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How We Know Recent Global Warming Is Not Natural

Posted on 7 February 2011 by dana1981

Dr. Roy Spencer, like Dr. Richard Lindzen (the subject of a few recent articles), is one of very few climate scientists who remain unconvinced that most of the the recent global warming has been caused by humans (anthropogenic).  Dr. Spencer has grown frustrated with the fact that most of his climate scientist colleagues conduct research under the premise that the recent warming is anthropogenic, and in an article on his blog, has thrown down the gauntlet:

"Show me one peer-reviewed paper that has ruled out natural, internal climate cycles as the cause of most of the recent warming in the thermometer record." 

This challenge is problematic for a few reasons.  Firstly, the fact that research has not ruled out a hypothesis does not mean the hypothesis necessarily has any validity.  For example, there have been no peer-reviewed papers ruling out leprechauns as the cause of most of the recent global warming, either.  But perhaps more importantly, our understanding that humans are causing global warming is not based on just one scientific study, but rather a very wide range of scientific evidence.

For example, scientists have measured the amount of heat being re-directed back towards the Earth's surface due to the increased greenhouse effect.  Quantifying the amount of global warming that this will cause simply involves multiplying the increased downward energy by the climate sensitivity.  As the name suggests, climate sensitivity is a measure of how sensitive the climate is to this build-up in heat - how much the planet will warm in response to an increase in the amount of greenhouse gases in the atmosphere.

Therefore, in order to argue that humans are not the driving force behind the current global warming, skeptics like Spencer and Lindzen require that the climate sensitivity to increasing greenhouse gases is low.  The problem with this position is that there are many lines of evidence that the planet will warm between 2 and 4.5 degrees Celsius (°C) if the amount of carbon dioxide (CO2) in the atmosphere doubles. 

For example, some scientists have studied the climate response to recent large volcanic eruptions, which can have a measurable impact on global temperatures.  Other studies have examined how the global temperature has changed in response to changes in solar activity.  Some other research has compared CO2 and global temperature changes over the past thousand years, and tens of thousands of years, and hundreds of thousands of years, and even millions of years ago.  We can even compare how the temperature has changed over the past century to human-caused atmospheric CO2 changes.  In every case we arrive at this same climate sensitivity range of 2 to 4.5°C, and the most likely value is 3°C for a doubling of atmospheric CO2.

If we take the lower end of this range, even a 2°C climate sensitivity would mean that humans have been responsible for more than half of the global warming over the past century.  So in order for Spencer and Lindzen to be right, all of these different lines of evidence which are in agreement with the likely range of climate sensitivity would all have to be somehow wrong, and all biased high.  Not an impossibility, but certainly not a likely scenario, either.

There are also many "fingerprints" of human-caused global warming.  For example, as the Earth's surface and lower atmosphere have been warming, the upper atmosphere has been cooling.  There are not many mechanisms which can explain these observations, but they are precisely what we would expect to see from human-caused global warming.  As the concentration of greenhouse gases in the lower atmosphere increases, they effectively trap more and more heat in this lower layer, causing it to warm and causing the layers above to cool.  Another human "fingerprint" is the higher rate of warming at night than during the day.   This is because at night, when the surface is cooler and not being bombarded by solar energy, the increased amount of greenhouse gases are able to make more of a difference in the surface temperature.

Dr. Spencer has proposed an alternative to the anthropogenic global warming theory.  He suggests that some unknown mechanism has caused global cloud cover to decrease over the past century.  Low-level clouds cause a cooling effect by reflecting sunlight, so if these types of clouds become less prevalent, it can cause the surface to warm.  However, this hypothesis cannot explain the "fingerprints" describe above.  A decrease in cloud cover would not cause the upper atmosphere to cool.  Nor would it cause nights to warm faster than days - quite the opposite.  Cloud reflectivity only plays a significant role during the day when being bombarded by sunlight.

Dr. Spencer also suggested in his blog post that the "null hypothesis" should be that global warming is caused by natural factors.  A null hypothesis is basically the default assumption which a scientific study sets out to disprove.  It's true that until recently, global warming (and cooling) has been caused by natural factors.  However, even natural climate changes must have a physical mechanism causing them.  Scientists have investigated these natural mechanisms (the Sun, volcanoes, the Earth's orbital cycles, etc.), and they simply cannot explain the global warming over the past century.  Spencer's new hypothesis - that some unknown mechanism is causing cloud cover to change, which in turn is driving global temperatures - is a new idea with very little supporting evidence.  Conversely, our understanding that human greenhouse gas emissions are driving global temperatures has a proverbial mountain of supporting evidence.

