 years, and tend to underestimate the long-term lower stratospheric cooling trend.

      This is perhaps the key issue, and has increasingly become a focus of the climate science literature.

      Still good news: global temperatures remain stable, at least for now., 14 October 2012
      Scientists explore causes of the pause in warming, perhaps the most important research of the decade, 17 January 2014
      One of the most important questions we face: when will the pause in global warming end?, 25 August 2013

      The trend since roughly 1998 is running at the low end of model forecasts. If the pause continues (no statistically significant warming of the surface atmosphere temperature), then the trend will drop below the range of model forecasts. This is one of the better illustrations, imo: a graphic by Ed Hawkins (Climate scientist in National Center for Atmospheric Science at the University of Reading), from his website, 2 February 2014:


      (2) Assessment of the first consensus prediction on climate change“, David J. Frame and and Dáithí A. Stone, Nature Climate Change, April 2013

      In 1990, climate scientists from around the world wrote the First Assessment Report of the Intergovernmental Panel on Climate Change. It contained a prediction of the global mean temperature trend over the 1990-2030 period that, halfway through that period, seems accurate. This is all the more remarkable in hindsight, considering that a number of important external forcings were not included. So how did this success arise? In the end, the greenhouse-gas-induced warming is largely overwhelming the other forcings, which are only of secondary importance on the 20-year timescale.

      (3) The models are today somewhat of a “dogs breakfast”, using parameterization instead of representation of all the key climate dynamics. For more about this see “What Are Climate Models Missing?“, Bjorn Stevens and Sandrine Bony, Science, 31 May 2013 — Abstract:

      Fifty years ago, Joseph Smagorinsky published a landmark paper describing numerical experiments using the primitive equations (a set of fluid equations that describe global atmospheric flows). In so doing, he introduced what later became known as a General Circulation Model (GCM). GCMs have come to provide a compelling framework for coupling the atmospheric circulation to a great variety of processes. Although early GCMs could only consider a small subset of these processes, it was widely appreciated that a more comprehensive treatment was necessary to adequately represent the drivers of the circulation.

      But how comprehensive this treatment must be was unclear and, as Smagorinsky realized, could only be determined through numerical experimentation. These types of experiments have since shown that an adequate description of basic processes like cloud formation, moist convection, and mixing is what climate models miss most.

      (4) Overestimated global warming over the past 20 years“, John C. Fyfe et al, Nature Climate Change, September 2013.

      Recent observed global warming is significantly less than that simulated by climate models. This difference might be explained by some combination of errors in external forcing, model response and internal climate variability.

      (5) Do GCM’s predict the climate… or macroweather?“, Shaun Lovejoy et al, Earth System Dynamics, 28 November 2013 — Abstract:

      We are used to the weather–climate dichotomy, yet the great majority of the spectral variance of atmospheric fields is in the continuous “background” and this defines instead a trichotomy with a “macroweather” regime in the intermediate range from ≈ 10 days to 10–30 yr ( ≈ 100 yr in the preindustrial period). In the weather, macroweather and climate regimes, exponents characterize the type of variability over the entire regime and it is natural to identify them with qualitatively different synergies of nonlinear dynamical mechanisms that repeat scale after scale. Since climate models are essentially meteorological models (although with extra couplings) it is thus important to determine whether they currently model all three regimes.

      Using last millennium simulations from four GCMs (global circulation models), we show that control runs only reproduce macroweather. When various (reconstructed) climate forcings are included, in the recent (industrial) period they show global fluctuations strongly increasing at scales > ≈ 10–30 yr, which is quite close to the observations. However, in the preindustrial period we find that the multicentennial variabilities are too weak and by analysing the scale dependence of solar and volcanic forcings, we argue that these forcings are unlikely to be sufficiently strong to account for the multicentennial and longer-scale temperature variability.

      A likely explanation is that the models lack important slow “climate” processes such as land ice or various biogeochemical processes.

      (6) Simplicity amid Complexity“, Isaac Held, Science, 14 March 2014 — Gated. Opening:

      We live in interesting times as we watch diverse effects of human activities on Earth’s climate emerge from natural variability. In predicting the outcome of this evolving inadvertent experiment, climate science faces many challenges, some of which have been outlined in this series of Science Perspectives (1–6): reducing the uncertainty in climate sensitivity; explaining the recent slowdown in the rate of warming and its implications for understanding internal variability; uncovering the factors that control how and where the land will become drier as it warms; quantifying the cooling due to anthropogenic aerosols; explaining the curious evolution of atmospheric methane; and predicting changes in extreme weather.

