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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 51 to 100 out of 119:

  1. re: Paltridge et al. A little misleading. Now show me some reproduction of the effect without using mixed sensors. Even Peikle rejects the paper. It cant be hard to find more detailed comment on this paper (and I dont mean breathless stuff off CA).
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  2. Great read. Every time I read the posts and comments I always have numerous questions, and come to the conclusion it is mind boggling complex. For instance John, your answer in 43, is there any way of knowing that global temperatures have risen or gone down in a smaller time span during geological time periods, say 200 years? Then what bothers me is: How much percentage of the total warming is due to humans? Isn't it the fact that climate goes in and out of equilibrium swinging from cold to warm and vice versa? Are we in a natural warming trend with AGW on top? If this is the case how much CO2 needs to be absorbed for instance by oceans, in other words how high would sea levels rise to get back to stability in climate? But then again CO2 seems not to be the only culprit.
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    Response: The natural temperature trend if humans weren't around would've been one of slight cooling (Meehl 2004). The following figure shows model results of how climate should've behaved with no man-made forcings:


    Figure 1: Climate model results from natural forcings compared to observations (black line). The red line is the average of the four-member ensemble. The pink shading is the model range. The blue line is the ensemble mean and the light blue shading is the ensemble range (Meehl 2004).

    CO2 is not the only culprit - there are many forcings that drive climate. But CO2 is the dominant forcing and of more concern, is the fastest rising forcing.
  3. Good post, John - was this the one that was intended to be no. 100? In one sense I agree with the skeptics that the science isn't "settled"; but to the extent that I do agree, it has more to do with the nature of science than the nature of AGW. Science doesn't "prove" things, it draws tentative conclusions from the available body of evidence, and continually revises its conclusions as new evidence comes in. Also, I can't remember ever hearing a scientist say that "the science is settled", so the whole argument seems like a straw person to me. Incidentally, should this post be listed as a response on the arguments page?
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    Response: No, this wasn't the planned #100, that one is yet to come (see if you can pick it :-)

    Nowadays when I add a new skeptic argument, I post it first as a blog post. Then I give it a day or two for the comments to nitpick all the typos which is a helpful form of proofreading/peer-review. Sometimes I find people misunderstand a point I was trying to make so I clarify the wording. Then once the dust has settled, I add it as a skeptic argument on the arguments page.

    Long story short, I've now added the 102nd skeptic argument "The science isn't settled". Not quite happy with "The skeptic argument" excerpt. I like to quote a really short, succinct explanation of the skeptic argument but haven't been able to find any skeptic article that really nailed it in a single paragraph. Sing out if you find a good example.
  4. HR says "What stopped natural runaway warming in the past?" I believe that we briefly looked at this before from a purely mathematical point of view. If a feedback effect is less in magnitude than the change that triggered it initially, there can be no runaway. As to the discussion on energy prices in the US, the fact is that energy conservation is almost totally absent from the mentalities here, from the end consumer to industries. Waste is pervasive. Energy prices could go significantly higher without too much pain provided the appropriate conservation measures are implemented.
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  5. (**John comment 50 doesn't seem to be displayed**) 51.scaddenp at 15:15 PM on 25 March, 2010 As we all know Pielke isn't a climate scientist. You reject every last word of it? It seems any paper that questions the concensus is rubbish. Is this how we come to a concensus? Even if the data they generate is flawed. And lets face it no data in climate science seems perfect. You still have to deal with the limitations of the empirical data they highlight. I think Trenberth's paper highlighted the poor data quality in the mid-upper troposphere as well. If it is the case that this region is key to water vapour feedback then it's not good enough to not know.
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  6. Well Oracle, when fresh water supplies dry up due to loss of glaciers in some parts of the world, & due to reduced rainfall in others, then a lot of people are going to regret their love of the warmer weather. Crops in warmer conditions also reach senescence earlier-meaning reduced biomass prior to harvesting (i.e. *less food*). So we'll have a combination of reduced rainfall & increased aging of crop plants in the various bread-baskets of the world-how do you think thats going to impact our quality of life? Meanwhile, some of the best means of reducing CO2 emissions also carry a number of related benefits-like the cost savings from weather proofing homes & businesses, reduced air pollution from the burning of coal & petrol, reduced stress from unnecessary time spent in traffic jams & the extension of the life of our many NON-RENEWABLE resources. Perhaps that is how the scientists need to sell it, because right now its only the "we'll be rooned" mantra of the Fossil Fuel industry that is getting through!