Skeptics like Spencer and Lindzen believe that the default assumption should be one which requires that a very large body of scientific evidence is wrong.  The only alternative hypothesis they have put forth cannot explain the many empirically-observed "fingerprints" which are consistent with human-caused global warming.  Although Spencer's unspecified "natural internal cycle" hypothesis has not been explicitly disproved, there is a very low likelihood that it is correct.  For this reason, we should operate under the assumption that humans are causing dangerous global warming - an assumption which is supported by a very large body of evidence - until the skeptics can provide solid reason to believe that this scientific theory is wrong.

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Comments 51 to 100 out of 106:

  1. Pirate @47, That is what people have been trying to tell you for ages now. That said, you forgot to include this part immediately below those questions: "Paleoclimatology offers help in answering each of these questions. Several of the paleoclimate studies reported in this web document have begun efforts to attribute past climate change to both natural and human causes, and to estimate how much of the current warming is due to humans (i.e., greenhouse warming). The best estimate is that about 50% of the observed global warming is due to greenhouse gas increases. The paleo record also tells us how much temperature change occurred in the past when carbon dioxide levels were different. Studies show that the 100 ppm reduction in carbon dioxide during the last glacial was accompanied by a 3°C cooling in the western tropical oceans. This amount of temperature change is consistent with the change predicted by numerical climate model simulations. Changes at higher latitudes were much larger and included the growth of large ice sheets." That was back in early 2009, and the contribution from GHGs is going to increase with time as GHG levels continue to escalate. Pirate are you suggesting that we should only take action if we have "complete" confidence? That would be absurd. The 95% confidence limits for expected climate sensitivity for doubling CO2 have been published (e.g., Annan and Hargreaves 2009) and calculated to lie between +1.5 and +4 K, with a most likely value of +3 K.
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  2. apiratelooksat50 - "I am not misrepresenting your argument..." You certainly misrepresented Dana in this post "Are you stating those forcings are not factors now?" and Dikran here "...are you of the position that only CO2 from human combustion of fossil fuels is the driving force?". Neither they nor anyone else I know of with reasonable knowledge of the subject has asserted that CO2 is the only forcing involved involved in climate. Just that it's the dominant one right now raising temperatures, which would otherwise have declined over the last 50 years. I think I'm fully justified in calling those posts strawman arguments. As to attributing current changes to "natural cycles", I suggest looking closely at the graph muoncounter provided. Current climate behavior (change rates) matches nothing seen in the Holocene or any previous interglacials, except perhaps the PETM event.
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  3. To me, Spencer's "challenge" indicates lack of insight in scientific processes. As long as we don't have complete descriptions, it is rather inappropriate to "rule out" anything. What we are doing, is looking for the models with the greatest explanative power relative to complexity. We also challenge these best explanations by testing the models in new situations, checking consistency in every possible way etc. It is rather futile to spend time "ruling out" possible explanations that are neither made explicit enough to be tested nor seem to be necessary. So, with Spencer's position, the challenge is, really, on him: To produce tests where the consensus models should be able to perform well, but they fail utterly. It is not enough to present special situations they have not been designed to model well, and where they therefore may fail considerably. Null hypotheses are usually picked as the "simplest" or "most natural" models, and hypothesis testing is mostly about rejecting the null hypothesis. Testing that is intended to provide support for the null hypothesis may be problematic, as the power of the test may be too low. Lots of denialist arguments rely on this, like "with this cold winter/high snow cover/seemingly falling temperatures/...., AGW must be minimal or non-existent". In the case of global warming, when the first null hypothesis of no warming has been rejected, the next step is of course to see if the effects established so far may explain the phenomena adequately. In this respect, Spencer's wishes are in a sense granted, in that "natural" factors, like solar irradiation, volcanism, aerosols and gases are taken into account. And so far, models which have included greenhouse gases have very often performed significantly better than models leaving them out. Thus, the initial null hypotheses of "no effect" are rejected, but this doesn't rule out the possibility that an entirely different modeling approach could lead to other results. But in a situation where the models work well, and rather easily include "new" phenomena, believing in entirely different explanations kicking out the well established factors looks like wishful thinking to me.
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  4. #47: "these questions remain to be answered" I'm not buying it. Those questions are answered numerous times on SkS, often in discussions in which you've participated. Yet you continually return to the unsubstantiated 'natural cycles' hokum. Perhaps you should be the one answering the questions: what natural cycles are you proposing? what are the 'natural forcings'? Have they already been considered in the models that require an anthropogenic forcing to match the temperature record? Do they stand up to scrutiny? Or do you propose 'magic clouds' a la Spencer? "if we've only had 0.8 degree C warming in the past 150 years" It's the 0.8 degree since 1965 you should be concerned about. #49: "climate has regularly cycled through glacial and interglacial periods." Not relevant to the current situation. You're a science teacher, stay on task.
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  5. apiratelooksat50 @ 49 said... "I'm on record of saying that I am willing to consider CO2 as a contributor to global warming." So, you're willing to consider basic, well established, 150 year old physics? That's a good start. You'd be surprised how many can't even get that far.