      In addition to these challenges, the turbulent and chaotic atmospheric and oceanic flows seemingly limit predictability on various time scales. Is the climate system just too complex for useful prediction?

      (7) Simplicity amidst complexity (?)“, Judith Curry at her website Climate Etc, 17 March 2014 — Opening:

      Held’s article raises a very important issue – whether climate change is predominantly linear and dominated by external forcing, or whether natural internal variability is the intrinsic mode of variability on decadal to century timescales. In other words, is natural internal variability the icing on the cake, or the cake itself?

      While I like Held’s article in the sense that I find it to be provocative, I disagree with much of it. …

      (8) Recent observed and simulated warming“, John C. Fyfe and Nathan P. Gillett, Nature Climate Change, in press — Gated.

    2. “After 30 years, every single prediction would be a *true* blind prediction.”

      Hardly. It’s just curve fitting. And, curve fitting with a sufficiently dense base will always converge to a minimum error representation in real time. But, it has no predictive skill beyond the interval in which the fit occurs.

  2. Hello again!
    This will be an exposition of my ignorance on this topic, but that’s sort of the point. The following thoughts occur to me when I think about climate change, and they all come from documentaries that I have seen and websites that I have visited (as I am not a climatologist, or geologist, or in fact any of the obscure but utterly necessary ists). Very quickly, I have no idea whether human activity is impacting the Earth’s temperature and climate – I’m told that it is by some scientists, and that it’s not by others. More detail on this follows, but I’ll stick to the topic of CO2. The Earth appears to be slowly getting warmer (gradually by human standards – there’s even a graph here: but then agreement on why this should be, appears to be missing. Three documentaries I watched recently seem to tessellate on this issue.

    Iain Stewart ( stated in his series ‘How Earth Made Us’, that a working theory amongst geologists, is that the Himalyas rising when they did, (50 million years ago) cooled the Earth enough to make the sort of life that we are and see around us possible by reducing the amount of carbon in the atmosphere through a process of chemical weathering (spoken of here under the ‘rise of the Himalayas’ section Obviously, we have records of life going back much further than 50 million years ago (mya) and a quick look on the Wiki ( – the geological age right after the asteroid that hit the Earth and killed the dinosaurs, and, – the geological age we live in now) gives us the following – the world had more carbon in its air (500ppm) in the Paleogene era and was 4 degrees C warmer globally. This period enjoyed a ‘rapid diversification’ of mammal life.

    So, we can relax at least a little by concluding that warming the Earth up won’t end all life on the planet (I include that because I have heard people say that we could roast the globe to smithereens by dint of CO2 alone). We are told that food shortages, flooding, drinking water shortages and the chaos of mass migrations caused by affecting our weather patterns by making the atmosphere warmer and melting the ice caps, thereby flooding low-lying areas, would be catastrophic on our world of over 7 billion humans, and the logic that sharply rising sea levels and changing weather patterns would have an impact is, I think, unassailable. What is not known for sure it seems, is how much of a change and how fast will it happen if it is down to CO2 in the air?

    I have also watched ‘Chasing Ice’ – the documentary by James Balog and ‘An Inconvenient Truth’ – the documentary by Al Gore, and in both films, ice core data from the polar ice caps is used to point out that going back into the past an awfully long time by human standards (Al Gore gives us the figure 600,000 years), we can see that in the pre-industrial era, CO2 never really exceeded 300ppm in the atmosphere. Both men go on to state that our industrial era has pushed CO2 levels up beyond their historic norms to around 500ppm (although the website ‘CO2 Now’ puts that figure closer to 400ppm – – still a third higher than the pre-industrial age) and point out that this will warm the world up, as it always has in the past. This is a point that needs clearing up for the public (myself included) do higher leveles of CO2 make the world warmer, or not? I’m not a scientist. The Paleogene era had levels of CO2 100ppm higher than the present day of 400ppm and was 4 degrees warmer than the pre-industrial Neogene (300ppm max) era.