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  7. 54.Philippe Chantreau at 16:18 PM on 25 March, 2010 "the fact is that energy conservation is almost totally absent from the mentalities here" Here's a graph showing USA car fuel consumption. The modern world is a more efficient place in terms of energy use than previous generations. It's just we are luck to get to use much more of it, it's what makes our lives seem so pleasant.
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  8. "...there are still uncertainties in climate science and therefore action to cut CO2 emissions is premature." Why should "action to cut CO2 emissions" depend on whether warming correlates with CO2 or not? It could turn out that world leaders rationalize that the warming is tolerable or the lesser of two evils, or that it is actually on the whole beneficial to a majority etc. Why are scientists wearing two hats? (i.e., getting involved with recommendations, when their only charter is to investigate?)
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  9. If the science was settled those who visit and comment on this site would have nothing to discuss!
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  10. oracle2world wrote : "The overall problem with AGW, is not whether it is true or not. It is that people like warm weather, and don't like their taxes raised. There are winners and losers in change, like climate change, and it happens America, Canada, Northern Europe, and Russia make out like bandits. Access to more resources and less money to heat." However, people are not too keen on hot weather when it lasts too long. However, America, Canada, Northern Europe, and Russia won't like losing all that land (especially in their coastal capitals) to rising sea levels. However, people won't be too keen on taxes being raised to build flood defences to save their important towns and cities from flooding; or on their insurance premiums rocketing; or on their property prices devaluing; or on their water being restricted; or on their energy bills increasing; or on a host of other expensive and detrimental measures that will have to be enforced if we all sit back and wait for these 'lovely warm' temperatures. However, the permafrost melting is not very helpful vis a vis Methane; nor is its release from the oceans; nor is the thought of burning more carbon; nor the need to use more resources to keep cool. Best not to wish for what you will later deny ever having wanted.
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  11. In the last round of discussion, my posting was deleted, I assume for being off topic. Perhaps it is more on topic for this article. Who knows. I believe it is a fairly significant question however trivial, given that the science is mainly settled, so it shouldnt be too hard to answer. The question again is... why does Earth's average temperature happen to oscillate about 14 C (or whatever the number happens to be)? Referring to the diagram above, you could have this tug of war between positive and negative radiative forcing that leads to any temperature, and yet, for millions and millions of years, temperatures hovers around the same general area, give or take 10 C.
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  12. RSVP> It's probably off topic here too, but I find the question interesting. One answer would be "If there had been really huge temperature variations, we would not be here to record them". Another answer is suggested by the idea that in the long perspective the level of CO2 and the temperature is controlled by rock weathering. The removal of CO2 from the atmosphere due to weathering would have to be in equilibrium with the outgassing of CO2 from volcanos etc.. Of course, this raises a different question: Why does outgassing not change over the millions and millions of years?
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  13. @ProfMandia and unreal2r Specifically, the discussion on costs: 1. Without CCS will not achieve over the next 20-30 years a sufficient reduction in CO2 emissions. CCS is perhaps 70-80% of the cost of combating AGW. CCS is in no way improves the efficiency of energy - on the contrary - only generates costs. 2. Adoption of a AGW theory version of the IPCC (required haste) the effect of the introduction of large-scale too "young" technology for renewable energy. It harms the technology. For example, solar power - is still underdeveloped energy storage technology is at night - the day melting salt (NaCl, KCl, and others) - is still too inefficient technology. 3. Trenberth - one of the "creators" Climategate - the end justifies the means? 4. @ Scaddenp - bravo! I agree completely. The theory of risk - an acceptable degree of probability - an intolerable absolutizing (IPCC), the principle of the superiority of prevention ... Here I recommend the work of V. Klaus, a professor of economics and the Czech president: "Blue Planet in Green Shackles" (one of the chapters of this book) and http://www.guardian.co.uk/environment/cif-green/2009/may/01/vacla-klaus-emissions -Economy
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  14. "... how has climate responded to forcings in the past?" And here we return to the reliability of data from ice cores, on which based Hansen and Chylek. And open another Pandora's box (http://www.someareboojums.org/blog/?p=7) - huge doubts ...