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  6. Pirate - you keep bringing up the "CO2 lags temperature".Do you think this that is an unexpected result within current climate theory? (Its not). See CO2 lags temperature for more discussion.
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  7. Nice summary, John. Well done.
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  8. Pirate: I'm on record of saying that I am willing to consider CO2 as a contributor to global warming. You are? Really? Wow. That's a pretty impressive concession for a teacher of environmental science to make. Let us know when you get around to accepting it.
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  9. Thanks Kate (this one's mine, not John's).
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  10. #49: "climate has regularly cycled through glacial and interglacial periods." Yep, that's true-but those cycles have been driven by extremely large increasing in Total Solar Irradiance-due to changes in the Earth's orbit-followed by CO2 as a positive feedback after TSI peaks. TSI over the past 60 years has-if anything-been trending *downwards*, so cannot explain recent warming. Also, these past cycles occurred over a period of *tens of thousands of years*. When you really think about it, even a +8 degree change in temperature-over the space of even 10,000 years, amounts to an average of only +0.03 degrees per decade. Recent warming has occurred at a rate of +0.12 degrees per decade for 1950-2010 & +0.16 degrees per decade for 1980-2010. Now, if you can show me a *natural* cause for such rapid warming, I'd be very interested to hear it-but simply attributing it to "currently unknown natural cycles", without supporting evidence, just ain't gonna cut it!
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  11. Another point, Pirate. When climate change occurs naturally, CO2 *does* lag warming-within fairly well-defined bounds (between 200ppm & 280ppm). Between 1950-2010, though, CO2 rose *before* a significant rise in temperature can be detected. i.e. CO2 rose slowly throughout the entire 20th century, but the real upswing in temperatures doesn't begin until the 1970's. At the very least, CO2 increased precede the current warming trend by a good 20-40 years. Again, can you give us a *natural* cause to explain this? I doubt it. As to Milankovitch cycles, these operate on a time frame of *millenia*, not decades, & the next part of the cycle is meant to take us *away* from the sun-causing cooling-at least about 3,000 to 5,000 years from now.
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  12. I'm willing to consider CO2 (both manmade and natural) as significant "contributors" to global warming - but not "drivers". Since, we've been more or less steadily warming since the Little Ice Age, it appears that humans have been doing quite well.
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  13. apiratelooksat50 - that you're not even willing to consider the reality that CO2 is driving global warming shows an unfortunate closed-mindedness. You've also got it backwards. Humans aren't thriving because of the temperature increase - the temperature increase is a result of humans thriving (which is due to our massive use of artificially cheap fossil fuels). I also suggest you read the we're recovering from the LIA rebuttal.
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  14. apiratelooksat50@62 Prior to the industrial revolution, CO2 has mainly acted as a feedback, however there have been occasions when a large release of carbon has driven temperature changes. For example, the escape from the snowball Earth of the late Ordovician is pretty tough to explain without greenhouse gasses, or more recently there is the Paleocene–Eocene Thermal Maximum (PETM) event. Population growth in itself doesn't mean humans have been doing well. Mere reproductive success generally ends up hitting Malthusian limits, which is rarely an enjoyable experience for any species. Besides, I think you will find the causal link is in the other direction. BTW, have you come up with an example of an observation that would falsify the hypothesis of Spencer's challenge that you asserted was valid?
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  15. Dana @ 63 I've considered that CO2 can "drive" climate and rejected it. What do you mean by your reference of "artificially cheap fossil fuels"?
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  16. Temp, CO2 and human population. Kinda tied together ain't it? In what order - who knows?
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  17. Dikran @ 64, From what I've read, I am in tentative agreement that large releases of CO2 can have a temporary effect as a driver of global temperature. But, equilibration comes into play (i.e., after a major volcanic eruption) and temps go back to their normal phase, whether rising or falling. Start a pot of water boiling and drop in one ice cube. What happens? The rate of reaching boiling slows down temporarily until that ice cube is gone. But, then it rapidly goes back to the original trend.
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  18. Pirate @66, You continue to be disingenuous with your flippant and unsubstantiated remarks. People have repeatedly directed you to the science which demonstrates that the planet is experiencing a net positive energy imbalance on account of the radiative forcing from GHGs and that the majority of warming is attributable to the rapid increase in GHGs from human activities. From a paper to appear very soon in the prestigious Journal of Climate: "The role of human activity in the recent warming of extremely warm daytime temperatures Nikolaos Christidis, Peter A. Stott, Simon J. Brown Met Office, Hadley Centre for Climate Change, FitzRoy Road, Exeter, EX1 3PB, UK Abstract Formal detection and attribution analyses of changes in daily extremes give evidence of a significant human influence on the increasing severity of extremely warm nights and decreasing severity of extremely cold days and nights. We present an optimal fingerprinting analysis, which also detects the contributions of external forcings to recent changes in extremely warm days using non-stationary extreme value theory. Our analysis is the first that attempts to partition the observed change in warm daytime extremes between its anthropogenic and natural components and hence attribute part of the change to possible causes. Changes in the extreme temperatures are represented by the temporal changes in a parameter of an extreme value distribution. Regional distributions of the trend in the parameter are computed with and without human influence using constraints from the global optimal fingerprinting analysis. Anthropogenic forcings alter the regional distributions, indicating that extremely warm days have become hotter."
