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Is the science settled?

Posted on 24 March 2010 by John Cook

A common skeptic refrain is that "the science isn't settled", meaning there are still uncertainties in climate science and therefore action to cut CO2 emissions is premature. This line of argument betrays a fundamental misunderstanding of the nature of science. Firstly, it presumes science exists in a binary state - that science isn't settled until it crosses some imaginary line after which it's finally settled. On the contrary, science by its very nature is never 100% settled. Secondly, it presumes that poor understanding in one area invalidates good understanding in other areas. This is not the case. To properly answer the question, "is the science settled?", an understanding of how science works is first required.

Science is not about absolute proofs. It never reaches 100% certainty. This is the domain of mathematics and logic. Science is about improving our understanding by narrowing uncertainty. Different areas of science are understood with varying degrees of confidence. For example, while some areas of climate science are understood with high confidence, there are some areas understood with lower confidence, such as the effect on climate from atmospheric aerosols (liquid or solid particles suspended in the air). Aerosols cool climate by blocking sunlight. But they also serve as nuclei for condensation which leads to cloud formation. The question of the net effect of aerosols is one of the greater sources of uncertainty in climate science.

What do we know with high confidence? We have a high degree of confidence that humans are raising carbon dioxide levels in the atmosphere. The amount of CO2 emissions can be accurately calculated using international energy statistics (CDIAC). This is double checked using measurements of carbon isotopes in the atmosphere (Ghosh 2003). We can also triple check these results using observations of falling oxygen levels due to the burning of fossil fuels (Manning 2006). Multiple lines of empirical evidence increase our confidence that humans are responsible for rising CO2 levels.

We also have a high degree of confidence in the amount of heat trapped by increased carbon dioxide and other greenhouse gases. This is otherwise known as radiative forcing, a disturbance in the planet's energy balance. We can calculate with relatively high accuracy how much heat is trapped by greenhouse gases using line-by-line models which determine infrared radiation absorption at each wavelength of the infrared spectrum. The model results can then be directly compared to satellite observations which measure the change in infrared radiation escaping to space. What we find in Figure 1 is the observed increased greenhouse effect (black line) is consistent with theoretical expectations (red line) (Chen 2007). These results can also be double checked by surface measurements that observe more infrared radiation returning to Earth at greenhouse gas wavelengths (Evans 2006). Again, independent observations raise our confidence in the increased greenhouse effect.

Increased greenhouse effect - models vs observations
Figure 1: Increased greenhouse effect from 1970 to 2006. Black line is satellite observations. Red line is modelled results (Chen 2007).

So we have a lower understanding of aerosol forcing and a higher understanding of greenhouse gas forcing. This contrast is reflected in Figure 2 which displays the probability of the radiative forcing from greenhouse gases (dashed red line) and aerosol forcing (dashed blue line). Greenhouse gas forcing has a much higher probability constrained to a narrow uncertainty range. Conversely, the aerosol forcing has a lower probability and is spread over a broader uncertainty range.


Figure 2: Probability distribution functions (PDFs) from man-made forcings. Greenhouse gases are the dashed red curve. Aerosol forcings (direct and indirect cloud albedo) are the blue dashed curve. The total man-made forcing is the solid red curve (IPCC AR4 Figure 2.20b)

The important point to make here is that a lower understanding of aerosols doesn't invalidate our higher understanding of the warming effect of increased greenhouse gases. Poorly understood aspects of climate change do not change the fact that a great deal of climate science is well understood. To argue that the 5% that is poorly understood disproves the 95% that is well understood betrays an incorrect understanding of the nature of science.

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Comments 1 to 50 out of 119:

  1. Very cogent and well written.
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  2. From an article in The Economist:

    In any complex scientific picture of the world there will be gaps, misperceptions and mistakes. Whether your impression is dominated by the whole or the holes will depend on your attitude to the project at hand. You might say that some see a jigsaw where others see a house of cards. Jigsaw types have in mind an overall picture and are open to bits being taken out, moved around or abandoned should they not fit. Those who see houses of cards think that if any piece is removed, the whole lot falls down. When it comes to climate, academic scientists are jigsaw types, dissenters from their view house-of-cards-ists.


    http://www.economist.com/displayStory.cfm?story_id=15719298
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  3. This settles it! :) Just kidding.

    The Scientific Consensus is my attempt to show why we have enough confidence to take action now.

    I recently posted on Bart Verheggen's blog the following:

    I agree that waiting another 30 years will give us more validation but that is comparable to telling a person who we think may have cancer to wait 30 years to see if it kills him. If we are right about AGW, we do not have the luxury of waiting. I wish it were otherwise.
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  4. What you have left out of your discussion John is the effect of net response of the climate system. Dr Trenberth in his AUG09 paper "An Imperative for Climete Change Planning: tracking Earth's global energy" attributes in Fig 4. responses due to Radiative feedback of -2.8W/sq.m and water vapour and ice albedo feedbacks of +2.1W/sq.m giving a net response of -0.7 W/sq.m.

    This must be added to the net purported anthropogenic radiative forcings of 1.6 W/sq.m which reduces the total net imbalance to +0.9 W/sq.m.

    There is no direct measurement of these amounts in an atmosphere with an incoming net heat flux of roughly 240W/sq.m.

    There is also a wide range of uncertainty about the effect of doubling of CO2 to 560ppmv. Increasing surface and tropospheric temperature will raise outgoing longwave radiation (OLR)and some suggest a rise as low as 0.5 degK and others 2-6 degK for this doubling.

    Such a wide range is an indication that for practical climate change prediction - the claimed well known AG forcings are not much good for such purpose when large unknowns are added and subtracted.
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  5. I also like Nature's editorial take on this very topic about a month ago now. They mentioned that there's four areas where the science isn't really settled, and they're by and large dealing with predicted effects of climate change. But, to use the term "the science isn't settled" ends up playing into skeptics hands, when in fact we're using the term in a different manner.
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  6. Well, great article. Finally says aerosols have a lot of uncertainty. And science is never settled. So why don't we just completely discard the "settled" nonsense.