    My thinking on this then, goes like this. If Iain Stewart was right when he said that the Himalayas cooled the Earth down by reducing the carbon in the air, and if we accept that the Paleogene era was 4 degrees warmer than the pre-industrial Neogene era, and that the root cause of that was increased carbon in the air, which was reduced by the chemical weathering caused by the Himalayas, which kept Neogene era CO2 levels and temperatures below their Paleogenic norms, then why are we as a species arguing against the idea that increasing the CO2 levels in the atmosphere to Paleogenic levels will affect the global temperatures and weather patterns? This goes back to my question above – does increased CO2 in the air make the world warmer or not?

    More than that though, if we humans can alter CO2 levels in the air enough to take our climate back in geological time, what’s the ceiling on how warm extra CO2 makes things? The era that came before the asteroid, the Cretaceous, had CO2 levels of 1700 ppm (according to Wiki, but temperatures were no warmer than the Paleogenic age. (That’s possibly because CO2 acts as an insulator rather than as a heat generator, and there’s a limit to how effective any insulation can be, but then again, I’m not a scientist, so of course that could be way off. Perhaps the Neogene era is cooler than the Paleogene era for some other reason?). One assumption that a person could make then is that Paleogenic times had lots of mammals and the world was warmer – and that Cretaceous times were no warmer even with over three times as much CO2 as measured in ppm, so, so what? Problems can come, as the Wisconsin Department of Health Services tells us ( in that humans report complaints of “drowsiness and poor air” in environments that have 1000-2000 ppm CO2 (Cretaceous levels). How much CO2 are we capable of putting into the atmosphere? It should be stressed that the toxicity level of CO2 in humans is apparently MUCH higher than our current atmospheric levels (around 50,000-100,000 ppm).

    Overall, my thoughts on the topic are these – if we could have straight and direct, agenda-free answers to questions like these, we could begin to take in the meat of the climate change debate as a public. 1) Does increasing the level of CO2 in the atmosphere warm the world up or not? 2) What likely effects would such a warming have on our sea levels, soil health, sea water acidity, climate patterns, animal and insect life, human and animal diseases and global distribution of drinking water?

    If the CO2 issue is something to worry about and do something about, why aren’t we doing it? If it’s not, why are we talking about it? I’ve yet to see the TV news come out and say that current levels of CO2 look set to increase and return us to Paleological climate patterns and discuss the impact of that if it did happen. Is that because it’s utter rubbish, or is it simply indicative of the tendency to not examine a thing from every angle, top to bottom? No matter what anybody’s opinion on climate change is, there will be a truth (what actually happens) and, as we keep on telling ourselves, we’re smart enough as a species to measure things and predict what that truth is likely to be. Why then is there so much controversy about this? It seems that every time climate scientists come out and say “we’re changing the world by increasing the CO2 in the atmosphere”, we’ve got a large group of people chanting “no, we’re not”. It all falls to name calling and nothing gets done. Surely this stuff should be scientifically measureable and verifiable fact, and not a matter of opinion?

    Short version: Iain Stewart, geologist, said that the Earth is cooler than it was because there’s less carbon in the air, and that’s because of the Himalyas. If that’s the thing seperating us from the Paleogene climate of yesteryear, and we humans have built the CO2 halfway back up to pre-Himalayas levels again, why are we arguing the toss that increased CO2 will warm the world up?

    P.S. CO2 is just one of the gasses we release as a result of our activities. The same questions surround Methane, Carbon Monoxide et al…

    1. Michael,

      I strongly recommend reading summaries by the IPCC, UK Met Office, and NOAA. They explain these issues clearly, in terms useful for us laypeople.

      There is not anything remotely close to the degree of uncertainty among scientists as you describe.

      You are describing what I call the chaff tossed at us by political activists. Ten seconds reading their chatter is ten seconds or your life squandered.

      1. I was hoping you’d say something like that! I will get into reading those summaries in the week – not up to it today. It galls me that as you say, chaff from political activists can obfuscate an issue so badly. I will be back here when I’ve read those summaries :)

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  5. Any equivocation of “evidence of absence” with “absence of evidence” is a reification fallacy. When evidence is absent from a scientific test, the hypothesis must be discarded. To state that a hypothesis could still be true, in the absence of evidence, is to not understand the contextual and finite nature of any hypothesis/proposition.