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  19. Pirate - and if you continue to add ice cubes? CO2 is eventually removed by geological processes but at geological rates. Meanwhile, we keep adding CO2. What concerns me is that you can postulate all kinds of nonsense if you don't do the maths. Doing the maths means comparing the relative strengths of forcings and the effects on temperature. (That we you don't get the "recovering from LIA" nonsense).
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  20. I've considered that CO2 can "drive" climate and rejected it. So what psuedo-skeptic nonsense did you fall for? Got some peer-reviewed science to back your conclusion. What do you mean by your reference of "artificially cheap fossil fuels"? Fossil fuels are subsidized. That makes them artificially cheap. IEA estimated subsidies worldwide to be US$557B in 2008. See IEA report for the details. Ending subsidies is a good way to get an different energy structure started, but bad for fossil fuel company shareholders.
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  21. Pirate, just an addendum. Volcanoes make short-lived contribution (your ice-cube) because the aerosols are quickly gone. CO2 is not quickly gone.
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  22. #67: "equilibration comes into play (i.e., after a major volcanic eruption) and temps go back to their normal phase" It might be wise to check your facts, especially if you intend teaching this idea. Robock 2003 provides a thorough and definitive analysis. The June 15, 1991 Mount Pinatubo eruption was a large but relatively shortlived shock to the Earth’s atmosphere. Temperature and CO2 records conclusively show that a brief cooling and temporary reduction in the rate of increase of atmospheric CO2 were done with within 2-3 years of the eruption. So no, there's no 'equilibration,' whatever that is supposed to mean. But your right, temps went back to their normal phase -- increasing due to the forcing of anthropogenic CO2.
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  23. Marvin - fossil fuels are artificially cheap because we don't pay for the climate change or associated damages their co2 emissions cause. That's what economists call an "externality". Pirate - the whole reason the planet is warming is because it isn't in equilibrium, because of the ever-increasing co2 forcing. You continue to neglect physics.
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  24. You continue to neglect physics. To be precise, he continues to neglect physics that people here have repeatedly taken the time and trouble to explain to him, in this thread and others. Which is beginning to seem somewhat rude, as well as irrational.
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  25. apiratelooksat50@67 Good, we both agree that CO2 can be a temporary driver of climate. The next question is how long is temporary. The reason volcanos have a short lived effect is that the aerosols they eject into the atmosphere are short lived, and are gone in a couple of years. CO2 however is much longer lived, the adjustment time of CO2 is several hundred years, and full equilibriation takes tens to hundreds of thousands of years (because full equilibriation requires geological weathering to permanently remove the excess CO2 out of the active carbon cycle and into the lithosphere). There is a good book by David Archer called "The global carbon cycle", which explains the mechanisms involved in detail. The equilibriation from the PETM took on the order of 100,000 years - which is not very temporary from a human perspective (although it is a blink of the eye in geological terms). See Archers book, page 45 for details. Essentially, in your ice in a pan analogy, you need to take into account how long it takes to melt the ice. Sure the effect of CO2 is temporary, but that doesn't mean it is not relevant as "temporary" on a geological timescale is a very long time for us. However, you are continually refusing to answer the question I posed earlier. This sort of evasion is generally an indication that someone is not taking the discussion seriously and making a rhetorical argument rather than a scientific one. If you are not interested in the truth and only want to win a rhetorical debate, then perhaps this is not the site for you.
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  26. Dikran Can you please rephrase your question?
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  27. apiratelooksat50@76 Sure. For Spencers challenge to be valid, rather than merely rhetorical, the "null hypothesis" that the majority observed warming is due to the natural variability of the climate, must be a valid scientific hypothesis. A requirement of a scientific (rather than a non-scientific) hypothesis is that there exists at least the potential to disprove the hypothesis should it be false. This is a well established part of scientific method, stemming from the work of Karl Popper. It is my contention that the hypothesis of "natural variability" is unfalsifiable, simply becuase the mechanism of "natural variability" is left unspecified, which means there is no means of establishing which phenomena are consistent with the hypothesis and which are not. Thus *anything* we actually observe can be blithely attributed to "natural variability". It would be easy to prove my contention wrong, by giving an example of an amount of warming that is not consistent with the theory of "natural variation" and that was my challenge - specify a condition that is definitively excluded by Spencer's hypothesis. I am happy to clarify further any of these points, if required, but please try to specify exactly what it is that you don't understand.