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  15. First of all, Science is never settled. As soon as we believe that issues have been settled, we will stop progressing. No matter how confident people may be about a theory and no matter how accurate that theory may be, we can only continue to move forward if we allow healthy debate and not roll over at the whims of people who try to shove their perspective down our throats as being "true correct, beyond debate yadda yadda yadda". The least scientific method to prove a theory is to use graphs of data. While graphs serve to help one explain a theory, they do not prove anything. The biggest complaint I have with the current debate is the 100% focus on CO2 when we know there are so many other parameters that work together in setting the climate here on earth. Why the focus on CO2? Well that is the only way in which the IPCC can relate climate change to man's activities (which was their mandate when they were established by the UN. Consequently they have failed miserably in their attempt to shove the cause of climate change onto man. Their failure to recognize the important role that water vapor plays in the greenhouse effect to me is a significant shortfall in their reports. After all we do know that water vapor has a much greater greenhouse gas effect than does CO2.
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  16. Geo Guy writes: The biggest complaint I have with the current debate is the 100% focus on CO2 when we know there are so many other parameters that work together in setting the climate here on earth. Why the focus on CO2? As John discusses in this thread elsewhere on the site, CO2 is not the only driver of climate change. However, it is the largest single climate forcing today: Figure 1: Global mean radiative forcing of climate. Anthropogenic RFs and the natural direct solar RF are shown. (IPCC AR4 Figure 2.20a) Geo Guy continues: Their failure to recognize the important role that water vapor plays in the greenhouse effect to me is a significant shortfall in their reports. After all we do know that water vapor has a much greater greenhouse gas effect than does CO2. On the contrary, everyone recognizes the role of water vapor. But water vapor acts as a feedback, amplifying the forcing from CO2, other greenhouse gases, solar, etc.
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  17. HumanityRules - when a paper runs in the face of direct measurement and other analyses of the data, then there are good reasons to be doubting. When it is furthermore based instrumentation which is known to have erroneous trends due to improvements in sensors, then I certainly wouldnt jump to conclusions. Check back in a year and see what cites have been made of this paper. I also wouldnt overestimate the impact of these uncertainties on models. Sensitivity is established from multiple lines of evidence. This looks like a desperate clutching at straws to me.
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  18. In response to the response given to BlackCanvas above, the author has proved squat - except for supporting the hypothesis that given a model that has been constructed showing CO2 to be the cause of climate change, it is obvious that when you move that driving factor from the model, the obvious result will be cooling. That in no way supports the contention that man-generated CO2 caused a rise in global temperatures. For someone who espouses about the validity of the so-called "science" behind climate change the above statement suggest a complete lacking of what is cerdible and what isn't. Perhaps it is best said: "CLIMATE MODELS PROVE NOTHING!" - They simply project a relationship amongst parameters that has been modeled by the creator of the model. Simply because a model generates a relationship between C)2 and higher temperatures, it does not prove that relationship exists in the way portrayed in the model.
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  19. In response to Ned (#66). During the period from 1980 to roughly the present, the water vapor content of the atmosphere gre by an average of 1% per year, a rate that is significantly higher than that of CO2. However, contending that the so-called warming observed during that same period is solely attributed to growing CO2 concentrations is quite frankly hard to fathom. Putting water vapor into a subordinate role IMHO is like sticking your head into a pile of sand. It doesn't make sense. I also contend that any data posted from any IPCC report needs to be taken with a grain of salt, given the inaccuracies and the questionable process that was followed in producing and finalizing those reports. Given that water contributes anywhere from 35% to 75% towards the greenhouse effect, (65% to 85% when you include clouds) it certainly suggests it has a primary function in affecting climate on this planet. (On a comparative basis, CO2 is believed to account for 10% to 25%.) Finally the term radiative forcing was coined by the IPCC - so it's best that we use a different term - after all their mandate was not to identify the cause of global warming but rather instead they set out to prove global warming is attributable to man's activity.