    1. Jim,

      “absence” with “absence of evidence” is a reification fallacy. When evidence is absent from a scientific test, the hypothesis must be discarded.”

      That is not correct. A hypothesis is not discarded after inconclusive tests, but after sufficient accumulated *negative* evidence, *repeated* experimental failure to find proof, or change in the theories held by relevant scientists (up to paradigm change).

  6. Stranger in a Strange Land

    Here are six simple questions and their accompanying answers (i.e., “known knowns”) that form scientific statements and/or observations that have been repeatedly verified through careful experiments and/or observations. These statements are, I believe, both simple to grasp and are fundamental to understanding the debate about Climate Change and its AGW component.

    1) Is carbon dioxide a greenhouse gas?

    Answer = Yes. (Note: This was first postulated and confirmed in the early 19th century.)

    2) Are there other possible greenhouse gases?

    Answer = Yes. (e.g., methane, chlorofluorocarbons, etc.)

    3) Are there gases that can act to cool the atmosphere?

    Answer = Yes. (e.g.,aerosols that result in increased cloud cover that results in increased albedo)

    4) Do humans produce these gases (both warming and cooling) to the extent that their concentration in the atmosphere can be measured and that this increased concentration could, hypothetically speaking at least, lead to a change in energy levels trapped within the Earth’s atmosphere (i.e., Climate Change whether manifested as Global Warming or Global Cooling)?

    Answer = Yes.

    (Note. While the scientific consensus seems to be that the amount of greenhouse gases, especially carbon dioxide, produced by humans are the more important of the two types of gases produced by human activities, there is no doubt that cooling gases also play an important role in this discussion.)

    5) Considered over a long term time span (e.g., centuries, millennium, eons, etc.) is the Earth’s climate in a state of equilibrium or disequilibrium?

    Answer = Disequilibrium. (meaning that in the long run, Climate Change is the normal state of affairs.)

    6) Finally, are there other factors, aside from greenhouse gases (whether produced by natural processes such as volcanic activity or man-made) that affect the Earth’s climate?

    Answer = Yes. (For example, changes in the amount of solar radiation received, Earth’s orbital inclination, ocean and atmospheric circulation patterns, etc., etc., etc.)

    In my estimation, questions number 5 and 6 and their accompanying answers are critical to what comes next in this discussion.

    The first problem we are faced with is that there are a variety of factors at play in any discussion of the Earth’s climate, and a consideration of all these factors and their interactions can be quite bewildering and even a bit overwhelming, especially to a lay person.

    So let’s simplify the discussion somewhat, and consider four possible scenarios. Unfortunately as we shall see, the validity of any one of these particular scenarios is not easily established.

    We start with the fact that the Earth’s climate, when considered on a long term basis, is always in a state of relative instability and flux. (In fact, if it not for this climatic instability, it is highly unlikely that humans would ever have evolved in the first place.)

    With that fact kept firmly in mind (i.e., the Earth’s climate is in a long term state of flux), considering just the time span of the last 2-3 centuries (i.e., duration of the Industrial Revolution during which time humans have been introducing ever increasing amounts of greenhouse gases into the atmosphere) and without even looking or knowing what the data actually shows beforehand, we can predict with a fair degree of certainty that the Earth was either:

    a) Experiencing a cooling trend; or

    b) Experiencing a warming trend.

    (Of course, there is a third possibility, that the earth’s climate alternated between the two trends, but let’s just keep things as simple as possible for the purposes of this discussion.)

    Next, combining these two possible trends with the two possible basic hypotheses regarding the effect that human activity can have on the climate, i.e., that these activities can either affect the climate or cannot affect the climate (which, of course, would be the Null hypothesis), we now have four possible (basic) scenarios:

    1) The Earth was already in a (perhaps slight) warming trend for the last 2-3 centuries, and the introduction of greenhouse gases by humans accelerated and exacerbated this trend.

    2) The Earth was already in a warming trend for the last 2-3 centuries, but for whatever reason the introduction of greenhouse gases by humans did little or nothing to accelerate or exacerbate this trend.