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  28. Dikran, First, we would need to define and agree what constitute "natural internal cycles". Otherwise we would be arguing semantics. I see your point about using the scientific method and agree with it. I'm a big fan of Popper. Perhaps Spencer should define a hypothesis, though I am not sure his challenge requires a hypothesis to be formed.
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  29. apiratelooksat50@78 That is precisely the point I was making! It was not correct to assert that Spencer's challenge was valid simply becuase the definition of "natural internal cycles" was left unspecified, so the hypothesis was impossible to falsify. Essentially it is fine as rhetoric, but it isn't valid science. If you try and specify what "natural internal cycles" actually means and specify mechanisms to the point you can actually define what is and what isn't consistent with the hypothesis, you will end up with somthing rather like a coupled atmosphere-ocean general circulation model (AOGCM). At which point the experiment has already been done and it has been shown that the observered warming is not consistent with natural cycles, see the post by Daniel Bailey. Dr Spencer ought to be well aware of this, as it is "Frequently Asked Question 9.2" on page 702-3 in the most recent IPCC WG1 Scientific Basis Report. The spread of the model runs tells us what is consistent with our current knowledge of "natural variability" and the current warming lies outside the spread of the model runs if anthropogenic forcings are excluded, which means that the observed warming can't be explained by our best understanding of natural variability. P.S. If you think Spencer's challenge doesn't require a well-defined hypothesis, you do not understand Popper at all. Falsificationism requires as well define hypothesis, that much ought to be obvious to anyone who has even dipped into his writing, never mind a big fan!
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  30. apiratelooksat50: "Dr. Spencer is asking for a paper ruling out natural, internal climate cycles as the cause of "most" of the recent warming" That would be some paper - the one that knows everything. But is he really asking for that? Or is he merely exploiting rhetorically the unsurprising fact that no single paper exists which 'rules out the possibility of natural causes'? I'd suggest that it's the latter - and a clever sleight of hand by Spencer who finds himself with nothing of substance to offer as an alternative to AGW. It really boils down to this: until such time as Spencer actually publishes a proper alternative with sufficient detail that it can be falsified, he doesn't even have a hypothesis to challenge the mainstream theory of AGW. Just rhetoric.
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  31. apiratelooksat50: "I'm a big fan of Popper" - Based on past posts, I am going to guess that you are a fan of Popper in that you were exposed to his work in a philosophy of science college class and realized, in the absence of any particular issue, that Popper's methods would indeed move you towards the truth. Now you are struck by something (climate science (aka AGW)) that directly smacks your internal ideology or internal belief system in the face. Popper is still your man. So rather than keep posting the same erroneous claims here over and over - why don't you study Popper with AGW in mind? Hopefully your emotion-free acceptance of Popper when there wasn't something you are so vested in on the table will trump your current stubborn insistence on wrong ideas now. In short the challenge is to correctly use Popper to support any of your skeptic arguments. I realize you are trying to get past your blocks on climate science, and I appreciate that. But you are also very frustrating because 1) you don't appear to internalize any of the science that many, many posters have pointed out to you and 2) you teach science! Which makes it even more annoying that you don't understand it, and a crying shame that you are influencing the next generation with flawed logic. There is no problem questioning the science, there is a big problem with questioning the science, then rejecting the science with no valid reason. Go to Popper, and if philosophy is your strength and you ares still bogged down, check out W.V. Quine's Web of Belief. At least you will have some insight into why it is so important to you to reject well understood, mainstream science.