    However ...

    "To argue that the 5% that is poorly understood disproves the 95% that is well understood betrays an incorrect understanding of the nature of science."

    sort of ignores the 5% might be really really important. Doesn't disprove any of the other 95%. This is so common in science there is even a saying, that goes something like "Another Beautiful Theory Slain By An Ugly Fact". People have languished in prison for heinous crimes, convicted by evidence beyond a reasonable doubt, and later exonerated by DNA testing. Maybe 1% of the evidence changed the conclusion.

    If aerosols are poorly understood, and not modeled by the computer models ... none of this counts for much. The AGW theory of course is that small increases in a rare gas in the atmosphere has far ranging effects. Nothing unusual about a theory where a small amount of something effects big changes (aka catalysts).

    By the same token, aerosols have an enormous effect - and I don't think that is really under dispute. Volcanic eruptions, SO2 pollution, etc.

    So if a part of the theory is poorly understood, and not modeled, that can completely change the conclusions ... there is a problem. What they call a Big One.

    An automobile can have 99.9% of its parts working, proven, "settled", understood, and if a wheel falls off - we still consider it a failure.


    And let me explain what science is. The "best" theory is considered to be the least long-winded explanation for a dataset. Occam's Razor.

    We use the model that the earth goes around the sun, not because of any inherent "truth", but because it simplifies the mathematics enormously. The dataset, what dots of light move across the sky when, doesn't change regardless if you use the "universe revolves around the earth' model.

    The dataset of interest in climate change is temperature. CO2 emissions and increases caused by mankind, while interesting, are not exactly what concerns people per se.

    So, in line with Occam's Razor, what choices of the least long-winded explanation can be used for avg global temps over time?

    a. a convoluted theory with CO2 as key variable, that gets more and more convoluted all the time

    b. temps are within normal variance


    If b. above, then none of the whining about species disappearing, sea levels rising, etc., etc. matter either. Just one more challenge for life to adapt to, which it has for billions of years.


    So for anyone using the word "science" ... ask them about Occam's Razor, and if they appear puzzled, figure they are not a scientist. Sort of the "litmus test". Anyone here know what litmus paper is?
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  7. Ken,

    Here is what Bony et al. (2006) founbd when reviewing the literature:

    Water Vapor (1.80 ± 0.18 W/m2/K)
    Lapse Rate (-0.84 ± 0.26 W/m2/K)
    Clouds (0.69 ± 0.38 W/m2/K)
    Surface Albedo (0.26 ± 0.08 W/m2/K)

    Knutti and Hegerl (2008) and IPCC (2007) conclude that various observations show a climate sensitivity value of about 3oC, with a likely range of about 2 – 4.5oC and that 2C seems pretty well constrained if you throw out Lindzen's work.

    I will download that Trenberth paper now.

    Bony, et al. (2006). How well do we understand and evaluate climate change feedback processes? Journal of Climate, 19, 3445 - 3482.

    Knutti, R. & Hegerl, G. (2008). The equilibrium sensitivity of the earth's temperature to radiation changes. Nature Geoscience, (1), 735 - 743.
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  8. Percentage uncertainty is still too large in relation to the proposed costs (Stern Report).
    For example, CO2 from the soil (one of the main arguments of skeptics) has the same isotope ratio. The process of decomposition in the soil can not be examined from a satellite. CDIAC soil respiration determined on the basis of a properly working (Interannual variability in global soil Respiration, 1980-94.) Covering Although 14 years of research, but ...
    "Soil respiration in terrestrial ecosystems worldwide is estimated to be 50-75 Pg C/year (Raich and Schlesinger 1992 ). The carbon cycle in soil has attracted much attention because it accounts for the second largest flux from terrestrial ecosystems, behind gross primary production (100-120 Pg C/year). In comparison, fossil fuel emissions contribute over 5 Pg C/year. [...]"(Duke University - http://www.biology.duke.edu/bio265/ajm21/intro.html).

    @ jsam
    "Very cogent and well written."

    In a well-known magazine "Skeptic" containing treated acute assessment (review) in numerous publications throughout the skeptical science (not just the climate) is the article: http://www.skeptic.com/the_magazine/featured_articles/v14n01_climate_of_belief.html
    Let me quote just one sentence:
    "It turns out that uncertainties in the energetic responses of Earth climate systems are more than 10 times larger than the entire energetic effect of increased CO2."

    Very cogent and well written.?
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  9. Your characterisation of science puts me in mind of a recent book on the OJ Simpson trial by Vincent Buglosi, who prosecuted Charles Manson in the 1960s.

    OJ Simpson, almost everyone now agrees, was guilty of murdering his ex-wife and her lover. There was blood evidence, he fled when the cops tried to arrest him, he had a history of violence etc. Yet his defence team persuaded the jury of three simple propositions:

    - There was a chain of evidence which had to be strong at every link.
    - Any broken link destroys the chain, and therefore the whole case ("If the gloves don't fit, you must acquit").
    - The chain was tainted by an irredeemably racist cop, and you could never be sure that the cop had not "fitted up" all the other evidence.

    This is similar to the case against AGW - ALL the evidence must be beyond doubt, a single contrary piece of evidence "falsifies" the AGW case, "corrupt" scientists cannot be trusted ("Climategate").

    Bugliosi counters with another metaphor - the evidence is not a chain but a rope of many fibres. Some fibres may be weak, and even fail. But overall, it the combined strength of the fibres that make the case. One "falsification" does not destroy a case or a science - usually that fibre can be repaired. A jury may discount a single piece of contrary evidence if the remainder of the evidence is sufficiently strong (in their estimation). The can still make a decision "beyond reasonable doubt".