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  20. Geo Guy, you're way off base for the following reasons: 1) Water vapor is about 100 times more concentrated in the atmosphere than carbon dioxide, yet contributes about 70% of the *natural* Greenhouse effect compared to the 20-30% contribution of carbon dioxide-this makes CO2 20 times more potent-on a parts per million basis-than water vapor. 2) Given this fact, even a 1% rise in water vapor is not sufficient enough to give the rise in temperature-especially given the short lived nature of water vapor in the atmosphere, as compared to CO2 & methane. 2a) CO2 levels have risen by 110ppm above pre-industrial levels-almost all of it in the last 40 years-which actually represents an almost 1% rise per year in atmospheric CO2 levels. 3) Water vapor is just as likely to act to increase albedo (clouds) as it is to capture outgoing long-wave radiation.
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  21. re Geo Guy 08:37 AM on 26 March, 2010 Asserting falsehoods isn't helpful Geo Guy: Two here:
    Finally the term radiative forcing was coined by the IPCC - so it's best that we use a different term - after all their mandate was not to identify the cause of global warming but rather instead they set out to prove global warming is attributable to man's activity.
    (a) The IPCC was formed in 1988. The term "radiative forcing" has a long history in atmospheric science. Here's a paper from 1975, for example: D. W. Blake (1975) Radiative Forcing Of Annual And Semiannual Oscillations In Stratosphere Transactions-American Geophysical Union 56, 996-996. Therefore the term "radiative forcing" clearly couldn't have been "coined by the IPCC" could it, Geo Guy, since it was alread "coined" many years before the existence of the IPCC. (b) The IPCC wasn't set up "to prove global warming is attributable to man's activity." We can look at the IPCC mandate here: and see that your assertion is false.
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  22. Geo Guy - what causes water vapour increase - temperature rise. What causes temperature rise CO2. CO2 is the forcing - water is the feedback. Oh and so is albedo etc. It doesn't make sense to refer to feedbacks when looking for causes. Ditto, ice age cycle is driven by solar, not the CO2 feedback that amplifies it. On and on IPCC, PLEAZZE! The IPCC reviews and summaries the the published science. The talk about the "inaccuracies" is crock - so some human mistakes happen but is that the best you can do?? Note a lack of issue of WG1 which I bet has been heavily scrutinized. As for "radiative forcing" being coined by IPCC - where do you get these ideas? Do you understand it? Do you realise why it so useful? Want to google the published science that uses the term? You are at a website devoted to scientific answers to skeptic rubbish. Try looking at the articles.
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  23. Geo Guy at 08:37 AM on 26 March, 2010 Your post is a little confused about water vapour as a greenhouse gas Geo Guy. Water vapour partitions into the atmosphere according to the atmospheric temperature (and pressure). It's effectively the atmospheric temperature that governs the levels of water vapour on average. With an Earth atmosphere warmed by the sun, and containing greenhouse gases that amplify the atmospheric temperature above the Earth's blackbody temperature, water vapour will partition according to the atmospheric temperature (Clausius-Clapeyron equation), further amplifying the atmospheric temperature (since water vapour is a greenhouse gas). With a constant CO2/methane/nitrous oxide etc. level and a constant solar output, the atmosphere will settle around an equilibrium temperature, a significant contribution to which will be the water vapour that partitions into the warmed atmosphere. Now: raise the CO2 levels. The atmosphere will warm. Since the atmosphere warms so the atmospheric water vapour levels increase. Sinc water vapour is a greenhouse gas the CO2-induced warming is amplified. To what then do we attribute the enhanced warming? Strictly speaking some is from raised CO2 and some is from the resulting raised water vapour which partitions at higher partial pressure due to enhanced CO2-induced warming. However, in essence all of the warming is a consequence of the raised CO2, even 'though part of this is the warming from the CO2-induced enhancement of water vapour concentration (the water vapour feedback). The water vapour feedback applies to anything that enhances (or reduces, of course) the atmospheric temperature. So if the sun became a bit brighter (say) such that the direct atmospheric warming is 1 oC, and the resulting water vapour feedback adds an additional x of additional warming, then the total warming from the solar enhancement + water vapour feedback is something like 1 + x + x^2 + x^3 + x^4 ... which is 1/(1-x). So if the water vapour response to a 1 oC warming is 0.5 oC then the total warming (when everything comes to equilibrium) is 1/(1-0.5) = 2 oC. Again, strictly speaking we could say that 1 oC of warming is due to the sun being brighter and 1 oC is due to the water vapour. But all the warming is essentialy due to the sun being brighter, since the water vapour feedback is a direct result of thesun-induced warming in this case (that's pretty much what is meant by "feedback"). This is all pretty well understood, and the water vapour feedback is (of course!) taken into account. No one "puts water vapor into a subordinate role"!