    3) The Earth was actually (or should have been) in a cooling trend for the last 2-3 centuries, but the introduction of greenhouse gases by humans was enough to counter and/or offset this trend (i.e., our production of greenhouse gases helped to stabilize and even warm the climate to a slight degree).

    4) The Earth was actually in a cooling trend for the last 2-3 centuries, but the introduction of greenhouse gases by humans failed to counter this trend (i.e., our production of greenhouse gases was insufficient to stabilize or warm the climate).

    So now let’s look at the data, such as it is.

    We start by conceding that our measurements of the Earth’s temperature over the past century or so have been more or less correct, and that up until relatively recently (about 10-15 years ago) these measurements indicated that the Earth was experiencing a prolonged warming trend (albeit the degree and significance of this trend has been the subject of some debate).

    (Or, should you reject this data for whatever reason, you have a problem in that that there is no good evidence that the Earth was experiencing a prolonged cooling trend. In that case, you would be arguing that the Earth’s climatic regime for the past 2-3 centuries was stable, which is, of course, possible but counter to the long term historical trend as seen in the geological record (i.e., centuries, millennia, eons).)

    So assuming that the temperature measurements made over the course of the last century or so are correct and accurate, this would then mean that only scenarios 1 through 3 (as described above) could also be correct (i.e., our measurements indicate that the Earth was experiencing a prolonged warming trend over the past 2-3 centuries).

    Unfortunately, at this point in time, given the incredible complexity of modeling the climate (i.e., the huge, almost infinite number of variables and their interactions that must be considered) and especially the fact that we really have no way of knowing in what direction the climate would have been trending (i.e., cooling or warming) absent the introduction of human activity (i.e., we cannot test the validity of the Null hypothesis unless we can establish with absolute certainty that the Earth’s climate would have been stable in the absence of such activity), there is absolutely no way we can state with any degree of scientific certainty which of the three possible scenarios (as outlined above) is the true or likeliest scenario.

    Therefore, I believe the debate surrounding Climate Change and its human induced component (e.g., AGW) is way overdone and overplayed by both sides to equal measure.

    And since we really cannot say with any degree of scientific certainty how much Climate Change is the result of human activity and, just as importantly, in all likelihood never will be able to do so, all of these heated arguments and name calling over the issue are largely a waste of precious time and resources.

    At the same time I believe that there can (or should be) no debate that the climate is changing (always has and always will), and that the focus of our efforts should therefore, be to mitigate and prepare for that change.

    I also firmly believe that we need to explore and develop our use of renewable clean energy sources as quickly and urgently as possible, but for non-climate change based or related reasons. (Peak Oil being the most important but also general environmental reasons as the extraction and use of fossil fuels is a fairly dirty and unhealthy affair).

    1. Stranger,

      I find this quite odd. We have excellent explanations at all levels — from introductory for children to professional for climate scientists — of these things, prepared by experts. What is the point of this kind of amateur analysis? Why should anyone read this, let alone give credence to it?

    2. Stranger in a Strange Land

      Well I thought the title of your thread had something to do with getting to the heart of the climate debate. So my effort was something I had been thinking about lately, an attempt to simplify matters down to the their most basic elements, such that even that “child” could easily understand the problem.

      But you could you point to even one fundamental flaw in my reasoning or argument here? If so, then I would be glad to re-consider it.

      One important point I was trying to make was that if you can’t even meet basic preconditions for establishing a null hypothesis, then any exhortation to data and statistical analysis is rendered meaningless, and you can really make no scientific statements re Climate Change.

      We don’t have a reliable baseline from which to measure change, make coherent statements, or most important of all, useful predictions.

      To tell you the truth, while I have learned much from reading your articles re climate change, unfortunately at the same I have found many of your replies to those posting on your site condescending, tedious, overbearing, and sanctimonious.

      But apparently you would rather obfuscate then educate.

      You seem to operate with somewhat of a closed mind (e.g., Your answer to why the rise in global temperatures has leveled off. According to you it can only be because the previous predictions re AGW were all wrong. But how do you know that the increases in energy retained by the Earth are not now being absorbed by some other as yet unknown and undiscovered mechanism or accounted for by some other phenomenon at work? The answer is, you can’t. Of course, when and if something along these lines is ever discovered, it will be “well of course, the answer was there all along”. But in the meantime you heartily dismiss any who disagree with you and do not seem to entertain that this could be a possibility.)