    Bugliosi's view is close to the science philosopher's view of science - only when evidence against a theory begins to accumulate (several fibres start to break) will scientists contemplate a new or alternative theory. These are what Thomas Kuhn called "paradigm shifts".

    Climate science has a pretty strong bundle of fibres comprising the evidence, which you set out here. The AGW paradigm is paramount in climate science, but of course is never 100% beyond doubt.
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  10. Dear #9 ... and what about the Duke rape case? The prosecutor indeed covered up information that exonerated the defendents. Academics signed a letter piling on without a second thought. And for what? The academics had nothing riding on the outcome of the case. The prosecutor had won his election, he could have released the evidence, ended the case, and moved on.

    The OJ case was circumstantial, which is ALWAYS a difficult case to try. The cop committed perjury on the witness stand. The glove doesn't fit, and DNA tests in other jurisdictions have been falsified. The standard was reasonable doubt. Monday morning quarterbacks thought the standard had been reached, the jury didn't. That is our system of justice. Even if the simpliest explanation is that OJ was the doer.


    To push your rope analogy, imagine a rope with a lot of fuzz, like yarn. It looks thick, but the fuzz makes it difficult to determine how strong it is. It could be a piece of yarn, or a piece of steel wire inside.

    AGW assumes inside the fuzz is something, others say no one knows, not enough to trash the world's economy.
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  11. You have left out black carbon (soot), which is a very effective agent in melting snow, even in the absence of any warming. Of course, it can increase temperatures as well by decreasing surface albedo in snowy regions, hence increasing ASR (Absorbed Shortwave Radiation).

    Early 20th century warming of the North Atlantic region is due to this soot effect. Even now soot from American industry and wildfires is deposited on Greenland snow en masse.

    It is also the kind of pollution that can easily be mitigated, with immediate local benefits.



    On the other hand, regarding CO2 you have only demonstrated two points beyond any reasonable doubt.

    1. Atmospheric carbon dioxide level is increasing

    2. CO2 does absorb (and emit) IR radiation at certain wavelengths


    It is a far cry from demonstrating it makes Earth warmer indeed.
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  12. oracle2world states that addressing AGW will trash the world's economy. Hardly. Not addressing AGW will CERTAINLY trash the world's economy.

    Please see: The Copenhagen That Matters by Thomas L. Friedman in the NY Times.

    An excerpt:


    Although it still generates the majority of its electricity from coal, since 1990, Denmark has reduced its greenhouse gas emissions by 14 percent. Over the same time frame, Danish energy consumption has stayed constant and Denmark’s gross domestic product has grown by more than 40 percent. Denmark is the most energy efficient country in the E.U.; due to carbon pricing, through energy taxes, carbon taxes, the ‘cap and trade’ system, strict building codes and energy labeling programs. Renewable resources currently supply almost 30 percent of Denmark’s electricity. Wind power is the largest source of renewable electricity, followed by biomass. … Today, Copenhagen puts only 3 percent of its waste into landfills and incinerates 39 percent to generate electricity for thousands of households.


    Cap and trade has also worked in the US with regard to sulfur dioxide (SO2) emissions. SO2 emissions lead to acid rain and during the 1980s, acid rain was devastating lakes and forests in the east. In 1988, Congress passed a cap and trade scheme to reduce these emissions by 50%. By 2004, regulated polluters reduced their emissions by 40% more than required! The Dept. of Energy estimates that the cost to limit emissions ended up being a mere 0.6 percent of the polluters operating expenses.

    When CFCs were to be regulated/banned, there were similar claims of economic hardship. Like the other claims, these have not panned out.

    I also point you to:

    How to Talk to a Conservative about Climate Change which addresses costly consequences to a "do-nothing" approach to AGW.
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  13. So-called 'skeptics' also like to use the 'argument' : 'See, the science isn't settled, despite what you and your scientists say !'

    When asked to point out who actually says that, the response is usually along the lines of 'Fat Al Gore said it, to boost his fortune'. Or something like that.

    When asked to actually prove it, all I have ever seen is a report about Al Gore giving evidence before some US Committee, where the reporter writes that that is what Al Gore has stated. Nothing definite or proven, but more than adequate for denial purposes.
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  14. #8 That paper was very interesting. Appears to be peer-reviewed to boot.

    Focuses on general circulation models, uncertainty, and "parameters" which I keep reading about. When something isn't understood, a parameter is used, that of course supports the conclusion desired.
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  15. Oh, and ProfMandia has just reminded me of another so-called 'skeptic' fallacy, recently re-posted : tackling AGW will 'trash the world's economy'.

    Usually followed-up by : 'The poor (who I am very concerned about indeed) will be the ones most affected. Is that what you want : cos that's what you'll get.'
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  16. oracle2world, you have the application of Occam's Razor backwards here. Since most of the uncertainty involves negative feedbacks, the default assumption should be that warming will in fact occur.

    We can say with a high degree of confidence that we are increasing the concentrations of CO2, CH4, N2O, halocarbons, etc. in the atmosphere. We also have a high degree of confidence that all of the above act as greenhouse gases, reducing the outgoing flux of longwave radiation. We have a high degree of confidence that a reduction in outgoing LWR will warm the planet until outgoing LWR comes back into balance. Finally, we have a high degree of confidence that on a planet with oceans, this warming will then be amplified by a well understood water vapor feedback.

    There are less well understood positive and negative feedbacks. You can argue that one or another of these is overestimated or underestimated.

    But the simplest and most coherent position is that the world is going to warm because of the stuff listed above. If you want to make the case that it's not going to warm, your argument becomes more complicated and uncertain, because you have to either explain away the basic physics or get into the ugly details of biogeochemical feedbacks.
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  17. Nothing is absolute certainty. If we expected to understand everything in life to an absolute certainty, society wouldn't function.