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  24. Chris is back! Good to read you again! HR, your graph of auto mileage shows excellent progress for 20 years, then little to no progress until 2005. The average fuel consumed per vehicle is in fact on the increase since the early 90s. Nothing to brag about. Do you have any figures on how it has been in Europe?
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  25. Yes, I was going to make the same observation Phillipe. How much of the increase in efficiency is actually the result of Americans buying more European & Asian cars I wonder? We all know that US Auto makers fought tooth & nail against mandated efficiency standards-& where are they now?
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  26. Marcus, short answer: better but nowhere near where they could be. Truth is, the US wastes a lot of energy. The electrical grid is also a significant problem. Plethoric intermediates (brokers types) only add to the problem, since their ways of making money do not necessarily go in the direction of best overall efficiency (remember Enron). Misplaced subsidies also work against efficiency: a small business owner would get a better tax rebate from claiming a large SUV than a compact sedan for example. This is somewhat OT, so we should probably drop the issue for now.
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  27. Thank you Marcel Bokstedt for the reply to the question..."why does Earth's average temperature happen to oscillate about 14 C (or whatever the number happens to be)?" I dont know if it takes so much science or just plain common sense. Considering that the Moon's temperature goes from 123 C down to -233 yields a median of -55C, telling you that -55 C is where temperatures on the Earth would tend to go in the absence of its atmosphere. So if temperature holds roughly around 14 C (as it does on Earth), this can be attributed to all "greenhouse" effects combined. My point being that if anything, for Earth, there is a natural tendency towards cooling... NOT warming. The Earth's temperature is not free floating but "grounded" in a value that is generally driven by its distance from the Sun, and that temperature is much lower than what we are used to. Also, as I tried to say before, graphs such as Figure 2 above, or that which Ned posted, tell you nothing about where temperatures should end up, however they do make an assumption of water being in specific state, (i.e., slightly above its triple point).
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  28. #66 Ned at 06:29 AM on 26 March, 2010 "water vapor acts as a feedback, amplifying the forcing from CO2" It depends on global upper troposphere average log absolute humidity trend, which is unknown. Radiosonde balloon measurements indicate a decreasing trend in absolute value, but are questioned. Remote sensing (satellites) is not quite up to the task yet either. Both spectral and vertical resolution are poor, humidity reconstructions are based on sophisticated model calculations, their validity depends on hidden assumptions.
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  29. Berényi Péter writes: "It depends on [...]" What is the "it" in that sentence?
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  30. RSVP writes: Considering that the Moon's temperature goes from 123 C down to -233 yields a median of -55C, telling you that -55 C is where temperatures on the Earth would tend to go in the absence of its atmosphere. So if temperature holds roughly around 14 C (as it does on Earth), this can be attributed to all "greenhouse" effects combined. This is more or less right. The Earth has a higher albedo than the Moon, so with no greenhouse effect the Earth would actually be a bit cooler than the Moon. You're right that this temperature differential is proof of the existence of the greenhouse effect (which should go without saying, but someone keeps disbelieving it over in this other thread) and that it's due to the combination of all greenhouse gases, not just CO2 (mostly water vapor in fact). So that's all well and good. However, RSVP continues: My point being that if anything, for Earth, there is a natural tendency towards cooling... NOT warming. At first I was confused by this, but I think I understand what you mean. We need CO2 to keep the Earth from freezing over, right? Of course, too much CO2 would be unpleasant (cf Venus). For the foreseeable future, though, there is no physical mechanism that could either eliminate the greenhouse effect and freeze us, or create a runaway greenhouse and broil us. Whew! Insofar as there is a long-term natural trend, there are two things to keep in mind: (1) On a timescale of hundreds of millions of years, the sun is getting brighter, which would naturally tend to cause the Earth to heat up (and eventually this will become unstoppable). (2) On the other hand, on the same timescale, CO2 is being removed from the atmosphere and sequestered in carbonate rocks, reducing the greenhouse effect and cooling the planet. So far, over the long term (say, the Phanerozoic Era) the Earth's temperature has generally cooled, meaning that (2) has had a bigger impact than (1). Of course, there's a lower bound below which CO2 can't go, and at some point in the distant future the increasing irradiance will swing the thermostat back towards "broil"....) However, that's all pretty much irrelevant on the timescales we care about (tens, hundreds, thousands, or even millions of years). Right now there's no danger of an abrupt decrease in the greenhouse effect. Instead, the danger is entirely on the "warm" side, especially if we keep burning coal.