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  32. Dikran This is an excerpt from a post on another thread that I did. I hope it's not OT. We may actually find some common ground! In statistics, a null hypothesis is a hypothesis that is presumed true until statistical evidence in the form of a hypothesis test indicates otherwise. For example, in a clinical trial of a new drug, the null hypothesis might be that the new drug is no better, on average, than the current drug. We would write H0: there is no difference between the two drugs on average. Special consideration is given to the null hypothesis, due to the fact that the null hypothesis relates to the statement being tested, whereas the alternative hypothesis relates to the statement to be accepted if/when the null is rejected. H0 can be “not rejected”, or H0 can be “rejected in favor of H1”. It can never be concluded to "reject H1", or even "accept H1". “Not rejecting H0", does not necessarily mean that the null hypothesis is true, it only suggests that there is not sufficient evidence against H0 in favor of H1. Rejecting the null hypothesis then, suggests that the alternative hypothesis may be true.. Prior to discussion of the anthropogenic global warming (AGW) hypothesis it should be established that the Earth’s climate has gone through relatively extensive cyclical changes in temperature throughout its history. In the case of warming, the lag between temperature and CO2 is explained as follows: as ocean temperatures rise, oceans release CO2 into the atmosphere. In turn, this release amplifies the warming trend, leading to yet more CO2 being released. In other words, increasing CO2 levels become both the cause and effect of further warming. This positive feedback is necessary to trigger the shifts between glacials and interglacials as the effect of orbital changes is too weak to cause such variation. Additional positive feedbacks which play an important role in this process include other greenhouse gases, and changes in ice sheet cover and vegetation patterns. The fundamental AGW hypothesis is based on the following scientifically verifiable facts: 1) CO2 is a greenhouse gas (GHG) and contributes to the greenhouse effect by absorbing and emitting radiation within the thermal infrared range thus warming the Earth. 2) Through the use of fossil fuels over the past 150 years, humans have contributed to the current rise in atmospheric CO2 levels from 280 ppm to 390 ppm. The AGW hypothesis (H1) then basically states that: current human CO2 emissions significantly affect the climate outside of natural variations. Therefore, the null hypothesis (H0) is: human CO2 emissions do not significantly affect the climate and the variations are the result of natural processes. There are a number of rational and viable scientific objections that have been raised against various parts of the hypothesis, from the nature and sign of the forcings considered and unconsidered, to the existence of natural thermostatic mechanisms. It is the onus of the supporters of the H1 hypothesis to establish enough evidence to reject H0. That is, show where the climate has changed from any historically established norms. First, the climate must be acting significantly anomalously or abnormally. Second, the anomaly must be explained by human actions. And, third modeling (predicting) cannot be used as explanations or facts.
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    Moderator Response: [muoncounter] A link to the prior comment is far preferable to repetition. To be fair, a link to prior rebuttals is also warranted. No point re-inventing the wheel.
  33. I'm a big fan of Popper. Then you may want to bear this quote in mind: "[T]he role of evidence is, in the main, to correct our mistakes, our prejudices, our tentative theories — that is, to play a part in the critical discussion, in the elimination of error."
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  34. apiratelooksat50@82 Firstly, it is incorrect to say that in statistics the null hypothesis is presumed to be true and the alternative hypothesis false. The p-value is the probability of the observations IF you assume that the null hypothesis is true, but that does not mean that we presume the null hypothesis is true. However, classical Fisherian hypothesis tests don't use the alternative hypothesis at all, so it may be that the data are even less likely under the alternative hypothesis than under the null when the null has been rejected! The underpinnings of frequentist statistical tests are rather subtle, and it is not surprising that people often misinterpret them in this way. In short, if you can't reject the null, then both hypotheses remain plausible, it doesn't mean you can reject the alternative hypothesis. What it does mean is that you shouldn't claim the alternative hypothesis is true based only on that specific observation. That is not the same thing as presuming the null is true at all. "And, third modeling (predicting) cannot be used as explanations or facts." O.K., you have just demonstrated that you don't have the first clue about Popper. Without making predictions, no hypothesis can ever be falsified, predictions cannot be made without a model, even if it is implicit. Models and predictions are not used as explanations or facts, so that is a straw man anyway, they allow you to test hypotheses against observations by telling you the consequences of the assumptions underpinning your hypothesis. That is not the same as saying they provide explanations or facts, and indeed nobody is saying that.
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  35. Dikran, Every reference I find about the null hypothesis basically states the following as found at Psychology Wiki: "In statistics, a null hypothesis (H0) is a hypothesis set up to be nullified or refuted in order to support an alternative hypothesis. When used, the null hypothesis is presumed true until statistical evidence, in the form of a hypothesis test, indicates otherwise — that is, when the researcher has a certain degree of confidence, usually 95% to 99%, that the data does not support the null hypothesis. It is possible for an experiment to fail to reject the null hypothesis. It is also possible that both the null hypothesis and the alternate hypothesis are rejected if there are more than those two possibilities.it isn't statistically approved" Also, I know full well how modeling (predicting) is used. That statement was made to set the ground rules for those who are under the false assumptions that models are fact. You and I may not do that, but others do.
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  36. apiratelooksat50 - The vital point is that the null hypothesis must make predictions too, not just the alternative hypothesis. If the null hypothesis is undefined (i.e., anything fits the null) then there can be no distinction made between the two hypotheses. Hence, Spencer's challenge is specious. Until a null (with some underlying hypothesized mechanism, and confidence intervals on it's predictions) is specified, he's talking leprechauns. I agree with Dikran - all hypotheses have models, implicit or explicit, which are used to make predictions. You then test the observations against those, and see which one is statistically borne out by the data, given observed noise.
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  37. apiratelooksat50: "Also, I know full well how modeling (predicting) is used." I've always been under the impression that modeling was a set of possible specific scenarios rather than predictions.
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  38. KR I agree that the way Spencer's challenge is worded makes it difficult to make a null hypothesis. We established that earlier. Also, the models (predictions) cannot be used as factual unless determined to be true by observations.