    We ride in a car, knowing there's a chance we'll end up in an accident. We fly in a plane, knowing there's a chance we'll end up in crash. But, we still drive. And we still fly. Why? We, and those around us have reached a consensus that, for all practical purposes, it's safe to drive, and it's safe to fly.

    The so-called "skeptics" imply that climate science has only worked the issue of climate change from one angle. If that were true, then these "skeptics" are claiming the science doesn't work from a position of skepticism. That's not how this works. Scientists are skeptical, and they check the other side of the argument to cross-check their results. If they miss something, someone else will be sure to call them on it later. They work to answer the question, "can something else explain the results that have been seen?"

    Is climate change caused by "natural variation?" To some degree (excuse the pun) there are natural forces at work. But under cross-checking, these forces cannot account for the changes we're seeing today. Natural forces cannot account for current changes.

    Now what about past variation, or current, short-term fluctuations? These have been explained. There are viable, credible explanations for natural causes for these variations.

    But the current changes cannot be explained, using the same causes for past changes. So yes, there have been changes in the past - all caused by natural forcings. And there are short-term fluctuations - el nino, shifts in the jet stream, etc.

    But overall, there has been a rise in global temps that cannot be explained by natural forces. There has been NO credible reason for this other than humans causing it.

    Is this known to an absolute certainty? No. But next time you drive or fly, ask yourself, "How can I be certain I won't die in a fiery crash?" Then decide if you should continue driving or flying, or just get out and walk. After all, science gave you that car and plane. It took a "settled science" to create that.

    In closing, to anyone who continues to repeat the chants about "there is no consensus", "it's all natural variation", and "it's happened before", I'm skeptical of your claims. Prove your case in a positive manner, instead of throwing up negative arguments, like "what about this", or "what about that". Ok, what about YOUR claims? Where's the proof? I am skeptical of your claims.
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  18. Dear Ned:

    "... Since most of the uncertainty involves negative feedbacks, the default assumption should be that warming will in fact occur."

    How about the default assumption is that the result is uncertain? I don't believe anyone disputes the earth has warmed out of a glaciation 8,000 years ago in our CURRENT ice age (yes we are still in an ice age), and warmed out of a little ice age.

    The question is whether mankind has a discernable effect on climate. Now you can get a true conclusion from false premises, and every single AGW argument could be false but still correctly conclude mankind is bad bad bad. (Even a blind squirrel stumbles across an acorn from time to time.)


    However, if the negative feedbacks are not understood, then absolutely no conclusion about future temperatures can be made. None. Nada.

    Additional cloud cover could easily swamp any contribution of CO2. Within the uncertainty that is as valid a guess as any other.

    Not well understood means just that, no one knows. Basing conclusions on "I don't know" is just another WAG, that climate enthusiasts have no shortage of.
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  19. Hello Oracle2world

    The CO2 explanation is rather easy to understand and explains the Earth climate extremely well during the entire Phanerozoic including the hothouse Eocene and also the snowball Earth events during the Proterozoic. It also does a remarkable job of explaining the climate on Venus.

    The natural variablity you refer to isn't a scientific argument. It does not explain anything, does not pretict anything and cannot be falsified or proven. All one can say is that the Earth can freeze over solid or become an insufferable hothouse rather arbitrarily and any observed change inbetween would be within the natural variability of the Earth climate. Fifty years from now the Earth will have a climate somewhere between a snowball and a hot house. You think?

    I guess why you are confused is that there are lots of other stuff which affects the climate besides atmospheric CO2 and taking everything into account gets pretty complicated. But the CO2 bit is pretty easy.

    Also, we are going to run out of fossil fuels. We are just not sure when and the sooner we prepare for that, the cheaper the cost to the economy. It has never been demonstrated that ignoring the AGW problem is less costly than addressing the problem. Denier arguments concerning the economy are pretty weak compared to AGW theory. Heck, replacing the Appalachian water shed lost to mountain top removal is probably enough to break the economy all by itself even if we didn't burn the stuff.

    I don't understand why it isn't economic suicide not to address AGW. Deniers have never explained that.

    best regards

    Tony
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  20. However, if the negative feedbacks are not understood, then absolutely no conclusion about future temperatures can be made. None. Nada.

    I don't think that's a productive method for dealing with uncertainty. It's much more useful to try to characterize the uncertainty and use that to guide decisionmaking.

    If you're building a school in California, you don't know when and where and how large the next earthquake will be. Do you (a) ignore earthquakes, since they can't be accurately predicted; or (b) use models to estimate the risk, then build in an extra safety margin to account for the uncertainty?
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  21. You may notice Danish elctricity comes at a price.
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  22. As originally stated quite clearly, science is never "100% certain": There is always room for possible improvement, even for revolution.

    However, when the best minds in the field have moved on from a hotly contested issue amongst them (as AGW was for many decades), the rest of us can most profitably assume that they're probably right.

    Degrees of certainty are subjective and personal. However, I thought it would be an interesting mental exercise to compare the different degrees of confidence I have in the big picture of AGW (that combustion of fossil fuels is dramatically increasing the concentration of atmospheric CO2, and that this increase is LARGELY responsible for the warming trend of the last 150 years, albeit with some moderation by sulfate aerosols), with my confidence in other scientific theories:

    HIGHEST CONFIDENCE:
    - The applicability of special relativity, thermodynamics
    - The common descent of all known life-forms on Earth

    HIGH CONFIDENCE:
    - AGW (the big picture, as described above)
    - The applicability of quantum mechanics (big picture, without extraordinary interpretations)
    - The evolution of life as a random, completely unguided process

    LESS CONFIDENCE:
    - Astrophysical theories about anything: Cosmology, stellar evolution, dark matter
    - The applicability of general relativity
    - The applicability of the Standard Model in particle physics

    NO REAL CONFIDENCE:
    - Theories of Everything: Strings, M-Branes

    These choices, of course, reflect both what I do know and what I DON'T know. But with respect to AGW, I believe that the big picture will stand: There are very likely to be mechanisms that we will understand better in 20 or 50 years, and some of these may make changes in the magnitude of the expectations by 20 - 30%. But they won't flip the sign, and they won't take it to 0; indeed, at the present, most of the unknowns seem more likely to lead to faster warming than cooler; the main countervailing impact is the question of clouds.
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  23. Oracle2world,

    First, nuclear power is not a "solution" to AGW. It's one element of a response, the value and feasibility and timing of which depends on a number of variables, including logistical and financial and legislative issues. It would need to be accompanied by other measures that, I suspect, you'd be likely to oppose.