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  31. #79 Ned at 21:56 PM on 26 March, 2010 "What is the "it" in that sentence?" The sign of the water vapor feedback loop, of course. There is a rather strong positive feedback if we keep relative humidity constant on all levels (as it is routinely done in computational models of climate). Whether Mother Nature complies with this requirement is not known.
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  32. Profmandia #7, #25, Ned#66 BP#78 Glad you had a look at the Trenberth paper because I find the overall calculation of the Earth's energy imbalance the most relevant measure of potential warming or cooling. Dr Trenberth's paper estimates that the net overall imbalance is +0.9W/sq.m from net radiative effects which equals 145E20 Joules/year. He can only account for about 0.55W/sq.m (about 80E20 Joules/year)in the energy budget for warming oceans, melting ice, warming land etc. He muses over whether the rest is hidden in the oceans below 2000m (recently found in part by von Schukmann but disputed by BP and at variance with several other ocean heat analyses) Within the 0.9W/sq.m imbalance is embedded the climate reponses from Fig4 of Dr Trenberth's paper. The radiative feedback from increasing Earth's temperature of -2.8W/sq.m is based on Stefan-Boltzman Eqan for 255degK and a surface temperature rise of 0.75 degK which seems to apply faily well to the troposphere for the planet above the 'equilibrium temperature' of pre-industrial times. The critical point is what will be the negative radiative feedback for the postulated 3degK rise in surface temperature (doubling of CO2) when applied to Fig 4 of Dr Trenberth's paper where a doubling of CO2 would by IPCC formula increase CO2 radiative forcing to 3.7W/sq.m and other GHG forcings by unknown amounts. The key to this is what portion of the 3degK rise also applies to the troposphere and what will be the increase in the Earth's overall OLR and 'equilibrium temperature'. Humidity and lapse rate are critical parameters around which there is much discussion and uncertainty. Your thoughts gentlemen?
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  33. Berényi Péter, I don't think we're going to throw out Clausius–Clapeyron any time soon. The evidence for a positive water vapor feedback is discussed in some detail on John's page Water vapor is the most powerful greenhouse gas. This can be easily seen over the long term, but it also manifests itself via interannual variability e.g. following the eruption of Mt Pinatubo. I think Solomon et al. 2010 does a nice job of discussing both the long-term role of water vapor as a positive feedback and its shorter-term role in sub-decadal scale variability.
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  34. Ned, folks could use some common sense, I guess. If water vapor feedback on CO2 warming is positive, then it is positive on any kind of warming, right? Even on warming caused by some random increase of humidity. At this point one can safely forget about carbon dioxide and start worrying about dihydrogen monoxide pollution. For we have an almost infinite supply of the liquid form of this stuff with an open surface exceeding 3.6 × 1014 m2. As temperature gets higher, the Clausius–Clapeyron relation ensures ever higher rates of evaporation. Or does it? The final state is a H2O atmosphere with trace amounts of nitrogen and oxygen. Surface pressure is 2.6 × 107 Pa, temperature above 600 K. It is called a runaway greenhouse. Can last for some ten million years, molecules split by UV in upper atmosphere, hydogen escapes to space, are left with plenty of oxygen but no water. Limestone releases CO2 slowly, Earth is transformed to hell. Somehow it never happens. Why? Because dihydrogen monoxide feedback is not positive. If it would be positive, the scenario described above is inevitable. It is not climate science, not even physics. Just plain old math. Plus the empirical fact we are still alive. Water feedback should be slightly negative, very close to neutral. Greenhose effect is saturated. So. The one million dollar question to climate scientists is not whether water vapor feedback is positive or negative, but how this negative feedback loop works?