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  39. apiratelooksat50@85 I get my understanding of hypothesis tests from statistics textbooks and discussions with experienced statisticians (my research is in a branch of statistics). Frequentist hypothesis tests are widely misunderstood in the sciences, psychology is no different. Not being able to reject the null hypothesis does not mean the alternative hypothesis is false. It is easy to demonstrate that this is true. Say I have a double headed coin and you want to test whether the coin is biased or not. In that case, the null hypothesis is that the coin is fair and so p(head)=p(tail)=0.5. If I flip the coin 4 times and get a head each time, then the p-value = 0.5^4 = 0.0625. That is greater than 0.05, so we are unable to reject the null hypothesis, does that mean the alternative hypothesis is false? No, it just means we haven't seen enough data to establish that the coin is not fair. Re your comment on models. The way models were used to establish that the observed warming is inconsistent with our best understanding of natural variability was not to provide explanations or facts, but to generate testable predictions. Do you agree then that the material in FAQ 9.2 in the IPCC report answers Dr Spencers challenge? I see you have repeated your comment in 88, after it had already been pointed out that the output of models is not treated as such.
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    Moderator Response: [muoncounter] Modeling-specific discussion should go to Models are unreliable. [Dikran Marsupial] my comment was on how the models are used rather than whether they are reliable, any discussion of the latter topic definitely belongs on the thread muoncounter mentions, I'll happily discuss that topic there.
  40. Pirate: the existence of natural thermostatic mechanisms. For (hopefully) the last time, this question has been raised many times over the decades, and investigated in painstaking detail, and the evidence really does not support the existence of a natural mechanism that can account for the current amount and rate of warming. That's largely why AGW is so widely accepted. In other words, that horse bolted from the stable some time ago, and will probably not be coming back no matter how earnestly you peer at the horizon. Saying "But there could be a natural thermostatic mechanism, so let's act as though there is!" is not rational, not scientific...it's not anything but an avoidance maneuver. You're coming perilously close to creating a mechanistic version of the "God of the Gaps": In the absence of definitive proof — which any good Popperian knows is not forthcoming — every uncertainty becomes "evidence" for the only ideologically acceptable explanation for warming. However, the really interesting question here is not the degree of scientific support for AGW, but why a relatively small group of people who would ordinarily respect that degree of support reflexively dismiss it in this instance. (It's also interesting that so many people who claim to believe in "personal responsibility" and "market forces" would go so far out of their way to dismiss human agency, and to misrepresent the scientific information on which we must base our "rational" choices. But that's a rant for another day and another site.) That statement was made to set the ground rules for those who are under the false assumptions that models are fact. You and I may not do that, but others do. Can you give us a specific example of a climate scientist who assumes that "models are fact"? Because if you can't, this is simply another strawman. Which brings up a question that often comes to mind when I'm reading "skeptical" arguments: Why would I trust amateurs who can't form logically coherent arguments, or get basic facts straight, to have a better grasp of climatology than professional climatologists? This may sound insulting, but the intent is constructive: We'd all benefit from logical, coherent, well-informed criticisms of the AGW consensus, instead of the same old handwaving and misconceptions.
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  41. XPLAlN at 03:14 AM on 10 February, 2011, I totally agree with you regarding "But is he really asking for that?" though I think he is asking tongue in cheek rather than playing sleight of hand. I am left wondering whether Spencer is quietly chuckling to himself or pulling his hair in frustration out as he watches those who tie themselves in knots having overlooked what is most obvious to others.
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  42. Johnd if it is so obvious but ignored, why is Spencer not putting it in a paper? Spencer throws all sorts of wild stuff on his blog to get the denialosphere excited but what has he published lately (or ever) that is fundamentally running counter to the consensus model of Earth Climate? I'm as unimpressed with Spencer as when the errors in his work were uncovered by others.
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  43. You know, I do grow tired of this ongoing furphy that the modest warming of the 17th through 19th centuries *caused* the growth in human population. If that were true, then we should have seen similar population booms during the Medieval Warm Period. What we *actually* see, though, is several major famines, the Bubonic Plague & the collapse of several large civilizations (the Anasazi, the Mayans & the Khmer). The real cause of the population growth from the 17th century on can be summed up in one phrase-The Enlightenment. The unchaining of Science from the shackles of religion allowed for massive leaps forward in medicine, agriculture & manufacturing. This, in turn, allowed for better nutrition, better living standards, & improvements in infant mortality & life expectancy. We are now, however, starting to reap a bitter harvest from these past benefits-with overpopulation, pollution & climate change being a major threat to our continued success. It doesn't help when people like Pirate adopt the typical "head-in-the-sand" approach to these problems-esp. as he's supposedly a *teacher*!
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  44. #93: "ongoing furphy that the modest warming of the 17th through 19th centuries *caused* the growth in human population." Especially when the furphy (great word, that) is promoted by the same people who cry foul when anyone points out that temperature increase correlates with atmospheric CO2 increase. That's unacceptable; 'correlation isn't cause!' But warming correlation with population is a valid cause? Does denial require the ability to be hypocritical or is it an after market add-on?