    Second, a number of "treehuggers" -- a term that seems to me to violate this site's commenting guidelines, BTW -- are indeed "hopping all over nuclear," precisely because they think it's necessary to reduce CO2 emissions. This reappraisal of nuclear power has actually been going on for years, so I'm a bit surprised you don't know about it.

    Here's a story from 2006.

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  • There is another strong reason for considering the general picture of AGW as settled. The reason is that there is no alternativ theory that explains the climate record we have.

    With a "theory" I mean a model with an underpinning in theoretical science (physics), which does give precise verifiable predictions. Such a theory is vulnerable in many ways - a climate theory can be falsified by inconvenient data from this century, by various historical data going back millions of years, by attacks on its theoretical foundations etc. The more possibilities to falsify it, the better for the theory: If the attacks don't kill it, they strengthens it.

    AGW has survived a strong onslaught for a long time. There is no alternative climate theory which has an even faintly resembling status. There are some thoughts which have ended up as "skeptical arguments" on this site, but nothing coherent, nothing that has a strong theorertical backing and gives predictions (or post-dictions) for a large number of measurable quantities.

    The fact that there are so many "skeptical arguments" shows that AGW is a strong theory - it can be attacked in many ways.

    Don't misunderstand me. Actually I see a lot of weak spots and unclear areas in the AGW theory. But it is an honest, falsifiable theory. And no one has been able to come up with a competing explanation with an even faintly resembling status.

    I'm sure there will be modifications of the climate models, as we come to understand the climate better. But I don't see even the beginning of a "paradigm shift" away from AGW. There is no new paradigm in sight to build that shift around.
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  • Dear Oracle2world (#9)

    I did not follow the OJ case closely, but it is only a metaphor. Don't get hung up on it. Simpson's success in avoiding a guilty verdict at his first trial came from an $1million+ defence team who knew how to exploit human doubts and human empathy.

    My point is that opponents of AGW are similarly engaging with human emotions. Knowing the case is scientifically unanswerable, they are using similar fallacious arguments as were used in the OJ case. It is a case that tells us something about how we form a judgement from evidence, and how we so often can get it wrong.
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  • BTW, the Trenberth paper is available here:

    http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/EnergyDiagnostics09final2.pdf

    A great paper for the science provided but it is also a great paper because it clearly shows how scientists think, i.e. they are not looking for reasons to support AGW, they are just looking for answers and using data get those questions answered.
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  • oracle2world:

    "How about the default assumption is that the result is uncertain?"

    Well, when I drive to work tomorrow, there is a low probability that I will be involved in a car smash, the outcome is undertain so it is ok not to wear my seat belt? I will be dropping my daughter at school - should I tell her not to bother with her seat belt because the chance of a car smash is "uncertain"?

    The possible negative consequences would be so catastrophic that I fully intend to wear my seatbelt, even with the low expectation of a smash, and make sure my daughter has "belted up".

    Suppose out best theory says that the global surface temperature will change by between -1C and +4C between now and 2100. Should we bet the farm on the -1C being more correct than the +4C, given that a rise over +1.5C would be catastrophic for large regions of planet earth?

    There is a very important Prudential Principle that says we act in good time to take preventive action as efficiently as possible.
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  • Marcel (#27) - Well said.

    As for the on-going policy discussions on this thread, keep in mind:

    1. Climate science and policy are 2 different things. The consensus is that the science of AGW/ACC is real. Policy consensus is highly debatable.

    2. The timing of the effects of climate change are still unclear. We see changes now. We can predict other changes, given different rates of rising global temperatures. But there will be effects. Some too rapid for societies or ecosystems to adjust. Food riots? That's nothing compared to water riots.

    Overall though, there is growing concern that even if we halt all CO2 output, and other forcing effects of humans immediately, we may not be able to stop these effects.

    We just don't know where that tipping point is with a high degree of certainty. (That's where we continue to learn more about the positive/negative forcings on our climate.) Have we passed the tipping point? Are we near it? Is it far enough in the future that we can stem the tide of negative effects with proposed policy changes? That's the uncertain part of climate change.

    But the science proving our contribution to AGW/ACC to the point of consensus is solid and sound.
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  • I found this a very well written article addressing the most fundamental concern I have always had for AGW -
    CO2.

    Correlation or causation.

    Do any models and charts show the margins of error of the instruments used to gather the data and then compare it to the CO2 correlations? Can the effects of water vapor be removed from the studies to better isolate the effects of CO2? It all seems to easily be explained as results that are well within the noise characteristics of the studies!

    Having close friends who design space stations where deciding whether to paint portions white or black because they caused drastic effects on the thermal expansion of the material and the localized heat effects constantly points me back to the issue that black soot resting on the ground from coal power plants probably cause more radiative energy collection than an entire atmosphere of increased CO2 levels produced by man (by probably orders of magnitudes). Our knowledge of clouds and how they function in regards to reflecting or absorbing the suns energy is still a complete mystery(being the largest contributor by 20x more than any other to atmospheric warming effects). I feel the information showing we have increased the levels of C02 in the atmosphere are clear. The effects are extremely unclear (isolation of only gas effects in parts per million in effecting thermal radiation have never been shown).