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  35. Berényi Péter at 03:45 AM on 27 March, 2010 Don't think anyone's going to fall for that BP! Since the water vapour response is positive (after all we can measure the increased water vapour concentration in the atmosphere as a result of warming over the last 30-odd years, pretty much as predicted), and we haven't had your scary runaway scenario, it follows that the latter isn't "inevitable" as you assert. Therefore something's wrong with your argument. Can you spot it?
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  36. Berényi Péter, I don't think you understand the mathematics of feedbacks. You might want to reread the comment by Chris above. A positive feedback does not imply a "runaway" system unless the feedback coefficient f is >= 1. For positive feedbacks 0 < f < 1, the total increase from the feedback will be 1/(1-f), as Chris says. As you yourself said, It is not climate science, not even physics. Just plain old math. However, it's important to have the math correct. This is a common mistake -- many people assume that a positive feedback must increase without bound.
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  37. Oh, dear, Chris. Sorry about that. Looks like we were responding simultaneously. Chris writes: Therefore something's wrong with your argument. Can you spot it? I'm afraid I might have given a small hint there. :-)
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  38. I looked up 'Gish gallop' and Google found this list of a hundred or so claims often rushed through by people claiming anything they can except the IPCC explains climate, often found on blogs; just in case you'd missed the list, here it is: http://www.dailyexpress.co.uk/posts/view/146139
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  39. Ken Lambert at 01:04 AM on 27 March, 2010 Ken I think you need to clarify your "key" point, before anyone can consider addressing it: i.e.:
    The key to this is what portion of the 3degK rise also applies to the troposphere and what will be the increase in the Earth's overall OLR and 'equilibrium temperature'. Humidity and lapse rate are critical parameters around which there is much discussion and uncertainty.
    Obviously a 3degK rise is "the increase in the Earth's.........'equilibrium temperature'. So it's not obvious (to me anyhow!) what your "key" point actually is....
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  40. No problem Ned. I suspect Peter knows all this anyway. After all the only alternative is that all those thousands of scientists have inadvertently messed up over the nature of feedbacks...................... ....Doh!
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  41. Chris #89 Obviously a 3degK rise is "the increase in the Earth's.........'equilibrium temperature'. So it's not obvious (to me anyhow!) what your "key" point actually is.... No Chris, a 3degK rise at the surface if it translates directly to the emitting temperature of the atmosphere will increase the OLR using the (Stefan) S-B equation as follows: Current OLR = 238.5W/sq.m, Pre-industrial OLR = 235.7 Current emitting temperature = 255degK Pre-industrial emitting temperature = 254.25 degK For a 3 degK rise in emitting temperature (above pre-industrial levels) the new OLR will be: (257.25/254.25)^4 x 235.7 = 247.0 W/sq.m. Rise in OLR is 247.0 - 235.7 = 11.3W/sq.m (11.3W/sq.m increase in outgoing longwave radiation) The rise in CO2 radiative forcing from doubling of CO2 to 560 ppmv from pre-industrial levels of 280 ppmv will be (using the IPCC Eqan) : 5.35ln(560/280) = 3.7W/sq.m Therefore to balance the CO2 radiative forcing of 3.7W/sq.m, the emitting temperature of the atmosphere only has to rise by (using inverted S-B) : (239.4/235.7)^0.25 x 255 = 255.995 degK - 255 = 1.0 degK You can do the numbers with slightly different OLR (aroung 240) and temperature (around 255) and get a very similar result. So for a 3 degK rise to be the result of CO2 doubling alone, there must be only a 1 degK rise in the emitting temperature of the atmosphere. The extra 2 degK difference in the rises must be in the increased greenhouse effect (complex feedbacks, back radiation etc etc) which is theroized due to increased CO2 and increased water vapour. While brings us to the critical effects of water vapour and CO2 - where BP #84 and Ned #86 are fighting it out. Let's have a result boys - the answer is the key to the whole AGW CO2 theory. (
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  42. To illustrate the point about positive feedbacks, here are graphs of two cases, one where f > 1 (resulting in a runaway increase) and one, like the real-world positive water vapor feedback, where 0 < f < 1, so that the temperature increase is bounded (2C in this case):
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  43. Ken Lambert writes: Let's have a result boys - the answer is the key to the whole AGW CO2 theory. Personally, I'm pretty comfortable with the range of climate sensitivities given in AR4 (2 to 4.5 C, with an expected value somewhere around 3 C). It seems unlikely to be far off in either direction and it's certainly the best estimate we have now.