      Remember, as Shakespeare once said, “There are more things in Heaven and Earth than are dreamt of in your philosophies…”

      And as someone else once said (I think it was Mark Twain), “There are three kinds of lies: Lies, damn lies, and statistics”.

      You seem to think that statistics could never be a lie, when clearly they can be.

      But not to worry, I won’t bother you with any more posts that you needn’t give “credence to”…

      1. Stranger,

        In a debate about building a bridge, that does not mean that everybody takes paper and designs one. That’s not how public policy debates work. There are many questions we can debate: what experts say, what constitutes sufficient evidence to impell action, balancing risks-evidence-costs, balancing this need against other needs.

        These are all complex matters on which every citizen can speak.

        But I don’t understand why amateur analysis of technical matters helps. If you child needed brain surgery, would you like me to provide my analysis of the medical situation and alternatives — starting from first principles? You’d say I was a distraction at a stressful important time — and rightly so.

  7. Hullo!

    I said I’d be back and so here I am. I tried to find climate change stuff on the NOAA site ( but it seems to be more about weather – I can be a bit of a thickie so I might have looked in the wrong place. More direct was the UK Met Office, where they are plain on the issue of human impact on climate ( stating that “there is an underlying trend of warming that is almost certainly caused by man’s activities.” The summary of the IPCC ( says much the same thing (p.3) “A key finding of the WGI AR5 is, “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.””

    So, as you have said, there is little daylight between the actual scientists on the issue there. I read another blog called that specialises in all matters EU (specifically with regards to the UK and its relationship to the EU) and on there, they periodically have stuff about climate change, largely calling the IPCC summaries out as bunkum ( and it’s that that I’m talking about. Either the scientists are right, and we should shut up and take our medicine with regards this CO2-climatechange-global warming issue, or the scientists are paid stooge henchmen alarmists as the people over at eureferendum keep on saying. This next quote comes from the following article “All true science, of course, has here been thrown out of the window. There is no rising trend in atmospheric humidity. Put the Arctic and the Antarctic together and there is more polar sea ice today than at any time since satellite records began in 1979. Not even the IPCC predicts a temperature rise of 5ºC.” ( posted February 2014. Christopher Booker time and again calls hoax on the idea of global warming and states explicity that the IPCC is up to no good:

    “Each time it would emerge just how shamelessly these Summaries had distorted the actual evidence, picking out the scary bits, which themselves often turned out not to have been based on proper science at all.

    The most glaring example was the IPCC’s 2007 report, which hit the headlines with those wildly alarmist predictions that the Himalayan glaciers might all be gone by 2035; that global warming could halve African crop yields by 2050; that droughts would destroy 40 per cent of the Amazon rainforest.

    Not until 2010 did some of us manage to show that each of these predictions, and many more, came not from genuine scientific studies but from scaremongering propaganda produced by green activists and lobby groups (shown by one exhaustive analysis to make up nearly a third of all the IPCC’s sources).” (Taken from posted April 2014).

    I, like most people have no trouble believing what scientists tell me when lots of them tell me the same thing, but when an expert blogger re-posts the words of a working journalist who accuses the IPCC of shaky practice, it casts into doubt the force of what the IPCC are saying, which is a shame if they’re actually right. The arguments for the layperson of the IPCC and the UK Met Office are compelling, and it frustrates me that even sensible people are saying that they’re wrong. It’s an unfortunate mess and it shouldn’t have gotten this way. As you said above, you wouldn’t want just anybody advising you on brain surgery, so why do we accept it on climate science? Either it’s happening, or it’s not. The UK Met Office is sure that it is happening, and that we are the major cause outside and beyond natural variability, so it ought to be beyond question, surely? (For the record, I have anecdotally witnessed changing weather patterns over the course of my lifetime in and around Liverpool, with it tending to be slightly hotter and slightly wetter as the years go on, and with the seasons seeming to move around and with the weather locally often bearing little resemblance to what the TV weathermen said it was going to be like. I find it easy therefore to accept that our climate is changing, even where I read people telling me adamantly that it’s not.)

  8. Pingback: p → q and CO2 | Episyllogism

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