    We need to step back, try to isolate as many components as possible so we can scientifically determine what we actually know and what we do not know. Trial and error. True isolated research studies of CO2 gas fluctuations in parts per million in atmospheric conditions, removing effects of containers, liguids, and solids which may bias the results tremendously.

    By taking a complex system, isolating the components and understanding their effects, then putting them together piece by piece into a system we can begin to understand the truth. I have not seen anything close to this approach yet in looking for the scientific evidence to support AGW. Just correlation papers without proving causation.

    Can anyone help steer me to meaningful scientific information?
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  • Like so many other skeptical “cocktails”, this one is 2 parts straw man, 1 part red herring, with a dash of plausibility, shaken, not stirred.

    The "straw man" misrepresents the degree to which scientists both recognize and acknowledge that there are still legitimate areas of uncertainty and imprecision in our understanding. In this regard, the IPCC and the climate community have been very frank, in general. For example, see:
    NASA: Global Climate Change Uncertainties

    One almost never hears actual climate scientists saying, "The science is settled" (or if they do say something like that, it's usually misunderstood), whereas one hears this frequently from skeptics. I'm particularly bothered when skeptics precede their complaint that ‘the science isn't settled’ with the disingenuous lead-in, "I'm tired of hearing... (that the science is settled)" If they are so tired of hearing this, why do they keep saying it?

    The "red herring" aspect of the argument represents an apparent effort to shift the dialog away from the actual scientific evidence toward a contrived argument over whether the scientific "gestapo" is trying to stifle dissent and suppress alternative views. There is, unfortunately, a tiny dash of plausibility to this, although there’s no indication that it has posed a serious problem in the peer-reviewed literature. Focusing on an imagined conspiracy to suppress debate is a distraction from consideration of the real evidence.

    One recurrent straw man entails confounding of two distinct conclusions reached by the IPCC: 1) "Warming of the climate system is unequivocal..." and 2) "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations."
    Here's how one AGW skeptic combined these two statements in a recent Op/Ed piece in the Wall Street Journal (21 Feb 2010):
    "'Unequivocal." That's quite a claim in this skeptical era, so it's been enlightening to watch the unraveling of the absolute certainty of global warming caused by man."

    Tragically, what is unraveling in this “skeptical era” is honest debate.
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  • The sceptics now tend to say, "the science isn't settled", because for a long time politicians and others have been saying, "the science IS settled".

    And from their standpoint those politicians are right. I would suggest that from any practical, meaningful point of view anyone but a scientist would be very sensible to believe that at 95% probability, to all intents and purposes, the science IS settled. At those odds, to stake one's children's future on that 5% doubt is sheer irresponsibility.

    Of course, that's not to say scientists should not constantly test and retest the theories while ever any doubt remains; until a time arrives when to continue questioning whether the world is really flat puts the remaining sceptics firmly in the lunatic fringe. Though, of course, there's still a very faint chance they could be right...
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  • The "it will cost too much" or "it will wreck the economy" arguments are among the most misdirected. In relative terms, fixing the levees around New Orleans would have been much more economical than repairing the damage - without accounting for the human consequences. If you apply Occam retrospectively it becomes pretty apparent that, on the off chance the still "unsettled" science has some probabilistic merit, it will be far less costly to act now than wait until every property within surge distance of an ocean or tidal estuary is rendered valueless.
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  • Re # 21 Danish energy comes at a price... from the EU official source here: http://www.energy.eu/#domestic it's not so outrageously expensive as the Wiki article clims.
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  • Ken Lambert's argument in #4 has been irritating me for quite a while (on a separate forum). My understand of the physics is not good enough to understand the energy balance equations fully enough, but there are three problems I see with it.

    1. He assumes that co2 sensitivity is at the lower range predicted. As far as I can see the minimum co2 sensitivity should be about 1.6ºC - the observed data does not support lower figures.

    2. that the negative feedback effects are at the upper range of the confidence interval and the positive feedback effects and co2 responses are at the lower end of their confidence intervals - i.e. he is assuming non random distribution of the parameter estimates, which is a big nono without evidence to back it up.

    3. There's a bit of wishful thinking - I think he's making the assumption that co2 sensitivity figures apply only to the first doubling in co2 levels - so to take his conservative estimate that if co2 doubles on pre-industrial levels by 2050 then we get 1.6ºC warming, but then a further doubling by say 2100 will not cause the same warming. This seems to me theoretically suspect.

    So can anyone help me understand the problems with Ken's argument better, or have I already hit the nail on the head?
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  • John you might want to look at the "95% probability" business, which, as on this thread, gets misinterpreted wildly. The kind of probability being referred to in science is to do with an individual experiment. You do an experiment, you get a set of results, you do statistical calculations to work out what is the probability (based on number of samples, number of results in a certain direction) that the result could be due to chance.

    This isn't the case, in any meaningful sense, with global warming. There is no "experiment", there are multiple observations of an astonishing range of different kinds. Some of these observations do lend themselves to statistical analysis - for example storm frequency, numbers of record high temperatures, Arctic ice extent, comparison between temperatures in different decades. Others do not - for example species movements, glacier retreat, droughts, ocean acidification, breeding and flowering seasons.

    But the point is that ALL of these observations, statistically based or not, head in the same direction. So the question really becomes - what is the probability that all of these observations would trend in the same direction? You can't, as far as I know, calculate a formal statistical probability on this, it would be meaningless. But even taking the ones where you can work out individual probabilities, what are the chances that you would get 95% here, 90% there, on a series of individual observations, where these observations all rely on a well known physical property of greenhouse gases? And then add the non-statistical trends. The "chances" of this set of observations all being due to chance must be trillions to one, not 20 to 1.
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  • #32 Turboblocke at 08:26 AM on 25 March, 2010
    "it's not so outrageously expensive as the Wiki article claims"

    On current rate 0.2671 € cents is 35.59 US cents. It is not much cheaper than the 42.89 US cents found in the wiki article. Remember, US price is 9.28 US cents/kWh.