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  44. A couple of points here in re: water vapor and its feedback. The primary thing to keep in mind about WV vis a vis CO2 is that WV condenses and precipitates out of the atmosphere. It is this fact that explains the partitioning of WV and lets us know where negative feedbacks associated with WV might come from. For instance, if we assumed that cloudiness increases proportionally with concentration of WV this would be a negative feedback. Likewise, if precipitation increased in proportion to the conc. of WV. Neither of these propositions is at all unlikely IMO. Finally, one should never forget that WV feedback(whatever its magnitude or sign for all but the very recent *atmospheric* temperature changes has *already happened*. There may be some other temperature changes coming along "in the pipeline", but WV adjusts to a temperature change in a period of months or so. Cheers, :)
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  45. Ken L. What you're missing is that the way greenhouse gasses work is to "take a chunk out" of the S-B emission curve. The OLR at two different temperatures can only be related by (T1/T2)^4 if both emission spectra have the same shape relative to the ideal S-B spectrum. In this case, the entire mechanism by which the temperature is changed is a widening and deepening of the absorption lines so that, in equilibrium the OLR at the higher temperature but with more absorption lines is actually the same as it would be at the lower temperature and a pre-industrial atmosphere.
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  46. Well, not the "entire" mechanism of course. Albedo changes scale the entire spectra relative to the S-B spectra, and any change in solar input dictates what "equilibrium" means. But right now greenhouse gasses are the dominant mechanism.
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  47. shawnhet, it's not concentration that matters for your argument, it's relative humidity. Also consider that precipitations counteract, or limit, cloudiness increase; the water in the rain drops must come from somewhere after all.
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  48. You are quite right, John! The science is settled, but some pieces of science are more settled than others. There is only one problem: the combination of all these relative uncertainties is unknown. The heat trapping effect of carbon dioxide is well understood, at least for a hypothetical planet without water and aerosols. The saturation of the heat trapping by CO2 at sea level is also well understood. The increased heat trapping by CO2 in the higher troposphere as predicted by the models, is well understood, but not empirically verified. Santer et al (Int. J. Clim. 28(2008), 1703-1722), could not find the hot spot, nor could Douglass et al, (Int J. Clim (2007) DOI: 10.1002/joc.1651) prove that the hot spot does not exist. The effect of heat trapping by CO2 on water vapour and clouds is poorly understood. The only possible conclusion is that the total effect of all these factors is not well understood. That question is settled, as long as no better understanding is available. There is high confidence that the global climate has been warming since about 1800, although the datasets (GISS, HadCRU) cannot be verified independently. There is no high confidence that the warming in the last 30 years is exceptional, nor that anything in the pattern of warming in the last 200 years is closely related to the concentration of CO2. The relationship of the global temperature with patterns of ocean circulation is much better than the relationship with the CO2 concentration. There is a lot of evidence, that the climate is much more complicated than could follow from the high understanding of heat trapping by CO2 alone. So we can try to cut CO2-emissions, but whether that has any effect on the global climate is fully unknown. Some pieces of science are less settled than others!
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  49. fydijkstra, when i see comments with kind of "randomly distributed" claims plus a few references i usually check. For example, Santer et al. 2008 do not say what you claim, just the opposite. Anyway, it's quite strange that the story of the so (inappropiately) called hot spot keeps flowing around us while a dusty shelf would be more appropiate. It's indeed a basic physical response of our atmosphere not GCM or AGW, not even a skeptic argument. Other claims are inconsistent as well, e.g. warming is not exceptional or no warming pattern related to CO2. Your comment looks more like a piece of propaganda than of climate science.
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  50. fydijkstra, I think a frequent logical misconception is to somehow separate a natural greenhouse warming from AGW (although this manoeuvre may well be justified or even indispensable in a political debate). Just consider a noisy recorder output from any experimental measurement. If you take the baseline for granted, you can of zoom into the graph, focus on the noisy ups and downs and complain that nobody will ever be able to predict the future. Zoom out to get the whole picture. The more GHGs, the warmer. That's it. BTW, Ned, chris, the discussion on WV, feedbacks that run away and those that won't was highly instructive.
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