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  45. The evidence that the climate is being changed by man does not exist. The IPCC predicted an average trend of 3.9celsius/century from theoretical computer models. these models are not based on observations. they respond to what the modeller puts in to them(not very scientific) However actual satellite observations from the RSS and UAH satellite data sets show this trend to be a mere 0.3celsius/century(see SPPI global temperature data index.) Since coming out of the Little Ice Age in 1850 it is to be expected that there would be some warming. however the rate of warming in the second half of the 20th century has been exactly the same as the rate of warming 1918-1940 when clearly human carbon dioxide could not possibily have been the cause.One must consider all of geological time not the small 130 years of the instrument record. This geological record shows for example the MWP(Medieval Warm Period 950-1300) to be four degrees warmer than today. Pollen samples taken from Baffin Island also show that temperatures 5000 years ago were five degrees warmer than today. the alarmists are wrong! As for numbers Dr Spencer and Professor Lindzen are in good company. In fact Dr Art Robinson has listed over 31 000 graduate scientists including over 9000 PHds who reject antropogenic global warming as responsible for climate change.(see www.petitionproject.com) Also populartechnology.net/2009/10/peer-reviewed----------html lists 850 peer reviewed scientific papers who all reject AGW as the cause of climate change.
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    Moderator Response: [Daniel Bailey] Welcome to Skeptical Science! There is an immense amount of reference material discussed here and it can be a bit difficult at first to find an answer to your questions. That's why we recommend that newcomers do as JMurphy has just suggested to you below. I also recommend watching this video on why CO2 is the biggest climate control knob in Earth's history. Further general questions can usually be be answered by first using the Search function in the upper left of every Skeptical Science page to see if there is already a post on it (given the plethora of posts [I get paid extra for using big words and alliteration :-) ] odds are, there is). Or you can search by Taxonomy. When you have questions, please post them on the most appropriate thread. Remember to use the Preview function (avoids html tag errors) and to construct your comments in compliance with the Comments Policy. I'm afraid the vast majority of your comment is simply incorrect. The warming of the globe is an accepted fact. That humans are causing a good part of it is accepted at over a 90% scientific certainty level. Only the anthropogenic contribution (which did not exist in the paleo record) completes the picture, explaining the warming we can empirically see and measure in the absence of other forcings. Else we would be measuring a decades-long cooling trend. Which we aren't: Forcings, except for CO2, have been flat for nearly 40 years. Temperatures continue to climb, and that rate of climb is still increasing (as are CO2 levels).
  46. Wow, fixtures23, you could do with some reading on some of those claims you are making - quite the Gish gallop, eh ? For your enlightenment and further education try these links : Newcomers Start Here The Big Picture Most Used Skeptic Arguments That should help you become more aware of the facts. As for Popular Technology, trawl your way through this link and see what you are aligning yourself with. By the way, where did you get all that false information from in the first place ?
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  47. 95 Fixtures23, Oh my! Welcome to the site, the folks here are very open-minded and love discussing science. I see JMurphy has already suggested that you visit the "Newcomers Start Here", "The Big Picture" and Most Used Skeptic Arguments". Also, be sure to check the comments policy. I think you will find them very helpful. Cheers!
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  48. I was translating this article and there's one thing I don't undertand. The article says that:
    even a 2°C climate sensitivity would mean that humans have been responsible for more than half of the global warming over the past century.
    However, I don't see how climate sensitivity can affect the distribution between different climate forcings. Natural forcings alone would likely have cooled the planet, so I think we are likely responsble for more than 100% of the warming. Given that ΔT=ΔRF*S, with a given temperature rise (ΔT = 0.8ºC), the fact that climate sensitivity (S) is low, would just imply that the net radiative forcing (ΔRF) has been rather high (i.e. high RF and not that high temp rise), and if the climate sensitivity is high, that would just imply that the net radiative forcing (ΔRF) has been rather low (i.e. low RF and high temp rise). But I don't think that this affects the distribution among forcings, i.e., humans would still be the major contributors to global warming. So I don't see the relationship that the sentence I quoted above means to establish, and I even think the sentence is understating our likely contribution to global warming. Cheers.
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  49. Jesus - the possibility exists that there is a 'natural' factor we are not accounting for. For example, Roy Spencer's "internal radiative forcing" hypothesis. If climate sensitivity is sufficiently low, it opens up a window where an unknown 'natural' effect could account for a majority of the recent warming. But sensitivity would have to be well below 2°C, and there would have to be a very strong natural effect that we're not accounting for. It's exceptionally unlikely, but not impossible.
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  50. Poptech, fixtures23 has all the look of a bot. Do you agree with the position of fixtures23 regarding the science?
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