    Also, only about 20% of Danish electricity is generated by (extremely expensive) wind turbines. The rest is produced by nuclear plants and/or imported from Sweden and Norway.
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  • So apparently 95% certainty isn't high enough to take "expensive" actions to curtail CO2 emissions. If a doctor told you he was 95% sure that the black mark on the X-Ray was a malignant tumor-a tumor which will kill you without expensive & debilitating chemotherapy-would you say "oh well, I'd rather just take my chances"? Unlikely.
    The whole cost thing is a total straw man anyway. Most of the best methods for GHG mitigation also come with numerous side-benefits. For example using car-pooling or public transport to commute to work every day, instead of driving yourself, will reduce transport-related CO2 emissions, but they'll also reduce your commuting costs, reduce on long-term vehicle maintenance costs, reduce commuting-based stress (& hence lift worker productivity) & reduce levels of harmful emissions such as benzene (a carcinogen) & particulate emissions (a cause of lung disease & asthma). Of course there's the added benefit that it will make oil last longer too. By the sound of it, the only *cost* will be borne by the oil industry, who will see reduced profits due to less petrol being sold. So that leaves me of the view that most contrarians are simply acting to protect the financial interests of the fossil fuel industry!
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  • Berenyi, by world standards the United States pays an unusually low price for electricity. Here in Australia the average price of electricity is around AU$0.25/kw-h, yet we get very little of our electricity from renewable sources-so there seems little correlation between electricity type & electricity costs (a fact further emphasized by a look at the domestic energy price list provided by Turboblocke). Also, whilst the cost of renewable energy technologies has actually fallen over the last 20 years (& is predicted to continue-due to improvements in materials costs & storage technologies) the price of electricity from coal & nuclear have risen, & are predicted to rise further as the fuels become more scarce & as the price of oil & diesel continue to increase. Might I also remind you that the price of coal-fired electricity in the late 1800's & early 1900's was around US$3.00/kw-h (in today's terms), but this didn't stop the development of an electricity grid!
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  • kdkd> I am not an expert on this stuff, I'm trying to learn, but I think that the numbers quoted by Ken Lambert are not directly relevant to the question. In the paper, Trenberth tries to figure out how heat moves around different parts of the Earth. The "imbalance" is heat that has not been accounted for. However, the global warming does show up in the balance as the "radiative feedback" of -2.8 W/sq.m, which is supposed to correspond to the observed increase in temperature of 0.75 degrees C.

    According to Trenberths paper, the imbalance was very small 40 years ago, but has now grown substantially. It seems that we don't know exactly where it goes. That we don't know what happens to it makes Trenberth sad (cf the purloined letter), but he assumes that besides warming the surface of the planet, it goes into warming the ocean, making clouds and such.

    Clever guys, please correct me if I have misunderstood.
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  • nernt, #28:

    Isolating the effects of the different greenhouse gases can be done using models, but is not trivial, because they do not just add up linearly: The effect of water vapor and CO2 is not the same as the sum of the effects of each alone: It just doesn't work that way.

    Unfortunately, the atmospheric physics involved in understanding how the models work is not too simple either. You could look at Pierrehumbert's book, if you're up for the math. A historically oriented approach is Weart's "The discovery of global warming", at the AIP website: http://www.aip.org/history/climate/summary.htm

    The scientific support is not based only on correlations, as if people had seen a trend and then tried to explain it. The PREDICTION of global warming was made over 100 years ago, and argued for several decades. The correlation comes as a CONFIRMATION of an expected result: That's very different from a "post hoc, ergo propter hoc" ("after this, therefore because of this") approach. It's more like "I was looking for this, and here it is!"
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  • I take your point on the evolutionary development of science. I also think that most, if not all, of paragraphs 2 and 3 are non-contraversial for alarmists and nearly all deniers.

    You skipped an important and contraversial point with regard to CO2 radiative forcing. The energy trapped by CO2, as shown by figure 1, is insufficient to cause the catastrophic effects imagined by the IPCC. It requires help from water vapour, whats the certainty around that? Because this seems more contraversial than CO2 itself. Again most thinking skeptics seem to accept CO2 as a mild GHG.

    About the last paragraph. It seems that many of the possible 'natural' variations in the system a poorly understood and this lack of knowledge seems to strengthen the case for CO2. Convince me that the certainty we have about CO2 isn't in some part derived from the uncertainty we have about other parts of the sytem such as clouds, aerosols, the bioshpere etc.

    Something missing from this article is future projections. Take this work from Loehle which suggests many possible snenarios for future CO2 levels, many of which fall below the IPCC lower limit. I wonder about the speculative nature of this process.

    You seem to have highlighted some of the less contraversial aspects of climate science.
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  • loehle link

    http://www.ncasi.org/publications/Detail.aspx?id=3282
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  • "what's the certainity about water vapour?
    What's the uncertainty? Straight dependence on temperature. Can you point me to the controversy?

    As to others, the uncertainties are bounded. To cause a rise in temperature you have to a trend in the others.

    At the moment we have a model for climate which does an excellent job of accounting for past and present climate at many different levels. This does not discount the possibility of some unknown which will give rise to an even better model - but that's not the way to bet. Got grandchildren you want to stake on the possibility of some future better model giving us less rapid warming? Me, I am too risk-averse. The prediction is at least good enough for killing all subsidies on fossil fuel and investment in sustainable energy instead.
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  • "Straight dependence on temperature."

    What stopped natural runaway warming in the past? Negative feedbacks?

    Moralising about grandchildren is pointless - I see your future warming and raise you stunted economic growth in the developing world.
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    Response: "What stopped natural runaway warming in the past? Negative feedbacks?"

    This is a very interesting question - I've been reading about this in Hansen's Storms of my Grandhildren. There are a number of factors. One is that the sun's output was lower back in the days when CO2 was much higher (in fact, it is BECAUSE the sun's output was lower that CO2 was higher but that's a discussion for another time).

    Another factor is that warming in the past was over geological time periods, thousands or millions of years, so over these periods, negative feedbacks have stopped natural runaway warming. This is because negative feedbacks also act over thousands or millions of years - continental weathering removes CO2 from the atmosphere, terrestrial sinks absorb CO2, etc.

    The difference between then and now is that current warming is happening so fast that these long-term negative feedbacks don't have time to make a significant impact in slowing down the warming. I find this a particularly fascinating (albeit disturbing) subject and would like to take some time to track down Hansen's references and write a post about it. Now, to find some time...
  • From what I've read, CO2 by itself, can raise atmospheric temps by maybe 2oC, and the global climate models have to assume that cloud effects must provide positive reinforcement for CO2 to raise temps further. It also is my understanding that scientists are divided on whether clouds provide positive or negative reinforcement, and by how much.

    Is it not the case that until cloud effects are better understood, the case for AGW will remain truly unsettled?
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    Response: "Is it not the case that until cloud effects are better understood, the case for AGW will remain truly unsettled?"

    Arguably the key question surrounding global warming is climate sensitivity. I didn't touch on it in this post as I'm planning to devote a post on this subject shortly. We've established empirically that more CO2 is trapping more heat which raises temperatures. The big question is whether feedbacks amplify or reduce this warming. When you add up water vapor, clouds, ice sheet albedo, etc, is the net feedback positive or negative? And how big is it?

    We can sidestep the issue of all the various individual feedbacks and jump straight to the question of net feedback by looking at empirical data - how has climate responded to forcings in the past? A multitude of studies, looking at different periods, using different metrics, all tend to cluster around a single answer - the climate sensitivity for doubled CO2 is 3°C.

    This gives us the final overall answer to how climate will respond to rising CO2. The net feedback is positive and the climate is fairly highly sensitive to changes in energy balance. So while we have a lower understanding of the individual feedback components, multiple lines of empirical observations give us a higher understanding of the net feedback response.
  • 'Moralising about grandchildren is pointless - I see your future warming and raise you stunted economic growth in the developing world."

    I see one as more deadly than the other and I am unconvinced about the "stunted economic growth" bit in developing world. They can use renewables too. At least they are no WORSE off if their fossil fuel use is capped and developed world reduces.

    This is still frankly dodging the risk analysis. You want to trust an unknown and probably non-existent model rather than a known and working one on grounds that have no basis in science.

    daisym: There is at least a reasonable convergence between model estimates of sensitivity and empirical estimates. These alluded to uncertainties have been greatly reduced between TAR and AR4.
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  • HumanityRules, as to the Loehle link in #41 you posted; I find his various curves oddly chosen, lacking (as he states) any kind of descriptive model, and selected to fit 1/4 of the data in the paper he's arguing about. I've discussed that in a few posts here, which I'll link to rather than boring people again...

    I can over-fit a near infinite number of curves to data given choices as to the number of free parameters and error levels. That has no consequence to the consensus view unless (a) the consensus view fits the data poorly, (b) the alternative view fits better, (c) this points towards a different model, and (d) this alternative model allows predictions, testing, and confirmation.

    Loehles curves only satisfy (b) for a subset of the data.
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  • #35 Berényi Péter:
    Yes, Denmark's electricity prices are about triple those in the USA. But Denmark also uses about half the electricity per capita as the USA does. Slightly less than half the total energy usage per capita, in fact (including all sources of energy).

    So the *real* cost of electricity in Denmark is only about 1.5 times what it is in the USA.

    Enforcing energy-efficiency standards could easily reduce consumption in the USA by 20-30% over the next few decades. In nearly all cases, the net cost would be zero or negative (i.e. people would save money) in the long term, even just based on current cost (ignoring any future increases in the cost of oil, coal, or any form of carbon tax). Why is that not worth doing?

    Personal anecdote: I recently bought a diesel-powered car. I now spend about $25 per week on fuel, where I used to spend $45 (diesel & petrol are about the same price per litre here at the moment). Going for a more fuel-efficient vehicle saves me $1000 a year on fuel costs, and it didn't cost any more than an equivalent petrol vehicle. What's not to like? (I'm unsure of how well the new car would go on 100% biodiesel, but that's a possibility, too).
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  • "What's the uncertainty?" I don't know but.....

    This analysis which takes the data through to 2007 (beyond trenberth). It shows a mixed picture of water vapour trends in the troposhere. It also suggests that present models have got things wrong. It also says
    "Put the other way around, increases in total column water vapor in response to global warming do not necessarily indicate positive water vapor feedback, since very small decreases of water vapor in the mid-to-upper troposphere can negate the effect of large increases in the boundary layer."

    Trends in middle- and upper-level tropospheric humidity
    from NCEP reanalysis data.
    Garth Paltridge & Albert Arking & Michael Pook
    Theor Appl Climatol (2009) 98:351–359

    So a "Straight dependence on temperature" seems a little to simplistic.
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  • Humanity Rules, given the cost of fossil fuels these days, I'd argue that our continued reliance on them will have a far, *far* greater chance of stunting the economies of developing countries than a shift to a low carbon economy. The US DoE is already trialling a number of Biomass Power plants which make use of waste methane to efficiently generate both electricity & heat-all whilst removing a potent greenhouse gas from the atmosphere. Also, as the source of fuel is local-& cheap-it will allow for more rapid economic development. No doubt the fossil fuel industry will do its level best to kill projects like this-as it hurts their bottom line. Thats the real choice we face here HR: allowing our planet to keep warming vs hurting the profits of the fossil fuel industry. Guess which option I'll pick?
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